The present thesis addresses the growth kinetics, chemical constitution, morphology and atomic transport mechanisms of zirconium-oxide films, as grown by the dry, thermal oxidation of single-crystalline Zr surfaces at low oxidation temperatures. To this end, bare (i.e. without a native oxide) well-defined single-crystalline Zr(001) and Zr(100) surfaces were exposed to oxygen gas in the temperature range of T = 300-450 K. The current study, for the first time, presents a direct comparison of the

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... initial oxidation of single-crystalline Zr surfaces with basal and prism orientations. The relationships between the oxidation kinetics, the developing microstructure and the crystallographic orientation of the parent metal substrate have been established by application of various (surface-)analytical techniques. On the basis of the thus-obtained results, a Zr oxidation mechanism in the low-temperature regime (< 500 K) has been proposed. As evidenced by ellipsometry, after a short initial stage of fast oxide-film growth, a near-limiting thickness of the oxide film is attained at T < 375 K on both surfaces. Distinct differences in the oxidation kinetics for the two Zr substrate orientations become apparent at T > 375 K: the Zr(100) plane oxidizes more readily than the more densely-packed Zr(001) plane under the same experimental conditions. At T > 375 K, the oxidation rate of Zr becomes governed by thermally-activated dissolution and diffusion of oxygen into the Zr substrate. The changes in the local chemical states of Zr and O in the thin zirconium-oxide films have been investigated with increasing oxidation temperature. To this end, the oxide-film valence-bands (VB) and the Auger-parameters of Zr and O in the grown oxide films were resolved from measured XPS spectra of the oxidized Zr surfaces in the oxidation-temperature range of T = 300-450 K. The changes in the shape of the oxide-film VB spectra and the local chemical states of Zr and O in the oxide films evidence that the oxide films grown at T ≤ 400 K are [...]