AVS 60th International Symposium and Exhibition
    Surface Science Friday Sessions
       Session SS-FrM

Paper SS-FrM10
Dependence on Experimental Ambient of Surface Photovoltage Transients in Nanostructured Oxide Surfaces and Interfaces

Friday, November 1, 2013, 11:20 am, Room 201 A

Session: Oxides and Semiconductors: Structure and Reactivity
Presenter: Y.M. Strzhemechny, Texas Christian University
Authors: Y.M. Strzhemechny, Texas Christian University
P.R. Chapagain, Texas Christian University
A. Nemashkalo, Texas Christian University
S. Pant, Texas Christian University
E.S. Davis, Texas Christian University
Correspondent: Click to Email
Kelvin probe-based surface photovoltage (SPV) measurements were employed to monitor super-bandgap transients in nanostructured oxide specimens placed in different environments – high vacuum, He gas, N2 gas, etc. In general, contactless SPV transient experiments in semiconductors and insulators can provide information about surface/subsurface state densities and their cross sections, and these experiments sometimes reveal intricate illumination-mediated charge recombination mechanisms, especially in materials with a complex microstructure. The SPV time-domain response of the surface/subsurface states could also be significantly affected by the experimental environment, which was addressed in this work. Light-dark transient SPV were studied in several oxide systems with nanostructured morphologies at room temperature using a white light source: a nanoporous silicon permeated with Ni and Co nanoparticles, ZnO thin films on Si, as well as sol-gel samples on Si substrates containing titania/zirconia/silica mixed with noble metal nanoparticles. Some of the latter samples were also irradiated with a flux of Ti+ ions. In most of these systems we observed nontrivial dynamics of charge redistribution in response to illumination changes and a strong dependence on the ambient. E.g., in the nanoporous Si samples, sharp ‘light on’/‘light off’ voltage spikes were detected in the He and N2 gas environments, indicating several distinct charge exchange mechanisms occurring on dissimilar time scales. However, experiments on these specimens in high vacuum revealed a very different, albeit nontrivial response. On the other hand, for the multicomponent sol-gel thin films, a significant distinction was observed between the as-received and ion-irradiated samples. While for the as-received films the saturation curves in the N2 and vacuum environments were similar, the irradiated samples yielded a much slower charge dynamics in vacuum compared to that in the N2 atmosphere. We discuss possible mechanisms responsible for the observed SPV dynamics, related to the complex microstructure and its interaction with the environment.