You missed us!
Here are some abstracts of talks that we have given.

Controlling and Measuring Local Composition and Properties in Lipid Bilayer Membranes
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We describe measurement and control of the local structure of model membranes at the molecular scale. Local composition of and structures within membranes are critical elements of cellular processes such as transport, adhesion, infection, transformation, and immune response. We control local composition and structure through manipulation of (local) membrane curvature. Our tools include multibeam optical tweezers, dual micropipette aspiration, molecular recognition, and rapid, simultaneous, high-resolution, three-dimensional, multi-color fluorescence imaging. Our model membranes of choice are giant unilamellar vesicles prepared from multi-component lipid mixtures. We use lipid components known to phase segregate into domains large enough to resolve with optical microscopy. We analyze the effects of membrane curvature on the local composition of multi-component lipid bilayers. There is an interdependent relationship between local structure, composition, and curvature. We obtain quantitative measurements of the membrane components by perturbing the membrane surface and monitoring the corresponding change in the local structure. We use these model systems to study the interactions of the membrane with cytoskeletal proteins such as tubulin, and have learned to quantitate and to control the chemical interactions of the lipids with the protein.

Creating Nanostructures through Self- and Directed Assembly
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select molecules to choose the intermolecular interaction strength and the structures formed within the film. We also apply selective chemistry and self-assembly to form multilayers on patterns formed with conventional nanolithographic techniques to reach higher resolution, greater precision, and chemical versatility in nanostructures that we create.

Single Molecule Motors
Will Hancock, Department of BioEngineering, The Pennsylvania State University, University Park, PA 16802, USA and Paul S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Molecular Rulers
P. S. Weiss,¹ M. E. Anderson,¹ G. N. Taylor,¹ and M. W. Horn<sup>2

1</sup>Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
²Department of Engineering Science and Mechanics, The Pennsylvania State University, University Park, PA 16802, USA

We combine conventional lithographic techniques with chemical self-assembly for the creation of nanostructures whose spacing and edge resolution reach nanometer-scale precision. The controlled placement and thickness of self-assembled multilayers composed of alternating layers of complementary chemical pairs form precise “molecular ruler” resists to produce tailored, lithographically defined patterns. We have advanced the use of molecular rulers through a number of new and continuing strategies. We have demonstrated two methods of multilevel molecular ruler processing using photolithography. We have explored new complementary chemical couples for the resist materials. We have continued our work on non-conventional parent structures created by self-assembly processes. We have also advanced our ability to make multiple generation and sacrificial structures.

Advancing Nanolithography
Susan Trolier-McKinstry, Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA and Beth Anderson, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Immobilized Gold Nanoparticles on Alkanethiolate Self-Assembled Monolayers with Inserted Alkyldithiols
R. K. Smith, G. Woehrle, S. U. Nanayakkara, B. A. Mantooth, J. E. Hutchison, and P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We report the immobilization of gold nanoparticles atop octanethiolate self-assembled monolayers with inserted 1,10–decanedithiol tethers. Insertion of the tethering molecules through the vapor phase and through long exposure times in the solution phase leads to high fractional surface coverage; however, under these conditions the molecules can form ill-defined structures that prevent the reliable adsorption of nanoparticles. The assemblies are treated with dithiothreitol to ensure that the surface of the monolayer presents pendent thiols; ellipsometry, contact angle goniometry, and scanning tunneling microscopy are used to monitor the chemical nature of the inserted films. The lack of mobility of the bound nanoparticles allows for careful study with scanning probe microscopes.

Exploring and Controlling the Atomic-Scale World
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Stay tuned for several talks and posters from our group!

Controlling and Measuring Local Composition and Properties in Lipid Bilayer Membranes
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We describe measurement and control of the local structure of model membranes at the molecular scale. Local composition of and structures within membranes are critical elements of cellular processes such as transport, adhesion, infection, transformation, and immune response. We control local composition and structure through manipulation of (local) membrane curvature. Our tools include multibeam optical tweezers, dual micropipette aspiration, molecular recognition, and rapid, simultaneous, high-resolution, three-dimensional, multi-color fluorescence imaging. Our model membranes of choice are giant unilamellar vesicles prepared from multi-component lipid mixtures. We use lipid components known to phase segregate into domains large enough to resolve with optical microscopy. We analyze the effects of membrane curvature on the local composition of multi-component lipid bilayers. There is an interdependent relationship between local structure, composition, and curvature. We obtain quantitative measurements of the membrane components by perturbing the membrane surface and monitoring the corresponding change in the local structure. We use these model systems to study the interactions of the membrane with cytoskeletal proteins such as tubulin, and have learned to quantitate and to control the chemical interactions of the lipids with the protein.

Creating Nanostructures through Self- and Directed Assembly
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Controlling Single Molecules by Tailoring Intermolecular Interactions: Applications in Surface Patterning and Molecular Electronics
Penelope A. Lewis, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We have investigated the role of intermolecular interactions in self-assembled monolayers of amide-containing alkanethiolates on Au{111}.  In addition to van der Waals interactions that are present within n-alkanethiolate self-assembled monolayers, hydrogen bonding between adjacent buried amide groups contributes to the stability of the amide-alkanethiolates on the surface.  We have shown that the added hydrogen bonding interaction can be useful for patterning self-assembled monolayers and can drive phase separation in monolayers of amide-alkanethiolates and n-alkanethiolates. In addition, hydrogen bonding affects the packing structure of the amide-alkanethiol monolayers which can be used to advantage in molecular electronic studies. We have studied conjugated oligo(phenylene-ethynylenes) inserted into amide-containing alkanethiolate self-assembled monolayers using scanning tunneling microscopy in order to determine their physical and electronic properties when surrounded by the hydrogen-bonded matrix.  We observe fewer switching events between the ON and OFF states than previously reported for n-alkanethiolate matrices and attribute this to the rigidity imparted by the hydrogen bonds of the amide groups in the matrix.  Furthermore, we demonstrate bias-dependent switching as a result of hydrogen bonding between the substituents of the inserted oligo(phenylene-ethynylene) and the matrix molecules.  These studies demonstrate that the intermolecular interactions in self-assembled monolayers can have a crucial effect on the physical and chemical properties of the film and of embedded molecules.

Extracting Single Molecule Statistics from Scanning Probe Images
B. A. Mantooth and P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Scanning probe microscopes have enabled the unprecedented real-space visualization of single molecules and atoms on surfaces. Analyses of time-resolved sequences of these images allow the quantification of site-specific interactions and dynamics of adsorbed species. We have used scanning tunneling microscopy to measure systems including the dynamic behavior of electronic switching in oligo(phenylene-ethynylene) molecules for application in molecular electronics, to probe and to quantify the weak substrate-mediated interactions in benzene overlayers on Au{111} at 4 K, and to characterize concerted motions of molecular cascades in these benzene overlayers.

Understanding the Adsorbate-Substrate and Substrate Mediated Interaction Potentials on Au111
Jason Monnell (Departments of Chemistry and Physics, The Pennsylvania State University), Joshua Stapleton (Departments of Chemistry and Materials Science, The Pennsylvania State University), Shawn Dirk, James Tour (Department of Chemistry and Center for Nanoscale Science and Technology, Rice University), David Allara (Departments of Chemistry and Materials Science, The Pennsylvania State University), Paul Weiss (Departments of Chemistry and Physics, The Pennsylvania State University)

We compare the structures and properties of alkanethiolate and alkaneselenolate monolayers on Au{111}. Using molecules of the same length, we observe topographic tunneling height differences between the analogous species that elucidate molecular and contact conductivity differences. We use apparent tunneling barrier height imaging to separate the contributions of the contact conductance, the molecular backbone, and the tunnel junction.

Understanding the Adsorbate-Substrate and Substrate Mediated Interaction Potentials on Au111
E. Charles H. Sykes, Brent Mantooth, Patrick Han, and Paul Weiss Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We have studied the ordering and dynamics of CS₂ and C₆H₆ physisorbed on Au{111} at 4 K using scanning tunneling microscopy. The weakly bound state of the molecules allows one to probe the weak intermolecular interactions that dominate ordering in such systems. Preferred adsorption of CS2 at specific surface sites is observed and correlated to the positions of standing waves arising from interaction of surface state electrons with surface steps. CS₂ molecules have increased interactions with the areas of high electron density on the peaks of standing waves arising from electrons close to the Fermi energy. The importance of this result is discussed in terms of the fundamental surface physics of adsorbate/metal bonding. Using an automated approach to monitor single benzene molecule motion on the same Au surface we are, for the first time, able to quantify substrate-mediated interaction strength using a simple Arrhenius approach. We demonstrate that these weak, attractive, through-substrate forces control the growth of benzene overlayers on Au and we show how benzene self-orders in well defined structures that maximize these interactions.

Elucidation of the electronic properties of alkanethiolate-stabilized gold clusters and nanoparticles using scanning tunneling microscopy
Thomas P. Pearl (North Carolina State University), Sanjini U. Nanayakkara, Rachel K. Smith, Brent A. Mantooth, Paul S. Weiss (The Pennsylvania State University), Gerd H. Woehrle, James E. Hutchison (University of Oregon)

The single electron transport properties of metallic nanoparticles have led to a great interest in their potential integration into nanoscale electronics. Here, we discuss and compare the electronic characteristics of isolated, solution-derived octanethiolate-stabilized gold nanoclusters [Au₁₁(S(CH₂)₇CH₃)₁₀] and nanoparticles [Au₁₀₁(S(CH₂)₇CH₃)₄₃], observed in both cryogenic (4 K, UHV) and ambient conditions using scanning tunneling microscopy (STM) and spectroscopy (STS). The clusters and particles (d_CORE=0.8 \pm 0.2 nm and 1.5 \pm 0.5 nm, respectively) are synthesized in solution by ligand exchange of their phosphine-stabilized analogues with octanethiol and are subsequently immobilized on alkanethiolate self-assembled monolayers with inserted dithiol molecules. At low and room temperatures, the Au₁₁ clusters demonstrate clear Coulomb blockade behavior, with zero-conductance gaps resulting from quantum size effects; the Au₁₀₁ nanoparticles also show blockade behavior at room temperature.

Creating Nanostructures through Self- and Directed Assembly
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select molecules to choose the intermolecular interaction strength and the structures formed within the film. We also apply selective chemistry and self-assembly to form multilayers on patterns formed with conventional nanolithographic techniques to reach higher resolution, greater precision, and chemical versatility in nanostructures that we create.

Utilizing self-assembled multilayers in lithographic processes for nanostructure fabrication
M. E. Anderson,¹ M. W. Horn,² and P. S. Weiss^1
1Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
²Department of Engineering Science and Mechanics, The Pennsylvania State University, University Park, PA 16802, USA

Fundamental understanding of chemical self-assembly has undergone much investigation and is now at the forefront for patterning surfaces and for the creation of hierarchical structures with nanoscale precision. We apply self-assembly to form multilayers on structures formed by nanolithographic techniques to create patterns with spacings in the 10-100 nm regime. The key is to use robust multilayers, which do not contain pinhole defects (unlike monolayers) and are able to withstand the rigors of lithographic processing. Controlled placement and thickness of these multilayers form “molecular ruler” resists to measure the spacings precisely between lithographically defined structures. We have demonstrated this approach with nanostructures generated by electron beam and photolithography, as well as those based entirely on self-assembly. We will discuss our approaches to designing and patterning complex nanostructures by exploiting methods of directed self-assembly to build molecular ruler resists with independently controlled materials and spacings.

Scanning Tunneling Microscopy and Lateral Force Microscopy Studies of Microcontact Printed SAMs
R. K. Smith,¹ C. E. Inman,² J. E. Hutchison,² and P. S. Weiss^1
1Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
²Department of Chemistry, The University of Oregon, Eugene, OR, USA

Soft lithography techniques such as microcontact printing have led to the ability to place molecules positively upon surfaces with great precision. However, both the elastomeric materials used in the "stamping" process and the chemical nature of the molecular "inks" can lead to compromised edge resolution and the blurring of boundaries between printed and backfilled molecules. We use scanning tunneling microscopy and lateral force microscopy to examine the order of these assemblies as well as the sharpness between domains of molecules on both the small and large scales. We print molecules with strong self-interactions to minimize their diffusion across the surface, and we use a stamp composed of multiple elastomers to minimize spreading of the stamp upon contact with the surface during the printing process while still maintaining conformal contact. We examine and quantify the exchange between printed and backfilled molecules.

New Tools for Nanoscale Analyses
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Scanning probe microscopes allow unprecedented views of surfaces and the site-specific interactions and dynamics of adsorbates and nanostructures. Our efforts to identify and to measure the local chemical, physical, electronic, optical, nonlinear, and mechanical properties of adsorbates and nanostructures. We have extended the capabilities of scanning probe microscopes in several ways; two in particular will be highlighted. First, we discuss how we follow the dyanmics of single molecule devices. Then, we address the single molecule/particle measurement issue in accumulating sufficient data to accumulate statistically meaningful distributions so as to enable systematic variations in molecular design, conditions, and environment to determine the functions, dynamics and mechanisms in such diverse areas as single molecule electronics, single molecule motors, 1D diffusion, and molecular motion between interacting lattices.

