Technical. This project addresses research toward greater understanding and implementing ar-rangement of materials at shrinking dimensions, and the ability to successfully integrate new ma-terials with better properties or materials that would provide new functionalities. The project aims for advanced processing methods that can organize materials at nano-scale dimensions with precise placement having the necessary quality and reliability, for example, to realize concepts for new types of device structures involving single electron tunneling effects (transistors, mem-ory, quantum cellular automata), quantum computing architectures, and integration of III-V ma-terials with group IV substrates for high-speed channels or optical devices. Self-assembly meth-ods alone can arrange structures at these length scales, but cannot place structures at specific lo-cations. The approach is to combine self assembly with a top-down patterning method to direct growth. The project seeks to create topographic templates made up of uniform and size-selecting features through a 'strain-engineering' mechanism. These templates will then be used to nucleate high quality, crystalline nanostructures at specified locations on substrates by self-assembly methods that would occur on the templates. This is expected to provide a route to creating new structures with an arbitrary lateral arrangement and the potential for combining lattice mis-matched materials with silicon that would not be achievable through thin film growth with high quality. Strained SixGe1-x layers will be grown on silicon substrates that have been locally modi-fied at specific sites using a focused ion beam, resulting in pyramidal pit formation at each site with a characteristic size, dependent on strain. The pit edges will be used to provide four closely spaced nucleation sites. Studies will be done on how the template formation is influenced by various patterning parameters and by kinetics during heteroepitaxial growth using ultra high vac-uum sputtering. Studies will also be done to determine how these templates can be used to influ-ence the growth of dissimilar materials under different kinetic conditions. The growth of lattice-mismatched semiconductors (Ge on Si) as well as other materials such as silicides will be ex-plored. Characterization studies will be done to understand the effects on resulting morphology, crystal/interface structure, composition, and uniformity?items which will influence electrical properties and the potential usefulness for device applications. These studies will also include the effect of very small surface discontinuities, defects, or impurities on nucleation processes in technologically important material systems. Non-Technical. The project addresses fundamental research issues in a topical area of elec-tronic/photonic materials science having technological relevance. In addition to graduate student participation, undergraduates will also be directly involved and gain hands-on experience using advanced research tools. Increasing undergraduate research participation at early stages in their education will be a primary focus, with particular encouragement given to women and minori-ties. This undergraduate research will be leveraged to help promote these activities to local high schools, by demonstrating examples of practical hands-on research they will have the opportu-nity to participate in as engineering students. Connections will be made to industry by providing additional examples to students. Many aspects of this research will also be incorporated into new nanotechnology and electromagnetic properties courses and used as supplemental research pro-jects associated with other courses to integrate research and education more effectively.
The results from this project have contributed to the field of materials science and nanoengineering in general by providing greater insight into the areas of focused ion beam nanoscale processing of materials, crystallization due to ion implantation, and the behavior of thin film catalysts for carbon nanotube growth on bulk metallic substrates. The experiments have been based on the themes of controlled formation of nanostructures at specific locations and the integration of nanostructures with dissimilar substrates. Specifically, we have first implanted gallium ions into specific locations on a substrate surface using a focused ion beam, and then created surface nanoislands of gallium by annealing the substrates after implantation. We have also converted these surface islands into compounds through a plasma nitridation process, resulting in the formation of the rock-salt structure of GaN. Secondly, we have deposited SiGe thin films on our focused ion beam patterned substrates under kinetically limited conditions using magnetron sputtering in order to force strain relieving islands to form at these patterned sites. These islands will form at the sites due to differences in the surface topography. Finally, we have also investigated the use of a single thin film catalyst, also deposited by sputtering, onto bulk copper foils in order to directly grow dense vertical forests of carbon nanotubes on these substrates using thermal chemical vapor deposition. These are of interest for electrode structures for charge storage devices and have been tested for capacitive behavior. This project has provided research opportunities for two graduate students and four undergraduate students. The NSF support has made it possible for the students to be trained on a variety of nanofabrication and materials characterization tools. Three senior design projects were completed as a part of this project. One grad student has finished his dissertation and is now employed by Hitachi. The students were also given multiple opportunities to attend conferences to present their work. Ten journal publications have resulted so far from this work and two conference proceedings papers. Three more papers are currently in progress.
