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Ultra-thin films of Cr2O3(0 0 0 1) grown on Cr(1 1 0) were investigated by reflection absorption infrared spectroscopy (RAIRS). An absorption band at 720 cm−1 is assigned to a longitudinal optical phonon of Cr2O3. With increasing O2 exposure, this absorption band shifts to higher frequency, which is qualitatively explained by a simple spring model. After successive oxidation with 18O2 and 16O2, two absorption bands corresponding to Cr 2 18 O 3 and Cr 2 16 O 3 were distinctly observed suggesting that oxygen diffusion hardly occurs during the oxide growth. Temperature dependence of the RAIRS spectrum taken from the Cr2O3 film revealed that the absorption band position shifts to lower frequency along with broadening of the band width. Anharmonic coupling with low-frequency phonons and effects of the antiferromagnetic to paramagnetic phase transition are discussed.

We report experimental results on the interaction of hydrogen with monolayer thin Ag and Au films grown on a Pt(1 1 1) substrate, measured with thermal desorption spectroscopy (TDS) and nuclear reaction analysis (NRA). We found that H2 dissociative adsorption is activated on both thin film surfaces. Atomic hydrogen was found to adsorb on the Ag and Au films on Pt(1 1 1) with main desorption temperatures of 160 and 120 K, respectively. The monolayer thin Ag and Au films on Pt(1 1 1) are chemically similar to the (1 1 1) surfaces of bulk Ag and Au, respectively.

The adsorption structure of NO on the Pt(1 1 1) surface at low temperature (90–130 K) was studied by dynamical analysis of low-energy electron diffraction and reflection absorption infrared spectroscopy. Three different 2×2 patterns were identified and their experimental intensity vs. voltage curves ( I – V curves) were compared with dynamically calculated I – V curves for the models including the tilted (bent) NO geometry. The differences of I – V curves can be recognized by virtue of the wider incident electron energy range than the previous dynamical analysis. The most promising interpretation is that NO occupies three sites sequentially depending on the NO coverage. In this interpretation, NO first adsorbs at the threefold fcc hollow site, next at the atop site and last at the threefold hcp hollow site. The NO saturation coverage is 0.75 ML ( 1 ML =1.5×10 −15 molecules/cm 2 ). The NO species at the atop site is tilted and those at both hollow sites are upright. Our new model agrees well with the recent density functional theory calculation and explains the experimental results better than the previous model, in which NO transits from the bridge site to the atop site with increasing coverage.

The adsorption and photoreaction of NO on Ag films deposited on Pt(1 1 1) were investigated at 90 K by reflection-absorption infrared spectroscopy (RAIRS). Similar to Ag(1 1 1), NO molecules were found to be converted into (NO) 2 and N 2 O on the Ag films. At an Ag thickness of 1 ML, however, a new adsorption state that reveals a RAIRS band at 1848 cm −1 is present on the surface. The (NO) 2 dimer species was found to react into N 2 O, while the reaction of the new species was substantially suppressed. Upon photon irradiation with a wavelength of 193 nm, the three adsorption species on Ag(1 ML)/Pt(1 1 1) were depleted from the surface. The origin of the newly found species and the photoreaction mechanism are discussed.

The adsorption and initial absorption of hydrogen (H2) by Pd(1 0 0) at T=100–160 K are investigated by thermal desorption spectroscopy (TDS) and nuclear reaction analysis, which enables a depth-resolved determination of the hydrogen concentration at and below the Pd surface. Under 3×10−8 mbar H2 and T 130 K H-migration from such a near-surface hydride phase to the deeper bulk of the metal occurs and a solution of H in Pd is formed by means of facile diffusion. This bulk dissolved hydrogen emerges as a broad structure in TDS at T=200–260 K exhibiting a tailing at high temperatures characteristic of diffusion-controlled desorption kinetics.