17 results on '"Sudipta Roy Barman"'
Search Results
2. Role of Li+ and Fe3+ in modified ZnO: Structural, vibrational, opto-electronic, mechanical and magnetic properties
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C. P. Vinod, Sajal Biring, Shubhra Bajpai, Shuvam Sarkar, Sk Riyajuddin, Shun-Wei Liu, Mahmud Khan, Kaushik Ghosh, Gaurav Bajpai, Somaditya Sen, Dharma R. Basaula, Sudipta Roy Barman, and Igamcha Moirangthem
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010302 applied physics ,Materials science ,Band gap ,Process Chemistry and Technology ,Doping ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Crystallographic defect ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Ion ,Ferromagnetism ,Chemical physics ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,Crystallite ,0210 nano-technology ,Wurtzite crystal structure ,Solid solution - Abstract
When Fe is doped in ZnO, a situation of charge imbalance is created due to the higher charge of Fe3+. A charge balance may be obtained by co-doping Li+0.5Fe3+0.5 combinations. A solid solution of Zn1-x(Fe0.5Li0.5)xO (0 ≤ x ≤ 0.03125) is synthesized with this viewpoint. The crystallites belong to a wurtzite P63mc space group, with lattice parameters a, b and c increasing nominally for x = 0.0156 and thereafter remaining invariant. The size varies in the range ~ 60–142 nm. Interstitials of Li and Zn ions are formed. Along with Fe3+ substitution these defects are reasons for O interstitials. These oxygen interstitials increase the red emission while reduction of oxygen vacancies reduces the green emission. These point defects create structural distortion and strain which can generate Zn vacancies. Bandgap reduces due to shallow defects. Mid-bandgap states due to oxygen interstitials and Fe 3d-O 2p hybridization result in NIR emission. On the other hand the crystal surface deforms due to Li addition which hardens the materials. A weak ferromagnetism appears at very low temperature which is enhanced by Li+ addition. Long range exchange mechanism between Fe3+ ions appears in the samples, mediated by magnetic polarons due to point defects.
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- 2019
3. Parameter dependent fabrication of Chromium nano-structures on Au(111) surface
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Abhishek Rai, Vipin Kumar Singh, Sudipta Roy Barman, and J. Nayak
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Monatomic gas ,Fabrication ,Materials science ,Condensed matter physics ,Nucleation ,02 engineering and technology ,Surfaces and Interfaces ,Substrate (electronics) ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Transition metal ,Nano ,Materials Chemistry ,Nanometre ,0210 nano-technology ,Deposition (law) - Abstract
Circular and rectangular Cr islands of nanometre size and monoatomic height exhibit an impromptu long range order on locally stepped Au(111) surface with narrow terraces. The circular islands are detached from the {100} microfaceted Au(111) step edges and nucleate between a pair of discommensuration lines of the herringbone reconstruction on ≈ 9.5 nm wide terraces. In contrast, the rectangular islands are attached to the {111} microfaceted step edges and are formed on even narrower terraces of ≈ 6 nm width. Both types of islands prefer the hcp region of the substrate as the nucleation centre. Cr deposition at elevated temperatures such as 470 K results in formation of triangular islands and spiral dislocations on wide substrate terraces. Interestingly however, at higher coverages of 3–4 ML, huge elongated ridges that are 90–260 nm in length, 10–20 nm in width and up to almost 3 nm height are observed. These ridges occur primarily along 1 1 ¯ 0 > direction, with the rest forming at an angle of 60 or 120° with respect to this direction.
