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

Nanocell Approach to a Molecular Computer
J. M. Tour, Rice University, D. L. Allara, Penn State, M. A. Reed, Yale University, and P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Controlling and Measuring Molecular-Scale Properties for Molecular Nanoelectronics
Rachel K. Smith and Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Controlling and Measuring Local Composition and Properties in Lipid Bilayer Membranes
T. G. D'Onofrio, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Controlling and Measuring Local Composition and Properties in Lipid Bilayer Membranes
T. G. D'Onofrio, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Controlling and Placing Molecules in Monolayers and Membranes
P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

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

We explore new phenomena in the function and control of molecules at the nanometer scale and smaller. We seek to exploit these phenomena by developing the means to connect our molecules to the microscopic and macroscopic worlds. I will illustrate our approach with examples from our work in self-assembly and molecular electronics.

We use intermolecular interactions to direct molecules into desired positions. In many experiemnts, we use and develop scanning probe microscopes to determine both structures and the electronic, optical, chemical, physical, mechanical, and other local properties. The tools developed allow us to measure the environment-dependent electronic structure, bonding, photon emission, high frequency conductivity, and ferroic response with unprecedented resolution.

In analogous experiments on biological membranes, we control and measure local composition and structure in order to control biological properties such as infection, transport, adhesion, and immune response. We use fluorescent probes, optical & mechanical manipulation, and cytoskeletal elements for these purposes.

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

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

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

As the scales of devices shrink or change more disruptively, so must our ability to place and to measure these devices and their underlying components. Tremendous opportunities exist in developing the sensitivity to probe chemical, physical, electronic, optical, mechanical, and other properties at the nanometer scale and below. I will show some of the capabilities that have been developed and how we have applied these in molecular electronics and in related areas. Our ability to make variations at the atomic scale, chemically and otherwise, gives us the capability to determine the sensitivity of properties to precise structures and thus to tailor these properties. Since measurements with scanning probe microscopes, the tools of choice, can (must) be made on a single nanostructure at a time, we are able to measure monodisperse samples and to guide the selection, synthesis, and assembly of optimized structures. We use intermolecular interactions 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 on single or bundled molecules. We use and develop scanning probe microscopes to determine both local structures and the electronic and other local properties. We have applied these to isolate molecules with electronic function to determine the mechanisms of function, and the relationships between molecular structure, environment, connection, coupling, and function. We have been able to demonstrate that single molecules can function as multistate switches, and have determined important aspects of the mechanism, function, and persistence of switching. We will discuss the origins of switching and the relevant aspects of the molecular structure and environment required.

Single Molecule Electronics
P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

As the scales of devices shrink or change more disruptively, so must our ability to place and to measure these devices and their underlying components. Tremendous opportunities exist in developing the sensitivity to probe chemical, physical, electronic, optical, mechanical, and other properties at the nanometer scale and below. I will show some of the capabilities that have been developed and how we have applied these in molecular electronics and in related areas. Our ability to make variations at the atomic scale, chemically and otherwise, gives us the capability to determine the sensitivity of properties to precise structures and thus to tailor these properties. Since measurements with scanning probe microscopes, the tools of choice, can (must) be made on a single nanostructure at a time, we are able to measure monodisperse samples and to guide the selection, synthesis, and assembly of optimized structures. We use intermolecular interactions 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 on single or bundled molecules. We use and develop scanning probe microscopes to determine both local structures and the electronic and other local properties. We have applied these to isolate molecules with electronic function to determine the mechanisms of function, and the relationships between molecular structure, environment, connection, coupling, and function. We have been able to demonstrate that single molecules can function as multistate switches, and have determined important aspects of the mechanism, function, and persistence of switching. We will discuss the origins of switching and the relevant aspects of the molecular structure and environment required.

Conductance Switching in Single Molecules
Z. J. Donhauser and P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Controlling and Measuring Local Composition and Properties in Lipid Bilayer Membranes
T. G. D'Onofrio, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Controlling and measuring local composition and properties in lipid bilayer membranes
P. S. Weiss and T. G. D'Onofrio, Department of Chemistry, 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 membranes is a critical element of cellular processes such as transport, infection, and uptake. We control local composition through manipulation of (local) membrane curvature. Our tools include multibeam optical tweezers, dual micropipette aspiration, 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.

Heterostructured Nanoparticles
R. T. Langlois, R. K. Smith, and P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Placing, connecting, measuring and controlling molecular electronics
P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions 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 on single or bundled molecules. We use and develop scanning probe microscopes to determine both local structures and the electronic and other local properties. We have applied these to isolate molecules with electronic function to determine the mechanisms of function, and the relationships between molecular structure, environment, connection, coupling, and function. We have been able to demonstrate that single molecules can function as multistate switches, and have determined important aspects of the mechanism, function, and persistence of switching. We will discuss the origins of switching and the relevant aspects of the molecular structure and environment required.

Controlling and Measuring Local Composition and Properties in Lipid Bilayer Membranes
Paul S. Weiss, Terry G. D’Onofrio, Anne E. Counterman,Chris W. Binns, Elizabeth H. Muth, and Chris D. Keating, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Placing Connecting, Measuring and Controlling Single Molecular Electronics
Paul S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Self-Assembly
Rachel Smith and P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

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

Exploiting and Controlling Intermolecular Interactions for Precise Placement and Connection of Molecules
P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, to serve as test structures for measurements on single or bundled molecules, and to control biological function. We use and develop scanning probe and optical microscopies to determine both local structures and the electronic and other local properties.

We have applied these to isolate molecules with electronic function to determine the mechanisms of function, and the relationships between molecular structure, environment, connection, coupling, and function. We have been able to demonstrate that single molecules can function as multistate switches, and have determined important aspects of the mechanism, function, and persistence of switching. We will discuss the origins of switching and the relevant aspects of the molecular structure and environment required.

Exploiting and Controlling Intermolecular Interactions for Precise Placement and Connection of Molecules
P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions 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 on single or bundled molecules. We use and develop scanning probe microscopes to determine both local structures and the electronic and other local properties. We have applied these to isolate molecules with electronic function to determine the mechanisms of function, and the relationships between molecular structure, environment, connection, coupling, and function. We have been able to demonstrate that single molecules can function as multistate switches, and have determined important aspects of the mechanism, function, and persistence of switching. We will discuss the origins of switching and the relevant aspects of the molecular structure and environment required.

We apply selective chemistry and self-assembly in combination with conventional nanolithographic techniques to reach higher resolution, greater precision, and chemical versatility in the nanostructures that we create. The key to these approaches is using precise, robust molecular layers that attach selectively to specific patterned substrate materials. In one approach, we apply precise-thickness multilayers (termed “molecular rulers”) to nanolithographically created structures and use these multilayers as resists for lift-off. The thickness and thus the spacing of the resultant structures can be controlled down to 5 nm, with control to 1 nm or better. We have demonstrated this approach both with e-beam generated structures as well as those based entirely on self-assembly. An additional advantage of molecular rulers is the inherent capability to displace the molecular resist chemically, and thus to remove the resist material simply and completely. We can also use molecular rulers with carefully designed parent structures to create complex structures that would be difficult to generate by conventional means. These can be made still more complicated by the selective application and use of sacrificial intermediate or parent generation structures. We will discuss our approaches to pattern design and creation using this method. Another approach involves forming nanostructures and then chemically functionalizing them selectively to produce substrates with patterns in chemical and physical properties. These can be used for further selective patterning, or as bases for molecular devices and device arrays. Of particular concern in reacting such structures is the role of the reaction exothermicity in heating and modifying the underlying nanostructures. Our molecular-scale measurements of this process, and approaches to circumvent such problems will be presented.

The Short and Winding Road to Nanoscience
P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

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

Exploiting Intermolecular Interactions for Ultrahigh Resolution Nanolithography
P. S. Weiss, A. Hatzor, M. E. Anderson, J. D. Monnell, and A. Wissner-Gross, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

We apply selective chemistry and self-assembly in combination with conventional nanolithographic techniques to reach higher resolution, greater precision, and chemical versatility in the nanostructures that we create. The key to these approaches is using precise, robust molecular layers that attach selectively to specific patterned substrate materials.

In one approach, we apply precise-thickness multilayers (termed “molecular rulers”) to nanolithographically created structures and use these multilayers as resists for lift-off (Fig. 1).1 The thickness and thus the spacing of the resultant structures can be controlled down to 5 nm, with control to 1 nm or better. We have demonstrated this approach both with e-beam generated structures as well as those based entirely on self-assembly. An additional advantage of molecular rulers is the inherent capability to displace the molecular resist chemically, and thus to remove the resist material simply and completely.

We can also use molecular rulers with carefully designed parent structures to create complex structures that would be difficult to generate by conventional means. These can be made still more complicated by the selective application and use of sacrificial intermediate or parent generation structures. We will discuss our approaches to pattern design and creation using this method.

Another approach involves forming nanostructures and then chemically functionalizing them selectively to produce substrates with patterns in chemical and physical properties. These can be used for further selective patterning, or as bases for molecular devices and device arrays. Of particular concern in reacting such structures is the role of the reaction exothermicity in heating and modifying the underlying nanostructures. Our molecular-scale measurements of this process, and approaches to circumvent such problems will be presented.

