Preparation of ultra-thin oxide windows on titanium for TEM analysis

Using submerged jet electropolishing, extremely thin (less than 10 nm), continuous, thermal oxide "windows" have been prepared on polycrystalline titanium (Ti). The preparation technique is described in detail. It has allowed a systematic investigation of the structure of thermal surface oxide layers on Ti in the thickness range 6-40 nm, corresponding to oxidation temperatures 100-450 degrees C. Auger electron spectroscopy was used for oxide characterization and for depth profiling to determine oxide thickness. The thinnest oxides, less than 10 nm, are amorphous, morphologically homogeneous, and with essentially no contrast in the transmission electron microscopy (TEM) pictures. As the oxide thickness is increased up to 40 nm, a texture corresponding to the grain structure of the oxidized metal becomes gradually more visible. At the same time the oxide becomes increasingly more crystalline. The results are compared with previously published corresponding results for thicker anodic oxides on Ti.