101 results on '"Abir De Sarkar"'
Search Results
2. Experimental and computational insights into luminescence in atomically precise bimetallic Au6−nCun(MPA)5 (n = 0–2) clusters
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Aarti Devi, Harshita Seksaria, Dipankar Bain, Sarita Kolay, null Rashi, Abir De Sarkar, and Amitava Patra
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General Physics and Astronomy ,Physical and Theoretical Chemistry - Abstract
Bimetallic nanoclusters (NCs) have emerged as a new class of luminescent materials for potential applications in sensing, bio-imaging, and light-emitting diodes (LEDs).
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- 2023
3. Valley Hall effect in graphene-like SnX ( X=Si , Ge) buckled monolayers with high charge carrier mobility and low lattice thermal conductivity
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Manish Kumar Mohanta, Fathima IS, and Abir De Sarkar
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- 2023
4. Spin-Current Modulation in Hexagonal Buckled ZnTe and CdTe Monolayers for Self-Powered Flexible-Piezo-Spintronic Devices
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I. S. Fathima, Abir De Sarkar, Manish Kumar Mohanta, and Amal Kishore
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Semiconductor ,Piezoelectric coefficient ,Materials science ,Spintronics ,business.industry ,Piezotronics ,Electric field ,Wide-bandgap semiconductor ,Optoelectronics ,General Materials Science ,Density functional theory ,business ,Piezoelectricity - Abstract
The next-generation spintronic device demands the gated control of spin transport across the semiconducting channel through the replacement of the external gate voltage source by the piezo potential, as experimentally demonstrated in Zhu et al. ACS Nano, 2018, 12 (2), 1811-1820. Consequently, a high level of out-of-plane piezoelectricity together with a large Rashba spin splitting is sought after in semiconducting channel materials. Inspired by this experiment, a new hexagonal buckled two-dimensional (2D) semiconductor, ZnTe, and its iso-electronic partner, CdTe, are proposed herewith. These 2D materials show a strong spin-orbit coupling (SOC), which is evidenced by a large Rashba constant of 1.06 and 1.27 eV·A, respectively, in ZnTe and CdTe monolayers. Moreover, these Rashba semiconductors exhibit a giant out-of-plane piezoelectric coefficient (d33) = 88.68 and 172.61 pm/V, and can thereby generate a high piezo potential for gating purposes in spin field-effect transistors (spin-FETs). While the low elastic stiffness implies the mechanical flexibility or stretchability in these monolayers. The Rashba constants are found to be effectively modulated via external perturbations, such as strain and electric field. The wide band gap provides ample room for modulation in its electronic properties via external perturbations. Such scope is severely limited in previously reported narrow band gap Rashba semiconductors. The fascinating results found in this work indicate their great potential for applications in next-generation self-powered flexible-piezo-spintronic devices. Moreover, a new class of hexagonal buckled ZnX (X: S, Se, or Te) monolayers is proposed herein based on their previously synthesized bulk counterparts, while their electronic, mechanical, piezoelectric, and thermal properties have been thoroughly investigated using the state-of-art density functional theory (DFT).
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- 2021
5. Nanocatalytic Interface to Decode the Phytovolatile Language for Latent Crop Diagnosis in Future Farms
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Mahima Chandel, Prem Kumar, Anu Arora, Sarita Kataria, Sunil Chandra Dubey, Djanaguiraman M, Kamaljit Kaur, Bandana Kumari Sahu, Abir De Sarkar, and Vijayakumar Shanmugam
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Oxygen ,Farms ,Norisoprenoids ,Electrodes ,Analytical Chemistry ,Language - Abstract
Crop diseases cause the release of volatiles. Here, the use of an SnO
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- 2022
6. Hot Hole Cooling and Transfer Dynamics from Lead Halide Perovskite Nanocrystals Using Porphyrin Molecules
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Srijon Ghosh, Raihan Ahammed, Amitava Patra, Abir De Sarkar, Goutam Ghosh, Kritiman Marjit, and Arnab Ghosh
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Materials science ,Halide ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Porphyrin ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,General Energy ,Thermalisation ,Lead (geology) ,Nanocrystal ,chemistry ,Chemical physics ,Molecule ,Astrophysics::Earth and Planetary Astrophysics ,Physical and Theoretical Chemistry ,0210 nano-technology ,Perovskite (structure) - Abstract
A deep understanding of hot carrier (HC) dynamics is important to improve the performance of optoelectronic devices by reducing the thermalization losses. Here, we investigate the hot hole cooling ...
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- 2021
7. Anisotropy in colossal piezoelectricity, giant Rashba effect and ultrahigh carrier mobility in Janus structures of quintuple Bi2X3 (X = S, Se) monolayers
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Nilakantha Tripathy and Abir De Sarkar
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General Materials Science ,Condensed Matter Physics - Abstract
Due to the asymmetric structures, two-dimensional Janus materials have gained significant attention in research for their intriguing piezoelectric and spintronic properties. In the present work, quintuple Bi2X3 (X = S, Se) monolayers (MLs) have been modified to create stable Janus Bi2X2Y (X ≠ Y = S, Se) MLs that display piezoelectricity in both the planes along with Rashba effect. The out-of-plane piezoelectric constant (d 33) is 41.18 (−173.14) pm V−1, while the in-plane piezoelectric constant (d 22) is 5.23 (6.21) pm V−1 for Janus Bi2S2Se (Bi2Se2S) ML. Including spin–orbit coupling in the Janus MLs results in anisotropic giant Rashba spin splitting (RSS) at the Γ point in the valence band, with RSS proportional to d 33. The Rashba constant along the Γ–K path, α R Γ − K , is 3.30 (2.27) eV Å, whereas along Γ–M, α R Γ − M is 3.58 (3.60) eV Å for Janus Bi2S2Se (Bi2Se2S) ML. The MLs exhibit ultrahigh electron mobility (∼5442 cm2V−1s−1) and have electron to hole mobility ratio of more than 2 due to their tiny electron-effective masses. The flexibility of the MLs allows for a signification alteration in its properties, like band gap, piezoelectric coefficient, and Rashba constant, via mechanical (biaxial) strain. For the MLs, band gap and d 33 value are enhanced with compressive strain. The d33 value of Janus Bi2Se2S reaches 4886.51 pm V−1 under compressive strain. The coexistence of anisotropic colossal out-of-plane piezoelectricity, giant RSS, and ultrahigh carrier mobilities in Janus Bi2S2Se and Bi2Se2S MLs showcase their tremendous prospects in nanoelectronic, piezotronics, and spintronics devices.
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- 2023
8. Insights into selected 2D piezo Rashba semiconductors for self-powered flexible piezo spintronics: material to contact properties
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Fathima IS, Manish Kumar Mohanta, and Abir De Sarkar
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General Materials Science ,Condensed Matter Physics - Abstract
The new paradigm in electronics consists in realizing the seamless integration of many properties latent in nanomaterials, such as mechanical flexibility, strong spin–orbit coupling (Rashba spin splitting—RSS), and piezoelectricity. Taking cues from the pointers given on 1D ZnO nanowires (ACS Nano 2018 12 1811–20), the concept can be extended to multifunctional two-dimensional (2D) materials, which can serve as an ideal platform in next-generation electronics such as self-powered flexible piezo-spintronic device. However, a microscopically clear understanding reachable from the state-of-the-art density functional theory-based approaches is a prerequisite to advancing this research domain. Atomic-scale insights gained from meticulously performed scientific computations can firmly anchor the growth of this important research field, and that is of undeniable relevance from scientific and technological outlooks. This article reviews the scientific advance in understanding 2D materials hosting all the essential properties, i.e. flexibility, piezoelectricity, and RSS. Important 2D semiconducting monolayers that deserve a special mention, include monolayers of buckled MgX (X = S, Se, Te), CdTe, ZnTe, Janus structures of transition metal trichalcogenides, Janus tellurene and 2D perovskites. van Der Waals multilayers are also built to design multifunctional materials via modulation of the stacking sequence and interlayer coupling between the constituent layers. External electric field, strain engineering and charge doping are perturbations mainly used to tune the spintronic properties. Finally, the contact properties of these monolayers are also crucial for their actual implementation in electronic devices. The nature of the contacts, Schottky/Ohmic, needs to be carefully examined first as it controls the device’s performance. In this regard, the rare occurrence of Ohmic contact in graphene/MgS van der Waals hetero bilayer has been presented in this review article.
