Rayees Ahmad Zargar

Synthesis and Characterization of Screen Printed Zn0.97Cu0.03O Thick Film for Semiconductor Device Applications

The studies on doped ZnO thick films deposited over large surface area are still a very promising area of research and development. We report characteristic properties of thick film of Zn0.97Cu0.03O prepared by the economic screen printing technique. The film was characterized by XRD, SEM, diffused reflectance, FTIR, and dark resistivity measurement techniques. The XRD and SEM studies revealed polycrystalline, single phase, porous, and granular surface morphology of this Cu doped ZnO thick films. The direct band gap energy of this film determined by diffuse reflectance technique is 3.18 eV. IR transmission spectrum measured in 4000–600 cm−1 region at ambient temperature confirmed the incorporation of Cu2

Importance of structural distortions in enhancement of transition temperature in FeSe1 − xTex superconductors

Temperature (12 K <= T <= 300 K) dependent extended x-ray absorption fine structure (EXAFS) studies at the Fe K edge in FeSe1-xTex (x = 0, 0.5 and 1.0) compounds have been carried out to understand the reasons for the increase in T-C upon Te doping in FeSe. While local distortions are present near superconducting onset in FeSe and FeSe0.5Te0.5, they seem to be absent in non superconducting FeTe. Of crucial importance is the variation of anion height. In FeSe0.5Te0.5, near the superconducting onset, the two heights, h(Fe-Se) and h(Fe-Te) show a nearly opposite behaviour. These changes indicate a possible correlation between Fe-chalcogen hybridization and the superconducting transition temperature in these Fe-chalcogenides.

Synthesis and Characterization of Vanadium Doped Zinc Oxide Thick Film for Chemical Sensor Application

Zinc oxide and vanadium pentoxide nanoparticles derived by chemical coprecipitation route were used to cast Zn0.96V0.04O thick film by screen printing method. The structural, morphological, optical, and electrical properties of the film were characterized by powder XRD, SEM, Raman, UV-VIS, and DC conductivity techniques. XRD pattern, SEM image, and Raman spectrum of the film confirm the single phase formation of Wurtzite structure with preferential orientation along [] plane, minor variation in lattice parameters, and vanadium ions substitution at zinc sites. Zn0.96V0.04O pellet has been used for sensing ammonia vapor concentrations in 20–50°C temperature range which exhibits maximum responsiveness and sensitivity at 30°C. The minor variations in resistance are observed with ammonia vapor concentration. The adsorption of ammonia vapors through weak hydrogen bonding and its insertion into lattice by nitrogen lone pairs donation at vacant/defect sites in lattice caused by vanadium doping are considered to explain gas sensing mechanism.

EPR Spectroscopy of Different Sol Concentration Synthesized Nanocrystalline-ZnO Thin Films

Nanocrystalline zinc oxide (nc-ZnO) thin films were grown on p-type silicon substrate through spin coating by sol-gel process using different sol concentrations (10 wt.%, 15 wt.%, and 25 wt.%). These films were characterized by high resolution nondestructive X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDS) attachment, and electron paramagnetic resonance (EPR) techniques to understand variations in structural, morphological, and oxygen vacancy with respect to sol concentration. The film surface morphology changes from nanowall to nanorods on increasing sol concentration. EPR spectra revealed the systematic variation from ferromagnetic to paramagnetic nature in these nc-ZnO films. The broad EPR resonance signal arising from the strong dipolar-dipolar interactions among impurity defects present in nc-ZnO film deposited from 10 wt.% sol has been observed and a single strong narrow resonance signal pertaining to oxygen vacancies is obtained in 25 wt.% sol derived nc-ZnO film. The concentrations of impurity defects and oxygen vacancies are evaluated from EPR spectra, necessary for efficient optoelectronic devices development.

Structural, electrical and magnetic features of Kagomé YBaCo4O7 system

Abstract Polycrystalline yttrium barium cobaltite (YBaCo4O7) powdered sample was prepared by conventional solid state reaction route using high purity yttrium oxide, barium carbonate and cobalt oxide. The as-prepared sample was characterized by XRD diffraction, SEM/EDAX, Raman analytical techniques, resistivity and magnetization measurements for structural, morphological, electrical and magnetic properties assessment. XRD pattern confirms the single phase formation of the sample without any impurity. SEM image shows the hexagonal growth of the crystal and EDAX spectrum reveals stoichiometric composition of as prepared sample. The variation in electrical resistivity from 90 K to 300 K follows the variable range hopping conductivity mechanism. The strong broad overlapped Raman peaks of Co–O and Y–O stretching and bending vibrations of tetrahedral CoO4 with included components of YO6 of octahedral symmetry are obtained at 542 cm−1, 486 cm−1 and 636 cm−1, 436 cm−1, respectively. DC magnetic susceptibility exhibits very weak ferromagnetism below 80 K and does not obey Curie-Weiss law.

Impact of Inter-Wall Distance on Physical Properties of Metal-Semiconducting Double Walled Carbon Nanotube Quantum Dot

Here we report the effect of inter-wall distance of CNT on transmission probabilities of electrons and holes as well as their binding energies. The binding energies were calculated using the variational method within the effective mass approximation and confinement potential. The barrier transmission probabilities of electrons and holes were also calculated using varying potential barrier height and quantum mechanical tunnelling. The binding energy is found to be decreasing with inter-wall distance. We find the presence of outer wall causes a decrease in the transmission probability. For a given core radius, the transmission probability of hole increases linearly with increasing hole energy. CNT QDs of inter-wall distance 3 nm resembles to type II core-shell quantum dot (CSQD). The observed results were compared with the previous investigations. The inter-wall distance causes a decrease in the transmission probability.

Upper critical field and AC-Susceptibility studies on FeTe0.5Se0.5 superconductor

In this study we present synthesis and characterization of FeTe0.5Se0.5 sample that has been prepared by solid state reaction route by encapsulation of stoichiometric high purity (5N) ingredients in an evacuated quartz tube at 750 °C. The resultant compound is crystallized in single phase tetragonal structure with space group P4/nmm, having lattice parameters a = 3.792(1) A and c = 6.0081(3) A. The studied compound is superconducting at below 13K in both magnetic and transport measurements. Further superconductivity is barely affected by external applied magnetic field, giving rise to upper critical field of above 180 Tesla at 0 K. The sample is studied extensively for AC susceptibility measurements in superconducting state. The AC drive field and frequency are varied from 1-13 Oe and 33-9999 Hz respectively. It is concluded that though the grain boundaries of this superconductor are mainly metallic the minor (undetectable in XRD) foreign phases and the role of porosity cannot be ruled out completely. Thi...

Synthesis and characterization of Fe3O4: Porous carbon nanocomposites for biosensor application

Fe3O4:Porous carbon (Fe3O4:PC) nano-magnetic composites were prepared by using different weight fractions of acid treated PC by the chemical co-precipitation route and annealed at 573 K, 773 K and 973 K temperatures in inert N2 gas atmosphere for 2 hrs to obtain desired stoichiometry of nanocomposites. The structural, morphological and magnetic properties of these composites were characterized by powder XRD, TEM, EPR and VSM analytical techniques. The crystallinity of the composites, g-value and spin concentration increases with increasing annealing temperature. TEM images confirmed the formation of nanosized ferrite nanoprticles whose size increases from 23 nm to 54 nm on increasing annealing temperature. Porous carbon increases porosity, coercivity and reduces saturation magnetization of these prepared nanocomposites.