Formation of CdSe nanoclusters in SiOx thin films

CdSe nanoclusters embedded in silicon oxide layers are produced by sequential physical vapor deposition of SiOx (x≈1.5) and CdSe on crystalline silicon substrates at room temperature. High-resolution electron microscopy is used to prove the formation of CdSe nanoclusters as well as to study their shape, size and structure. Cross-sectional electron micrographs of the as-deposited samples reveal clusters with nearly spherical shapes, which are not arranged in a plane. The spatial distribution of the CdSe clusters follows the surface morphology of the SiOx films. The average size of the nanoclusters is about two times greater than the nominal thickness of the CdSe layers deposited. Upon annealing the samples at 670 K for 80 min, a slight size increase is observed accompanied by some improvement in crystallinity of the CdSe nanoclusters. The σ/a ratio (a: average size of nanocrystals, σ: half-width at half-maximum of size distribution) found for 1-nm CdSe deposited on 20-nm SiOx is 0.13–0.14, while for 2-nm CdSe deposited on 40-nm SiOx it is 0.19.