Using (18)O/(16)O exchange to probe an equilibrium space-charge layer at the surface of a crystalline oxide: method and application.
The use of an (18)O/(16)O exchange experiment as a means for probing surface space-charge layers in oxides is examined theoretically and experimentally. On the basis of a theoretical treatment, isotope penetration profiles are calculated for (18)O/(16)O exchange across a gas-solid interface and subsequent diffusion of the labelled isotope through an equilibrium space-charge layer depleted of mobile oxygen vacancies and into a homogeneous bulk phase. Profiles calculated for a range of conditions all have a characteristic shape: a sharp drop in isotope fraction close to the surface followed by a normal bulk diffusion profile. Experimental (18)O profiles in an exchanged (001) oriented single crystal of Fe-doped SrTiO(3) were measured by time-of-flight secondary ion mass spectrometry (ToF-SIMS). By extracting the space-charge potential from such profiles, we demonstrate that this method allows the spatially resolved characterization of space-charge layers at the surfaces of crystalline oxides under thermodynamically well-defined conditions.
De Souza
Roger A
RA
Institut für Physikalische Chemie, RWTH Aachen, Aachen, Germany. desouza@pc.rwth-aachen.de
Martin
Manfred
M
D003460:Crystallization; D015335:Molecular Probes / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D010103:Oxygen Isotopes; D018629:Spectrometry, Mass, Secondary Ion / Q000379:methods; D013499:Surface Properties; D013816:Thermodynamics
D015335:Molecular Probes; D010087:Oxides; D010103:Oxygen Isotopes; D010100:Oxygen