Adjunct Professor of Physics

B.A., M.S. Physics 1968 U. Penn

Ph.D. Physics 1974 Cornell – Condensed Matter, Prof. R.O. Pohl – Thermal properties of disordered solids

Postdoc 1974-1976 Div. Eng. Appl. Phys., Harvard, Prof. D. Turnbull – Crystallization and structural relaxation in amorphous selenium

1976-1986 Exxon Research & Engineering – staff scientist – engineering surface reflectance with topology, structure of oil through light scattering

1986 – 2013 General Atomics, sr. staff scientist to chief scientist, inertial fusion technology – magnetic properties of high temperature superconductors, inertial fusion target characterization, energy transport in high energy density solids

2013- present U. Penn, adjunct prof. structural equilibration in amorphous selenium

 

“I attended graduate school (Cornell) at a time when researchers were first starting to appreciate that there were unique properties associated with disorder. My dissertation investigated the low temperature thermal properties of glasses ([1] and Fig. 1), and in a post-doc (Harvard) looked into the dynamics of amorphous selenium annealed below its glass transition. Then job opportunities led me into other areas – the structure of crude oil and inertial fusion[2] amongst them – only recently joining the Fakhraai lab and returning to my initial interest in disorder.”

Research interests:
I wondered how far the phenomenon of ultra-stable thin films could be expanded from the molecular solids in which they have been found to date. Their stability arises from a combination of anomalously high surface mobility and slow deposition rate. Amorphous selenium seemed a likely candidate; the vapor-deposited segments have similar mass to the organic molecules, but do not display the necessary surface mobility. We are now looking at optically-induced shape transformations. Initial experiments with selenium were interesting [3], but the advent of Covid switched my activity to molecular dynamics investigations of the role mobility plays in stabilizing films.

[1] “Low energy excitations in disordered solids: A story of the ‘Universal’ phenomenon of structural tunneling,” R.B. Stephens, X. Liu, (World Scientific, 2021) ISBN-13: 978-9811217241.

[2] “Kα fluorescence measurement of relativistic electron transport in the context of fast ignition,” Phys Rev E 69, 066414 (2004), R.B. Stephens, R.A. Snavely, Y. Aglitskiy, F. Amiranoff, C. Andersen, D. Batani, S.D. Baton, T. Cowan, R.R. Freeman, T. Hall, S.P. Hatchett, J.M. Hill, M.H. Key, J.A. King, J.A. Koch, M. Koenig, A.J. MacKinnon, K.L. Lancaster, E. Martinolli, P. Norreys, E. Perelli-Cippo, M. Rabec Le Gloahec, C. Rousseaux, J.J. Santos, and F. Scianitti.

[3] “Polyamorphism of vapor-deposited amorphous selenium in response to light,” A. Zhang, Y. Jin, T. Liu, R.B. Stephens, Z. Fakhraai, Proc. Nat. Acad. Sci. 117, 24076 (2020).