M. Gandais

Size of Cd(S,Se) quantum dots in glasses: Correlation between measurements by high‐resolution transmission electron microscopy, small‐angle x‐ray scattering, and low‐frequency inelastic Raman scattering

The average sizes of Cd(S,Se) quantum dots in glasses have been measured for the same samples by using three methods: high‐resolution transmission electron microscopy, low‐frequency inelastic Raman scattering, and small‐angle x‐ray scattering. Three samples with crystal sizes of 5.5–8, 9–12, and 17 nm have been studied. For each method the interaction mode and the underlying assumptions in measuring the size are discussed. The correlation between the measurements is good and points out a narrow size distribution. The discrepancies observed for the smallest sizes are discussed with respect to the probe and the interactions used by each technique. They may be ascribed to structural effects.

Growth of CdSe nanocrystals in ion-implanted SiO2 films

Ion implantation technique has been used for the preparation of semiconductor nanocrystals in SiO2 films deposited on semiconductor and quartz substrates. The structural properties of the films have been investigated by using low temperature optical spectroscopy and high resolution electron microscopy. It is found that nucleation of the semiconductor phase can take place in the course of implantation with high ion dose. The profile of both the concentration and the mean size of nanocrystals over the film thickness is determined by the initial distribution of ions over the thickness and can be varied in a controlled manner with the use of sequential ion implantations with various energies and doses.

CdS nanocrystal growth in thin silica films: evolution of size distribution function

Abstract The kinetics of semiconductor nanocrystal formation and growth as a result of solid solution phase decomposition in semiconductor-doped thin silica films fabricated by a co-sputtering technique was investigated. Two regimes of decomposition, attributed to the stages of nucleation and of growth at the expense of dissolved matter, were studied. The shape of the nanocrystal size distribution was investigated in the various stages of the phase decomposition process. Various parameters of the decomposition process including surface tension of nanocrystals, diffusion constant, characteristic time of decomposition were estimated.

Epitaxial growth of ZnS on CdS in CdS/ZnS nanostructures

CdS/ZnS core/shell-like nanostructures have been elaborated by using the chemistry of colloids. The structural properties of the CdS core and the CdS/ZnS core-shell have been studied by high resolution transmission electron microscopy (HRTEM). The morphology and the structures of CdS have been determined. In a second step, the epitaxy of ZnS on CdS and the CdS/ZnS interface have been investigated. The accommodation mode between both materials by partial dislocations has been evidenced. Finally, the ZnS layer grows with the same structure as the CdS core, which is either in the cubic blende-type structure or in the hexagonal wurtzite-type structure.

Correlation between structural and optical properties of PbS nanocrystals

Abstract PbS semiconductor nanocrystals have been synthesized in order to study the modifications of their optical properties in relation to their size. The synthesis has been carried out by using the techniques of colloid chemistry. A fast evolution of the optical absorption spectrum has been noticed following synthesis. Immediately after the synthesis reaction, the samples exhibit a structured absorption spectrum with three well-defined excitonic peaks. Within a few minutes, the peaks progressively disappear and a structureless spectrum occurs. A procedure of stabilization of the colloids has been set up in order to allow the study of the structural and optical properties at different stages of their evolution. Fiber-like nanocrystals (2.5 × 25 nm) and platelets have been found in the early stages of the synthesis and nearly cubic nanocrystals (13 nm) are found in later stages of evolution.

Earliest stages of crystal growth in a silicate glass containing titanium and zirconium as nucleating elements — HRTEM and XAS study

Abstract The earliest stages of crystallization have been studied for a SiO2-Al2O3-Li2O glass-ceramics containing a few percent of titanium and zirconium as nucleating elements. After heat treatments at temperatures ranging between T=750°C and T=860°C, the growth process has been studied by combining HRTEM (high resolution transmission electron microscopy) and XAS (X-ray absorption spectrometry). A fine phase separation has been found in the parent glass (≈ 7 nm in size) independent of the presence of the nucleating elements. From HRTEM, the earliest crystalline phase has been definitely stated as being TiZrO4. The incorporation of titanium atoms into TiZrO4 crystals is correlated with a change of their coordinance from 4 to 6, directly evidenced in XAS spectra by the “prepeak” analysis at titanium K-edge. The crystallization of the aluminosilicate occurs after full precipitation of TiZrO4. In glass ceramics, the number of aluminosilicate and TiZrO4 crystals per unit volume are nearly equal, in good agreement with heterogeneous nucleation of the silicate solid solution on TiZrO4 crystals. For samples heat treated at 750°C and 780°C, the number of TiZrO4 crystallites is constant for a given temperature. These crystallites grow until the matrix becomes free of zirconium atoms. Their growth activation energy has been found to be 400±50 kJ/mol.

Transmission Electron Microscope Study of Experimentally Deformed K-Feldspar Single Crystals

AbstractA set of sanidine single crystals were previously deformed at 700° C in a Griggs triaxial press with different crystallographic orientations of the core so as to induce dislocation glide of different slip systems respectively. Deformed crystals have been studied by transmission electron microscopy (TEM) and the activated slip systems have been characterized for two orientations.(010)[001] and (001)1/2[

Structural properties of coated nanoparticles: The CdS/ZnS nanostructure

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