Dependence of thermal oxidation behavior of silicon nanocrystallites

Three kinds of nanosilicon crystallites were prepared by different methods in high vacuum. All of them were composed of tiny silicon crystallites whic h were initially only mildly oxidized before annealing, but their behavior upon annealing in vacuum differed substantially depending on the environmen t in which they resided. XPS analyses revealed that the unencapsulated nano particles tended to oxidize quite quickly, whereas the nanoparticles sandwi ched between layers of Al2O3 matrices were oxidized rather slowly even unde r intense annealing. In the zinc/silicon nanocrystalline mixture, the oxida tion of the Sio state was even faster than that of the intermediate Si-+1,S i-+2,Si-+3 states. Both the stability and formation processes of the Si-O b onds in the partially oxidized states differed considerably with different environmental surroundings. However, in all cases, the Si-O bonds of the fu lly oxidized Si+4 state remained the most stable, to which the less oxidize d states tend to gravitate eventually.