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The growth of water on thin SiO 2 films on Si wafers at vapor pressures between 1.5 and 4 torr and temperatures between -10 and 21 o C has been studied in situ using Kelvin Probe Microscopy and X-ray photoemission and absorption spectroscopies. From 0 to 75% relative humidity (RH) water adsorbs forming a uniform film 4-5 layers thick. The surface potential increases in that RH range by about 400 mV and remains constant upon further increase of the RH. Above 75% RH the water film grows rapidly, reaching 6-7 monolayers at around 90% RH and forming a macroscopic drop near 100%. The O K-edge near-edge X-ray absorption spectrum around 75% RH is similar to that of liquid water (imperfect H-bonding coordination) at temperatures above 0 °C and ice-like below 0 °C . 1 IntroductionAt ambient conditions all materials on earth are exposed to water vapor that produces films on their surfaces. The thickness and structure of this film is determined by the interaction forces between the surface and the adsorbed water molecules and has important implications for industrial, environmental and biological processes. One fundamental question is the range of the surface-induced modifications, if any, of the structure of water. In other words, how many layers are needed for water to reach its bulk structure? Not surprisingly the study of water at interfaces is a very active field, as demonstrated by the numerous review articles on this topic published in recent years. [1][2][3][4] Oxide surfaces are particularly important and have received considerable attention. 5 One of the most important oxides is amorphous SiO 2 because of its widespread presence in silicon technology and in natural minerals. [6][7][8] The surface of amorphous SiO 2 is usually modeled by a mixture of the (111) and (100) surfaces of hydroxylated β-cristobalite, which expose single and geminal hydroxyl groups, respectively. 9 On a fully hydroxylated (100) surface these groups are sufficiently close to each other that H-bonded networks can be formed. In the (111) surface the hydroxyl groups are more separated so that no H-bonds can form between them.The structure of water in contact with different SiO 2 surfaces has been studied both theoretically [10][11][12][13] and experimentally [14][15][16][17][18] . These studies have predicted an ordered hexagonal water layer on the hydroxylated surface of quartz (0001) 13 and a hexagonal ice-like structure on a fully hydroxylated β-cristobalite (100) surface. 10 However there is some controversy about the stability of such monolayer structures at room temperature. 12 No ice-like structure has been predicted for cristobalite (111) and the most favorable site for water molecules has been predicted to be a hollow site with the molecules forming 2 or 3 H-bonds with surface silanol groups. 11 Based on optical experiments an ice-like monolayer on amorphous SiO 2 has been proposed at room temperature and 10% relative humidity (RH). 14 Information on the structure of water films thicker than a monolayer is much scarcer. Sumfrequency ...

The chemical nature of copper and copper oxide (Cu 2 O) surfaces in the presence of CO 2 and H 2 O at room temperature was investigated using ambient pressure x-ray photoelectron spectroscopy. The studies reveal that in the presence of 0.1 torr CO 2 several species form on the initially clean Cu, including carbonate CO 3 2 , CO 2 δ-and C 0 , while no modifications occur on an oxidized surface. The addition of 0.1 ML Zn to the Cu results in the complete conversion of CO 2 δ-to carbonate. In a mixture of 0.1 torr H 2 O and 0.1 torr CO 2 , new species are formed, including hydroxyl, formate and methoxy, with H 2 O providing the hydrogen needed for the formation of hydrogenated species.