The Colors of Silicon

Abstract

Abstract When silicon samples are thinned and backlit, they display a series of colors; from deep red in the thicker (-5-10 μm) regions, to orange and yellow in thinner regions, to effectively transparent in the thinnest regions, This colorful effect can be used as a technique for monitoring the thickness of cross-sectional samples prepared for transmission electron microscopy (TEM). As seen in Figure 1, a cross-sectional TEM sample of a thin, indium tin oxide (ITO) film on glass was being investigated, A sample was prepared for low-angle ion milling by the Barna method with the addition of an adjacent piece of silicon for a thickness indicator. The colors of silicon could then be monitored to indicate when the ITO/glass sample was thin enough for TEM examination. In the figure, the arrow indicates the region of interest on the ITO/glass sample. This figure was produced by photographing the entire TEM sample through an optical microscope, backlit with a standard quartzhalogen illuminator.