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- 2019
4. Anderson localization of electron states in a quasicrystal
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Pampa Sadhukhan, Sudipta Roy Barman, Marie-Cécile de Weerd, Vincent Fournée, Prabhat Mandal, Vipin Kumar Singh, Marian Krajčí, Julian Ledieu, Andrei Gloskovskii, Shuvam Sarkar, Ian R. Fisher, UGC-DAE Consortium for Scientific Research (UGC-DAE ), Bhabha Atomic Research Centre (BARC), Government of India, Department of Atomic Energy-Government of India, Department of Atomic Energy, Slovak Academy of Sciences (SAS), Deutsches Elektronen-Synchrotron [Hamburg] (DESY), Homi Bhabha National Institute (HBNI), Institut Jean Lamour (IJL), Université de Lorraine (UL)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), and Stanford University
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Physics ,Anderson localization ,Condensed matter physics ,Photoemission spectroscopy ,Fermi level ,Quasicrystal ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Variable-range hopping ,symbols.namesake ,Quasiperiodic function ,0103 physical sciences ,symbols ,Density of states ,[PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci] ,ddc:530 ,Density functional theory ,010306 general physics ,0210 nano-technology ,ComputingMilieux_MISCELLANEOUS - Abstract
Physical review / B 103(24), L241106 (2021). doi:10.1103/PhysRevB.103.L241106, The influence of disorder on the critical electron states in a quasiperiodic lattice is a subject of intense research. In this work, we report the occurrence of Anderson localization in an icosahedral (i) polygrain quasicrystal Al-Pd-Re due to site disorder using hard x-ray photoemission spectroscopy, resistivity, and density functional theory (DFT). Photoemission spectroscopy shows that the density of states is enhanced at the Fermi level in polygrain i-Al-Pd-Re compared to single-grain i-Al-Pd-Re. In contrast, the conductivity of the former is an order of magnitude reduced compared to the latter, indicating that these electron states are localized. DFT shows that these states originate primarily from Re 5d-Pd 4d hybridization and are enhanced in polygrain i-Al-Pd-Re due to compositional difference, but are broadened because of disorder that brings about Anderson localization. This is established by the Mott variable range hopping behavior of conductivity, and the estimated localization length is 23 Å., Published by Inst., Woodbury, NY
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- 2021
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5. Tuning of ferromagnetic behavior of GaN films by N ion implantation: an experimental and first principle-based study
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Santanu Ghosh, S. R. Barman, Sudipta Roy Barman, Preetam Singh, Ulrich Kentsch, Arvind Singh, Pankaj Srivastava, Vikash Mishra, Zichao Li, and Sunil Kumar
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010302 applied physics ,Materials science ,Condensed matter physics ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,ferromagnetism ,Spectral line ,Electronic, Optical and Magnetic Materials ,nitrogen interstitials ,Ion implantation ,Unpaired electron ,Ferromagnetism ,X-ray photoelectron spectroscopy ,tuning ,Interstitial defect ,0103 physical sciences ,First principle ,ion implantation ,Metalorganic vapour phase epitaxy ,0210 nano-technology ,defects - Abstract
Magnetic properties of N-ion implanted GaN films (150 nm) have been reported. It is found that GaN films grown by the MOCVD technique show strong room temperature ferromagnetic behavior, which can be tuned by implanting N-ions at different fluences (1 × 1015 to 5 × 1016 ions-cm−2). Presence of implanted N at interstitial sites of the GaN host matrix is indicated from the strain observed in GaN by analysis of XRD data. PL spectra show presence of different types of defects in the as deposited film and engineering of defects after N-ion implantation. XPS spectra of Ga 3d-core level and valence band reveal the bonding of implanted N with the host Ga and/or N. The origin of ferromagnetic behavior is ascribed to unpaired electrons created at N sites due to Ga vacancies. First principle-based calculations also confirm ferromagnetism due to Ga vacancies and the reduction of magnetic behavior in Ga deficient GaN with N-ion implantation at interstitial site. The systematic reduction in the saturation magnetic moment value after N-ion implantation is explained on the basis of pairing of the unpaired electrons due to the bond formation of interstitial N with Ga and N present in the host matrix.