Exploiting Intermolecular Interactions for Ultrahigh Resolution Nanolithography
P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

We apply selective chemistry and self-assembly in combination with conventional nanolithographic techniques to reach higher resolution, greater precision, and chemical versatility in the nanostructures that we create. The key to these approaches is using precise, robust molecular layers that attach selectively to specific patterned substrate materials.

In one approach, we apply precise-thickness multilayers (termed “molecular rulers”) to nanolithographically created structures and use these multilayers as resists for lift-off (Fig. 1).1 The thickness and thus the spacing of the resultant structures can be controlled down to 5 nm, with control to 1 nm or better. We have demonstrated this approach both with e-beam generated structures as well as those based entirely on self-assembly. An additional advantage of molecular rulers is the inherent capability to displace the molecular resist chemically, and thus to remove the resist material simply and completely.

We can also use molecular rulers with carefully designed parent structures to create complex structures that would be difficult to generate by conventional means. These can be made still more complicated by the selective application and use of sacrificial intermediate or parent generation structures. We will discuss our approaches to pattern design and creation using this method.

Another approach involves forming nanostructures and then chemically functionalizing them selectively to produce substrates with patterns in chemical and physical properties. These can be used for further selective patterning, or as bases for molecular devices and device arrays. Of particular concern in reacting such structures is the role of the reaction exothermicity in heating and modifying the underlying nanostructures. Our molecular-scale measurements of this process, and approaches to circumvent such problems will be presented.

Exploiting and Controlling Intermolecular Interactions for Precise Placement and Connection of Molecules
P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions 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 on single or bundled molecules. We use and develop scanning probe microscopes to determine both local structures and the electronic and other local properties. We have applied these to isolate molecules with electronic function to determine the mechanisms of function, and the relationships between molecular structure, environment, connection, coupling, and function. We have been able to demonstrate that single molecules can function as multistate switches, and have determined important aspects of the mechanism, function, and persistence of switching. We will discuss the origins of switching and the relevant aspects of the molecular structure and environment required.

We apply selective chemistry and self-assembly in combination with conventional nanolithographic techniques to reach higher resolution, greater precision, and chemical versatility in the nanostructures that we create. The key to these approaches is using precise, robust molecular layers that attach selectively to specific patterned substrate materials. In one approach, we apply precise-thickness multilayers (termed “molecular rulers”) to nanolithographically created structures and use these multilayers as resists for lift-off. The thickness and thus the spacing of the resultant structures can be controlled down to 5 nm, with control to 1 nm or better. We have demonstrated this approach both with e-beam generated structures as well as those based entirely on self-assembly. An additional advantage of molecular rulers is the inherent capability to displace the molecular resist chemically, and thus to remove the resist material simply and completely. We can also use molecular rulers with carefully designed parent structures to create complex structures that would be difficult to generate by conventional means. These can be made still more complicated by the selective application and use of sacrificial intermediate or parent generation structures. We will discuss our approaches to pattern design and creation using this method. Another approach involves forming nanostructures and then chemically functionalizing them selectively to produce substrates with patterns in chemical and physical properties. These can be used for further selective patterning, or as bases for molecular devices and device arrays. Of particular concern in reacting such structures is the role of the reaction exothermicity in heating and modifying the underlying nanostructures. Our molecular-scale measurements of this process, and approaches to circumvent such problems will be presented.

Switching of Single Molecules
Z. J. Donhauser and P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Molecular electronics is rapidly emerging as a viable possibility for the creation of inexpensive, ultra-dense, high-capacity devices. Among the most promising molecular electronic candidates are conjugated phenylene ethynylene oligomers, which have already demonstrated functionality as diodes, wires and switches. However, most experiments have studied these molecules in groups of thousands. Using self-assembly techniques combined with scanning tunneling microscopy (STM), we can isolate the molecules and determine their physical and electronic properties as individuals and as small groups.

We use self-assembled monolayers (SAMs) of alkanethiolates on gold as matrices in which we spatially and electronically isolate the phenylene ethynylene oligomer molecules. These candidate molecules selectively adsorb at defect sites in the host SAM, binding to the gold surface with a sulfur "alligator clip". Because of the limited space in the host monolayer defect sites, molecules inserted in the film are forced to orient themselves nearly normal to the surface. This allows us to individually address inserted molecules with the tip of the scanning tunneling microscope and probe them end-to-end.

We have observed that single phenylene ethynylene oligomer molecules inserted into dodecanethiolate SAMs reversibly switch conductance states. This is manifested as a change in the apparent height of the molecules in STM images. Topographically higher states can be considered to have a higher conductance, while molecules that are topographically lower correspond to a lower conductance state.

We mediate the amount of stochastic switching of the inserted molecules by controlling the degree of order of the host film. To this end, we have developed a simple self-assembly strategy to modify the amount of order in the host monolayer. Poorly ordered monolayers were produced using a short monolayer deposition time. Insertion of guest molecules into these monolayers resulted in a higher switching rate compared to typical alkanethiolate SAMs. Conversely, molecules inserted into well-ordered SAMs have a lower switching rate. A two-step vapor annealing technique was developed to increase the order in the host monolayers, and to reduce the space around inserted molecules. First, the candidate molecules were inserted into a typical host monolayer. Then, new alkanethiolate matrix molecules were introduced from the vapor phase, surrounding the inserted molecules, and further restricting their motion. This was shown to be an effective means to reduce switching of phenylene ethynylene oligomers inserted into alkanethiolate monolayers.

Reducing the thickness of the host monolayer by using decanethiolate and octanethiolate matrices reveals that that the molecules switch between at least three states. When inserted in dodecanethiolate SAMs, only the highest state is readily visible as a distinct protrusion. Reducing the length of the monolayer to decanethiolate or octanethiolate allows us to discriminate between two discrete lower conductance states. The two highest states are separated by an apparent height of the 3 Å. The mean apparent height of the lowest conductance state is less than that of octanethiolate, preventing an absolute determination of its height.

Single Molecule Electronics
Z. J. Donhauser and P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

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

Exploiting Intermolecular Interactions for Ultrahigh Resolution Nanolithography
P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Synthesis and Characterization of Core–Organic–Shell Nanoparticles: Heterogeneous Metal Colloids for Optoelectronic Devices
Read Langlois, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Exploiting and Controlling Intermolecular Interactions for Precise Placement and Connection of Molecules
P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Measuring and Controlling Single Molecule Devices
P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Electrical Conductance Measurements Through ErSi₂ Nanowire Using Dual Probe Scanning Tunneling Microscopy
H. Tanaka, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA
Y. Shingaya, T. Nakayam, and M. Aono, RIKEN & Osaka University, Japan.

Exploiting & Controlling Intermolecular Interactions for the Precise Placement & Connection of Molecules
P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

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

We use intermolecular interactions 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 on single or bundled molecules. We use and develop scanning probe microscopes to determine both local structures and the electronic and other local properties. We have applied these to isolate molecules with electronic function to determine the mechanisms of function, and the relationships between molecular structure, environment, connection, coupling, and function. We have been able to demonstrate that single molecules can function as multistate switches, and have determined important aspects of the mechanism, function, and persistence of switching. We will discuss the origins of switching and the relevant aspects of the molecular structure and environment required.

We apply selective chemistry and self-assembly in combination with conventional nanolithographic techniques to reach higher resolution, greater precision, and chemical versatility in the nanostructures that we create. The key to these approaches is using precise, robust molecular layers that attach selectively to specific patterned substrate materials. In one approach, we apply precise-thickness multilayers (termed “molecular rulers”) to nanolithographically created structures and use these multilayers as resists for lift-off. The thickness and thus the spacing of the resultant structures can be controlled down to 5 nm, with control to 1 nm or better. We have demonstrated this approach both with e-beam generated structures as well as those based entirely on self-assembly. An additional advantage of molecular rulers is the inherent capability to displace the molecular resist chemically, and thus to remove the resist material simply and completely. We can also use molecular rulers with carefully designed parent structures to create complex structures that would be difficult to generate by conventional means. These can be made still more complicated by the selective application and use of sacrificial intermediate or parent generation structures. We will discuss our approaches to pattern design and creation using this method. Another approach involves forming nanostructures and then chemically functionalizing them selectively to produce substrates with patterns in chemical and physical properties. These can be used for further selective patterning, or as bases for molecular devices and device arrays. Of particular concern in reacting such structures is the role of the reaction exothermicity in heating and modifying the underlying nanostructures. Our molecular-scale measurements of this process, and approaches to circumvent such problems will be presented.

We use intermolecular interactions 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 on single or bundled molecules. We use and develop scanning probe microscopes to determine both local structures and the electronic and other local properties. We have applied these to isolate molecules with electronic function to determine the mechanisms of function, and the relationships between molecular structure, environment, connection, coupling, and function. We have been able to demonstrate that single molecules can function as multistate switches, and have determined important aspects of the mechanism, function, and persistence of switching. We will discuss the origins of switching and the relevant aspects of the molecular structure and environment required.

