Growth mechanism of the ultra-thin oxide films on metal substrates

Wilde, M.*; Fukutani, Katsuyuki*; Moritani, Kosuke; Yoshigoe, Akitaka ; Teraoka, Yuden

Our previous real-time synchrotron X-ray photoelectron spectroscopy (XPS) investigations of the growth kinetics of ultra-thin Al $_{2}$ O $_{3}$ films on NiAl(100) in O $_{2}$ have revealed a strong acceleration of the oxidation reaction by water. To clarify the oxidation mechanism, the present study examines whether the growth rate acceleration by H $_{2}$ O correlates with an increased oxide thickness, as would be expected within the Cabrera-Mott model at large surface hydroxyl (OH) coverages. We thus evaluate the saturation thickness of the Al $_{2}$ O $_{3}$ films from the take-off angle dependence of Al2p XPS emission signals from the oxide overlayer (Al $^{3+}$ ) and the metallic NiAl substrate (Al $^{0}$ ). The results confirm our expectation that at temperatures where OH is stable on Al $_{2}$ O $_{3}$ , H $_{2}$ O oxidation should yield slightly thicker Al $_{2}$ O $_{3}$ films than those grown in O $_{2}$ . This confirms our hypothesis that the rate acceleration by H $_{2}$ O below 500K is due to its ability to provide a higher stationary oxidant (OH) coverage than O $_{2}$ . Consistent with the thermal stability of surface OH groups, the H $_{2}$ O-related effects decrease at higher oxidation temperatures.

Language	:	English
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Meeting title	:	2nd International Workshop on Oxidation Reactions
Held date	:	2006/05
Location (city)	:	Suita
Location (country)	:	Japan
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Keywords	:	no keyword
Research Facility	:	SPring-8(大型放射光施設)
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Cooperating Institute	:	東京大学

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Registration No. : BB20060391
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