Purushottam Chakraborty - Academia.edu (original) (raw)

Papers by Purushottam Chakraborty

Solid State Communications, 1994

ABSTRACT

Surface Engineering, 2006

Abstract: Ultraviolet (UV) visible spectroscopy, atomic force microscopy and grazing incidence X-... more Abstract: Ultraviolet (UV) visible spectroscopy, atomic force microscopy and grazing incidence X-ray reflectivity have been used to study morphology of Au nanoparticles grown by direct current (DC) magnetron sputter deposition on hard (glass) and soft amorphous (polystyrene films on quartz) substrates. Au nanoparticles are found to be ellipsoidal showing an increase in ellipticity?[? a/b, a (b)= semimajor (semiminor) axis] with decrease in polystyrene film thickness from 250 to 20 nm, where b remains almost invariant around 3 ...

Surface and Interface Analysis, 2003

Abstract A gold–copper alloy with a nominal composition of Cu 3 Au but with a tetragonal (c= 4a) ... more Abstract A gold–copper alloy with a nominal composition of Cu 3 Au but with a tetragonal (c= 4a) structure is observed to form at Au/Cu interfaces of gold/copper multilayers deposited on amorphous substrates by dc magnetron sputtering. The formation of this non-equilibrium structure (tentatively D0 23) under-ambient conditions is detected by secondary ion mass spectrometry, x-ray diffraction and high-resolution cross-sectional transmission electron microscopy. Co-sputtering of Au and Cu under similar conditions produces only ...

Philosophical Magazine, 2014

ABSTRACT We report on the enhanced ultraviolet (UV) photoconductivity of zinc oxide (ZnO) nanostr... more ABSTRACT We report on the enhanced ultraviolet (UV) photoconductivity of zinc oxide (ZnO) nanostructures in vacuum. Nanoparticles and nanorods of ZnO were fabricated using a simple cost-effective solid state grinding method. Morphology of the nanostructures was studied using transmission electron microscopy, while the optical properties were investigated using UV–visible absorption and photoluminescence spectroscopy. The emission spectra of the nanostructures revealed the existence of various native defect states of ZnO and also indicated the presence of surface adsorbed water molecules. In the photoconductivity measurements, although the ZnO nanoparticles exhibited lower photoconductivity in comparison to the nanorods, a similar trend of photoresponse was observed for both the cases. An initial decrease in the photoconductivity followed by a large enhancement was observed in vacuum compared to that in ambient condition. Such unusually increased photoconductivity has been correlated to the desorption of physisorbed water molecules from nanostructure surfaces under vacuum. This desorption is responsible for the rise in dark current and an initial decrease in photoconductivity. Continual UV irradiation in vacuum leads to the desorption of chemisorbed water molecules from the defect sites of the nanostructures, resulting in the occurrence of high photoconductivity.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2003

Journal of Nuclear Materials, 1985

Journal of Applied Physics, 1994

A detailed study of magnesium indiffusion in lithium niobate (LiNbO3) crystal is presented. The a... more A detailed study of magnesium indiffusion in lithium niobate (LiNbO3) crystal is presented. The aim of the work was to obtain a comprehensive understanding of the diffusion process as a function of film thickness, temperature, diffusion time, crystal cut-direction. The secondary-ion-mass spectrometry technique was employed to obtain magnesium concentration depth profiles. Our results show that the strongest factor that controls the diffusion process is the temperature. A noticeable increase of the diffusion coefficient is observed with increasing temperature. The diffusion time has a small effect on the diffusion coefficient, but if the former is less than a certain value, the deposited MgO film does not diffuse completely. On the other hand, if it is quite long it will enter into the annealing regime. Diffusion parameters to realize buried waveguides (which reduce the coupling loss between single-mode fibers and diffused waveguides) have also been derived. The present studies could...

