Weiss Group Image Gallery - Being Reconstructed

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This series of images are discussed in our Science paper, Molecular Rulers for Scaling Down Nanostructures, A. Hatzor, P. S. Weiss, Science 291, 1019 (2001).

A series of field emission scanning electron microscope (FESEM) images showing gold dots of different sizes and shapes and a gold ring formed in the center of hollow parent structures.

A field emission scanning electron microscopy image showing a ~30 nm gold dot formed in the center of a hollow gold parent structure supported on an oxidized Si substrate. This nanostructure was fabricated by a 'molecular ruler' resist process developed to extend the range of conventional nanolithography techniques.

The scaling-down process forms a gold ring connected to two thin gold channels on opposite sides. The gold channel size is ~15 nm. The ring and channels are formed in between a parent circle and two L-shaped structures.

"Parent" gold hollow square of a different hole size. The square in the center was formed similarly to the circle shown in the first image.

Field emission scanning electron microscopy images depicting stages of a nanostructure reduction process. From top to bottom, gaps between "parent" gold traces on oxidized Si are reduced from ~110 nm to ~65 nm (third row left) and ~25 nm (third row right) by 10-layer and 20-layer molecular ruler resists, respectively. Thin metal wires ~65 nm (bottom left) and ~25 nm (bottom right) wide, respectively, are formed, separated by precisely determined gaps from each of the parent gold traces.

The scanning tunneling microscope allows us to observe individual molecules on metal substrates. However, studies of surface motion are often limited by the speed of diffusion relative to the rate of data acquisition. One way to overcome this problem is by introducing surface species with strong adsorbate-adsorbate interactions. This is true of the system pictured below, a self-assembled monolayer of an alkanethiol on Au{111}.

The interactions in this system are strong enough to slow down the rate of diffusion on the gold surface. This movie shows the motion of single-atom steps over several scans:

MPEG version (27 K)

When a mixture of different alkanethiols is deposited onto the gold substrate, sometimes the interactions between similar molecules allow the molecules to phase-segregate into domain structures. In these images, mixtures of ester-terminated and methyl-terminated alkanethiols were used.

Domains in a 3:1 mixed composition alkanethiol SAM

Domains in a 1:3 mixed composition alkanethiol SAM

Domains in a 1:1 mixed composition alkanethiol SAM

Domain coalescence over a 37 minute interval in a 3:1 mixed composition SAM

However, the following images show random distribution in other mixed monolayers. The first example shows a mixture of two methyl-terminated alkanethiols of different lengths, while the second example shows a mixture of an alkanethiol chain with an arenethiol chain. The failure to coalesce in these cases may be due to weaker interactions between the chains, or because of the greater concentration ratios in the mixtures.

Random distribution in a 19:1 mixed composition alkanethiol SAM

3-D view of the previous image

Random distribution in a mixed composition alkanethiol/arenethiol SAM

2.4M MPEG of wire-like molecules inserted into an alkanethiol self-assembled monolayer

Other methods of monitoring surface motion with the STM include cooling the sample to slow the diffusion rate, and measuring the residence time of species at specific surface sites. Both of these techniques have been used in our studies of benzene molecules on Cu{111}.

Benzene molecules accumulate at step edges on Cu{111}

3-D close up of the previous image

We have also developed a microscope capable of studying insulating substrates, by using an alternating current to tunnel electrons back and forth between the surface and the tip. This ACSTM produced these images of a lead silicate microchannel plate. The hole in the center of the image is a defect in the surface; the edge of one of the channels is shown as a giant cliff.

Lead silicate glass surface

Inside the defect in the previous image

31 July 2013

For more pictures and data, be sure to visit our virtual poster!

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