Pankaj Srivastava - Academia.edu (original) (raw)
Uploads
Papers by Pankaj Srivastava
Journal of Physics: Condensed Matter, 1996
UvA-DARE (Digital Academic Repository) Polarized x-ray absorption spectroscopy of unoccupied elec... more UvA-DARE (Digital Academic Repository) Polarized x-ray absorption spectroscopy of unoccupied electronic states near the Fermi level in the Bi2Sr2CaCu2O8+x system
Physica C: Superconductivity, 1995
Polarised X-ray absorption (XAS) measurements have been made on high-quality superconducting Bi2S... more Polarised X-ray absorption (XAS) measurements have been made on high-quality superconducting Bi2Sr2CaCu2Os+y (Bi2212) single crystals to investigate the microscopic electronic structure in the normal and superconducting state of the system. The Cu L 3 XAS results led us to conclude that either there are no holes of 3dzz symmetry, or if any, they are insignificant in number. On the other hand, the O K XAS results show the presence of a significant density of p~ symmetry orbitals for itinerant holes. An increase in the 3d9_L/3d 9 ratio estimated from the Cu L 3 XAS measurements was observed while going from the normal to the superconducting state of the system. The results are discussed in the light of the structural distortions taking place below T c.
Advanced Materials Letters
Semiconductor Science and Technology, 2003
Silicon oxide-silicon nitride (ON) stack layers have been formed by mercury sensitized photochemi... more Silicon oxide-silicon nitride (ON) stack layers have been formed by mercury sensitized photochemical vapour deposition (photo-CVD) of silicon nitride layers over thermally grown and photo-CVD deposited silicon oxide layers on p-type Si (100) substrates. The properties of these two groups of samples were studied using Fourier transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS) and capacitance-voltage measurements. Photo-CVD deposited nitrogen-rich
Scripta Materialia, 2010
A systematic study of hydrogenated amorphous silicon nitride films deposited by varying gas flow ... more A systematic study of hydrogenated amorphous silicon nitride films deposited by varying gas flow rate ratio (R = SiH 4 /NH 3) using Photo-Chemical Vapour Deposition reveal that as R is increased, dominant phase changes from silicon oxynitride to silicon nitride with embedded silicon nanoclusters. The change in photoluminescence spectral features in these films is attributed to quantum confinement effect. The results suggest that hydrogen plays a crucial role in overall phase evolution and in-situ formation of Si nanoclusters embedded in silicon nitride matrix.
Modern Physics Letters B, 1990
This study is based on our hypothesis that predicts the possibility of Y–Ba–Ni–O superconductor. ... more This study is based on our hypothesis that predicts the possibility of Y–Ba–Ni–O superconductor. A comparative study of Y–Ba–Cu–O and 10% Ni doped Y–Ba–Cu–O (having T c as high as 84 K) is presented. Resistivity, XRD, oxygen content and Cu–K-XANES measurements are reported.
Journal of Synchrotron Radiation, 1999
ABSTRACT
Journal of Magnetism and Magnetic Materials, 1999
ABSTRACT
Current Applied Physics, 2010
Nanoparticle Pb 1Àx Fe x Se (0.00 6 x 6 0.16) thin films have been deposited on quartz, glass and... more Nanoparticle Pb 1Àx Fe x Se (0.00 6 x 6 0.16) thin films have been deposited on quartz, glass and silicon substrates by chemical bath deposition technique. Structural and optical properties of the films with iron concentration 0.00 6 x 6 0.16 indicate that the films grow as single-phase Pb 1Àx Fe x Se ternary alloys with rocksalt structure and with direct optical band gaps (E g) that increase with decrease in grain size and have values larger than 0.28 eV of the bulk PbSe. Average grain size in films grown at fixed bath temperature T b of 85°C is observed to decrease from 72 to 22 nm whereas lattice parameter is observed to increase from 6.12 to 6.14 Å with increase in Fe concentration from x = 0.00 to x = 0.16. The observed blue shift in film materials originates from quantum confinement in the nanograins. Nanoparticle Pb 1Àx Fe x Se/ single crystal Si heterojunctions show rectifying behavior. On illumination of heterojunctions with visible light current is observed to increase in forward and reverse bias. This increase in current in the presence of visible light is considered to be due to carrier multiplication by Auger electron emission.
