Jeewan Sharma

Comparative studies of different concretes on the basis of some photon interaction parameters

Different photon interaction parameters viz. linear attenuation coefficient, mass attenuation coefficient, penetration depth, equivalent atomic number, exposure buildup factor have been computed for seven different concretes (ordinary, hematite-serpentine, ilmenite-limonite, basalt-magnetite, ilmenite, steel-scrap and steel magnetite) in the energy region of 0.015-15.0MeV. The computed parameters were studied as a function of incident photon energy, chemical composition and penetration depth of the selected concretes. It has been observed that among the selected concretes, steel magnetite offers maximum value for linear attenuation coefficient, mass attenuation coefficient, equivalent atomic number and least values in terms of penetration depth equivalent to mean free path and exposure buildup factors. Hence, it is concluded that it offers better shielding among the selected concretes. It is expected that in case of any nuclear accident, the presented buildup factor data may be helpful in estimating the effective dose given to people living in buildings constructed from one of the selected concretes.

Effect of biocompatible glutathione capping on core–shell ZnS quantum dots

Glutathione capped quantum dots are a potential candidate for different applications like ligand exchange in living cells, cell imaging and detection of glucose levels. Keeping these in mind, glutathione capped ZnS quantum dots were synthesized by using the thiol group of the capping agent by chemical precipitation method. Morphological characterizations were done by XRD and TEM. X-ray diffraction (XRD) measurements showed that the nanocrystals have Zinc Blende structure. Grain size and particle size shows a little variation with glutathione capping. Optical characterizations were done by UV–visible absorption, FTIR and energy resolved photoluminescence. UV–visible studies shows that the band gap also shows a small variation with glutathione capping. FTIR studies confirm glutathione capping on the surface of ZnS quantum dots. Room temperature energy resolved photoluminescence spectrum of samples exhibited a defect-related blue emission band. However, the PL properties seem to start tunability at higher concentration of glutathione which is a very good sign for extending this research further.

Structural and optical properties of ZnO thin films deposited by sol–gel method: effect of stabilizer concentration

AbstractnNanocrystalline thin films of ZnO were successfully deposited on Si substrate via sol–gel method using zinc acetate dehydrate as a precursor and 2-methoxy ethanol as a solvent. The effect of stabilizer concentration on the structural and optical properties of the ZnO thin film was investigated as the stabilizer concentration affects the growth orientation of ZnO thin films prepared by sol–gel method. The growth in (002) plane of hexagonal structure is preferred in many applications as the 2-dimensional Zn atoms population is highest in this orientation. The growth of (002)-oriented ZnO films was optimized with the concentration of the stabilizer (triethanolamine). The crystal structures of the samples were analyzed using X-ray diffractometer confirming the polycrystalline nature and hexagonal structure of films. In order to estimate the preferential crystallite orientation quantitatively, the texture coefficient (Tc) was calculated. The particle size and strain was also found to change with concentration of stabilizer. SEM results confirm the formation of nanocrystalline thin films with homogeneous morphology. Photoluminescence characteristics show a direct band gap transition which shifts towards lower wavelength with increase in stabilizer concentration. It was observed that the stabilizer concentration is the most important factor to grow a highly (002)-oriented ZnO film along c-axis.

Nanostructured BN–TiO2 composite with ultra-high photocatalytic activity

Boron nitride and titanium oxide composite (BN–TiO2) photocatalyst endowed with high specific surface area and large pore size was synthesized by ice bath method. These large pore sizes in the materials (pore diameter 43.88 A) were conducive to the movement of larger molecules or groups in the pore path and for effective use of active sites. The high specific surface area (BET, 103.66 m2 g−1) was beneficial for catalytic oxidation on the surface. In BN–TiO2 composite, the presence of B–O–Ti–O contributed to the pore structure optimization and higher photocatalytic activity with a narrow band gap (2.91 eV). The methylene blue photodegradation rate of BN–TiO2 is 79% in 200 min, higher than that with TiO2 only (32%) in the visible region. This study reports the synthesis of BN–TiO2 photocatalysts with high surface area, large pore size, good photocatalytic performance and reusability. BN–TiO2 has potential applications in practical environmental purification.

Structural and optical properties of silica capped ZnS:Mn quantum dots

AbstractnIn the present work, the structural and optical properties of Silica capped ZnS:Mn quantum dots (QDs) has been reported. Chemical precipitation technique was used to form the core–shell nanostructures. The results indicate that the Silica capped ZnS:Mn QDs has cubic Zinc Blende structure and its grain size is about 2xa0nm as demonstrated by X-ray diffraction (XRD). Transmission electron microscopy images showed that the presence of Silica capping on ZnS:Mn QDs can prevent their agglomeration by cluster formation and their particle size (2–3xa0nm) well matches with XRD results. The selected area diffraction pattern shows a set of sharp rings corresponding to the (111), (220) and (311) lattice planes of the cubic phase of ZnS which proves the polycrystalline behaviour. Band gap studies were done by UV–visible spectroscopy and presence of Silica have been confirmed by EDAX and FTIR analysis. Photoluminescence studies shows emission wavelength as well as intensity to be tunable with Silica capping. As Silica capped ZnS:Mn QDs can control various parameters of ZnS:Mn, they are suitable material for specific kind of tunable optoelectronic devices.

