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The oxidation kinetics of polycrystalline hafnium (Hf) at room temperature a d low oxygen pressure (Poz -lo-' Ton) has been studied by x-ray photoelectron spectroscopy (XPS). After a chemisorption stage for exposures < 5 L, Hf suboxides are initially formed and are dominant until -25 L. HfO, appears at -10 L. Above 25 L, HfO, grows by oxidation of the suboxides, whereas the oxide film thickness remains constant. Above 500 L, a saturation region is obse~ed that corresponds to an oxide layer of 12 hi thick with an average composition HfO,., .

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