Probing Nanoparticle Assemblies and Substrate Effect on Self-Assembled Monolayers
D. J. Fuchs, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Measuring and Controlling Molecular-Scale Properties for Molecular Devices
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Measuring and Controlling Molecular-Scale Properties for Molecular Devices
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Measuring and Controlling Molecular-Scale Properties for Molecular Devices
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select molecules to choose the intermolecular interaction strength and the structures formed within the film. We also apply selective chemistry and self-assembly to form multilayers on patterns generated with conventional nanolithographic techniques to reach higher resolution, greater precision, and chemical versatility in the nanostructures created.

Exploring the properties of nano-materials: self assembled monolayers, platelets and particles
J. D. Monnell, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Measuring and Controlling Molecular-Scale Properties for Molecular Devices
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Measuring and Controlling Molecular-Scale Properties for Molecular Devices
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Creating Nanostructures through Self- and Directed Assembly
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select molecules to choose the intermolecular interaction strength and the structures formed within the film. We also apply selective chemistry and self-assembly to form multilayers on patterns formed with conventional nanolithographic techniques to reach higher resolution, greater precision, and chemical versatility in nanostructures that we create.

Manipulating Interfaces to Gain Control of Biological, Chemical, and Physical Properties
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Studies of hydrogen on and in Pd{111} at 4 K utilizing scanning tunneling microscopy and spectroscopy
E. C. H. Sykes, L. C. Fernandez Torres, and P. S. Weiss, Departments of

The interaction of hydrogen with palladium is an important one in terms of many industrially relevant processes such as catalysis, fuel cells, hydrogen storage and metal imbrittlement. For this reason the adsorption and absorption of hydrogen by Pd has been the subject of much work over last few decades, both experimental and theoretical. In this presentation we present low temperature scanning tunneling microscopy and spectroscopy data about hydrogen on and in Pd{111}. Adsorption of low exposures of hydrogen has allowed us to induce motion of atomic hydrogen at 4 K using the STM. The motion has been ascribed to inelastic tunneling of electrons; inelastic electron tunneling spectroscopy (IETS) corroborates this assignment, and the hydrogen atom diffusion barrier has been determined. Adsorption of high exposures of hydrogen results in formation of two ordered overlayer structures: (1x1)-H and (/3x/3)-2H. Absorption of hydrogen into subsurface sites in Pd, concurrent with H diffusion from the bulk results in STM-tip-induced vacancy ordering and Pd{111} lattice distortion. We discuss our ability to selectively populate subsurface sites with hydrogen and present a full STM characterization of this state.

The Ullmann coupling reaction: Atomic scale study of the reactive intermediates and products of a surface catalyzed reaction
Sanjini U. Nanayakkara, E. Charles H. Sykes, Luis C. Fernández-Torres, Patrick Han and P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802, USA.

The term “active site” refers to the regions of a catalyst where the reactants undergo product formation via a low energy intermediate state and is of utmost importance to our understanding of surface reactivity. This means that catalytic surfaces are not uniformly active, but contain unique sites with special chemical, physical, and electronic properties that enhance reactivity. Since Taylor formulated the theory of catalysis in 1925,¹ many researchers have attempted to obtain direct information on the nature of the active site. Since the advent of scanning tunneling microscopy (STM), many groups have contributed to an understanding of chemisorption and catalysis on an atomic scale.²

We present an atomic-scale study of the Ullmann coupling reaction on Cu{111} using low temperature STM and scanning tunneling spectroscopy (STS). We have studied the reactive intermediates and the products of the Ullmann coupling reaction between bromobenzene (PhBr) molecules, which form biphenyl (BP) at room temperature (293 K).³ Bent and co-workers have shown that the Ullmann coupling reaction between two iodobenzene (PhI) molecules to form BP (C6H₅-C₆H₅) takes place with 100% selectivity on Cu{111} using temperature programmed desorption experiments (TPD).⁴ A schematic of the Ullmann coupling reaction is shown in Figure 1. We performed two sets of experiments based on the coverage dependent TPD studies done by Bent and co-workers on this reaction. We exposed a Cu{111} single crystal to bromobenzene (PhBr) at 293 K and imaged at 4 K using STM. At a low PhBr exposure, we were able to identify the structure of the reactive intermediates on the surface and the active sites of the Ullmann coupling reaction. At a high PhBr exposure, we imaged the product biphenyl and identified the surface bound species BP, and atomic bromine, using their STS signatures.

We demonstrate that PhBr molecules dissociatively chemisorb at 293 K and form phenyl intermediates, which travel distances of up to a few 1000 Å over Cu{111} terraces to bind preferentially at step edges. This preference is due to the anisotropic electron density distribution at the step edges. We identify the surface step edge as the active site of this reaction on Cu{111} for C-C bond formation. Once two phenyl intermediates combine to form biphenyl, these product molecules diffuse onto the terraces and arrange as clusters. Our interpretations of the preferred adsorption sites and the intermolecular interactions of adsorbates are explained in terms of the local electronic perturbations on the surface by surface steps and adsorbates.⁵

Figure 1: Schematic of Ullmann coupling reaction. (X=I,Br)


Figure 2: (a) Low coverage: 175 Å × 175 Å area (I_t = 160 pA; V = -0.2 V) illustrating the preferential binding of the phenyl intermediates at steps in the [110] direction. (b) High coverage: 340 Å × 340 Å area (It = 12 pA; V = -0.75 V) showing BP (protrusions) formed at the steps and atomic bromine (depressions) on the terraces.

Molecular Engineering of Molecular Switches
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Molecular Engineering of Single Molecule Devices and Molecular Assemblies
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use molecular design, tailored syntheses, intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, electronic function and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select and tailor molecules to choose the intermolecular interaction strength and the structures formed within the film. We selectively test hypothesized mechanisms for electronic function by varying molecular design, chemical environment, and measurement conditions to enable or to disable functions and control of these molecules with predictive and testable means.

Creating Nanostructures through Self- and Directed Assembly
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select molecules to choose the intermolecular interaction strength and the structures formed within the film. We also apply selective chemistry and self-assembly to form multilayers on patterns formed with conventional nanolithographic techniques to reach higher resolution, greater precision, and chemical versatility in nanostructures that we create.

Micro-contact printing using adamantanethiolate self-assembled monolayers
Arrelaine A. Dameron, Rachel K. Smith, Jennifer R. Hampton, and Paul S. Weiss
Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We have fabricated 1-adamantanethiolate self assembled monolayers (SAMs) on Au{111} and characterized them with scanning tunneling microscopy (STM). The adamantanethiolate SAMs are highly ordered and have less prominent domain boundaries than alkanethiolate SAMs, but the adamantanethiol molecules are easily displaced by other molecules both during and after SAM formation. This susceptibility to displacement makes theses molecules appealing as transient monolayers for the temporary protection of surfaces, or as backfilling agents on patterned surfaces. Using STM and lateral force microscopy (LFM) we have studied the molecular order and stability of micro-contact printed SAMs using adamantanethiolates and compared them to similar systems using alkanethiolates.

Constructing surface mounted molecular rotors
Tao Ye¹, Tomohide Takami², James M. Tour³, Ken ichi Sugiura⁴, and Paul S. Weiss^1
1Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA
²Visionarts Research, Inc, Japan
³Department of Chemistry, Rice University
⁴Department of Chemistry, Tokyo Metropolitan University

We attempt to assemble surface mounted molecular rotors through a shaft-fan design. In a host alkanethiol self-assembled monolayer matrix, a shaft, a pyridine terminated oligo phenylene ethylene thiol is inserted. The fan of the rotor assembly, a metal porphyrin, is attached to the shaft via axial ligation with the pyridine terminal. These supramolecular structures are characterized by scanning tunneling microscopy (STM). We perform a systematic investigation on parameters such as the chain length of the alkanethiol matrix and the meter center of the porphyrins. We will discuss the STM contrast mechanism of these structures.

Pattern stability in microcontact printed self assembled monolayers
Jennifer R. Hampton¹, Rachel K. Smith¹, Arrelaine A. Dameron¹, Christina E. Inman², James E. Hutchison², and Paul S. Weiss^1
1Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
²Department of Chemistry and Materials Science Institute, University of Oregon, 1253 University of Oregon, Eugene, OR 97403-1253

We have used microcontact printing to pattern self assembled monolayers (SAMs) on Au{111} using a variety of molecules with different terminal groups and internal functionalities. The resulting patterned films were monitored over time with scanning tunneling and lateral force microscopies to examine the degree of order of the components and the overall pattern resolution. By varying the molecules used for the printed and backfilled regions of the SAM, we have explored the effect of intermolecular interactions on pattern lifetimes. Pattern stability is enhanced in films that have larger interactions between molecules in one component of the SAM.

Molecular engineering to test the mechanism of conductance switching for a variety of conjugated molecules
Amanda M. Moore¹, Brent A. Mantooth¹, Zachary J. Donhauser¹, Arrelaine Dameron¹, Francisco M. Maya², Jacob W. Ciszek², Yuxing Yao², James. M. Tour², and Paul S. Weiss^1
1Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
²Department of Chemistry and Center for Nanoscale Science and Technology, Rice University, MS-222, 6100 Main Street, Houston, TX 77251-1892

Phenylene ethynylene oligomers have been studied as candidates for molecular electronic devices using scanning tunneling microscopy. These molecules were inserted into host alkanethiolate self-assembled monolayers for isolation and individual addressability. Many different hypotheses and theoretical predictions have been put forth to describe conductance switching. We have tested several of these through variations in the molecular design of our molecular switches and have concluded that the only mechanism consistent with all the switching data are that changes in the molecule-substrate bond hybridization leads to the observed conductance changes.

Self-assembled multilayers creating tailored resists for nanostructure fabrication
Mary E. Anderson¹, Erin M. Carter¹, Adam R. Kurland¹, Charan Srinivasan², Mark W. Horn², and Paul S. Weiss^3
1Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA
²Department of Engineering Science & Mechanics, The Pennsylvania State University, University Park, PA 16802, USA
³Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Self-assembly in combination with lithographic processing can be used to create nanostructures with precise spacing and edge resolution reaching the nanometer-scale. A molecular ruler resist of self-assembled multilayers is selectively deposited on initial lithographically defined gold structures. This resist can be tuned to a desired thickness based on the number of layers deposited. Then, metal is deposited on the sample and the resist is removed, yielding spacings between metal structures dependent on the tailored resist’s dimensions. Work is underway to build molecular ruler resists independently either by capping selected regions of growth or by orthogonal growth of two different multilayer systems. A scheme in development is electroless metal deposition of the secondary metal to improve resist lift-off. Molecular ruler resists can withstand the rigors of lithographic processing and are being developed to advance this method toward device fabrication.

Studies of hydrogen on Pd{111} at 4 K utilizing scanning tunneling microscopy and spectroscopy
Luis C. Fernández-Torres, E. Charles H. Sykes, Patrick Han, Sanjini U. Nanayakkara, and Paul S. Weiss
Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

The interaction of hydrogen with Pd{111} has been investigated with low temperature scanning tunneling microscopy and spectroscopy. Palladium is unique in its ability to both adsorb and absorb hydrogen. Adsorption of low exposures of hydrogen has allowed for the observation of tip-induced hydrogen atom diffusion at 4 K. The diffusion of atomic hydrogen at 4 K has been ascribed to inelastic tunneling of electrons; inelastic electron tunneling spectroscopy (IETS) corroborates this assignment, and the hydrogen atom diffusion barrier has been determined. Adsorption of high exposures of hydrogen results in formation of two ordered overlayer structures: (1x1)-H and (v3xv3)-2H. Absorption of hydrogen into subsurface sites in Pd, concurrent with H diffusion from the bulk, have been attributed as the predominant reasons for two observed phenomena: tip-induced vacancy ordering, and Pd{111} lattice distortion.

Ullmann coupling reaction: Structure and interactions of the reactive intermediates and products of a surface-catalyzed reaction
Sanjini U. Nanayakkara, E. Charles H. Sykes, Luis C. Fernández-Torres, Patrick Han, and Paul S. Weiss
Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We present an atomic-scale study of the Ullmann coupling reaction between aromatic halides, which form biaryls on a Cu{111} surface, utilizing low temperature scanning tunneling microscopy and spectroscopy. Chemical identification of the surface-bound intermediates has been achieved using their spectroscopic signatures. We demonstrate that when the bromobenzene molecules dissociatively chemisorb at 293 K, they form phenyl intermediates, which travel distances of up to a few 1000 Å over bare Cu{111} terraces to bind preferentially at step edges. We attribute this effect to the anisotropic electron density distribution at the steps. We illustrate that C-C bond formation only takes place at the steps, and once phenyl intermediates combine to form biphenyl molecules and the adsorption sites at the steps are saturated, these molecules diffuse onto the terraces. Our observations of intermolecular interactions on the molecular scale are explained in terms of the local electronic perturbations by surface defects and adsorbates.

