Prabhat Tiwari | Ucet - Academia.edu (original) (raw)

Papers by Prabhat Tiwari

Research paper thumbnail of Characterization of Ba0.5Sr0.5TiO3 thin film capacitors produced by pulsed laser deposition

Integrated Ferroelectrics, 1995

Abstract High crystallinity Ba0. 5Sr0. 5TiO3 thin films were deposited on LaAlO3 substrates by pu... more Abstract High crystallinity Ba0. 5Sr0. 5TiO3 thin films were deposited on LaAlO3 substrates by pulsed laser deposition. A conductive metallic oxide, SrRuO3, provided not only a good bottom electrode for Ba0. 5Sr0. 5TiO3 but also an excellent seed layer for epitaxial growth ...

Research paper thumbnail of Deposition of epitaxial yttria-stabilized zirconia on single-crystal Si and subsequent growth of an amorphous SiO2 interlayer

Philosophical Magazine Letters, 1995

A processing technique is developed to fabricate single-crystal yttria-stabilized zirconia (YSZ) ... more A processing technique is developed to fabricate single-crystal yttria-stabilized zirconia (YSZ) on amorphous Si02 on (100) single-crystal Si. The YSZ layer shows high crystallinity with an ion beam channelling minimum of 11% from Rutherford backscattering. Even though there is a thick intervening amorphous SiOz layer between the Si and the YSZ, the single-crystal YSZ layer is aligned with the crystal Si. The tilt and rotation variations are 0.64" and 1.1 1" respectively, based on X-ray diffraction o-rocking curves on [lo01 and 4 scans on [202] of YSZ films. The epitaxial nature of the YSZ on the thick Si02 layer (from 10 to 1OOnm) is further confirmed by high-resolution cross-sectional transmission electron microscopy analysis. This processing and the resulting multilayer structure might provide a new option for fabricating innovative microelectronic devices.

Research paper thumbnail of Preparation of diamondlike carbon films by high-intensity pulsed-ion-beam deposition

Journal of Applied Physics, 1994

Gregory P. Johnston, a) Prabhat Tiwari, Donald J. Rej, Harold A. Davis, William J. Waganaar, Ross... more Gregory P. Johnston, a) Prabhat Tiwari, Donald J. Rej, Harold A. Davis, William J. Waganaar, Ross E. Muenchausen, Kevin C. Walter, and Michael Nastasi Los Alamos National Laboratory, MS-E526, Los Alamos, New Mexico 87545 Howard K. Schmidt, Nalin Kumar, ...

Research paper thumbnail of Preparation of high quality YBa2Cu3O7-δ thick films on flexible Ni-based alloy substrates with textured buffer layers

IEEE Transactions on Applied Superconductivity, 1995

High current YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thick films on flexible nickel substr... more High current YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thick films on flexible nickel substrates with textured buffer layers were fabricated. Highly textured yttria-stabilized-zirconia (YSZ) buffer layers were deposited by using ion beam assisted deposition (IBAD). Pulsed laser deposited YBCO films were not only c-axis oriented with respect to the film surface but also strongly in-plane textured. The in-plane mosaic spread of YBCO films was/spl sim/10/spl deg/. A critical current density of 8/spl times/10/sup 5/ A/cm/sup 2/ was obtained at 75 K and zero field for thin YBCO films. It was also demonstrated that thick YBCO films with a high critical current and excellent magnetic field dependence at liquid nitrogen temperature can be obtained on flexible nickel substrates by using the textured buffer layers. Issues encountered in producing the films were discussed.>

Research paper thumbnail of Fabrication of biaxially oriented YBCO on (001) biaxially oriented yttria-stabilized-zirconia on polycrystalline substrates

Ion-assisted, ion-beam sputter deposition is used to obtain (001) biaxially oriented films of cub... more Ion-assisted, ion-beam sputter deposition is used to obtain (001) biaxially oriented films of cubic yttria stabilized zirconia (YSZ) on polycrystalline metal substrates. Yttrium barium copper oxide (YBCO) is then heteroepitaxially pulse laser deposited onto the YSZ. Phi scans of the films show the full-width-half maxima of the YSZ (202) and the YBCO (103) reflections to be 14 deg and 10 deg, respectively. Our best dc transport critical current density measurement for the YBCO is 800,000 A/sq cm at 75 K and 0 T. At 75 K, the total dc transport current in a 1 cm wide YBCO film is 23 A.