Journal of Applied Physics, 1995

Mg diffusion in Ti-diffused LiNbO3 (Ti/Mg:LiNbO3) optical waveguides has been studied. Secondary ... more Mg diffusion in Ti-diffused LiNbO3 (Ti/Mg:LiNbO3) optical waveguides has been studied. Secondary ion mass spectrometry has been used to obtain Ti/Mg dopant concentration profiles. Comparison of the diffusion behavior of Mg in pure LiNbO3 and titanium-diffused LiNbO3 (Ti:LiNbO3) has been made. A numerical study, based on semivectorial finite difference method to determine the coupling loss between single-mode fibers and Ti/Mg:LiNbO3 optical waveguides has been performed. It has been demonstrated that the use of Mg can reduce the asymmetry-induced coupling loss to almost zero. A method that predicts the best relative position of the fiber axis with respect to the surface of Ti/Mg:LiNbO3 waveguides has been presented.

Applied Surface Science, 2014

Applied Surface Science, 1993

ABSTRACT

Applied Physics A, 2013

ABSTRACT We report on the defect dominated light emission and ultraviolet (UV) photoconductivity ... more ABSTRACT We report on the defect dominated light emission and ultraviolet (UV) photoconductivity characteristics of ZnO nanorods fabricated using a facile, cost-effective and catalyst free thermal decomposition route under varying reaction temperatures. The morphological and structural studies reveal the formations of homogeneous quality nanorods in large scale at the highest reaction temperature of 6000C. The luminescence feature of the nanorods is dominated by the defect related emission over the typical band edge emission. The variation of band edge and native defect related emissions response of the samples has been correlated to the morphology and microstructure. In photoconductivity studies, the I-V characteristics of the ZnO NRs prepared at different reaction temperatures in dark and under UV illumination (λ = 366 nm) follow the power law i.e. . An enhanced ultraviolet photodetection has been observed in the nanorods fabricated at the highest reaction temperature of 6000C. The sample prepared at highest reaction temperature of 6000C exhibits UV photosensitivity value (photo-to-dark current ratio) of around 1.18×103, which is much higher in magnitude compared to that of the samples prepared at lower reaction temperatures. Enhancement in the photoconductivity can be assigned to the development of uniformity and homogeneity of the nanorods.

International Journal of Modern Physics B, 1991

In recent years, the availability of intense continuous radiation sources, such as electron synch... more In recent years, the availability of intense continuous radiation sources, such as electron synchrotrons and laser-induced hot plasmas, has given rise to a renewed interest in soft x-ray and x-uv reflectivity measurements. Such studies were, for a long time, hindered because of mainly two reasons. First, it was really difficult to generate soft x-rays in the laboratories and second, there was no possibility for practical implementation and design of optical systems, such as focusing elements, mirrors, etc. associated with that particular wavelength region. Soft x-rays, with wavelength range usually from 10 to about 200 angstroms, can produce images of higher resolution than visible light due to their shorter wavelength. For years, physicists have wanted to construct an x-ray microscope that would exploit the ability of soft x-rays to detect small structures. The need for such an instrument is clear. The resolution of light microscopes is limited by the comparatively long wavelength ...

Excellent detection sensitivity, high dynamic range and good depth resolution make the Secondary ... more Excellent detection sensitivity, high dynamic range and good depth resolution make the Secondary ion Mass spectrometry (SIMS) technique extremely powerful for the chemical analysis of surfaces and interfaces of condensed matter systems. However, a serious problem in SIMS analysis is its "matrix effect" that hinders the quantification of a certain species in a sample and consequently, probing the composition of surfaces or interfaces by SIMS is greatly hindered. Appropriate corrective measures are therefore, needed to calibrate the secondary ion currents into respective concentrations for accurate compositional analysis. Working in the MCs+-SIMS mode (M - element to be analyzed, Cs+ - bombarding ions) can circumvent the matrix effect. The emission process for the species M0 is decoupled from the MCs+ ion formation process, in analogy with the ion formation in secondary neutral mass spectrometry (SNMS), resulting in a drastic decrease in matrix effect in the MCs+ - SIMS mode. Although this technique has fou...

