Anshu Goyal

Removal of sulphur mustard, sarin and simulants on impregnated silica nanoparticles.

Silica nanoparticles of diameter, 24-75 nm and surface area, 875 m(2)/g were synthesized using aero-gel route. Thereafter, nanoparticles were impregnated with reactive chemicals, and used as reactive adsorbent to study the removal of toxic nerve and blister chemical warfare agents and their simulants from solutions. Trichloroisocyanuric acid impregnated silica nanoparticles showed the best performance and indicated physisorption followed by chemisorption/degradation of toxicants. This indicated their suitability as universal decontaminant for nerve and blister agents. This system showed a decrease in t(1/2) from 1210 to 2.8 min for the removal of king of chemical warfare agents, i.e., sulphur mustard. Hydrolysis, dehydrohalogenation and oxidation reactions were found to be the route of degradation of toxicants over impregnated silica nanoparticles.

Study of energy band discontinuity in NiZnO/ZnO heterostructure using X-ray photoelectron spectroscopy

A heterostructure based on ZnO and Ni doped ZnO (NiZnO) thin films has been prepared on c-plane sapphire substrate by pulsed laser deposition technique. X-ray photo electron spectroscopy has been utilized to study the energy band discontinuities, i.e., valence band offset (ΔEv) and conduction band offset (ΔEc) at the interface of NiZnO and ZnO thin films. A type-II band alignment is identified at the interface of prepared heterostructure from the computed data, which is attractive for the realization of efficient optoelectronic devices.

Band gap bowing parameter in pseudomorphic AlxGa1−xN/GaN high electron mobility transistor structures

A method for evaluation of aluminium composition in pseudomorphic AlxGa1−xN layer from the measured photoluminescence (PL) peak energy is presented here. The layers were grown by metalorganic chemical vapor deposition and characterized by high resolution X-ray diffraction (HRXRD), PL, cathodoluminescence, and atomic force microscopy. We estimated the value of biaxial stress in pseudomorphic AlxGa1−xN layers grown on sapphire and silicon carbide substrates using HRXRD scans. The effect of biaxial stress on the room temperature band edge luminescence in pseudomorphic AlxGa1−xN/GaN layers for various aluminium compositions in the range of 0.2 < x < 0.3 was determined. The value of pressure coefficient of band gap was also estimated. The stress corrected bowing parameter in AlxGa1−xN was determined as 0.50 ± 0.06 eV. Our values match well with the theoretically obtained value of bowing parameter from the density functional theory.

Comparative study of wet sulfur passivation process on GaSb (100) surface

ABSTRACT A comparative study for the pristine and sulfur passivated surfaces of gallium antimonide (GaSb) grown using molecular beam epitaxy is presented with the results recorded through X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques. The as-grown GaSb surfaces were treated separately with 20% aqueous ammonium sulphide, ((NH4)2S), at 60°C for 10 m, aqueous sodium sulfide nonahydrate (Na2S.9H2O) with molarity 1 for 4 m at room temperature and base-thioacetamide (base-TAM) with molarity 0.18 for 40 m at 70°C. AFM topography shows the formation of very clean and flat surface for base-TAM treated GaSb. XPS results reveal lowest concentration of Ga2O3for GaSb surface treated with base-TAM.

Non-destructive determination of ultra-thin GaN cap layer thickness in AlGaN/GaN HEMT structure by angle resolved x-ray photoelectron spectroscopy (ARXPS)

Angle resolved X-ray photoelectron spectroscopy (ARXPS) and secondary ion mass spectrometry (SIMS) investigations have been carried out to characterize the GaN cap layer in AlGaN/GaN HEMT structure. The paper discusses the qualitative (presence or absence of a cap layer) and quantitative (cap layer thickness) characterization of cap layer in HEMT structure non-destructively using ARXPS measurements in conjunction with the theoretical modeling. Further the relative sensitive factor (RSF=σGaσAl) for Ga to Al ratio was estimated to be 0.963 and was used in the quantification of GaN cap layer thickness. Our results show that Al/Ga intensity ratio varies with the emission angle in the presence of GaN cap layer and otherwise remains constant. Also, the modeling of this intensity ratio gives its thickness. The finding of ARXPS was also substantiated by SIMS depth profiling studies.

