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HL: Fachverband Halbleiterphysik

HL 26: Interfaces and Surfaces

HL 26.4: Talk

Monday, March 14, 2011, 16:45–17:00, POT 06

Lithium Diffusion at Silicon Surfaces — •David Krix, Hatice Karacuban, and Hermann Nienhaus — Faculty of Physics, Center for Nanointegration Duisburg-Essen, University of Duisburg-Essen, 47048 Duisburg, Germany

Lithium-ion batteries are in common use in a large number of modern electrical appliances. In the quest for ever higher storage capacities new electrode materials are needed which will eventually replace the commonly used graphite anodes. Silicon is a promising candidate due to its enormous storage capacity for lithium but suffers from a large density difference between the lithium containing and lithium free phase. Nano-structured materials (particles, wires etc.) promise to remedy this problem. Transport processes at the surface of silicon anode surfaces are therefore of keen interest.

We have studied the diffusion of lithium into silicon under UHV conditions and at low temperatures (150-180 K) using Auger and X-ray photoelectron spectroscopy. Thin layers of lithium were deposited on pristine H-passivated Si(001) and oxygen modified surfaces at a temperature (120 K) that effectively suppresses the diffusion, although a thin layer of silicide forms at the interface right away. At sufficiently high temperatures diffusion of lithium into the bulk sets in, which can be monitored through the attenuation of the silicon signal underneath the metallic lithium film. The formation of surface silicide is a thermally activated process with an activation energy of 0.49 eV.