Applied Physics A, 2012
ABSTRACT We report variable temperature resistivity measurements and mechanisms related to electr... more ABSTRACT We report variable temperature resistivity measurements and mechanisms related to electrical conduction in 200 keV Ni2+ ion implanted ZnO thin films deposited by vapor phase transport. The dc electrical resistivity versus temperature curves show that all polycrystalline ZnO films are semiconducting in nature. In the room temperature range they exhibit band conduction and conduction due to thermionic emission of electrons from grain boundaries present in the polycrystalline films. In the low temperature range, nearest neighbor hopping (NNH) and variable range hopping (VRH) conduction are observed. The detailed conduction mechanism of these films and the effects of grain boundary (GB) barriers on the electrical conduction process are discussed. An attempt is made to correlate electrical conduction behavior and previously observed room temperature ferromagnetism of these films.
Europhysics Letters (epl), 2010
We report the impact of post-deposition thermal annealing (in nitrogen ambient) on the evolution ... more We report the impact of post-deposition thermal annealing (in nitrogen ambient) on the evolution of an interfacial layer between a hydrogenated amorphous silicon nitride (a-SiNx :H) thin film and a Si(100) substrate and its correlation with electrical properties. X-ray reflectivity measurements reveal that the SiNx films under different post annealing temperatures demonstrate variation in the density, thickness and roughness. Also it is found that the interface state density (Dit) is directly related to the interfacial layer density of the film rather than to the surface and interface roughness.
Bulletin of Materials Science, 2006
Superconducting bulk MgB 2 samples have been synthesized by employing sintering technique without... more Superconducting bulk MgB 2 samples have been synthesized by employing sintering technique without using any additional process steps, generally undertaken in view of the substantial loss of magnesium, during heat treatment. Starting with Mg rich powders having different atomic ratios of Mg : B, as against the nominally required Mg : B = 1 : 2 ratio, we have obtained superconducting MgB 2 samples of different characteristics. The effect of excess Mg in the starting mixture and processing temperature on the phase-formation, transition temperature (T C ) and critical current density (J C ) have been investigated by electrical transport and a.c. susceptibility measurements. The X-ray diffraction and X-ray photoelectron spectroscopic analyses of MgB 2 bulk samples have been carried out to understand the role of excess Mg and the effect of processing temperature. It is established that MgB 2 samples with high critical current density can be synthesized from a Mg rich powder having Mg : B in 2 : 2 ratio, at temperatures around 790°°C. Critical current density has been found to vary systematically with processing temperature.
Journal of Physics: Condensed Matter, 1996
UvA-DARE (Digital Academic Repository) Polarized x-ray absorption spectroscopy of unoccupied elec... more UvA-DARE (Digital Academic Repository) Polarized x-ray absorption spectroscopy of unoccupied electronic states near the Fermi level in the Bi2Sr2CaCu2O8+x system
Physica C: Superconductivity, 1995
Polarised X-ray absorption (XAS) measurements have been made on high-quality superconducting Bi2S... more Polarised X-ray absorption (XAS) measurements have been made on high-quality superconducting Bi2Sr2CaCu2Os+y (Bi2212) single crystals to investigate the microscopic electronic structure in the normal and superconducting state of the system. The Cu L 3 XAS results led us to conclude that either there are no holes of 3dzz symmetry, or if any, they are insignificant in number. On the other hand, the O K XAS results show the presence of a significant density of p~ symmetry orbitals for itinerant holes. An increase in the 3d9_L/3d 9 ratio estimated from the Cu L 3 XAS measurements was observed while going from the normal to the superconducting state of the system. The results are discussed in the light of the structural distortions taking place below T c.
Advanced Materials Letters
Semiconductor Science and Technology, 2003
Silicon oxide-silicon nitride (ON) stack layers have been formed by mercury sensitized photochemi... more Silicon oxide-silicon nitride (ON) stack layers have been formed by mercury sensitized photochemical vapour deposition (photo-CVD) of silicon nitride layers over thermally grown and photo-CVD deposited silicon oxide layers on p-type Si (100) substrates. The properties of these two groups of samples were studied using Fourier transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS) and capacitance-voltage measurements. Photo-CVD deposited nitrogen-rich
Scripta Materialia, 2010
A systematic study of hydrogenated amorphous silicon nitride films deposited by varying gas flow ... more A systematic study of hydrogenated amorphous silicon nitride films deposited by varying gas flow rate ratio (R = SiH 4 /NH 3) using Photo-Chemical Vapour Deposition reveal that as R is increased, dominant phase changes from silicon oxynitride to silicon nitride with embedded silicon nanoclusters. The change in photoluminescence spectral features in these films is attributed to quantum confinement effect. The results suggest that hydrogen plays a crucial role in overall phase evolution and in-situ formation of Si nanoclusters embedded in silicon nitride matrix.