We apply selective chemistry and self-assembly in combination with conventional nanolithographic techniques to reach higher resolution, greater precision, and chemical versatility in the nanostructures that we create. We have demonstrated this approach both with e-beam generated structures as well as those based entirely on self-assembly. We will discuss our approaches to pattern design and creation using this method.

Expanding the Capabilities of the Scanning Tunneling Microscope
K. F. Kelly, Department of Electrical Engineering, Rice University, Houston, TX, USA

Scanning probe microscopes allow unprecedented views of surfaces and the site-specific interactions and dynamics of adsorbates. Our efforts to identify and to characterize atoms and molecules on surfaces and how it is that the scanning tunneling microscope images these surfaces and adsorbates will be discussed. We have extended the capabilities of scanning probe microscopes in several ways; two in particular will be highlighted.

Recent advances in tunable microwave frequency AC scanning tunneling microscopy (STM) allow dopant profiling at unprecedented resolution. We apply nonlinear tunable microwave frequency AC scanning tunneling microscopy and spectroscopy to profiling dopants at ultrahigh resolution in semiconductors. With microwave difference frequency (MDF) measurements of uniformly doped Si, we have shown that we are sensitive to both dopant type and density. The MDF signal versus the applied bias voltage gives a spectral signature characteristic of dopant type and density. We are then able to use a spectroscopic imaging mode to map the dopant density at ultrahigh resolution.

In the second part of the talk, advanced image processing techniques which extend the scientific capabilities of STM will be presented. A digital image tracking algorithm based on Fourier-transform cross-correlation has been developed to correct for instrumental drift in scanning tunneling microscope images. The technique was developed to eliminate cumulative tracking errors associated with fractional pixel drift. This tracking algorithm was used to monitor conductance changes associated with different conformations in conjugated molecular switch molecules and to trace the diffusion of individual benzene molecules on Ag{110}. We will also discuss image processing techniques to analyze the degree of intermixing in binary mixtures of alkanethiolate self-assembled monolayers imaged by STM.

How We Do Science
P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Nanometer-Scale Electronics and Storage
K. F. Kelly, Department of Electrical Engineering, Rice University, Houston, TX, USA

The ability to control the placement of molecules is essential for the patterning and fabrication of nanoscale devices. We apply selective chemistry and self-assembly in combination with conventional nanolithographic techniques to reach higher resolution, greater precision, and chemical versatility in the nanostructures that we create. To gain a greater understanding of the self-assembly process, we have imaged a variety of alkanethiol and other thiol-derivatized self-assembled monolayers (SAMs) with the scanning tunneling microscope (STM). In conjunction with this, we have recently investigated the role of internal functionality in SAMs of a family of amide-containing alkanethiol molecules on Au{111} using STM. The introduction of an internal amide-functionality induces spontaneous, room-temperature separation between these molecules and alkanethiols. This is in contrast to the random-mixing we have observed in co-adsorbed alkanethiol SAMs and demonstrates another method for controlling nanoscale patterning in these systems.

We have also utilized these self-assembled monolayers to isolate molecules with electronic function to determine the mechanisms of function, and the relationships between molecular structure, environment, connection, coupling, and function. We use self-assembly techniques in combination with STM to study candidate molecular switches individually and in small bundles. Alkanethiol SAMs on gold are used as a host two-dimensional matrix to isolate and to insulate electrically the molecular switches. We then individually address and electronically probe each molecule using STM. The conjugated molecules exhibit reversible conductance switching, manifested as a change in the topographic height in the STM images. The origins of switching and the relevant aspects of the molecular structure and environment required will be discussed.

Controlling and Measuring Local Composition and Properties in Lipid Bilayer Membranes
P. S. Weiss and T. G. D'Onofrio, Department of Chemistry, 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 membranes is a critical element of cellular processes such as transport, adhesion, infection, and uptake. We control local composition through manipulation of (local) membrane curvature. Our tools include multibeam optical tweezers, dual micropipette aspiration, 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.

Molecular Imprinting of Dendrimers
Arrelaine Dameron, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Quartz Crystal Microbalances in Biosensor Applications
Julia Heetderks, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Conductance Switching in Single Molecules*
Z. J. Donhauser, T. P. Pearl and P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

We have studied functionalized phenylene ethynylene oligomers as candidate molecular electronic devices using scanning tunneling microscopy (STM). A simple self-assembly strategy has been demonstrated that allows us to control monolayer structure, placement of individual molecules, and switching activity of individual molecules. Alkanethiolate self-assembled monolayers (SAMs) were used as host matrices to isolate and to insulate individual candidate molecular electronic devices. The isolated molecules were individually addressed and electrically probed using STM imaging and spectroscopy. The guest molecules exhibit reversible conductance switching, manifested as a change in the topographic height in STM images. High and low conductance states are visible when the molecules are inserted in dodecanethiolate SAMs, but the low conductance states are of the same height or lower than the host matrix. Using thin alkanethiolate matrices (as low as octanethiolate) reveals that the molecules can occupy at least three discrete conductance states. The amount and rate of active switching can be mediated by the structure of the host matrix. Poorly ordered SAMs were produced using a short deposition time; molecules inserted in these monolayers have a high switching activity. Well-ordered SAMs were produced using a vapor annealing procedure, which has been demonstrated with mixed alkanethiolate monolayers. Guest molecules inserted in vapor annealed SAMs have a low switching activity.

*Mort Traum Award Finalist

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

We use intermolecular interactions 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 on single or bundled molecules. We use and develop scanning probe microscopes to determine both local structures and the electronic and other local properties. We have applied these to isolate molecules with electronic function to determine the mechanisms of function, and the relationships between molecular structure, environment, connection, coupling, and function. We have been able to demonstrate that single molecules can function as multistate switches, and have determined important aspects of the mechanism, function, and persistence of switching. We will discuss the origins of switching and the relevant aspects of the molecular structure and environment required.

Conductance Switching in Single Molecules
Z. J. Donhauser, T. P. Pearl and P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

We have studied functionalized phenylene ethynylene oligomers as candidate molecular electronic devices using scanning tunneling microscopy (STM). A simple self-assembly strategy has been demonstrated that allows us to control monolayer structure, placement of individual molecules, and switching activity of individual molecules. Alkanethiolate self-assembled monolayers (SAMs) were used as host matrices to isolate and to insulate individual candidate molecular electronic devices. The isolated molecules were individually addressed and electrically probed using STM imaging and spectroscopy. The guest molecules exhibit reversible conductance switching, manifested as a change in the topographic height in STM images. High and low conductance states are visible when the molecules are inserted in dodecanethiolate SAMs, but the low conductance states are of the same height or lower than the host matrix. Using thin alkanethiolate matrices (as low as octanethiolate) reveals that the molecules can occupy at least three discrete conductance states. The amount and rate of active switching can be mediated by the structure of the host matrix. Poorly ordered SAMs were produced using a short deposition time; molecules inserted in these monolayers have a high switching activity. Well-ordered SAMs were produced using a vapor annealing procedure, which has been demonstrated with mixed alkanethiolate monolayers. Guest molecules inserted in vapor annealed SAMs have a low switching activity.

Probing single molecules using low temperature scanning tunneling microscopy
T. P. Pearl, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Single Molecule Switches*
Z. J. Donhauser and P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

*MRS Student Award Finalist

Measuring and Controlling Nanometer-Scale Properties in Molecules and Assemblies
P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions to direct molecules and nanoparticles into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements on single or bundled molecules. We use and develop scanning probe microscopes to determine both local structures and the local electronic, optical, mechanical and other properties. We have applied these to isolate molecules with electronic function to determine the mechanisms of function, and the relationships between molecular structure, environment, connection, coupling, and function. We have also used these tools to probe ferroic films, distributed nanostructures, and nanoparticle arrays.

Single Molecule Switches*
Z. J. Donhauser and P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

*MRS Student Award Finalist

Controlling and Measuring Local Composition and Properties in Self-Assembled Systems: Monolayers and Membranes
P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Probing single molecules using low temperature scanning tunneling microscopy
T. P. Pearl, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Controlling and Measuring Local Composition and Properties in Self-Assembled Systems: Monolayers and Membranes
P. S. Weiss, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Probing single molecules and nanoclusters using low temperature scanning tunneling microscopy
T. P. Pearl, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

TBA
Beth Anderson, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Control of Energy Transport in Conjugated Polymers using an Ordered Mesoporous Silica Matrix
Sanjini Nanyakkara, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA

Single Molecule Electronics
Z. J. Donhauser, Departments of Chemistry & Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Probing Single Molecule Switches Using Scanning Tunneling Microscopy
Z. J. Donhauser, Departments of Chemistry & Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Molecular electronics is rapidly emerging as a viable possibility for the creation of inexpensive, ultra-dense, high-capacity electronic devices. Using self-assembly techniques combined with scanning tunneling microscopy (STM) we have studied one promising family of molecular electronic candidates, phenylene ethynylene oligomers. Self-assembled monolayers (SAMs) of alkanethiolates on gold were used as matrices to spatially and electronically isolate guest oligomers and to control their position and orientation. We have observed that phenylene ethynylene oligomers inserted into alkanethiolate films can behave as molecular switches, reversibly changing conductance between at least three states. This change in conductance is manifested as a change in the apparent height of the molecules in STM images. Topographically higher states can be considered to have a higher conductance, while molecules that are topographically lower correspond to a lower conductance state. We have demonstrated that stochastic switching of the inserted molecules can be mediated by controlling the amount of local order in the host monolayers. To this end, a novel vapor annealing technique has been demonstrated that is an effective means to reduce the switching of inserted molecules. We have found that the single molecule switching that we observe is consistent with a tilting of the inserted molecules.

