Arunava Gupta - Academia.edu (original) (raw)

Papers by Arunava Gupta

Bulletin of the American Physical Society, Mar 19, 2013

Microelectronics Reliability, 1993

Current Opinion in Solid State and Materials Science, 1997

Abstract In the past five years thin film techniques such as pulsed laser deposition and molecula... more Abstract In the past five years thin film techniques such as pulsed laser deposition and molecular beam epitaxy have been effectively utilized for the growth of metastable and artificially structured oxides. Most of the work is related to cuprates, and a number of novel cuprate materials, including some exhibiting superconductivity, have been synthesized as epitaxial films. They are stabilized by growth on a lattice-matched substrate, with control of the stacking sequence of the various layers at nearly the atomic level in the structured films. Artificially layered ferroelectric and magnetic oxides exhibiting enhanced properties have also been fabricated.

Applied Physics Letters, 2000

We demonstrate that Si layers overgrown on GaN/sapphire substrate structures can be transferred o... more We demonstrate that Si layers overgrown on GaN/sapphire substrate structures can be transferred onto host substrates by using the technique of laser-induced metallization of GaN at the GaN/sapphire interface via the reaction GaN=Ga+1/2N2. This may allow the grafting of films of Si onto substrates such as glass or plastic for microelectronic applications. We examine the debonding mechanism and propose that it occurs due to pressures of the order of a few thousand atmospheres generated with the release of nitrogen from the GaN metallization reaction.

APS Meeting …, 2008

Epitaxial CrO 2 thin films were grown on TiO 2 (110) substrates using chemical vapor deposition (... more Epitaxial CrO 2 thin films were grown on TiO 2 (110) substrates using chemical vapor deposition (CVD) using a CrO 3 precursor as described elsewhere [1]. In-plane angular dependent ferromagnetic resonance (FMR) measurements confirm a uniaxial in-plane anisotropy with the easy axis ...

Physical Review Letters, May 8, 2012

Ca 3 Co 4 O 9 has a unique structure that leads to exceptionally high thermoelectric transport. H... more Ca 3 Co 4 O 9 has a unique structure that leads to exceptionally high thermoelectric transport. Here we report the achievement of a 27% increase in the room-temperature in-plane Seebeck coefficient of Ca 3 Co 4 O 9 thin films. We combine aberration-corrected Z-contrast imaging, atomic-column resolved electron energy-loss spectroscopy, and density-functional calculations to show that the increase is caused by stacking faults with Co 4+-ions in a higher spin state compared to that of bulk Ca 3 Co 4 O 9. The higher Seebeck coefficient makes the Ca 3 Co 4 O 9 system suitable for many high-temperature waste-heat-recovery applications.

Applied Physics Letters, Aug 10, 1998

A field effect transistor fabricated with an oxide channel has been shown to demonstrate switchin... more A field effect transistor fabricated with an oxide channel has been shown to demonstrate switching characteristics similar to conventional silicon metal oxide field effect transistors. This device is believed to operate via a Mott metal-insulator transition induced by the gate field, and offers a potential technology alternative for the regime beyond silicon scaling limitations.

Springer series in materials science, 2007

Epitaxial CrO 2 thin films deposited on HF-cleaned TiO 2 (100) substrates exhibit very strong str... more Epitaxial CrO 2 thin films deposited on HF-cleaned TiO 2 (100) substrates exhibit very strong strain anisotropy, while those grown without the HF treatment step are essentially strain-free and display bulk-like magnetic properties. The HF treatment enhances the surface smoothness of the TiO 2 (100) substrate thus leading to the growth of epitaxially strained CrO 2 films. The magnetic easy axis of these films changes orientation with thickness, switching from the in-plane c-axis direction for relatively thick films to the b-axis direction for thinner films (< 50 nm). Similarly, over a thickness range, a change of the easy axis direction is also observed with lowering temperature. Ion-beam irradiation of the substrate surface prior to growth also results in the growth of strained CrO 2 films, although the amount of strain is less than that observed for HF-treated substrates. The magnetic properties as a function of thickness have also been studied for as-deposited 'thick' CrO 2 films that are slowly chemically etched down in thickness. Unlike asgrown thin films below 50 nm thickness that have the easy axis along the b-direction, the chemically etched down CrO 2 thin films of equivalent thickness retain their easy axis alignment along the c-direction, but display a significantly enhanced coercivity. The observed differences in the switching behavior between the as-deposited films and those that are chemically etched can be qualitatively attributed to changes in the strain relaxation mechanism.

