Phase transitions of bismuth clusters

X-ray diffraction patterns, extended X-ray absorption fine structure, and optical absorption coefficients were measured in order to investigate the size-dependence of structural and optical phase transitions of bismuth clusters. Contrary to the case of 15-nm thick films, peaks due to crystalline Bi were not observed in X-ray diffraction patterns of as-deposited 0.5-nm thick films. Optical absorption coefficients of the 0.5-nm thick films are small compared with those of 100-nm thick films, and an optical gap appears in the 0.5-nm thick films. These results show directly the phase transition of bismuth clusters from semi-metallic nanocrystalline to semiconducting amorphous-like clusters with decreasing size.