Surface Space-Charge Potential and Oxygen Surface Exchange Coefficient of SrTiO3: The Effect of Surface Orientation

O-18(2)/O-16(2) exchange experiments on terminated (100), (110), and (111) oriented samples of single-crystal SrTiO3 are used to study the effect of surface orientation on the oxygen surface exchange coefficient kO*\[k_{\rm{O}}<^>*\] and the surface space-charge potential phi(0). Isotope exchanges are carried out at temperatures 922 < T/K < 1073 at an oxygen activity aO(2) = 0.2 in dry conditions (aH(2)O < 10(-7.7)); isotope profiles are measured subsequently by secondary ion mass spectrometry. Isothermal kO*$k_{\rm{O}}<^>*$ values are found to vary by less than one order of magnitude, with kO*(111)approximate to kO*(110)>kO*(100)$k_{\rm{O}}<^>*(111) \approx k_{\rm{O}}<^>*(110){\bm{ > }}k_{\rm{O}}<^>*(100)$. All kO*$k_{\rm{O}}<^>*$ data are consistent with a change in the activation enthalpy of surface exchange from 3.0 eV at high temperatures to 1.8 eV at lower temperatures. The transition is attributed to a change from a charge-transfer mechanism at high temperatures to a mechanism involving surface OH species. The transition temperature depends on the surface orientation, T-tr(111) approximate to T-tr(110) > T-tr(100). Values of phi(0) obtained varied between 0.50 V and 0.37 V, with isothermal values obeying phi(0)(111) approximate to phi(0)(110) < phi(0)(100). phi(0) data is analysed to obtain the OH- surface coverage for the low-temperature regime. Similarities between the behavior of phi(0) and that of kO*$k_{\rm{O}}<^>*$ are highlighted.

Automated summary

The effect of surface orientation on oxygen surface exchange coefficient and surface space-charge potential in single-crystal SrTiO3 is studied. The results show that surface orientation has a significant influence on these properties.