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MSE Seminar - Dr. Steve Davis, Northwestern University
Monday, April 4, 2016 - 3:30pm
Dr. Steve Davis, Walter P. Murphy Professor of Engineering Sciences and Applied Mathematics
McCormick School of Engineering
Northwestern University (NAE/NAS)
Nanowire Growth and Stability
Nanowires have multitudes of applications in electronic industries. A favorite method of growth is by the VLS method in which a liquid droplet of catalyst is placed on a solid substrate, the atmosphere is saturated with a gas, and growth of a wire occurs perpendicular to the substrate, with as much as an aspect ratio of 10,000. In this lecture we shall describe the stepwise growth of the wire and show that multiple steps may grow. Further, we shall describe the onset of asymmetrical growth by examining the asymmetric instability of the droplet. This may be the precursor to helically-growing wires.
Stephen H. Davis is the Walter P. Murphy Professor of Engineering Sciences and Applied Mathematics and (by courtesy) Mechanical Engineering at Northwestern University. He received his Ph.D. Mathematics, MS Mathematics and his B.E.E. Electrical Engineering from Rensselaer Polytechnic Institute in Troy, NY. Professor Davis has received recognition from the National Academy of Engineering, National Academy of Sciences, American Academy of Arts and Sciences. He received the ISI Highly Cited Researcher Award, the G.I. Taylor Medal, Society of Engineering Science, 2001 and the Fluid Dynamics Prize, American Physical Society 1994.
Professor Davis works in the area of interfacial dynamics and stability. The interfaces can be in small-scale hydrodynamics in which two immiscible fluids are separated by an interface having surface tension, e.g. thin films, spreading Dof liquid on solid, and thermocapillary effects. The interfaces can be in systems with phase transformations in which, say, a liquid and its frozen counterpart are separated by a front having surface energy.
The main questions to be answered involve the nonlinear dynamic states of the system, their stability, nonlinear evolution, and pattern selection. Interfacial waves in fluids propagate, steepen, and evolve into three-dimensional complex wave systems, perhaps chaotic. Interfaces in solidification become cellular or dendritic and can lead to oscillatory states. Thin, continuous solid films of semi-conductors formed by vapor deposition can break up into islands as a result of crystal-mismatch stresses.
The means of analyzing such systems involves modelling, asymptotic and numerical methods. The answers have both practical and intrinsic interest.