AVS 53rd International Symposium
    Applied Surface Science Friday Sessions
       Session AS-FrM

Paper AS-FrM12
Studies of Vanadium Pentoxide Thin Films as a Function of Number of Lithium Ion Intercalation Cycles

Friday, November 17, 2006, 11:40 am, Room 2005

Session: Thin Film Characterization
Presenter: J.E. Castle, University of Surrey, UK
Authors: J.E. Castle, University of Surrey, UK
A.M. Salvi, Universita' della Studi della Basilicata, Italy
N Ibris, Universita' della Studi della Basilicata, Italy
D. Alamarguy, Laboratoire de Genie Electrique de Paris, France
Correspondent: Click to Email
The intercalation of vanadium pentoxide by lithium ions leads to a change in optical properties, a process that is of value in thin-film electrochromic devices. The extent of intercalation can be measured, electrochemically, from the charge capacity of the film, and is in good agreement with that determined spectroscopically by X-ray photoelectron spectroscopy (XPS). On de-intercalation there is again good agreement. However XPS might not be able to detect low level of Li retained in trapping sites within the film. Since such retention could be a source of chemical degradation we have examined the concentration of lithium ions, either within the lattice or at boundaries and interfaces within the structure, by depth profiling using secondary ion mass spectrometry (SIMS). SIMS is a valuable tool for the analytical determination of Li, for which it has excellent sensitivity. In this study films of V2O5 deposited on ITO-glass coupons by a sol/gel process were challenged by increasing numbers of charge-discharge cycles, ranging from 72 to 598 full cycles. The samples were characterised by XPS and then examined in the de-intercalated state by ToFSIMS. The lithium depth profiles for four samples are compared. These profiles are broadly similar, with a marked build up of Li at the interface with the indium tin oxide (ITO). Although lithium is retained, the integrated quantity is very small and below detection by XPS. However the profiles are of interest because of the marked accumulation of Li at the interface with ITO.