OPTICAL-PROPERTIES OF CARBON CLUSTERS EMBEDDED IN SIO2-FILMS

Raman spectra were measured for carbon-doped SiO2 thin films prepared by an rf cosputtering method. The changes in the spectra were systemat ically studied as a function of the annealing temperature. From a deta iled analysis of the spectra, the following conclusions were drawn. In the as-deposited films, very small carbon clusters are embedded in th e SiO2 matrices. When the films are annealed at 600 degrees C, graphit e-like sp(2) bonds begin to develop in the clusters. Upon annealing wi th higher temperatures, the size of sp(2) bond clusters increases. How ever, the growth of graphite microcrystals can be ruled out, since hig h-resolution transmission electron microscopic images of the samples a nnealed at 1000 degrees C do not show lattice fringes due to graphite microcrystals. The samples annealed at 1000 degrees C were found to ex hibit an extinction hump around 220 nm, very similar to that seen in t he interstellar extinction spectra.