Dr. Frazer Williams, Lott Distinguished Professor Emeritus
University of Nebraska-Lincoln
206N Walter Scott Engineering Center
Lincoln, Nebraska 68588-0511
Dr. Williams’ interests include electrical breakdown of gases and semiconductors, plasma processing of semiconductors, interactions of charged, small particles in room-temperature plasmas, and nanofabrication techniques using porous alumina matrices.
Atmospheric-pressure gasses generally break down via a streamer process. Streamers are needle-like, conductive regions in plasma. The enhanced electric field region at the tip(s) of streamers allows propagation of ionized regions in applied field well below that required for significant electron avalanche multiplication. Dr. Williams’ group has been active in studying these phenomena using high-speed photography, and in modeling them using numerical techniques. Semiconductors longer than about 1 mm appear to break down via a similar process. Dr. Williams’ group has studied this phenomenon in silicon using time-resolved shadowgraphic techniques.
Plasma processing is an important technique for manufacturing electronic devices. Complex interactions between the plasma and the neutral feedgas result in highly reactive species that readily etch materials such as silicon a GaAs. Dr. Williams’ group has studied the etching of GaAs with methane-based plasmas by applying high-resolution infrared absorption spectroscopy and conventional emission spectroscopy.
Small, charged particles can be levitated in a thin, horizontal layer in a plasma, and within this layer Coulomb repulsion between the particles can produce a regular, crystal-like, arrangement (sometimes called a Coulomb crystal) of these particles. These “crystals” may offer interesting opportunities for novel fabrication technology. Dr. Williams’ group has been studying these “Crystals” theoretically, trying to understand better the “crystallization”, with the goal of determining the issues influencing the “lattice” spacing.
Aluminum can be oxidized electrochemically to produce a layer of Al2O3 on the surface of an aluminum substrate. Under the proper conditions this layer forms with a dense array of pores with diameter in the 100nm range. It is possible to cause these pores to form in a regular array which can be used as a mask for evaporation or for etching of patterns onto semiconductor surface of a Ge substrate, and other purposes.
“Experimental Study of Streamers in Pure N2 and N2/O2 and a 13 cm Gap”, W. J. Yi and P. E. Williams, J. Phys. D: Appl. Phys. 35, 205-218 (2002).
“Self-assembled Networks with Neural Computing Attributes,” S. Bandyopadhyay, L. Menon, N. Kouklin, P. F. Williams, and N.J. Ianno, Smart Mater. And Struct. 11, 761-766 (2002). <
The Electrostatic Interaction of Charged, Dust-Particle Pairs in Plasmas”, M. E. Markes and P. F. Williams, Phys. Lett. A 278, 152-158 (2000).
“Plasma Processing of Semiconductors”, P. F. Williams, ed. (Kluwer, Dordrecht, 1997).
- F. E. Peterkin, Ph. D., 1994, now at Naval Surface Weapons Center, Dahlgren, VA. Thesis: “Breakdown Studies of High Voltage Silicon and Gallium Arsenide Photoconductive Switches.”
- B. J. Hankla, Ph. D., 1996, now at Naval Surface Weapons Center, Dahlgren, VA. Thesis: “Role of Filamentation in the Initiation of Surface Related Breakdown in Silicon.”
- W. J. Yi, Ph. D., 1997, now is senior manager with Samsung, Seoul, Korea. Thesis: “Study of Streamers in a Point-Plane Gap.”