Colloquium Series: Dr. Mark Spitler, UNC, Visiting Scholar

Dr. Mark Spitler

Visiting Scholar to UNC Chapel Hill

Department of Chemistry

TITLE: A General Physical Model Describing Band Bending in Semiconductor Electrodes for Solar Fuels Production

 Abstract:

Semiconductor electrodes have been investigated extensively as substrates for solar fuels production in the form of gaseous hydrogen or liquid fuels from reduction of CO₂. These fuels result from reactions requiring electron transfer from the conduction band of semiconductor electrodes biased under accumulation or inversion conditions. This work describes a general physical model from the solid state physics literature for band bending under bias that encompasses degeneracy situations in the electrode under accumulation and inversion, with a scope that is greater than the present model in use that assumes all donors are fully ionized. In an illustration of the general model, experimental capacitance measurements with p-Si, n-Si, and n-InP have been made with a TBAPF₆ electrolyte in acetonitrile. Results in the accumulation region show the dependence of band bending in the semiconductor upon the electrolyte concentration in solution, potential charge quantization at the surface, and the shifting of the band edge energies with respect to a reference electrode. Examination of the inversion region reveals a deep depletion behavior where techniques other than impedance measurements are required to measure surface charge carrier concentrations.

Bio:

Mark Spitler has been a Visiting Scholar in the Chemistry Department at UNC since 2019. He retired to UNC from the U. S. Department of Energy (DOE) where he had been a Program Manager for solar research in the Office of Basic Energy Sciences for a decade. The time at the DOE was supplemented by three years on detail to the DOE from the National Renewable Energy Laboratory in Golden, Colorado. For this work he was named a AAAS Fellow.

He received his B.S. in Chemistry from Stanford University in 1972 and completed his PhD in Physical Chemistry in 1977 at the University of California at Berkeley under the direction of Melvin Calvin. This was followed by postdoctoral work with Heinz Gerischer at the Fritz Haber Institute in West Berlin from 1977 to 1978.

His career began in the Chemistry Department at Mount Holyoke College capped by a sabbatical year with Arthur Nozik at SERI (now NREL.) Following this was a decade in the manufacture of solar cells and in R&D with the Polaroid Corporation, and then a decade in entrepreneurial business in the Boston area. From there he was called to the DOE to manage solar research.

His research interests cover solar photoconversion with particular focus on semiconductor photoelectrochemistry and dye sensitization of semiconductors. These interests include closely related topics in photographic and imaging science.