Research paper thumbnail of Fabrication and characterization of high temperature superconductor Josephson junctions with a novel device design

IEEE Transactions on Applied Superconductivity, 1995

A unique normal-metal (N) layer construction was used to fabricate high temperature superconducti... more A unique normal-metal (N) layer construction was used to fabricate high temperature superconducting (S) YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// SNS Josephson junctions. The normal-metal included a gradient Pr-doped Y/sub 1-x/Pr/sub x/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// layer which was composed of a light doping (x=0.1) next to both YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// electrodes, a slightly higher doping (x=0.3) towards the center, and a doping concentration of x=0.5 in the middle of the N-layer. A gradient of the doping profile of the N-layer instead of an abrupt one provides good thermal, structural, and chemical compatibility between adjacent regions. The multilayer configuration of the gradient Pr-doped N-layers on YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// showed good growth structure as confirmed by X-ray diffraction and Rutherford backscattering channeling tests. The SNS junctions fabricated in such a way showed resistively shunted junction current vs voltage characteristics above 77 K. Microwave induced Shapiro steps above 77 K and voltage modulation of dc SQUIDs at 77 K were both demonstrated with this technology.>

Research paper thumbnail of Studies of the correlated electron system SmB 6

Physica B-condensed Matter, 1996

We have prepared high-quality, single crystals of SmB 6 under various conditions to improve sampl... more We have prepared high-quality, single crystals of SmB 6 under various conditions to improve sample quality. We have measured the resistivity and magnetic susceptibility from room to liquid-helium temperatures to sort samples. We have applied pulsed magnetic fields as high as 50 T at temperatures as low as 40 mK while measuring resistivity. Our samples are of higher quality than previously known. All solvent-grown, single-crystal samples should be etched to remove a surface conductivity.

Research paper thumbnail of Superconducting Tl2Ba2CaCu2O8 thin films prepared by post-annealing in a flow-through multiple-zone furnace

IEEE Transactions on Applied Superconductivity, 1995

Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ thin films mere prepared first time by use of a multiple-zo... more Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ thin films mere prepared first time by use of a multiple-zone flow-through thallination process. Thallous oxide was volatilized from condensed thallium oxide in a low temperature source zone and convectively transported to a higher temperature thallination zone in which initially amorphous Ba/sub 2/CaCu/sub 2/O/sub 5/ precursor films were located. By careful control of the source temperature, film temperature, flow rate, anneal time, and rates of heat up and cool down, smooth Tl/sub 2/Ba/sub 2/CaCuO/sub 8/ thin films ware prepared on [100] LaAlO/sub 3/ with the following properties: inductive T/sub c/ of 107.6 K and 80% transition width of 1.3 K, transport J/sub c/ at 75 K of 1.3/spl times/10/sup 5/ A/cm/sup 2/, and R/sub s/ at 10 GHz and 80 K of 1.3 m/spl Omega/. The scalability of the process to large area film processing was demonstrated by the preparation of Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ thin films on LaAlO/sub 3/ three-inch diameter wafers.>

Research paper thumbnail of Preparation of high quality YBa/sub 2/Cu/sub 3/O/sub 7-δ/ thick films on flexible Ni-based alloy substrates with textured buffer layers

IEEE Transactions on Applied Superconductivity, 1995

High current YBa2Cu3O7-δ (YBCO) thick films on flexible nickel substrates with textured buffer la... more High current YBa2Cu3O7-δ (YBCO) thick films on flexible nickel substrates with textured buffer layers were fabricated. Highly textured yttria-stabilized-zirconia (YSZ) buffer layers were deposited by using ion beam assisted deposition (IBAD). Pulsed laser deposited YBCO films were not only c-axis oriented with respect to the film surface but also strongly in-plane textured. The in-plane mosaic spread of YBCO films was∼10°.