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- 2021
6. Unravelling oxygen driven α to β phase transformation in tungsten
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Shambhu Nath Jha, Virginie Serin, Aloke Kanjilal, Anil K. Sinha, Sudipta Roy Barman, Ashok Kumar Yadav, Vijay Kumar, Sébastien Joulié, Mohammad Balal, Alain Claverie, Ananya Chattaraj, Centre d'élaboration de matériaux et d'études structurales (CEMES), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie de Toulouse (ICT-FR 2599), Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Institut de Chimie du CNRS (INC)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut de Chimie du CNRS (INC)-Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA), Matériaux Multi-fonctionnels et Multi-échelles (CEMES-M3), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Université Toulouse III - Paul Sabatier (UT3), Matériaux et dispositifs pour l'Electronique et le Magnétisme (CEMES-MEM), Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Université de Toulouse (UT)-Institut National des Sciences Appliquées (INSA)-Université de Toulouse (UT)-Institut de Chimie de Toulouse (ICT), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT)-Centre National de la Recherche Scientifique (CNRS), and Université de Toulouse (UT)-Centre National de la Recherche Scientifique (CNRS)-Institut National des Sciences Appliquées - Toulouse (INSA Toulouse)
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Materials for devices ,Materials science ,Absorption spectroscopy ,lcsh:Medicine ,chemistry.chemical_element ,02 engineering and technology ,Tungsten ,01 natural sciences ,Oxygen ,Article ,X-ray photoelectron spectroscopy ,Impurity ,Ab initio quantum chemistry methods ,Phase (matter) ,0103 physical sciences ,lcsh:Science ,Condensed-matter physics ,Theory and computation ,010302 applied physics ,Nanoscale materials ,Multidisciplinary ,lcsh:R ,021001 nanoscience & nanotechnology ,chemistry ,Chemical physics ,[PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci] ,lcsh:Q ,Limiting oxygen concentration ,0210 nano-technology - Abstract
Thin films of β-W are the most interesting for manipulating magnetic moments using spin–orbit torques, and a clear understanding of α to β phase transition in W by doping impurity, especially oxygen, is needed. Here we present a combined experimental and theoretical study using grazing incidence X-ray diffraction, photoelectron spectroscopy, electron microscopy, and ab initio calculations to explore atomic structure, bonding, and oxygen content for understanding the formation of β-W. It is found that the W films on SiO2/Si have 13–22 at.% oxygen in A15 β structure. Ab initio calculations show higher solution energy of oxygen in β-W, and a tendency to transform locally from α to β phase with increasing oxygen concentration. X-ray absorption spectroscopy also revealed local geometry of oxygen in β-W, in agreement with the simulated one. These results offer an opportunity for a fundamental understanding of the structural transition in α-W and further development of β-W phase for device applications.
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- 2020
7. Role of antisite disorder, electron-electron correlations, and a surface valence transition in the electronic structure of CeMnNi4
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Sudipta Roy Barman, Pampa Sadhukhan, Ashish Chainani, Pratap Raychaudhuri, Sunil Wilfred D′Souza, Aparna Chakrabarti, Andrei Gloskovskii, Rajendra S. Dhaka, S. K. Dhar, and Vipin Kumar Singh
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Physics ,Valence (chemistry) ,Spin polarization ,Condensed matter physics ,Fermi level ,02 engineering and technology ,Electron ,Electronic structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,symbols.namesake ,X-ray photoelectron spectroscopy ,0103 physical sciences ,symbols ,Valence band ,Density functional theory ,010306 general physics ,0210 nano-technology - Abstract
${\mathrm{CeMnNi}}_{4}$ exhibits an unusually large spin polarization, but its origin has baffled researchers for more than a decade. We use bulk sensitive hard x-ray photoelectron spectroscopy (HAXPES) and density functional theory based on the Green's function technique to demonstrate the importance of electron-electron correlations of both the Ni $3d$ (${U}_{\text{Ni}}$) and Mn $3d$ (${U}_{\text{Mn}}$) electrons in explaining the valence band of this multiply correlated material. We show that Mn-Ni antisite disorder as well as ${U}_{\text{Ni}}$ play a crucial role in enhancing its spin polarization: Antisite disorder broadens a Ni $3d$ minority-spin peak close to the Fermi level (${E}_{F}$), while an increase in ${U}_{\text{Ni}}$ shifts it toward ${E}_{F}$, both leading to a significant increase of minority-spin states at ${E}_{F}$. Furthermore, the rare occurrence of a valence state transition between the bulk and the surface is demonstrated highlighting the importance of HAXPES in resolving the electronic structure of materials unhindered by surface effects.
