IN-SITU GRAZING-INCIDENCE X-RAY-DIFFRACTION AND ELECTRON-MICROSCOPIC STUDIES OF SMALL GOLD CLUSTERS

Small gold clusters having diameters of 1-3 nm have been studied by us ing x-ray-diffraction and electron microscopy. Large amounts of small gold clusters generated by the inert-gas vapor-condensation method wer e deposited on a silicon wafer cooled down to 92 K to avoid coalescenc e growth and grazing-incidence x-ray-diffraction intensity from the co ld cluster deposit was measured in situ. The diffraction pattern was a nalyzed and compared quantitatively with calculated patterns from seve ral structural models considering the observed size distribution and f ound to be explainable approximately by a decahedral structure with ge ometrically closed shells. Electron-microscopic observations for gold clusters deposited sparsely on an amorphous carbon film at room temper ature were also performed and decahedral multiply-twinned clusters 2-3 nm in diameter were frequently observed. This result agrees well with the x-ray statistical result, suggesting that the most dominant struc ture of small gold clusters prepared under our experimental conditions is the decahedral structure. The present experiments have demonstrate d that an extremely weak x-ray-diffraction signal from such a small cl uster can be measured quantitatively by preparing a cold cluster depos it. [S0163-1829(98)02408-4].