P. B. Barman

An optical study of a-Ge20Se80- xInx thin films in sub-band gap region

The present paper reports a study of optical parameters, refractive index (n) and extinction coefficient (k), by analysing the transmission spectrum of thin films prepared from samples of Ge20Se80−xInx (x = 0, 5, 10, 15, 20) in the range 400–1500 nm. The dispersion parameters are calculated by using the Wemple–DiDomenico model. The optical band gap of the thin films is obtained by Tauc plots. The variation in the optical parameters for different thin films is explained on the basis of the presence of defect states and the change in the average bond energy of the system. The dielectric constants (er and ei) and optical conductivity (σ) of the thin films are also reported.

Effect of deposition parameters and semi-empirical relations between non-linear refractive index with linear refractive index and third order susceptibility for a-Ge20Se70-xIn10Bix thin films

Present work reports the influence of deposition parameters, i.e., the effect of the type of substrate on the optical properties of a-Ge20Se70-xIn10Bix (x = 0, 2, 4, 6, 8, and 10) thin films. Optical constants were accurately determined by envelope method using transmission spectra in the wavelength region of 400–1800 nm. The order obtained for the refractive index is nmica > nmicroscope glass > nquartz for different substrates used in the deposition of thin films. The bandgap of the film deposited on mica substrate is smallest as compared to the bandgap of the films deposited on microscopic glass and quartz. To open the possibility of the use of chalcogenide glasses for non-linear switching, these vitreous systems were studied with respect to their non-linear susceptibility and refractive index. Third-order optical susceptibility (χ(3)) is evaluated from changes of index of refraction using Wang approximations. We examined the dependence of susceptibility on the absorption edge, thereby showing that the ...

Correlation between the physical and optical properties of thea-Ge–Se–In–Bi system

A correlation between physical and optical properties of the Ge20Se70− x In10Bi x (x = 0, 2, 4, 6, 8, 10) glassy system is presented. The density of the alloys increases with an increase of the Bi content, which accounts for the concurrent increase in refractive index. The molar volume (Vm ) has been calculated from the densities and follows the same trend as that of the optical gap. A linear relation has been found between the cohesive energy (calculated using a chemical-bond approach) and the optical gap (experimental and theoretical). The cohesive energy and the optical gap decrease with increase in Bi content. A decrease of electronegativity also accompanies the decrease of optical gap. The relationship between the optical gap and the chemical composition in the a-Ge–Se–In–Bi glasses has been examined using two parameters: the average heat of atomization and the average coordination number (⟨r⟩). The mean bond energy (⟨E⟩) and the glass transition temperature (Tg ) are calculated using the Tichy-Ticha approach. ⟨E⟩ shows maxima at chemical thresholds. Thickness-dependence studies of the optical gap and the refractive index show that optical gap increases with increased thickness, whereas no significant change has been found in the refractive index for all compositions.

Synthesis, structural and optical properties of Ag doped ZnO nanoparticles with enhanced photocatalytic properties by photo degradation of organic dyes

In present paper chemical route based synthesis of Ag doped ZnO nanoparticles (NPs) by co-precipitation method is reported to develop ZnO NPs for photo catalytic application. XRD confirms the structural purity of ZnO NPs. FESEM and TEM study reveals the surface and ultra structure morphology of NPs. EDAX study confirms the purity and homogeneity of NPs. The Ag/ZnO NPs with different weight percentage of Ag relative to ZnO were applied under visible light irradiation for evaluating heterogeneous photo catalytic degradation of methylene blue (MB) and Brilliant blue (BB) respectively. The presence of Ag in ZnO enhance MB and BB dye degradation effectiveness from 96.78 to 98.66 and 82.15 to 97.36% for pure ZnO and maximum Ag doped ZnO (x = 0.1) respectively. In comparison of MB and BB final degradation ability, MB dyes have more effective photo catalytic efficiency towards different oxidizing species to degradation process.

Thickness-dependent optical properties and nonlinear refractive index of a-Ge–Se–In thin films

The present work reports the study of linear optical properties of a-Ge20Se80−xInx (x = 0, 5, 10, 15, 20) system as a function of film thickness and at different Se/In ratio using transmission spectra. Optical gap increases with the increase in film thickness, whereas no significant change is found in the linear refractive index for all the compositions. To evaluate their potential applications for all-optical ultrafast switching devices, we report the effect of In alloying on the nonlinear refractive index and third-order susceptibility (χ(3)), evaluated from the changes of index of refraction using Wang approximations. Comparative higher values of susceptibility of the order of 10−11 (in esu) are found and show a maximum at In = 10 at.%. The largest value of susceptibility can be expected for materials with higher values. Different formulations were used to predict the nonlinear behavior of Ge–Se–In system. The addition of In to Ge20Se80−xInx glass leads to an increase in the nonlinear refractive index, almost 500 times that of fused silica. A comparison of our results shows a good agreement with values available in the literature. High nonlinearity of Ge–Se–In glasses makes them suitable for optical generation and Raman amplification.

