Strachan Group

Our work on the surface potential of few-layer graphene films is featured as the recent cover article of the January 2009 issue of Nano Letters.

Using electrostatic force microscopy we probe the charge screening features of few-layer graphene films.

The work was performed in collaboration with S. S. Datta, E. J. Mele , and A. T. Johnson.


Crystallographic etching of few-layer graphene which we recently reported in Nano Letters was highlighted by Nature Nanotechnology.

By utilizing metallic nanoparticles, we are able to etch few-layer graphene samples along specific crystallographic directions.

This work was performed in collaboration with S. S. Datta, S. M. Khamis , and A. T. Johnson.



Research

Our group does experimental condensed matter research. We are currently focused on a variety of investigations in nanoscale materials. Materials constrained to the nanoscale can show a diverse array of novel and surprising behavior as their sizes are reduced towards atomic dimensions. Research in nanoscale materials is highly interdisciplinary; taking concepts and techniques from a variety of disciplines, such as solid state and semiconductor physics, soft matter materials, electrochemistry, materials science, and electrical engineering. Our research utilizes a wide variety of measurement and fabrication techniques including low-temperature measurements, novel electronics, surface and polymer chemistry, high resolution electron microscopy, scanning probe microscopy, photo and electron-beam lithography, and chemical vapor deposition.



Nano and molecular scale electronics

Molecular-scale structures have the potential to be the smallest devices possible. To realize this exciting possibility requires novel approaches to their design and fabrication. One such structure that we are actively exploring is the single molecule transistor, whereby extremely small (atomic-scale) electrodes are designed that can make contact to single molecule-scale objects. Making the molecular-scale contacts is impossible to achieve through current nanolithography techniques. So we are currently investigating new ways to achieve these contacts.

Below are some images of a novel electromigration technique we have recently developed which forms the electrodes as the electrical current pushes the metallic ions of the nano-structure. The technique utilizes a novel "self balancing" technique of electromigration where a large number of electrodes pairs can be fabricated simultaneously. The top image is the array of electrodes, the lower left image is the electrical processing, and lower right images are the resulting nano-electrodes. The work appeared in Nano Letters and was performed in collaboration with D. E. Johnston and A. T. Johnson.


Nanoscale materials and quantum confinement

Constraining materials on the nanometer scale can lead to a host of quantum size-effects. Our group focuses on the fabrication and study of a number of materials confined to one dimension (nanowires) and zero dimensions (quantum dots). One material of particular interest is graphene, a sheet of carbon atoms arranged into a hexagonal honeycomb structure.

We have recently developed a technique for constructing nanoribbons of graphene with certain crystallographic orientations. The image at right is made by an atomic force microscope and shows a few-layer graphene sample etched along crystallographic directions with Fe nanoparticles. The work appeared in Nano Letters and was performed in collaboration with S. S. Datta, S. M. Khamis, and A. T. Johnson.


High resolution electron microscopy of nano-electronics

Utilizing custom hybrid transmission electron microscopy holders, we investigate the evolution of nanoscale systems and devices through simultaneous electronic measurement and high resolution imaging.

The high resolution imaging provides important atomic-scale characteristics of systems that evolve at the nanoscale. Play the video on the left which shows a narrow metallic constriction evolving due to electromigration. The conductance of the junction is simultaneously monitored in real-time via electrical measurements, and is shown below the video. The simultaneous measurements suggest that the nanowire evolves due to a layer-by-layer removal of atoms on its surface.

The work appeared in Physical Review Letters and was performed in collaboration with D. E. Johnston, B. S. Guiton, S. S. Datta, P. K. Davies, D. A. Bonnell, and A. T. Johnson.


Electrostatic interactions at the nanoscale

Materials can have a variety of novel electrostatic properties at their surfaces and interfaces when constrained on the nanometer scale. To probe the local properties of these systems we utilize scanning probe techniques which are sensitive enough to detect subtle interactions while also providing the necessary spatial resolution.

The image at right shows the electrostatic profile of few-layer graphene which is correlated to the number of layers. The measurements are made by using both atomic force and electrostatic force microscopies. The work appeared in Nano Letters and was performed in collaboration with S. S. Datta, E. J. Mele, and A. T. Johnson.