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Enhanced Ionic Conduction at the Film/Substrate Interface in LiI Thin Films Grown on Sapphire(0001)

Published online by Cambridge University Press:  21 February 2011

D. Lubben  and
F. A. Modine
D. Lubben
Affiliation:
Solid State Division, Oak Ridge National Laboratory, P.O.Box 2008, Oak Ridge, TN 37831-6030.
F. A. Modine
Affiliation:
Solid State Division, Oak Ridge National Laboratory, P.O.Box 2008, Oak Ridge, TN 37831-6030.
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Abstract

The ionic conductivity of LiI thin films grown on sapphire(0001) substrates has been studied in situ during deposition as a function of film thickness and deposition conditions. LiI films were produced at room temperature by sublimation in an ultra-high-vacuum system. The conductivity of the Lil parallel to the film/substrate interface was determined from frequency-dependent impedance measurements as a function of film thickness using Au interdigital electrodes deposited on the sapphire surface. The measurements show a conduction of ∼5 times the bulk value at the interface which gradually decreases as the film thickness is increased beyond 100 nm. This interfacial enhancement is not stable but anneals out with a characteristic log of time dependence. Fully annealed films have an activation energy for conduction (σT) of ∼0.47 ± .03 eV, consistent with bulk measurements. The observed annealing behavior can be fit with a model based on dislocation motion which implies that the increase in conduction near the interface is not due to the formation of a space-charge layer as previously reported but to defects generated during the growth process. This explanation is consistent with the behavior exhibited by CaF2 films grown under similar conditions.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 318: Symposium Ca – Interface Control of Electrical, Chemical, and Mechanical Properties , 1993 , 445
Copyright
Copyright © Materials Research Society 1994

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