Pinku Saha - Academia.edu (original) (raw)

Papers by Pinku Saha

$Research paper thumbnail of Monitoring of the recovery of ion-damaged 4H-SiC with in situ synchrotron X-ray diffraction as a tool for strain-engineering$

Journal of Materials Science

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

The Journal of Physical Chemistry Letters

Journal of Applied Physics, 2022

The β phase of tungsten has attracted great interest for spintronic applications due to its highe... more The β phase of tungsten has attracted great interest for spintronic applications due to its higher spin Hall angle compared to other elemental solids and large spin–orbit torque, but the stability of this phase is yet to be well understood as many different results are there in the literature mainly based on the film thickness, temperature, and overall growth conditions. The growth of films by sputter deposition has emerged as a promising technique to achieve β-W owing to its compatibility with current spintronic technology. We demonstrate here the efficient ability of dc magnetron sputtering to grow stable β-W films up to a thickness of ∼180 nm at room temperature by varying a set of deposition parameters like pressure, power, and deposition time and discuss the various underlying mechanisms. From these results, the optimized set of deposition parameters for growing β-W films is given. A clear understanding of the influence of oxygen in the atomic structure of β-W is obtained by va...

A detailed high pressure study is carried out on 1T MoTe2 using X-ray diffraction(XRD) and Raman ... more A detailed high pressure study is carried out on 1T MoTe2 using X-ray diffraction(XRD) and Raman spectroscopy measurements upto about 30.5 GPa. High pressure XRD measurements show no structural transition. All the lattice parameters exhibit anomalous changes in the pressure region 8.4 to 12.7 GPa. Compressibility of the sample is found to be reduced by almost four times above 12.7 GPa with respect to that below 8.4 GPa. The anomalies in the Raman mode corresponding to the out of plane vibrations of Mo atoms sitting in the unit cell surface indicate a strong electron phonon coupling possibly mediated by differential strain inside the unit cell.

Cornell University - arXiv, Aug 12, 2015

We have carried out a detailed experimental investigation on CuO using dielectric constant, ac re... more We have carried out a detailed experimental investigation on CuO using dielectric constant, ac resistance, Raman spectroscopy and X-ray diffraction measurements at high pressures and room temperature. Both dielectric constant and dielectric loss show anomalous peak in the pressure range 3.4-4.4 GPa indicating a ferroelectric transition. Raman studies show anomalous behaviour of the A g mode with a slope change in the mode frequency and a minimum in the mode FWHM at 3.4 GPa indicating a strong spin phonon coupling along [1 0-1] direction. A step like behaviour in the intensity of the A g is observed at 3.4 GPa, indicating a change in polarization of the mode. A maximum in the intensity of the (2 0-2) Bragg peak at 3.4 GPa points to the occurrence of critical scattering due to emergence of magnetic exchange interaction. All our experimental evidences show to the presence of reentrant type-II multiferroic behaviour in CuO at 4 GPa.

$Research paper thumbnail of Anomalous compressibility in 1T$^\prime$ MoTe$_{2}$ single crystal:High pressure Raman and structural studies$

Cornell University - arXiv, Jan 6, 2020

A detailed high pressure study is carried out on 1T ′ MoTe 2 using X-ray diffraction(XRD) and Ram... more A detailed high pressure study is carried out on 1T ′ MoTe 2 using X-ray diffraction(XRD) and Raman spectroscopy measurements upto about 30.5 GPa. High pressure XRD measurements show no structural transition. All the lattice parameters exhibit anomalous changes in the pressure region 8.4 to 12.7 GPa. Compressibility of the sample is found to be reduced by almost four times above 12.7 GPa with respect to that below 8.4 GPa. The anomalies in the Raman mode corresponding to the out of plane vibrations of Mo atoms sitting in the unit cell surface indicate a strong electron phonon coupling possibly mediated by differential strain inside the unit cell.