New Journal of Physics, May 25, 2012

We report on electrically switchable polarization and ferroelectric domain scaling over a thickne... more We report on electrically switchable polarization and ferroelectric domain scaling over a thickness range of 5-100 nm in BiFeO 3 films deposited on [110] vicinal substrates. The BiFeO 3 films of variable thickness were deposited with SrRuO 3 bottom layer using the pulsed laser deposition technique. The domains are engineered into preferentially oriented patterns due to substrate vicinality along the [110] direction. The domain width scales closely with the square root of film thickness, in agreement with the Landau-Lifschitz-Kittel (LLK) law. Switching spectroscopy piezo-response force microscopy provides clear evidence for the ferroelectric switching behavior in all the films.

Advanced Materials, Jun 12, 2017

Crystal Growth & Design, Mar 1, 2023

Journal of Physical Chemistry B, Jul 22, 2014

We present a model electrode system comprised of nanostructured Ti electrode sensitized with Ag@A... more We present a model electrode system comprised of nanostructured Ti electrode sensitized with Ag@Ag 2 S core-shell nanoparticles (NPs) for visible light driven photoelectrochemistry studies. The nanostructured Ti electrode is coated with Ti@TiO 2 nanowires (NW) to provide a high surface area for efficient light absorption and efficient charge collection from the Ag@Ag 2 S NPs. Pronounced photoelectrochemical responses of Ag@Ag 2 S NPs under visible light were obtained and attributed to collective contributions of visible light sensitivity of Ag 2 S, the local field enhancement of Ag surface plasmon, enhanced charge collection by Ti@TiO 2 NWs, and the high surface area of the nanostructured electrode system. The shell thickness and core size of the Ag@Ag 2 S core-shell structure can be controlled to achieve optimal photoelectrochemical performance. XPS, XRD, SEM, high resolution TEM, AC impedance and other electrochemical

Journal of the American Chemical Society, Nov 22, 2010

Journal of Alloys and Compounds, May 1, 2020

We synthesize the Fe x Co 1Àx TiSb series of alloys (0 < x < 1) through arc melting. On the cobal... more We synthesize the Fe x Co 1Àx TiSb series of alloys (0 < x < 1) through arc melting. On the cobalt-rich side, we successfully synthesize CoTiSb in the C1b half-Heusler crystal structure. At the Fe 0.25 Co 0.75 TiSb composition, we find the alloy to be composed of CoTiSb-rich grains with iron segregation at grain boundaries. At the prototypical half-Heusler composition Fe 0.5 Co 0.5 TiSb, we synthesize a single phase, comprised of equiaxed grains, showing signatures of a C1b crystal structure with a lattice constant of 0.5918 nm in X-ray diffraction data. Conductivity measurements indicate the Fe 0.5 Co 0.5 TiSb half-Heusler phase to be semiconducting with a small band gap of the order of 0.1 eV. A density functional theorybased cluster expansion study of the configurational order of Fe, Co in the half-Heusler structure shows mixing to be weakly unfavorable, indicating Fe/Co solid solution in the Fe 0.5 Co 0.5 TiSb alloy at all but very low temperatures, in agreement with the single phase with C1b symmetry found in experiments. Our calculations indicate the perfectly stoichiometric compound to be semi-metallic or metallic. However, an addition of 0.5 electrons results in a semiconducting state in agreement with experimental resistivity measurements and slight Fe-, Co-rich off-stoichiometry in the as-synthesized Fe 0.5 Co 0.5 TiSb sample. Further, our calculations indicate the nonmagnetic, ferromagnetic and antiferromagnetic states to be energetically within a few meV/atom of one another, consistent with the observation of extremely low magnetic moment. On the iron-rich side, at the Fe 0.75 Co 0.25 TiSb composition, we synthesize a twophase mixture of the Fe 0.5 Co 0.5 TiSb phase and a secondary antimony-rich phase with composition roughly Sb 1.8 Ti 1.5 Fe, and at the FeTiSb composition, we find a two-phase mixture of a previously-reported Heusler-based Fe 1.5 TiSb phase and the antimony-rich phase.

