Evolution of Si suboxides into Si nanocrystals during rapid thermal annealing as revealed by XPS and Raman studies

Si nanocrystals (nc-Si) were synthesized by rapid thermal annealing of magnetron-sputtered amorphous SiOx films. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were employed to study the evolution of chemical structures and the rapid growth of nc-Si. XPS results reveal five chemical structures of Si in the as-deposited films corresponding to silicon oxidation states: Sin+ (n=0, 1, 2, 3 and 4). Their bonding structures are found to be inhomogeneous, and far from that predicted by the random-bonding model. XPS and Raman spectra suggest that the formation of amorphous Si nanoclusters had already taken place in the as-deposited samples. Formation of nc-Si was realized through a combination of thermal decomposition and the diffusion process. Upon thermal annealing, Si suboxides (Si2O, SiO and Si2O3) decompose into Si and SiO2, resulting in the rapid growth of nc-Si.