On the accurate measurement of oxygen self-diffusivities and surface exchange coefficients in oxides via SIMS depth profiling

Abstract Oxygen diffusivity in oxides is usually determined via gas/solid exchange experiments in an atmosphere enriched as to the concentration of the rare stable isotope 18 O. The kinetics of the 16 O and 18 O isotope exchange at the surface is usually described by the surface exchange coefficient, K . The analytical solution of the diffusion problem suggests the definition of a characteristic time constant, τ ≡ D / K 2 . This time constant determines the duration that is necessary to reach equilibrium between the 18 O gas concentration and the 18 O concentration at the surface of the solid. The simultaneous determination of D and K by secondary ion mass spectrometry (SIMS) depth profiling works well in a large parameter range of D and K . However, at low temperatures, the simultaneous determination of D and K may be subject to severe errors. To overcome this problem, the possibility to determine D and K separately will be discussed.