Reactively sputtered GaAsxN1-x thin films

Thin films of GaAsxN1−x alloys were deposited by reactive rf magnetron sputtering of GaAs target with a mixture of argon and nitrogen as the sputtering gas. Growth rate was found to decrease from ~ 7 μm/h to ~ 2 μm/h as the nitrogen content increased from 0% to 40%. XRD and TEM studies of the films reveal the presence of hexagonal GaN with a significant increase of the lattice parameters in a narrow range of composition of the sputtering gas (5–10% nitrogen), which is attributed to the incorporation of arsenic. The limited availability of nitrogen in the sputtering atmosphere is found to encourage the incorporation of arsenic in the alloy films. Optical absorption coefficient spectra of the films were obtained from reflection and transmission data. The effect of arsenic incorporation is seen in the optical absorption spectra of the films, which show a continuous shift of the absorption edge to lower energies with respect to that of gallium nitride.© Elsevie

Homology modeling and docking studies of Plasmodium falciparum telomerase reverse transcriptase with berberine and some of its derivatives

The telomerase reverse transcriptase (TERT) sequence from Plasmodium falciparum provides valuable information for the design of specific anti-telomerase drugs. The present study deals with the interaction of pfTERT against berberine derivatives to derive novel analogues. Berberine intercalates DNA, thereby inhibits DNA synthesis and PfTERT. This indicated that P. falciparum telomerase might be a potential target for malaria chemotherapy. The nature of the interactions between A three-dimensional structural model of PfTERT was constructed using multiple sequence alignment and homology modeling procedures, followed by extensive molecular dynamics calculations. The analogues of berberine were successfully docked into the binding pocket of the protein. The hydrogen bonds were analyzed along with the binding energy was observed. The binding energy were found to be -8.36, -8.36, -8.23, -11.34, -10.51, -3.56, +186.20, -5.99, -1.10 and -7.48 in Kcal/mol with reference drugs. The least binding energy was found to be -11.34 Kcal/mol which determines that the most effective analogue. As a result this can be used as antiplasmodial drug

Non-destructive determination of ultra-thin GaN cap layer thickness in AlGaN/GaN HEMT structure by angle resolved x-ray photoelectron spectroscopy (ARXPS)

Angle resolved X-ray photoelectron spectroscopy (ARXPS) and secondary ion mass spectrometry (SIMS) investigations have been carried out to characterize the GaN cap layer in AlGaN/GaN HEMT structure. The paper discusses the qualitative (presence or absence of a cap layer) and quantitative (cap layer thickness) characterization of cap layer in HEMT structure non-destructively using ARXPS measurements in conjunction with the theoretical modeling. Further the relative sensitive factor (RSF=σGaσAl) for Ga to Al ratio was estimated to be 0.963 and was used in the quantification of GaN cap layer thickness. Our results show that Al/Ga intensity ratio varies with the emission angle in the presence of GaN cap layer and otherwise remains constant. Also, the modeling of this intensity ratio gives its thickness. The finding of ARXPS was also substantiated by SIMS depth profiling studies

Highly oriented GaN films grown on ZnO buffer layer over quartz substrates by reactive sputtering of GaAs target

Polycrystalline GaN films were deposited on quartz and ZnO buffer layers over quartz by reactive sputtering of a GaAs target in 100% nitrogen at 550 °C and 700 °C. Micro-structural investigations of the films were carried out using high resolution X-ray diffraction, atomic force microscopy and Raman spectroscopy. GaN films deposited on ZnO buffer layers exhibit strongly preferred (0002) orientation of crystallites. In particular, the film deposited at 700 °C on ZnO buffer layer over amorphous quartz substrate showed large crystallite size, both along and perpendicular to growth direction, strong and nearly complete c-axis orientation of crystallites with tilt of ~ 2.5° and low value of micro-strain ~ 2 × 10− 3. The significant improvement in crystallinity and orientation of crystallites in the GaN film is attributed to the presence of the ZnO buffer layer on quartz substrate and its small lattice mismatch (1.8%) with GaN.© Elsevie

Parameter window of diamond growth on GaN films by microwave plasma chemical vapor deposition