Elucidation of the electronic properties of immobilized alkanethiolate-stabilized gold clusters and nanoparticles using scanning tunneling microscopy
Rachel K. Smith¹, Sanjini U. Nanayakkara¹, Brent A. Mantooth¹, Gerd Woehrle², James E. Hutchison², and Paul S. Weiss^1
1Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
²Department of Chemistry and Materials Science Institute, University of Oregon, 1253 University of Oregon, Eugene, OR 97403-1253

The single electron transport properties of metal nanoparticles have led to great interest in their potential integration into nanoscale electronics. Here, we discuss and compare the electronic characteristics of isolated, solution-derived, and ligand-stabilized gold clusters (Au₁₁L₁₀) and nanoparticles (Au₁₀₁L₄₃], taken in both cryogenic (4 K, UHV) and ambient conditions using scanning tunneling microscopy and spectroscopy. The clusters and particles (d_CORE = 0.8 nm and 1.5 ± 0.5 nm, respectively) are immobilized on alkanethiolate self-assembled monolayers with inserted dithiol molecules. We thoroughly characterize the self-assembled monolayer surface to which the nanostructures are attached with both local probes and ensemble measurements. At low temperature, the Au₁₁ clusters demonstrate Coulomb blockade behavior, with zero-conductance gaps resulting from quantum size effects.

Pattern stability in microcontact printed self assembled monolayers
Jennifer R. Hampton¹, Rachel K. Smith¹, Arrelaine A. Dameron¹, Christina E. Inman², James E. Hutchison², and Paul S. Weiss^1
1Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
²Department of Chemistry and Materials Science Institute, University of Oregon, 1253 University of Oregon, Eugene, OR 97403-1253

We have used microcontact printing to pattern self assembled monolayers (SAMs) on Au{111} using a variety of molecules with different terminal groups and internal functionalities. The resulting patterned films were monitored over time with scanning tunneling and lateral force microscopies to examine the degree of order of the components and the overall pattern resolution. By varying the molecules used for the printed and backfilled regions of the SAM, we have explored the effect of intermolecular interactions on pattern lifetimes. Pattern stability is enhanced in films that have larger interactions between molecules in one component of the SAM.

Extracting single molecule statistics from scanning probe images
Brent A. Mantooth and Paul S. Weiss
Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Scanning probe microscopes have enabled the unprecedented real-space visualization of single molecules and atoms on surfaces. Analyses of time-resolved sequences of these images allow the quantification of site-specific interactions and dynamics of adsorbed species. We have used scanning tunneling microscopy to measure systems including the dynamic behavior of electronic switching in oligo(phenylene-ethynylene) molecules for application in molecular electronics, to probe and to quantify the weak substrate-mediated interactions in benzene overlayers on Au{111} at 4 K, and to characterize concerted motions of molecular cascades in these benzene overlayers.

Elucidation of the electronic properties of immobilized alkanethiolate-stabilized gold clusters and nanoparticles using scanning tunneling microscopy
Rachel K. Smith¹, Sanjini U. Nanayakkara¹, Brent A. Mantooth¹, Gerd Woehrle², James E. Hutchison², and Paul S. Weiss^1
1Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
²Department of Chemistry and Materials Science Institute, University of Oregon, 1253 University of Oregon, Eugene, OR 97403-1253

The single electron transport properties of metal nanoparticles have led to great interest in their potential integration into nanoscale electronics. Here, we discuss and compare the electronic characteristics of isolated, solution-derived, and ligand-stabilized gold clusters (Au₁₁L₁₀) and nanoparticles (Au₁₀₁L₄₃], taken in both cryogenic (4 K, UHV) and ambient conditions using scanning tunneling microscopy and spectroscopy. The clusters and particles (d_CORE = 0.8 nm and 1.5 ± 0.5 nm, respectively) are immobilized on alkanethiolate self-assembled monolayers with inserted dithiol molecules. We thoroughly characterize the self-assembled monolayer surface to which the nanostructures are attached with both local probes and ensemble measurements. At low temperature, the Au₁₁ clusters demonstrate Coulomb blockade behavior, with zero-conductance gaps resulting from quantum size effects.

Fluorescence microscopy investigation of lipid dynamics in model membranes
Julia J. Heetderks¹ and Paul S. Weiss^2
1Departments of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA
²Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Giant unilamellar vesicles and supported lipid bilayers are used to model lipid domain formation in membranes. Lipid packing in the membranes are monitored and modulated by the incorporation of low concentrations of various fluorescent lipid analogues into the lipid bilayers. Multi-probe labeling of a two-lipid, two-phase membrane is shown to have up to four uniquely labeled domain types, three within the gel phase, on the curved vesicle surface. These results will be compared to those for supported bilayers, which have negligible curvature, and can be measured at high resolution with scanning probe microscopy for more detailed spatial analyses of phase separation. The comparison between these membrane model systems will also further elucidate the role of curvature in lipid domain formation.

Utilizing Self-assembled Multilayers in Lithographic Processes for Nanostructure Fabrication
M. E. Anderson, P. S. Weiss, Departments of Chemistry and Physics, and M. W. Horn, Department of Engineering Science and Mechanics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Chemical self-assembly come to the forefront for patterning surfaces and for the creation of hierarchical structures with nanoscale precision. We apply self-assembly to form multilayers on structures formed by nanolithographic techniques to create patterns with spacings in the 10-100 nm regime.1-3 The key is to use robust multilayers, which do not contain pinhole defects (unlike monolayers) and are able to withstand the rigors of lithographic processing. Controlled placement and thickness of these multilayers form “molecular ruler” resists that accurately determine the spacings between lithographically defined structures (Fig. 1). We have demonstrated this approach with nanostructures generated by electron beam and photolithography, as well as those based entirely on self-assembly.

In this paper, we report on recent results both in designing and patterning complex nanostructures by exploiting methods of directed self-assembly to build molecular ruler resists with independently controlled materials and spacings. We report here a method to accomplish this purpose by combining photolithography and molecular rulers. After forming the molecular resist, conventional photoresist is spin-cast onto the wafer and the photomask is aligned with the parent structure to place daughter structures only in selected locations. After exposure, development, metal deposition, and lift-off of both the photoresist and molecular resist, the final product is a wafer with daughter structures and gaps selectively oriented to create the desired hierarchical nanostructures (Fig. 2).

Creating Nanostructures through Self- and Directed Assembly
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Creating Nanostructures through Self- and Directed Assembly
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Creating Nanostructures through Self- and Directed Assembly
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select molecules to choose the intermolecular interaction strength and the structures formed within the film. We also apply selective chemistry and self-assembly to form multilayers on patterns formed with conventional nanolithographic techniques to reach higher resolution, greater precision, and chemical versatility in nanostructures that we create.

The single electron transport properties of metal nanoparticles have led to great interest in their potential integration into nanoscale electronics. Here, we discuss and compare the electronic characteristics of isolated, solution-derived, and ligand-stabilized gold clusters (Au₁₁L₁₀) and nanoparticles (Au₁₀₁L₄₃], taken in both cryogenic (4 K, UHV) and ambient conditions using scanning tunneling microscopy and spectroscopy. The clusters and particles (d_CORE = 0.8 nm and 1.5 ± 0.5 nm, respectively) are immobilized on alkanethiolate self-assembled monolayers with inserted dithiol molecules. We thoroughly characterize the self-assembled monolayer surface to which the nanostructures are attached with both local probes and ensemble measurements. At low temperature, the Au₁₁ clusters demonstrate Coulomb blockade behavior, with zero-conductance gaps resulting from quantum size effects.

The limits of soft lithographic techniques: Pattern stability and molecular order
Jennifer R. Hampton, Arrelaine A. Dameron, Rachel K. Smith, Paul S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Soft lithography techniques such as dip-pen nanolithography (DPN) and microcontact printing (µCP) are promising alternatives to traditional nanofabrication methods; however, little is known about the properties of the resulting structures. Using scanning tunneling microscopy (STM) and lateral force microscopy (LFM), we are exploring the fundamental limits of these new technologies to allow for precise control of desired patterns and optimizing the molecular interactions to yield stable structures. We have used µCP and DPN to pattern self assembled monolayers (SAMs) on Au{111} using a variety of molecules with different terminal groups and internal functionalities. The resulting patterned films were monitored over time with STM and LFM to examine the degree of order of the components and the overall pattern resolution. We have found that backfilling the unpatterned areas with a different molecule enhances the long-term stability of the patterns. By varying the molecules used for the printed and backfilled regions of the SAM, we are exploiting intermolecular interactions to control pattern lifetimes as a means to gain stability on the molecular scale.

Comparative Conductance of Chalcogen-Terminated Molecules on Au{111}
Jason D. Monnell,(1) Joshua J. Stapleton,(2) Shawn M. Dirk,(3) James M. Tour,(3,*) David L. Allara,(2,*) and Paul S. Weiss(1,*) (1) Departments of Chemistry and Physics, 104 Davey Laboratory, The Pennsylvania State University, University Park, PA 16802-6300 (2)Departments of Chemistry and Materials Science, 104 Chemistry Research Building, The Pennsylvania State University, University Park, PA 16802-6300 (3) Department of Chemistry and Center for Nanoscale Science and Technology, Rice University, Houston, TX 77005

In order to assess the conductance of a single molecule, it must be isolated, then interrogated. In order to do this, a self-assembled monolayer is used as a host matrix into which single molecules are inserted. The structures and electronic properties of two host matrices, n-alkanethiolate [CH₃(CH₂)_nS- n = 9 and 11] and n???????–alkaneselenolate [CH₃(CH₂)_nSe- n = 9 and 11] self assembled monolayers on Au{111} are characterized. Simultaneously acquired apparent tunneling barrier height (ATBH) and scanning tunneling microscopy (STM) images reveal that n-alkanethiolate molecules have a lower barrier to tunneling and thus higher conductances than equivalent n-alkaneselenolates. A two-barrier tunneling model is used to elucidate the molecular and contact conductances of the two families of molecules. This model is then extended using decanethiolate as an internal standard to compare the conductances of related molecules, including 3-mercapto-N-nonylpropionamide, a-?-alkanedithiol, and 4,4’-di(ethynylphenyl)-1-benzenethiol.

One of the main goals in the use of scanning probes in surface science is to exploit the local capabilities of the probes to gain insight into the mechanism of industrial heterogeneous processes on the molecular level. To this end, the understanding of adsorbate-adsorbate, substrate-adsorbate interactions, and collective movement of molecules over surfaces becomes central in bridging the gap between the fundamental and practical aspects of surface processes. Here we present a low temperature ultrahigh vacuum scanning tunneling microscopy (STM) study of small organic molecules adsorbed on Au{111} at 4 K. In this work, cyanogens (C₂N₂), carbon dioxide (CS₂) and benzene, were investigated independently. We have used differential conductance imaging, time-lapse STM imaging and digital tracking to investigate the effect of substrate morphology on molecular self assembly, visualize substrate-adsorbate electronic interactions, observe molecular cascade motion and confirm through statistics the concerted nature of these cascade motions.

Creating and Controlling Nanostructures through Self- and Directed Assembly
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select molecules to choose the intermolecular interaction strength and the structures formed within the film. We also apply selective chemistry and self-assembly to form multilayers on patterns formed with conventional nanolithographic techniques to reach higher resolution, greater precision, and chemical versatility in nanostructures that we create.

A Physical Model of Axonal Damage Due to Oxidative Stress: Radical-Induced Degradation of Liposome-Encapsulated Microtubules
Paul S. Weiss¹ Anne E. Counterman,¹ Terrence G. D'Onofrio,¹ and Anne Milasincic Andrews^2
1Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
²Department of Chemistry and Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA 16802-6300, USA

We model oxidative stress in axons using photogenerated radicals in a simplified membrane-encapsulated microtubule system. We have used fluorescence and differential interference contrast microscopies to monitor photochemically-induced microtubule breakdown on the supported region of membrane in encapsulating synthetic liposomes, in which lipid composition can be controlled. We demonstrate that the kinetics of microtubule degradation are influenced by the lipid saturation level, fluorescent probe concentration, and presence of free-radical scavengers. This system may be used to model the effects of oxidative stress in neuropathies such as Parkinson’s, Huntington’s, or Alzheimer’s diseases, and even reproduces some morphologies found in vivo.

Displacement Printing of Adamantanethiolate Self-Assembled Monolayers

A. A. Dameron, J. R. Hampton, R. K. Smith, and P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Extracting Single Molecule Statistics from Scanning Probe Images

B. A. Mantooth, J. R. Hampton, R. K. Smith, P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Scanning probe microscopes have enabled the unprecedented real-space visualization of single molecules and atoms on surfaces. Analyses of time-resolved sequences of these images allow the quantification of site-specific interactions and dynamics of adsorbed species. We have used scanning tunneling microscopy to probe and to quantify the weak substrate-mediated interactions in benzene overlayers on Au{111} at 4 K, and to characterize concerted motions of molecular cascades in these benzene overlayers. We use similar techniques to characterize the correlation of CO adsorption site with the charge density waves of the surface state of Ag{111}.

