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Now showing items 1 - 16 of 18

  • High precision measurement of Compton scattering in the 5 GeV region

    Ambrozewicz, P.   Ye, L.   Prok, Y.   Larin, I   Ahmidouch, A.   Baker, K.   Baturin, V   Benton, L.   Bernstein, A.   Burkert, V   Clinton, E.   Cole, P. L.   Collins, P.   Dale, D.   Danagoulian, S.   Davidenko, G.   Demirchyan, R.   Deur, A.   Dolgolenko, A.   Dutta, D.   Dzyubenko, G.   Evdokimov, A.   Fedotov, G.   Feng, J.   Gabrielyan, M.   Gan, L.   Gao, H.   Gasparian, A.   Gevorkyan, N.   Gevorkyan, S.   Glamazdin, A.   Goryachev, V   Guo, L.   Gyurjyan, V   Hardy, K.   He, J.   Isupov, E.   Ito, M. M.   Jiang, L.   Kang, H.   Kashy, D.   Khandaker, M.   Kingsberry, P.   Klein, F.   Kolarkar, A.   Konchatnyi, M.   Korchin, O.   Korsch, W.   Kosinov, O.   Kowalski, S.   Kubantsev, M.   Kubarovsky, A.   Kubarovsky, V   Lawrence, D.   Li, X.   Levillain, M.   Lu, H.   Ma, L.   Martel, P.   Matveev, V   McNulty, D.   Mecking, B.   Micherdzinska, A.   Milbrath, B.   Minehart, R.   Miskimen, R.   Mochalov, V   Morrison, B.   Mtingwa, S.   Nakagawa, I   Overby, S.   Pasyuk, E.   Payen, M.   Park, K.   Pedroni, R.   Phelps, W.   Protopopescu, D.   Rimal, D.   Ritchie, B. G.   Romanov, D.   Salgado, C.   Shahinyan, A.   Sitnikov, A.   Sober, D.   Stepanyan, S.   Stephens, W.   Tarasov, V   Taylor, S.   Teymurazyan, A.   Underwood, J.   Vasiliev, A.   Vishnyakov, V.   Weygand, D. P.   Wood, M.   Zhang, Y.   Zhou, S.   Zihlmann, B.  

    The cross section of atomic electron Compton scattering gamma + e -> gamma' + e' was measured in the 4.400-5.475 GeV photon beam energy region by the PrimEx collaboration at Jefferson Lab with an accuracy of 2.6% and less. The results are consistent with theoretical predictions that include next-to-leading order radiative corrections. The measurements provide the first high precision test of this elementary QED process at beam energies greater than 0.1 GeV. (C) 2019 The Author(s). Published by Elsevier B.V.
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  • Ion sputter-deposition and in-air crystallisation of Cr2AlC films

    Vishnyakov, V.   Crisan, O.   Dobrosz, P.   Colligon, J.S.  

    Ternary alloys of composition close to Cr 2AlC have been deposited by ion beam sputtering onto unheated and heated to 380degC Si substrates. As-deposited films are amorphous. Annealing of the film in vacuum at 700degC leads to crystallisation with 39.2 nm crystallites. Crystallisation also can be achieved by annealing in air but there is also partial oxidation of the film surface to the depth of approximately 120 nm, which represents an oxide layer less than 5% of the total film thickness. There is an increase of lattice size along the c-axis during crystallisation in air, which indicates a small incorporation of oxygen. Film structure and crystallisation have also been analysed by Raman spectroscopy. Changes in Raman spectra in Cr 2AlC have been correlated with the film crystallisation and it was observed that MAX-phase related peaks become clearly defined for the crystallised film. [All rights reserved Elsevier].
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  • Ion sputter-deposition and in-air crystallisation of Cr2AlC films

    Vishnyakov, V.   Crisan, O.   Dobrosz, P.   Colligon, J. S.  

