S. Hazra

Morphology of thin silver film grown by dc sputtering on Si(001)

The morphology and growth mechanism of silver films approximately 150 A in thickness on Si(001) substrates have been studied by atomic force microscopy and x-ray reflectivity. The thin films prepared by dc sputtering at room temperature are composed of islands of silver. The shape and size distribution of these islands are studied using these two complementary measurement techniques.

Electrical relaxation mechanism in unconventional bismuth cuprate glasses

The frequency dependent dielectric constant and loss of the unconventional bismuth cuprate glasses have been presented in wide temperature and frequency ranges. Alternating current dielectric loss peak has been observed in the measurable frequency range at higher temperatures, where the measured ac conductivity approaches the dc conductivity. The temperature range where ac loss peak has been observed, varies systematically with glass composition. The dielectric data at these temperature ranges have been analyzed in terms of different theoretical models to find out the possible relaxation mechanism. It has been observed that the dipolar relaxation model with a distribution of relaxation times can best explain the experimental data. The dipolar relaxation occurs due to the hopping of charge carriers between different localized valence states of copper ions within a range of energies near the mobility edge. High value of the dielectric constant observed in these glasses can be attributed to the influence of ...

Structural properties of unconventional lead cuprate glass

Glass formation and structural properties of the unconventional lead cuprate glasses of compositions (CuO) x (PbO) 100− x (mol %), are reported for the first time. X-ray diffraction and electron microscopic studies show that the glass formation occurs for x = 15-50 mol%. The compositional dependence of the density, molar volume, and glass transition temperature suggests that all glass compositions in this domain have the same topology and network connectivity. The glass structure is built up of [PbO 4 ] tetrahedral units. On heat treatment above glass transition temperatures, the glasses crystallize to CuO and PbO. Electron Spin Resonance (ESR) spectra of the glass compositions consist of broad resonance lines.

Morphology of nanostructured materials

Here we shall discuss the importance of grazing incidence X-ray scattering techniques in studying morphology of nanostructured materials confined in thin films and multilayers. In these studies, the shapes, sizes, and structures of nanostructured materials and their distribution in composites are investigated. These studies are important for understanding properties that may deviate considerably from the known bulk properties. We shall first outline basics of three X-ray scattering techniques, namely X-ray reflectivity, grazing incidence small-angle X-ray scattering, and grazing incidence diffraction, used for these studies. We shall then demonstrate the utility of these techniques using some known results.

Structural studies of binary iron vanadate glass

Structural studies of iron vanadate glasses were carried out using differential thermal analysis, infrared (IR) and Mossbauer spectroscopy. Glasses with cross-linking density higher than the vitreous V2O5 were obtained by introducing Fe2O3 in the V2O5 matrix. Mossbauer spectra are consistent with an interpretation in which iron ions exist as Fe3+ with tetrahedral coordination in the glass compositions. IR spectra indicate that Fe3+ ions occupy substitutional positions in all glass compositions, without affecting the VO bond vibration.

Glass formation in the PbO-Fe2O3 system with high PbO content

We report glass formation in the binary Fe 2 O 3 -PbO system with high PbO content by studying X-ray diffraction (XRD), infrared (IR) absorption and differential thermal analysis (DTA)

Substrate and drying effect in shape and ordering of micelles inside CTAB–silica mesostructured films

Deviation from a perfect 2D-hexagonal (p6m) structure, for CTAB–silica mesostructured films prepared by adding different amounts of excess ethanol to a solution of CTAB and TEOS just before spin coating on OH- and H-terminated Si substrates, is observed from combined X-ray reflectivity and grazing incidence small angle X-ray scattering measurements. Such a deviation can be well understood in terms of the shape and ordering of the micelles, with or without the silica coating layers contribution, inside the film. For example, cylindrical shaped micelles, which are initially circular on a hydrophilic OH-terminated Si substrate in order to form a perfect 2D-hexagonal structure, become elliptical (extended along the in-plane) on a hydrophobic H-terminated Si substrate to form a slightly compressed 2D-hexagonal structure due to a different attachment of the film to the substrate. With time, due to the drying of the silica materials and its restricted movement along the in-plane direction, the films on both the substrates are compressed along the out-of-plane direction only, to form observed centered rectangular (c2mm) structures. Also, due to the asymmetric shrinkage, stress is developed, which deteriorates the ordering in the film. The final shape of the micelles, including the silica coating layers contribution, shows maximum and minimum deviations from the circular shape inside the thick film on a OH–Si substrate and the thin film on a H–Si substrate, respectively. The deviation in the shape of the micelles itself, which is of actual importance, seems to be maximum and minimum inside the thick film on a H–Si substrate and the thin film on a OH–Si substrate, respectively, and is essentially determined by the substrate nature and initial silica wall thickness.

Correlation between local structure and refractive index of e-beam evaporated (HfO2–SiO2) composite thin films

In the present work we have reported the results of investigations on local structures of e-beam evaporated (HfO2–SiO2) composite thin films by synchrotron based extended x-ray absorption fine structure measurements. It has been observed that for the composite film with 10% SiO2 content, both Hf–O and Hf–Hf bond lengths are less than their values in pure HfO2 film. However the bond lengths subsequently increase to higher values as the SiO2 content in the composite films is increased further. It has also been observed that at the same composition of 10% SiO2 content, the films have smallest grain sizes (as obtained from atomic force microscopy measurements) and highest refractive index (as obtained from spectroscopic ellipsometry (SE) measurements) which suggests that the e-beam evaporated HfO2–SiO2 composite films with 10% SiO2 content leads to the most compact amorphous thin film structure.

Morphology of nanocermet thin films: X-ray scattering study

Abstract The morphology of ceramic–metal (cermet) thin films is studied by surface-sensitive X-ray scattering techniques. Grazing incidence small angle X-ray scattering (GISAXS) experiments carried out at LURE with a 2D detector show that metal clusters of nanometer size, known as nanoparticles, are dispersed in the thin film. Analyses of the X-ray reflectivity along with the diffuse scattering allow to predict the formation of layers of nanoparticles along the growth direction of the films. The formation of such cumulative-disordered layers in one direction is likely to be related to the boundary condition in the reduced dimension.

AC conductivity of unconventional bismuth cuprate glass

The frequency dependence of the AC electrical conductivity of different compositions of bismuth cuprate glasses has been presented in the temperature range 80 - 400 K. The conductivity data have been analysed in terms of different theoretical models to determine the possible conduction mechanism. Analysis of the conductivity data and the frequency exponent shows that the correlated barrier hopping of electrons between and ions in the glasses is the most favourable mechanism for AC conduction. The different parameters obtained from the fits of this model to the experimental data are reasonable. The high value of the dielectric constant observed in this glass system can be attributed to the influence of the high polarizability of the ions of the unconventional network former on the AC response.