Thickness-dependent dc conductivity of lithium borate glasses

Berkemeier F, Abouzari MRS, Schmitz G

Zusammenfassung

Amorphous lithium borate films are prepared by ion-beam sputtering using a 0.2 Li2O center dot 0.8 B2O3 glass as a target material. The films of a thickness between 7 and 700 nm are deposited onto silicon substrates between two metallic AlLi electrodes serving as electrical contacts. dc conductivities of the glass layers of different thicknesses are determined by temperature-dependent impedance measurements. An increase of the specific dc conductivity of about 3 orders of magnitude is observed, when the thickness of the layers decreases from 120 down to 7 nm. This conductivity increase in the case of very thin films leads to an absolute conductance per unit area of 0.32 Omega(-1) cm(-2) at 25 degrees C, which is sufficient for technical application of the glass layers in solid-state ionic devices. Three alternative explanations are suggested to explain this nontrivial conductivity increase: structural modifications at the interfaces, the formation of space-charge regions, and the existence of randomly distributed ion-conducting channels.