Materials Letters, Jun 1, 2014

Dye sensitized solar cells are commonly fabricated using expensive platinum as a counter electrod... more Dye sensitized solar cells are commonly fabricated using expensive platinum as a counter electrode material. We demonstrate for the first time the use of CuSbS 2 as a replacement for platinum in dye sensitized solar cells. The performance of solar cells using CuSbS 2 is found to be comparable with that using platinum counter electrode.

Journal of Applied Physics, Nov 21, 2022

Epitaxial films of multiferroic BiFe1−xCoxO3 (BFCO) with 0≤x≤0.35 are grown on (001)-oriented SrT... more Epitaxial films of multiferroic BiFe1−xCoxO3 (BFCO) with 0≤x≤0.35 are grown on (001)-oriented SrTiO3 and SrRuO3 buffered SrTiO3 substrates using the pulsed laser deposition technique. The effect of structural transformation from rhombohedral to tetragonal phase with increasing cobalt substitution on the magnetic, electrical, and piezo-/ferroelectric properties is investigated. Piezoresponse force microscopy is used to quantify the coercive voltage from the phase hysteresis loops for different thickness films to investigate the semi-empirical Kay–Dunn scaling law with varying cobalt concentrations. For the rhombohedral structure, a reduction of the coercive voltage is observed with increasing substitution of Fe by Co. The coercive voltage of a 10 nm BFCO (x=0.35) film is found to be 0.63 V, which is 67% lower than that of a pure BiFeO3 (BFO) (1.9 V) film of the same thickness. Cobalt substitution also leads to changes in the magnetic and electrical properties due to modification of spin ordering and reduction of the bandgap, respectively. Further, to validate the experimental results, we have performed theoretical calculations using density functional theory. The theoretical results indicate a reduction in unit cell volume and enhancement in net magnetization can be achieved with cobalt substitution, in agreement with experimental results. Partial Co substitution can, thus, provide a pathway to realize BFO-based nonvolatile magnetoelectric devices with reduced operating voltage.

Physica C-superconductivity and Its Applications, Jun 1, 1988

ABSTRACT This paper reports on progress made at IBM in the fabrication of HiTc dc SQUIDs (Superco... more ABSTRACT This paper reports on progress made at IBM in the fabrication of HiTc dc SQUIDs (Superconducting QUantum Interference Devices)1,2. We have fabricated SQUIDs from polycrystalline YBa2Cu3Oy samples on MgO substrates3 and from epitaxial films on SrTiO3 (100) substrates4. The films were patterned using either ion-implanting to selectively convert the superconductor into an insulator without actually removing any material1,5, laser ablation to pattern a loop into the film by removing material6, or a conventional ion milling process to selectively remove material using a photoresist mask. In the case of the polycrystalline films, the naturally occurring grain boundaries provide the weak link or Josephson junction behavior in a stripe that is much larger in size than the superconducting coherence length. We have measured the noise amplitude of one such SQUID made on MgO to be about 1 × 10-5PhiO/Hz1/2 at 1000 Hz and 40 K. Loops formed from true epitaxial films containing many twin boudaries will not operate as dc SQUIDs unless the films are damaged across each link. A SQUID formed in this way operated in liquid nitrogen and had an estimated white noise performance of 1 × 10-3Phi0/Hz1/2 at 74 K.