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- 2023
9. Hexagonal and tetragonal ScX (X = P, As, Sb) nanosheets for optoelectronics and straintronics
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Harshita Seksaria, Arneet Kaur, Khushwant Singh, and Abir De Sarkar
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General Physics and Astronomy ,Surfaces and Interfaces ,General Chemistry ,Condensed Matter Physics ,Surfaces, Coatings and Films - Published
- 2023
10. Engineering Catalytically Active Sites by Sculpting Artificial Edges on MoS 2 Basal Plane for Dinitrogen Reduction at a Low Overpotential
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Renu Rani, Ashmita Biswas, Raihan Ahammed, Taniya Purkait, Anirban Kundu, Subhajit Sarkar, Mamta Raturi, Abir De Sarkar, Ramendra Sundar Dey, and Kiran Shankar Hazra
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Biomaterials ,General Materials Science ,General Chemistry ,Biotechnology - Published
- 2023
11. Group-IV(A) Janus dichalcogenide monolayers and their interfaces straddle gigantic shear and in-plane piezoelectricity
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Abir De Sarkar, Pradip Nandi, Ashima Rawat, Nityasagar Jena, and Raihan Ahammed
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Electron mobility ,symbols.namesake ,Materials science ,Piezoelectric coefficient ,Strain engineering ,Condensed matter physics ,Monolayer ,symbols ,Stacking ,General Materials Science ,Janus ,van der Waals force ,Piezoelectricity - Abstract
Inversion symmetry in the 1T-phase of pristine dichalcogenide monolayer MX2 (M = Ge, Sn; X = S, Se) is broken in their Janus structures, MXY (M = Ge, Sn; X ≠ Y = S, Se), which induces an in-plane piezoelectric coefficient, d22 = 4.09 (2.15) pm V-1 and a shear piezoelectric coefficient, d15 = 7.90 (13.68) pm V-1 in the GeSSe (SnSSe) monolayer. High flexibility arising from the small Young's modulus (60-70 N m-1) found in these Group-IV(A) Janus monolayers makes them suitable for large-scale strain engineering. Application of 7% uniaxial tensile strain increases d22 and d15 colossally to 267.07 pm V-1 and 702.34 pm V-1, respectively, thereby reaching the level of bulk piezoelectric perovskite materials. When the Janus GeSSe monolayers are stacked to form a van der Waals (vdW) homo-bilayer, d22 lies between 19.87 and 73.26 pm V-1, while d15 falls into the range between 83.01 and 604.34 pm V-1, depending on the stacking order. The chalcogen exchange energies and overall stabilities of the monolayers and bilayers confirm the feasibility of their experimental synthesis. Moreover, hole mobility in the GeSSe monolayer is greater than the electron mobility along its zigzag directions (μe = 883 cm2 V-1 s-1 and μh = 1134 cm2 V-1 s-1). Therefore, the semiconducting, flexible, and piezoelectric Janus GeSSe monolayer and bilayers are immensely promising for futuristic applications in energy harvesting, nanopiezotronic field-effect transistors, atomically thin sensors, shear/torsion actuators, transducers, self-powered circuits in nanorobotics, and electromechanical memory devices, and biomedical and other nanoelectronic applications.
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- 2021
12. Electronic Band Structure and Ultrafast Carrier Dynamics of Two Dimensional (2D) Semiconductor Nanoplatelets (NPLs) in the Presence of Electron Acceptor for Optoelectronic Applications
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Anusri Medda, Abir De Sarkar, Rajesh Bera, Ashima Rawat, Avisek Dutta, and Amitava Patra
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chemistry.chemical_classification ,Materials science ,business.industry ,Chalcogenide ,Electron acceptor ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,General Energy ,Semiconductor ,chemistry ,Optoelectronics ,Physical and Theoretical Chemistry ,business ,Electronic band structure ,Carrier dynamics ,Ultrashort pulse - Abstract
Two-dimensional (2D) cadmium chalcogenide nanoplatelets (NPLs) have been grown as an emerging material for optoelectronic applications because of their unique properties. Here, we investigate the c...
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- 2020
13. Ultrahigh Out-of-Plane Piezoelectricity Meets Giant Rashba Effect in 2D Janus Monolayers and Bilayers of Group IV Transition-Metal Trichalcogenides
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Raihan Ahammed, Nityasagar Jena, Ashima Rawat, Manish K. Mohanta, null Dimple, and Abir De Sarkar
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Materials science ,Condensed matter physics ,Point reflection ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Piezoelectricity ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Out of plane ,General Energy ,Transition metal ,Group (periodic table) ,Monolayer ,Janus ,Physical and Theoretical Chemistry ,0210 nano-technology ,Rashba effect - Abstract
The simultaneous occurrence of gigantic piezoelectricity and Rashba effect in two-dimensional materials are unusually scarce. Inversion symmetry occurring in MX3 (M= Ti, Zr, Hf; X= S, Se) monolayer...
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- 2020
14. Electronic Structure Modulation of 2D Colloidal CdSe Nanoplatelets by Au25 Clusters for High-Performance Photodetectors
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Anusri Medda, Amitava Patra, Avisek Dutta, Manish Kumar Mohanta, Abir De Sarkar, and Dipankar Bain
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Materials science ,business.industry ,Photodetector ,Electronic structure ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Nanoclusters ,Colloid ,General Energy ,Semiconductor ,Modulation ,Optoelectronics ,Physical and Theoretical Chemistry ,business - Abstract
The electronic interactions between colloidal two dimensional (2D) semiconductor nanoplatelets (NPLs) and Au nanoclusters (NCs) remains unexplored which is decisive for optoelectronic applications....
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- 2020
15. Experimental and Theoretical Study into Interface Structure and Band Alignment of the Cu2Zn1–xCdxSnS4 Heterointerface for Photovoltaic Applications
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Nelson Y. Dzade, Sachin R. Rondiya, Santosh K. Haram, Abir De Sarkar, Raihan Ahammed, Yogesh Jadhav, Sandesh Jadkar, Hirendra N. Ghosh, and Tanmay Goswami
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Materials science ,Band gap ,business.industry ,Energy Engineering and Power Technology ,engineering.material ,Band offset ,law.invention ,chemistry.chemical_compound ,chemistry ,law ,Solar cell ,Materials Chemistry ,Electrochemistry ,engineering ,Chemical Engineering (miscellaneous) ,Optoelectronics ,Charge carrier ,Direct and indirect band gaps ,Density functional theory ,CZTS ,Kesterite ,Electrical and Electronic Engineering ,business - Abstract
To improve the constraints of kesterite Cu2ZnSnS4 (CZTS) solar cell, such as undesirable band alignment at p–n interfaces, bandgap tuning, and fast carrier recombination, cadmium (Cd) is introduced into CZTS nanocrystals forming Cu2Zn1–xCdxSnS4 through cost-effective solution-based method without postannealing or sulfurization treatments. A synergetic experimental–theoretical approach was employed to characterize and assess the optoelectronic properties of Cu2Zn1–xCdxSnS4 materials. Tunable direct band gap energy ranging from 1.51 to 1.03 eV with high absorption coefficient was demonstrated for the Cu2Zn1–xCdxSnS4 nanocrystals with changing Zn/Cd ratio. Such bandgap engineering in Cu2Zn1–xCdxSnS4 helps in effective carrier separation at interface. Ultrafast spectroscopy reveals a longer lifetime and efficient separation of photoexcited charge carriers in Cu2CdSnS4 (CCTS) nanocrystals compared to that of CZTS. We found that there exists a type-II staggered band alignment at the CZTS (CCTS)/CdS interface, from cyclic voltammetric (CV) measurements, corroborated by first-principles density functional theory (DFT) calculations, predicting smaller conduction band offset (CBO) at the CCTS/CdS interface as compared to the CZTS/CdS interface. These results point toward efficient separation of photoexcited carriers across the p–n junction in the ultrafast time scale and highlight a route to improve device performances.
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- 2020
16. Nanoscale Interfaces of Janus Monolayers of Transition Metal Dichalcogenides for 2D Photovoltaic and Piezoelectric Applications
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Ashima Rawat, Manish Kumar Mohanta, Nityasagar Jena, null Dimple, Raihan Ahammed, and Abir De Sarkar
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Van der waals heterostructures ,Materials science ,Photovoltaic system ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Piezoelectricity ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,General Energy ,Transition metal ,Monolayer ,Janus ,Physical and Theoretical Chemistry ,0210 nano-technology ,Nanoscopic scale - Abstract
Using first-principles calculations, we demonstrate a combination of two emergent fields, type II van der Waals heterostructures and Janus structures, for the purpose of optimizing the harvesting o...
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- 2020
17. Tweaking the Physics of Interfaces between Monolayers of Buckled Cadmium Sulfide for a Superhigh Piezoelectricity, Excitonic Solar Cell Efficiency, and Thermoelectricity
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Manish Kumar Mohanta and Abir De Sarkar
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Electron mobility ,Materials science ,business.industry ,Energy conversion efficiency ,Heterojunction ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Solar energy ,01 natural sciences ,Piezoelectricity ,Cadmium sulfide ,0104 chemical sciences ,chemistry.chemical_compound ,Solar cell efficiency ,Semiconductor ,chemistry ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business - Abstract
Interfaces of heterostructures are routinely studied for different applications. Interestingly, monolayers of the same material when interfaced in an unconventional manner can bring about novel properties. For instance, CdS monolayers, stacked in a particular order, are found to show unprecedented potential in the conversion of nanomechanical energy, solar energy, and waste heat into electricity, which has been systematically investigated in this work, using DFT-based approaches. Moreover, stable ultrathin structures showing strong capabilities for all kinds of energy conversion are scarce. The emergence of a very high out-of-plane piezoelectricity,
- Published
- 2020
18. Electronic, quantum transport and optical properties analysis of doped phosphorene sheet
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Sukhbir Singh, Abir De Sarkar, and Inderpreet Kaur
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Materials science ,Condensed matter physics ,Health, Toxicology and Mutagenesis ,010401 analytical chemistry ,Doping ,Public Health, Environmental and Occupational Health ,Soil Science ,Function (mathematics) ,010501 environmental sciences ,01 natural sciences ,Pollution ,0104 chemical sciences ,Analytical Chemistry ,Quantum transport ,Phosphorene ,chemistry.chemical_compound ,chemistry ,Environmental Chemistry ,Waste Management and Disposal ,0105 earth and related environmental sciences ,Water Science and Technology ,Electronic properties - Abstract
A density functional framework has been used to explore the geometrical stability and electronic properties of phosphorene sheet. The non-equilibrium Green’s function approach has also been utilize...