Physical Review B

A detailed high pressure investigation is carried out using x-ray diffraction, Raman spectroscopy... more A detailed high pressure investigation is carried out using x-ray diffraction, Raman spectroscopy and low temperature resistivity measurements on hexagonal ZrSe 2 having an excess of 3 at.% Zr. Structural studies show that the sample goes through a gradual structural transition from hexagonal to monoclinic phase, with a mixed phase in the pressure range 5.9 GPa to 14.8 GPa. Presence of minimum in the c/a ratio in the hexagonal phase and a minimum in the full width half maximum of the A 1g mode at about the same pressure indicate to an electronic phase transition. The sample shows a metallic characteristic in its low temperature resistivity data at ambient pressure, which persist till about 5.1 GPa and can be related the presence of slight excess Zr. At and above 7.3 GPa, the sample shows a metal to semiconductor transition with opening of a very small band gap, which increases with pressure. The low temperature resistivity data show an upturn, which flattens with increase in pressure. The phenomenological analysis of the low temperature resistivity data indicate to the presence of Kondo effect in the sample, which may be due to the excess Zr.

Bulletin of the American Physical Society, Mar 16, 2021

We report the measurements of the thermal conductivity (κ) of iron (Fe) and nickel (Ni) at high p... more We report the measurements of the thermal conductivity (κ) of iron (Fe) and nickel (Ni) at high pressures and high temperatures. κ values are estimated from the temperature measurements across the sample surface in a laser heated diamond anvil cell (LHDAC) and using the COMSOL software. Near-isothermal κ’s are observed to increase with pressure in both the metals due to the increase of density of the pressed metals. In both metals κ’s are observed to follow a sharp fall during melting at different pressure points and are consistence with the other multi-anvil measurements. Constant values of κ in these metals during melting at different pressures reveal the loss of long range order, which creates independent movement of atomic metals. The melting temperature measured in these metals from the sudden drop of κ-values are in a good agreement with the other melting measurements in LHDAC. The results obtained in this study is expected to provide an insight to the studies on the planets M...

arXiv: Materials Science, 2016

Thermal conductivity of the most abundant element in the planetary core, Iron (Fe) is measured up... more Thermal conductivity of the most abundant element in the planetary core, Iron (Fe) is measured up to Earth's outer core pressure sim120\sim 120sim120 GPa. The measurements are carried out using the laser heated diamond anvil cell facility, where the absorbed power by Fe metal foil is calculated using thermodynamical equation. The thermal conductivity of gamma−Fe\gamma-Fegamma−Fe linearly increases up to a maximum experimental pressure 40 GPa. Thermal conductivity of epsilon−Fe\epsilon-Feepsilon−Fe measured by us shows a saturated value sim\simsim 52 ($\pm$ 5) Wm−1K−1Wm^{-1}K^{-1}Wm−1K−1 in the pressure range 77 - 120 GPa. At different pressures temperature dependence of thermal conductivity show a sharp drop during melting, which indicates the formation of liquid layer resulting in a thermal buffer to the heat conduction.

$Research paper thumbnail of Strain induced electronic transition in 1T′ MoTe2: high pressure Raman, x-ray diffraction, resistivity measurements and first principles theoretical studies$

Electronic Structure, 2021

A detailed high pressure study is carried out on 1T′ MoTe2 using x-ray diffraction (XRD) and Ram... more A detailed high pressure study is carried out on 1T′ MoTe2 using x-ray diffraction (XRD) and Raman spectroscopy measurements up to about 30.5 GPa along with a room temperature resistivity measurement up to 14.3(4) GPa and density functional theory calculations. Though high-pressure XRD measurements show no structural transition, all the lattice parameters exhibit anomalous changes in the pressure region 8.4 to 12.7 GPa. The compressibility of the sample is found to be reduced by almost four times above 12.7 GPa with respect to that below 8.4 GPa. The anomalies in the Raman mode corresponding to the out of plane vibrations of Mo atoms sitting in the unit cell surface indicate a strong electron–phonon coupling possibly mediated by differential strain inside the unit cell. A rapid decrease in resistivity value up to about 7.0(2) GPa of pressure agrees well with the increase in the density of states (DOS) at the Fermi energy with pressure. Pressure evolution of band structure, as well ...