The Ullmann coupling reaction: Structure of the reactive intermediates and products of a surface catalyzed reaction

Sanjini U. Nanayakkara, E. Charles H. Sykes, Luis C. Fernández-Torres, Patrick Han and Paul S. Weiss*, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We present an atomic-scale study of the Ullmann coupling reaction on Cu{111} using low temperature scanning tunneling microscopy and spectroscopy. We have studied the reactive intermediates and the products of the Ullmann coupling reaction between bromobenzene molecules, which form biphenyl at room temperature (293 K). Chemical identification of the surface-bound species has been achieved using their tunneling spectroscopic signatures. We demonstrate that bromobenzene molecules dissociatively chemisorb at 293 K and form phenyl intermediates, which travel distances of up to a few 1000 Å over Cu{111} terraces to bind preferentially at step edges. This preference is due to the anisotropic electron density distribution at the step edges. We identify the surface step edge as the active site of this reaction on Cu{111} for C-C bond formation. Once two phenyl intermediates combine to form biphenyl, these product molecules diffuse onto the terraces and arrange as clusters. Our interpretations of the preferred adsorption sites and the intermolecular interactions of adsorbates are explained in terms of the local electronic perturbations on the surface by surface steps and adsorbates.

Assembly of Synthetic Molecular Motors on Surfaces
T. Takami, Visionarts Research, Japan, T. Ye, The Pennsylvania State University, J. M. Tour, Rice University, K.-I. Sugiura, Tokyo Metropolitan University, Tokyo, Japan, and P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We attempt to assemble synthetic molecular motors mounted on Au{111} and graphite surfaces. Two kinds of molecular motors are proposed: (1) in-plane rotation of molecular rotors: the substrate-bound shaft of the rotor assembly, a metal porphyrin is attached to the shaft through axial ligation with a pyridine group, (2) perpendicular rotation of molecular rotors: sandwich porphyrins are used for the tables to stand on the surface and a perpendicular bifunctional shaft is attached between the porphyrins. The rotation of the molecular motors will be imaged with scanning tunneling microscope (STM) in air and in solution, and will be detected via single molecule resonance spectroscopy with alternating current STM (ACSTM).

Molecular engineering to test the mechanism of conductance switching for a variety of conjugated molecules

Amanda M. Moore¹, Brent A. Mantooth¹, Zachary J. Donhauser¹, Arrelaine A. Dameron¹, Jacob W. Ciszek², Francisco Maya², Yuxing Yao², James M. Tour², and Paul S. Weiss¹

(1) Department of Chemistry, The Pennsylvania State University, 152 Davey Laboratory, University Park, PA 16802
(2) Department of Chemistry and Center for Nanoscale Science and Technology, Rice University

Phenylene ethynylene oligomers have been studied as candidates for molecular electronic devices using scanning tunneling microscopy. These molecules were inserted into host alkanethiolate self-assembled monolayers for isolation and individual addressability. Many different hypotheses and theoretical predictions have been put forth to describe conductance switching. We have tested several of these through variations in the molecular design of our molecular switches and have concluded that the only mechanism consistent with all the switching data are that changes in the molecule-substrate bond hybridization leads to the observed conductance changes.

Self-assembled Multilayers Creating Tailored Resists for Nanostructure Fabrication
M. E. Anderson, E. M. Carter, A. R. Kurland, C. Srinivasan, M. W. Horn, P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Designing and patterning complex hierarchical assemblies by exploiting methods of directed self-assembly in combination with a variety of lithographic techniques has been an active area of research for patterning in the sub-100 nm regime. We have used self-assembled multilayers to create molecular ruler resists to define nanostructures with precise spacing and edge resolution reaching the nanometer-scale.^1-3 A molecular ruler resist of self-assembled multilayers, composed of alternating layers of a,w-mercaptoalkanoic acids and coordinated metal ions, is selectively deposited on initial lithographically defined gold structures. This resist can be tuned based on the number of layers deposited to a desired thickness (routinely between 10-100 nm). Then, metal is deposited on the sample and the resist is removed, yielding spacings between metal structures dependent on the dimensions of the tailored resist. Work is underway to build molecular ruler resists independently either by capping selected regions of growth or by orthogonal growth of two different multilayer systems. A scheme in development is electroless metal deposition of the secondary metal, where the ruler resist both defines the structure spacing and inhibits deposition for selective metal placement. Molecular ruler resists can withstand the rigors of lithographic processing and are being developed to advance this method toward device fabrication.

Elucidation of the Electronic Properties of Immobilized Alkanethiolate-Stabilized Gold Clusters and Nanoparticles Using Scanning Tunneling Microscopy
P. S. Weiss, R. K. Smith, S. U. Nanayakkara, B. A. Mantooth, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
G. Woehrle and J.E. Hutchison, Department of Chemistry, University of Oregon, Eugene, OR, USA

The single electron transport properties of metal nanoparticles have led to great interest in their potential integration into nanoscale electronics. Here, we discuss and compare the electronic characteristics of isolated, solution-derived, and ligand-stabilized gold clusters (Au₁₁L₁₀) and nanoparticles (Au₁₀₁L₄₃), taken in both cryogenic (4 K, UHV) and ambient conditions using scanning tunneling microscopy and spectroscopy. The clusters and particles (d_CORE = 0.8 nm and 1.5 ± 0.5 nm, respectively) are immobilized on alkanethiolate self-assembled monolayers with inserted dithiol molecules. We thoroughly characterize the self-assembled monolayer surface to which the nanostructures are attached with both local probes and ensemble measurements. At low temperature, the Au₁₁ clusters demonstrate Coulomb blockade behavior, with zero-conductance gaps resulting from quantum size effects.

Molecular Rulers: Advancing Nanolithography to Smaller Scales and Greater Precision
P. S. Weiss, M. E. Anderson, E. M. Carter, M. A. Horn, A. Kurland, H. Tanaka, and G. N. Taylor, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We combine conventional lithographic techniques with chemical self-assembly for the creation of nanostructures whose spacing and edge resolution reach nanometer-scale precision. The controlled placement and thickness of self-assembled multilayers composed of alternating layers of complementary chemical pairs form precise “molecular ruler” resists to produce tailored, lithographically defined patterns. We have advanced the use of molecular rulers through a number of new and continuing strategies. We have demonstrated two methods of multilevel molecular ruler processing using photolithography, in order to show that these processes are compatible with conventional methods now used for device production. We have also explored non-conventional parent structures created by self-assembly processes both for producing nanostructures and for elucidating fundamental aspects of multilayer assembly as they apply to this method. We have also demonstrated the ability to make multiple generation and selectively positioned structures.

A quantitative study of the long-range interactions between bromine islands on Cu{111} mediated by the surface state at elevated temperatures is presented. Randomly distributed bromine adatoms are immobile at 293 K, but when annealed to 600 K the adatoms become mobile and aggregate to form islands. The interaction potential between these islands has been determined by evaluating the distance distribution between the bromine islands from a series of scanning tunneling microscopy images taken at 4 K. By only taking two-body interactions into consideration, we demonstrate that the interaction potential is oscillatory in nature with potential energy minima observed at 12, 26 and 41 Å. This corresponds to a period of half the Fermi wavelength of Cu{111}. Unlike previous quantitative studies of long-range interactions between single metal adatoms on Cu{111} at temperatures up to 21 K,[1,2] we do not observe long-range interactions up to ~70 Å due to the shorter coherence length of the Cu surface state at elevated temperatures. Our findings indicate the pair potential exists only up to 40 Å, which is in good agreement with the coherence length of ~34 Å of the Cu{111} surface state at 600 K.[3] In this study we present conclusive evidence that the perturbations due to the surface state are important and relevant in mediating interactions between adsorbates at catalytically relevant temperatures.

[1] Repp, J.; Moresco, F.; Meyer, G.; Rieder, K.H.; Hyldgaard, P.; Persson, M. Phys. Rev. Lett. 2000, 85, 2981.
[2] Knorr, N.; Brune, H.; Epple, M.; Hirstein, A.; Schneider, M.A.; Kern, K. Phys. Rev. B 2002, 65, 115420.
[3] Fujita, D.; Amemiya, K.; Yakabe, T.; Neoj, H.; Sato, T.; Iwatsuki, M. Phys. Rev. Lett. 1997, 78, 3904.

Creating Nanostructures through Self- and Directed Assembly
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select molecules to choose the intermolecular interaction strength and the structures formed within the film. We also apply selective chemistry and self-assembly to form multilayers on patterns formed with conventional nanolithographic techniques to reach higher resolution, greater precision, and chemical versatility in nanostructures that we create.

DNA Nanostructures: Fabrication, Characterization, and Applications
T. J. Mullen, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Exploring the properties of nano-materials: self assembled monolayers, platelets and particles
J. D. Monnell and P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Measuring and Controlling Molecular-Scale Properties for Molecular Devices
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Exploring and Controlling the Atomic-Scale World
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Precise Nano-Scale Assemblies
Rachel K. Smith, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Measuring and Controlling Molecular-Scale Properties for Molecular Devices
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Multimode Scanning Probe Microscopies
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
and
K. F. Kelly, Department of Electrical and Computer Engineering, Rice University, Houston, TX

Development of AC Scanning Tunneling Microscopy
A. M. Moore and P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Manipulation of Subsurface Hydrogen and Excitation of Surface Hydrogen Atoms on Palladium
A. A. Dameron, L. C. Fernandez-Torres, E. C. H. Sykes, S. U. Nanayakkara, and P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Physical Models of Membrane-Cytoskeleton and Membrane-Surface Interactions
P. S. Weiss, Anne Milasincic Andrews, Anne Counterman, Susan Gillmor, and Julia Heetderks, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Giant unilamellar lipid vesicles are used to study interactions of model membranes with cytoskeletal components and surfaces. Through fluorescence and differential interference contrast microscopies, we monitor the photochemically-induced microtubule breakdown within encapsulated synthetic liposomes of controlled compositions. Microtubule formation by polymerization of tubulin inside a lipid vesicle stretches the spherical membrane into an elongated shape. Attack by UV excited free radicals from a lipid-soluble fluorescent probe causes degradation of vesicle-encapsulated microtubules, and shrinkage of the elongation. In this system, we model the effects of oxidative stress in neuropathies such as Parkinson's, Huntington's, or Alzheimer's diseases. Our experimental system appears sufficient even to reproduce some morphologies found in vivo through the isolation of specific molecules that compose the membranes and structural elements of nerve cells, as well as to probe the roles of anti-oxidants in preventing this damage. As we investigate the oxidative degradation of microtubules within vesicles, similarly we isolate the lipid actors in our studies of membrane to external surface interactions, selectively including the effects of proteins, cholesterol, and extracellular matrix components. Vesicle-to-surface investigations are of particular interest to biomaterials, bioengineering, drug delivery and artificial implant device projects. We simultaneously define and vary surface morphology and surface chemistry using nanolithography and surface functionalization. In close proximity to the surface, the dual-labeled, two-phase vesicles offer a unique system to study cell to basement membrane interactions. Previously, we have demonstrated the curvature-composition relationship within vesicles. In mimicking the basement membrane morphology, we relate membrane composition and adhesion to the surface functionalization and topography.

Measurements of Precise Nanoparticles and Nanoparticle Assemblies
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We discuss and compare the measured electronic characteristics of isolated, solution-derived, and ligand-stabilized gold clusters (Au₁₁L₁₀) and nanoparticles (Au₁₀₁L₄₃), taken in both cryogenic (4 K, UHV) and ambient conditions using scanning tunneling microscopy and spectroscopy. The clusters and particles (d_CORE = 0.8 nm and 1.5 ± 0.5 nm, respectively) are immobilized on alkanethiolate self-assembled monolayers with inserted dithiol tethers. We thoroughly characterize the self-assembled monolayer surface to which the nanostructures are attached with both local probes and ensemble measurements. At low temperature, the Au₁₁ clusters demonstrate Coulomb blockade behavior, with zero-conductance gaps resulting from quantum size effects. Surprisingly, chemically identical particles produce different families of tunneling spectra, comparable to previous results for heterogeneous distributions of particles.

Measuring and Controlling Molecular-Scale Properties for Molecular Devices
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Molecular Engineering of Single Molecular Switches and Molecular Assemblies
P. S. Weiss, A. A. Dameron, and A. M. Moore, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use molecular design, tailored syntheses, intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, electronic function and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select and tailor molecules to choose the intermolecular interaction strength and the structures formed within the film. We selectively test hypothesized mechanisms for electronic switching by varying molecular design, chemical environment, and measurement conditions to enable or to disable functions and control of these molecules with predictive and testable means.

Thin film growth of phthalocyaninato and porphyrinato doubledecker and triple-decker molecules at phenyloctane/graphite interface
Tomohide Takami,^A,B, Tao Ye,^B Paul S. Weiss,^B Dennis P. Arnold,^C Ken-ichi Sugiura,^D and Jianzhuang Jiang,^E
AVisionarts Research
^BDepartments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
^CQueensland Univ. Tech.
^DTokyo Metro. Univ.
^EShandong Univ.

Introduction: Double-decker and triple-decker phthalocyanines and porphyrins have potential applications for molecular electronic devices such as molecular switches and synthetic molecular motors. Here we demonstrate the thin film growth of heteroleptic bis- and tris-phthalocyaninato and porphyrinato molecules at the liquid/solid interface of phenyloctane/graphite studied by scanning tunneling microscopy (STM).

