David Hutchison and Dr. Robert Davis, Department of Physics and Astronomy
We had planned on using the process outlined in the proposal for construction of a supercapacitor and solar cell, but decided to focus our energies on the solar cell idea since we thought we could make faster, more significant progress in that direction. We were able to determine the effect of catalyst layer thickness, 2 nm being the most ideal: thinner layers would give us growth that was too quick and thicker layers would give large, bendy nanotubes which would bridge across gaps where they shouldn’t be. We tried several diffusion barrier layers under the iron and found 25 nm of alumina to be the only one that gave us uniform, dense vertically-aligned growth. We succeeded in repeatably producing clean, high aspect ratio structures at the limit of our photolithographic resolution (1-2 um). We coated them successfully to various thicknesses with undoped silicon by low pressure chemical vapor deposition, and are currently collaborating with NREL in Colorado in order to have them deposit amorphous doped silicon layers by hotwire chemical vapor deposition, so that we can begin to test optical properties. Once optical transmission, reflection, and absorbance is measured, and if it looks promising, we can begin to make devices and test electrical characteristics.
This is a work in progress but the ORCA grant has provided invaluable opportunity for me to work on this. In the process I have become proficient in many important cleanroom and microscopy techniques, which will be a great advantage as I embark on a graduate degree next year.