Journal of Physics: Condensed Matter, 2021

A detailed temperature and pressure investigation on BiGdO 3 is carried out by means of dielectri... more A detailed temperature and pressure investigation on BiGdO 3 is carried out by means of dielectric constant, piezoelectric current, polarization-electric field loop, Raman scattering and x-ray diffraction measurements. Temperature dependent dielectric constant and dielectric loss show two anomalies at about 290 K (T r) and 720 K (T C). The later anomaly is most likely due to antiferroelectric to paraelectric transition as hinted by piezoelectric current and polarization-electric field loop measurements at room temperature, while the former anomaly suggests reorientation of polarization. Cubic to orthorhombic structural transition is observed at about 10 GPa in high pressure x-ray diffraction studies accompanied by anisotropic lattice parameter changes. An expansion about 30 % along a-axis and 15 % contraction along b-axis during the structural transition result in 9.5 % expansion in unit cell volume. This structural transition is corroborated by anomalous softening and large increase in full width half maximum (FWHM) of 640 cm −1 Raman mode above 10 GPa. Enhancement of large structural distortion and significant volume expansion during the structural transition indicate towards an antiferroelectric to ferroelectric transition in the system.

The Journal of Physical Chemistry C, 2021

We report a detailed high pressure study involving X-ray diffraction, Raman spectroscopy, and pho... more We report a detailed high pressure study involving X-ray diffraction, Raman spectroscopy, and photoluminescence measurements on a model Pb-free solar cell material Cs3Bi2Br9 halide perovskite. The ...

Journal of Applied Physics, 2020

We report high pressure X-ray diffraction and a detailed systematic Raman measurements on ReS 2 s... more We report high pressure X-ray diffraction and a detailed systematic Raman measurements on ReS 2 sample, which is mechanically exfoliated from a single crystal. A few new Bragg peaks are observed to emerge above 6 GPa indicating a structural transition from distorted 1T to distorted 1T ′ in triclinic structure. The same is corroborated by appearance of new Raman modes in the same pressure range. Softening of the Raman modes corresponding to Re atom vibrations are observed in the distorted 1T ′ phase in the pressure range 15-25 GPa. In the same pressure range the anomalous change in the volume is found to be induced by the lattice expansion. The volume expansion is related to the sliding of layers leading to octahedral distortion and increase in octahedral volume. The sample is found to be much incompressible above 25 GPa with respect to below 15 GPa data. The same is also reflected in the Raman mode shifts with pressure.

Journal of Physics: Condensed Matter, 2018

High pressure behaviour of nanocrystalline YCrO3 is investigated up to 10 GPa using electrical, m... more High pressure behaviour of nanocrystalline YCrO3 is investigated up to 10 GPa using electrical, magnetic, synchrotron x-ray diffraction and Raman spectroscopy measurements. High pressure dielectric constant measurements show a sharp peak at 4.5 GPa, though the sample is found to be in ferroelectric phase up to the highest pressure of our study from piezoelectric current measurements. X-ray diffraction measurements show absence of any structural phase transition, however anomalies are observed in the unit cell structural parameters at about 4.3 GPa and the Y-atom position shows a maximum shift at the same pressure. In the absence of any structural transition, anomalous behaviour of relevant Raman modes with minimum in the Raman band width at about same pressure indicate towards a spin-phonon interaction. AC magnetic measurements in the toroid anvil cell show an anomalous enhancement of magnetic moment above 4 GPa indicating a collective magnetic response of nanoparticles.

Journal of the American Ceramic Society, 2020

The solid solution 0.5Ba(T i 0.8 Zr 0.2)O 3 − 0.5(Ba 0.7 Ca 0.3)T iO 3 (BCZT) has become a promis... more The solid solution 0.5Ba(T i 0.8 Zr 0.2)O 3 − 0.5(Ba 0.7 Ca 0.3)T iO 3 (BCZT) has become a promising member of the lead-free piezoelectric materials because of its exceptionally high piezoelectric properties. In this study, we focus on studying pressure-dependent Raman spectroscopy, powder x-ray diffraction and dielectric constant measurements on BCZT. The data show several structural transitions are present, where the system from ambient mixed phase (tetragonal, P4mm+ orthorhombic Amm2) transforms into single phase (P4mm) at 0.26 GPa, then converts into cubic phase (Pm3m) at 4.7 GPa followed by another possible structural reordering around 10 GPa. Although there have been a lot of unanimity with the ambient crystallographic state of BCZT, our analysis justifies the presence of an intermediate orthorhombic phase in the Morphological Phase Boundary (MPB) of BCZT phase diagram. The transformation tetragonal to cubic is indicated by the Raman mode softening, unit cell volume change and the (T i/Zr)O 6 octahedra distortion, which coincides with the well-known ferroelectric-paraelectric transition of the system. The sudden drop in the dielectric constant value at 4.7 GPa also confirms the loss of ferroelectric nature of the BCZT ceramic.