Experiment: Double-decker and triple-decker phthalocyaninato and porphyrinato molecules were dissolved in 1-phenyloctane and the solution was dropped onto graphite. The STM measurements were performed in air at the solution/graphite interface.

Results and discussion: Figures show STM images of the mixed monolayer of naphthalocyaninelutetium- tetrat-butylphenylporphyrin (Nc-Lu-TPP) and naphthalocyanine-lutetiumoctaethylporphyrin (Nc-Lu-OEP) double-deckers before and after the manipulation of single Nc- Lu-OEP molecule with the STM tip by applying a voltage pulse. In this way, we succeeded in resolving and manipulating single molecules.

STM images of Nc-Lu-TPP and Nc-Lu-OEP mixture monolayer at phenyloctane/graphite interface, showing a single molecular manipulation (before and after). Sample bias: -0.6 V, tunnel current: 1 pA.

Observation of phthalocyanine and porphyrin double-decker and triple-decker monomolecular thin films on graphite by scanning tunneling microscopy
Tomohide Takami,^1,2, Tao Ye,² Paul S. Weiss,² Dennis P. Arnold,³ Ken-ichi Sugiura,⁴ and Jianzhuang Jiang,^5
1Visionarts Research
²Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
³Queensland Univ. Tech.
⁴Tokyo Metro. Univ.
⁵Shandong Univ.

Introduction: Double-decker and triple-decker phthalocyanines and porphyrins are promising candidates for molecular devices such as molecular switches and synthetic molecular motors. Here we demonstrate molecularly resolved observation of bis- and tris-phthalocyaninato metal complexes with STM.

Experiment: Absorbates were dissolved in 1-phenyloctane and the solution was dropped onto graphite. The STM measurements were performed in air at the solution/graphite interface.

Results and discussion: Figures show STM images of doubledeckers. The internal structures of the top phthalocyanines were observed and we could resolve the individual molecules. We also succeeded in manipulating single molecules with the STM tip.

Measuring and Controlling Molecular-Scale Properties for Molecular Devices
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Measuring and Controlling Molecular-Scale Properties for Molecular Devices
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Measuring and Controlling Atomic-Scale Properties of Precise Complex Assemblies
Rachel K. Smith, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Creating Nanostructures through Self- and Directed Assembly
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select molecules to choose the intermolecular interaction strength and the structures formed within the film. We also apply selective chemistry and self-assembly to form multilayers on patterns formed with conventional nanolithographic techniques to reach higher resolution, greater precision, and chemical versatility in nanostructures that we create.

The neurochip: An advanced nanomaterial for the development of novel biosensors and functionally-directed proteomics
Anne Milasincic Andrews,^1,2 Matthew E. Szapacs,^2,3 Ann-Sofie Cans,^1-3 Amit Vaish,² Jennifer L. Han,² Mary E. Anderson³ and P. S. Weiss^3,4
1Department of Veterinary Science
²Neuroscience Program, Huck Institutes for Life Sciences
³Department of Chemistry
⁴Department of Physics
The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select molecules to choose the intermolecular interaction strength and the structures formed within the film. We also apply selective chemistry and self-assembly to form multilayers on patterns formed with conventional nanolithographic techniques to reach higher resolution, greater precision, and chemical versatility in nanostructures that we create.

Measuring and Controlling Molecular-Scale Properties for Molecular Devices,
or:
Why the CBA Should Change Its Name
Paul S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use molecular design, tailored syntheses, intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, electronic function and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select and tailor molecules to choose the intermolecular interaction strengths and the structures formed within the film. We selectively test hypothesized mechanisms for electronic switching by varying molecular design, chemical environment, and measurement conditions to enable or to disable functions and control of these molecules with predictive and testable means. Critical to understanding these variations has been developing the means to make tens to hundreds of thousands of independent single-molecule measurements in order to develop sufficiently significant statistical distributions, comparable to those found in ensemble-averaging measurements, while retaining the heterogeneity of the measurements.

A New Technique for Nanoscale Patterning: Micro-Displacement Printing
Arrelaine A. Dameron, Jennifer R. Hampton, Thomas J. Mullen, J. Nathan Hohman, Susan D. Gillmor, Rachel K. Smith, and Paul S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Microcontact printing is a rapid and simple methodology that produces high spatial resolution of patterns over a large printing area. Here we demonstrate a new patterning technique that employs microcontact printing to replace pre-formed self-assembled monolayers (SAMs) selectively, which we call "displacement printing". We have fabricated 1-adamantanethiolate SAMs on Au{111} and characterized them with scanning tunneling microscopy (STM). The adamantanethiolate SAMs are highly ordered and have less prominent domain boundaries than alkanethiolate SAMs, but because of their low intermolecular interaction strength, adamantanethiolate molecules are easily displaced by other molecules both during and after SAM formation. Taking advantage of this property, we have used adamantanethiolate SAMs to pattern molecules on Au{111} using displacement printing. Using STM and lateral force microscopy (LFM), we have studied the molecular order of the printed features.

This technique results in ordered molecular regions of both the patterning ("displacing") molecule as well as the remaining adamantanethiolate. The existence of the adamantanethiolate SAM before patterning hinders lateral surface diffusion of the patterning molecules, which is problematic in conventional microcontact printing especially for molecules with low molecular weight, and therefore permits the use of molecules that are otherwise too mobile to pattern by other methods. We are currently extending this approach to other soft lithography methods, such as dip-pen nanolithography.

Creating Nanostructures through Self- and Directed Assembly
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select molecules to choose the intermolecular interaction strength and the structures formed within the film. We also apply selective chemistry and self-assembly to form multilayers on patterns formed with conventional nanolithographic techniques to reach higher resolution, greater precision, and chemical versatility in nanostructures that we create.

New Strategies in Self- and Directed Assembly
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Extending and Applying Self- and Directed Assembly
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Nanoscopic analyses: Single molecule characterization in molecular electronics and surface science
B. A. Mantooth^* and P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Time-resolved scanning tunneling microscope (STM) measurements of single molecules are used to determine the behavior and interactions of adsorbed species. This thesis describes the custom design of the scanning tunneling microscope hardware and software used to acquire molecular-resolution images. Using this instrument, two systems are characterized: the conductance switching of oligo (phenylene-ethynylene) (OPE) molecules inserted in \emph{n}-alkanethiolate self-assembled monolayers (SAMs), and the motion of benzene adsorbed on Au\{111\} at 4 K\@. For both systems, the use of digital image processing is applied to the analysis of time-resolved sequential images to determine changes in topographic features or overlayer structure. From these analyses we can determine the mechanism for conductance switching and quantify the weak adsorbate-adsorbate substrate-mediated interactions present in benzene overlayers. These types of analyses must be executed at the single molecule level, as no ensemble technique can observe the discrete behaviors observed by STM in these systems.

One of the ultimate miniaturizations in nanotechnology is molecular electronics, where electronic devices will potentially consist of individual molecules. Some of the molecules being investigated for application in molecular electronics are a family of OPE molecules. Ensemble measurements of these molecules have yielded hysteretic switching and negative differential resistance, both useful properties that enable memory and logic operations. We investigate these systems by inserting the molecule of interest in an inert SAM to isolate single molecules, probing each molecule with the STM tip on a single-molecule basis. We acquire time-resolved sequences of STM images over periods of up to several days or acquire real-time measurements at a rate of 10 kHz for 15 seconds, and observe that these molecules exhibit conductance switching such that their apparent height changes. Due to properties of the materials used to acquire STM images, the field of view may drift. A digital image tracking algorithm based on Fourier transform cross-correlation has been developed to correct for instrumental drift in STM images. Analyzing the apparent height of different molecules in variable SAM matrices as a function of time has enabled us to propose that conductance switching is the result of hybridization and/or conformational changes at the metal-molecule interface.

Through this work on OPE molecules we have 1) developed image processing tools to measure and quantify the behavior of single molecules, 2) demonstrated that single OPE molecules exhibit conductance switching, 3) using real-time topographic measurements we have probed the dynamics of conductance switching and found that conductance switching does not appear to be a random process, and 4) demonstrated that molecules exhibit multimodal distributions of apparent heights indicating that there may be more than one on and one off state for these molecules.

Using similar analyses, we have applied scanning tunneling microscopy to probe and to quantify the weak substrate-mediated interactions in benzene overlayers on Au{111} at 4 K. We observe that benzene molecules exhibit three types of motion, including 2D desorption, 2D adsorption, and simultaneous dislocations of many molecules (molecular cascades). Correlating the probability of 2D desorption with the number of nearest neighbors of the desorbing molecules enables the calculation of the magnitude of the adsorbate-adsorbate substrate-mediated interactions. We also observe chains of up to 12 molecules simultaneously moving in the same direction at the same time in an event we refer to as molecular cascades. These cascades are the result of translation of the overlayer structure and are highly correlated with 2D desorption and 2D adsorption.

The work on benzene molecules adsorbed on Au{111} has shown 1) that the application of digital image processing can yield quantitative values for adsorbate-adsorbate substrate-mediated interactions that depend on the number of nearest neighbors of an adsorbed molecule, and 2) that these molecules exhibit concerted motion resulting from a translation of the overlayer structure. This translation is propagated through substrate-mediated interactions and is initiated by the 2D adsorption/desorption of benzene molecules along the soliton wall.

The combination of the molecular resolution of scanning tunneling microscopy and the ability to acquire time-resolved images coupled with digital image processing enables the analysis of sequential images to yield an understanding of the behavior of single molecules. Through these analyses we can elucidate the mechanism that describes the dynamic processes we observe. The characterization of conductance switching of OPE molecules, the quantification of substrate-mediated interactions, and the observation of cascade motion are detectible \emph{only} by this type of single molecule analysis on many hundreds of molecules, as the ensemble measurements could never observe such behavior.

Lipid Bilayer Membrane Dynamics, Control, and Measurements
Paul S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Nanoscale Science
Paul S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Investigating Molecular Self-Assembly Using Scanning Tunneling Microscopy
Chris Pochas, Sanjini Nanayakkara, and Paul S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Scanning Tunneling Microscopy
Phil Cerami and Paul S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Microfluidic Flow Chamber Design for Vesicle Adhesion Studies
Emily Hiers, Susan Gillmor, and Paul S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Lipid vesicles provide a model for studying the mechanical properties of cell membranes. We have developed a platform to conduct detachment studies of vesicles on topographically patterned surfaces to study the influence of membrane mechanics on cell adhesion to surfaces. Commonly, these cell studies are performed using flow chambers that house the surface of interest. The shear stress at which the cells detach from the surface is quantified and is indicative of their adhesion strength. However, this strategy requires many experiments to collect a single data set because the flow rate is fixed for each experimental run and must be changed to produce each shear stress value. Our setup reduces the number of experiments required to collect data for vesicle detachment studies. For these experiments, we attach the vesicles to the surface through avidin-biotin linkages inside the flow field. Our preliminary design for a microfluidic flow chamber minimizes the number of samples, the amount of labor, and the number of experiments required to collect a data set. The device incorporates a chamber geometry that produces a range of shear stresses from a single flow rate. Future work entails optimizing the present devices, incorporating new design strategies and quantifying membrane adhesion, deformation and shear.

Exploring and Controlling the Atomic-Scale World
Research in the Weiss Group
Paul S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Molecular Switches, Backbones and Contacts
Roger van Zee, NIST, Gaithersburg, MD
Paul S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Development of a tunable microwave frequency alternating current scanning tunneling microscope
A. M. Moore, B. A. Mantooth, and P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We have built a scanning tunneling microscope (STM) capable of profiling dopants in semiconductor devices and test structures at sub-nanometer resolution. The alternating current signals, and thereby the dopant density and type, are obtained through a heterodyned signal. Two frequencies are applied to the STM tip and the nonlinearity of the tunnel junction mixes the frequencies, generating new signals including at the difference of the frequencies applied; this in combination with the DC bias yields information on the dopant density and type. This ultrahigh resolution (<1 nm) profiling tool enhances what is obtained through current metrology tools and will support semiconductor processing as the size scale of devices continues to decrease.

Single Molecular Motors
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
T. Takami, Visionarts Research, State College, PA, USA & Tokyo, Japan
T. Ye, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
K. I. Sugiura, Tokyo Metropolitan University, Tokyo, Japan
D. P. Arnold, Queensland University of Technology
J. Jiang, Shandong University
J. M. Tour, Rice University, Houston, TX, USA

We explore three families of synthetic molecular motors. One family is based on caltrops, one family is based on sandwich porphyrins, and the third is based on hybrid porphyrins. Each is surface bound and presents challenges in terms of attachment and operation. Operation will be driven with external electric fields. Measurements will initially be performed using high frequency tunable AC scanning tunneling microscopy, which should enable operation and measurement well above the lowest rotational levels of the molecules. We demonstrate placement of both isolated and ordered layers of oriented molecules on surfaces. We use electrochemical potential as well as specific chemical attachment to control motor function. We also demonstrate a photoswitchable "lock" that can be incorporated into the design of the molecules. Through synthetic chemistry and self-assembly, we can design and specify the interactions of neighboring and patterned motors.