Journal of Physics: Conference Series, 2007

IOPscience is a unique platform for IOP-hosted journal content providing site-wide electronic acc... more IOPscience is a unique platform for IOP-hosted journal content providing site-wide electronic access to more than 130 years of leading scientific research, and incorporates some of the most innovative technologies to enhance your user-experience.

Reference Module in Materials Science and Materials Engineering, 2022

Technology has made great developments in electronic device speed, but optical devices operate in... more Technology has made great developments in electronic device speed, but optical devices operate in the time domain unreachable to electronics. Optical devices have no competition in the time domain of less than 1 picosecond. Photonic devices can switch and process light signals without converting them into electronic form. The major advantages of these devices are speed and conservation of bandwidth. Switching is performed through changes in the refractive index of the material that are proportional to the light intensity. This particular feature is the result of third-order dielectric susceptibility, χ(3), or “optical Kerr susceptibility”, which is related to the nonlinear part of the total refractive index. Future prospects in photonic switching and information processing critically depend on the progress towards improved photonic materials with significantly enhanced Kerr susceptibilities. Optically isotropic materials like silica glasses that have inversion symmetry intrinsically possess some third-order optical nonlinearities at l ¼ 1.06 mm. This, combined with the extremely low absorption coefficient of silica glasses, allows all-optical switching between two waveguides embedded in a silica fibre simply by controlling the optical pulse intensity. Plasmonic nanoparticles in dielectric media lead to the generation of surface-plasmons in the neighbourhood of dielectric surfaces, resulting in a local evanescent field that experiences dielectric confinement. This field affects the coherent oscillation of dipoles in the conduction band thus enhancing the effective third-order nonlinearity. The strength of the nonlinearity is influenced by controlling the “surface plasmon resonance” (SPR) band by tuning the size and shape of the nanomaterials. The incorporation of metal nanoclusters in glasses has been found to induce desired third-order optical non-linearities in the composite at wavelengths very close to that of the characteristic SPR of the metal clusters. Ion implantation is a potential method for inducing colloid formation at a high local concentration unachievable by chemical doping or melt-glass fabrication process and for confining the nonlinearities to specific regions in various host matrices. Metal-ion-induced colloid generation in bulk silica glasses has shown that these nanocluster–glass composites under favourable circumstances have significant enhancement of χ(3) with picosecond to femtosecond temporal responses. The extraordinary achievements in developing such novel photonic materials have opened the way for advances in photonic devices, such as all-optical switching, coupled waveguides as a directional coupler, etc

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2011

Journal of Surface Investigation. X-ray, Synchrotron and Neutron Techniques, 2010

International Journal of Nanoscience, 2005

Our present work deals with the formation and thermal behavior of a nonbulk alloy phase confined ... more Our present work deals with the formation and thermal behavior of a nonbulk alloy phase confined within about 8 nm across the interfaces of Au/Cu multilayer systems. These multilayers deposited on silicon and float glass by DC magnetron sputtering have been studied by secondary ion mass spectrometry (SIMS), X-ray diffraction (XRD) and cross-sectional transmission electron microscopy (XTEM). Along with the highly oriented growth of the Cu and Au layers along [111], Cu 3 Au alloy was found to be present only at the Cu/Au interfaces in the nonbulk tetragonal D023 phase. Co -sputtering of Au and Cu under similar conditions produces only conventional fcc Cu 3 Au alloy phases, suggesting that interfacial confinement plays a significant role in producing the novel Cu 3 Au alloy phase in gold/copper multilayers. This novel phase is found to form only when the interfacial width is less than 10 nm. The D023 alloy phase tends to stabilize, rather than transforming to the bulk L12 phase, when the multilayer is vacuum-annealed at 150°C. As alloy formation spreads out of the interfaces (on vacuum annealing at 200°C), the dominant alloy is CuAu , consistent with the Cu:Au atomic ratio averaged over the multilayer.