New Tools for Measuring Ferroic Properties with Unprecendented Resolution
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 & Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Nanoscale Ferroic Materials for Use in Data Storage
J. R. Hampton, Departments of Chemistry & Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Ferromagnetic and ferroelectric materials have a wide variety of current and potential uses in data storage. In this talk, I will discuss a number of applications of nanoscale ferroic materials and describe several current and future experimental methods for measuring the magnetic and electric properties of these complex materials. I will present our recent results applying these experimental techniques to ferromagnetic samples (electrodeposited cobalt-copper bilayers and multilayers) and ferroelectric samples (lead titanate nanoparticles on surfaces).

A comparative scanning tunneling microscopy study of physisorbed linear quadrupolar molecules: C₂N₂ and CS₂ on Au{111} at 4 K
Patrick Han, Charles Sykes, Thomas Pearl, and P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Sub-monolayer and near-monolayer coverages of cyanogen (C2N2) and carbon disulfide (CS2) were independently dosed and studied on Au111 at 4 K. Low temperature scanning tunneling microscopy was used to investigate the intermolecular and substrate-adsorbate interactions of each of the two chemical species. Both molecules were found to be weakly physisorbed and to form incommensurate structures with respect to the Au111 lattice. The superlattice formed by the Au111 reconstruction was determined to have a pronounced effect on the aggregation of the adsorbates. The more quadrupolar C2N2 does not form an ordered structure and is easily moved by the scanning tunneling microscope tip at 4 K, it forms a 2D liquid-gas system. In contrast, the less quadrupolar CS2 forms a molecular herringbone lattice structure. The Au111 reconstruction also influences the direction of the CS2 ordered domains, aligning the direction of the CS2 molecular herringbone lattice unit cell in a 3-fold symmetry. These observations are discussed in terms of the current understanding of the dynamics of 2D solid/liquid–gas interfaces.

A classical electrophile-surface bond evidenced quantum mechanically via tip-induced CS₂ interaction with Friedel Oscillations on Au{111}
Charles Sykes, Patrick Han, and P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Sub-monolayer coverages of CS2 adsorbed on Au111 at 4 K were studied using scanning tunneling microscopy. The molecule forms well ordered islands on the terraces and molecular chains at the bottoms of the steps. The adsorption of the CS2 molecule at specific surface sites is explained in terms of the substrate electron density. Strong tip/molecule interactions are shown to be prevalent in this system at negative tip biases and yield images showing reversed corrugation. At low positive tip bias, the tip again perturbs the molecules, but in this regime the tip/molecule interaction is comparable to the molecule/surface interaction and higher residence times at certain surface sites are observed. This effect is explained fully in terms of the electrophilic CS2 molecule having 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.

Creating and Measuring Nanostructures Made Using 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. We control defect type and density in self-assembled monolayers in order to control access to the substrate of other molecules from solution or vapor, to control the mobility and stability within the film. We select molecules to choose the interaction strength between molecules 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 key is to use precise, robust molecular layers in which the defects in the initial layer or layers are healed as additional layers are added. The thickness and thus the spacing of the resultant structures can be controlled down to 5 nm, with control to 1 nm or better by using a selected number of layers of precisely known thickness. We have demonstrated this approach both with e-beam generated structures as well as those based entirely on self-assembly. An additional advantage of molecular rulers is the inherent capability to displace the molecular resist chemically, and thus to remove the resist material simply and completely. We can also use molecular rulers with carefully designed parent structures to create complex structures that would be difficult to generate by conventional means. These can be made still more complicated by the selective application and use of sacrificial intermediate or parent generation structures. We will discuss our approaches to pattern design and creation using this method.

Mediating Electronic Switching of Single Molecules by Varying the Interaction Strength of the Host Environment
Penelope A. Lewis, Paul S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA, Christina E. Inman, James E. Hutchison (University of Oregon), James M. Tour (Rice University)

We have studied conjugated phenylene ethynylene oligomers inserted into amide-containing alkanethiolate self-assembled monolayers (SAMs) using scanning tunneling microscopy. The inserted molecules are implicated as molecular electronic device candidates and have shown interesting functionality as switches and wires. We investigate the stochastic switching of these conjugated molecules. Our previous work has shown that the local environment of these molecular switches mediates their switching when they are inserted into n-alkanethiolate matrices. In the present work, we investigate the switching of these molecules inserted in hydrogen-bonding, amide-containing alkanethiolate SAM matrices. The hydrogen bonded networks can affect the switching rates and properties of the inserted molecules by the additional stability imparted by the host matrix.

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

We use intermolecular interactions 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 on single or bundled molecules.^1-3 We use and develop scanning probe microscopes to determine both local structures and the electronic and other local properties. We have applied these to isolate molecules with electronic function to determine the mechanisms of function, and the relationships between molecular structure, environment, connection, coupling, and function. We have been able to demonstrate that single molecules can function as multistate switches, and have determined important aspects of the mechanism, function, and persistence of switching. We will discuss the origins of switching and the relevant aspects of the molecular structure and environment required.

References
1) Are Single Molecular Wires Conducting? L. A. Bumm, J. J. Arnold, M. T. Cygan, T. D. Dunbar, T. P. Burgin, L. Jones II, D. L. Allara, J. M. Tour, and P. S. Weiss, Science 271, 1705 (1996).
2) Conductance Switching in Single Molecules Through Conformational Changes, Z. J. Donhauser, B. A. Mantooth, K. F. Kelly, L. A. Bumm, J. D. Monnell, J. J. Stapleton, D. W. Price, Jr., A. M. Rawlett, D. L. Allara, J. M. Tour, and P. S. Weiss, Science 292, 2303 (2001).
3) Matrix-Mediated Control of Stochastic Single Molecule Conductance Switching, Z. J. Donhauser, B. A. Mantooth, T. P. Pearl, K. F. Kelly, S. U. Nanayakkara, and P. S. Weiss, Japanese Journal of Applied Physics 41, 4871 (2002).

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, 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.

Fabrication, Observation and Measurement of Nanostructures
Hirofumi Tanaka, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Nanoscience and nanotechnology have been developing rapidly over the past decade. There are three major methods for continued development in this field; nano- fabrication, nano-observation and nano-measurement. In this presentation, I will share my experience in these three areas.

I. Nanolithography by Using Self-Assembled Molecular Ruler Method
A method that combines conventional lithographic techniques and chemical self-assembly processes to create precise spacings between structures with nanometer-scale resolution has been developed by our group (1). This chemical process creates a three-dimensional molecular resist composed of metal-organic coordinated multilayers produced by sequential solution-phase depositions until a desired thickness is achieved. The molecules composing the self-assembled multilayer can be used as “molecular rulers” to precisely and quantitatively control the size of the created structures. In this work, an array of polystyrene spheres was used instead of conventional lithographic techniques to make “parent” structures. A close-packed monolayer of polystyrene spheres (diameter ~ 400 nm) was used as a hard mask. Gold was deposited through this mask and lift-off of the spheres produced arrays of triangular gold dots, which were used as “parent” structures. Multilayers of 16-mercaptohexadecanoic acid and Cu2+ ions were selectively deposited as a molecular resist onto these gold dots followed by chromium deposition creating a daughter structure on the substrate. After lift-off of the molecular resist, uniform spacings between “parent” and “daughter” structures are observed using FESEM (Fig. 1). Nanometer-scale spacing can be controlled around the nanostructures by using the process described above. We can control the size of the gap by simply changing the number of layers in the molecular resist or by using molecules of different lengths. In the near future, many applications using this method are expected to impact nanofabrication, such as nanoelectronic devices and micromachines. (1) A. Hatzor and P. S. Weiss, Science 291, 1019 (2001).

