Gold nanoclusters deposited on silica via water as a buffer layer: Carbon monoxide-infrared reflection absorption spectroscopy and temperature programmed desorption characterization

The adsorption properties of carbon monoxide (CO) on gold nanoclusters grown through a buffer-layer-assisted-growth (BLAG) mechanism has been studied with infrared reflection absorption spectroscopy (IRAS) and temperature programmed desorption (TPD). The growth methodology consists of evaporation of gold atoms on top of an amorphous-solid-water covered SiO₂ substrate at 100K in ultra high vacuum. A subsequent anneal to 300K desorbs the water molecules, resulting in nanoclusters having a higher aspect ratio than nanoclusters deposited in the absence of the water buffer layer. IRAS shows the CO stretch frequency with and without the buffer layer is essentially identical (2106 ± 2 cm^-1). Moreover, the CO stretch frequency was independent of the BLAG cluster size (2 - 10 nm). TPD measurements indicate the interaction of CO with BLAG clusters is weaker than with directly deposited clusters as evidenced by a lower desorption temperature (170 - 190 K for BLAG vs. 230-240 K without). The high temperature tail of the TPD profiles above 200K is assigned to under-coordinated Au atoms that lie at the perimeter of the cluster and interact directly with the SiO₂ substrate.