Vacuum thermal oxidation methods, which are based on the concept of selective oxidations of chromium at low oxygen partial pressures, have been used for practical fabrication of protective oxide films on stainless steels. This passive oxide films was characterized to investigate the chemical composition by surface-sensitive photoelectron spectroscopy (PES). PES revealed that the 10 Angstrom thickness of Cr2O3 layer was formed in 450 degreesC and oxygen partial pressure of 1 x 10(-9) Torr, and a top layer was mixed with metallic chromium and oxygen exited Cr2O3 at the initial stage of oxidation. Photoemission electron microscope (PEEM) and the synchrotron radiation, which were tuned at the core level energy of iron and chromium components, were used to obtain the real time image acquisition of the initial forming phenomena with annealing process. (C) 2003 Elsevier Science B.V. All rights reserved.