%0 Journal Article
%A De Souza, R. A.
%A Gunkel, F.
%A Hoffmann-Eifert, S.
%A Dittmann, R.
%T Finite-size versus interface-proximity effects in thin-film epitaxial $SrTiO_3$
%J Physical review / B
%V 89
%N 24
%@ 1098-0121
%C College Park, Md.
%I APS
%M FZJ-2014-04651
%P 241401
%D 2014
%X The equilibrium electrical conductivity of epitaxial SrTiO3 (STO) thin films was investigated as a function of temperature, 950≤ T/K ≤1100, and oxygen partial pressure, 10−23≤ pO2/bar ≤1. Compared with single-crystal STO, nanoscale thin-film STO exhibited with decreasing film thickness an increasingly enhanced electronic conductivity under highly reducing conditions, with a corresponding decrease in the activation enthalpy of conduction. This implies substantial modification of STO's point-defect thermodynamics for nanoscale film thicknesses. We argue, however, against such a finite-size effect and for an interface-proximity effect. Indeed, assuming trapping of oxygen vacancies at the STO surface and concomitant depletion of oxygen vacancies—and accumulation of electrons—in an equilibrium surface space-charge layer, we are able to predict quantitatively the conductivity as a function of temperature, oxygen partial pressure, and film thickness. Particularly complex behavior is predicted for ultrathin films that are consumed entirely by space charge.
%F PUB:(DE-HGF)16
%9 Journal Article
%U <Go to ISI:>//WOS:000336917700001
%R 10.1103/PhysRevB.89.241401
%U https://juser.fz-juelich.de/record/155485