- Published
- 2020
19. Interfacial hybridization of Janus MoSSe and BX (X = P, As) monolayers for ultrathin excitonic solar cells, nanopiezotronics and low-power memory devices
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Manish Kumar Mohanta and Abir De Sarkar
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Materials science ,Piezoelectric coefficient ,business.industry ,Band gap ,Schottky barrier ,Heterojunction ,Piezoelectricity ,symbols.namesake ,Electric field ,Monolayer ,symbols ,Optoelectronics ,General Materials Science ,van der Waals force ,business - Abstract
In this work, we explored the interfacial two-dimensional (2D) physics and significant advancements in the application prospects of MoSSe monolayer when it is combined with a boron pnictide (BP, BAs) monolayer in a van der Waals heterostructure (vdWH) setup. The constructed vdWHs were found to be mechanically and dynamically stable, and they form type-II p–n heterojunctions. Thus, the photogenerated electron–hole pairs are spatially separated. In the BX/MoSSe vdWHs, the BX monolayer serves as excellent donor material for MoSSe, having an ideal donor band gap of ∼1.3 eV. The small value of the conduction band offset (CBO) between the individual monolayers in the vdWHs makes it an excellent candidate for solar energy harvesting in excitonic solar cells, where the power conversion efficiencies were calculated to be 22.97% (BP/MoSSe) and 20.86% (BAs/MoSSe). Also, more than four-fold enhancement in the out-of-plane piezoelectric coefficient (d33) was observed in the MoSSe-based vdWH relative to that in the MoS2-based vdWH owing to the intrinsic built-in vertical electric field in MoSSe. This is consistent with the out-of-plane piezoelectricity brought about by the alteration in symmetry at the metal–semiconductor Schottky junction, which has been observed experimentally [M.-M. Yang, Z.-D. Luo, Z. Mi, J. Zhao, S. P. E and M. Alexe, Nature, 2020, 584, 377–381]. The results obtained in this work provide useful insights into the design of nanomaterials for future applications in nano-optoelectronics, more efficient excitonic solar cells, and nanoelectromechanical systems (NEMS). Furthermore, this work demonstrates outstanding potential for the application of these vdWHs in superfast electronics, including low-power digital data storage and memory devices, where the tunnel current between the source and drain is effectively tunable using a normal electric field of small magnitude serving as the gate voltage.
- Published
- 2020
20. Electrochemically customized assembly of a hybrid xerogel material via combined covalent and non-covalent conjugation chemistry: an approach for boosting the cycling performance of pseudocapacitors
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Taniya Purkait, null Dimple, Navpreet Kamboj, Manisha Das, Subhajit Sarkar, Abir De Sarkar, and Ramendra Sundar Dey
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Supercapacitor ,Materials science ,Renewable Energy, Sustainability and the Environment ,Graphene ,Charge density ,02 engineering and technology ,General Chemistry ,Electrolyte ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Capacitance ,0104 chemical sciences ,law.invention ,Chemical engineering ,law ,Covalent bond ,Pseudocapacitor ,General Materials Science ,0210 nano-technology ,Current density - Abstract
Organic quinones conjugated with a conductive support like graphene via a covalent and/or non-covalent approach are emerging as low-cost and sustainable alternatives to conventional pseudocapacitive materials because of their fast and reversible redox kinetics. Herein, for the first time, reduced graphene oxide (rGO) networks functionalized with the eco-friendly dopamine (DA) moiety in a combined covalent and non-covalent manner have been explored by a facile hydrothermal synthesis method as high-performance pseudocapacitive materials. Further, a unique in situ electrochemical polymerization approach has been undertaken in an attempt to boost the overall storage capacity as well as cycling stability. Electrochemical tuning of the active material can result in an enhancement in the specific capacitance via dual improvement in faradaic and capacitive current as compared to the initial xerogel material, highlighting the significance of the in situ process. The electrode material shows a highest specific capacitance (CSP) of 348 F g−1 at a current density of 0.5 A g−1 in 1 M H2SO4 while retaining 60% of its initial capacitance even at a very high current density of 200 A g−1. A metal-free all-solid-state symmetric supercapacitor was developed with the in situ electropolymerized active material and the as-fabricated device exhibits an excellent CSP of 218 F g−1 at 0.325 A g−1 in 1 M PVA/H2SO4 gel electrolyte with a maximum energy density of 30.3 W h kg−1 and power density up to 13 kW kg−1. Most importantly, the material exhibited an extraordinary stability of 53 000 charge–discharge cycles while retaining 94% of its initial capacitance, while the device also shows an excellent capacitance retention of 92% even after 10 000 continuous cycles. Simultaneously, the DFT study was amended to understand the covalent and non-covalent interaction of the redox species, its charge storage mechanism and charge density distribution as well as to calculate the density of states.
- Published
- 2020
21. Exceptional mechano-electronic properties in the HfN2 monolayer: a promising candidate in low-power flexible electronics, memory devices and photocatalysis
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I. S. Fathima, Manish Kumar Mohanta, and Abir De Sarkar
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Free electron model ,Materials science ,business.industry ,Band gap ,General Physics and Astronomy ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Tunnel field-effect transistor ,01 natural sciences ,Flexible electronics ,0104 chemical sciences ,Semiconductor ,Electric field ,Monolayer ,Optoelectronics ,Direct and indirect band gaps ,Physical and Theoretical Chemistry ,0210 nano-technology ,business - Abstract
The response of the electronic properties of the HfN2 monolayer to external perturbation, such as strain and electric fields, has been extensively investigated using density functional theory calculations for its device-based applications and photocatalysis. The HfN2 monolayer is found to be a semiconductor showing a direct band gap of 1.44 eV, which is widely tunable by 0.9 eV via application of biaxial strain. Furthermore, the tunability in the band edges of the HfN2 monolayer straddling the water redox potential under a biaxial strain of ±10% makes it suitable for solar energy harvesting via photocatalytic applications over a wide range (0–7) of pH. The band gap can be decreased by 29.8% under a biaxial tensile strain of 10%. Upon incorporation of spin orbit coupling (SOC) a large spin splitting at the conduction band (Δc ∼ 314 meV) and a small splitting at the valence band (Δv ∼ 32 meV) are noted, which is attributable to the orbital composition of the band edges. The spin splitting in the band edges is found to be adjustable via biaxial compressive strain. The strain dependent mechanical properties and stability reveal the ability of the HfN2 monolayer to withstand a large magnitude of strain of up to ±10%, thereby bringing about a giant tunability in its Young modulus (Y) from 66 N m−1 to 283 N m−1, which is gainfully exploitable in flexible electronics. The tunability in Y over such a wide range has not been observed in other 2D materials. Moreover, the HfN2 monolayer undergoes a transition from a semiconducting to a metallic state under the application of a normal electric field or gate voltage of 0.48 V A−1, which may potentially serve as the OFF (semiconducting) and ON (metallic) state in devices. Interestingly, an electric field of such intensity has been realized experimentally using pulsed ac field technology. Such a small gate voltage will greatly lower its power consumption. The electronic origin of this transition from the OFF to the ON state is found to arise from unoccupied NFEG (Nearly Free Electron Gas) states. A HfN2 monolayer based tunnel field effect transistor (t-FET) is proposed herewith as a model device for low-power digital data storage, thereby paving new avenues in flexible electronics and memory devices.