Structural and Optical Characterization of β-Ga2O3 Thin Films Grown by Pulsed Laser Deposition

Polycrystalline β-Ga2O3 thin films were grown on sapphire substrate (0001) by pulsed laser deposition (PLD) technique. The crystalline structure and optical band gap were studied as a function of growth temperature, laser beam energy, annealing temperature and time. To tailor the band gap of β-Ga2O3 thin films by Al diffusion from the sapphire substrate the films were annealed for 24 h at different temperatures. The amount of Al diffusion was different for different temperatures of annealing which resulted in the increase of band gap as well as the shift of diffraction peaks to higher angles with increasing temperature. The annealed films showed high transparency in the deep UV region of the spectrum.

Low Temperature Deposited BST Thin Films for RF MEMS Switch

BST thin films of optimized target composition of Ba0.6Sr0.4TiO3 have been deposited on Cr-Au coated Si substrate by Pulsed Laser Deposition technique with low substrate temperature of 100°C using different laser energies (250 mJ, 300 mJ and 350 mJ). The structural, morphological and electrical studies have been carried out for all the films. The value of dielectric constant and dielectric loss for the film deposited with different laser energies were in the range of 18–20 and 0.04–0.07 respectively. The thickness of the film was 0.4 μm. All the films show higher resistivity (∼107Ω-cm) and high dielectric breakdown strength (∼500 kV/cm). The observed results suggest that the low temperature deposited BST thin films are suitable for RF MEMS Switch application.

Growth of ZnO nano films on Sapphire/GaAs/ Si substrates

ZnO films of Nano dimensions 70-250 nm were obtained on different substrates namely Sapphire/GaAs. Metallic Zn films were deposited by thermal evaporation method at room temperature under vacuum ~ 10-6 torr. These films were subsequently partially oxidized by chemical method followed by heat treatment at three different elevated temperatures 350degC,400degC, and 450degC in O2/air. These films were characterized by X-ray for phase analysis, Atomic Force Microscope (AFM) for surface related features . Surface steps flow mechanism drives the growth mode and ZnO nanoislands are well formed on c-axis sapphire due to less thermal mismatch between the film and the substrate.

COMPARISON OF PROPERTIES OF PLZT SYSTEM WITH DIFFERENT FORMULATIONS

We report the comparison of structural, dielectric, ferroelectric and piezoelectric properties of lanthanum-modified lead zirconate titanate (PLZT) ceramics with the substitution of 7 and 8 mol% La3+ content in PZT (65/35) by three different formulations. The three formulations are (i) cation compensated at A-site, (ii) valency compensated at A-site and (iii) all sites (A and B) compensated. Samples were prepared by solid-state reaction route. X-ray diffraction (XRD) study shows single-phase formation with rhombohedral structure in all the samples. Scanning electron microscopy (SEM) study shows variation in grain size with different formulations. Dielectric studies for all the PLZT samples have been carried out as a function of temperature (room temperature to 350°C) at few selected frequencies (0.1, 1, 10 and 100 kHz) showing characteristics of diffuse phase transition (DPT). Dielectric properties of the poled and unpoled samples at room temperature have also been compared. All these compositions show well-defined ferroelectric behavior with significant change in the coercive field (Ec). Maximum piezoelectric properties have been obtained for the PLZT system with 8 mol% La3+ prepared by formulation (i).

Sintering behaviour of samarium modified lead calcium titanate ceramics

Modified Lead Calcium Titanate (PCT) compositions with representative formula, Pb 0.76−x Sm x Ca 0.24 Ti 0.98 Mn 0.02 O 3 (x = 0–0.1 in steps of 0.02) were prepared by conventional dry ceramic method. Effects of samarium substitution on physical, structural properties and thermal behaviour of PCT ceramics are reported here. All the samples were subjected to XRD analysis and were found to have single phase with tetragonal structure up to 8 mol% Sm substitution. The variations of density and tetragonality have been studied with samarium content. Microstructural analysis shows the uniform grain growth with increasing Sm concentration. Dilatometric study has been done to predict sintering schedule of the green samples.