II. Electrical Conductance Measurement through ErSi₂ Nanowire Using Double-Probe Scanning Tunneling Microscopy
We have constructed a double probe scanning tunneling microscope (DP-STM), which is a novel technique for the development of future nanoscale devices. In this work, we apply the DP-STM for direct conductance measurements of one-dimensional (1D) nanostructures. P-type Si(001) with 0.01 Ocm resistivity is used as the substrate for these experiments. After annealing at 650 °C for 24 hrs, the Si(001) surface was cleaned by heating several times to approximately 1200 °C for a few seconds in an ultrahigh vacuum (UHV) chamber with a pressure below 1.0×10-9 Torr. To insure the substrate’s cleanliness, the surface structures were observed with a DP-STM at a pressure below 1×10-10 Torr. Erbium was then deposited on the substrate using an electron- bombardment deposition source. Substrate temperature during Er deposition was 620 °C. The deposition time was two minutes yielding sub-monolayer coverage of Er. After deposition, the sample temperature was maintained at 620 °C for two more minutes to promote completion of the chemical reaction between Er and Si. The surface of the sample was then observed again with one probe of the DP-STM. ErSi₂ nanowires self-assembled on the clean Si(001) surface as shown in Fig. 2. ErSi₂ nanowires run along a <110> axis of the Si(001) substrate with the dimensions 1-5 nm x 1-2 nm x ~1000 nm (width x height x length). In order to investigate crystallographic and electric properties of these crystalline ErSi₂ nanowires, we used our DP-STM as a “nano-tester”. The experimental results for the DP-STM measurements show that ErSi₂ nanowires are 1D metal conductors. Current-voltage curves, which are measured on a single ErSi₂ nanowire, always show linear dependence. In Fig. 3, the resistance of the ErSi₂ nanowire is plotted against its length. The resistance of nanowires is proportional to their length. The resistance per unit length is 1.2 kohm/nm along the ErSi₂ nanowire. The estimated resistivity is around 360 Ocm, which is 10 times larger in magnitude than the resistance expected based on the known resistivity of bulk ErSi₂, 35 Ocm. One of the reasons for such high resistance may be the elastically-elongated lattice spacing along the ErSi₂ nanowire as a result of the lattice mismatch between the ErSi₂ and Si(001) substrate (2). (2)Yong Chen, Douglas A. A. Ohlberg, Gilberto Medeiros-Ribeiro, Y. Austin Chang and R. Stanley Williams, Appl. Phys. Lett. 76, 4004 (2000).

Acknowledgment
The molecular ruler project (part I) was carried out in Weiss group at The Pennsylvania State Univ., USA. This work is now in progress with Prof. Paul Weiss, M. Anderson, L. P. Tan, M. Mihok and Dr. M. Horn. This work was partially collaborated with Prof. Haiwon Lee from Hanyang University, Korea. Multiprobe SPM project (part II) was carried out in Surface and Interface Lab., RIKEN, Japan. The equipment of Double Probe STM was constructed by Dr. T. Nakayama (present: National Institute for Material Science (NIMS)), Dr. C.-S. Jiang (present: National Renewable Energy Laboratory, USA), Dr. T. Okuda (present: Univ. of Tokyo) and Prof. M. Aono (present: NIMS) in RIKEN. The measurement was performed by myself and Dr. Y. Shingaya (present: NIMS) in RIKEN. This project is now continued by the Nakayama group in Nanomaterial Lab., NIMS. I was supported by a special postdoctoral fellowship in RIKEN during my stay. Hereby, I would like to express my great appreciation to their useful support. I also thank for inviting me to this conference.

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

As a result of a decade of fruitful and exciting collaboration with Dave Allara, we have devised strategies for placing molecules in self-assembled monolayers. Our early work together showed that these films were not at equilibrium and that we could control the exchange and motion of molecules by controlling the types and densities of film defects. We have since applied these strategies to isolate molecules with electronic function to determine the mechanisms of function, and the relationships between molecular structure, environment, connection, coupling, and function. We have shown how to use self- and directed assembly to control deposition and to build nanostructures based on self-assembly. Much remains to be understood in terms of retaining structures at the nanoscale while selectively reacting the films to pattern desired chemical functionality on the surface. We will discuss our current approaches to this goal.

Single Molecule Electronics
Z. J. Donhauser, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Applying Self- and Directed Assembly To Measure and To Operate Single Molecule Devices
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Advances in Nanolithography Using Molecular Rulers
M. E. Anderson,¹ L. P. Tan,¹ H. Tanaka,¹ M. Mihok,¹ M. W. Horn,² and P. S. Weiss^1
1Departments of Chemistry & Physics and
²Engineering Science and Mechanics
The Pennsylvania State University, University Park, PA 16802-6300, USA

The combination of conventional lithographic techniques with chemical self-assembly allows 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 a,?-mercaptoalkanoic acids and coordinated metal ions form precise “molecular ruler” resists to produce tailored, lithographically defined patterns. Initial structures created by conventional techniques are referred to as parents and subsequent structures generated by the molecular ruler process are identified as daughters, or subsequent generation structures. We have created tertiary generation structures, granddaughters, by forming molecular rulers on parent and daughter structures. These structures have sub-100 nm dimensions, and can be isolated by removing sacrificial parent and/or daughter structures. Other improvements to the molecular ruler procedure include increased throughput and reproducibility by automating the iterative nature of the procedure and by utilizing appropriate chemical lift-off solutions.

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

Molecular Rulers
M. E. Anderson,¹ L. P. Tan,¹ H. Tanaka,¹ M. Mihok,¹ M. W. Horn,² and P. S. Weiss^1
1Departments of Chemistry & Physics and
²Engineering Science and Mechanics
The Pennsylvania State University, University Park, PA 16802-6300, USA

The combination of conventional lithographic techniques with chemical self-assembly allows 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 a,?-mercaptoalkanoic acids and coordinated metal ions form precise “molecular ruler” resists to produce tailored, lithographically defined patterns. Initial structures created by conventional techniques are referred to as parents and subsequent structures generated by the molecular ruler process are identified as daughters, or subsequent generation structures. We have created tertiary generation structures, granddaughters, by forming molecular rulers on parent and daughter structures. These structures have sub-100 nm dimensions, and can be isolated by removing sacrificial parent and/or daughter structures. Other improvements to the molecular ruler procedure include increased throughput and reproducibility by automating the iterative nature of the procedure and by utilizing appropriate chemical lift-off solutions.

Advances in Nanolithography Using Molecular Rulers
M. E. Anderson,¹ L. P. Tan,¹ H. Tanaka,¹ M. Mihok,¹ M. W. Horn,² and P. S. Weiss^1
1Departments of Chemistry & Physics and
²Engineering Science and Mechanics
The Pennsylvania State University, University Park, PA 16802-6300, USA

The combination of conventional lithographic techniques with chemical self-assembly allows 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 a,w-mercaptoalkanoic acids and coordinated metal ions form precise “molecular ruler” resists to produce tailored, lithographically defined patterns. Initial structures created by conventional techniques are referred to as parents and subsequent structures generated by the molecular ruler process are identified as daughters, or subsequent generation structures. We report the creation of tertiary generation structures, granddaughters, created by forming molecular rulers on parent and daughter structures. These structures have sub-100 nm dimensions, and can be isolated by removing sacrificial parent and/or daughter structures. Other improvements to the molecular ruler procedure include increased throughput and reproducibility by automating the iterative nature of the procedure and by utilizing appropriate chemical lift-off solutions.

Exploiting Intermolecular Interactions for Nanoscale Control
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

Interactions within and between molecules can be measured, understood and exploited at unprecedented scales.¹ We will first explore atomic-scale measurements of these interactions. These can be direct interactions or can be mediated by electronic perturbations of the substrate on which these molecules are attached. We will then 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 will hear about both. Intelligently assembling such supramolecular systems is beginning to enable us to bridge the gap between nanolithography and chemistry.

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 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 on single or bundled molecules. We use and develop scanning probe microscopes to determine both local structures and the electronic, optical, mechanical, and other local properties. We have applied these to isolate molecules with electronic and electromechanical function to determine the mechanisms of function, and the relationships between molecular structure, environment, connection, coupling, and function. We have been able to demonstrate that single molecules can function as multistate electronic switches, and have determined important aspects of the mechanism, function, and persistence of switching. We will discuss the origins of switching and the relevant aspects of the molecular structure and environment required. We are expanding this work to understand the fundamentals of motor function at the atomic scale through the use of purposefully designed synthetic molecular motors. This nascent project and what we can learn from these studies will also be discussed.

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

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

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

We use intermolecular interactions 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 on single or bundled molecules. We use and develop scanning probe microscopes to determine local structures as well as the electronic and other local properties. We have applied these to isolated molecules with electronic and electromechanical function to determine the mechanisms of function, and the relationships between molecular structure, environment, connection, coupling, and function. We have demonstrated that single molecules can function as multistate electronic switches, and have determined important aspects of the mechanism, function, and persistence of switching. We will discuss the origins of switching and the relevant aspects of the molecular structure and environment required.

Measuring and Controlling Molecular-Scale Properties for Single 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

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.

Ordered local domain structures of decaneselenolate and dodecaneselenolate assemblies on Au{111}
J. D. Monnell (1), Joshua J. Stapleton (2), Jennifer J. Jackiw (1), Timothy D. Dunbar (3), William A. Reinerth Sr. (4), Shawn M. Dirk (5), James. M. Tour (5), David L. Allara (2), and Paul S. Weiss (1).
(1) Departments of Chemistry and Physics, Pennsylvania State University, 152 Davey Lab, University Park, PA 16802
(2) Departments of Chemistry and Materials Science, The Pennsylvania State University, 152 Davey Lab, University Park, PA 16802-6300
(3) Sandia National Laboratories
(4) Hybrid Plastics, 18237 Mount Baldy Circle, Fountain Valley, CA 92708
(5) Department of Chemistry and Center for Nanoscale Science and Technology, Rice University, MS-222, 6100 Main Street, Houston, TX 77251-1892

Co-existing adsorbate phases in high coverage decaneselenolate and dodecaneselenolate [CH₃(CH₂)_nSe-; n=9 and 11] self-assembled monolayers (SAMs) on Au{111} have been characterized by scanning tunneling microscopy (STM) and consist of two types: a linear missing-row structure and a densely packed distorted unit cell structure incommensurate with the underlying gold substrate, as revealed by the observation of a moiré pattern. Comparison of the alkaneselenolate data with analogous structural phases reported for alkanethiolate SAMs on Au{111} show that differences between the two systems can be understood on the basis that self-assembly is guided both by headgroup-headgroup as well as headgroup-substrate interactions. The structural conclusions are supported by excellent agreement of experimental lattice parameters and those derived from molecular packing models.