Bulletin of the American Physical Society, Mar 19, 2013

Microelectronics Reliability, 1993

Current Opinion in Solid State and Materials Science, 1997

Abstract In the past five years thin film techniques such as pulsed laser deposition and molecula... more Abstract In the past five years thin film techniques such as pulsed laser deposition and molecular beam epitaxy have been effectively utilized for the growth of metastable and artificially structured oxides. Most of the work is related to cuprates, and a number of novel cuprate materials, including some exhibiting superconductivity, have been synthesized as epitaxial films. They are stabilized by growth on a lattice-matched substrate, with control of the stacking sequence of the various layers at nearly the atomic level in the structured films. Artificially layered ferroelectric and magnetic oxides exhibiting enhanced properties have also been fabricated.

Applied Physics Letters, 2000

We demonstrate that Si layers overgrown on GaN/sapphire substrate structures can be transferred o... more We demonstrate that Si layers overgrown on GaN/sapphire substrate structures can be transferred onto host substrates by using the technique of laser-induced metallization of GaN at the GaN/sapphire interface via the reaction GaN=Ga+1/2N2. This may allow the grafting of films of Si onto substrates such as glass or plastic for microelectronic applications. We examine the debonding mechanism and propose that it occurs due to pressures of the order of a few thousand atmospheres generated with the release of nitrogen from the GaN metallization reaction.

APS Meeting …, 2008

Epitaxial CrO 2 thin films were grown on TiO 2 (110) substrates using chemical vapor deposition (... more Epitaxial CrO 2 thin films were grown on TiO 2 (110) substrates using chemical vapor deposition (CVD) using a CrO 3 precursor as described elsewhere [1]. In-plane angular dependent ferromagnetic resonance (FMR) measurements confirm a uniaxial in-plane anisotropy with the easy axis ...

Physical Review Letters, May 8, 2012

Ca 3 Co 4 O 9 has a unique structure that leads to exceptionally high thermoelectric transport. H... more Ca 3 Co 4 O 9 has a unique structure that leads to exceptionally high thermoelectric transport. Here we report the achievement of a 27% increase in the room-temperature in-plane Seebeck coefficient of Ca 3 Co 4 O 9 thin films. We combine aberration-corrected Z-contrast imaging, atomic-column resolved electron energy-loss spectroscopy, and density-functional calculations to show that the increase is caused by stacking faults with Co 4+-ions in a higher spin state compared to that of bulk Ca 3 Co 4 O 9. The higher Seebeck coefficient makes the Ca 3 Co 4 O 9 system suitable for many high-temperature waste-heat-recovery applications.

Applied Physics Letters, Aug 10, 1998

A field effect transistor fabricated with an oxide channel has been shown to demonstrate switchin... more A field effect transistor fabricated with an oxide channel has been shown to demonstrate switching characteristics similar to conventional silicon metal oxide field effect transistors. This device is believed to operate via a Mott metal-insulator transition induced by the gate field, and offers a potential technology alternative for the regime beyond silicon scaling limitations.

Springer series in materials science, 2007

Epitaxial CrO 2 thin films deposited on HF-cleaned TiO 2 (100) substrates exhibit very strong str... more Epitaxial CrO 2 thin films deposited on HF-cleaned TiO 2 (100) substrates exhibit very strong strain anisotropy, while those grown without the HF treatment step are essentially strain-free and display bulk-like magnetic properties. The HF treatment enhances the surface smoothness of the TiO 2 (100) substrate thus leading to the growth of epitaxially strained CrO 2 films. The magnetic easy axis of these films changes orientation with thickness, switching from the in-plane c-axis direction for relatively thick films to the b-axis direction for thinner films (< 50 nm). Similarly, over a thickness range, a change of the easy axis direction is also observed with lowering temperature. Ion-beam irradiation of the substrate surface prior to growth also results in the growth of strained CrO 2 films, although the amount of strain is less than that observed for HF-treated substrates. The magnetic properties as a function of thickness have also been studied for as-deposited 'thick' CrO 2 films that are slowly chemically etched down in thickness. Unlike asgrown thin films below 50 nm thickness that have the easy axis along the b-direction, the chemically etched down CrO 2 thin films of equivalent thickness retain their easy axis alignment along the c-direction, but display a significantly enhanced coercivity. The observed differences in the switching behavior between the as-deposited films and those that are chemically etched can be qualitatively attributed to changes in the strain relaxation mechanism.