Research paper thumbnail of Superconducting Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ thin films prepared by post-annealing in a flow-through multiple-zone furnace

IEEE Transactions on Applied Superconductivity, 1995

Tl2Ba2CaCu2O8 thin films mere prepared first time by use of a multiple-zone flow-through thallina... more Tl2Ba2CaCu2O8 thin films mere prepared first time by use of a multiple-zone flow-through thallination process. Thallous oxide was volatilized from condensed thallium oxide in a low temperature source zone and convectively transported to a higher temperature thallination zone in which initially amorphous Ba2CaCu2O5 precursor films were located. By careful control of the source temperature, film temperature, flow rate, anneal time,

Research paper thumbnail of Characterization of Ba0.5Sr0.5TiO3 thin film capacitors produced by pulsed laser deposition

Integrated Ferroelectrics, 1995

Abstract High crystallinity Ba0. 5Sr0. 5TiO3 thin films were deposited on LaAlO3 substrates by pu... more Abstract High crystallinity Ba0. 5Sr0. 5TiO3 thin films were deposited on LaAlO3 substrates by pulsed laser deposition. A conductive metallic oxide, SrRuO3, provided not only a good bottom electrode for Ba0. 5Sr0. 5TiO3 but also an excellent seed layer for epitaxial growth ...

Research paper thumbnail of Deposition of epitaxial yttria-stabilized zirconia on single-crystal Si and subsequent growth of an amorphous SiO2 interlayer

Philosophical Magazine Letters, 1995

A processing technique is developed to fabricate single-crystal yttria-stabilized zirconia (YSZ) ... more A processing technique is developed to fabricate single-crystal yttria-stabilized zirconia (YSZ) on amorphous Si02 on (100) single-crystal Si. The YSZ layer shows high crystallinity with an ion beam channelling minimum of 11% from Rutherford backscattering. Even though there is a thick intervening amorphous SiOz layer between the Si and the YSZ, the single-crystal YSZ layer is aligned with the crystal Si. The tilt and rotation variations are 0.64" and 1.1 1" respectively, based on X-ray diffraction o-rocking curves on [lo01 and 4 scans on [202] of YSZ films. The epitaxial nature of the YSZ on the thick Si02 layer (from 10 to 1OOnm) is further confirmed by high-resolution cross-sectional transmission electron microscopy analysis. This processing and the resulting multilayer structure might provide a new option for fabricating innovative microelectronic devices.

Research paper thumbnail of Preparation of diamondlike carbon films by high-intensity pulsed-ion-beam deposition

Journal of Applied Physics, 1994

Gregory P. Johnston, a) Prabhat Tiwari, Donald J. Rej, Harold A. Davis, William J. Waganaar, Ross... more Gregory P. Johnston, a) Prabhat Tiwari, Donald J. Rej, Harold A. Davis, William J. Waganaar, Ross E. Muenchausen, Kevin C. Walter, and Michael Nastasi Los Alamos National Laboratory, MS-E526, Los Alamos, New Mexico 87545 Howard K. Schmidt, Nalin Kumar, ...

Research paper thumbnail of Preparation of high quality YBa2Cu3O7-δ thick films on flexible Ni-based alloy substrates with textured buffer layers

IEEE Transactions on Applied Superconductivity, 1995

High current YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thick films on flexible nickel substr... more High current YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thick films on flexible nickel substrates with textured buffer layers were fabricated. Highly textured yttria-stabilized-zirconia (YSZ) buffer layers were deposited by using ion beam assisted deposition (IBAD). Pulsed laser deposited YBCO films were not only c-axis oriented with respect to the film surface but also strongly in-plane textured. The in-plane mosaic spread of YBCO films was/spl sim/10/spl deg/. A critical current density of 8/spl times/10/sup 5/ A/cm/sup 2/ was obtained at 75 K and zero field for thin YBCO films. It was also demonstrated that thick YBCO films with a high critical current and excellent magnetic field dependence at liquid nitrogen temperature can be obtained on flexible nickel substrates by using the textured buffer layers. Issues encountered in producing the films were discussed.>

Research paper thumbnail of Fabrication of biaxially oriented YBCO on (001) biaxially oriented yttria-stabilized-zirconia on polycrystalline substrates

Ion-assisted, ion-beam sputter deposition is used to obtain (001) biaxially oriented films of cub... more Ion-assisted, ion-beam sputter deposition is used to obtain (001) biaxially oriented films of cubic yttria stabilized zirconia (YSZ) on polycrystalline metal substrates. Yttrium barium copper oxide (YBCO) is then heteroepitaxially pulse laser deposited onto the YSZ. Phi scans of the films show the full-width-half maxima of the YSZ (202) and the YBCO (103) reflections to be 14 deg and 10 deg, respectively. Our best dc transport critical current density measurement for the YBCO is 800,000 A/sq cm at 75 K and 0 T. At 75 K, the total dc transport current in a 1 cm wide YBCO film is 23 A.

