David D. Allred received Alumni Professorship Award

A class of carbon-nanotube (CNT) composite materials was developed to take advantage of the precise high-aspect-ratio shape of patterned vertically grown nanotube forests. These patterned forests were rendered mechanically robust by chemical vapor infiltration and released by etching an underlying sacrificial layer. We fabricated a diverse variety of functional MEMS devices, including cantilevers, bistable mechanisms, and thermomechanical actuators, using this technique. A wide range of chemical-vapor-depositable materials could be used as fillers; here, we specifically explored infiltration by silicon and silicon nitride. The CNT framework technique may enable high-aspect-ratio MEMS fabrication from a variety of materials with desired properties such as high-temperature stability or robustness. The elastic modulus of the silicon-nanotube and silicon nitride-nanotube composites is dominated by the filler material, but they remain electrically conductive, even when the filler (over 99% of the composite's mass) is insulating. [2009-0197]

A series of 20 and 100 nm Fe(53)Pt(47) thin films sputter-deposited onto Si substrates have been thermally annealed using a pulsed thermal plasma arc lamp. A series of one, three or five pulses were applied to the thin films with widths of either 50 or 100 ms. The microstructure and magnetic properties of these annealed Fe(53)Pt(47) films are discussed according to the various annealing conditions and A1 to L1(0) phase transformation. Upon pulse annealing, the average in-plane grain size of 15 nm (nearly equivalent for both film thicknesses) was observed to increase to values near 20 nm. In general, increasing the pulse width or number of pulses increased the L1(0) order parameter, tetragonality of the c/a ratio and coercivity of the specimen. The exception to this trend was for five pulses at 100 ms for both film thicknesses, which indicated a reduction of the order parameter and coercivity. This reduction is believed to be a result of the interdiffusion of Fe and Pt into the Si substrate and the formation of iron oxide clusters in the grain boundaries characterized by atom probe tomography. (C) 2009 Published by Elsevier B.V.

We recently developed a fabrication process for carbon nanotube templated MEMS. The fabrication process involves growing a three dimensional pattern from carbon nanotube forests and filling that forest by chemical vapor infiltration to make a solid structure. This templating process allows us to fabricate extremely high aspect ratio microscale structures from a wide variety of materials. The nanotube structures can be hundreds of microns tall with lateral pattern dimensions down to a few microns. The chemical vapor infiltration has been shown with silicon and silicon nitride but could be extended to many other materials. In this paper, we investigate the microstructure of the filling material and extend the process to the fabrication of comb actuators.

Vanadium dioxide (VO2) single crystals undergo a structural first-order metal to insulator phase transition at approximately 68°C. This phase transition exhibits a resistivity change of up to 5 orders of magnitude in bulk specimens. We observe a 2-3 order of magnitude change in thin films of VO2. Individual particles with sizes ranging from 50 to 250 nm were studied by means of Transmission Electron Microscopy (TEM). The structural transition for individual particles was observed as a function of temperature. Furthermore, the interface between grains was also studied. We present our current progress in understanding this phase transition for polycrystalline thin films of VO2 from the view of individual particles.