Optical studies of Se-Bi-Te-Sb thin films by single transmission spectrum

Chalcogenide glasses are interesting materials on account of their infrared application. In present paper, thin films of quaternary chalcogenide glasses, Se80.5Bi1.5Te18 − xSbx, where x = 0, 2, 4, has been investigated for their optical properties using transmission spectra in the spectral range of 500–2500 nm. The refractive index shows the normal dispersion behavior and found to increase with increase in Sb content. Extinction coefficient has been observed decreases with Sb content.

Effect of Bi addition on the electrical properties of a-Ge?Se?In thin films

This paper reports on the steady state and transient photoconductivity of Ge20Se70−xIn10Bix (x = 2, 4, 6, 8, 10) thermally evaporated thin films. The dark conductivity (σd) increases with the increase in the Bi content. The value of σd increases slowly from x = 2 to x = 6, but for x ≥ 8 the increase is quite abrupt. Photoconductivity (σph) also increases with the increase in the Bi content. The dark activation energy (ΔEd) decreases with the increase in the Bi content. There is a drop in the photosensitivity (σph/σd) of films with the increase in Bi addition. The result of the intensity dependent steady state photoconductivity (σph) follows the power law with intensity (F), i.e. σph α Fγ where the value of γ is close to 0.5, suggesting the predominance of bimolecular recombination in these materials. The rise and decay of photocurrent show the increase in the differential lifetime (τd), with the increase in the Bi content, indicating a delay in the recombination rate of photo-generated charge carriers. This change is governed by the photo-generated carriers trapped in the intrinsic defects or light induced defect creation through structural changes. One can therefore also expect that the density of states increases with the increase in the Bi content in amorphous thin films. The dispersion parameter (α) of the localized state energy distribution, determined from the decay curves, is also reported.

Temperature dependent dual hydrogen sensor response of Pd nanoparticle decorated Al doped ZnO surfaces

Sputter deposited Al doped ZnO (AZO) thin films exhibit a dual hydrogen sensing response in the temperature range 40 °C–150 °C after surface modifications with palladium nanoparticles. The unmodified AZO films showed no response in hydrogen in the temperature range 40 °C–150 °C. The operational temperature windows on the low and high temperature sides have been estimated by isolating the semiconductor-to-metal transition temperature zone of the sensor device. The gas response pattern was modeled by considering various adsorption isotherms, which revealed the dominance of heterogeneous adsorption characteristics. The Arrhenius adsorption barrier showed dual variation with change in hydrogen gas concentration on either side of the semiconductor-to-metal transition. A detailed analysis of the hydrogen gas response pattern by considering the changes in nano palladium due to hydrogen adsorption, and semiconductor-to-metal transition of nanocrystalline Al doped ZnO layer due to temperature, along with material characterization studies by glancing incidence X-ray diffraction, atomic force microscopy, and transmission electron microscopy, are presented.

Enhancing the numerical aperture of lenses using ZnO nanostructure-based turbid media

Nanosheets, nanoparticles, and microstructures of ZnO were synthesized via a wet chemical method. ZnO films with a thickness of 44?46??m were fabricated by spray coating, and these have been investigated for their potential use in turbid lens applications. A morphology-dependent comparative study of the transmittance of ZnO turbid films was conducted. Furthermore, these ZnO turbid films were used to enhance the numerical aperture (NA) of a Nikon objective lens. The variation in NA with different morphologies was explained using size-dependent scattering by the fabricated films. A maximum NA of around 1.971 of the objective lens with a turbid film of ZnO nanosheets was achieved.

Effect of substitutional doping on temperature dependent electrical parameters of amorphous Se-Te semiconductors

Steady state current-voltage characteristics of the amorphous (Se80Te20)98Y2 (Y = Ag, Bi, Ge, Cd) semiconductors at different temperatures are reported. The measurements were performed using direct-current voltage bias to understand the basic conductivity mechanism and to evaluate the impact of each substituent on electrical response. The space charge limited conduction mechanism, and the density of states near Fermi level have been calculated. The difference in electrical response due to different substitutions in the glassy matrix is analyzed.