- Published
- 2020
22. Valley spin polarization in two-dimensional h−MN (M=Nb,Ta) monolayers: Merger of valleytronics with spintronics
- Author
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Raihan Ahammed and Abir De Sarkar
- Published
- 2022
23. Compressive strain-induced enhancement in valley polarization in β-phosphorene like SnS monolayers
- Author
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Fathima IS, Raihan Ahammed, Pradip Nandi, Ashima Rawat, and Abir De Sarkar
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General Physics and Astronomy ,Surfaces and Interfaces ,General Chemistry ,Condensed Matter Physics ,Surfaces, Coatings and Films - Published
- 2023
24. Interfacing Boron Monophosphide with Molybdenum Disulfide for an Ultrahigh Performance in Thermoelectrics, Two-Dimensional Excitonic Solar Cells, and Nanopiezotronics
- Author
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Manish Kumar Mohanta, Ashima Rawat, Nityasagar Jena, null Dimple, Raihan Ahammed, and Abir De Sarkar
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Materials science ,Doping ,Hydrostatic pressure ,Energy conversion efficiency ,Analytical chemistry ,Heterojunction ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Acceptor ,0104 chemical sciences ,Phosphorene ,chemistry.chemical_compound ,Lattice constant ,chemistry ,General Materials Science ,Direct and indirect band gaps ,0210 nano-technology - Abstract
A stable ultrathin 2D van der Waals (vdW) heterobilayer, based on the recently synthesized boron monophosphide (BP) and the widely studied molybdenum disulfide (MoS2), has been systematically explored for the conversion of waste heat, solar energy, and nanomechanical energy into electricity. It shows a gigantic figure of merit (ZT) > 12 (4) for p (n)-type doping at 800 K, which is the highest ever reported till date. At room temperature (300 K), ZT reaches 1.1 (0.3) for p (n)-type doping, which is comparable to experimentally measured ZT = 1.1 on the PbTe-PbSnS2 nanocomposite at 300 K, while it outweighs the Cu2Se-CuInSe2 nanocomposite (ZT = 2.6 at 850 K) and the theoretically calculated ZT = 7 at 600 K on silver halides. Lattice thermal conductivity (κl ≈ 49 W m-1 K-1) calculated at room temperature is lesser than those of black phosphorene (78 W m-1 K-1) and arsenene (61 W m-1 K-1). The nearly matched lattice constants in the commensurate lattices of the constituent monolayers help to preserve the direct band gap at the K point in the type II vdW heterobilayer of MoS2/BP, where BP and MoS2 serve as donor and acceptor materials, respectively. An ultrahigh carrier mobility of ∼20 × 103 cm2 V-1 s-1 is found, which exceeds those of previously reported transition metal dichalcogenide-based vdW heterostructures. The exciton binding energy (0.5 eV) is close to those of MoS2 (0.54 eV) and C3N4 (0.33 eV) single layers. The calculated power conversion efficiency (PCE) in the monolayer MoS2/BP heterobilayer exceeds 20%. It surpasses the efficiency in MoS2/p-Si heterojunction solar cells (5.23%) and competes with the theoretically calculated ones, as listed in the manuscript. Furthermore, a high optical absorbance (∼105 cm-1) of visible light and a small conduction band offset (0.13 eV) make MoS2/BP very promising in 2D excitonic solar cells. The out-of-plane piezoelectric strain coefficient, d33 ≈ 3.16 pm/V, is found to be enhanced 4-fold (∼14.3 pm/V) upon applying 7% vertical compressive strain on the heterobilayer, which corresponds to ∼1 kbar of hydrostatic pressure. Such a high out-of-plane piezoelectric coefficient, which can tune top-gating effects in ultrathin 2D nanopiezotronics, is a relatively new finding. As BP has been synthesized recently, experimental realization of the multifunctional, versatile MoS2/BP heterostructure would be highly feasible.
- Published
- 2019
25. Effective modulation of ohmic contact and carrier concentration in a graphene- MgX ( X=S,Se ) van der Waals heterojunction with tunable band-gap opening via strain and electric field
- Author
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Manish Kumar Mohanta, Anu Arora, and Abir De Sarkar
- Subjects
Materials science ,Condensed matter physics ,Graphene ,Band gap ,Contact resistance ,Wide-bandgap semiconductor ,Heterojunction ,Semimetal ,law.invention ,symbols.namesake ,law ,symbols ,van der Waals force ,Ohmic contact - Abstract
The development of low contact resistance at metal-semiconductor interfaces in next-generation transistors is being prioritized to improve device performance. By using density functional theory, an intrinsic Ohmic contact between a wide band gap semiconductor MgS and semimetal graphene is predicted herewith theoretically. The zero Schottky barriers in graphene/MgS van der Waals heterostructure (vdWH) can facilitate a high charge injection efficiency, whereas Ohmic contact can be induced in graphene/MgSe under small external perturbation. A comprehensive investigation of the modulation in the electronic contact properties is conducted under the application of vertical compressive strain and a perpendicular electric field to understand their role in the transport mechanism. Under vertical compressive strain, a band gap of \ensuremath{\sim}0.62 eV in graphene has been opened up. While under perpendicular electric field, the hole carrier concentration in graphene is found to be increased up to $\ensuremath{\sim}{10}^{14}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{--2}$. Moreover, this work circumvents the prevalent approaches in inducing an Ohmic contact and addresses solutions to very fundamental challenges in pristine graphene, i.e., band gap opening and its tunability, and modulation of carrier concentration. These interesting properties of vdWHs can open up new avenues for constructing these heterojunctions for multifunctional graphene-based field-effect transistors.
- Published
- 2021
26. Solar Energy Harvesting in Type II van der Waals Heterostructures of Semiconducting Group III Monochalcogenide Monolayers
- Author
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Ashima Rawat, Raihan Ahammed, null Dimple, Nityasagar Jena, Manish Kumar Mohanta, and Abir De Sarkar
- Subjects
Van der waals heterostructures ,Materials science ,Chalcogenide ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Solar energy harvesting ,symbols.namesake ,chemistry.chemical_compound ,Crystallography ,General Energy ,chemistry ,Group (periodic table) ,Monolayer ,symbols ,Physical and Theoretical Chemistry ,van der Waals force ,0210 nano-technology - Abstract
Type II van der Waals (vdW) heterobilayers of six group III chalcogenide monolayers (MX; M = Ga, In; X = S, Se, Te) have been systematically investigated and compared with the pristine monolayers v...
- Published
- 2019
27. Single-phase Ni5P4–copper foam superhydrophilic and aerophobic core–shell nanostructures for efficient hydrogen evolution reaction
- Author
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Navpreet Kamboj, Manisha Das, Ramendra Sundar Dey, Nityasagar Jena, Taniya Purkait, and Abir De Sarkar
- Subjects
Tafel equation ,Materials science ,Renewable Energy, Sustainability and the Environment ,Exchange current density ,02 engineering and technology ,General Chemistry ,Overpotential ,021001 nanoscience & nanotechnology ,Electrochemistry ,Electrocatalyst ,Catalysis ,Gibbs free energy ,symbols.namesake ,Chemical engineering ,symbols ,General Materials Science ,0210 nano-technology ,Hydrogen production - Abstract
The facile synthesis of a highly durable, low-cost and robust electrocatalyst for hydrogen generation from water is vital to address the existing environmental issues, as well as to provide an environmentally-friendly clean and green energy supply. Electrochemical deposition of single-phase nickel phosphide on galvanostatically deposited copper foam (Cuf@Ni5P4) core–shell nanostructure offers an innovation in the structural design of a new platform for novel electrocatalysts. The Cuf@Ni5P4 provides a superior three-dimensional conductive channel for ion transport during the catalytic process. The catalyst exhibits an excellent electrocatalytic activity towards the hydrogen evolution reaction (HER) in acidic media. The superhydrophilic and aerophobic properties of the porous electrode help the H2 gas bubbles to quickly leave the surface. Interestingly, it requires a very low overpotential of 90 mV for HER at a current density of 10 mA cm−2. The very small Tafel slope of 49 mV dec−1 and the very high exchange current density (∼0.76 mA cm−2) originate from the large electrochemically active surface area and the fast mass and electron transfer efficiency of the Cuf@Ni5P4 catalyst. A theoretical study was performed to investigate the mechanism underlying the HER activity in Cu-supported Ni5P4 at an atomic scale. Density functional theory (DFT) calculations suggest a very high negative Gibbs free energy change (ΔGH*) in Ni5P4 (0001)/Cu (111) upon hydrogen adsorption, which is actually responsible for the excellent HER activity of the catalyst. Furthermore, it shows remarkable durability for hydrogen generation under low (10 mA cm−2) and high current densities (160 mA cm−2) for >84 h with ∼96% retention of the overpotential, establishing a low-cost and efficient catalyst for sustainable, future energy generation strategies.
- Published
- 2019
28. Superhigh out-of-plane piezoelectricity, low thermal conductivity and photocatalytic abilities in ultrathin 2D van der Waals heterostructures of boron monophosphide and gallium nitride
- Author
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Manish Kumar Mohanta, Ashima Rawat, Dimple Dimple, Nityasagar Jena, Raihan Ahammed, and Abir De Sarkar
- Subjects
Electron mobility ,Materials science ,Condensed matter physics ,Phonon ,business.industry ,Gallium nitride ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Thermoelectric materials ,01 natural sciences ,0104 chemical sciences ,Phosphorene ,chemistry.chemical_compound ,symbols.namesake ,Lattice constant ,Semiconductor ,chemistry ,symbols ,General Materials Science ,van der Waals force ,0210 nano-technology ,business - Abstract
A stable 2D van der Waals (vdW) heterobilayer, constituted by boron monophosphide (BP) and Gallium Nitride (GaN) monolayers, has been explored for different kinds of energy conversion and nanoelectronics. The nearly matched lattice constants of GaN and BP are commensurate with each other in their lattice structures. The out-of-plane inversion asymmetry coupled with the large difference in atomic charges between the GaN and BP monolayers induces in the heterobilayer a giant out-of-plane piezoelectric coefficient (|d33|max ≈ 40 pm V-1), which is the highest ever reported in 2D materials of a finite thickness. It is much higher than the out-of-plane piezoelectric coefficient reported earlier in multilayered Janus transition metal dichalcogenide MXY (M = Mo, W; X, Y = S, Se, Te) (|d33|max = 10.57 pm V-1). Such a high out-of-plane piezoelectricity found in a BP/GaN heterobilayer can bring about gigantic strain-tunable top gating effects in nanopiezotronic devices based on the same. Moreover, electron mobility (∼104 cm2 V-1 s-1) is much higher than that of transition metal dichalcogenides and conventional semiconductors. The origin of low lattice thermal conductivity (κL ∼ 25.25 W m-1 K-1) in BP/GaN at room temperature, which is lower than that of black phosphorene (78 W m-1 K-1), buckled arsenene (61 W m-1 K-1), BCN (90 W m-1 K-1), MoS2 (34.5 W m-1 K-1) and WS2 (32 W m-1 K-1) monolayers, has been systematically investigated via phonon dispersion, lattice thermal conductivity, phonon lifetime and mode Grüneisen parameters. The valence band maximum (VBM) and conduction band minimum (CBM) arising from GaN and BP monolayers respectively result in a type II vdW heterobilayer, which is found to be thermodynamically favorable for photocatalytic water splitting in both acidic and neutral media. The exciton binding energies are comparable to those of MoS2 and C3N4 single layers, while the absorbance reaches as high as ∼105 cm-1 in the visible wavelength region. The emergence of high piezoelectricity, high carrier mobility, low lattice thermal conductivity and photocatalytic water splitting abilities in the proposed vdW heterobilayer signifies enormous potential for its versatile applications in nanoscale energy harvesting, e.g., nano-sensors in medical devices, future nanopiezotronics, 2D thermoelectrics and solar energy conversion.