New Journal of Physics, May 25, 2012

We report on electrically switchable polarization and ferroelectric domain scaling over a thickne... more We report on electrically switchable polarization and ferroelectric domain scaling over a thickness range of 5-100 nm in BiFeO 3 films deposited on [110] vicinal substrates. The BiFeO 3 films of variable thickness were deposited with SrRuO 3 bottom layer using the pulsed laser deposition technique. The domains are engineered into preferentially oriented patterns due to substrate vicinality along the [110] direction. The domain width scales closely with the square root of film thickness, in agreement with the Landau-Lifschitz-Kittel (LLK) law. Switching spectroscopy piezo-response force microscopy provides clear evidence for the ferroelectric switching behavior in all the films.

Advanced Materials, Jun 12, 2017

Crystal Growth & Design, Mar 1, 2023

Journal of Physical Chemistry B, Jul 22, 2014

We present a model electrode system comprised of nanostructured Ti electrode sensitized with Ag@A... more We present a model electrode system comprised of nanostructured Ti electrode sensitized with Ag@Ag 2 S core-shell nanoparticles (NPs) for visible light driven photoelectrochemistry studies. The nanostructured Ti electrode is coated with Ti@TiO 2 nanowires (NW) to provide a high surface area for efficient light absorption and efficient charge collection from the Ag@Ag 2 S NPs. Pronounced photoelectrochemical responses of Ag@Ag 2 S NPs under visible light were obtained and attributed to collective contributions of visible light sensitivity of Ag 2 S, the local field enhancement of Ag surface plasmon, enhanced charge collection by Ti@TiO 2 NWs, and the high surface area of the nanostructured electrode system. The shell thickness and core size of the Ag@Ag 2 S core-shell structure can be controlled to achieve optimal photoelectrochemical performance. XPS, XRD, SEM, high resolution TEM, AC impedance and other electrochemical

Journal of the American Chemical Society, Nov 22, 2010

Journal of Alloys and Compounds, May 1, 2020

We synthesize the Fe x Co 1Àx TiSb series of alloys (0 < x < 1) through arc melting. On the cobal... more We synthesize the Fe x Co 1Àx TiSb series of alloys (0 < x < 1) through arc melting. On the cobalt-rich side, we successfully synthesize CoTiSb in the C1b half-Heusler crystal structure. At the Fe 0.25 Co 0.75 TiSb composition, we find the alloy to be composed of CoTiSb-rich grains with iron segregation at grain boundaries. At the prototypical half-Heusler composition Fe 0.5 Co 0.5 TiSb, we synthesize a single phase, comprised of equiaxed grains, showing signatures of a C1b crystal structure with a lattice constant of 0.5918 nm in X-ray diffraction data. Conductivity measurements indicate the Fe 0.5 Co 0.5 TiSb half-Heusler phase to be semiconducting with a small band gap of the order of 0.1 eV. A density functional theorybased cluster expansion study of the configurational order of Fe, Co in the half-Heusler structure shows mixing to be weakly unfavorable, indicating Fe/Co solid solution in the Fe 0.5 Co 0.5 TiSb alloy at all but very low temperatures, in agreement with the single phase with C1b symmetry found in experiments. Our calculations indicate the perfectly stoichiometric compound to be semi-metallic or metallic. However, an addition of 0.5 electrons results in a semiconducting state in agreement with experimental resistivity measurements and slight Fe-, Co-rich off-stoichiometry in the as-synthesized Fe 0.5 Co 0.5 TiSb sample. Further, our calculations indicate the nonmagnetic, ferromagnetic and antiferromagnetic states to be energetically within a few meV/atom of one another, consistent with the observation of extremely low magnetic moment. On the iron-rich side, at the Fe 0.75 Co 0.25 TiSb composition, we synthesize a twophase mixture of the Fe 0.5 Co 0.5 TiSb phase and a secondary antimony-rich phase with composition roughly Sb 1.8 Ti 1.5 Fe, and at the FeTiSb composition, we find a two-phase mixture of a previously-reported Heusler-based Fe 1.5 TiSb phase and the antimony-rich phase.

