Formation of CdSe nanoclusters in SiO thin films

Abstract

CdSe nanoclusters embedded in silicon oxide layers are produced by sequential physical vapor deposition of SiO x x Ϸ 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 s /a ratio (a: average size of nanocrystals, s : 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. ᭧

Nanoparticle layers of CdSe buried in oxide and chalcogenide thin film matrices

“…This allows us to assume that, independently on the chemical nature of the surface, at the very beginning of CdSe film deposition embryos are formed at those surface positions at which the curvature and lattice stress are the greatest. The relatively narrow nanocluster size distribution observed [10] indicates that most likely further CdSe deposition does not create new embryos, but increases only the size of already existing nanoparticles. Figs.1a and b show that at low substrate temperatures and a thickness ratio of d matrix =d CdSe ¼ 20 the surface roughness of the 'matrix' layers is sufficient to ensure the formation of quasi-isolated CdSe nanoparticles.…”

“…Consecutive thermal evaporation of CdSe and the matrix material (SiO, or GeS 2 , or ZnSe) was carried out from two independent tantalum crucibles at a vacuum of B5 Â 10 À4 -10 À3 Pa [9,10]. The Corning 7059 glass, quartz and c-Si substrates used were not intentionally heated.…”

“…1b) that the crystal lattice of the particles is oriented randomly. The s=a ratio (a: average size of nanocrystals, s half-width at half-maximum of size distribution) found [10] for 1 nm CdSe deposited on 20 nm SiO x is 0.13, while for 2 nm CdSe deposited on 40 nm SiO x it is 0.19.…”

“…Only a minor increase of particle size has been observed in the SiO x -CdSe films accompanied by an improve- ment of the spherical appearance and crystallinity of the CdSe nanoparticles [10]. In the films with a chalcogenide matrix (GeS 2 (ZnSe)-CdSe) an appreciable material intermixing occurs at the interface even in as-deposited films and strong further alloying takes place upon annealing [19].…”

Quantum confinement effect in multilayer structure of alternate CdSe and SiOx insulator matrix thinfilms

“…Significant work has been done in analyzing the properties of CdSe/SiO x systems due to their applications in visible and near infrared regions where the insulator matrix is transparent [4][5][6]. Moreover, as surface valleys are present in SiO x matrix with a length up to several hundreds of nanometers, nanoclusters of semiconductor materials such as CdSe, ZnSe may be formed on the surface [7]. In addition, photoluminescence of CdSe nanocrystals is interesting on account of their changing emission wavelength with changing nanocrystallite size [8,9].…”