Modern Physics Letters B, 1990
This study is based on our hypothesis that predicts the possibility of Y–Ba–Ni–O superconductor. ... more This study is based on our hypothesis that predicts the possibility of Y–Ba–Ni–O superconductor. A comparative study of Y–Ba–Cu–O and 10% Ni doped Y–Ba–Cu–O (having T c as high as 84 K) is presented. Resistivity, XRD, oxygen content and Cu–K-XANES measurements are reported.
Journal of Synchrotron Radiation, 1999
ABSTRACT
Journal of Magnetism and Magnetic Materials, 1999
ABSTRACT
Current Applied Physics, 2010
Nanoparticle Pb 1Àx Fe x Se (0.00 6 x 6 0.16) thin films have been deposited on quartz, glass and... more Nanoparticle Pb 1Àx Fe x Se (0.00 6 x 6 0.16) thin films have been deposited on quartz, glass and silicon substrates by chemical bath deposition technique. Structural and optical properties of the films with iron concentration 0.00 6 x 6 0.16 indicate that the films grow as single-phase Pb 1Àx Fe x Se ternary alloys with rocksalt structure and with direct optical band gaps (E g) that increase with decrease in grain size and have values larger than 0.28 eV of the bulk PbSe. Average grain size in films grown at fixed bath temperature T b of 85°C is observed to decrease from 72 to 22 nm whereas lattice parameter is observed to increase from 6.12 to 6.14 Å with increase in Fe concentration from x = 0.00 to x = 0.16. The observed blue shift in film materials originates from quantum confinement in the nanograins. Nanoparticle Pb 1Àx Fe x Se/ single crystal Si heterojunctions show rectifying behavior. On illumination of heterojunctions with visible light current is observed to increase in forward and reverse bias. This increase in current in the presence of visible light is considered to be due to carrier multiplication by Auger electron emission.
Applied Physics A, 2012
ABSTRACT We report variable temperature resistivity measurements and mechanisms related to electr... more ABSTRACT We report variable temperature resistivity measurements and mechanisms related to electrical conduction in 200 keV Ni2+ ion implanted ZnO thin films deposited by vapor phase transport. The dc electrical resistivity versus temperature curves show that all polycrystalline ZnO films are semiconducting in nature. In the room temperature range they exhibit band conduction and conduction due to thermionic emission of electrons from grain boundaries present in the polycrystalline films. In the low temperature range, nearest neighbor hopping (NNH) and variable range hopping (VRH) conduction are observed. The detailed conduction mechanism of these films and the effects of grain boundary (GB) barriers on the electrical conduction process are discussed. An attempt is made to correlate electrical conduction behavior and previously observed room temperature ferromagnetism of these films.
Europhysics Letters (epl), 2010
We report the impact of post-deposition thermal annealing (in nitrogen ambient) on the evolution ... more We report the impact of post-deposition thermal annealing (in nitrogen ambient) on the evolution of an interfacial layer between a hydrogenated amorphous silicon nitride (a-SiNx :H) thin film and a Si(100) substrate and its correlation with electrical properties. X-ray reflectivity measurements reveal that the SiNx films under different post annealing temperatures demonstrate variation in the density, thickness and roughness. Also it is found that the interface state density (Dit) is directly related to the interfacial layer density of the film rather than to the surface and interface roughness.
Bulletin of Materials Science, 2006
Superconducting bulk MgB 2 samples have been synthesized by employing sintering technique without... more Superconducting bulk MgB 2 samples have been synthesized by employing sintering technique without using any additional process steps, generally undertaken in view of the substantial loss of magnesium, during heat treatment. Starting with Mg rich powders having different atomic ratios of Mg : B, as against the nominally required Mg : B = 1 : 2 ratio, we have obtained superconducting MgB 2 samples of different characteristics. The effect of excess Mg in the starting mixture and processing temperature on the phase-formation, transition temperature (T C ) and critical current density (J C ) have been investigated by electrical transport and a.c. susceptibility measurements. The X-ray diffraction and X-ray photoelectron spectroscopic analyses of MgB 2 bulk samples have been carried out to understand the role of excess Mg and the effect of processing temperature. It is established that MgB 2 samples with high critical current density can be synthesized from a Mg rich powder having Mg : B in 2 : 2 ratio, at temperatures around 790°°C. Critical current density has been found to vary systematically with processing temperature.