Ultrastable conductance measurements of self assembled monolayer supported phenylene-ethylene oligomers
Nanayakkara, Blake, Dameron, Zhang, Pochas, Weiss, Pearl, Uppili, Allara, and Tour, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We have used alkanthiolate self-assembled monolayers (SAMs) to fabricate support matrices for probing the charge transport properties of both isolated and bundled phenylene-ethylene oligomers (OPEs). By utilizing solution and vapor phase manipulation techniques, we can select the distribution of the OPE molecules within the SAM matrix. These fabrication techniques in combination with the spatial and energy resolution afforded by low temperature scanning tunneling microscopy and spectroscopy have enabled us to probe the electronic properties of these molecules. We have probed individual substituted OPE molecules in analogous environments to understand the effects of chemical substitution on charge transport. We aim to understand the conductance pathways of these molecules as a function of their chemical structure, physical environment and adsorption site.

Tunneling spectroscopy of self-assembled monolayers of 1-adamantanethiolate on single crystal metallic substrates
Kurland, Dameron, Han, Nanayakkara, and Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We measure local barrier height and differential conductance using ultrahigh vacuum scanning tunneling microscopy (STM) at 4 K to investigate the work function and local density of states, respectively, of individual adamantanethiolate molecules on a range of single crystal metallic substrates. These techniques allow us to probe specific electronic characteristics while simultaneously resolving the molecular lattice of the adamantanethiolate monolayers. Previously, we have shown that adamantanethiolate molecules form well-ordered hexagonally close-packed monolayers on the Au{111} surface. The complex and highly symmetric cage structure of adamantanethiolate results in weaker intermolecular interactions than those of alkanethiolate self-assembled monolayers. Taking advantage of these properties, we have implemented adamantanethiolate molecules in thin-film molecular lattices and as nanolithography patterning inks. We aim to exploit and to incorporate the unique physical and electronic interactions of adsorbed adamantanethiolate to understand and to tailor self-assembled nanostructures.

Microdisplacement printing
Dameron, Hampton, Smith, Mullen, Gillmor, and Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We demonstrate “micro-displacement printing”, which employs microcontact printing to replace pre-formed, easily-displaceable, 1-adamantenthiolate self-assembled monolayers (SAMs) selectively. This technique results in ordered molecular regions of both the displacing molecule as well as the remaining adamantanethiolate. The existence of the adamantanethiolate SAM before patterning hinders lateral surface diffusion of the patterning molecules, which is problematic in conventional microcontact printing, especially for molecules with low molecular weight, permitting the use of molecules that are otherwise too mobile to pattern by other methods. In addition, micro-displacement printing circumvents the need for solution processing during the initial patterning steps, a process that induces molecular exchange and edge roughening especially at the pattern interfaces. By additional processing, it is possible to eliminate the adamantanethiolate from the surface altogether, replacing it with a third (potentially low molecular weight) molecule. In this way, fabrication of a patterned SAM composed two mobile molecules is achievable, extending the capabilities of soft lithography.

Double-decker phthalocyanines/porphyrins at phenyloctane/graphite interfaces studied by scanning tunneling microscopy
T. Takami, Visionarts Research, State College, PA, USA & Tokyo, Japan
T. Ye, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
D. P. Arnold, Queensland University of Technology
K. I. Sugiura, Tokyo Metropolitan University, Tokyo, Japan
J. Jiang, Shandong University, China

Initial stages of the thin film growth and stacking of phthalocyanine with long alkyl chains and heteroleptic double-decker phthalocyaninato, naphthalocyaninato, and porphyrinato molecules at the liquid/solid interface between 1-phenyloctane and graphite have been studied by scanning tunneling microscopy (STM). STM observations at tunneling currents under 10 pA and scanning speeds slower than 1 line/s showed high resolution images clearly displayed the top layer of the phthalocyanine and double-decker molecules. We have shown a method to compose nano-structures to substitute the double-decker monolayer with different molecules by scratching the layer using an STM tip, and also manipulated the double-decker molecule with a voltage pulse from the STM tip.

Development of a tunable microwave frequency alternating current scanning tunneling microscope
A. M. Moore, B. A. Mantooth, and P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We have built a scanning tunneling microscope (STM) capable of profiling dopants in semiconductor devices and test structures at sub-nanometer resolution. The alternating current signals, and thereby the dopant density and type, are obtained through a heterodyned signal. Two frequencies are applied to the STM tip and the nonlinearity of the tunnel junction mixes the frequencies, generating new signals including at the difference of the frequencies applied; this in combination with the DC bias yields information on the dopant density and type. This ultrahigh resolution (<1 nm) profiling tool enhances what is obtained through current metrology tools and will support semiconductor processing as the size scale of devices continues to decrease.

AEI: Ultrastable conductance measurements of nano-scale assemblies
Nanayakkara, Smith, Weiss, Uppili, Allara, Tour, Woehrle, and Hutchison, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We have used alkanthiolate self-assembled monolayers (SAMs) to fabricate support matrices for probing charge transport properties in precise nano-scale assemblies, namely isolated and bundled phenylene-ethylene oligomers (OPEs) and ligand-stabilized nanoparticles. By utilizing solution and vapor-phase manipulation techniques, we can control the distribution of the OPE molecules within the SAM matrix. These fabrication techniques, in combination with the spatial and energy resolution afforded by low temperature scanning tunneling microscopy and spectroscopy have enabled us to probe their electronic properties. For Au nanoparticles (d_CORE = 0.8 nm and 1.5 ± 0.5 nm), we use inserted dithiol tethers to immobilize them on alkanethiolate SAM matrices. At low temperature, both nanoparticles demonstrate Coulomb blockade behavior, with zero-conductance gaps resulting from quantum size effects, and spectral hopping. This study assesses the impact of the chemical environment (tethering scheme) and physical environment (proximity of adjacent particles) on charge transport.

Probing lipid membrane responses to surface morphology
Gillmor, Heetderks, Wang, Du, and Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

The outer cellular membrane is a mixture of protein receptors, lipids and cholesterol whose organization is incompletely understood. Many cell membranes have complex interactions with the underlying basement membrane, and our investigations focus on lipid deformation due to adhesion to this support. We model the complex basement membrane structure chemically and topographically, through lithographically defined features for control over substrate morphology, and through chemical modification of the surface. Initially using simplified, lipid-only giant unilamellar vesicles (GUVs) as models, we probe the membrane behavior in response to surface topography. Biotin-labeled lipids allow us to tether vesicles to the surface and to investigate the role of adhesion proteins in deformation during vesicle-surface interactions. From our model, we measure the lipid membrane deformation due to topography. We model and categorize these responses in our simple system using phase field formulation and compare these findings to cell responses on topographically patterned surfaces.

A new technique for nanoscale patterning: Microdisplacement printing
Dameron, Hampton, Smith, Mullen, Gillmor, and Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We demonstrate “micro-displacement printing”, which employs microcontact printing to replace pre-formed, easily-displaceable, 1-adamantenthiolate self-assembled monolayers (SAMs) selectively. This technique results in ordered molecular regions of both the displacing molecule as well as the remaining adamantanethiolate. The existence of the adamantanethiolate SAM before patterning hinders lateral surface diffusion of the patterning molecules, which is problematic in conventional microcontact printing, especially for molecules with low molecular weight, permitting the use of molecules that are otherwise too mobile to pattern by other methods. In addition, micro-displacement printing circumvents the need for solution processing during the initial patterning steps, a process that induces molecular exchange and edge roughening especially at the pattern interfaces. By additional processing, it is possible to eliminate the adamantanethiolate from the surface altogether, replacing it with a third (potentially low molecular weight) molecule. In this way, fabrication of a patterned SAM composed two mobile molecules is achievable, extending the capabilities of soft lithography.

Nanoscale device structures created with self-assembled multilayers as building blocks and components
Anderson, Srinivasan, Raviprakash, Carter, Horn, and Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Self-assembled multilayers have been utilized in conjunction with conventional lithography to create metal electrode structures with precise proximal placement in the 10-50 nm regime. By controlled placement and thickness of these multilayers, the spacing between the electrodes can be fabricated with single nanometer resolution. Much effort has gone into developing the lithographic process steps to create nanogaps reproducibly with electrical integrity. The evaluation of our process has included a variety of tailored nanogaps and electrode dimensions resulting in an initial yield of ~90% (for electrode lengths less than or equal to 5 µm). We will present methods relevant to the processing parameters and data regarding the electronic characterization of our nanogaps. Also, the multilayers themselves are interesting complex nanomaterials; studies are underway to understand and manipulate their formation and electrical properties. We continue to push this technology toward architectures relevant for device fabrication and these techniques will be discussed as well.

Nanoscale device structures created with self-assembled multilayers as building blocks and components
Ye, Takami, Weiss, Sugiura, and Jiang, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Double-decker sandwiched phthalocyaninato/porphyrinate rare earth complexes (DD) are promising candidates to study rotational motions at the single molecule level. However, to achieve desired motions on a surface, their degree of freedom must be reduced by controlling spacing and orientation. A number of crown-ether-substituted DD molecules were successfully imaged under electrochemical conditions using Scanning Tunneling Microscopy. By introducing different substituents, we are able to control the spacing as well as the orientation of the adsorbed DD molecules. In contrast to corresponding monomers, many of the homoleptic DD molecules do not form long-range ordered structures, which we attribute to the interaction between the neighboring top decks. We observe changes in the surface packing of crown-ether- substituted DD molecules after addition of metal ions, suggesting that the host-guest recognition effect induces rotation of the top decks.

Self-assembled multilayers as building blocks and components of nanoscale device structures
M. E. Anderson,* C. Srinivasan,** R. Jayaraman,** E. M. Carter,* M. W. Horn,** and P. S. Weiss* Departments of Chemistry & Physics* and Engineering Science and Mechanics**, The Pennsylvania State University, University Park, PA 16802-6300, USA

Self-assembled multilayers have been utilized in conjunction with conventional lithography to create metal electrode structures with precise proximal placement in the 10-50 nm regime. By controlled placement and thickness of these multilayers, the spacing between the electrodes can be fabricated with single nanometer resolution. Much effort has gone into developing the lithographic process steps to create nanogaps reproducibly with electrical integrity. The evaluation of our process has included a variety of tailored nanogaps and electrode dimensions resulting in an initial yield of ~90% (for electrode lengths less than or equal to 5 µm). We will present methods relevant to the processing parameters and data regarding the electronic characterization of our nanogaps. Also, the multilayers themselves are interesting complex nanomaterials; studies are underway to understand and manipulate their formation and electrical properties. We continue to push this technology toward architectures relevant for device fabrication and these techniques will be discussed as well.

Substrate-Mediated Interactions
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Long-range intermolecular interactions mediated by the substrate are responsible for many effects on surfaces, including molecular ordering, formation of nanostructures, and aligning reactive intermediates in catalysis. We use scanning tunneling microscopy to probe the perturbations in the local (and extended) electronic structure directly, the resulting substrate-mediated interactions, and the effects of these interactions on the adsorbate structures and motion. We show that these interactions remain important in the placement of adsorbates at elevated temperatures and at ranges of tens of Ångstroms. Substrate-mediated interactions can also produce extended strings of intermediates that are not yet covalently bound. We describe our initial efforts in quantifying these interactions by recording both the locations and motion of many thousands of molecules. We describe a series of studies ranging in strength from systems with weak interactions (under 1 kJ/mole/molecule) all the way up to reactive systems.

Probing lipid membrane responses to surface morphology
S. D. Gillmor, J.J. Heetderks, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
X. Wang,
Q. Du, Department of Mathematics, The Pennsylvania State University,
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

The outer cellular membrane is a mixture of protein receptors, lipids and cholesterol whose organization is incompletely understood. Many cell membranes have complex interactions with the underlying basement membrane, and our investigations focus on lipid deformation due to adhesion to this support. We model the complex basement membrane structure chemically and topographically, through lithographically defined features for control over substrate morphology, and through chemical modification of the surface. Initially using simplified, lipid-only giant unilamellar vesicles (GUVs) as models, we probe the membrane behavior in response to surface topography. Biotin-labeled lipids allow us to tether vesicles to the surface and to investigate the role of adhesion proteins in deformation during vesicle-surface interactions. From our model, we measure the lipid membrane deformation due to topography. We model and categorize these responses in our simple system using phase field formulation and compare these findings to cell responses on topographically patterned surfaces.

Effects of Fluorescent Dyes on the Structure of Lipid Membranes
Julia J. Heetderks, P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Cell membranes are complex, dynamic mixtures of lipids, proteins, and cholesterol; their precise molecular organization is unknown. A common study model is the GUV (giant unilamellar vesicles, which are fluid-filled spherical bilayers) composed of lipids to mimic the cell membrane. Fluorescent dye molecules are often incorporated into the membrane to allow direct visualization of lipid organization. The percentage of incorporated fluorescent dye used is often quite high, up to 2% of the membrane in many studies. We show that even substantially lower fractions of dye have significant impact on the observed organization of the multi-component lipid membranes and the transition temperatures between mixed and separated phases.