- Published
- 2019
29. Conflux of tunable Rashba effect and piezoelectricity in flexible magnesium monochalcogenide monolayers for next-generation spintronic devices
- Author
-
Manish Kumar Mohanta, Abir De Sarkar, and Anu Arora
- Subjects
Materials science ,Piezoelectric coefficient ,Spintronics ,business.industry ,Chalcogenide ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Piezoelectricity ,0104 chemical sciences ,chemistry.chemical_compound ,Semiconductor ,chemistry ,Monolayer ,Optoelectronics ,General Materials Science ,Direct and indirect band gaps ,0210 nano-technology ,business ,Rashba effect - Abstract
The coupling of piezoelectric properties with Rashba spin-orbit coupling (SOC) has proven to be the limit breaker that paves the way for a self-powered spintronic device (ACS Nano, 2018, 12, 1811-1820). For further advancement in next-generation devices, a new class of buckled, hexagonal magnesium-based chalcogenide monolayers (MgX; X = S, Se, Te) have been predicted which are direct band gap semiconductors satisfying all the stability criteria. The MgTe monolayer shows a strong SOC with a Rashba constant of 0.63 eV A that is tunable to the extent of ±0.2 eV A via biaxial strain. Also, owing to its broken inversion symmetry and buckling geometry, MgTe has a very large in-plane as well as out-of-plane piezoelectric coefficient. These results indicate its prospects for serving as a channel semiconducting material in self-powered piezo-spintronic devices. Furthermore, a prototype for a digital logic device can be envisioned using the ac pulsed technology via a perpendicular electric field. Heat transport is significantly suppressed in these monolayers as observed from their intrinsic low lattice thermal conductivity at room temperature: MgS (9.32 W m-1 K-1), MgSe (4.93 W m-1 K-1) and MgTe (2.02 W m-1 K-1). Further studies indicate that these monolayers can be used as photocatalytic materials for the simultaneous production of hydrogen and oxygen on account of having suitable band edge alignment and high charge carrier mobility. This work provides significant theoretical insights into both the fundamental and applied properties of these new buckled MgX monolayers, which are highly suitable for futuristic applications at the nanoscale in low-power, self-powered multifunctional electronic and spintronic devices and solar energy harvesting.
- Published
- 2021
30. Insights into CrS2 monolayer and n-CrS2/p-HfN2 interface for low-power digital and analog nanoelectronics
- Author
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Manish Kumar Mohanta, Harshita Seksaria, and Abir De Sarkar
- Subjects
General Physics and Astronomy ,Surfaces and Interfaces ,General Chemistry ,Condensed Matter Physics ,Surfaces, Coatings and Films - Published
- 2022
31. Two-dimensional ultrathin van der Waals heterostructures of indium selenide and boron monophosphide for superfast nanoelectronics, excitonic solar cells, and digital data storage devices
- Author
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Abir De Sarkar, Amal Kishore, and Manish Kumar Mohanta
- Subjects
Electron mobility ,Materials science ,Band gap ,Bioengineering ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,chemistry.chemical_compound ,Photovoltaics ,General Materials Science ,Electrical and Electronic Engineering ,business.industry ,Mechanical Engineering ,Heterojunction ,General Chemistry ,021001 nanoscience & nanotechnology ,Acceptor ,0104 chemical sciences ,Semiconductor ,chemistry ,Nanoelectronics ,Mechanics of Materials ,Optoelectronics ,Boron phosphide ,0210 nano-technology ,business - Abstract
Semiconducting indium selenide (InSe) monolayers have drawn a great deal of attention among all the chalcogenide two-dimensional materials on account of their high electron mobility; however, they suffer from low hole mobility. This inherent limitation of an InSe monolayer can be overcome by stacking it on top of a boron phosphide (BP) monolayer, where the complementary properties of BP can bring additional benefits. The electronic, optical, and external perturbation-dependent electronic properties of InSe/BP hetero-bilayers have been systematically investigated within density functional theory in anticipation of its cutting-edge applications. The InSe/BP heterostructure has been found to be an indirect semiconductor with an intrinsic type-II band alignment where the conduction band minimum (CBM) and valence band maximum (VBM) are contributed by the InSe and BP monolayers, respectively. Thus, the charge carrier mobility in the heterostructure, which is mainly derived from the BP monolayer, reaches as high as 12 × 103 cm2 V−1 s−1, which is very much desired in superfast nanoelectronics. The suitable bandgap accompanied by a very low conduction band offset between the donor and acceptor along with robust charge carrier mobility, and the mechanical and dynamical stability of the heterostructure attests its high potential for applications in solar energy harvesting and nanoelectronics. The solar to electrical power conversion efficiency (20.6%) predicted in this work surpasses the efficiencies reported for InSe based heterostructures, thereby demonstrating its superiority in solar energy harvesting. Moreover, the heterostructure transits from the semiconducting state (the OFF state) to the metallic state (the ON state) by the application of a small electric field (∼0.15 V Å−1) which is brought about by the actual movement of the bands rather than via the nearly empty free electron gas (NFEG) feature. This thereby testifies to its potential for applications in digital data storage. Moreover, the heterostructure shows strong absorbance over a wide spectrum ranging from UV to the visible light of solar radiation, which will be of great utility in UV—visible light photodetectors.
- Published
- 2020
32. Exceptional mechano-electronic properties in the HfN
- Author
-
Manish Kumar, Mohanta, I S, Fathima, and Abir, De Sarkar
- Abstract
The response of the electronic properties of the HfN2 monolayer to external perturbation, such as strain and electric fields, has been extensively investigated using density functional theory calculations for its device-based applications and photocatalysis. The HfN2 monolayer is found to be a semiconductor showing a direct band gap of 1.44 eV, which is widely tunable by 0.9 eV via application of biaxial strain. Furthermore, the tunability in the band edges of the HfN2 monolayer straddling the water redox potential under a biaxial strain of ±10% makes it suitable for solar energy harvesting via photocatalytic applications over a wide range (0-7) of pH. The band gap can be decreased by 29.8% under a biaxial tensile strain of 10%. Upon incorporation of spin orbit coupling (SOC) a large spin splitting at the conduction band (Δc ∼ 314 meV) and a small splitting at the valence band (Δv ∼ 32 meV) are noted, which is attributable to the orbital composition of the band edges. The spin splitting in the band edges is found to be adjustable via biaxial compressive strain. The strain dependent mechanical properties and stability reveal the ability of the HfN2 monolayer to withstand a large magnitude of strain of up to ±10%, thereby bringing about a giant tunability in its Young modulus (Y) from 66 N m-1 to 283 N m-1, which is gainfully exploitable in flexible electronics. The tunability in Y over such a wide range has not been observed in other 2D materials. Moreover, the HfN2 monolayer undergoes a transition from a semiconducting to a metallic state under the application of a normal electric field or gate voltage of 0.48 V Å-1, which may potentially serve as the OFF (semiconducting) and ON (metallic) state in devices. Interestingly, an electric field of such intensity has been realized experimentally using pulsed ac field technology. Such a small gate voltage will greatly lower its power consumption. The electronic origin of this transition from the OFF to the ON state is found to arise from unoccupied NFEG (Nearly Free Electron Gas) states. A HfN2 monolayer based tunnel field effect transistor (t-FET) is proposed herewith as a model device for low-power digital data storage, thereby paving new avenues in flexible electronics and memory devices.
