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UV- visible reflectivity study of the synthesys and growth of nanocrystals obtained by ion implantation

The reflectivity (R) in the UV-visible range was used to study CdS nanocrystals obtained by implantation of Cd and S ions into SiO2 and subsequent annealing (Ta=300o-900oC). We demonstrate that such an analysis can give very useful information about the process of nanocrystal formation and growth. The synthesis of even a small fraction of CdS is readily observable through the appearance of interference fringes since the refractive index of CdS, nCdS, is substantially higher than that of SiO2, nSiO2. Extensive CdS synthesis, resulting in strong fringes, occurs for Ta ł500oC. In addition, for higher Ta, a peak in R with a maximum at 2.45 eV (R2.45) becomes discernable, indicating the formation of larger nanocrystals. It is shown that the blue shift of R2.45 relative to its energy in the bulk CdS closely corresponds to the shift of bandgap, Eg, with crystallite size and may therefore be used to estimate the size of the nanocrystals.

nanocrystals; Cadmium Sulfide; II-VI; implanta

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