Mushahid Husain

Electronegativity scale from X-ray photoelectron spectroscopic data

Abstract Electronegativity of atoms, based on Allred and Rochows method, has been re-estimated by calculating the effective nuclear charge by using the experimental values of the binding energies of the inner and valence states obtained from X-ray photoelectron spectroscopic data. The present method has the advantage that no arbitrary method of determining the screening constants is involved.

Determination of diode parameters of a silicon solar cell from variation of slopes of the I–V curve at open circuit and short circuit conditions with the intensity of illumination

An analytical method of determination of all the four diode parameters of the single exponential model of a silicon solar cell, namely shunt resistance Rsh, series resistance Rs, diode ideality factor n and reverse saturation current I0 from the variation of slopes of the I–V curve of the cell near short circuit and open circuit conditions with intensity of illumination in a small range of intensity, is presented for the first time. In a suitable range of intensity the variation of dI/dV at short circuit enables determination of Rsh, whereas the variation of dI/dV at open circuit enables determination of Rs, n and I0. The diode parameters of a silicon solar cell were determined with this method using I–V characteristics of the cell in 40–125 mW cm−2 intensity range of a simulated AM1.5 solar radiation. Theoretical I–V curves generated using so determined values of the diode parameters matched well with the experimental I–V curves of the cell obtained under various intensities of illumination in the above range.

Facile synthesis and step by step enhancement of blue photoluminescence from Ag-doped ZnS quantum dots

Our results pertaining to the step by step enhancement of photoluminescence (PL) intensity from ZnS:Ag,Al quantum dots (QDs) are presented. Initially, these QDs were synthesized using a simple co-precipitation technique involving a surfactant, polyvinylpyrrolidone (PVP), in de-ionised water. It was observed that the blue PL originated from ZnS:Ag,Al QDs was considerably weak and not suitable for any practical display application. Upon UV (365 nm) photolysis, the PL intensity augmented to ~170% and attained a saturation value after ~100 min of exposure. This is attributed to the photo-corrosion mechanism exerted by high-flux UV light on ZnS:Ag,Al QDs. Auxiliary enhancement of PL intensity to 250% has been evidenced by subjecting the QDs to high temperatures (200 °C) and pressures (~120 bars) in a sulphur-rich atmosphere, which is due to the improvement in crystallanity of ZnS QDs. The origin of the bright-blue PL has been discussed. The results were supported by X-ray phase analysis, high-resolution electron microscopy and compositional evaluation.

Synthesis and physical properties of FeSe1/2Te1/2 superconductor

One of the most important properties of very recently reported FeSe based superconductors is the robustness of their superconductivity under applied magnetic field. The synthesis and control of superconductivity in FeSe based compounds is rather a difficult task. Synthesis and physical property characterization for optimized superconductivity of FeSe1/2Te1/2 at 13 K is reported here. The compound crystallized in a tetragonal structure with lattice parameters a=3.8015(2) and c=6.0280(4) A. Magnetization measurements indicated bulk superconductivity with lower critical field (Hc1) of around 180 Oe. By applying Ginzburg–Landau theory, the Hc2(0) value is estimated to be ∼1840 kOe for the 90% of resistive transition. A heat capacity measurement revealed bulk superconductivity by a hump at Tc near 13 K and an expected decrease in the same was observed under an applied magnetic field.

The effect of nano-alumina on structural and magnetic properties of MgB2 superconductors

Nano-Al2O3 doped Mg1?xAlxB2 with 0?x?6% were synthesized by solid state reaction at 750??C in Fe tube encapsulation under a vacuum of 10?5?Torr. Resistance measurement shows that the Tc decreases with x and zero resistivity for x = 0 and 6% are obtained at 38 and 35?K, respectively. XRD measurement shows that the lattice parameter and cell volume also decrease monotonically with increasing doping levels. From this we infer that the Al has been substituted in the lattice of MgB2 at Mg sites. Resistivity measurement shows a systematic decrease in Tc with doping which also confirms the substitution of Al. Magnetization studies in the temperature range from 4 to 35?K and in the magnetic field up to 9?T shows a significant increase in the irreversibility field (Hirr), critical current density (Jc) and remanent magnetization (MR) with increasing concentration of the Al2O3 nanoparticle. At low fields we have observed large vortex instabilities (known as a vortex avalanche) associated with all doped samples. The vortex-avalanche effect is reduced with increasing temperature and vanishes near 20?K. The results are discussed in terms of local-vortex instabilities caused by doping of Al2O3 nanoparticles.

