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1/f noise measurements were performed on Ni/n-GaN Schottky barrier diode under forward bias over a wide temperature range from 80 to 300 K. The noise spectra exhibited frequency dependence proportional to 1/f 0 with c varying between 0.8 and 1.1 down to 1 Hz. The spectral power density of current fluctuations, S I , was found to decrease with increase in temperature. Current-voltage (I-V) characteristics of the diodes have been measured, and metal-semiconductor interface was found to be spatially inhomogeneous in the temperature range 80-300 K. The decrease in 1/f noise with increase in temperature is explained within the framework of spatial inhomogeneities model. V C 2012 American Institute of Physics. [http://dx.

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We report the near-edge x-ray absorption fine structure (NEXAFS) and x-ray magnetic circular dichroism (XMCD) experiments on well characterized Mn doped ZnO thin films that show ferromagnetism at room temperature. The NEXAFS measurements at O K edge clearly exhibit a preedge spectral feature which evolves with Mn doping, similar to one observed in hole-doped cuprates and manganites. The Mn L3,2 edge NEXAFS spectra exhibit divalent Mn apart from mixed valent Mn3+∕Mn4+ states. The spectral features of XMCD at Mn L3,2 edge demonstrate that ferromagnetism comes from Mn2+ ions and its dichroism shape is independent of Mn concentration.

Pristine and irradiated Raman and PL spectra of pure and Co-doped ZnO nanocrystals.

The present study reports the effect of Co doping on the structural, optical, magnetic, and electronic properties of CeO 2 nanoparticles (NPs) synthesized by a simple low-temperature co-precipitation method. Co doping was introduced by adding CoCl 3 with different mole percentages (0%, 2%, 4%, and 6%) to cerium nitrate, which resulted in room-temperature ferromagnetism (RTFM). TEM and XRD analysis showed that the Co-doped CeO 2 NPs are monodispersed with face centered cubic structure. The 6% Co-doped CeO 2 NPs showed a coercivity value of 155 Oe and saturation magnetization of 0.028 emu/g at room temperature. The electronic structures of the as-prepared CeO 2 and Codoped CeO 2 NPs were investigated by X-ray absorption near-edge structure (XANES) spectroscopy. The XANES spectra at Ce M-and L-edges clearly indicated a decrease in the valency state of Ce ions from Ce 4+ to Ce 3+ upon Co doping. This causes redistribution of oxygen ions and Co−Co bonding. The XANES study revealed that Co doping plays a prominent role in improving the ferromagnetism, as Co replaces the Ce site in the CeO 2 cubic lattice and the concentration of oxygen vacancies may not be high enough to form a delocalized impurity band for enhancing the magnetic percolation of Co-doped samples. The XANES spectra at Co L-edges indicate direct Co−Co bond formation in the CeO 2 lattices and also a weak bond with O ions. This is in agreement with the magnetic measurements which indicate that Co atoms induce enhancement in magnetic behavior in CeO 2 nanostructures.

A unique strategy for scavenging free radicals in situ on exposure to gamma irradiation in polyethylene (PE) nanocomposites is presented. Blends of ultra-high molecular weight PE and linear low-density PE (PEB) and their nanocomposites with graphene (GPEB) were prepared by melt mixing to develop materials for biomedical implants. The effect of gamma irradiation on the microstructure and mechanical properties was systematically investigated. The neat blend and the nanocomposite were subjected to gamma-ray irradiation in order to improve the interfacial adhesion between PE and graphene sheets. Structural and thermal characterization revealed that irradiation induced crosslinking and increased the crystallinity of the polymer blend. The presence of graphene further enhanced the crystallinity via crosslinks between the polymer matrix and the filler on irradiation. Graphene was found to scavenge free radicals as confirmed by electron paramagnetic resonance spectroscopy. Irradiation of graphene-containing polymer composites resulted in the largest increase in modulus and hardness compared to either irradiation or addition of graphene to PEB alone. This study provides new insight into the role of graphene in polymer matrices during irradiation and suggests that irradiated graphene-polymer composites could emerge as promising materials for use as articulating surfaces in biomedical implants.

The electronic structure of Cu-doped ZnO thin films, synthesized with a nominal composition of Zn1−xCuxO (x=0.03, 0.05, 0.07, and 0.10) by using spray pyrolysis method, has been investigated using near-edge x-ray absorption fine structure (NEXAFS) experiments at the O K- and the Cu L3,2-edges and resonant inelastic x-ray scattering (RIXS) measurements at Cu L3,2 edge. The Zn1−xCuxO thin films showed single phase wurtzite-hexagonal like crystal structure and ferromagnetic behavior at room temperature (RT). The intensity of the pre-edge spectral feature at the O K-edge increases with the Cu concentration, which clearly reveals that there is strong hybridization of O 2p–Cu 3d orbitals in the ZnO matrix. Spectral features of the Cu L3,2-edge NEXAFS exhibit multiple absorption peaks and appreciable x-ray magnetic circular dichroism signal that persists even at RT. These results demonstrate that Cu is in mixed valence state of Cu2+,3+/Cu1+, substituting at the Zn site and Cu2+/3+ ions are magnetically polarized. RIXS experiments at Cu L3 edge show strong d-d excitations due to localized nature of Cu ions in the ZnO matrix.