Solid State Communications, 1994

ABSTRACT

Surface Engineering, 2006

Abstract: Ultraviolet (UV) visible spectroscopy, atomic force microscopy and grazing incidence X-... more Abstract: Ultraviolet (UV) visible spectroscopy, atomic force microscopy and grazing incidence X-ray reflectivity have been used to study morphology of Au nanoparticles grown by direct current (DC) magnetron sputter deposition on hard (glass) and soft amorphous (polystyrene films on quartz) substrates. Au nanoparticles are found to be ellipsoidal showing an increase in ellipticity?[? a/b, a (b)= semimajor (semiminor) axis] with decrease in polystyrene film thickness from 250 to 20 nm, where b remains almost invariant around 3 ...

Surface and Interface Analysis, 2003

Abstract A gold–copper alloy with a nominal composition of Cu 3 Au but with a tetragonal (c= 4a) ... more Abstract A gold–copper alloy with a nominal composition of Cu 3 Au but with a tetragonal (c= 4a) structure is observed to form at Au/Cu interfaces of gold/copper multilayers deposited on amorphous substrates by dc magnetron sputtering. The formation of this non-equilibrium structure (tentatively D0 23) under-ambient conditions is detected by secondary ion mass spectrometry, x-ray diffraction and high-resolution cross-sectional transmission electron microscopy. Co-sputtering of Au and Cu under similar conditions produces only ...

Philosophical Magazine, 2014

ABSTRACT We report on the enhanced ultraviolet (UV) photoconductivity of zinc oxide (ZnO) nanostr... more ABSTRACT We report on the enhanced ultraviolet (UV) photoconductivity of zinc oxide (ZnO) nanostructures in vacuum. Nanoparticles and nanorods of ZnO were fabricated using a simple cost-effective solid state grinding method. Morphology of the nanostructures was studied using transmission electron microscopy, while the optical properties were investigated using UV–visible absorption and photoluminescence spectroscopy. The emission spectra of the nanostructures revealed the existence of various native defect states of ZnO and also indicated the presence of surface adsorbed water molecules. In the photoconductivity measurements, although the ZnO nanoparticles exhibited lower photoconductivity in comparison to the nanorods, a similar trend of photoresponse was observed for both the cases. An initial decrease in the photoconductivity followed by a large enhancement was observed in vacuum compared to that in ambient condition. Such unusually increased photoconductivity has been correlated to the desorption of physisorbed water molecules from nanostructure surfaces under vacuum. This desorption is responsible for the rise in dark current and an initial decrease in photoconductivity. Continual UV irradiation in vacuum leads to the desorption of chemisorbed water molecules from the defect sites of the nanostructures, resulting in the occurrence of high photoconductivity.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2003

Journal of Nuclear Materials, 1985

Journal of Applied Physics, 1994

A detailed study of magnesium indiffusion in lithium niobate (LiNbO3) crystal is presented. The a... more A detailed study of magnesium indiffusion in lithium niobate (LiNbO3) crystal is presented. The aim of the work was to obtain a comprehensive understanding of the diffusion process as a function of film thickness, temperature, diffusion time, crystal cut-direction. The secondary-ion-mass spectrometry technique was employed to obtain magnesium concentration depth profiles. Our results show that the strongest factor that controls the diffusion process is the temperature. A noticeable increase of the diffusion coefficient is observed with increasing temperature. The diffusion time has a small effect on the diffusion coefficient, but if the former is less than a certain value, the deposited MgO film does not diffuse completely. On the other hand, if it is quite long it will enter into the annealing regime. Diffusion parameters to realize buried waveguides (which reduce the coupling loss between single-mode fibers and diffused waveguides) have also been derived. The present studies could...

