The development of high-efficiency, low-price photovoltaic devices relies on epitaxially grown layers of ternary chalcopyrites. The question addressed in this study is to which extent the near stoichimetric composition of CuInS2 grown on hydrogen terminated Silicon, Si (111), varies cross the sample area. The method usually employed [1] for such analysis is Argon-Rutherford Backscattering (RBS), whose spatial resolution, however, is limited to the order of millimeters. This limit can readily be overcome by electron microscopic and electron spectroscopic means.

For observation and recording of the energy loss spectra in the transmission electron microscope, samples were carefully prepared by mechanic polishing and ion-milling. The thinning began with polishing the Si substrate on ALLED diamond lapping films, down to 10 μm and a final ion-milling in a Gatan ion-thinning equipment from the Si-side (Ar+ 3 kV, the incident angle less than 7°).Spectra were taken by means of a Gatan image filter (GIF - 100) in a Philips CM200 FEG electron microscope operated at 200 kV.