Vineet Sharma

CdS nanofilms: Synthesis and the role of annealing on structural and optical properties

Cadmium sulfide (CdS) nanofilms have been deposited on the glass substrate using the chemical bath technique. Cadmium chloride and thiourea have been used as Cd2+ and S2− ion sources with ammonia as a complexing agent in the presence of a nonionic surfactant. The deposited films have been annealed in air at 373 K, 473 K, 573 K, and 673 K ± 5 K temperature. The effect of the annealing on the structure, morphology, and optical properties of CdS nanofilms has been studied. CdS films have been characterized by X-ray diffraction, scanning electron microscopy, energy dispersive x-ray analysis, and UV-Vis-NIR spectrophotometer. The CdS films have been found to be nanocrystalline in nature with the zinc blende structure. The direct bandgap has been determined. Various parameters, viz. the grain size, inter-planer spacing, lattice constant, dislocation density, microstrain, surface morphology, absorption coefficient, and optical bandgap has been calculated and found to vary with annealing. The results have been ex...

Effect of In additive on the electrical properties of Se–Te alloy

Electrical measurements are done on Se85−xTe15Inx (x = 0, 2, 4, 6 and 10 at%) thin films. The dark conductivity (σd) increases and the activation energy (ΔEd) decreases as the In concentration increases. The photoconductivity (σph) also increases with the increase in In concentration. The photosensitivity (σph/σd) decreases sharply after the In incorporation. The charge carrier concentration (nσ) is calculated with the help of dc conductivity measurements. The value of nσ increases as the In concentration increases. The results are explained on the basis of an increase in the density of localized states present in the mobility gap.

CdS nanofilms: Effect of film thickness on morphology and optical band gap

CdS nanofilms of varying thickness (t) deposited by chemical bath deposition technique have been studied for structural changes using x-ray diffractometer (XRD) and transmission electron microscope (TEM). XRD analysis shows polycrystalline nature in deposited films with preferred orientation along (002) reflection plane also confirmed by selected area diffraction pattern of TEM. Uniform and smooth surface morphology observed using field emission scanning electron microscope. The surface topography has been studied using atomic force microscope. The optical constants have been calculated from the analysis of %T and %R spectra in the wavelength range 300 nm-900 nm. CdS nanofilms show a direct transition with red shift. The optical band gap decreases while the refractive index increases with increase in thickness of nanofilms.

Effect of Te on linear and non-linear optical properties of new quaternary Ge-Se-Sb-Te chalcogenide glasses

We report linear and non-linear optical properties of a new quaternary chalcogenide glass series Ge19-ySe63.8Sb17.2Tey (y = 0, 2, 4, 6, 8, 10). In linear optical properties; refractive index, extinction coefficient and the Tauc gap are reported and their variation with Te content has been discussed. In non-linear properties; third order nonlinear susceptibility and non-linear refractive index has been discussed. The variation of non-linear refractive index has also been reported with normalized photon energy. A correlation between the Tauc gap and nonlinear refractive index has been discussed. Results indicate that these materials may find applications in modern optical devices.

Structural transition in II-VI nanofilms: Effect of molar ratio on structural, morphological, and optical properties

Cadmium sulphide nanofilms have been deposited by chemical bath deposition technique on glass substrates. The effect of S/Cd molar ratio on the structural, morphological, and optical properties of CdS nanofilms has been investigated. Structural parameters have been analyzed using x-ray diffractometer. Scanning electron microscope and energy dispersive x-ray analyzer have been used to study surface morphology and elemental composition of nanofilms, respectively. The optical properties of the nanofilms have been studied for varying S/Cd molar ratio. The variation in S/Cd molar ratio induces reorientation in lattice structure of the nanofilms and a phase transition has been observed with changing molar ratios. The modification in properties with varying S/Cd ratio has been discussed in terms of quantum confinement and compared with theoretical results based on effective mass approximation and tight binding model.