Journal of Applied Physics, 1995

Mg diffusion in Ti-diffused LiNbO3 (Ti/Mg:LiNbO3) optical waveguides has been studied. Secondary ... more Mg diffusion in Ti-diffused LiNbO3 (Ti/Mg:LiNbO3) optical waveguides has been studied. Secondary ion mass spectrometry has been used to obtain Ti/Mg dopant concentration profiles. Comparison of the diffusion behavior of Mg in pure LiNbO3 and titanium-diffused LiNbO3 (Ti:LiNbO3) has been made. A numerical study, based on semivectorial finite difference method to determine the coupling loss between single-mode fibers and Ti/Mg:LiNbO3 optical waveguides has been performed. It has been demonstrated that the use of Mg can reduce the asymmetry-induced coupling loss to almost zero. A method that predicts the best relative position of the fiber axis with respect to the surface of Ti/Mg:LiNbO3 waveguides has been presented.

Applied Surface Science, 2014

Applied Surface Science, 1993

ABSTRACT

Applied Physics A, 2013

ABSTRACT We report on the defect dominated light emission and ultraviolet (UV) photoconductivity ... more ABSTRACT We report on the defect dominated light emission and ultraviolet (UV) photoconductivity characteristics of ZnO nanorods fabricated using a facile, cost-effective and catalyst free thermal decomposition route under varying reaction temperatures. The morphological and structural studies reveal the formations of homogeneous quality nanorods in large scale at the highest reaction temperature of 6000C. The luminescence feature of the nanorods is dominated by the defect related emission over the typical band edge emission. The variation of band edge and native defect related emissions response of the samples has been correlated to the morphology and microstructure. In photoconductivity studies, the I-V characteristics of the ZnO NRs prepared at different reaction temperatures in dark and under UV illumination (λ = 366 nm) follow the power law i.e. . An enhanced ultraviolet photodetection has been observed in the nanorods fabricated at the highest reaction temperature of 6000C. The sample prepared at highest reaction temperature of 6000C exhibits UV photosensitivity value (photo-to-dark current ratio) of around 1.18×103, which is much higher in magnitude compared to that of the samples prepared at lower reaction temperatures. Enhancement in the photoconductivity can be assigned to the development of uniformity and homogeneity of the nanorods.

International Journal of Modern Physics B, 1991

In recent years, the availability of intense continuous radiation sources, such as electron synch... more In recent years, the availability of intense continuous radiation sources, such as electron synchrotrons and laser-induced hot plasmas, has given rise to a renewed interest in soft x-ray and x-uv reflectivity measurements. Such studies were, for a long time, hindered because of mainly two reasons. First, it was really difficult to generate soft x-rays in the laboratories and second, there was no possibility for practical implementation and design of optical systems, such as focusing elements, mirrors, etc. associated with that particular wavelength region. Soft x-rays, with wavelength range usually from 10 to about 200 angstroms, can produce images of higher resolution than visible light due to their shorter wavelength. For years, physicists have wanted to construct an x-ray microscope that would exploit the ability of soft x-rays to detect small structures. The need for such an instrument is clear. The resolution of light microscopes is limited by the comparatively long wavelength ...

Excellent detection sensitivity, high dynamic range and good depth resolution make the Secondary ... more Excellent detection sensitivity, high dynamic range and good depth resolution make the Secondary ion Mass spectrometry (SIMS) technique extremely powerful for the chemical analysis of surfaces and interfaces of condensed matter systems. However, a serious problem in SIMS analysis is its "matrix effect" that hinders the quantification of a certain species in a sample and consequently, probing the composition of surfaces or interfaces by SIMS is greatly hindered. Appropriate corrective measures are therefore, needed to calibrate the secondary ion currents into respective concentrations for accurate compositional analysis. Working in the MCs+-SIMS mode (M - element to be analyzed, Cs+ - bombarding ions) can circumvent the matrix effect. The emission process for the species M0 is decoupled from the MCs+ ion formation process, in analogy with the ion formation in secondary neutral mass spectrometry (SNMS), resulting in a drastic decrease in matrix effect in the MCs+ - SIMS mode. Although this technique has fou...