    Ternary alloys of composition close to Cr2AlC have been deposited by ion beam sputtering onto unheated and heated to 380 degrees C Si substrates. As-deposited films are amorphous. Annealing of the film in vacuum at 700 degrees C leads to crystallisation with 39.2 nm crystallites. Crystallisation also can be achieved by annealing in air but there is also partial oxidation of the film surface to the depth of approximately 120 nm, which represents an oxide layer less than 5% of the total film thickness. There is an increase of lattice size along the c-axis during crystallisation in air, which indicates a small incorporation of oxygen. Film structure and crystallisation have also been analysed by Raman spectroscopy. Changes in Raman spectra in Cr2AlC have been correlated with the film crystallisation and it was observed that MAX-phase related peaks become clearly defined for the crystallised film. Crown Copyright (c) 2013 Published by Elsevier Ltd. All rights reserved.
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  • The FLINT setup for studying cumulative processes with photon production

    Alekseev, I.   Belogurov, S.   Vishnyakov, V.   Golutvin, A.   Goryachev, V.   Dzyubenko, G.   Dolgolenko, A.   Zagreev, B.   Kiselev, S.   Korol'ko, I.   Larin, I.   Leksin, G.   Mikhailov, K.   Polozov, P.   Prokudin, M.   Svirida, D.   Stavinskii, A.   Stolin, V.   Sharkov, G.  

    A setup is developed at the Institute for Theoretical and Experimental Physics for studying cumulative processes in hA and AA interactions with photon and pi 0-meson production in the central region of rapidities at high transverse momenta. Lead glass calorimeters and a charged particle rejection system are the main components of the setup. A fast trigger for a high-energy cumulative particle, based on detection of Cherenkov radiation in the lead glasses, is realized in the setup.
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  • Nuclear targets for a precision measurement of the neutral pion radiative width

    Martel, P.   Clinton, E.   McWilliams, R.   Lawrence, D.   Miskimen, R.   Ahmidouch, A.   Ambrozewicz, P.   Asratyan, A.   Baker, K.   Benton, L.   Bernstein, A.   Cole, P.   Collins, P.   Dale, D.   Danagoulian, S.   Davidenko, G.   Demirchyan, R.   Deur, A.   Dolgolenko, A.   Dzyubenko, G.   Evdokimov, A.   Feng, J.   Gabrielyan, M.   Gan, L.   Gasparian, A.   Glamazdin, O.   Goryachev, V.   Gyurjyan, V.   Hardy, K.   Ito, M.   Khandaker, M.   Kingsberry, P.   Kolarkar, A.   Konchatnyi, M.   Korchin, O.   Korsch, W.   Kowalski, S.   Kubantsev, M.   Kubarovsky, V.   Larin, I.   Matveev, V.   McNulty, D.   Milbrath, B.   Minehart, R.   Mochalov, V.   Mtingwa, S.   Nakagawa, I.   Overby, S.   Pasyuk, E.   Payen, M.   Pedroni, R.   Prok, Y.   Ritchie, B.   Salgado, C.   Sitnikov, A.   Sober, D.   Stephens, W.   Teymurazyan, A.   Underwood, J.   Vasiliev, A.   Verebryusov, V.   Vishnyakov, V.   Wood, M.  

    A technique is presented for precision measurements of the area densities, rho T, of approximately 5% radiation length carbon and (208)Pb targets used in an experiment at Jefferson Laboratory to measure the neutral pion radiative width. The precision obtained in the area density for the carbon target is +/- 0.050%, and that obtained for the lead target through an X-ray attenuation technique is +/- 0.43%. (C) 2009 Elsevier B.V. All rights reserved.
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  • Photocatalytic activity of reactively sputtered and directly sputtered titania coatings

    Farahani, N.   Kelly, P. J.   West, G.   Ratova, M.   Hill, C.   Vishnyakov, V.  

    It is well known that, depending on deposition conditions, the structure of titania coatings may be amorphous, anatase or rutile, or a mixture of phases, and that the anatase phase is the most promising photocatalyst for the degradation of organic pollutants. The formation of anatase depends on the energy delivered to the growing film, which in turn depends on the operating parameters chosen. In this study, titania coatings have been deposited onto glass substrates by pulsed magnetron sputtering both from metallic targets in reactive mode and directly from oxide powder targets. The as-deposited coatings were analysed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and micro-Raman spectroscopy. Selected coatings were then annealed at temperatures in the range of 400-700 degrees C and re-analysed. The photocatalytic activity of the coatings has been investigated through measurements of the degradation of organic dyes, such as methyl orange, under the influence of UV and fluorescent light sources. Further sets of coatings have been produced both from metallic and powder targets in which the titania is doped with tungsten. These coatings have also been analysed and the influence of the dopant element on photocatalytic activity has been investigated. It has been found that, after annealing, both sputtering processes produced photo-active surfaces and that activity increased with increasing tungsten content over the range tested. Furthermore, the activity of these coatings under exposure to fluorescent lamps was some 50-60% of that observed under exposure to UV lamps. (C) 2011 Elsevier B.V. All rights reserved.
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  • Thermally induced phase and photocatalytic activity evolution of polymorphous titania

    Mandjoub, N.   Allen, N.   Kelly, P.   Vishnyakov, V.  

