Formation of CdSe nanoclusters in SiO x thin films

Abstract

CdSe nanoclusters embedded in silicon oxide layers are produced by sequential physical vapor deposition of SiO x ( 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 SiO x 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 SiO x is 0.13–0.14, while for 2-nm CdSe deposited on 40-nm SiO x it is 0.19.