Detection of protective oxide layers on Cr formed by exposure to air by STEM-ELS method

Relatively thick (1000 Å) and very thin (30 Å) Cr specimens have been observed with scanning transmission electron microscopy (STEM) and energy-loss spectroscopy (ELS). They show marked differences in both diffraction (selected area electron diffraction and microdiffraction) and composition (ELS) data. The extra 2.5 Å ring in SAED and oxygen K edge loss peak in ELS are attributed to the protective oxide layer formed at the surface of Cr by exposure to air at 25°C. The average thickness of the layer is estimated to be about 10 Å.