A Tracer Diffusion Study of Diverse Photo‐Ionic Phenomena in Strontium Titanate

Advanced Functional Materials, vol. 36

Abstract

Abstract By generating photo‐ionic phenomena, super‐bandgap illumination has opened up a new and promising avenue for modulating the thermodynamic and kinetic properties of compound semiconductors. In this study, three photo‐ionic phenomena—modifying a surface reaction rate, altering an ionic space‐charge layer, and changing bulk nonstoichiometry—are examined directly for the model system SrTiO 3−δ . 18 O 2 / 16 O 2 exchanges with and without UV illumination, with subsequent ion‐beam analysis, are employed to obtain as a function of temperature the respective, characteristic quantities: oxygen surface exchange coefficients , surface space‐charge potentials Φ 0 , and bulk oxygen tracer diffusion coefficients . Two strong interfacial photo‐ionic effects are found: at T = 796 K, for example, UV illumination enhanced by a factor of 10 2.5 and lowered Φ 0 by 25%. No significant change in is observed, placing bounds on the UV‐induced change of bulk nonstoichiometry δ. The enhancement of and the depression of Φ 0 ( T ) are described with analytical models that include a temperature‐independent, UV‐generated increase in electron concentration. The enhancement of from UV illumination is found to be limited at lower temperatures by a parallel enhancement mechanism. This study thus resolves inconsistencies in reported photo‐ionic phenomena and furthermore provides a firm, quantitative foundation for future exploration.

Authors 4

1. David M. Schwenkel Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Physical Chemistry RWTH Aachen University Landoltweg 2 52056 Aachen Germany

   Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, 52056 Aachen, Germany

2. Timon F. Kielgas Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Physical Chemistry RWTH Aachen University Landoltweg 2 52056 Aachen Germany

   Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, 52056 Aachen, Germany

3. George Frederick Harrington

   University of Bath

   Affiliation as printed

   Department of Chemistry University of Bath Claverton Down Bath BA2 7AY United Kingdom

   Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY United Kingdom

4. Roger A. De Souza corresponding Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Physical Chemistry RWTH Aachen University Landoltweg 2 52056 Aachen Germany

   Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, 52056 Aachen, Germany