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- 2019
8. Unique Dirac and Triple point fermiology in simple transition metals and their binary alloys
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Aftab Alam, Chanchal K. Barman, Biswarup Pathak, Shuvam Sarkar, Sudipta Roy Barman, and Chiranjit Mondal
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Physics ,Condensed Matter - Materials Science ,Electromotive force ,Condensed matter physics ,Magnetoresistance ,Strongly Correlated Electrons (cond-mat.str-el) ,Triple point ,Astrophysics::High Energy Astrophysical Phenomena ,Dirac (software) ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,symbols.namesake ,Condensed Matter - Strongly Correlated Electrons ,0103 physical sciences ,symbols ,Condensed Matter::Strongly Correlated Electrons ,Nernst equation ,010306 general physics ,0210 nano-technology ,Fermi Gamma-ray Space Telescope ,Surface states - Abstract
Noble metal surfaces (Au, Ag and Cu etc.) have been extensively studied for the Shockley type surface states (SSs). Very recently, some of these Shockley SSs have been understood from the topological consideration, with the knowledge of global properties of electronic structure. In this letter, we show the existence of Dirac like excitations in the elemental noble metal Ru, Re and Os based on symmetry analysis and first principle calculations. The unique SSs driven Fermi arcs have been investigated in details for these metals. Our calculated SSs and Fermi arcs are consistent with the previous transport and photo-emission results. We attribute these Dirac excitation mediated Fermi arc topology to be the possible reasons behind several existing transport anomalies, such as large non-saturating magneto resistance, anomalous Nernst electromotive force and its giant oscillations, magnetic breakdown etc. We further show that the Dirac like excitations in these elemental metal can further be tuned to three component Fermionic excitations, using symmetry allowed alloy mechanism.
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- 2019
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9. Electronic structure of Au-Sn compounds grown on Au(111)
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Shuvam Sarkar, S. R. Barman, Sudipta Roy Barman, Pampa Sadhukhan, Tufan Roy, Aparna Chakrabarti, and Vipin Kumar Singh
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Condensed Matter - Materials Science ,Materials science ,Photoemission spectroscopy ,Annealing (metallurgy) ,Intermetallic ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,Kinetic energy ,01 natural sciences ,Spectral line ,Crystallography ,X-ray photoelectron spectroscopy ,0103 physical sciences ,Density functional theory ,010306 general physics ,0210 nano-technology - Abstract
The electronic structure of Au-Sn intermetallic layers of different compositions grown on Au(111) to the thickness of several nanometers has been studied in this work. The layer, interface and the substrate related components in the Au 4$f$ and Sn 4$d$ core-level spectra obtained using x-ray photoelectron spectroscopy (XPS) vary with deposition parameters to reveal the details of the Au-Sn formation. While AuSn is grown by deposition at room temperature, Au rich compounds form as a result of heat treatment through inter diffusion of Au and Sn. Deposition at high temperature forms more Au rich compositions compared to post annealing at the same temperature due to the kinetic energy of the impinging Sn atoms in the former case. Post annealing, on the other hand, stabilizes the bulk phases such as AuSn and Au$_5$Sn and exhibits an activated behavior for transition from the former to the latter with increasing temperature. The XPS valence band spectra of AuSn and Au$_{5}$Sn layers show good agreement with the density functional theory calculation, indicating that these have the bulk structure reported in literature. However, the influence of anti-site defects is observed in Au$_5$Sn. Low energy electron diffraction study reveals that although the AuSn layer is ordered, its top surface is disordered at room temperature. Surface order is obtained by annealing or deposition at elevated temperatures and dispersing bands are observed by angle resolved photoemission spectroscopy. Both electron-like and hole-like bands are evident for the ($\sqrt{3}$$\times$$\sqrt{3}$)R30$^{\circ}$ phase, while a nearly free electron-like parabolic surface state is observed for the p(3$\times$3)R15$^{\circ}$ phase., Comment: Phys. Rev. B (in press); 38 pages, 14 figures and 1 table in main text and 3 figures and 5 tables in supplementary material
