Dr. Channing Ahn received his PhD from the University of Bristol in 1985. He serves as a lecturer for Beginning and Advanced Electron Microscopy. His research is described below.
One of the great impediments in the determination of physical properties of nanophase solids, especially metals, prepared by inert gas condensation has been the relative difficulty in consolidating large quantities of these particles to high density in the absence of cumbersome mechanical handling. These procedures generally introduce impurities at grain boundaries and thus result in ambiguity in pinpointing the specific role of grain boundary energy in the unique properties of solids formed from nanoparticles. We overcame this problem by developing a system and process which we call ballistic consolidation. The apparatus consists of a particle synthesis chamber which is separated from the deposition chambers by a nozzle. Nanoparticles are produced in the first chamber by standard inert gas condensation techniques using material evaporated by Joule heating methods. This consolidation process mimics standard physical vapor deposition processes like evaporation and sputtering and yields thin films with microstructures similar to those described by Movchan and Demchishan. The greatest advantage this process offers is its ability to preserve the nanophase microstructure of particles formed in the flow. Because of the high momentum of particles being deposited, this process may also be a good candidate as an alternative to other deposition schemes used in metallization onto high aspect ratio semiconductor substrates.
We continue to develop and apply surface analysis by reflection electron energy loss spectroscopy during growth by molecular beam epitaxy. This work has shown sub-monolayer sensitivity of contaminants in the form of hydrocarbons, as well as of constituents of interest for lattice matched systems. Recently, we completed work on Sn on Si based systems and are initiating efforts on GaAs based structures in collaboration with the Jet Propulsion Lab. Soon we will complete the development of a parallel detection system so that extended fine structure analysis can be used in conjunction with RHEED in pinpointing ordering of atomic constituents at surfaces.
Atwater, H. A.; Wong, S. S.; Ahn, C. C.; Nikzad, S.; Frase, H. N. Analysis of Monolayer Films During Molecular-beam Epitaxy by Reflection Electron-Energy-Loss Spectroscopy. Surface Science. 1993;
Bowman, R. C.; Luo, C. H.; Ahn, C. C.; Witham, C. K.; Fultz, B. The Effect of Tin on the Degradation of LaNi5-YSny Metal-hydrides During Thermal Cycling. Journal Of Alloys And Compounds. 1995;
Nikzad, S.; Wong, S. S.; Ahn, C. C.; Smith, A. L.; Atwater, H. A. In-situ Reflection Electron-Energy-Loss Spectroscopy Measurements of Low-temperature Surface Cleaning for Si Molecular-beam Epitaxy. Applied Physics Letters. 1993;
Pearson, D. H.; Ahn, C. C.; Fultz, B. Measurements Of 3d Occupancy From Cu L(2,3) Electron-energy-loss Spectra Of Rapidly Quenched CuZr, CuTi, CuPd, CuPt, And CuAu. Physical Review B-Condensed Matter. 1994;
Pearson, D. H.; Ahn, C. C.; Fultz, B. White Lines and D-Electron Occupancies for the 3d And 4d Transition-metals. Physical Review B Condensed Matter. 1993;
Wong, S. S.; He, G.; Nikzad, S.; Ahn, C. C.; Atwater, H. A. Local Order Measurement in SnGe Alloys and Monolayer Sn Films on Si with Reflection Electron-Energy-Loss Spectrometry. Journal Of Vacuum Science & Technology A Vacuum Surfaces And Films. 1995;