    TiO(2) nano-powders were prepared by hydrolysing titanium tetraisopropoxide at room temperature. The resulting products were dried at 382 K and then annealed at temperatures up to 1172 K for 1 h. Raman analysis showed different titania phase structures depending on the thermal treatment. A mixture of brookite and anatase was observed in the as-prepared sample and after thermal treatment at 472 K and 672 K, a mixture of anatase and rutile was observed at 872 K and 972 K, while a pure rutile phase was identified at 1172 K. Quantitative XRD analysis revealed nano-powders phase composition and crystallite sizes. The photoactivity was assessed by photoinduced degradation of methyl orange. All anatase-brookite compositions have showed high photoactivity while the best values were observed for ;the sample calcined at 472 K. (C) 2010 Elsevier B.V. All rights reserved.
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  • Structure formation of TiB2-TiC-B4C-C hetero-modulus ceramics via reaction hot pressing

    Popov, O.   Chornobuk, S.   Vishnyakov, V.  

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  • Ti3SiC2-formation during Ti–C–Si multilayer deposition by magnetron sputtering at 650?°C

    Vishnyakov, V.   Lu, J.   Eklund, P.   Hultman, L.   Colligon, J.  

    Titanium Silicon Carbide films were deposited from three separate magnetrons with elemental targets onto Si wafer substrates. The substrate was moved in a circular motion such that the substrate faces each magnetron in turn and only one atomic species (Ti, Si or C) is deposited at a time. This allows layer-by-layer film deposition. Material average composition was determined to Ti0.47Si0.14C0.39 by energy-dispersive X-ray spectroscopy. High-resolution transmission electron microscopy and Raman spectroscopy were used to gain insights into thin film atomic structure arrangements. Using this new deposition technique formation of Ti3SiC2 MAX phase was obtained at a deposition temperature of 650 °C, while at lower temperatures only silicides and carbides are formed. Significant sharpening of Raman E2g and Ag peaks associated with Ti3SiC2 formation was observed.
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  • Ti3SiC2-formation during Ti-C-Si multilayer deposition by magnetron sputtering at 650 degrees C

    Vishnyakov, V.   Lu, J.   Eklund, P.   Hultman, L.   Colligon, J.  

    Titanium Silicon Carbide films were deposited from three separate magnetrons with elemental targets onto Si wafer substrates. The substrate was moved in a circular motion such that the substrate faces each magnetron in turn and only one atomic species (Ti, Si or C) is deposited at a time. This allows layer-bylayer film deposition. Material average composition was determined to Ti0.47Si0.14C0.39 by energy-dispersive X-ray spectroscopy. High-resolution transmission electron microscopy and Raman spectroscopy were used to gain insights into thin film atomic structure arrangements. Using this new deposition technique formation of Ti3SiC2 MAX phase was obtained at a deposition temperature of 650 degrees C, while at lower temperatures only silicides and carbides are formed. Significant sharpening of Raman E-2g and A(g) peaks associated with Ti3SiC2 formation was observed. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.
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  • Nanoparticle formation by the debris produced by femtosecond laser ablation of silicon in ambient air

    Semaltianos, N. G.   Perrie, W.   Vishnyakov, V.   Murray, R.   Williams, C. J.   Edwardson, S. P.   Dearden, G.   French, P.   Sharp, M.   Logothetidis, S.   Watkins, K. G.  