- Published
- 2020
33. Coupled spin and valley polarization in monolayer HfN2 and valley-contrasting physics at the HfN2−WSe2 interface
- Author
-
Manish Kumar Mohanta and Abir De Sarkar
- Subjects
Physics ,Spin states ,Spintronics ,Condensed matter physics ,Heterojunction ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Omega ,symbols.namesake ,0103 physical sciences ,Valleytronics ,Monolayer ,symbols ,Direct and indirect band gaps ,van der Waals force ,010306 general physics ,0210 nano-technology - Abstract
Despite extensive studies on coupled spin and valley physics, occurrence of these properties is currently limited to transition-metal dichalcogenides (TMDCs) and graphene. Therefore, exploration of materials beyond TMDCs and graphene is necessary for a further advancement in valleytronics. In this work, the $\mathrm{Hf}{\mathrm{N}}_{2}$ monolayer, a theoretically reported semiconductor having a direct band gap has been investigated in-depth for its applications in valleytronics and spintronics. It exhibits a large valley spin splitting (VSS) \ensuremath{\sim}314 meV at the conduction band (CB) due to strong spin-orbit coupling (SOC). Such a large VSS at the CB is unique and comparable to that of tungsten-based dichalcogenide monolayers at its valence band (VB). The spin splitting is nearly insensitive to small in-plane strain, whereas the optical transition frequencies between the spin states $({\ensuremath{\omega}}_{\mathrm{up}},\phantom{\rule{4pt}{0ex}}{\ensuremath{\omega}}_{\mathrm{down}})$ in the CB and VB is effectively strain tunable. Inspired by the experimentally observed higher exciton lifetime 1.8 ns in $\mathrm{MoS}{\mathrm{e}}_{2}/\mathrm{WS}{\mathrm{e}}_{2}$ type-II van der Waals heterostructure (vdWH) than in the monolayers \ensuremath{\sim}2.1 (2.5) $ps$ in monolayer $\mathrm{Mo}{\mathrm{S}}_{2}$ $(\mathrm{W}{\mathrm{S}}_{2})$, a type-II (vdWH) prototype has been demonstrated by stacking $\mathrm{Hf}{\mathrm{N}}_{2}$ monolayer over $1\mathrm{H}\ensuremath{-}\mathrm{WS}{\mathrm{e}}_{2}$ monolayer for an extended lifetime of valley polarized excitons and large magnitude of spin splitting at both CB and VB. The elastic properties highlight the robustness of $\mathrm{Hf}{\mathrm{N}}_{2}$ monolayer and vdWH, as the bending modulus and critical buckling strain are found to be superior to that in graphene. Further, carrier mobility calculated using the deformation potential theory in $\mathrm{Hf}{\mathrm{N}}_{2}/\mathrm{WS}{\mathrm{e}}_{2}$ is as high as ${\ensuremath{\mu}}_{h}=16\phantom{\rule{4pt}{0ex}}\ifmmode\times\else\texttimes\fi{}{10}^{3}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}{\mathrm{V}}^{1}{\mathrm{s}}^{\ensuremath{-}1}$. Moreover, this work introduces the $\mathrm{Hf}{\mathrm{N}}_{2}$ monolayer as an exceptionally promising valleytronic material having valley properties complementary to that of Group VI TMDC. This is a report on valley contrasting physics and VSS at the CB, which would strongly motivate experimentalists to synthesize and explore this predicted two-dimensional material.
- Published
- 2020
34. Ultra-low lattice thermal conductivity and giant phonon-electric field coupling in hafnium dichalcogenide monolayers
- Author
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null Dimple, Manish Kumar Mohanta, Ashima Rawat, Nityasagar Jena, Raihan Ahammed, and Abir De Sarkar
- Subjects
Materials science ,Condensed matter physics ,Phonon ,Anharmonicity ,02 engineering and technology ,Grüneisen parameter ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Thermoelectric materials ,01 natural sciences ,Heat capacity ,Brillouin zone ,symbols.namesake ,0103 physical sciences ,Thermoelectric effect ,symbols ,General Materials Science ,010306 general physics ,0210 nano-technology ,Debye model - Abstract
Phonons in crystalline solids are of utmost importance in governing its lattice thermal conductivity (k L). In this work, k L in hafnium (Hf) dichalcogenide monolayers has been investigated based on ab initio DFT coupled to linearized Boltzmann transport equation together with single-mode relaxation-time approximation. Ultra-low k L found in HfS2 (2.19 W m-1 K-1), HfSe2 (1.23 W m-1 K-1) and HfSSe (1.78 W m-1 K-1) monolayers at 300 K, is comparable to that of the state-of-art bulk thermoelectric materials, such as, Bi2Te3 (1.6 W m-1 K-1), PbTe (2.2 W m-1 K-1) and SnSe (2.6 W m-1 K-1). Gigantic longitudinal-transverse optical (LO-TO) splitting of up to 147.7 cm-1 is noticed at the Brillouin zone-centre (Γ-point), which is much higher than that in MoS2 single layer (∼2 cm-1). It is driven by the colossal phonon-electric field coupling arising from the domination of ionic character in the interatomic bonds and Born effective or dynamical charges as high as 7.4e on the Hf ions, which is seven times that on Mo in MoS2 single layer. Enhancement in k L occurs in HfS2 (2.19 to 4.1 W m-1 K-1), HfSe2 (1.23 to 1.7 W m-1 K-1) and HfSSe (1.78 to 2.2 W m-1 K-1) upon the incorporation of the non-analytic correction term. Furthermore, the mode Gruneisen parameter is calculated to be as high as ∼2.0, at room temperature, indicating a strong anharmonicity. Moreover, the contribution of optical phonons to k L is found to be ∼12%, which is significantly high than that in single-layer MoS2. Large atomic mass of Hf (178.5 u), small phonon group velocities (4-5 km s-1), low Debye temperature (∼166 K), low bond and elastic stiffness (Young's modulus ∼75 N m-1), small phonon lifetimes (∼6 ps), low specific heat capacity (∼17 J K-1 mol-1) and strong anharmonicity are collectively found to be the factors responsible for such a low k L. These findings would be immensely helpful in designing thermoelectric interconnects at the nanoscale and 2D material-based energy harvesters.
- Published
- 2020
35. Proton-Triggered Fluorescence Switching in Self-Exfoliated Ionic Covalent Organic Nanosheets for Applications in Selective Detection of Anions
- Author
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Harpreet Singh, Manisha Devi, Santanu Kumar Pal, Abir De Sarkar, Nityasagar Jena, Mohamed Musthafa Iqbal, and Yogendra Nailwal
- Subjects
Materials science ,Proton ,Ionic bonding ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,01 natural sciences ,Fluorescence ,Exfoliation joint ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Covalent bond ,General Materials Science ,0210 nano-technology ,Guanidine - Abstract
The exfoliation of covalent organic frameworks into covalent organic nanosheets (CONs) not only helps to reduce fluorescence turn-off phenomena but also provides well-exposed active sites for fast response and recovery for various applications. The present work is an example of rational designing of a structure constructed by condensing triaminoguanidinium chloride (TG
- Published
- 2020
36. Emergence of high piezoelectricity along with robust electron mobility in Janus structures in semiconducting Group IVB dichalcogenide monolayers
- Author
-
Dimple Dimple, Nityasagar Jena, Ashima Rawat, Raihan Ahammed, Manish Kumar Mohanta, and Abir De Sarkar
- Subjects
Electron mobility ,Piezoelectric coefficient ,Materials science ,Condensed matter physics ,Renewable Energy, Sustainability and the Environment ,Ionic bonding ,02 engineering and technology ,General Chemistry ,Electron ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Piezoelectricity ,0104 chemical sciences ,Chalcogen ,Monolayer ,General Materials Science ,Janus ,0210 nano-technology - Abstract
Piezoelectric nanomaterials have been emerging as flagship materials for harvesting nanoelectromechanical energy. Pristine, semiconducting 1T-MX2 (M = Zr and Hf; X = S, Se, and Te) monolayers are intrinsically centrosymmetric, and hence non-piezoelectric. This inversion symmetry is broken in their Janus monolayer (non-centrosymmetric) structures, leading to the emergence of a high degree of piezoelectricity in them. This brings along a new dimension in nanoscale piezoelectricity, as the origin of this piezoelectricity is predominantly ionic in nature, in contrast to the 1H-MoS2 monolayer, where it is of electronic character. DFT calculations reveal the piezoelectric coefficient (d22 = 4.68–14.58 pm V−1) in these Janus monolayers to be much higher than that in single layer 1H-MoS2 (d11 = 2.99 pm V−1). 9% uniaxial tensile strain applied along the arm-chair direction is found to raise d22 in HfSSe Janus monolayers to 123.04 pm V−1, which reaches the level of piezoelectric coefficients in the state-of-the-art perovskites. The major contribution of the ionic component to the piezoelectric coefficient is attributable to the predominance of ionic character in the interatomic bonds in these monolayers, which arises from the decoupled band edges, i.e., no hybridization between the band edge states (chalcogen-p and metal-d). Contrarily, 1H-MX2 (M = Mo and W; X = S, Se, and Te) monolayers with coupled band edges are held together mainly by covalent bonds, resulting in the dominance of electronic contribution to piezoelectricity. The nature of band edges causes a lower deformation potential for electrons in 1T Hf and Zr based dichalcogenide monolayers and their Janus structures with respect to 1H-MX2 (M = Mo and W; X = S, Se, and Te) monolayers. This induces a much higher electron mobility in the former than in 1H-MX2 (M = Mo and W; X = S, Se, and Te) monolayers. The carrier mobility calculated using Lang et al.'s formalism [Phys. Rev. B, 2016, 94, 235306] agrees well with the experimentally measured electron mobility. Our predictive findings underscore the imminent need to synthesize these 1T-MX2 semiconducting Janus structures to induce a high level of piezoelectricity together with robust electron mobility.
