Lithium depth profiling in thin electrochromic WO3 films

Abstract

Li profiles in sol-gel prepared electrochromic WO3 thin films have been characterized using three different techniques: neutron depth profiling (NDP), secondary ion mass spectrometry (SIMS), and elastic recoil detection (ERD). The results have been evaluated with respect to their concentration sensitivity and depth resolution. NDP and SIMS led to comparable results in terms of the shape of the profiles. The NDP results were quantified by using a calibration sample. NDP has the advantage that it is a quantitative nondestructive technique while SIMS has a very high sensitivity and depth resolution. Another advantage of NDP is that there is very little risk of neutron-induced Li migration during the measurement because of the very low energy of the incoming thermal neutrons. ERD was found to have a limited depth resolution, attributable to deterioration of the sample as a result of ion bombardment. However, the absolute amount of Li can be very accurately quantified with this technique.