Nanoparticles of Cd(S,Se) grown in silicate glasses study by High Resolution Transmission Electron Microscopy (HRTEM) assisted by image treatment

Abstract

CdSxSe1-x doped glasses have raised large interest in the recent past years. They are commercially available as sharp cut-off filters with optical absorption edge varying from yellow to deep red as the composition x varies from 1 to 0, according to the properties of bulk Cd(S,Se) compounds, On the other hand glasses prepared in laboratory present different optical properties in relation with excitonic confinement when the semiconductor grains are smaller than 5nm : increase of the third order nonlinear optical susceptibility, shift of the absorption edge toward higher energy, quantum size effects. In order to improve the understanding of the optical properties, it is important to get fine structural informations on the semiconductor phase : crystallographic structure (which may be different than in bulk materials), morphology, size and defects. Comparatively to optical investigations, there have been few structural studies of the semiconductors doped glasses. HRTEM is potentially a powerful method for examining nanocrystals in low concentration within glass. Practically however, the sharpness of the crystal images is reduced by the presence of background signal originating mainly from glass. Numerical treatment of filtering through Fourier transformation presents several advantages. A large part of the signal originating from glass (at low frequencies) and from statiscal noise (at high frequencies) may be suppressed as shown in Figures 1 and 2. The Fourier transform (Figure 2c) may be used for measuring the lattice parameters more easely than the lattice image.