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- 2019
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10. Spontaneous Reduction of Copper(II) to Copper(I) at Solid-Liquid Interface
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Anupam Prasoon, Vasant Sathe, Nirmalya Ballav, Plawan Kumar Jha, Pampa Sadhukhan, Sudipta Roy Barman, and Shammi Rana
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Chemical process ,Materials science ,Reducing agent ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Copper ,Electron transport chain ,Chemical reaction ,Redox ,0104 chemical sciences ,chemistry ,Chemical engineering ,Oxidizing agent ,General Materials Science ,Physical and Theoretical Chemistry ,Thin film ,0210 nano-technology - Abstract
Oxidation and reduction reactions are of central importance in chemistry as well as vital to the basic functions of life and such chemical processes are generally brought about by oxidizing and reducing agents, respectively. Herein, we report the discovery of an interfacial reduction reaction (IRR) - without the use of any external reducing agent. In course of metal-ligand coordination, spontaneous reduction of Cu(II) to Cu(I) at a solid-liquid interface was observed-unlike in a liquid-phase reaction where no reduction of Cu(II) to Cu(I) was occurred. High-quality thin films of a new coordination network compound bearing a Fe(II)-CN-Cu(I) link were fabricated by IRR and employed for efficient electro-catalysis in the form of oxygen reduction reaction. Also, thermally activated reversible structural phase transition modulated the electron transport property in thin film. This work unveils the importance of chemical reactions at solid-liquid interfaces that can lead to the development of new functional thin film materials.
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- 2018
11. Enhancement of the density of states at the Fermi level due to oxygen atoms in noble metals
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Sudipta Roy Barman and Aparna Chakrabarti
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Materials science ,Alloy ,chemistry.chemical_element ,FOS: Physical sciences ,02 engineering and technology ,engineering.material ,01 natural sciences ,Oxygen ,Metal ,symbols.namesake ,0103 physical sciences ,Materials Chemistry ,010306 general physics ,Condensed Matter - Materials Science ,Condensed matter physics ,Fermi level ,Materials Science (cond-mat.mtrl-sci) ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Brillouin zone ,Oxygen atom ,chemistry ,visual_art ,engineering ,Density of states ,visual_art.visual_art_medium ,symbols ,Related disorder ,0210 nano-technology - Abstract
The interaction of oxygen with noble metals such as silver has been an important topic of research for many decades. Here, we show occurrence of a peak in the density of states (DOS) at the Fermi level ($E_F$) when oxygen atoms occupy disordered substitutional positions in noble metals such as Ag, Au or Ag-Au alloy. This results in large enhancement of DOS at $E_F$ with respect to Ag or Au metal. Its origin is attributed to O 2$p$ related disorder broadened flat band that straddles almost all the high symmetry directions of the Brillouin zone. Our work suggests that if a large concentration of disordered oxygen can be realized in nano-structures of noble metals, it may lead to interesting phenomenon., 7 figures
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- 2018
12. Swift heavy ion irradiation-induced modifications in the electrical and surface properties of β-Ga2O3