Functionalization and characterization of ZnS quantum dots using biocompatible l -cysteine

In this work, the functionalization of ZnS quantum dots using the thiol group of l-cysteine for different concentrations has been reported. Chemical precipitation method was used for the synthesis of nascent as well as l-cysteine functionalized ZnS quantum dots for optimized values of pH and molar concentrations of the precursors. Morphological studies were done by X-ray diffraction (XRD) and TEM. Optical measurements were done by UV–visible, Fourier transform infrared (FTIR) and energy resolved photoluminescence studies. Particle size was calculated by using Brus equation. Appreciable changes in morphological and optical properties of ZnS quantum dots were observed in few cases. XRD results shows that, the primary crystallite size decreases with increasing the capping concentration, however, the crystal structure remain same for all the used concentrations of l-cysteine. UV–visible analysis shows that band gap and particle size is also tunable with l-cysteine capping. FTIR studies confirmed l-cysteine capping on the surface of quantum dots. As l-cysteine is non toxic and stable compound, the surface modification of ZnS quantum dots with l-cysteine not only prevents the aggregation of quantum dots but also make them available for the interaction with the target materials and make them suitable for specific biomedical applications.

Effect of deposition temperature on structural, optical and electrical properties of nanocrystalline SnSe thin films

SnSe thin films have been prepared by chemical bath deposition method at different substrate temperature. The influence of deposition temperature on structural, optical and electrical properties of polycrystalline SnSe films have been investigated using X-ray diffraction, optical absorbance and conductivity measurements. The X-ray diffraction study reveals the orthorhombic structure of the SnSe films oriented along the (111) direction. The structural parameters such as lattice spacing, crystallite size, strain, number of crystallites per unit area and dislocation density have been evaluated. Optical absorbance measurement indicates the existence of direct allowed band gap in the range 1.50–1.91xa0eV. The dark conductivity (σd) and photoconductivity (σph) measurement in the temperature range (278–385xa0K), indicates that the conduction in these materials is through an activation process having one activation energy. σd and σph values decrease with the decrease of crystallite size. The value of photosensitivity, carrier life time and trap depth have also been calculated.

Study of structural, optical and electrical parameters of ZnSe powder and thin films

Nanocrystalline ZnSe powder and thin film forms have been synthesized via chemical bath deposition technique. The ZnSe thin films are deposited onto ultrasonically clean glass substrates in an aqueous alkaline medium using sodium selenosulphate as Se2− ion source. The ZnSe powder and thin film are characterized by structural, optical and electrical properties. It is confirmed from X-ray diffraction study that cubic phase is present in ZnSe thin film form with (111) as preferred orientation and hexagonal phase is present in ZnSe powder form with (100) as preferred orientation. Optical absorption measurement indicates the existence of direct allowed optical transition with a wide energy gap and blue shift in the fundamental edge has been observed in both cases. The optical band gap of ZnSe powder is greater than the thin film. The electrical conductivity (both dark and photoconductivity) measurements are also carried out in different temperature range and variation in activation energy has been calculated.

Electrical characterization of nanocrystalline zinc selenide thin films

In the present paper, we have studied the effect of photo-illumination on electrical properties of nanocrystalline ZnSe thin films. The ZnSe thin films with different grain sizes (coherently diffracting domains) have been prepared. The semiconducting material with the composition Zn25Se75 has been prepared using melt-quenching technique. Thermal evaporation technique has been used to prepare nanocrystalline ZnSe thin films on highly cleaned glass substrates at different partial pressures of Ar gas. The grain size has been controlled by the partial pressure of inert gas. The grain size has been calculated using X-ray diffraction plots. Mobility activation has been studied from the photocurrent decay curves. The effective density of states (Neff), frequency factor (S), and trap depth (E) have been calculated for all the films having different grain sizes. Three different types of trap levels have been found in these films. There is a linear distribution of traps having different energies below the conduction band. The increase in photoconductivity is explained in terms of built in potential barriers (ϕb) at the grain boundaries.

Enhanced moisture sensing properties of a nanostructured ZnO coated capacitive sensor

This work reports the enhancement in sensitivity of a simple and low-cost capacitive moisture sensor using a thin film of zinc oxide (ZnO) nanoparticles on electrodes. The ZnO nanoparticles are systematically characterized using X-ray diffraction, atomic force microscopy, transmission electron microscopy, BET surface area analysis, Fourier transform infrared spectroscopy, and UV-visible and photoluminescence (PL) spectroscopy. The average crystallite size of the ZnO nanoparticles is ∼16 nm with a surface roughness of ∼3 nm. Blue emission in the PL spectrum confirms the presence of oxygen vacancy dipoles, which are responsible for enhancing the dielectric properties of the ZnO nanoparticles. The effect of the ZnO nanoparticles on the sensitivity of a moisture sensor cell has been studied using wheat grains with a moisture content from 7% to 25%. An enhancement in sensitivity of 36.4% at 1 MHz and 97.4% at 500 Hz has been observed. A detailed sensing mechanism is proposed and the enhancement in sensing has been explained based on the interaction of ZnO with water vapor and the dielectric behavior of the nanostructured ZnO. The present results establish ZnO as a sensing material for improving the utility of moisture sensors.