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

Abstract

Nanoparticles of CdSe embedded in amorphous SiO x , GeS 2 and polycrystalline ZnSe thin films have been produced by sequential physical vapour deposition of CdSe and one of the matrix materials. High-resolution electron microscopy has been used to prove the formation of CdSe nanoparticles. Particles with nearly spherical shape were observed whose spatial distribution follows the surface morphology of the 'matrix' films. The mechanism of nanoparticle formation on a rough surface has been discussed. It has been found that annealing of SiO x -CdSe films at 973 K leads to the formation of isolated CdSe nanoparticles homogeneously distributed in the matrix. Quantum-size increase in the optical band gap of CdSe nanoparticles has been observed in all matrices used. r

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

“…One can expect quantum size effects in this range of crystallite sizes [7]. This result agrees well with the results reported in literatures [13,18]. Microstrain is one of the causes for quantum size effects in multilayer system due to heap arrangement [15].…”

“…Therefore it is expected that thin layers of CdSe nanocrystals may be filled in the surface wells of relatively thick (50 nm) SiO x matrix layer. This will lead to the formations of nano-sized regions on the surface of SiO x matrix [18]. This results in broad peaks in XRD spectra of the samples S1 and S2.…”

“…Typically absorption edge gets related to transition that takes place between the highest valence band and the lowest conduction band of CdSe semiconductor [27]. Here, the energy equivalent to the absorption edges of the samples S2 (%1.54 eV) and S3 (%1.6 eV) is lesser than the band gap of bulk CdSe (1.74 eV) [18]. Thus, these transitions corresponding to absorption edges of S2 and S3 could not have taken place between valence and conduction band energy levels of CdSe nanocrystals.…”

Chalcogenide nanowires by evaporation–condensation

“…Quasi-1D metal trichalcogenide compounds [6] and quasi-2D layered metal dichalcogenides [7] have been reported. Recent interest on nanostructures has lead to research on chalcogenide nanotubes [8], nanoparticles by several synthesis techniques [9][10][11][12][13][14][15], layered structures [16,17], films [18], and nanoscale photostructural changes [19]. In traditional semiconductor systems, there has been success with the vaporliquid-solid (VLS) method [20,21] of growing Si whiskers.…”

Structural and optical properties of CdTe/CdSe heterostructure multilayer thin films prepared by physical vapor deposition technique

“…4b) but not in the spectra of CdTe and CdSe single-layer thin films (Fig. 4a), which may be related to electronic transitions between discrete hole and electron energy levels in the valance and conduction bands due to spin-orbit coupling (Nesheva et al 2002). As a result of spin-orbit interaction, valance band of CdTe semiconductor splits into an energetically higher and lower components which were usually labeled as U 7 v and U 8 v .…”