Conductance switching of single molecules in alkanethiolate self assembled monolayers^*
Amanda M. Moore¹, Zachary J. Donhouser¹, James. M. Tour, and Paul S. Weiss¹. (1) Departments of Chemistry and Physics, The Pennsylvania State University, 152 Davey Laboratory, Box 39, University Park, PA 16802,  (2) Department of Chemistry and Center for Nanoscale Science and Technology, Rice University

Phenylene ethynylene oligomers (OPE) have been studied as candidates for molecular electronic devices using scanning tunneling microscopy (STM). These molecules were inserted into host alkanethiolate self-assembled monolayers (SAMs) for isolation and individual addressability. OPE molecules were probed using STM and exhibited reversible conductance switching which is viewed as a change in the topographic height of the molecule in the STM images. The rate of active switching has been shown to be mediated by the structure of the host matrix. Using shorter chain alkanethiolate SAMs we have shown multistate switching of these molecules and have suggested a tilting mechanism for the different conductance states. Analysis of this switching mechanism has involved in changing functionality, bonding, size and rotational freedom of the molecules under study.

^*Winner: Best Poster Award

Dynamics and Conductance of Conjugated Molecules Supported in Momolayer Matrices Studied by Low Temperature Scanning Tunneling Microscopy
S. U. Nanayakkara,¹ T. P. Pearl¹, J. M. Tour,² and P. S. Weiss^1
1 Departments of Chemistry and Physics, The Pennsylvania State University, 152 Davey Laboratory, University Park, PA 16802
²Department of Chemistry and Center for Nanoscale Science and Technology, Rice University, Houston, TX

Phenylene-ethylene oligomers inserted in alkanethiolate self assembled monolayers deposited on Au(111), have been probed using high gap impedance, low temperature scanning tunneling microscopy. Previous work has shown that these molecules undergo conformational switching between two discrete conductance states under ambient conditions. This behavior has now been addressed using variable temperature microscopy at 300 K, 77 K, and 4 K to characterize the role of the inserted molecule structure and the host matrix environment with regards to these dynamics. Additionally, the insertion and isolation of these molecules in thin films, in combination with the spatial and energy resolution afforded at low temperatures, enables us to probe the electronic properties of single molecules and the role of chemical structure and environment in conductance pathways. These measurements are crucial for comparison with measurements performed on monolayers and bundles of these oligomers, which have been studied for use in molecular electronic devices.

Switching dynamics of ladder molecules in low defect self assembled monolayers
A. A. Dameron,¹ J. W. Ciszek², J. M. Tour,² and P. S. Weiss^1
1 Departments of Chemistry and Physics, The Pennsylvania State University, 152 Davey Laboratory, University Park, PA 16802
²Department of Chemistry and Center for Nanoscale Science and Technology, Rice University, Houston, TX

We have fabricated 1-adamantanethiolate self assembled monolayers (SAMs) on Au(111) and characterized them with scanning tunneling micrsocopy. Adamantanethiol molecules have a bulky cage structure and orient in both fcc and hcp packing structures. The adamantanethiolate SAMs display fewer defect sites and less prominent domain boundaries than alkanethiolate SAMs. The switching dynamics of 2-thioacetylphenanthrene ("ladder molecules") and 4-thioacetyl-biphenyl molecules were studied by insertion of the molecules into both adamantanethiolate and short chain alkanethiolate SAMs. The switching dynamics in the two SAMs are similar; in both cases the molecules insert primarily into the defect sites in the monolayer and display switching between two states.

Elucidation of the Electronic Properties of Alkanethiolate-Stabilized Gold Clusters and Nanoparticles Using Scanning Tunneling Microscopy^*
R. K. Smith,¹ S. U. Nanayakkara,¹, B. A. Mantooth,¹ T. P. Pearl¹, G. E. Woehrle,² J. E. Hutchison,² and Paul S. Weiss^1
1 Departments of Chemistry and Physics, The Pennsylvania State University, 152 Davey Laboratory, Box 39, University Park, PA 16802
²Department of Chemistry, University of Oregon, Eugene, OR.

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 (I(V)) characteristics of isolated, solution-derived octanethiolate-stabilized gold clusters [Au₁₁(S(CH₂)₇CH₃)₁₀] and nanoparticles [Au₁₀₁(S(CH₂)₇CH₃)₄₃], taken in both cryogenic (4K, UHV) and ambient conditions using scanning tunneling microscopy (STM) and spectroscopy (STS). The clusters and particles (d_CORE=0.8 ± 0.2 nm and 1.5 ± 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 temperature, 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.

^*Winner: Best Poster Award

We use and extend scanning tunneling microscopy (STM) to explore structures, interactions, and perturbations on surfaces due to adsorbed molecules, and particles. This has required the development of new tools with atomic-scale views of the surface. We have developed a photon emission STM for characterization of nanoparticle and molecular systems, and an optical excitation STM to characterize excited states of quantum dots and nanoparticles. We measure and characterize surface bound or adsorbed nanometer-scale features with the high spatial resolution of STM and the additional information (e.g. electronic and optical properties, chemical environment) gained from our hybrid tools.

Photolithographic structures with precise controllable nanometer–scale spacings created by molecular rulers
M. E. Anderson,¹ L. P. Tan,¹ M. Mihok,¹ H. Tanaka,¹ M. Horn,² and P. S. Weiss¹.
(1) Departments of Chemistry and Physics, The Pennsylvania State University, 152 Davey Laboratory, University Park, PA 16802,
(2) Department of Engineering Science and Mechanics, The Pennsylvania State University, University Park, PA 16802.

We have studied the switching of conjugated phenylene ethynylene oligomers inserted into hydrogen-bonding amide-alkanethiolate self-assembled monolayers (SAMs) using scanning tunneling microscopy. The phenylene ethynylene oligomers show stability in two conductance states, an ON and an OFF state. Our previous work showed that the local environment of these molecular switches mediates their switching when they are inserted into n-alkanethiolate matrices. With the more tightly bonded matrices we observe fewer switching events between the ON and OFF state than previously reported for n-alkanethiolate matrices and attribute this to the hydrogen bonds of the amide groups in the matrix. Furthermore, we demonstrate bias-dependent switching as a result of hydrogen bonding between the inserted phenylene ethynylene oligomers and the matrix molecules. We show that it is possible to control switching based on the chemical functionality of the surrounding environment of inserted molecules.

Electronic properties of Au nanoparticles covalently attached to Au{111} via 1,10-decanedithiol
D. J. Fuchs and P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

1,10-decanedithiol molecules are inserted into a n-decanethiol [CH3(CH2)9SH] self-assembled monolayer (SAM) on Au{111} and are charcterized by scanning tunneling microscopy (STM). Bifunctional molecules are inserted into the SAM for the covalent attachment of monolayer protected gold nanoparticles. The gold nanopaarticles are synthesized with short chain alkylthiol ligands to promote binding. Electronic properties are compared to proximate pairs and assmeblies of gold nanoparticles.

Mediating electronic switching of single molecules using chemical interactions
Penelope A. Lewis¹, Christina E. Inman², James. M. Tour³, James E. Hutchison², and Paul S. Weiss¹.
(1) Department of Chemistry, The Pennsylvania State University, 152 Davey Laboratory, University Park, PA 16802,
(2) Department of Chemistry and Materials Science Institute, University of Oregon, 1253 University of Oregon, Eugene, OR 97403-1253,
(3) Department of Chemistry and Center for Nanoscale Science and Technology, Rice University, MS-222, PO Box 1892, Houston, TX 77251-1892

We have studied the switching of conjugated phenylene ethynylene oligomers inserted into hydrogen-bonding amide-alkanethiolate self-assembled monolayers (SAMs) using scanning tunneling microscopy. The phenylene ethynylene oligomers show stability in two conductance states, an ON and an OFF state. Our previous work showed that the local environment of these molecular switches mediates their switching when they are inserted into n-alkanethiolate matrices. With the more tightly bonded matrices we observe fewer switching events between the ON and OFF state than previously reported for n-alkanethiolate matrices and attribute this to the hydrogen bonds of the amide groups in the matrix. Furthermore, we demonstrate bias-dependent switching as a result of hydrogen bonding between the inserted phenylene ethynylene oligomers and the matrix molecules. We show that it is possible to control switching based on the chemical functionality of the surrounding environment of inserted molecules.