- Published
- 2018
37. A comprehensive study on carrier mobility and artificial photosynthetic properties in group VI B transition metal dichalcogenide monolayers
- Author
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Ashima Rawat, Nityasagar Jena, Dimple Dimple, and Abir De Sarkar
- Subjects
Electron mobility ,Materials science ,Renewable Energy, Sustainability and the Environment ,02 engineering and technology ,General Chemistry ,Electron ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Transition metal dichalcogenide monolayers ,0104 chemical sciences ,symbols.namesake ,Chemical physics ,Monolayer ,symbols ,General Materials Science ,Density functional theory ,Charge carrier ,Nernst equation ,0210 nano-technology ,Order of magnitude - Abstract
2D semiconducting transition-metal-dichalcogenides (TMDCs) have drawn a surge of research interests in ultra-thin nanoelectronics and optoelectronics, owing to their moderate charge carrier mobility. Due to a large variation in reported data on charge carrier mobilities of these free-standing monolayers, a more accurate determination of carrier mobilities is a must. This article highlights room temperature carrier mobilities calculated in group-VI B TMDC (i.e., MX2 (M = Mo, W; X = S, Se, Te)) monolayers via a systematic comparison of reliable models used within the framework of density functional theory. Additionally, piezoelectric effects on carrier mobility have been incorporated. The robust formulation by Lang et al. [Phys. Rev. B, 2016, 94, 235306] gives the most accurate estimation, where the carrier (i.e. electron or hole) mobility and the ratio of hole to electron mobility reach closest to the experimentally measured value. The higher mobility of holes with respect to electrons is attributed to the smaller deformation potential of the holes, while smaller carrier effective masses and larger elastic moduli cause larger carrier mobility in WX2 relative to MoX2. Carrier mobility is found to drop from S to Te and also from W to Mo in MX2 on account of the decrease in the elastic moduli, which is consistent with the increase in the macroscopic static dielectric constant. Erroneously high electron mobility (>1000 cm2 V−1 s−1), which is two orders of magnitude higher than the experimental ones, has been disputably reported earlier for MoTe2 and WS2 monolayers. It owes its origin to the ultrasmall deformation potential found therein. High (∼1.4–2.3) hole to electron mobility ratio in MX2 monolayers is found to occur in our work as MoSe2 > WS2 > MoS2 > WSe2 > WTe2 > MoTe2. This large carrier mobility ratio will facilitate an efficient separation of electron–hole pairs, which is particularly useful in optoelectronic applications, e.g., photovoltaics, photocatalysis and artificial photosynthesis. In all terms including optical absorbance, a WS2 monolayer is found to be most suitable for photophysical processes. Using the Nernst formulation, water splitting and CO2 photoreduction on WS2 are found to be favorable over a wide range of pH.
- Published
- 2018
38. Atomistic manipulation of interfacial properties in HfN2/MoTe2 van der Waals heterostructure via strain and electric field for next generation multifunctional nanodevice and energy conversion
- Author
-
Manish Kumar Mohanta, Abir De Sarkar, and Ashima Rawat
- Subjects
Materials science ,business.industry ,Energy conversion efficiency ,General Physics and Astronomy ,Heterojunction ,Surfaces and Interfaces ,General Chemistry ,Condensed Matter Physics ,Solar energy ,Surfaces, Coatings and Films ,law.invention ,symbols.namesake ,Photovoltaics ,law ,Piezotronics ,Solar cell ,symbols ,Optoelectronics ,Direct and indirect band gaps ,van der Waals force ,business - Abstract
This work sheds light on the intrinsic properties of HfN2 monolayer and its synergistic combination with MoTe2 for diverse applications in thermoelectricity, photovoltaics, piezotronics and digital/analog electronics using the state of art density functional theory. Using Boltzmann transport theory, a low lattice thermal conductivity of 0.49 W m - 1 K - 1 at 300 K along with high waste heat to electricity conversion efficiency (i.e., thermoelectric figure of merit, ZT = 2.28) is predicted for monolayer HfN2. On the other hand, a type-II van der Waals heterostructure (vdWH) is formed with 1H-MoTe2 monolayer, where low conduction band offset and direct band gap leads to high power conversion efficiency (PCE) of 21.44% in HfN2/MoTe2 excitonic solar cell. Moreover, it can be employed in designing multifunctional next-generation excitonic solar cells where electricity can be simultaneously generated from solar energy and the waste heat thrown out by the solar cell. The tunable electronic properties under perpendicular electric field highlights its application in both analog and digital electronics. The built-in electric field at the interface together with broken inversion symmetry along z-direction induces out-of-plane piezoelectricity (d33), which is in excellent agreement with experimental evidence (ACS Appl. Nano Mater. 2020, 3, 11979–11986). d33 further increases 3.5 times under vertical compressive strain.
- Published
- 2021
39. Interfacing 2D M2X (M = Na, K, Cs; X = O, S, Se, Te) monolayers for 2D excitonic and tandem solar cells
- Author
-
Abir De Sarkar, Anu Arora, and Ashima Rawat
- Subjects
Electron mobility ,Materials science ,Tandem ,Band gap ,Energy conversion efficiency ,Binding energy ,Analytical chemistry ,General Physics and Astronomy ,Heterojunction ,02 engineering and technology ,Surfaces and Interfaces ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,symbols.namesake ,Monolayer ,symbols ,van der Waals force ,0210 nano-technology - Abstract
High photovoltaic efficiency with a staggered type II band alignment has been found in the heterobilayers of relatively less explored dialkali metal oxides and chalcogenides, using DFT-D3 and HSE06 functional. Out of all the type II van der Waals (vdW) heterostructures which are possible through a combination of any two individual monolayers stacked on top of one another, K2O/Cs2O, K2S/Cs2S, and K2Se/Cs2S heterobilayers are found to exhibit a high-power conversion efficiency (PCE) of 21.56%, 19.31%, and 16.43% respectively along with high carrier mobility (>104 cm2/V.s) and high visible light absorption coefficient (α ~ 105 cm−1). Therefore, these heterobilayers will be highly useful in photovoltaic applications. The PCE in the tandem solar cells comprising of the wider band gap, Na2Te/K2Se, in the top cell, and the narrower bandgap, K2O/Cs2O, in the bottom cell, is observed to reach close to 30%. The binding energies in K2O/Cs2O, K2S/Cs2S, and K2Se/Cs2S heterobilayers are found to be −36.38, −28.99, and −29.52 meV/A2 at the interlayer layer distance of 3.30 A, 2.75 A, and 4.0 A respectively, at equilibrium. The large magnitude of negative binding energy indicates the exothermicity and experimental feasibility in the process of formation of these vdW heterostructures.
- Published
- 2021
40. Concurrence of negative in-plane piezoelectricity and photocatalytic properties in 2D ScAgP2S6 monolayers
- Author
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Ashima Rawat, null Dimple, Raihan Ahammed, and Abir De Sarkar
- Subjects
In plane ,Materials science ,Strain (chemistry) ,Monolayer ,Photocatalysis ,General Materials Science ,Concurrence ,Composite material ,Condensed Matter Physics ,Piezoelectricity - Published
- 2021
41. Strain-Induced Optimization of Nanoelectromechanical Energy Harvesting and Nanopiezotronic Response in a MoS2 Monolayer Nanosheet
- Author
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Nityasagar Jena, null Dimple, Shounak Dhananjay Behere, and Abir De Sarkar
- Subjects
Materials science ,Strain (chemistry) ,Orders of magnitude (temperature) ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Piezoelectricity ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Stress (mechanics) ,General Energy ,Zigzag ,Monolayer ,Shear stress ,Direct and indirect band gaps ,Physical and Theoretical Chemistry ,Composite material ,0210 nano-technology - Abstract
Besides the intrinsic semiconducting direct band gap in monolayer MoS2 (ML-MoS2), piezoelectricity arises in it due to the broken inversion symmetry. This underscores the need to unveil the simultaneous response of piezoelectric and semiconducting properties to different modes of strain. The present study explores a synergic coupling between these two properties in adaptive nanopiezotronic devices, using density functional theory. Out of the different strain types studied, shear strain and uniaxial tensile strain applied along the zigzag direction are found to be most effectual in fortifying the piezoelectric properties in ML-MoS2. Shear strain is found to raise both the piezoelectric stress (e11) and strain (d11) coefficients by 3 orders of magnitude, while uniaxial tensile strain increases the same by 2 orders of magnitude for an applied mechanical strain of 5%. The effect is found to be even stronger upon reaching the elastic limit, which is found to lie within 5–10% strain for different strain modes s...
