Gamma induced changes in Makrofol/CdSe nanocomposite films

In our present work, we applied ex-situ casting procedure to prepare a nanocomposite (NCP) from Makrofol polycarbonate (PC) and CdSe nanoparticles. The CdSe nanoparticles were prepared by thermolysis procedure in the presence of N2 gas flow. Rietveld refinement of x-ray data illustrated that the CdSe accustoms cubic zinc blend structure of a 6.057 Å lattice parameter and 2 nm typical grain size. Samples from the prepared NCP were exposed to γ dosages (20-250 kGy). The modifications induced in the NCP films owing to γ dosages have been studied. The γ irradiation (50-250 kGy) causes the crosslinks that reduces the optical bandgap from 4.15 to 3.81 eV; associated with an increase in dielectric parameters and refractive index. This is attributed to the increase of the mass fraction of the disordered regions as specified by XRD. The PC-CdSe NCP was found to have reaction to color modification which makes it suitable in saleable reproduction on printing press.

Synthesis and characterization of ZnS-based quantum dots to trace low concentration of ammonia

In the present work, a solution-based co-precipitation method has been adopted to synthesize pure and cobalt-doped ZnS quantum dots and characterized by XRD, SEM, TEM with EDX, FTIR and gas sensing properties. XRD analysis has shown a single phase of ZnS quantum dots having a zinc blend structure. TEM and XRD line broadening indicated that the average crystallite size in the sample is in the range of 2 to 5 nm. SEM micrographs show spherical-shaped quantum dots. FTIR studies show that cobalt has been successfully doped into the ZnS cubic lattice. EDX spectra have analyzed the elemental presence in the samples and it is evident that the spectra confirmed the presence of cobalt (Co), zinc (Zn), oxygen (O), and sulphur (S) elements only and no other impurities are observed. The ZnS-based quantum dot sensors reveal high sensitivity towards 50 ppm of ammonia vapors at an operating temperature of 70 °C. Hence, ZnS-based quantum dots can be a promising and quick traceable sensor towards ammonia sensing applications with good response and recovery time.

Effect of the lattice mismatch on the efficiency of the GaAs nanowire/Si substrate solar cell

The effect of the crystal lattice mismatch between single p-GaAs nanowire grown on p-Si substrate on the solar cell efficiency is studied. The study is performed by measuring the I-V curves under red (wavelength=650 nm) laser illumination. The measurement of the single nanowire was done by conductive atomic force microscopy (C-AFM). The measured curve was reproduced by numerical simulations accounting piezoresistance and piezoelectric effects. The analysis demonstrated the presence of the tensile (2%) zinc blend insert at the interface between nanowire and substrate induced by crystal lattices mismatch. Strained insert at the interface changes the polarity of the photogenerated current and increases the efficiency by 2 times.

Study of dynamic and thermodynamic properties of zinc-blend and wurtzite cadmium sulfide (CdS) using density functional theory

The dynamic and thermodynamic properties of wurtzite (wz) and zinc-blend (zb) CdS are investigated within the density functional theory using different approximation methods such as LDA, PBE, and DFT+U. Hellmann–Feynman approach is implemented for the relaxation of atomic position for both phases. To guarantee the accuracy of calculation, the convergence test of total energy with respect to energy cutoff and k-point sampling is performed. The dynamic properties such as phonon dispersion, phonon density of state, frequency along with high symmetry points, static and dynamic polarizability, and dielectric constants are calculated. The obtained values are compared with previous theoretical results. DFT + U approximation gives a good result that is consistent with the available theory. Moreover, the vibrational energy, vibrational free energy, entropy, electron chemical potential, and constant-volume specific heat are obtained within LDA, PBE, and DFT + U approximations.

Functionalization of Doped ZnO through Solution Route Synthesis: A study Using Spectroscopy & Density of States

ZnO is one of the widely studied materials for multidimensional applications, viz. semiconductor material, catalysts, solid-state devices, etc. The primary functionalization is carried out by doping the required element (s) within the ZnO matrix, which can exist in either zinc blend or the wurtzite form. The present research reports synthesis of ZnO doped by Cr, Y, and Eu at two dopant concentrations. The synthesis technique is optimized using dual fuels during solution auto combustion synthesis. Detailed analysis of X-ray diffraction study reveals a comparative analysis of the peak area and FWHM magnitude. The influence of the doping element on the ZnO is studied in terms of UV and photoluminescence spectra. The highest bandgap of 3.08 eV is reported with Eu as the dopant within ZnO compared to Y, which shows lower bandgap energy of 2.44 eV. The density of states study of ZnO is found to be continuous with a significant nodal region within -3.4 to -2.4 eV. However, in the doped systems, irrespective of the dopant, nodal regions are more with specific band regions in the ZnO-Y/ZnO-Eu system. Irrespective of dopant type, doping within ZnO significantly influences the states in the conduction band.

Robust Geometries for Second-Harmonic-Generation in Microrings Exhibiting a 4-Bar Symmetry

Microring resonators made of materials with a zinc-blend or diamond lattice allow exploiting their 4-bar symmetry to achieve quasi-phase matching condition for second-order optical nonlinearities. However, fabrication tolerances impose severe limits on the quasi-phase matching condition, which in turn degrades the generation efficiency. Here, we present a method to mitigate these limitations. As an example, we studied the geometry and the pump wavelength conditions to induce the second-harmonic generation in silicon-based microrings with a second-order susceptibility χzxy(2)≠0. We found the best compromises between performances and experimental requirements, and we unveil a strategy to minimize the impacts of fabrication defects. The method can be easily transferred to other material systems.

Preparation and Characterization of CdS/CdTe Device for Radiation Sensing

Several Techniques had been applied to measure Ionizing Radiation. Majority of thistechniques are costly and very complicated. We focus on this research to chemically deposition of CdS to formwith CdTe junction x-ray sensor. CdTe has been electrodeposited onto CdS/FTO glass substrate to formwith previously fabricated CdS layer 4 µm thickness. The optimum potential for CdTe deposition hasbeen studied by potentiostat measurement, it shows that -1.3 is the optimum working potential. The XRDanalysis showed that the CdTe films have highly oriented crystallites with the cubic phase zinc blend withpreferred orientation (111). The band gap Eg extrapolated to be 1.4 eV. Four stacked sensors wereconnected in series to measure the device performance. It was observed that amplitude of the pulseformed due to exposed FTO/CdS/CdTe/Mo detector to X-ray of 33 keV and 1mA intensity is 1.03 V.

Characterization of GaSb thin films with excess Ga grown by RF magnetron sputtering

Understanding the behavior of excess Ga is important for fabrication methods that employ the sputtering of GaSb-based materials. This is due to the comparatively low vapor pressure of Ga, which can result in GaSb becoming Ga-rich under experimental conditions. In this study, the growth and characterization of nonstoichiometric polycrystalline GaSb thin films with excess Ga, grown by RF magnetron sputtering, are reported. Ga content was adjusted by mixing N2 in the Ar sputtering gas. The structural properties indicate that the grown thin films maintain the zinc blend structure of GaSb, and have an induced tensile strain along a direction parallel to the substrate. Excess Ga segregates towards the film surface and forms micro/nanoclusters. The internal tensile strain and the Ga cluster formation have little effect on the intrinsic properties of GaSb. These findings could lead to the fabrication of GaSb-based thin films using sputtering with excellent mass productivity.