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Sharma, S.K.,Kaur, N.,Lee, B.,Kim, C.,Lee, S.,Kim, D.Y. Elsevier 2015 Current Applied Physics Vol.15 No.suppl2
Well-aligned Y-doped ZnO (YZO) nanorod arrays were synthesized on YZO-seeded quartz glass substrates by hydrothermal method. The diameter and the density of the YZO nanorods were effectively controlled by modifying the grain morphology of the seed layer. The microstructures of the seed grains were manipulated by vacuum annealing (300-800 <SUP>o</SUP>C), and the texture of the seed grains significantly affected the physical properties of the YZO nanorods. From analyses of microstructural and optical properties of the YZO nanorods, the size and the density of the YZO nanorods were observed to strongly depend on those of the seed grains that could be controlled by annealing temperatures. The simple and scalable method proposed here could be beneficial for the controllable growth of vertically-aligned YZO nanorod arrays and their nano-device fabrications.
Y-doped zinc oxide (YZO) nanoflowers, microstructural analysis and test their antibacterial activity
Sharma, S.K.,Sudheer Pamidimarri, D.V.N.,Kim, D.Y.,Na, J.G. Elsevier 2015 Materials Science and Engineering C Vol.53 No.-
Self-assembled 3D flower-like yttrium-doped zinc oxide (YZO) microstructures composed of nanorods were prepared by hydrothermal-precipitation, and tested their antibacterial activity. The morphological, structural, and compositional properties of YZO nanoflowers were characterized by various techniques, which confirmed a well-crystallized wurtzite hexagonal phase. X-ray photoelectron spectroscopy (XPS) of YZO nanopowder showed the 3d core level spectra of yttrium (Y), which formed by two components at about 158.2eV (3d<SUB>5/2</SUB>) and 160.4eV (3d<SUB>3/2</SUB>). The antibacterial activity of YZO nanoflowers were investigated using both gram-positive and gram-negative microorganisms. Enhancement in antibacterial activity was observed by the incorporation of yttrium (Y: 2at.%) of nanorod-based-flowers because of increased surface area. The prepared YZO nanocomposite showed potential as an antibacterial agent with applications in controlling the spread of infections and also the ability of fast antibacterial activity which can hinder the re-emergence of infection.
Ferromagnetism in Chemically-synthesized Co-doped ZnO
샤런드라쿠마르,Y. J. Kim,B. H. Koo,최희규,이찬규,S. K. Sharma,M. Knobel,S. Gautam,K. H. Chae 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.3
We report room temperature ferromagnetism (RTFM) in Co-doped ZnO (Zn1−xCoxO; x = 0.01 − 0.05) powder synthesized using a co-precipitation method. Our magnetometry data reveal a weak FM behavior at RT in the range 0.01 < x < 0.05. FM by magnetic FM moment steadily decreases with increasing dopant. The O K-edge near-edge X-ray absorption fine structure (NEXAFS) spectra indicate that O vacancies increases with increasing Co concentration and that the sample with x ≥ 0.03 has more broadening at 535 and 540 eV, which may be due to the oxygen vacancies. Co in the ZnO host reveals a +2 oxidation state via the K edge NEXAFS spectra.
Mole-controlled growth of Y-doped ZnO nanostructures by hydrothermal method
Heo, S.,Lee, Y.,Sharma, S.K.,Lee, S.,Kim, D.Y. Elsevier 2014 Current Applied Physics Vol.14 No.11
We investigated the mole-controlled growth of Y-doped ZnO (YZO) nanostructures by the hydrothermal synthesis techniques. Through controlling the aqueous solution's mole concentration, we could modify the morphological and structural properties of YZO. The shape of YZO becomes a nanometer-sized rod when using a relatively low mole concentration, whereas the morphology is changed to be flat and mosaic when using a relatively high mole concentration. Since the aqueous solution's mole concentration decides the amount of hydroxide, we ascribe the mole-controlled morphological changes to the alteration of chemical potential during the hydrothermal chemical reaction.