We report here, a detailed study of the parameter window of the deposition pressures to grow the diamond films on GaN coated quartz substrates using microwave plasma deposition technique. Hexagonal GaN films of 5 µm coated on quartz are used as substrates for diamond deposition in the pressure range of 80–140 Torr, using microwave plasma chemical vapor deposition (MPCVD) technique. The diamond films are characterized by scanning electron microscopy, XRD, photoluminescence and Raman spectroscopy. Scanning electron microscope image shows that the nucleation density of the films is high and we can deposit a continuous film for a deposition time ranging for 6–8 h. Oriented growth of diamond has been observed at higher pressure.© Elsevie

New insight into the growth of monolayer MoS2 flakes using an indigenously developed CVD setup: a study on shape evolution and spectroscopy

Monolayer MoS2 has received special consideration owing to its intriguing properties and its potential to revolutionize modern technologies. Atmospheric pressure chemical vapor deposition (APCVD) is the traditional method to grow uniform and high-quality MoS2 flakes in a controlled manner. Little is known, however, about their synthesis mechanism and shape evolution. Herein, we report the synthesis of monolayer MoS2 flakes at atmospheric pressure using a home-built CVD setup. A wide range of shapes are grown from triangular shapes to many point stars, via in-between shapes such as four and six-point stars, using the weight ratio variation of MoO3 and S precursors at different growth temperatures. Further, the properties of the as-grown MoS2 flakes are probed by optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), Raman spectroscopy, photoluminescence (PL), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS), confirming that they are regular and good in quality. Moreover, the synthesis pathway and different shape formations are explained on the basis of the fluid model and the growing rate of Mo, S zigzag edges. Thus, this work provides a better insight into the synthesis mechanism of monolayer MoS2 and represents a significant step towards realizing potential future applications

As-pyrolyzed sugarcane bagasse possessing exotic field emission properties

The present study aims to demonstrate the application of sugarcane bagasse as an excellent field emitter. Field emission property of as-pyrolyzed sugarcane bagasse (p-SBg) before and after the plasma treatment has been investigated. It has been observed that electronic nature of p-SBg transformed from semiconducting to metallic after plasma treatment. Maximum current and turn-on field defined at 10 mu A/cm(2) was found to be 800 mu A/cm(2) and 2.2 V/mu m for as-pyrolyzed sugarcane bagasse (p-SBg) and 25 mu A/cm(2) and 8.4 V/mu m for H-2-plasma treated p-SBg. These values are found to be better than the reported values for graphene and activated carbon. In this report, pyrolysis of bagasse has been carried in a thermal chemical vapor deposition (Th-CVD) system in inert argon atmosphere. Scanning electron microscopy (SEM), X-ray Diffraction (XRD), High-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) have been used to study the structure of both pre and post plasma-treated p-SBg bagasse's sample. HRTEM study reveals that carbonaceous structures such as 3D-nanographene oxide (3D-NGO), graphite nanodots (GNDs), carbon nanotubes (CNTs), and carbon onions are present in both pre-treated and plasma-treated p-SBg. Hence, we envision that the performed study will be a forwarding step to facilitate the application of p-SBg in display devices

Ion irradiation-induced, localized sp(2) to sp(3) hybridized carbon transformation in walls of multiwalled carbon nanotubes

In this report, ion irradiation-induced localized sp(2) to sp(3) hybridized carbon transformation in multiwalled carbon nanotubes (MWCNTs) was observed after irradiating MWCNTs with high-energy Au+8 ions (100 MeV). The used MWCNTs were grown using cobaltocene and benzene as catalyst and carbon source, respectively'by the thermal CVD technique and consist of both unfilled and Co-filled tubes. Prior to irradiation, the MWCNT sample was characterized using scanning electron microscope and micro-Raman and photoluminescence spectrometers. The effect of ion fluence on MWCNT walls and transformation of sp(2) to sp(3) sites was analyzed by Raman spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. We found that as the fluence increased, the localized transformation from sp(2) to sp(3) sites occurred in the walls of MWCNTs, which was evident by the emergence of peak at approximately 1543 cm(-1) associated with the G peak in tetrahedral amorphous carbon (ta-C) and the vanishing of 2D band (2700 cm(-1)). Furthermore, we observed broadening in D and G, with slight shift in their positions and consistent decrease in 2D band intensity, as fluence increased