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Bhera Ram Tak, Dinakar Kanjilal, K. Prajna, Rajendra Singh, K. Asokan, B. K. Panigrahi, Shuvam Sarkar, N. Manikanthababu, and Sudipta Roy Barman
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010302 applied physics ,chemistry.chemical_classification ,Materials science ,Physics and Astronomy (miscellaneous) ,Schottky barrier ,Binding energy ,Analytical chemistry ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Fluence ,Divalent ,Ion ,Swift heavy ion ,chemistry ,X-ray photoelectron spectroscopy ,0103 physical sciences ,Irradiation ,0210 nano-technology - Abstract
The electrical device characteristics of Ni/β-Ga2O3 vertical Schottky barrier diodes (SBDs) were measured in situ during the irradiation of 120 MeV Ag7+ swift heavy ions (SHIs). These devices exhibit SHI irradiation-induced degradation with 120 MeV Ag7+ ions in the ion fluence ranges of 1 × 1010 to 1 × 1012 ions/cm2. The height of the Schottky barrier is found to decrease from 1.11 to 0.93 eV, and the ideality factor increases from 1.16 to 2.06. These changes indicate the degradation of the device with SHI irradiation. A significant four orders increase is observed in the leakage current density from 4.04 × 10−8 to 1.98 × 10−4 A/cm2 at −1 V, and the series resistance also increases from 3.38 × 103 to 1.15 × 104 Ω. X-ray photoelectron spectroscopy measurements show that the Ga ions are present in divalent and trivalent states with the spectral features having the binding energies centered at 20.2 eV and 19.9 eV (Ga 3d core-levels) before and after ion irradiation. The O 2s peak shifts to 23.7 eV, and there is an increase in intensity and peak broadening due to the change in the trivalent to divalent state of Ga due to the irradiation. The O(I) peak appears at 530.7 eV in the pristine sample with the Ga–O bonding with the Ga3+ state in pure Ga2O3. Moreover, there is a significant change in the intensity and the peak width of O(II) centered at 533.0 eV after ion irradiation at the fluence of 1 × 1012 ions/cm2. This indicates that there is an increase in the surface adsorbed/lattice oxygen, resulting in GaO.
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- 2020
13. Electronic structure and morphology of thin surface alloy layers formed by deposition of Sn on Au(1 1 1)
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Pampa Sadhukhan, Abhishek Rai, Kuntala Bhattacharya, Dhanshree Pandey, Aparna Chakrabarti, Vipin Kumar Singh, Shuvam Sarkar, and Sudipta Roy Barman
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Materials science ,Low-energy electron diffraction ,Fermi level ,Analytical chemistry ,General Physics and Astronomy ,Fermi energy ,Angle-resolved photoemission spectroscopy ,02 engineering and technology ,Surfaces and Interfaces ,General Chemistry ,Substrate (electronics) ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,law.invention ,symbols.namesake ,X-ray photoelectron spectroscopy ,law ,symbols ,Scanning tunneling microscope ,0210 nano-technology ,Electronic band structure - Abstract
We demonstrate formation of thin AuSn and Au2Sn surface alloy layers at room and elevated substrate temperatures ( T S = 413–493 K), respectively by the deposition of Sn on Au(1 1 1) using core-level X-ray photoelectron spectroscopy and scanning tunneling microscopy. Low energy electron diffraction patterns show different surface structures: p(3 × 3) R15 ° at room temperature for AuSn, 2 1 1 3 at T S = 413 K and ( 3 × 3 ) R30 ° at T S = 493 K for Au2Sn. Angle resolved photoemission spectroscopy reveals evolution of bands from an electron-like surface state to appearance of a hole-like band structure corresponding to AuSn and Au2Sn. The 2 1 1 3 phase of Au2Sn, which has a unit cell of oblique symmetry, exhibits an interesting linear band that meets at the Fermi level in the zone-center and have Fermi velocity comparable to graphene. Thus, our study establishes that Au-Sn bimetallic surface alloys have interesting electronic properties with potential for future applications.
