B. Walsh

A simple, reliable technique for making electrical contact to multiwalled carbon nanotubes

A simple method of making reliable electrical contact to multiwalled carbon nanotubes is described. With these contacts, current in the mA range can be routinely passed through individual multiwalled nanotubes without adverse consequences, thus allowing their resistance to be measured using a common multimeter. The contacts are robust enough to withstand temperature excursions between room temperature and 77 K. I(V) data from different multiwalled nanotubes are presented and analyzed.

Correlating the location of structural defects with the electrical failure of multiwalled carbon nanotubes

Electrical failure of carbon nanotubes was investigated by obtaining I(V) data with a voltage ramp from a rope of multiwalled carbon nanotubes. Noncontact scanning force microscope images were obtained before and after each I(V) curve until electrical failure of the tube resulted. Following this procedure, it was possible to correlate a defect on the surface of a nanotube with the exact location of the tube failure.

Guided self-assembly of Au nanocluster arrays electronically coupled to semiconductor device layers

We report the controlled deposition of close-packed monolayer arrays of ∼5-nm-diam Au clusters within patterned regions on GaAs device layers, thus demonstrating guided self-assembly on a substrate which can provide interesting semiconductor device characteristics. Uniform nanometer scale ordering of the clusters is achieved by a chemical self-assembly process, while micron scale patterning is provided by a soft lithographic technique. Scanning tunneling microscope imaging and current–voltage spectroscopy indicate the Au nanoclusters are strongly coupled electronically into the underlying semiconductor substrate while exhibiting only weak electronic coupling in the lateral plane.

Adhesion Maps Using Scanning Force Microscopy Techniques

A technique has been developed that allows a real-time measurement of the lift-off force required to remove a scanning force microscope tip from a substrate. Both topography and adhesion maps are obtained simultaneously, allowing the correlation between topography and adhesion properties to be studied. Quantitative values of important adhesion parameters can be extracted from these data. A number of examples are given which illustrate the utility of this technique.

Nanoelectronic device applications of a chemically stable GaAs structure

We report on nanoelectronic device applications of a nonalloyed contact structure which utilizes a surface layer of low-temperature grown GaAs as a chemically stable surface. In contrast to typical ex situ ohmic contacts formed on n-type semiconductors such as GaAs, this approach can provide uniform contact interfaces which are essentially planar injectors, making them suitable as contacts to shallow devices with overall dimensions below 50 nm. Characterization of the native layers and surfaces coated with self-assembled monolayers of organic molecules provides a picture of the chemical and electronic stability of the layer structures. We have recently developed controlled nanostructures which incorporate metallic nanoclusters, a conjugated organic interface layer, and the chemically stable semiconductor surface layers. These studies indicate that stable nanocontacts (4 nm×4 nm) can be realized with specific contact resistances less than 1×10−6 Ω cm2 and maximum current densities (1×106 A/cm2) comparable ...

Self-assembly based approaches for metal/molecule/semiconductor nanoelectronic circuits

This paper describes a technological approach which combines the nanoscale elements available from molecular devices and self-assembled molecular/nanoparticle systems with semiconductor devices which can provide the gain or bistability required for computational functionality. The architectural motivation for these configurations and experimental demonstrations of several key technologies for this hybrid approach are described.