The parallel conductivities of films of the pure material, with thicknesses ranging from 35 to 300nm and grown epitaxially onto Al2O3(012) substrates, were studied by using the molecular beam epitaxy technique. The overall conductivities of the films were found to increase with decreasing thickness. A detailed investigation of the overall conductance, as a function of thickness, permitted deconvolution of the bulk and boundary effects. The latter was attributed to distinct space-charge effects in the interface between the film and the Al2O3 substrate. The extrinsic Debye length, λ, was estimated to be about 8nm at 593K; corresponding to an impurity content of 1018/cm3 (assuming a singly-ionized dopant). This was consistent with the fact that a constant boundary contribution was observed for all of the films with a thickness greater than 4λ. It was also consistent with the Debye length which had been observed previously report in CaF2/BaF2 heterolayers, fabricated by using the same technique, in which a low-temperature enhancement was also attributed to space charges in the BaF2. The conductance seemed to be affected, by strain effects, only below 370C.

Ionic Conductivity of Epitactic MBE-Grown BaF2 Films. X.X.Guo, J.Maier: Surface Science, 2004, 549[3], 211-6