June 23, 2003
FRONTIERS IN MATERIALS SCIENCE
VINSE COLLOQUIUM SERIES
Dr. Max Lagally
Department of Materials Science and Engineering
University of Wisconsin-Madison
"Nanoscience and Technology on Silicon: Directed Assembly, Strain Engineering, and Materials Integration"
Abstract. Future generations of micro- and optoelectronic devices will require approaches beyond the conventional in terms of materials fabrication and integration at the nanoscale. From the point of view of technology, great advantage can be gained if it could "all be done on silicon". That is also fortunate from a scientific viewpoint, as Si is the model semiconductor for fundamental studies of surfaces, growth, and electrical properties. In this talk I describe several efforts that use Si to create nanoscale structures and investigate nanoscale properties: as a template for self-organized growth, an integration platform, a mechanical element, and, finally, a semiconductor. 1) Strain driven self-assembly of faceted nanocrystals during semiconductor heteroepitaxy can form quantum dots (QDs) that may be attractive for a range of electronic or optoelectronic devices. I describe a simple process of directed assembly of Ge QDs on Si that also allows us to develop an understanding of the mechanism of directed assembly. 2) Using silicon-on-insulator (SOI) as a template, we discovered that the GE QDs that grow on the thin Si template can act as a nanostressor that distorts the Si layer and causes the oxide underneath to flow. 3) Growth of films on SOI rather than Si also brings with it unique defect generation mechanisms. I will describe dislocation formation using low-energy electron microscopy (LEEM) as the primary tool. 4) Using MEMS techniques, we build a device that can artificially stress a Si membrane and grow on these membranes to investigate the effect of added uniaxial stress on the diffusion, nucleation, and coarsening of nanostructures and films. 5) Using a unique method to place catalyst in specific small spots on a Si surface, we can then grow carbon nanotubes across contacts. Photoconductivity measurements suggest that these nanotubes are phototransistors, also opening the possibility of nanoscale chemical sensing with electronic readout. It really can all be done (well, almost) on Si!
- Supported by NSF, DARPA, ONR