Research paper thumbnail of Fabrication and characterization of high temperature superconductor Josephson junctions with a novel device design

IEEE Transactions on Applied Superconductivity, 1995

A unique normal-metal (N) layer construction was used to fabricate high temperature superconducti... more A unique normal-metal (N) layer construction was used to fabricate high temperature superconducting (S) YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// SNS Josephson junctions. The normal-metal included a gradient Pr-doped Y/sub 1-x/Pr/sub x/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// layer which was composed of a light doping (x=0.1) next to both YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// electrodes, a slightly higher doping (x=0.3) towards the center, and a doping concentration of x=0.5 in the middle of the N-layer. A gradient of the doping profile of the N-layer instead of an abrupt one provides good thermal, structural, and chemical compatibility between adjacent regions. The multilayer configuration of the gradient Pr-doped N-layers on YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// showed good growth structure as confirmed by X-ray diffraction and Rutherford backscattering channeling tests. The SNS junctions fabricated in such a way showed resistively shunted junction current vs voltage characteristics above 77 K. Microwave induced Shapiro steps above 77 K and voltage modulation of dc SQUIDs at 77 K were both demonstrated with this technology.>

Research paper thumbnail of Studies of the correlated electron system SmB 6

Physica B-condensed Matter, 1996

We have prepared high-quality, single crystals of SmB 6 under various conditions to improve sampl... more We have prepared high-quality, single crystals of SmB 6 under various conditions to improve sample quality. We have measured the resistivity and magnetic susceptibility from room to liquid-helium temperatures to sort samples. We have applied pulsed magnetic fields as high as 50 T at temperatures as low as 40 mK while measuring resistivity. Our samples are of higher quality than previously known. All solvent-grown, single-crystal samples should be etched to remove a surface conductivity.

Research paper thumbnail of Superconducting Tl2Ba2CaCu2O8 thin films prepared by post-annealing in a flow-through multiple-zone furnace

IEEE Transactions on Applied Superconductivity, 1995

Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ thin films mere prepared first time by use of a multiple-zo... more Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ thin films mere prepared first time by use of a multiple-zone flow-through thallination process. Thallous oxide was volatilized from condensed thallium oxide in a low temperature source zone and convectively transported to a higher temperature thallination zone in which initially amorphous Ba/sub 2/CaCu/sub 2/O/sub 5/ precursor films were located. By careful control of the source temperature, film temperature, flow rate, anneal time, and rates of heat up and cool down, smooth Tl/sub 2/Ba/sub 2/CaCuO/sub 8/ thin films ware prepared on [100] LaAlO/sub 3/ with the following properties: inductive T/sub c/ of 107.6 K and 80% transition width of 1.3 K, transport J/sub c/ at 75 K of 1.3/spl times/10/sup 5/ A/cm/sup 2/, and R/sub s/ at 10 GHz and 80 K of 1.3 m/spl Omega/. The scalability of the process to large area film processing was demonstrated by the preparation of Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ thin films on LaAlO/sub 3/ three-inch diameter wafers.>

Research paper thumbnail of Preparation of high quality YBa/sub 2/Cu/sub 3/O/sub 7-δ/ thick films on flexible Ni-based alloy substrates with textured buffer layers

IEEE Transactions on Applied Superconductivity, 1995

High current YBa2Cu3O7-δ (YBCO) thick films on flexible nickel substrates with textured buffer la... more High current YBa2Cu3O7-δ (YBCO) thick films on flexible nickel substrates with textured buffer layers were fabricated. Highly textured yttria-stabilized-zirconia (YSZ) buffer layers were deposited by using ion beam assisted deposition (IBAD). Pulsed laser deposited YBCO films were not only c-axis oriented with respect to the film surface but also strongly in-plane textured. The in-plane mosaic spread of YBCO films was∼10°.

Research paper thumbnail of Superconducting Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ thin films prepared by post-annealing in a flow-through multiple-zone furnace

IEEE Transactions on Applied Superconductivity, 1995

Tl2Ba2CaCu2O8 thin films mere prepared first time by use of a multiple-zone flow-through thallina... more Tl2Ba2CaCu2O8 thin films mere prepared first time by use of a multiple-zone flow-through thallination process. Thallous oxide was volatilized from condensed thallium oxide in a low temperature source zone and convectively transported to a higher temperature thallination zone in which initially amorphous Ba2CaCu2O5 precursor films were located. By careful control of the source temperature, film temperature, flow rate, anneal time,