Materials Letters, Jun 1, 2014

Dye sensitized solar cells are commonly fabricated using expensive platinum as a counter electrod... more Dye sensitized solar cells are commonly fabricated using expensive platinum as a counter electrode material. We demonstrate for the first time the use of CuSbS 2 as a replacement for platinum in dye sensitized solar cells. The performance of solar cells using CuSbS 2 is found to be comparable with that using platinum counter electrode.

Journal of Applied Physics, Nov 21, 2022

Epitaxial films of multiferroic BiFe1−xCoxO3 (BFCO) with 0≤x≤0.35 are grown on (001)-oriented SrT... more Epitaxial films of multiferroic BiFe1−xCoxO3 (BFCO) with 0≤x≤0.35 are grown on (001)-oriented SrTiO3 and SrRuO3 buffered SrTiO3 substrates using the pulsed laser deposition technique. The effect of structural transformation from rhombohedral to tetragonal phase with increasing cobalt substitution on the magnetic, electrical, and piezo-/ferroelectric properties is investigated. Piezoresponse force microscopy is used to quantify the coercive voltage from the phase hysteresis loops for different thickness films to investigate the semi-empirical Kay–Dunn scaling law with varying cobalt concentrations. For the rhombohedral structure, a reduction of the coercive voltage is observed with increasing substitution of Fe by Co. The coercive voltage of a 10 nm BFCO (x=0.35) film is found to be 0.63 V, which is 67% lower than that of a pure BiFeO3 (BFO) (1.9 V) film of the same thickness. Cobalt substitution also leads to changes in the magnetic and electrical properties due to modification of spin ordering and reduction of the bandgap, respectively. Further, to validate the experimental results, we have performed theoretical calculations using density functional theory. The theoretical results indicate a reduction in unit cell volume and enhancement in net magnetization can be achieved with cobalt substitution, in agreement with experimental results. Partial Co substitution can, thus, provide a pathway to realize BFO-based nonvolatile magnetoelectric devices with reduced operating voltage.

Physica C-superconductivity and Its Applications, Jun 1, 1988

ABSTRACT This paper reports on progress made at IBM in the fabrication of HiTc dc SQUIDs (Superco... more ABSTRACT This paper reports on progress made at IBM in the fabrication of HiTc dc SQUIDs (Superconducting QUantum Interference Devices)1,2. We have fabricated SQUIDs from polycrystalline YBa2Cu3Oy samples on MgO substrates3 and from epitaxial films on SrTiO3 (100) substrates4. The films were patterned using either ion-implanting to selectively convert the superconductor into an insulator without actually removing any material1,5, laser ablation to pattern a loop into the film by removing material6, or a conventional ion milling process to selectively remove material using a photoresist mask. In the case of the polycrystalline films, the naturally occurring grain boundaries provide the weak link or Josephson junction behavior in a stripe that is much larger in size than the superconducting coherence length. We have measured the noise amplitude of one such SQUID made on MgO to be about 1 × 10-5PhiO/Hz1/2 at 1000 Hz and 40 K. Loops formed from true epitaxial films containing many twin boudaries will not operate as dc SQUIDs unless the films are damaged across each link. A SQUID formed in this way operated in liquid nitrogen and had an estimated white noise performance of 1 × 10-3Phi0/Hz1/2 at 74 K.