A concept for molecular electronics exploiting carbon nanotubes as both molecular device elements and molecular wires for reading and writing information was developed. Each device element is based on a suspended, crossed nanotube geometry that leads to bistable, electrostatically switchable ON/OFF states. The device elements are naturally addressable in large arrays by the carbon nanotube molecular wires making up the devices. These reversible, bistable device elements could be used to construct nonvolatile random access memory and logic function tables at an integration level approaching 10 12 elements per square centimeter and an element operation frequency in excess of 100 gigahertz. The viability of this concept is demonstrated by detailed calculations and by the experimental realization of a reversible, bistable nanotube-based bit.

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Nearly monodisperse iron nanoclusters have been used to define the diameters of carbon nanotubes grown by chemical vapor deposition (CVD). Iron nanoparticles with average diameters of 3, 9, and 13 nm were used to grow carbon nanotubes with average diameters of 3, 7, and 12 nm, respectively. Transmission electron microscopy studies of the nanotubes show that the as-grown nanotubes are single-walled carbon nanotubes (SWNTs) or thin multiwalled carbon nanotubes (MWNTs) with 2 or 3 layers. Investigations of the growth conditions also demonstrate that the supply of carbon reactant is critical for enabling the growth of large diameter nanotubes from large iron nanoclusters, and that the growth temperature is especially important for achieving high-quality large diameter nanotubes. The implications of these results and possible applications of the nanotubes are discussed.

Metallic single-walled carbon nanotubes have been proposed to be good one-dimensional conductors. However, the finite curvature of the graphene sheet that forms the nanotubes and the broken symmetry due to the local environment may modify their electronic properties. We used low-temperature atomically resolved scanning tunneling microscopy to investigate zigzag and armchair nanotubes, both thought to be metallic. "Metallic" zigzag nanotubes were found to have energy gaps with magnitudes that depend inversely on the square of the tube radius, whereas isolated armchair tubes do not have energy gaps. Additionally, armchair nanotubes packed in bundles have pseudogaps, which exhibit an inverse dependence on tube radius. These observed energy gaps suggest that most "metallic" single-walled nanotubes are not true metals, and they have implications for our understanding of the electronic properties and potential applications of carbon nanotubes.

The structural and mechanical properties of single-walled carbon nanotubes (SWNTs) make them ideal tips for scanning probe microscopies such as atomic force microscopy (AFM). However, the ideal nanotube probe, which corresponds to an individual SWNT, has been difficult to produce in high yield. To overcome this difficulty, a straightforward and easily implemented method that enables very high-yield fabrication of individual SWNT probes has been developed. This new method is based upon the observation that microfabricated tips can "pick up" vertically aligned SWNTs grown from planar substrate surfaces. Substrates with isolated, vertically aligned SWNT are first prepared by chemical vapor deposition and then imaged with commercial microfabricated silicon AFM tips. The silicon tips pick up individual SWNTs from the substrate during imaging to create well-aligned SWNT probes. The SWNT tips have been etched using a procedure that allows variation of the nanotube length with 2 nm control. Studies of gold nanocluster standards demonstrate that these individual SWNT tips are capable of high resolution and robust imaging in air and fluids, and thus these tips are expected to open up new opportunities in nanoscale science and technology.

Traditional nanostructured design of cerium oxide catalysts typically focuses on their shape, size, and elemental composition. We report a different approach to enhance the catalytic activity of cerium oxide nanostructures through engineering high density of oxygen vacancy defects in these catalysts without dopants. The defect engineering was accomplished by a low pressure thermal activation process that exploits the nanosize effect of decreased oxygen storage capacity in nanostructured cerium oxides.

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A low cost nanosphere lithography method for patterning and generation of semiconductor nanostructures provides a potential alternative to the conventional top-down fabrication techniques. Forests of silicon pillars of sub-500 nm diameter and with an aspect ratio up to 10 were fabricated using a combination of the nanosphere lithography and deep reactive ion etching techniques. The nanosphere etch mask coated silicon substrates were etched using oxygen plasma and a time-multiplexed ‘Bosch’ process to produce nanopillars of different length, diameter and separation. Scanning electron microscopy data indicate that the silicon etch rates with the nanoscale etch masks decrease linearly with increasing aspect ratio of the resulting etch structures.