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- 2020
14. Layer-by-Layer-Assembled AuNPs-Decorated First-Generation Poly(amidoamine) Dendrimer with Reduced Graphene Oxide Core as Highly Sensitive Biosensing Platform with Controllable 3D Nanoarchitecture for Rapid Voltammetric Analysis of Ultratrace DNA Hybridization
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Rengarajan Venkatesan, Huangxian Ju, Abhishek Rai, Venkataraman Dharuman, María Belén Camarada, Rajendiran Rajesh, Yangping Wen, Sudipta Roy Barman, Kumarasamy Jayakumar, and M. Maniraj
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Dendrimers ,Materials science ,Metal Nanoparticles ,02 engineering and technology ,Biosensing Techniques ,010402 general chemistry ,Electrochemistry ,01 natural sciences ,law.invention ,law ,Dendrimer ,Polyamines ,General Materials Science ,Graphene ,Layer by layer ,Poly(amidoamine) ,DNA ,Electrochemical Techniques ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Chemical engineering ,Covalent bond ,Colloidal gold ,Graphite ,Gold ,0210 nano-technology ,Biosensor - Abstract
The structure and electrochemical properties of layer-by-layer-assembled gold nanoparticles (AuNPs)-decorated first-generation (G1) poly(amidoamine) dendrimer (PD) with reduced graphene oxide (rGO) core as a highly sensitive and label-free biosensing platform with a controllable three-dimensional (3D) nanoarchitecture for the rapid voltammetric analysis of DNA hybridization at ultratrace levels were characterized. Mercaptopropinoic acid (MPA) was self-assembled onto Au substrate, then GG1PD formed by the covalent functionalization between the amino terminals of G1PD and carboxyl terminals of rGO was covalently linked onto MPA, and finally AuNPs were decorated onto GG1PD by strong physicochemical interaction between AuNPs and −OH of rGO in GG1PD, which was characterized through different techniques and confirmed by computational calculation. This 3D controllable thin-film electrode was optimized and evaluated using [Fe(CN)6]3–/4– as the redox probe and employed to covalently immobilize thiol-functionalized...
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- 2018
15. Carbon doping controlled thermoluminescent defect centers in nanoporous alumina for ion beam dosimetry
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Sudipta Roy Barman, Saif A. Khan, D. Kanjilal, Aloke Kanjilal, René Hübner, D. Das, Vipin Kumar Singh, S. Bhowmick, and S. Pal
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010302 applied physics ,Photoluminescence ,Materials science ,Ion beam ,Nanoporous ,Analytical chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Thermoluminescence ,Amorphous solid ,Ion ,chemistry ,X-ray photoelectron spectroscopy ,0103 physical sciences ,0210 nano-technology ,Carbon - Abstract
The flexibility of amorphous anodized alumina (AAO) in developing radiation dosimeter for hadron therapy is reported by controlled carbon ion implantation, followed by thermoluminescence (TL) measurements. The efficacy of amorphous AAO in controlling TL sensitivity is found to be governed by an increase in F+ defect centers as a function of carbon concentration, as revealed from the close resemblance of the trend in photoluminescence intensity. Moreover, its nanoporous structure is demonstrated to be advantageous for defect engineering due to the increase in the surface-to-volume ratio. Detailed X-ray photoelectron spectroscopy analysis suggests the formation of F+ centers by substituting Al3+ ions with C2+ in the vicinity of oxygen vacancies, where depth-dependent study showed the evolution of conducting channels owing to sp2 hybridized C–C bonding, leading to a differential charging effect. This work provides a direction to tune nanoporous AAO in its amorphous form for future ion beam dosimetry.