Indian Journal of Physics, 2020

In this work, a double-sided laser-heated diamond anvil cell facility for studies at extreme cond... more In this work, a double-sided laser-heated diamond anvil cell facility for studies at extreme conditions of pressure and temperature that has been developed is described in detail. Phase transitions occurring at extreme conditions can be mapped by accurate measurements of pressure and temperature. Micrometer-sized diamond crystals having regular facets have been synthesized at a pressure of 18 GPa and temperature 1785 K, which is confirmed by visual inspection, micro-Raman and field emission scanning electron micrograph measurements. A low-temperature gradient is observed across the sample surface during the formation of micrometer-sized diamond crystals. Our observation restricts the use of steel gasket as it can react with carbon (C) transported from the diamond anvil. The reaction of C with one of the potential thermal insulating medium Al 2 O 3 is observed in the X-ray diffraction measurements.

$Research paper thumbnail of High pressure anomalies in exfoliated MoSe2: resonance Raman and x-ray diffraction studies$

Materials Research Express, 2020

Detailed high pressure Resonance Raman (RR) Spectroscopy and x-ray diffraction (XRD) studies are ... more Detailed high pressure Resonance Raman (RR) Spectroscopy and x-ray diffraction (XRD) studies are carried out on 3–4 layered MoSe 2 obtained by liquid exfoliation. Analysis of ambient XRD pattern and RR spectra indicate the presence of a triclinic phase along with its parent hexagonal phase. Slope change in the linear behavior of reduced pressure (H) with respect to Eulerian strain (f E ) is observed at about 13 GPa in hexagonal phase and at about 17 GPa for the triclinic phase. High pressure Raman measurements using two different pressure transmitting media (PTM) show three linear pressure regions, separated by pressure values around which anomalies in the structure are observed. A broad minimum in the FWHM values of E 2 g 1 mode at about 10–12 GPa indicate to an electron-phonon coupling. Above 33 GPa the sample completely gets converted to the triclinic structure, which indicates the importance of strain in structural as well as electronic properties of two dimensional materials.

Journal of Applied Physics, 2018

A detailed high pressure X-ray diffraction and Raman spectroscopy study is carried out on monolay... more A detailed high pressure X-ray diffraction and Raman spectroscopy study is carried out on monolayer WS 2 and nanocrystalline WS 2. The monolayer sample is obtained by liquid exfoliation. Photoluminescence and Raman measurements show it to consist of a monolayer. Careful analysis of ambient and high pressure data indicates the emergence of a triclinic phase at about 5.8 GPa in patches embedded in the parent hexagonal phase. This raises a question mark over the structural purity of the exfoliated monolayer materials beyond certain stress conditions. Raman mode values and their full width at half maximum of the monolayer sample show anomalous changes at about 27 GPa, the pressure where the sample completely gets converted to the triclinic structure indicating the importance of strain in structural as well as electronic properties of two dimensional materials.

Geoscience Frontiers, 2020

Thermal conductivity (k) of Iron is measured up to about 134 GPa. The measurements are carried ou... more Thermal conductivity (k) of Iron is measured up to about 134 GPa. The measurements are carried out using the single sided laser heated diamond anvil cell, where the power absorbed by a Fe metal foil at hotspot is calculated using a novel thermodynamical method. Thermal conductivity of fcc (γ) À Fe increases up to a pressure of about 46 GPa. We find thermal conductivity values in the range of 70-80 Wm À1 K À1 (with an uncertainty of 40%), almost constant with pressure, in the hcp (ε) phase of Fe. We attribute the pressure independent k above 46 GPa to the strong electronic correlation effects driven by the electronic topological transition (ETT). We predict a value of thermal conductivity of ε-Fe of about 40 AE 16 Wm À1 K À1 at the outer core of Earth.