Scanning Microscopy


Surface oxidation of polished natural specimens of chalcopyrite (CuFeS2) at temperature between 23°C and 300°C in air has been characterized by Auger electron and X-ray photoelectron spectroscopies. The reaction products consisted of an outer iron oxide layer and an intermediate copper rich sulfide layer. Several different oxides and sulfides were consistent with the electron spectroscopy data, so specimens were analyzed as a function of time and temperature at selected 20 μm diameter areas with an optical microreflectometer (OMR). Since the optical properties of a compound are unique, a reflectance model with three homogeneous layers was used to calculate reflectance curves by varying the compound in and thickness of each layer. The reaction products were modelled as Cu5FeS4 in contact with the CuFeS2 and Cu2S as an intermediate layer between Cu5FeS4 and the outer oxide. The outer oxide was most consistent with Fe3O4. Relative layer thicknesses were calculated from a series of balanced chemical equations, and Cu5FeS4 was much thicker than Cu2S with total thickness increasing with increasing temperature. The total film layer thicknesses calculated at 23°C were between 10nm and 35nm. At 200°C the film thickness varied from 8nm to 51nm with greater thicknesses associated with longer reaction times. Thicknesses at 300°C ranged from 12nm to 85nm.

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