Directed assembly and separation of self-assembled monolayers via electrochemical processing
T. J. Mullen, A. A. Dameron, J. R. Hampton, P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We have directed separation in self-assembled monolayers (SAMs) on Au{111} using electrochemical desorption and characterized them with scanning tunneling microscopy (STM) and cyclic voltammetry (CV). Separated domains of 1-dodecanthiolate were created by solution insertion into 1-adamantanethiolate SAMs. The adamantanethiolate domains were selectively desorbed by applying a reductive potential. Subsequently, the samples were immersed in 1-octanethiolate solution, thereby producing SAMs with separated domains of dodecanthiolate and octanethiolate. We have investigated the molecular order of each lattice type with STM. The apparent height difference in the STM images and the two distinct cathodic peaks observed with CV indicate distinct separated domains. The fractional coverages of each lattice before and after electrochemical desorption were calculated using both STM images and cyclic voltammograms. Using this electrochemical process, high-resolution chemically patterned surfaces with application in areas ranging from microelectronics to biocompatible systems have been assembled and characterized with molecular precision.

Determining ink transport during dip-pen nanolithography by dual ink experiments
A. A. Dameron, J. R. Hampton, P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We have investigated the transport mechanism of the inks typically used in dip-pen nanolithography by patterning both hydrophilic and hydrophobic thiol inks on the same Au{111} substrate. The use of two inks with opposite contrast in lateral force microscopy images allows visualization of the later-patterned ink with respect to a previously-patterned structure. When a hydrophobic ink is written on top of a pre-existing hydrophilic structure, the second ink is observed at the outsides of the hydrophilic structure and the writing speed is greatly accelerated. In the reverse case, the hydrophilic ink is also observed to a lesser extent on the outsides of the previously patterned hydrophobic ink. However, the writing speed is slowed down. This striking difference highlights the important role substrate hydrophobicity plays, both on the surface as well as the ink itself, in determining the transport properties of thiol inks in dip-pen nanolithography.

Tunneling spectroscopy of precise, ligand-stabilized nanoparticles and nanoparticle assemblies
Nanayakkara, Smith, Weiss, Pearl, Woehrle, and Hutchison, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We discuss and compare the measured electronic properties of isolated, solution-derived, and ligand-stabilized gold clusters (Au₁₁L₁₀) and nanoparticles (Au₁₀₁L₄₃), in both cryogenic (4 K, UHV) and ambient conditions using scanning tunneling microscopy and spectroscopy. The clusters and particles (d_CORE = 0.8 nm and 1.5 ± 0.5 nm, respectively) are immobilized on alkanethiolate self-assembled monolayer matrices with inserted dithiol tethers. We thoroughly characterize the self-assembled monolayer surfaces to which the nanostructures are attached with both local probes and ensemble measurements. At low temperature, both Au11L10 clusters and Au101L43 nanoparticles demonstrate Coulomb blockade behavior, with zero-conductance gaps resulting from quantum size effects, and spectral hopping. This study assesses the impact of the chemical environment (tethering scheme) and physical environment (proximity of adjacent particles) on the charge transport properties.

Measuring and Controlling Molecular-Scale Properties for Molecular Devices
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use molecular design, tailored syntheses, intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, electronic function and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select and tailor molecules to choose the intermolecular interaction strengths and the structures formed within the film. We selectively test hypothesized mechanisms for electronic switching by varying molecular design, chemical environment, and measurement conditions to enable or to disable functions and control of these molecules with predictive and testable means. Critical to understanding these variations has been developing the means to make tens to hundreds of thousands of independent single-molecule measurements in order to develop sufficiently significant statistical distributions, comparable to those found in ensemble-averaging measurements, while retaining the heterogeneity of the measurements.

Exploiting Self- and Directed Assembly for Nanolithography
Arrelaine Dameron, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Controlling Molecular Assemblies through Intermolecular Interactions
Arrelaine Dameron, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Atomically Precise Directed Chemistry and Assembly
Sanjini Nanayakkara, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Precise Nanoscale Assemblies: Au Clusters and Self-Assembled Monolayers
Rachel Smith, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Creating Nanostructures through Self- and Directed Assembly
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select molecules to choose the intermolecular interaction strength and the structures formed within the film. We selectively test hypothesized mechanisms for electronic switching by varying molecular design, chemical environment, and measurement conditions to enable or to disable functions and control of these molecules with predictive and testable means. Critical to understanding these variations has been developing the means to make tens to hundreds of thousands of independent single-molecule measurements in order to develop sufficiently significant statistical distributions, comparable to those found in ensemble-averaging measurements, while retaining the heterogeneity of the measurements.

Subsurface Imaging
L. Novotny, University of Rochester
S. J. Stranick, NIST
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
K. F. Kelly, Rice University
S. Ünlü, Boston University
P. S. Carney, University of Illinois at Urbana Champaign
B. Goldberg, Boston University

Chemically Advanced Nanolithography:
Self-Assembled Films as Building Blocks & Components of Nanoscale Structures
M. E. Anderson, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Creating Nanostructures through Self- and Directed Assembly
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select molecules to choose the intermolecular interaction strength and the structures formed within the film. We selectively test hypothesized mechanisms for electronic switching by varying molecular design, chemical environment, and measurement conditions to enable or to disable functions and control of these molecules with predictive and testable means. Critical to understanding these variations has been developing the means to make tens to hundreds of thousands of independent single-molecule measurements in order to develop sufficiently significant statistical distributions, comparable to those found in ensemble-averaging measurements, while retaining the heterogeneity of the measurements.

Measuring and Controlling Intermolecular Interactions
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select molecules to choose the intermolecular interaction strength and the structures formed within the film. We selectively test hypothesized mechanisms for electronic switching by varying molecular design, chemical environment, and measurement conditions to enable or to disable functions and control of these molecules with predictive and testable means. Critical to understanding these variations has been developing the means to make tens to hundreds of thousands of independent single-molecule measurements in order to develop sufficiently significant statistical distributions, comparable to those found in ensemble-averaging measurements, while retaining the heterogeneity of the measurements.

Creating Nanostructures through Self- and Directed Assembly
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select molecules to choose the intermolecular interaction strength and the structures formed within the film. We also apply selective chemistry and self-assembly to form multilayers on patterns formed with conventional nanolithographic techniques to reach higher resolution, greater precision, and chemical versatility in nanostructures that we create.

Measuring and Controlling Intermolecular Interactions
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select molecules to choose the intermolecular interaction strength and the structures formed within the film. We selectively test hypothesized mechanisms for electronic switching by varying molecular design, chemical environment, and measurement conditions to enable or to disable functions and control of these molecules with predictive and testable means. Critical to understanding these variations has been developing the means to make tens to hundreds of thousands of independent single-molecule measurements in order to develop sufficiently significant statistical distributions, comparable to those found in ensemble-averaging measurements, while retaining the heterogeneity of the measurements.

American Vacuum Society National Meeting, Boston, MA, USA, Monday 31 October - Friday 3 November 2005.

Directed Assembly and Separation of Self-Assembled Monolayers via Electrochemical Processing
T. J. Mullen, A. A. Dameron, J. R. Hampton, and P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We have directed separation in self-assembled monolayers (SAMs) on Au{111} using electrochemical desorption and characterized them with scanning tunneling microscopy (STM) and voltammetry. Separated domains of 1-dodecanthiolate were created by solution insertion into 1-adamantanethiolate SAMs. The adamantanethiolate domains were selectively desorbed by applying a reductive potential. Subsequently, the samples were immersed in 1-octanethiol solution, thereby producing SAMs with separated domains of dodecanthiolate and octanethiolate. We have investigated the molecular order of each lattice type with STM. The apparent height difference in the STM images and the two distinct cathodic peaks observed with voltammetry indicate distinct separated domains. The fractional coverages of each lattice before and after electrochemical desorption were calculated using both STM images and voltammograms. Using this electrochemical process, high-resolution chemically patterned surfaces with application in areas ranging from microelectronics to biocompatible systems have been assembled and characterized with molecular precision.

American Vacuum Society National Meeting, Boston, MA, USA, Monday 31 October - Friday 3 November 2005.

Nanometer-scale Structures Created using Molecular Self-Assembly for Building Blocks and Components
M. E. Anderson, C. Srinivasan, R. Jayaraman, E. M. Carter, M. W. Horn, and P. S. Weiss, Departments of Chemistry, Physics, and Engineering Science & Mechanics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Molecular self-assembly plays an important role in the development of many nanolithographic techniques acting as building blocks and/or an active components for nanometer-scale devices. We have utilized self-assembled multilayers in conjunction with conventional lithography to create metal electrode structures with precise proximal placement in the 10-50 nm regime.^1-3 By controlled placement and thickness of these multilayers (building blocks), the spacing between the electrodes can be fabricated with single nanometer resolution. Much effort has gone into developing the lithographic process steps to create precise nanometer-scale gaps reproducibly with electrical integrity.⁴ We will present methods relevant to the processing parameters and data regarding the electronic characterization of these nanogaps. The optimization of lithographic processes compatible with self-assembly has opened a novel avenue for directed chemical patterning of multi-component self-assembled films. The multilayers themselves are interesting complex nanometer-scale materials; studies are underway to understand and to manipulate their formation and electrical properties. We continue to push this technology toward architectures relevant for device fabrication; these techniques will be discussed.

¹A. Hatzor and P. S. Weiss, Science 291, 1019 (2001).
²M. E. Anderson et al., Journal of Vacuum Science and Technology B 20, 2739 (2002).
³M. E. Anderson et al., Journal of Vacuum Science and Technology B 21, 3116 (2003).
⁴M. E. Anderson et al., MicroElectronic Engineering, in press.

American Vacuum Society National Meeting, Boston, MA, USA, Monday 31 October - Friday 3 November 2005.

Effects of Fluorescent Dyes on the Structure of Lipid Membranes
J. J. Heetderks and P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Cell membranes are complex, dynamic mixtures of lipids, proteins, and cholesterol; their precise mode of molecular organization is unknown. Transient associations of molecules form â?olipid raftsâ?? in active cells that may affect membrane-associated protein activity. One model to study the lipid component of these molecular interactions is the giant unilamellar vesicle (GUV). The lipids, without contribution from membrane proteins, cytoskeletal structures, cholesterol, or outside forces, form domains in GUVs when the conditions are within an appropriate range of the multi-dimensional phase diagram of lipid composition and temperature. Fluorescently labeled phospholipids and lipid analogues are used at low concentrations to visualize the vesicles and domains, and are found to influence measured membrane properties, even at concentrations below those typically used in structural studies. Through basic membrane organization measurements, we determine the effects on the vesicle properties for which the labeling is responsible. We incorporate varying amounts of fluorescent dyes into 2-phase vesicles and find clear divisions of gel and fluid domains at room temperature. The temperature is then slowly raised while monitoring the membrane domains until the domains melt into one homogeneous phase. Preliminary results show that the incorporation of several common fluorescent labels in the membrane cause measurable changes in the demixing temperatures of the two-phase vesicles at less than one percent dye concentration.

American Vacuum Society National Meeting, Boston, MA, USA, Monday 31 October - Friday 3 November 2005.

Ultrastable Conductance Measurements of Self-Assembled Monolayer Supported Phenylene-Ethylene Oligomers
S. U. Nanayakkara, M. M. Blake, A. A. Dameron, R. Zhang, C. Pochas, M. Kim, P. S. Weiss, T. P. Pearl, S. Uppili, D. Allara, J. M. Tour, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA; and Department of Chemistry, Rice University, Houston, TX, USA.

We have used alkanethiolate self-assembled monolayers (SAMs) to fabricate support matrices for probing the charge transport properties of both isolated and bundled phenylene-ethylene oligomers (OPEs). By utilizing solution- and vapor-phase manipulation techniques, we can select the distribution of the OPE molecules within the SAM matrix. These fabrication techniques, in combination with the spatial and energy resolution afforded by low temperature scanning tunneling microscopy and spectroscopy, have enabled us to probe the electronic properties of these molecules. We have probed individual substituted OPE molecules in analogous environments to understand the effects of chemical substitution on charge transport. We aim to understand the conductance pathways of these molecules as a function of their chemical structure, physical environment and adsorption site.

American Vacuum Society National Meeting, Boston, MA, USA, Monday 31 October - Friday 3 November 2005.

Probing Lipid Membrane Responses to Surface Morphology
S. D. Gillmor, J. J. Heetderks, X. Wang, Q. Du, and P. S. Weiss, Departments of Chemistry, Physics, and Mathematics, The Pennsylvania State University, University Park, PA 16802-6300, USA

The outer cellular membrane is a mixture of protein receptors, lipids and cholesterol whose organization is incompletely understood. Many cell membranes have complex interactions with the underlying basement membrane, and our investigations focus on lipid deformation due to adhesion to this support. We model the complex basement membrane structure chemically and topographically, through lithographically defined features for control over substrate morphology, and through chemical modification of the surface. Initially using simplified, lipid-only giant unilamellar vesicles (GUVs) as models, we probe the membrane behavior in response to surface topography. Biotin-labeled lipids allow us to tether the vesicles to the surface and to investigate the role of adhesion proteins in the deformation during the vesicle-surface interactions. From confocal microscopy, we image the profile of the vesicle on both planar and topographically patterned substrates. From our model system, we measure the lipid membrane deformation due to the topography, and we compare these findings with the line tension characterization in the literature.1 We model and categorize these responses in our simple system using phase field formulation and compare these findings to cell responses on topographically patterned surfaces.