Superparamagnetic La doped Mn–Zn nano ferrites: dependence on dopant content and crystallite size

Magnetic nanoparticles are found to exhibit exciting and substantially distinct magnetic properties due to high surface-to-volume ratio and several crystal structures in comparison to those discovered in their bulk counterparts. The properties of nanoparticles also largely depend on the route of their synthesis. In the present work, we report the synthesis of superparamagnetic nanoparticles of Mn0.5Zn0.5La x Fe2−x O4 (x = 0, 0.025, 0.050, 0.075, 0.1) ferrites by co-precipitation method. Structural, morphological and elemental study has been performed using x-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), FESEM and EDS. Different structural parameters (crystallite size, interplanar spacing and lattice constant) have been calculated from XRD. Formation of cubical spinel structure has been confirmed from XRD and FTIR. Cation distribution for all the samples has been proposed and used for calculation of various theoretical parameters. Magnetic properties have been investigated using vibrating sample magnetometer at room temperature and show transition between paramagnetic and superparamagnetic behavior. Maximum saturation magnetization and magnetic moment have been obtained at x = 0.050. The results are attributed to the solubility of La in Mn–Zn ferrite and the size of nanoparticles. The samples have also been analyzed for dielectric, electric and optical properties. For x ≤ 0.050, a blue shift in absorbance and photoluminescence measurements has been observed due to quantum confinement.

Structural Rigidity, Percolation and Transition-Temperature Study of the Ge19Se81-xSbx System

Selenium-based glasses are attractive candidate materials because of their low transmission losses and other optical properties. In the present paper, samples of Ge19Se81-xSbx (x = 0, 4, 8, 12, 16, 17.2, 20) were prepared by using the melt-quench technique, and their X-ray diffraction spectra were studied. Some of the physical parameters were calculated theoretically. It was observed that the glass transition temperature increased up to x = 17.2 and then decreased whereas the theoretically calculated band-gap decreased with increasing Sb content.

Effect of light intensity and temperature on the recombination mechanism in a-(Ge20Se80)99.5Cu0.5 thin film

The temperature dependence of electrical conductivity measurements has been studied in the dark as well as in the presence of light in vacuum evaporated thin films of (Ge20Se80)99.5Cu0.5. The dark conductivity increases exponentially with temperature. The temperature dependence of steady state photoconductivity at different intensities indicates that photoconductivity is also thermally activated. These measurements ensure the presence of mono- and bimolecular recombination regions. Transient photoconductivity measurements at different temperatures and light intensities show that the photocurrent passes through a maximum before attaining the steady state. The results have been explained in terms of the multiple-trapping model with photoconductivity kinetics determined by trap-controlled recombination.

New Quaternary Sb-Se-Ge-In Chalcogenide Glasses: Linear and Nonlinear Optical Properties

Chalcogenide glasses find extensive applications in infrared (IR) devices and optical communication. Optical parameters of Sb10Se65Ge25−yIny thin films, deposited by the thermal evaporation technique, have been analyzed using ultraviolet–visible-near IR spectroscopy. The transitions in the forbidden gap are indirect. The effect of indium (In) alloying on the nonlinear optical parameters has been studied. A shift in optical absorption edge towards higher wavelength shows that the width of the localized states changes, which affects the optical parameters of the system. The high nonlinearity of these glasses makes them suitable for optical regeneration and Raman amplification.

Physical Analysis of Structural Transformation in Ge-Incorporated a-SbxSe100-x System

Chalcogenide glasses are suitable for far-infrared and imaging applications. In the present study, Sb10Se90-xGex (x=0, 19, 21, 23, 25, 27) system has been chosen to study structural transformations via physical parameters. Bulk samples with x = 0, 19, 21, 23, 25 and 27 have been prepared using the melt-quenching technique. A theoretical study of the ternary glass system revealed that there was a significant change in the structural environment of the system due to rigidity percolation, which took place as Se was replaced by Ge, and hence resulted in changes in other physical parameters of the system.