    The debris produced by fermosecond laser ablation (180 fs, 775 nm, 1 kHz) of Si in ambient air is deposited around the ablated craters in a circular zone with diameters between similar to 40 and 300 gm for laser fluences (F) in the region F=0.2-8 J/cm(2). The debris consists of nanoparticles. The mean height of the nanoparticles increases with laser fluence (from similar to 70 to 500 nm for fluences in the range F=0.25-4.38 J/cm(2)) but at high fluences (F= 8 J/cm(2)) becomes equal to similar to 170 nm. The average horizontal dimension of the nanoparticles increases with laser fluence. Their average vertical dimension increases in proportion to their average horizontal dimension, but at high fluences becomes much smaller than their corresponding average horizontal dimension. The nanoparticles were found to be single crystals with d spacing of 1.71 +/- 0.09 angstrom (corresponding to {311}). (C) 2007 Elsevier B.V. All rights reserved.
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  • Topography development on selected inert gas and self-ion bombarded Si

    Vishnyakov, V.   Carter, G.   Goddard, D.T.   Nobes, M.J.  

    An AFM and SEM study of the topography induced by 20 keV Si + , Ar + and Xe + ion bombardment of Si at 45deg incidence angles and for ion fluences between 10 17 and 10 20 cm -2 has been undertaken at room temperature. All species generate an atomic scale random roughness, the magnitude of which does not increase extensively with ion fluence, suggesting the operation of a local relaxation process. This nanometre scale roughness forms, for Ar and Xe, a background for coarser micrometre scale structures such as pits, chevrons and waves. Apart from isolated etch pits Si + irradiation generates no repetitive micrometre scale structures. Xe + irradiation produces well developed transverse waves while Ar + irradiation results in isolated chevron-like etch pit trains and ripple patches. This latter pattern evolves, with increasing ion fluence, to a corrugated facet structure. The reasons for the different behaviours are still not fully clarified
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  • SEM and Raman study of thermally treated TiO(2) anatase nanopowders: Influence of calcination on photocatalytic activity

    Mandjoub, N.   Allen, N.   Kelly, P.   Vishnyakov, V.  

    Titania (TiO(2)) nanopowders called PC 500, synthesised by the sulphate process, were annealed in air at temperatures of up to 1022K for 30 min. The X-ray Diffraction (XRD) indicates that the thermal annealing resulted in coarsening of the average crystallite size from 13 to 72 nm. However, Scanning Electron Microscopy (SEM) reveals persistence of platelet-like structures which survive up to temperatures around 900K. This implies that the crystals at least partially grow within the plates in 2D confinement. This implies that direct usage of Scherrer equation in this case should be approached with care. Raman spectra peak positions and the Full-Width-at-Half-Maximum (FWHM) values changed considerably after calcinations crystal growth, while, material composition and oxygen content remain unchanged. The Raman peak behaviour can be cautiously attributed to the first order phonon confinement phenomena, but both, 20 and 3D models of confinement should be accounted. The highest photoactivity, as indicated by photoinduced degradation of a mono azo dye methyl-orange (C(14)H(14)N(3)SO(3)Na), was observed in material treated at 773 K. (C) 2010 Elsevier B.V. All rights reserved.
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  • Behavior of Semi-volatile Particles under a Laser and Electron Beam - Influence on the Quality of Analytical Results

    Worobiec, A.   Potgieter-Vermaak, S.   Darchuk, L.   Vishnyakov, V.   Potgieter, H.   Van Grieken, R.  

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  • Ne+, Ar+ and Xe+ ion bombardment induced and suppressed topography on Si

    Vishnyakov, V.   Carter, G.  

    The topographic evolution of Si irradiated at room temperature with Ne+, Ar+ and Xe+ ions in the energy range 5-40 keV at 45° to the substrate normal at high ion fluences has been studied. Other than isolated etch pits no topography results from Ne+ bombardment at all energies or from Ar+ bombardment at 5 and 10 keV. Ar+ bombardment at 20 keV, however, initially produces transverse low-amplitude waves which transform, with increasing erosion, into larger amplitude corrugated and facetted wavelike structures. The present data do not conform to existing model predictions but do suggest that, technically, light low energy gas ions can be used to inhibit roughening during sputtering erosion. Xe+ ion bombardment, on the other hand, produces clearly-defined transverse wave structures on the surface, which are inimical to sputter-profiling applications. However, Xe+ bombardment-induced morphology, when exposed to further 20 keV Ne+ or 10 keV Ar+ bombardment loses its rippled habit, indicating that such irradiation can be employed to cure the deleterious roughening processes as well as inhibit roughening.
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  • Scanning tunnelling microscopy observations of the evolution of small-scale topography on gold surfaces following irradiation with low-energy argon ions

    Vishnyakov, V.   Donnelly, S. E.   Carter, G.  

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