American Vacuum Society National Meeting, Boston, MA, USA, Sunday Monday 31 October - Friday 3 November 2005.

Tunneling Spectroscopy of Self-Assembled Monolayers of 1-adamantanethiolate on Single Crystal Metallic Substrates
A. R. Kurland, A. A. Dameron, P. Han, S. U. Nanayakkara, and P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We measure local barrier height and differential conductance using ultrahigh vacuum scanning tunneling microscopy (STM) at 4 K to investigate the work function and local density of states, respectively, of individual adamantanethiolate molecules on a range of single crystal metallic substrates. These techniques allow us to probe specific electronic characteristics while simultaneously resolving the molecular lattice of the adamantanethiolate monolayers. Previously, we have shown that adamantanethiolate molecules form well-ordered hexagonally close-packed monolayers on the Au{111} surface. The complex and highly symmetric cage structure of adamantanethiolate results in weaker intermolecular interactions than those of alkanethiolate self-assembled monolayers. Taking advantage of these properties, we have implemented adamantanethiolate molecules in thin-film molecular lattices and as nanolithography patterning inks. We aim to exploit and to incorporate the unique physical and electronic interactions of adsorbed adamantanethiolate to understand and to tailor self-assembled nanostructures.

Development of a Tunable Microwave Frequency Alternating Current Scanning Tunneling Microscope to Profile Dopant Density in Semiconductors
A. M. Moore, B. A. Mantooth, and P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We have built a scanning tunneling microscope (STM) capable of profiling dopants in semiconductor devices and test structures at sub-nanometer resolution. The alternating current signals, and thereby the dopant density and type, are obtained through a heterodyned signal. Two frequencies are applied to the STM tip and the nonlinearity of the tunnel junction mixes the frequencies, generating new signals including at the difference of the frequencies applied; this in combination with the DC bias yields information on the dopant density and type. This ultrahigh resolution (<1 nm) profiling tool enhances what is obtained through current metrology tools and will support semiconductor processing as the size scale of devices continues to decrease.

Creating Nanostructures through Self- and Directed Assembly
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select molecules to choose the intermolecular interaction strength and the structures formed within the film. We selectively test hypothesized mechanisms for electronic switching by varying molecular design, chemical environment, and measurement conditions to enable or to disable functions and control of these molecules with predictive and testable means. Critical to understanding these variations has been developing the means to make tens to hundreds of thousands of independent single-molecule measurements in order to develop sufficiently significant statistical distributions, comparable to those found in ensemble-averaging measurements, while retaining the heterogeneity of the measurements.

Probing Lipid Membrane Responses to Surface Morphology
S. D. Gillmor, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Ultrastable Conductance Measurements of Self-Assembled Supported Phenylene-Ethynylene Oligomers
S. U. Nanayakkara, M. M. Blake, A. A. Dameron, R. Zhnag, C. Pochas, M. Kim, P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
T. P. Pearl, Department of Physics, North Carolina State University, Raleigh, NC
S. Uppili, D. L. Allara, Departments of Chemistry and Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA
J. M. Tour, Department of Chemistry, Rice University, Houston, TX, USA

Measuring and Controlling Molecular-Scale Properties for Molecular Devices
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use molecular design, tailored syntheses, intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, electronic function and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select and tailor molecules to choose the intermolecular interaction strengths and the structures formed within the film. We selectively test hypothesized mechanisms for electronic switching by varying molecular design, chemical environment, and measurement conditions to enable or to disable functions and control of these molecules with predictive and testable means. Critical to understanding these variations has been developing the means to make tens to hundreds of thousands of independent single-molecule measurements in order to develop sufficiently significant statistical distributions, comparable to those found in ensemble-averaging measurements, while retaining the heterogeneity of the measurements. We quantitatively compare the conductances of molecule-substrate junctions. We demonstrate the importance of these junctions in conductance switching of single molecules.

Combining Conventional Lithography with Molecular Self-Assembly to Build Nanostructures and Pattern Surfaces
M. E. Anderson, C. Srinivasan, J. N. Hohman, M. W. Horn, and P. S. Weiss, Departments of Chemistry, Physics, and Engineering Science & Mechanics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Molecular self-assembly plays an essential role in the development of many nanolithographic techniques acting as a building block and/or an active component. In conjunction with conventional lithography, we have fabricated metal structures with precise proximal placement using self-assembled multilayers as lift-off resists (building blocks) and chemically patterned surfaces with functionalized films using self-assembled monolayers as the components. We have created metal electrodes with nanometer-scale separations using the selective placement and controllable dimensions of self-assembled multilayers. The thickness of this multilayer lift-off resist can be tailored defining the spacing between the electrodes with single nanometer resolution in the 10-50 nm regime.^1-4 Much effort has gone into developing the lithographic process steps to create nanogaps reproducibly with electrical integrity.5 An important aspect of this process is a lithographic resist, which is robust enough to withstand the deposition of self-assembled multilayers without compromising their formation. This optimized lithographic method and resist compatible with self-assembly has opened a novel avenue for us to direct the chemical patterning of multi-component self-assembled films. For our process, photolithography is utilized to pattern our resist atop a self-assembled monolayer (SAM) on a gold substrate. Then the exposed region of the SAM is removed, another component SAM is inserted, and then the resist is removed maintaining the functionality that has been patterned onto the substrate. A major advantage of this technique is that the different components (SAMs) of the film are shielded by the resist against displacement and intercalation. Additional benefits of this process over other unconventional methods for chemical patterning are the ability to have multiple levels of alignment, reproducible one-to-one feature size transfer, and parallel processing. We present this research outlining our work developing methods for the integration of self-assembly with lithographic processing for future applications ranging from molecular electronics to sensor platforms.

¹ A. Hatzor and P.S. Weiss, Science 291, 1019 (2001).
² M. E. Anderson et al., Journal of Vacuum Science and Technology B 20, 2739 (2002).
³ M. E. Anderson et al., Journal of Vacuum Science and Technology B 21, 3116 (2003).
⁴ M. E. Anderson et al., submitted.
⁵ M. E. Anderson et al., MicroElectronic Engineering 78-79, 248 (2005).

Combining self-assembly with new lithographic methods for the fabrication of reliable nanometer-scale device structures
C. Srinivasan, M. E. Anderson, M. W. Horn, and P. S. Weiss, Departments of Chemistry, Physics, and Engineering Science & Mechanics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We create metal electrode structures with precise proximal placement in the 10-40 nm regime by combining the superior qualities of traditional top-down and bottom-up lithography. Selective self-assembly of mercaptoalkanoic acids on patterned gold structures is utilized to grow films of metal-organic coordinated multilayers, whose thickness is controlled with nanometer scale resolution tailored by the number of molecular layers and their lengths. These films are employed as lift-off resists to create tailored gaps between lithographically patterned metal electrodes.^1-3 The evaluation of our process has included a variety of electrode dimensions and tailored nanogaps resulting in an initial yield of ~90% (for electrode lengths less than or equal to 5 um).⁴ To improve the electrical fidelity of our device structures, a new negative-tone lithographic process, which is more compatible with self-assembly techniques, has been developed. Electrode dimensions have been scaled down to the sub-100 nm regime using e-beam lithography. Methods are also underway to diversify the materials compatible with our technique and to tailor the heights of initial and secondary structures to be identical. We will report on the improved electrical fidelity of electrodes fabricated using these new processes. The optimization of lithographic processes compatible with self-assembly has opened a novel avenue to create nanoscale architectures for reliable device fabrication. We continue to push this technology toward mainstream industrial manufacturing and these techniques will be discussed.

¹ A. Hatzor and P.S. Weiss, Science 291, 1019 (2001).
² M. E. Anderson et al., Journal of Vacuum Science and Technology B 20, 2739 (2002).
³ M. E. Anderson et al., Journal of Vacuum Science and Technology B 21, 3116 (2003).
⁴ M. E. Anderson et al., MicroElectronic Engineering 78-79, 248 (2005)

Atomically Precise Directed Chemistry and Assembly
Sanjini Nanayakkara, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Probing Lipid Membrane Responses to Surface Morphology
S. D. Gillmor, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Probing Lipid Membrane Responses to Surface Morphology
S. D. Gillmor, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Precise Complex Molecular and Nanoparticle Assemblies for Photonics
P. S. Weiss, R. K. Smith, S. U. Nanayakkara, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
G. Woehrle and J. E. Hutchison, Materials Science Institute, University of Oregon, Eugene, OR, USA

We discuss and compare the measured electronic characteristics of isolated, solution-derived, and ligand-stabilized gold clusters (Au₁₁L₁₀) and nanoparticles (Au₁₀₁L₄₃), taken in both cryogenic (4 K, UHV) and ambient conditions using scanning tunneling microscopy and spectroscopy. The clusters and particles (d_CORE = 0.8 nm and 1.5 ± 0.5 nm, respectively) are immobilized on alkanethiolate self-assembled monolayers with inserted dithiol tethers. We thoroughly characterize the self-assembled monolayer surface to which the nanostructures are attached with both local probes and ensemble measurements. At low temperature, the Au₁₁ clusters demonstrate both spectral hopping and Coulomb blockade behavior, with zero-conductance gaps resulting from quantum size effects. Surprisingly, chemically identical particles produce different families of tunneling spectra, comparable to previous results for heterogeneous distributions of particles.

Measurements of photon emission excited with tunneling electrons from parts of single nanoparticles indicate that there are opportunities for photonic coupling in the near field. These and the underlying measurements will be discussed.

Creating Nanostructures through Self- and Directed Assembly
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select molecules to choose the intermolecular interaction strength and the structures formed within the film. We also apply selective chemistry and self-assembly to form multilayers on patterns formed with conventional nanolithographic techniques to reach higher resolution, greater precision, and chemical versatility in nanostructures that we create.

Substrate-Mediated Interactions
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Long-range intermolecular interactions mediated by the substrate are responsible for many effects on surfaces, including molecular ordering, formation of nanostructures, and aligning reactive intermediates in catalysis. We use scanning tunneling microscopy to probe the perturbations in the local (and extended) electronic structure directly, the resulting substrate-mediated interactions, and the effects of these interactions on the adsorbate structures and motion. We show that these interactions remain important in the placement of adsorbates at elevated temperatures and at ranges of tens of Ångstroms. Substrate-mediated interactions can also produce extended strings of intermediates that are not yet covalently bound. We describe our initial efforts in quantifying these interactions by recording both the locations and motion of many thousands of molecules. We describe a series of studies ranging in strength from systems with weak interactions (under 1 kJ/mole/molecule) all the way up to reactive systems.

Measuring and controlling molecular-scale properties for molecular devices
P. S. Weiss, A. M. Moore; A. A. Dameron; B. A. Mantooth, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
J. M. Tour, Department of Chemistry, Rice University, Houston, TX, USA
J. E. Hutchison, Materials Science Institute, University of Oregon, Eugene, OR, USA

We use molecular design, tailored syntheses, intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world and to serve as test structures for measurements of single or bundled molecular switches. Interactions within and between molecules can be measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, electronic function and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures and patterns. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select and tailor molecules to choose the intermolecular interaction strength and the structures formed within the film. We selectively test hypothesized mechanisms for conductance switching by varying molecular design, chemical environment and measurement conditions to enable or to disable functions and control of these molecules with predictive and testable means.

Nanostructured neurotransmitter-derivatized surfaces for biosensor development
A. M. Andrews, M. E. Szapacs, A. Cans, A. U. Vaish, J. L. Han, M. E. Anderson, P. S. Weiss, Departments of Veterinary Science, Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Essential to selective molecular recognition of small molecules on capture surfaces is the ability to tether these probes so that they are readily accessible for binding. This is particularly challenging for small probes where the tether alters a significant fraction of the probe molecule. We have developed a number of methods for overcoming the problems associated with the design of such materials and apply these to a surface functionalized with the small molecule neurotransmitter serotonin (5-hydroxytryptamine). Here, serotonin is covalently bound to a self-assembled alkanethiolate monolayer at varying surface coverages and surrounded with a molecular surface of oligoethylene glycol. We demonstrate access and specific recognition of serotonin by comparing the capture from solution of antibodies directed against serotonin and we further demonstrate that this surface resists nonspecific protein adsorption. "Neurotransmitter chips" will be used to identify selective molecular recognition elements for future biosensor applications in experiments designed to investigate the role of serotonin in psychiatric and neurodegenerative disorders and their treatment. Furthermore, this approach is readily translatable to surfaces patterned with multiple neurotransmitters, as well as other with other small molecules of biological importance.

Return to the Abstracts of Upcoming Talks.
Return to the Weiss Group Home Page. 7 February 2016
psw