Investigation of lipid domain structure through physical methods of perturbation and measurement
Julia J. Heetderks and Paul S. Weiss.
Departments of Chemistry and Physics, The Pennsylvania State University, 152 Davey Laboratory, University Park, PA 16802

We employ widefield and fluorescence optical microscopy to study domain segregation in giant unilamellar vesicles (GUVs). We are particularly interested in the relationship between membrane curvature and local composition/ structure. We simultaneously image gel and fluid regions using fluorescent probes that localize preferentially into each phase and an emission splitter to divide the signals; we also follow the domains in real time with rapid three-dimensional imaging. In some simple two-component vesicles, we have observed unlabeled regions of membrane in the center of labeled gel-phase domains. We propose possible explanations for this repeatable phenomenon, which has not yet been addressed in the literature. We have developed several methods for physically deforming GUVs; the current studies employ micropipette aspiration to change the curvature of a small section of membrane or to extrude a lipid nanotube (tether) from the main body of the vesicle. Reorganization of labeled domains is observed upon perturbation of the membrane.

Mediating electronic switching of single molecules using chemical interactions
Penelope A. Lewis¹, Christina E. Inman², James. M. Tour³, James E. Hutchison², and Paul S. Weiss¹.
(1) Departments of Chemistry and Physics, The Pennsylvania State University, 152 Davey Laboratory, University Park, PA 16802,
(2) Department of Chemistry and Materials Science Institute, University of Oregon, 1253 University of Oregon, Eugene, OR 97403-1253,
(3) Department of Chemistry and Center for Nanoscale Science and Technology, Rice University, MS-222, PO Box 1892, Houston, TX 77251-1892

We have studied the switching of conjugated phenylene ethynylene oligomers inserted into hydrogen-bonding amide-alkanethiolate self-assembled monolayers (SAMs) using scanning tunneling microscopy. The phenylene ethynylene oligomers show stability in two conductance states, an ON and an OFF state. Our previous work showed that the local environment of these molecular switches mediates their switching when they are inserted into n-alkanethiolate matrices. With the more tightly bonded matrices we observe fewer switching events between the ON and OFF state than previously reported for n-alkanethiolate matrices and attribute this to the hydrogen bonds of the amide groups in the matrix. Furthermore, we demonstrate bias-dependent switching as a result of hydrogen bonding between the inserted phenylene ethynylene oligomers and the matrix molecules. We show that it is possible to control switching based on the chemical functionality of the surrounding environment of inserted molecules.

Investigation of lipid domain structure through physical methods of perturbation and measurement
Julia J. Heetderks and Paul S. Weiss.
Departments of Chemistry and Physics, The Pennsylvania State University, 152 Davey Laboratory, University Park, PA 16802

We employ widefield and fluorescence optical microscopy to study domain segregation in giant unilamellar vesicles (GUVs). We are particularly interested in the relationship between membrane curvature and local composition/ structure. We simultaneously image gel and fluid regions using fluorescent probes that localize preferentially into each phase and an emission splitter to divide the signals; we also follow the domains in real time with rapid three-dimensional imaging. In some simple two-component vesicles, we have observed unlabeled regions of membrane in the center of labeled gel-phase domains. We propose possible explanations for this repeatable phenomenon, which has not yet been addressed in the literature. We have developed several methods for physically deforming GUVs; the current studies employ micropipette aspiration to change the curvature of a small section of membrane or to extrude a lipid nanotube (tether) from the main body of the vesicle. Reorganization of labeled domains is observed upon perturbation of the membrane.

Free radical-induced degradation of vesicle-encapsulated microtubules
A. E. Counterman, T. G. D'Onofrio, and P. S. Weiss.
Departments of Chemistry and Physics, The Pennsylvania State University, 152 Davey Laboratory, University Park, PA 16802

Polymerization of tubulin inside a lipid vesicle forms a microtubule that stretches the membrane into a tube-like extension at the point of membrane contact. In this work, differential interference contrast and fluorescence microscopy are used to characterize microtubule breakdown resulting from oxidative stress in lipsomes and the resulting perturbation of the supported region of membrane. Microtubule breakdown is initiated by UV excitation of 6-(9-anthroyloxy)stearic acid, a lipid-soluble fluorescent probe. Degradation of vesicle-encapsulated microtubules is caused by production of free radicals formed upon UV excitation of the fluorescent probe. The kinetics of microtubule degradation are influenced by the lipid saturation level, fluorescent probe concentration, and presence of free-radical scavengers. At high concentrations of fluorophore, a pearled morphology of the membrane is observed upon degradation of the microtubule. We propose that this model system may have utility in investigating the effects of oxidative stress in neuropathies such as Alzheimer's disease.

Near-Field Microwave Microscopy
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

We use intermolecular interactions 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 on single or bundled molecules. We use and develop scanning probe microscopes to determine local structures as well as the electronic and other local properties. We have applied these to isolated molecules with electronic and electromechanical function to determine the mechanisms of function, and the relationships between molecular structure, environment, connection, coupling, and function. We have demonstrated that single molecules can function as multistate electronic switches, and have determined important aspects of the mechanisms, function, and persistence of switching. We will discuss the origins of switching and the relevant aspects of the molecular structure and environment required.

We have applied these same ideas to the control and measurement of the placement of molecules within membranes, ultimately in order to control biological function. Chemical, mechanical, and optical control along with optical measurements enable this work. The coupling of the membrane to cytoskeletal structure has been explored using this strategy.

Exploring and Controlling the Atomic-Scale World: Life in the Weiss Group
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 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 on single or bundled molecules. We use and develop scanning probe microscopes to determine local structures as well as the electronic and other local properties. We have applied these to isolated molecules with electronic and electromechanical function to determine the mechanisms of function, and the relationships between molecular structure, environment, connection, coupling, and function. We have demonstrated that single molecules can function as multistate electronic switches, and have determined important aspects of the mechanism, function, and persistence of switching. We will discuss the origins of switching and the relevant aspects of the molecular structure and environment required.

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 will first explore atomic-scale measurements of these interactions. These can be direct interactions or can be mediated by electronic perturbations of the substrate to which these molecules are attached. We will then 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 control defect type and density in self-assembled monolayers in order to control access to the substrate of other molecules from solution or vapor, to control the mobility and stability within the film. 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 key is to use precise, robust molecular layers in which the defects in the initial layer or layers are healed as additional layers are added. The thickness and thus the spacing of the resultant structures can be controlled down to 5 nm, with control to 1 nm or better by using a selected number of layers of precisely known thickness. We have demonstrated this approach with electron beam generated and photolithographic structures as well as those based entirely on self-assembly. We will discuss our approaches to pattern design and creation using these methods.

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 will first explore atomic-scale measurements of these interactions. These can be direct interactions or can be mediated by electronic perturbations of the substrate to which these molecules are attached. We will then 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 control defect type and density in self-assembled monolayers in order to control access to the substrate of other molecules from solution or vapor, to control the mobility and stability within the film. 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 key is to use precise, robust molecular layers in which the defects in the initial layer or layers are healed as additional layers are added. The thickness and thus the spacing of the resultant structures can be controlled down to 5 nm, with control to 1 nm or better by using a selected number of layers of precisely known thickness. We have demonstrated this approach with electron beam generated and photolithographic structures as well as those based entirely on self-assembly. We will discuss our approaches to pattern design and creation using these methods.

Exploiting Intermolecular Interactions for Nano-Scale Control
P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions 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 on single or bundled molecules. We use and develop scanning probe microscopes to determine local structures as well as the electronic and other local properties. We have applied these to isolated molecules with electronic and electromechanical function to determine the mechanisms of function, and the relationships between molecular structure, environment, connection, coupling, and function. We have demonstrated that single molecules can function as multistate electronic switches, and have determined important aspects of the mechanisms, function, and persistence of switching. We will discuss the origins of switching and the relevant aspects of the molecular structure and environment required.

We have applied these same ideas to the control and measurement of the placement of molecules within membranes, ultimately in order to control biological function. Chemical, mechanical, and optical control along with optical measurements enable this work. The coupling of the membrane to cytoskeletal structure has been explored using this strategy.

 Photolithographic structures with precise controllable nanometer-scale spacings created by molecular rulers

M. E. Anderson,* L. P. Tan,* M. Mihok,* H. Tanaka,* M. W. Horn,** and P. S. Weiss*
*Departments of Chemistry & Physics, and **Department of Engineering Science and Mechanics,
The Pennsylvania State University, University Park, PA 16802-6300, USA.

    The combination of conventional lithographic techniques with chemical self-assembly allows 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 α,ω-mercaptoalkanoic acids and coordinated metal ions form precise molecular ruler resists to produce tailored, lithographically defined patterns.(1,2)  This resist is selectively deposited onto initial parent gold structures, metal is deposited, and the resist is lifted off, thereby leaving daughter structures whose spacing from the parent depends on the thickness of the resist.  For future device fabrication with this technique, it would be advantageous to position these gaps selectively on the surface.  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.

 (1) A. Hatzor and P.S. Weiss, Science 291, 1019 (2001).

