Materials Science Research Lecture
***Refreshments at 3:45pm in Noyes lobby
Abstract:
Amorphous (glassy) materials lack structural order, making them difficult to describe or to calculate their properties compared to crystalline materials which consist of spatially repeated atoms. This difficulty, however, does not preclude their applicability or scientific impact. Various properties, including topological electronic states, seem to rely on the periodicity of the lattice for their derivation, yet are found in amorphous materials; recent advances have enabled explanation. Intriguingly, there exists the notion of an "ideal glass", which while remaining thoroughly disordered, lacks imperfections in that disorder and thus approaches the uniqueness of a crystal, including low entropy. LIGO (laser interferometric gravitational observatory) relies on amorphous coatings for their mirrors; mechanical losses in these coatings are the limiting noise factor and are associated with universal yet poorly understand atomic motions associated with defects in the amorphous structure. Amorphous silicon (a-Si) is the single material where these losses can be tuned over several decades, from below detectable limits to high in the range commonly seen in glassy systems, in a way seemingly connected with creating a near-ideal glass. IR optical absorption is similarly reduced when hydrogen is added, below that of crystalline Si. Dielectric losses are also reduced, but not by orders of magnitude. I will discuss the underlying phenomena of these results, which lie in a hidden order.
More about the Speaker:
Dr. Frances Hellman is a professor at the University of California Berkeley in the Departments of Physics and of Materials Science and Engineering, as well as a faculty staff scientist in the Materials Sciences Division of Lawrence Berkeley National Lab. She served previously as Physics Department Chair, and more recently as Dean of the Division of Mathematical and Physical Sciences in the College of Letters and Sciences, while continuing to be actively engaged in research and teaching, and just completed a term as President of the American Physical Society (APS). She has nearly 200 publications and 4 patents, and has supervised the research of many undergraduate and graduate students.
Dr. Hellman is a world-leading expert in thin film growth and nanocalorimetry measurements, particularly of vapor deposited thin amorphous films, both magnetic and non-magnetic. She and her research group developed micro/nanocalorimeters that won the APS Keithley Award in 2006 "in recognition of using emerging micromachining techniques to significantly extend the range of calorimetry into the realm of nanoscale science by construction of Si based microcalorimeters capable of operating in extreme environments with unprecedented sensitivity and accuracy." She is a recognized leader in magnetic materials, particularly in advancing the understanding of the importance of interfaces and spin orbit coupling for amorphous materials, and in deepening our understanding of their magnetic and thermodynamic properties, and was invited to be a member of LIGO, the gravitational wave observatory, in recognition of her contributions to understanding low loss optical coating materials.
Dr. Hellman is an elected member of the American Academy of Arts and Sciences (2013) and an elected fellow of the APS (1997). She is strongly engaged in scientific public outreach, including being a visiting scientist at the San Francisco Exploratorium, and she is deeply committed to educational activities that help increase diversity in science.
She holds a doctorate in applied physics from Stanford University (1985) and a bachelor's degree in physics from Dartmouth College (1978). She was a post-doc at AT&T Bell Labs, followed by appointment and many years as professor at UC San Diego, and came to UC Berkeley in 2004. She is married to Warren Breslau, a UCSB alum, plays in a band with her siblings and loves live theater, scuba diving and hiking trips around the world.