Analysis of lithium transport in electrochromic multilayer films by neutron depth profiling

Thin film 'rocking-chair' type cells hold great promise for 'smart window' and rechargeable battery applications. Smart windows alter the transmissivi ty between any two states over the solar spectrum by electrical current mod ulation, which causes lithium ions to migrate back and forth between the tw o electrochromic layers, This paper reports measurement of the lithium dist ribution in each layer and transport between layers by the method of neutro n depth profiling (NDP). Samples are irradiated by a beam of 'cold' neutron s that induce the Li-6(n,alpha)H-3 reaction. Both the intensity and energy of the reaction products-the alpha-particles and tritons-are measured by su rface barrier detectors. Comparing the emission intensity with that of a kn own standard leads to quantitative determination of the lithium concentrati ons. The energy loss of the emitted charged particles due to interactions w ith the matrix provides a direct measurement of the depth of the originatin g lithium nucleus. The non-destructive nature of the NDP technique allows i n situ measurements of the lithium concentration under different voltage bi as conditions, The data acquisition method and data analysis techniques are explained. Results of the concentration measurements as a function of bias are presented. possible applications into other lithium multilayers are al so discussed. Copyright (C) 2000 John Wiley & Sons, Ltd.