Structural and magnetic properties of chemically synthesized Fe doped ZnO
Kumar, Shalendra,Kim, Y. J.,Koo, B. H.,Sharma, S. K.,Vargas, J. M.,Knobel, M.,Gautam, S.,Chae, K. H.,Kim, D. K.,Kim, Y. K.,Lee, C. G. American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7
<P>We report on the synthesis of Fe-doped ZnO with nominal composition of Zn0.99Fe0.01O by using a coprecipitation method. X-ray diffraction and selective area electron diffraction studies reveal a single phase wurtzite crystal structure without any secondary phase. Field emission transmission electron microscopy measurements infer that Zn0.99Fe0.01O have nanorod-type microstructures. Magnetic hysteresis measurement performed at different temperatures show that Zn0.99Fe0.01O exhibits a weak ferromagnetic behavior at room temperature. A detailed investigation of the electronic and local structure using O K-, Fe L-3,L-2 near edge x-ray absorption fine structure suggests that Fe is substituting Zn in ZnO matrix and is in Fe3+ state. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3073933]</P>
Varshney, M.,Sharma, A.,Shin, H.J.,Lee, H.H.,Jeon, T.Y.,Lee, B.H.,Chae, K.H.,Won, S.O. Pergamon Press 2017 The Journal of physics and chemistry of solids Vol.110 No.-
Carbon-supported Pt and PtNi nanoparticles (NPs) were synthesized using a borohydride reduction method. Structural properties were studied by synchrotron X-ray diffraction (XRD) and the size/shape of the NPs was determined by transmission electron microscope (TEM). X-ray absorption spectroscopy with its two amendments; X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), has been employed to investigate the local electronic/atomic structure surrounding the Pt and Ni atoms. XANES results, at Pt L<SUB>3</SUB>-edge and Ni K-edge, have shown fractional oxidation of Pt and Ni atoms. The Pt3Ni1NPs have exhibited a lower bond distance of Pt-Ni shell and higher coordination number of Pt-Ni shells, indicating the alloy formation between Pt and Ni. We further have demonstrated that the Pt and PtNi NPs can serve as effective photocatalysts towards the degradation of water pollutant dye (methyl orange (MO)). By considering the interband charge-transfer of Pt (5d →6sp), a tentative mechanism is proposed to understand the photocatalytic degradation of MO dye molecules by Pt/PtNi NPs under the light irradiation.
3-Naphthylindoles as new promising candidate antioxidant, antibacterial, and antibiofilm agents
Sharma, K.,Baral, E. R.,Akhtar, M. S.,Lee, Y. R.,Kim, S. H.,Wee, Y. J. Springer Science + Business Media 2017 Research on chemical intermediates Vol.43 No.4
<P>Indole derivatives have attracted significant attention in organic synthesis and bioactivity research owing to their substantial biological activity. In the present study, several 3-naphthylindole analogues were synthesized by direct arylation of 1-diazonaphthalene-2-(1H)-ones by rhodium(II)-catalyzed cross-coupling reaction and their antioxidant and antibacterial properties evaluated. Among the analogues tested, compound 3m displayed the highest antioxidant activity [as evaluated by ferric reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) tests], whereas compound 3c exhibited the lowest activity. The compounds were also screened against biofilm-forming bacterial species (Gram-negative Escherichia coli and Pseudomonas aeruginosa as well as Gram-positive Staphylococcus aureus and Bacillus cereus). Compounds 3b, i, j, p displayed potent antibacterial activity against E. coli. Similarly, compound 3p exhibited activity superior to quercetin (4.2 mu g/mL) by completely inhibiting biofilm formation by E. coli. Moreover, the half-maximal inhibitory concentration (IC50) values of compounds 3e, j against B. cereus were comparable to that of standard quercetin.</P>
Use of 1.7 kV and 3.3 kV SiC Diodes in Si-IGBT/ SiC Hybrid Technology
Y. K. Sharma,L. Coulbeck,P. Mumby-Croft,Y. Wang,I. Deviny 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.9
Replacing conventional Si diodes with SiC diodes in Si insulated gate bipolar transistor (IGBT) modules is advantageous as it can reduce power losses significantly. Also, the fast switching nature of the SiC diode will allow Si IGBTs to operate at their full high-switching-speed potential, which at present conventional Si diodes cannot do. In this work, the electrical test results for Si-IGBT/4HSiC- Schottky hybrid substrates (hybrid SiC substrates) are presented. These substrates are built for two voltage ratings, 1.7 kV and 3.3 kV. Comparisons of the 1.7 kV and the 3.3 kV Si-IGBT/Si-diode substrates (Si substrates) at room temperature (20 C, RT) and high temperature (H125 C, HT) have shown that the switching losses in hybrid SiC substrates are miniscule as compared to those in Si substrates but necessary steps are required to mitigate the ringing observed in the current waveforms. Also, the effect of design variations on the electrical performance of 1.7 kV, 50 A diodes is reported here. These variations are made in the active and termination regions of the device.