September 22, 2003
FRONTIERS IN MATERIALS SCIENCE
VINSE COLLOQUIUM SERIES
Dr. Deyu Li
Department of Mechanical Engineering
University of California, Berkeley
"Phonon and Molecular Transport in Individual Nanowires and Nanotubes"
Abstract. One-dimensional (1D) materials such as various kinds of nanowires and nanotubes are attracting increasing attention due to their fundamental scientific significance and extensive potential applications. Transport phenomena in nanowires and nanotubes could be significantly different from that in bulk materials because of boundary effects and size confinement. In contrast to the extensive studies on electron transport, investigation of phonon and molecular transport in 1D nanostructures have been initiated only very recently. However, the phonon and molecular transport in nanowires and nanotubes are very important to the design of nanoelectronic devices, nanowire-based thermoelectric devices, and nanotube-based bioanalysis and bioseparation devices. In this talk, I will describe a technique using a batch-fabricated suspended microheater device to measure thermophysical properties of individual 1D nanostructures. With this technique, thermal conductivities of individual single crystalline Si nanowires with diameters of 22, 37, 56, and 115 nm were measured and a theoretical analysis was carried out. Results show that boundary scattering could reduce the Si nanowire thermal conductivity more than two orders of magnitude from the bulk value. In addition, the experimental data for a 22 nm diameter Si wire suggest phonon dispersion relation change due to confinement. Thermal conductivities observed for Si/SiGe superlattice nanowires suggest that different mechanisms may control the transport of different frequency phonons, which provides us some insight for engineering the phonon transport and manipulating the materials� thermal conductivity. The double layer structure in the solution near a solid surface presents some possibilities to make novel nanofluidic devices. A nanofluidic device based on individual silica nanotubes has been designed and fabricated for ion and biomelocular transport studies. Ion transport studies in different concentration KCl solutions through the nanotube have been carried out. Possibilities of using a gate to control the ion flow in the nanotube and possible applications of this device to biomolecular sensing and separation will be discussed.