Journal of Physics: Conference Series, 2007

IOPscience is a unique platform for IOP-hosted journal content providing site-wide electronic acc... more IOPscience is a unique platform for IOP-hosted journal content providing site-wide electronic access to more than 130 years of leading scientific research, and incorporates some of the most innovative technologies to enhance your user-experience.

Reference Module in Materials Science and Materials Engineering, 2022

Technology has made great developments in electronic device speed, but optical devices operate in... more Technology has made great developments in electronic device speed, but optical devices operate in the time domain unreachable to electronics. Optical devices have no competition in the time domain of less than 1 picosecond. Photonic devices can switch and process light signals without converting them into electronic form. The major advantages of these devices are speed and conservation of bandwidth. Switching is performed through changes in the refractive index of the material that are proportional to the light intensity. This particular feature is the result of third-order dielectric susceptibility, χ(3), or “optical Kerr susceptibility”, which is related to the nonlinear part of the total refractive index. Future prospects in photonic switching and information processing critically depend on the progress towards improved photonic materials with significantly enhanced Kerr susceptibilities. Optically isotropic materials like silica glasses that have inversion symmetry intrinsically possess some third-order optical nonlinearities at l ¼ 1.06 mm. This, combined with the extremely low absorption coefficient of silica glasses, allows all-optical switching between two waveguides embedded in a silica fibre simply by controlling the optical pulse intensity. Plasmonic nanoparticles in dielectric media lead to the generation of surface-plasmons in the neighbourhood of dielectric surfaces, resulting in a local evanescent field that experiences dielectric confinement. This field affects the coherent oscillation of dipoles in the conduction band thus enhancing the effective third-order nonlinearity. The strength of the nonlinearity is influenced by controlling the “surface plasmon resonance” (SPR) band by tuning the size and shape of the nanomaterials. The incorporation of metal nanoclusters in glasses has been found to induce desired third-order optical non-linearities in the composite at wavelengths very close to that of the characteristic SPR of the metal clusters. Ion implantation is a potential method for inducing colloid formation at a high local concentration unachievable by chemical doping or melt-glass fabrication process and for confining the nonlinearities to specific regions in various host matrices. Metal-ion-induced colloid generation in bulk silica glasses has shown that these nanocluster–glass composites under favourable circumstances have significant enhancement of χ(3) with picosecond to femtosecond temporal responses. The extraordinary achievements in developing such novel photonic materials have opened the way for advances in photonic devices, such as all-optical switching, coupled waveguides as a directional coupler, etc

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2011

Journal of Surface Investigation. X-ray, Synchrotron and Neutron Techniques, 2010

International Journal of Nanoscience, 2005

Our present work deals with the formation and thermal behavior of a nonbulk alloy phase confined ... more Our present work deals with the formation and thermal behavior of a nonbulk alloy phase confined within about 8 nm across the interfaces of Au/Cu multilayer systems. These multilayers deposited on silicon and float glass by DC magnetron sputtering have been studied by secondary ion mass spectrometry (SIMS), X-ray diffraction (XRD) and cross-sectional transmission electron microscopy (XTEM). Along with the highly oriented growth of the Cu and Au layers along [111], Cu 3 Au alloy was found to be present only at the Cu/Au interfaces in the nonbulk tetragonal D023 phase. Co -sputtering of Au and Cu under similar conditions produces only conventional fcc Cu 3 Au alloy phases, suggesting that interfacial confinement plays a significant role in producing the novel Cu 3 Au alloy phase in gold/copper multilayers. This novel phase is found to form only when the interfacial width is less than 10 nm. The D023 alloy phase tends to stabilize, rather than transforming to the bulk L12 phase, when the multilayer is vacuum-annealed at 150°C. As alloy formation spreads out of the interfaces (on vacuum annealing at 200°C), the dominant alloy is CuAu , consistent with the Cu:Au atomic ratio averaged over the multilayer.