Infrared reflection absorption spectroscopy (IRAS) has been used to study CO adsorption on Au clusters ranging in size from 1.8 to 3.1 nm, supported on TiO(2). The adsorbed CO vibrational frequency blue-shifts slightly (approximately 4 cm(-)(1)) compared to that adsorbed on bulk Au, whereas the heats of adsorption (-DeltaH(ads)) increase sharply with decreasing cluster size, from 12.5 to 18.3 kcal/mol.

CO adsorption on a Pd(111) single-crystal surface was investigated using in situ polarization modulation infrared reflection absorption spectroscopy (PM-IRAS) within the pressure range 10 -6 -800 mbar. The coverage-dependent CO overlayer structures found on the Pd(111) surface are identical throughout this pressure regime, that is, no new surface species at elevated pressures or adsorbate-induced substrate reconstructions were observed. The transition from an adsorbate superstructure dominated by bridged-bound CO to an adsorbate overlayer having 3-fold/atop CO sites was followed by varying the adsorbate pressure over 9 orders of magnitude. The derived phase diagram indicates an apparent activation energy of 44.35 ( 1.63 kJ/mol for the bridged-to-3-fold-hollow/atop transition. A comparison between these data and recent sum frequency generation (SFG) results is made.

IRAS studies of CO adsorption on the Au(110)-(1 × 2) surface were performed as a function of CO pressure and sample temperature. It was found that with increasing coverage, the CO IRAS absorption shifts red from 2118 to 2108 cm -1 . Clausius-Clapeyron data analysis yielded a heat of CO adsorption (-∆H ads ) of 10.9 kcal/mol at low coverages and 7.8 kcal/mol at coverages greater than 19%.

Recent advances in nanotechnology have yielded materials and structures that offer great potential for improving the sensitivity, selectivity, stability, and speed of next-generation chemical gas sensors. To fabricate practical devices, the "bottom-up" approach of producing nanoscale sensing elements must be integrated with the "top-down" methodology currently dominating microtechnology. In this letter, the authors illustrate this approach by coupling a single-crystal SnO 2 nanowire sensing element with a microhotplate gas sensor platform. The sensing results obtained using this prototype sensor demonstrate encouraging performance aspects including reduced operating temperature, reduced power consumption, good stability, and enhanced sensitivity.