Abstract
Sum frequency generation (SFG) spectroscopy was applied to investigate D(2)O adsorption on atomic layer deposition (ALD)-grown Al(2)O(3), ZrO(2), and TiO(2) films at 94 ± 1 K. Film composition and thickness were characterized by ellipsometry and X-ray photoelectron spectroscopy (XPS). Additional SFG measurements were conducted on the SiO(2)/Si wafer and on a CoO film prepared by oxidizing Co foil. At D(2)O exposure below 3000 L, the spectra were dominated by interfacial features originating from the ice-oxide interface. These spectra exhibited a weak, broad O-D stretching band (OD(3)) centered at 2650 cm(-1), tentatively attributed to (dissociated) water molecules to water molecules hydrogen-bonded to the oxide surface; this assignment was supported by the absence of the OD(3) feature on the SiO(2)/Si substrate. A sharp peak at 2730 cm(-1) was also observed and assigned to the "free" O-D stretch (non-hydrogen-bonded with any neighboring molecule) of surface D(2)O molecules pointing into the vapor phase. Upon increasing D(2)O exposure, both the OD(3) and "free" OD bands decreased in intensity and were replaced by weakly hydrogen-bonded OD(2) and strongly hydrogen-bonded OD(1) modes associated with the ice-vapor interface. As the exposure increased further, the OD(2) and OD(1) bands shifted to lower wavenumbers (2310 to 2284 cm(-1)) and became stronger, with the OD(1) mode exhibiting a larger red shift and more pronounced intensity enhancement. No significant differences in water structure were observed on the Al(2)O(3), ZrO(2), and CoO films at the ice-vapor interfaces, apart from an approximately fivefold reduction in intensity on CoO, which is attributed to signal scattering from the rough CoO film/Co foil surface. However, when D(2)O exposure reached ≥30 000 L, the OD(1) band on the TiO(2) surfaces decreased substantially in intensity and shifted to much lower wavenumbers (2065 cm(-1) at 30 000 L; 2030 cm(-1) at 102 000 L) than on Al(2)O(3) (2283 cm(-1) at 90 000 L), ZrO(2) (2293 cm(-1) at 30 000 L), and CoO (2284 cm(-1) at 900 000 L), indicating specific hydrogen-bonding interactions on the TiO(2) surface.