Hydroxylation of Ultrathin Al2O3/NiAl(110) Films at Environmental Humidity

• Published in: Journal of physical chemistry. C 2014-12, Vol.118 (50), p.29340-29349
• Main Authors: Shavorskiy, A, Müller, K, Newberg, J. T, Starr, D. E, Bluhm, H
• Format: Article
• Language: English
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp505587t

We have investigated the reaction of ultrathin Al2O3/NiAl(110) films with water vapor from ultrahigh vacuum to relative humidities (RH) up to 10%, over the temperature range from −5 to 65 °C, using ambient pressure X-ray photoelectron spectroscopy (APXPS) and scanning tunneling microscopy (STM). The APXPS experiments show a sharp onset of oxide/hydroxide film growth at ∼0.01% RH, coupled with an increase of the oxygen-to-aluminum ratio, most likely because of the adsorption of OH and H2O species at the oxide surface and their reaction with Al from the NiAl substrate, which leads to a thickening of the oxide film at RH > 0.01%. The STM measurements support the results from APXPS and reveal a change in surface morphology when the Al2O3/NiAl(110) sample was exposed to relative humidities greater than 0.01%.