An enhanced conductivity was observed in thin films which were evaporated onto a sapphire substrate. The interface conductivity parallel to the surface was measured for film thicknesses of up to 300nm. It was found that the specific conductivity, in the first 30nm next to the sapphire, exceeded the bulk conductivity by almost one order of magnitude. It was concluded that the specific conductivity decreased exponentially with increasing distance from the sapphire surface, and reached the bulk value at a distance of 300nm. The conductivity of a 35nm film at temperatures of between 25 and 120C indicated that the activation energy was equal to 0.40eV. This value was in good agreement with the activation energy of bulk LiI in the extrinsic region.

E.Schreck, K.Läuger, K.Dransfeld: Zeitschrift für Physik B, 1986, 62[3], 331-4