Event
MSE Seminar: Dr. Ray Phaneuf, UMD
Wednesday, November 6, 2024
3:30 p.m.
Room 2108 Chemical and Nuclear Engineering Building
Sherri Tatum
301-405-5240
statum12@umd.edu
A Patterning Based Approach Toward Hierarchically Structured Materials
Abstract: The next frontier beyond nanotechnology is arguably assembly at the meso-scale: that range of sizes from 10’s to 100’s of nm, with expectations of emergent properties at this scale. It has been argued that a hybrid approach combining top-down, and bottom-up aspects will be needed to accomplish assembly of nanostructures into meso-scale assemblies on a practical time scale. In this talk I present an example of just such an approach – using an artificially fabricated template along with molecular beam epitaxial growth in the presence of a kinetic barrier to direct the assembly on nm-scale growth mounds into mesoscale arrays. We show via both kinetic Monte Carlo (kMC) simulations and molecular beam epitaxial (MBE) growth experiments that patterning in the presence of an “Ehrlich_Schwoebel” diffusion barrier at step edges can be used to direct assembly of a series of “higher-order commensurate” mound-on-template structures. We find that in the initial stage of growth, the pattern directs the spontaneous formation of multilayer islands at 2-fold bridge sites between neighboring nanopits along crystal orientation. However, as growth continues, the height of mounds at 2-fold bridge “self-limits”: the mounds cease to grow. Beyond this point an initially less favored 4-fold bridge site for mounds dominates and a different pattern of self-assembled mounds begins. We find that the transient pattern amplification during growth proposed by Tadayyon-Eslami et al. is correlated with self-limiting behavior of mounds. We also propose that a minimum, ‘critical terrace size’ at the top of each mound is responsible for the observed self-limiting growth (SLG) behavior.
Bio: Ray Phaneuf is a Professor and Past Interim Chair in the Materials Science and Engineering Department at the University of Maryland. He joined the University of Maryland in 1985, where he used electron diffraction to study phase transformations on stepped Si(111) surfaces, resulting in the identification of a thermodynamically driven faceting associated with the formation of the (7x7) reconstruction. In 1989 he visited Ernst Bauer’s group in Clausthal, Germany, using low energy electron microscopy (LEEM) to image this faceting in real time. In 2000 he joined the Materials Science and Engineering Department, and began studies of directed self-organization during growth and sublimation on semiconductor surfaces, using lithographic patterning. In 2006 he was a visiting professor at the National Nanotechnology Laboratory, in Lecce, Italy. He is the author of more than 100 papers and has given over 40 invited talks on his work in the US, Europe and Japan. He was named the Laboratory for Physical Sciences Faculty Researcher of the year in 2002. In addition to MSE, he has affiliate positions in Physics and ECE, and was a founding member of the UM-MRSEC at the University of Maryland. He was the founding Coordinator of the Interdisciplinary Minor Program in Nanoscience and Technology. In 2019 he was named a Fellow of the American Physical Society for: “development of novel industrial applications of thin film techniques including coatings for the protection of cultural heritage objects against corrosion and directed-assembly of nanostructures on semiconductor surfaces”. In 2021 he was named a visiting scholar at the University of Venice Ca’ Foscari, studying electrokinetic desalination techniques for accelerated desalination of cultural heritage objects made from limestone and exposed to seawater.
His current research is in directing self-assembly of nanostructures at the mesoscale, probing the kinetics of film growth via ALD, and application of nanotechnology to the conservation of cultural heritage objects.
