Effect of Thermal Annealing on Boron Diffusion, Micro-structural, Electrical and Magnetic properties of Laser Ablated CoFeB Thin Films

We report on Boron diffusion and subsequent crystallization of Co$_{40}$Fe$_{40}$B$_{20}$ (CoFeB) thin films on SiO$_2$/Si(001) substrate using pulsed laser deposition. Secondary ion mass spectroscopy reveals Boron diffusion at the interface in both amorphous and crystalline phase of CoFeB. High-resolution transmission electron microscopy reveals a small fraction of nano-crystallites embedded in the amorphous matrix of CoFeB. However, annealing at 400$^\circ$C results in crystallization of CoFe with \textit{bcc} structure along (110) orientation. As-deposited films are non-metallic in nature with the coercivity (H$_c$) of 5Oe while the films annealed at 400$^\circ$C are metallic with a H$_c$ of 135Oe.Comment: 16 pages, 6 figure

Highly c-axis oriented growth of GaN film on sapphire (0001) by laser molecular beam epitaxy using HVPE grown GaN bulk target

Growth temperature dependant surface morphology and crystalline properties of the epitaxial GaN layers grown on pre-nitridated sapphire (0001) substrates by laser molecular beam epitaxy (LMBE) were investigated in the range of 500-750 degrees C. The grown GaN films were characterized using high resolution x-ray diffraction, atomic force microscopy (AFM), micro-Raman spectroscopy, and secondary ion mass spectroscopy (SIMS). The x-ray rocking curve full width at a half maximum (FWHM) value for (0002) reflection dramatically decreased from 1582 arc sec to 153 arc sec when the growth temperature was increased from 500 degrees C to 600 degrees C and the value further decreased with increase of growth temperature up to 720 degrees C. A highly c-axis oriented GaN epitaxial film was obtained at 720 degrees C with a (0002) plane rocking curve FWHM value as low as 102 arc sec. From AFM studies, it is observed that the GaN grain size also increased with increasing growth temperature and flat, large lateral grains of size 200-300 nm was obtained for the film grown at 720 degrees C. The micro-Raman spectroscopy studies also exhibited the high-quality wurtzite nature of GaN film grown on sapphire at 720 degrees C. The SIMS measurements revealed a non-traceable amount of background oxygen impurity in the grown GaN films. The results show that the growth temperature strongly influences the surface morphology and crystalline quality of the epitaxial GaN films on sapphire grown by LMBE

Near Fermi level Electronic Structure of Pr1−x_{1-x}Srx_xMnO3_3: Photoemission Study

In this study, we report the observation of a pseudogap associated with the insulator-metal transition in compositions of Pr$_{1-x}$Sr$_x$MnO$_3$ system with no charge ordering. Our valence band photoemission study shows that the observed shifts in the near Fermi level density of states are abrupt at the Curie transtion and occur over an energy scale of $\sim$ 1 eV, strongly suggesting that the charge-ordering gap observed earlier in other manganites and the pseudogap observed here may indeed have same origin. These results could be understood within the framework of models based on electronic phase separation where it has been shown that the pseudogap is a generic feature of the mixed-phase compositions. Also, our band structure calculations on Pr$_{0.75}$Sr$_{0.25}$MnO$_3$ show the possible existence of half-metallicity in this system.Comment: 5 pages, 5 figure

Electronic structure of Pr0.67_{0.67}Ca0.33_{0.33}MnO3_3 near the Fermi level studied by ultraviolet photoelectron and x-ray absorption spectroscopy

We have investigated the temperature-dependent changes in the near-$E$$_F$ occupied and unoccupied states of Pr$_{0.67}$Ca$_{0.33}$MnO$_3$ which shows the presence of ferromagnetic and antiferromagnetic phases. The temperature-dependent changes in the charge and orbital degrees of freedom and associated changes in the Mn 3$d$ - O 2$p$ hybridization result in varied O 2$p$ contributions to the valence band. A quantitative estimate of the charge transfer energy ($E$$_{CT}$) shows a larger value compared to the earlier reported estimates. The charge localization causing the large $E$$_{CT}$ is discussed in terms of different models including the electronic phase separation.Comment: 19 pages, 7 figures, To be published in Phy. Rev.

Transformation of Waste Coal Fly Ash into Zeolites for Environmental Applications

The generation of a large quantity of waste coal fly ash (CFA) via coal combustion process during power generation is of major concern as disposal of such huge quantity of fly ash causes serious threats to the environment. There is an exigent need to find out the proper solution for its disposal/utilization to reduce its harmful effects. The composition of waste coal fly ash mostly consists of silica and alumina. Hence, the researchers are tempted to utilize waste coal fly ash as a starting ingredient to make value-added materials like zeolites. It is anticipated that such research efforts will act as a valuable aid to reduce the disposal cost of fly ash and ultimately reduce harmful effects of fly ash to the environment. In this review, various synthesis methods to synthesize different types of zeolites from CFA, such as Zeolite-A, Zeolite-X and Zeolite-P, have been summarized and their potential for various applications such as sorption and catalysis has been explored

Staphylococcal Enterotoxin A Induces Small Clusters of HLA-DR1 on B Cells

The superantigen SEA causes non-specific hyperactivation of T and B cells at low concentrations. Studies of mutants or soluble proteins suggest SEA is bivalent for its ligand, MHC class II. However, the interaction between these molecules on intact cells is unknown. On primary mouse B cells expressing the MHC class II allele HLA-DR1, measurements of Förster Resonance Energy Transfer between HLA-DR1 molecules on SEA-treated cells indicated specific clustering, not observed in untreated or monovalent superantigen treated cells. Tomographic visualization and electron microscopy of immunogold-labeled SEA-treated B cells revealed small clusters of surface HLA-DR1 (≤4 gold labels). These results present direct visual evidence of SEA-mediated clustering of MHC class II molecules on treated antigen presenting cells, and provide a new structural approach to addressing problems of this nature

Capacity of optical reading, Part 1: Reading boundless error-free bits using a single photon

We show that nature imposes no fundamental upper limit to the number of information bits per expended photon that can, in principle, be read reliably when classical data is encoded in a medium that can only passively modulate the amplitude and phase of the probe light. We show that with a coherent-state (laser) source, an on-off (amplitude-modulation) pixel encoding, and shot-noise-limited direct detection (an overly-optimistic model for commercial CD/DVD drives), the highest photon information efficiency achievable in principle is about 0.5 bit per transmitted photon. We then show that a coherent-state probe can read unlimited bits per photon when the receiver is allowed to make joint (inseparable) measurements on the reflected light from a large block of phase-modulated memory pixels. Finally, we show an example of a spatially-entangled non-classical light probe and a receiver design---constructable using a single-photon source, beam splitters, and single-photon detectors---that can in principle read any number of error-free bits of information. The probe is a single photon prepared in a uniform coherent superposition of multiple orthogonal spatial modes, i.e., a W-state. The code, target, and joint-detection receiver complexity required by a coherent-state transmitter to achieve comparable photon efficiency performance is shown to be much higher in comparison to that required by the W-state transceiver.Comment: 11 pages, 12 figures, v3 includes a new plot characterizing the photon efficiency vs. encoding efficiency tradeoff for optical reading. The main technical body of the paper remains unaltere