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- 2018
16. Intermediate stages of surface state formation and collapse of topological protection to transport in Bi2Se3
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Abhishek Rai, Sudipta Roy Barman, Kunjalata Majhi, Abhishek Banerjee, Rajamohan Ganesan, and P. S. Anil Kumar
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Surface (mathematics) ,Coupling ,Work (thermodynamics) ,Condensed matter physics ,Chemistry ,Physics ,02 engineering and technology ,State (functional analysis) ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Topology ,01 natural sciences ,symbols.namesake ,Dirac fermion ,Topological insulator ,0103 physical sciences ,symbols ,Centre for Nano Science and Engineering ,General Materials Science ,Thin film ,010306 general physics ,0210 nano-technology ,Surface states - Abstract
Surface states consisting of helical Dirac fermions have been extensively studied in threedimensional topological insulators. Yet, experiments to date have only investigated fully formed topological surface states (TSS) and it is not known whether preformed or partially formed surface states can exist or what properties they could potentially host. Here, by decorating thin films of Bi2Se3 with nanosized islands of the same material, we show for the first time that not only can surface states exist in various intermediate stages of formation but they exhibit unique properties not accessible in fully formed TSS. These include tunability of the Dirac cone mass, vertical migration of the surface state wave-function and the appearance of mid-gap Rashba-like states as exemplified by our theoretical model for decorated TIs. Our experiments show that an interplay of Rashba and Dirac fermions on the surface leads to an intriguing multi-channel weak anti-localization effect concomitant with an unprecedented tuning of the topological protection to transport. Our work offers a new route to engineer topological surface states involving Dirac-Rashba coupling by nano-scale decoration of TI thin films, at the same time shedding light on the real-space mechanism of surface state formation in general.
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- 2017
17. Quasiperiodic ordering in thick Sn layer on $i$-Al-Pd-Mn: A possible quasicrystalline clathrate
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Deborah L. Schlagel, Sudipta Roy Barman, Shuvam Sarkar, Marek Mihalkovic, Marian Krajčí, M. Maniraj, Abhishek Rai, Ajay Kumar Shukla, Vipin Kumar Singh, Thomas A. Lograsso, Pampa Sadhukhan, and Katariina Pussi
- Subjects
Condensed Matter - Materials Science ,Materials science ,Condensed matter physics ,Photoemission spectroscopy ,Clathrate hydrate ,Nucleation ,Quasicrystal ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Fermi energy ,01 natural sciences ,Surface energy ,010305 fluids & plasmas ,Condensed Matter - Other Condensed Matter ,Quasiperiodic function ,0103 physical sciences ,010306 general physics ,Pseudogap ,Other Condensed Matter (cond-mat.other) - Abstract
Realization of an elemental solid-state quasicrystal has remained a distant dream so far in spite of extensive work in this direction for almost two decades. Here, we report the discovery of quasiperiodic ordering in a thick layer of elemental Sn grown on icosahedral ($i$)-Al-Pd-Mn. The STM images and the LEED patterns of the Sn layer show specific structural signatures that portray quasiperiodicity but are distinct from the substrate. Photoemission spectroscopy reveals the existence of the pseudogap around the Fermi energy up to the maximal Sn thickness. The structure of the Sn layer is modeled as a novel form of quasicrystalline clathrate on the basis of the following: Firstly, from ab-initio theory, the energy of bulk Sn clathrate quasicrystal is lower than the high temperature metallic $\beta$-Sn phase, but higher than the low temperature $\alpha$-Sn phase. A comparative study of the free slab energetics shows that surface energy favors clathrate over $\alpha$-Sn up to about 4 nm layer thickness, and matches $\beta$-Sn for narrow window of slab thickness of 2-3 nm. Secondly, the bulk clathrate exhibits gap opening near Fermi energy, while the free slab form exhibits a pronouced pseudogap, which explains the pseudogap observed in photoemission. Thirdly, the STM images exhibit good agreement with clathrate model. We establish the adlayer-substrate compatibility based on very similar (within 1%) the cage-cage separation in the Sn clathrate and the pseudo-Mackay cluster-cluster separation on the $i$-Al-Pd-Mn surface. Furthermore, the nucleation centers of the Sn adlayer on the substrate are identified and these are shown to be a valid part of the Sn clathrate structure. Thus, based on both experiment and theory, we propose that 4 nm thick Sn adlayer deposited on 5-fold surface of $i$-Al-Pd-Mn substrate is in fact a metastable realization of elemental, clathrate family quasicrystal., Comment: 10 figures in the Manuscript and the 8 figures in the Supplementary material
- Published
- 2017
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