Effect of temperature on the validity of the einstein relation in heavily doped semiconductors

An analytical expression of the modified form of the Einstein relation in heavily doped semiconductors in which Gaussian band tails are formed near the lower limit of heavy doping is derived for studying the temperature dependence of the diffusivity-mobility ratio of the carriers in such semiconductors. It is found that, with increasing temperature from relatively low values, the ratio first increases in a nonlinear manner and then decreases till, at high temperatures, it approaches its value corresponding to the non-degenerate condition resulting in a peak over a narrow range of temperatures.     

Electrodeposition of ferrocenoyl peptide disulfides

Using electrodeposition of cyclic and acyclic Fc-peptide disulfides tightly-packed Fc-peptide monolayers were conveniently formed, which exhibit significant differences in their electron transfer kinetics.     

Painlevé test for long-wave,short-wave interaction equation. II

In a previous communication we discussed the integrability of a long-wave, short-wave interaction equation for very restricted values of the parameters in the framework of the theory laid down by Weisset al. Here we proceed with the analysis in the sense of Weisset al., considering values of parameters other than those we used previously. We observe that for the combination of parameters for which a Lax pair was obtained by another approach (Newell), the equations considered pass the Painlevé test for integrability in the sense of Weisset al. We discuss several other combinations of parameters that do not pass the test. For these cases no Lax Pair was reported by Newell.     

Limit cycles in a forced Lorenz system

We consider a Lorenz system where the control parameter is sinusoidally modulated. Limit cycles appear where previously there were strange attractors. Perturbation theory is used to estimate the critical amplitude of the modulation for which limit cycles appear.     

Nano-powders of Na0.5K0.5NbO3 made by a sol–gel method

Sodium potassium niobate (NKN) nano-particle powders were synthesised through the thermal decomposition of a sol–gel NKN precursor. Powders and gels were characterised by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). Hydrated carbonate phases formed as a result of reaction with evolved vapours during organic decomposition, and by reaction of NKN powders with H₂O and CO₂ on exposure to air. The primary particle size of the powders increased from <50 to <250 nm as decomposition temperatures were raised from 500 to 950 °C.     

Quasi-one dimensional graphite ribbon structures in the presence of a magnetic field and the on-site Coulomb correlation at half-filling

We have presented the role of the Coulomb interaction (U) and the magnetic field [(B)\vec]\vec{B} on the ground state properties of the quasi-one dimensional graphite ribbon structures at half-filling. Mean field Hartree-Fock Approximation is used to study the systems. To understand the boundary effects in graphite structures, we have compared the results of these systems with those of the square lattice ribbon structures. Studying the density of states, the Drude weight and the charge gap, we have drawn the U – B phase diagrams for the zigzag and the armchair graphite ribbons.     

Role of dopant concentration and surface coating on photophysical properties of CdS: Eu3+ nanocrystals

Here, we report the role of dopant concentration and surface coating of CdS: Eu3+ nanocrystals on the modification of crystal structure and their photoluminescence properties by steady-state and time resolved fluorescence studies. It is found that photoluminescence properties are sensitive to the crystal structure which is controlled by surface coating and dopant concentration. The emission intensity of the peak at 614 nm (5D0 --> 7F2) of the Eu3+-ions is found to be sensitive to the doping and surface coating of CdS nanocrystals. It is found that the average decay times tau are 248, 353 and 499 micros for 0.25, 0.5 and 1.0 mol% Eu ions doped into CdS nanocrystals, respectively. From the decay time measurements, it is evident that the energy transfer occurs from CdS nanoparticles to Eu3+ ions and the calculated energy transfer efficiency from CdS nanoparticles to Eu3+ ions is 9.2 and 35% for Eu3+ ions coated and doped CdS nanoparticles, respectively. Our analysis suggests that site symmetry of ions plays a very important role in the modifications of radiative and nonradiative relaxation mechanisms.     

Role of oxygen impurity in growth and magnetic properties of Ni83Fe17 permalloy thin films

To study the influence of oxygen impurities in the sputtering atmosphere on microstructure, and the magnetic and magnetotransport properties, thin films of Ni₈₃Fe₁₇ were deposited under dc magnetron sputtering technique into which regulated oxygen gas was introduced. The partial pressure of oxygen was varied from 2×10⁻⁷ to 3×10⁻⁶ mbar. X-ray diffraction patterns indicate the reduction of grain growth with increasing the oxygen partial pressure. The grain microstructure and the composition were confirmed through high resolution transmission electron microscopy attached with Scanning Transmission Electron Microscopy (STEM). Transition from canted to rectangular magnetic hysteresis loop was observed through magnetization measurements for samples prepared under higher oxygen partial pressure which implies the structural changes in the magnetic domain formation. These observations were further confirmed through the measurements of anisotropic magnetoresistance properties.