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To investigate the influence of small amounts of impurities on the initial oxidation of copper, copper oxidation was carried out at 400 and 800°C in 0.1 MPa oxygen atmosphere by using 99.5% ͑2 N͒ and 99.9999% ͑6 N͒ pure specimens. Oxidation of 6 N copper at 400°C for 60 s showed that the number density of Cu 2 O oxide islands beneath the thin CuO layer varied with the face of copper crystals, and the nucleation of Cu 2 O occurred preferentially at grain boundaries. At an elevated temperature of 800°C, nucleation of Cu 2 O oxide islands beneath the thin CuO layer occurs faster and uniformly over the surface. In contrast to 6 N copper, initial oxidation of 2 N copper is much hindered at 400°C, but this tendency is interestingly weakened at 800°C. The possible roles of impurity elements in the initial oxidation were discussed. The nonmetallic elements of Se and Te segregated in the vicinity of the surface of 2 N copper during the previous annealing process were concluded to play different roles in initial oxidation at 400 and 800°C by considering their thermodynamic behaviors.

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