(2) M. E. Anderson, R. K. Smith, Z. J. Donhauser, A. Hatzor, P. A. Lewis,  L. P. Tan, H. Tanaka, M. W. Horn, and P. S. Weiss, Journal of Vacuum Science and Technology B 20, 2739 (2002).

Switching dynamics of ladder molecules in low defect self assembled monolayers
Arrelaine A. Dameron, Paul S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA
Jacob W. Ciszek, James M. Tour, Department of Chemistry and Center for Nanoscale Science and Technology, Rice University

We have fabricated 1-adamantanethiolate self assembled monolayers (SAMs) on Au(111) and characterized them with scanning tunneling micrsocopy.¹  Adamantanethiol molecules have a bulky cage structure and orient in both fcc and hcp packing structures. The adamantanethiolate SAMs display fewer defect sites and less prominent domain boundaries than alkanethiolate SAMs. The switching dynamics of  2-thioacetylphenanthrene ("ladder molecules") and 4-thioacetyl-biphenyl molecules were studied by insertion of the molecules into both adamantanethiolate and short chain alkanethiolate SAMs.  The switching dynamics in the two SAMs are similar; in both cases the molecules insert primarily into the defect sites in the monolayer and display switching between two states.

[1] L. F. Charles, M. S. Thesis, The Pennsylvania State University (1999).

Conductance switching of single molecules in alkanethiolate self assembled monolayers
Amanda M. Moore, Zachary J. Donhauser,  Paul S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA, James M. Tour, Department of Chemistry and Center for Nanoscale Science and Technology, Rice University

Phenylene ethynylene oligomers (OPE) have been studied as candidates for molecular electronic devices using scanning tunneling microscopy (STM). These molecules were inserted into host alkanethiolate self-assembled monolayers (SAMs) for isolation and individual addressability. OPE molecules were probed using STM and exhibited reversible conductance switching which is viewed as a change in the topographic height of the molecule in the STM images. The rate of active switching has been shown to be mediated by the structure of the host matrix. Using shorter chain alkanethiolate SAMs we have shown multistate switching of these molecules and have suggested a tilting mechanism for the different conductance states. Analysis of this switching mechanism has involved in changing functionality, bonding, size and rotational freedom of the molecules under study.

Molecule-metal surface interactions evidenced quantum mechanically via tip-induced CS₂ interaction with Friedel Oscillations on Au{111}
E. C. H. Sykes, P. Han and P. S. Weiss Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

.Sub-monolayer coverages of CS₂ adsorbed on Au{111} at 4 K were studied using scanning tunneling microscopy. The molecule forms well ordered islands on the terraces and molecular chains at the bottoms of the steps. The adsorption of the CS₂ molecule at specific surface sites is explained in terms of the substrate electron density. Strong tip/molecule interactions are shown to be prevalent in this system at negative tip biases and yield images showing reversed corrugation. At low positive tip bias, the tip again perturbs the molecules, but in this regime the tip/molecule interaction is comparable to the molecule/surface interaction and higher residence times at certain surface sites are observed. This effect is explained fully in terms of the CS₂ molecule having 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.

Mediating Electronic Switching of Single Molecules Using Chemical Interactions
Penelope A. Lewis, Paul S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA, Christina E. Inman, James E. Hutchison (University of Oregon), James M. Tour (Rice University)

We have studied conjugated phenylene-ethynylene oligomers inserted into amide-containing alkanethiolate self-assembled monolayers using scanning tunneling microscopy in order to determine their physical and electronic properties when surrounded by a hydrogen-bonded matrix. The phenylene-ethynylene oligomers show stability in two conductance states, an ON and an OFF state. We observe fewer switching events between the ON and OFF states than previously reported for n-alkanethiolate matrices and attribute this to the rigidity due to 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 oligophenylene-ethynylene and the matrix molecules. We demonstrate that the chemical and physical environment of proposed molecular devices is crucial to their function and can be exploited to impart tunable electronic properties.

Electronic properties of Au nanoparticles covalently attached to Au{111} via 1,10-decanedithiol
D. J. Fuchs and P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

1,10-decanedithiol molecules are inserted into a n-decanethiol [CH3(CH2)9SH] self-assembled monolayer (SAM) on Au{111} and are charcterized by scanning tunneling microscopy (STM). Bifunctional molecules are inserted into the SAM for the covalent attachment of monolayer protected gold nanoparticles. The gold nanopaarticles are synthesized with short chain alkylthiol ligands to promote binding. Electronic properties are compared to proximate pairs and assmeblies of gold nanoparticles.

Session Title: Advances in Scanning Probes

Elucidation of the Electronic Properties of Isolated Alkanethiolate-Passivated Undecagold Clusters by Low Temperature Scanning Tunneling Microscopy and Spectroscopy

Gerd Woehrle and James E. Hutchison. Department of Chemistry and Materials Science Institute, University of Oregon, 1253 University of Oregon, Eugene, OR, 97403, hutch@oregon.uoregon.edu.

We have studied the electronic properties of isolated, octanethiolate-stabilized undecagold clusters [Au₁₁(S(CH₂)₇CH₃)₁₀] using low temperature scanning tunneling microscopy (STM) and spectroscopy (STS). The clusters, d_CORE = 0.8 ± 0.2 nm, were immobilized by inserted dithiol molecules in an alkanethiolate self-assembled monolayer (SAM) on Au(111). The clusters were synthesized in solution by ligand exchange of Au₁₁(PPh₃)₈Cl₃ with octanethiol, resulting in a complete octanethiolate ligand shell, and were subsequently deposited upon a SAM. The geometry of the STM tip-vacuum-gold cluster-SAM-Au(111) assembly can be modeled as a double barrier tunnel junction, which may give insight into controlling the movement of single or small numbers of electrons. Discrete quantum energy levels are more evident in this cluster size range where the atomic character of the metal is prominent.  We have observed Coulomb blockade of these clusters at 4 K. The current-voltage characteristics show uneven spacing between adjacent current steps, showing quantized energy states. The observed, large zero-conductance gaps result from quantum size effects, where the bound octanethiolate ligand shell further reduces the free volume in which the electrons can move. This study assesses the impact of sub-nanometer sized clusters on single electron transport properties, enlightening the future of nanoscale electronics.

Microtubule Degradation via Oxidative Damage to Unsaturated Lipids and Protection Against This Attack
X. A. Perez, T. G. D'Onofrio, A. E. Counterman, A. Hatzor and P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We have constructed models of axons that employ lipid bilayer membranes encapsulating microtubules. We have shown that radical generation in the membrane results in the catastrophic collapse of the microtubules. The radicals were generated photochemically both from UV-absorbing dyes and from unsaturated (brain polar extract) lipids. The rate of microtubule collapse was monitored via time-lapse optical and fluorescence microscopies. The effect of the attack could be delayed or prevented by employing radical scavengers in the lipid or in the surrounding aqueous environment. The effects of these protection strategies were quantified. The collapse of the microtubules leads to "pearled" membrane structures that were at least partially reversible over time. These methods will now be applied to determine the roles of specific lipids implicated in axonal degeneration in aging primates and Alzheimer's Syndrome.
Support Contributed By: National Science Foundation

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 will first explore atomic-scale measurements of these interactions. These can be direct interactions or can be mediated by electronic perturbations of the substrate to which these molecules are attached. We will then 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 control defect type and density in self-assembled monolayers in order to control access to the substrate of other molecules from solution or vapor, to control the mobility and stability within the film. 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 key is to use precise, robust molecular layers in which the defects in the initial layer or layers are healed as additional layers are added. The thickness and thus the spacing of the resultant structures can be controlled down to 5 nm, with control to 1 nm or better by using a selected number of layers of precisely known thickness. We have demonstrated this approach with electron beam generated and photolithographic structures as well as those based entirely on self-assembly. We will discuss our approaches to pattern design and creation using these methods.

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

We use intermolecular interactions 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 on single or bundled molecules. We use and develop scanning probe microscopes to determine local structures as well as the electronic and other local properties. We have applied these to isolated molecules with electronic and electromechanical function to determine the mechanisms of function, and the relationships between molecular structure, environment, connection, coupling, and function. We have demonstrated that single molecules can function as multistate electronic switches, and have determined important aspects of the mechanism, function, and persistence of switching. We will discuss the origins of switching and the relevant aspects of the molecular structure and environment required.

Elucidation of the electronic properties of alkanethiolate-stabilized gold clusters and nanoparticles using scanning tunneling microscopy
R. K. Smith, S. U. Nanayakkara, B. A. Mantooth, T. P. Pearl, and P. S. Weiss, Departments of Chemistry and Physics, The Pennsylvania State University, University Park, PA 16802-6300, USA

We use intermolecular interactions 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 on single or bundled molecules. We use and develop scanning probe microscopes to determine local structures as well as the electronic and other local properties. We have applied these to isolated molecules with electronic and electromechanical function to determine the mechanisms of function, and the relationships between molecular structure, environment, connection, coupling, and function. We have demonstrated that single molecules can function as multistate electronic switches, and have determined important aspects of the mechanism, function, and persistence of switching. We will discuss the origins of switching and the relevant aspects of the molecular structure and environment required.

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7 February 2016
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