Optical band gap and optical constants in a-GaxTe100-x thin films

Abstract The optical band gap and optical constants for a-Ga x Te 100− x thin films have been measured as a function of photon energy. The optical band gap is found to increase with the increase in Ga content in the a-Ga x Te 100− x system. The spectral dependence of optical constants shows that the refractive index ( n ) decreases while the extinction coefficient ( k ) increases with photon energy.

Effect of oxygen plasma on field emission characteristics of single-wall carbon nanotubes grown by plasma enhanced chemical vapour deposition system

Field emission properties of single wall carbon nanotubes (SWCNTs) grown on iron catalyst film by plasma enhanced chemical vapour deposition system were studied in diode configuration. The results were analysed in the framework of Fowler-Nordheim theory. The grown SWCNTs were found to be excellent field emitters, having emission current density higher than 20 mA/cm2 at a turn-on field of 1.3 V/μm. The as grown SWCNTs were further treated with Oxygen (O2) plasma for 5 min and again field emission characteristics were measured. The O2 plasma treated SWCNTs have shown dramatic improvement in their field emission properties with emission current density of 111 mA/cm2 at a much lower turn on field of 0.8 V/μm. The as grown as well as plasma treated SWCNTs were also characterized by various techniques, such as scanning electron microscopy, high resolution transmission electron microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy before and after O2 plasma treatment and the findings are be...

Superconductivity in SmFe1−xCoxAsO (x=0.0–0.30)

We report synthesis, structural details, and magnetization of SmFe1−xCoxAsO with x ranging from 0.0 to 0.30. It is found that Co substitutes fully at Fe site in SmFeAsO in an isostructural lattice with slightly compressed cell. The parent compound exhibited known as the spin density wave (SDW) character is below at around 140 K. Successive doping of Co at Fe site suppressed the SDW transition for x=0.05 and later induced superconductivity for x=0.10, 0.15, and 0.20, respectively, at 14, 15.5, and 9 K. The lower critical field as seen from magnetization measurements is below 200 Oe. The appearance of bulk superconductivity is established by wide open isothermal magnetization M(H) loops. Superconductivity is not observed for higher content of Co, i.e., x≥0.30. Clearly the Co substitution at Fe site in SmFe1−xCoxAsO diminishes the Fe SDW character, introduces bulk superconductivity for x between 0.10 and 0.20 and finally becomes nonsuperconducting for x above 0.20. The Fe2+ site Co3+ substitution injects mob...

Anomalous control mechanism in a B-Z type oscillator involving fructose as organic substrate

Abstract In order to elucidate the mechanism of Ce 4+ +BrO 3 − +H 2 SO 4 +fructose [F] oscillatory reaction which has no apparent bromine removal mechanism, detailed experimental studies have been undertaken to investigate (i) [Br − ] at different time intervals during oscillations, (ii) effect of addition of (a) Br − during oscillations, (b) fructose and BrO 3 − after stoppage of oscillations and (c) tartaric acid [TA], below the lower critical limit of [F] for oscillations. A reaction mechanism has been suggested which involves active participation of free radicals and which also correctly predicts most of the observed oscillatory features.

Adsorption sites of hydrogen atom on pure and Mg-doped multi-walled carbon nanotubes

Hydrogen adsorption sites on pure multiwalled carbon nanotube (MWCNT) and Mg-doped MWCNTs material system have been investigated using molecular dynamics (MD) simulations as well as quantum chemical calculations. Through combining MWCNTs with Mg, the hydrogen adsorption sites energy on this Mg-MWCNTs system is found to be larger than that of the pure MWCNTs. Additionally, it was found that, through Mg-doping, new adsorption sites for hydrogen molecules are created in comparison with undoped nanotubes. It is also found that H atom is preferably adsorbed at every place near magnesium atom.