- Published
- 2017
42. A comparative and a systematic study on the effects of B, N doping and C-atom vacancies on the band gap in narrow zig-zag graphene nanoribbons via quantum transport calculations
- Author
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Abir De Sarkar, Sukhbir Singh, and Inderpreet Kaur
- Subjects
Materials science ,Dopant ,Condensed matter physics ,business.industry ,Band gap ,Mechanical Engineering ,Doping ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Semiconductor ,Mechanics of Materials ,0103 physical sciences ,Atom ,General Materials Science ,Density functional theory ,010306 general physics ,0210 nano-technology ,business ,Graphene nanoribbons - Abstract
Density functional theory(DFT) coupled to non-equilibrium green’s function has been performed to explore avenues to open band gap in graphene nanoribbons in order to reach a high current on/off ratio for their potential applications in transistors and futuristic nanodevices. Introduction of defects such as C-atom vacancies and doping with elements lying on either side of carbon in the periodic table have been invoked to engineer the band gap in narrow zig-zag nanoribbons. By varying the concentration of B and N dopants in zig-zag nanoribbon (ZGNR), their electronic structure is transformed to that of p-type and n-type semiconductor. A maximum band gap of 0.98 eV, 0.88 eV and 0.89 eV is achieved upon incorporating carbon-atom vacancies, boron doping and nitrogen doping respectively. Transport properties have been analyzed through the calculation of transmission spectrum and I–V characteristics. Doped and defective ZGNRs reported herewith show non-linearity in the current-voltage characteristics. The highest current value achieved by doping and defect is 16.5,39 μA for boron dopant, 18, 27 μA for nitrogen and 25.5, 30.2 μA for defects.
- Published
- 2017
43. Electronic and transport behavior of doped armchair silicene nanoribbons exhibiting negative differential resistance and its FET performance
- Author
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Abir De Sarkar, Inderpreet Kaur, Bijender Singh, and Sukhbir Singh
- Subjects
010302 applied physics ,Materials science ,Condensed matter physics ,Silicene ,General Chemical Engineering ,Doping ,Nanotechnology ,02 engineering and technology ,General Chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Nanoelectronics ,0103 physical sciences ,Density of states ,Density functional theory ,Field-effect transistor ,0210 nano-technology ,Electronic band structure ,High-κ dielectric - Abstract
In the present work, density functional theory (DFT) combined with non-equilibrium Green’s function (NEGF) formalism is performed. The electronic properties (band structure and density of states) and transport properties (transmission spectrum and I–V characteristics) of armchair silicene nanoribbons (ASiNRs) doped with various elements, such as Al, Ga, In, Tl, P, As, Sb and Bi, are investigated. The negative differential resistance is observed for each doped ASiNR. The most geometrically stable structure and the maximum peak current to valley current (Ip/Iv) ratio is observed in indium (In) doped ASiNRs. Finally, In doped ASiNRs are proposed for field effect transistor (ASiNR-FET) formation using the high dielectric constant value of lanthanum oxide (La2O3 = 29) at different applied gate voltages (−0.1 to 0.4 V). The In doped ASiNR device shows a negative differential resistance phenomenon, which can be controlled by an applied gate voltage. It is found that doping with In in the electrodes and scattering region provides a higher drain current, and higher Ion/Ioff and Ip/Iv ratios. Our results have great application in digital devices and memory devices, and high frequency applications for future nanoelectronics.
- Published
- 2017
44. A porous, crystalline truxene-based covalent organic framework and its application in humidity sensing
- Author
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Vijay K. Tomer, Harpreet Singh, Nidhi Sharma, Abir De Sarkar, Devadutta Nepak, Santanu Kumar Pal, Kamalakannan Kailasam, Indu Bala, and Nityasagar Jena
- Subjects
Materials science ,Renewable Energy, Sustainability and the Environment ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,Fluorene ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensation reaction ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,Covalent bond ,Organic chemistry ,Molecule ,General Materials Science ,0210 nano-technology ,Boron ,Porosity ,Powder diffraction ,Covalent organic framework - Abstract
Truxene is employed as a building block to successfully synthesize novel covalent organic frameworks (COFs). The condensation reaction between truxene (10,15-dihydro-5H-diindeno[1,2-a:1′,2′-c]fluorene, TX) and 1,4-phenylenediboronic acid (DBA) results in a crystalline COF with boron ester linkages (COF-TXDBA) and a surface area of 1526 m2 g−1, as confirmed by powder X-ray diffraction (PXRD) and Brunauer–Emmett–Teller (BET) surface area measurements. This is the first study where nanochannels generated by periodic COF planar layers are shown to ease the interactions of the boron ester linkages with the water molecules for efficient humidity sensing. The COF-TXDBA based % RH sensor exhibits a change of 3 orders of magnitude in impedance in the 11–98% RH range, with response and recovery times of 37 s and 42 s, respectively. The response transients measured by switching COF-TXDBA sensor back and forth in 4 loops of % RH range displays excellent reversibility of the sensor with a deviation of 2.3% in the switching process.
- Published
- 2017
45. Nano-structured hybrid molybdenum carbides/nitrides generated in situ for HER applications
- Author
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Ritu Rai, Shambhu Nath Jha, R.T. Rajendra Kumar, Nidhi Tiwari, Abir De Sarkar, Ashok K. Ganguli, Seema Gautam, Debnath Bhattacharyya, and Vivek Bagchi
- Subjects
Materials science ,Electrolysis of water ,Renewable Energy, Sustainability and the Environment ,Inorganic chemistry ,Nanoparticle ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,Nitride ,Overpotential ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrocatalyst ,01 natural sciences ,0104 chemical sciences ,Carbide ,Catalysis ,chemistry ,Molybdenum ,General Materials Science ,0210 nano-technology - Abstract
A nanohybrid material containing carbon-supported molybdenum carbide and nitride nanoparticles of size ranging from 8 to 12 nm exhibits excellent HER catalytic activity. This molybdenum based catalyst (MoCat) is designed as a highly efficient, low-cost (precious-metal-free), highly stable electrocatalyst for water electrolysis in acidic media, and synthesized using a simple methodology. These nanoparticles (β-Mo2C and γ-Mo2N) were produced in situ using a metal precursor and C/N source via a controlled solid state reaction. An overpotential of 96 mV for driving a current density of 10 mA cm−2 was measured for the MoCat catalyst, which is very close to that of commercially available Pt/C catalysts (61 mV).
- Published
- 2017
46. Experimental and Theoretical Study into Interface Structure and Band Alignment of the Cu
- Author
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Sachin R, Rondiya, Yogesh, Jadhav, Nelson Y, Dzade, Raihan, Ahammed, Tanmay, Goswami, Abir, De Sarkar, Sandesh, Jadkar, Santosh, Haram, and Hirendra N, Ghosh
- Subjects
photovoltaic ,grain boundary ,cation substitution ,band offset ,ultrafast carrier dynamics ,earth-abundant material ,Article ,interfacial engineering - Abstract
To improve the constraints of kesterite Cu2ZnSnS4 (CZTS) solar cell, such as undesirable band alignment at p–n interfaces, bandgap tuning, and fast carrier recombination, cadmium (Cd) is introduced into CZTS nanocrystals forming Cu2Zn1–xCdxSnS4 through cost-effective solution-based method without postannealing or sulfurization treatments. A synergetic experimental–theoretical approach was employed to characterize and assess the optoelectronic properties of Cu2Zn1–xCdxSnS4 materials. Tunable direct band gap energy ranging from 1.51 to 1.03 eV with high absorption coefficient was demonstrated for the Cu2Zn1–xCdxSnS4 nanocrystals with changing Zn/Cd ratio. Such bandgap engineering in Cu2Zn1–xCdxSnS4 helps in effective carrier separation at interface. Ultrafast spectroscopy reveals a longer lifetime and efficient separation of photoexcited charge carriers in Cu2CdSnS4 (CCTS) nanocrystals compared to that of CZTS. We found that there exists a type-II staggered band alignment at the CZTS (CCTS)/CdS interface, from cyclic voltammetric (CV) measurements, corroborated by first-principles density functional theory (DFT) calculations, predicting smaller conduction band offset (CBO) at the CCTS/CdS interface as compared to the CZTS/CdS interface. These results point toward efficient separation of photoexcited carriers across the p–n junction in the ultrafast time scale and highlight a route to improve device performances.
- Published
- 2019
47. Valley drift and valley current modulation in strained monolayer MoS2
- Author
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Nityasagar Jena, null Dimple, Raihan Ahammed, Ashima Rawat, Manish Kumar Mohanta, and Abir De Sarkar
- Subjects
Physics ,Condensed matter physics ,Spintronics ,Band gap ,Exciton ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Brillouin zone ,Condensed Matter::Materials Science ,0103 physical sciences ,Valleytronics ,Density functional theory ,Local-density approximation ,010306 general physics ,0210 nano-technology ,Wave function - Abstract
Elastic-mechanical deformations are found to dramatically alter the electronic properties of monolayer (ML) $\mathrm{Mo}{\mathrm{S}}_{2}$; particularly, the low-energy Bloch bands are responsive to a directional strain. In this study, in-plane uniaxial deformation is found to drift the low-energy electron/hole valleys of strained $\mathrm{ML}\text{\ensuremath{-}}\mathrm{Mo}{\mathrm{S}}_{2}$ far away from $K/K'$ points in the Brillouin zone (BZ). The amount of drift differs notably from hole to electron bands, where the conduction band minimum (CBM) drifts nearly 2 times more than the valence band maximum (VBM) in response to a progressively increasing strain field (0--10%). The resulting strain-induced valley asymmetry/decoherence can lift the momentum degeneracy of valley carriers at the $K$ point, thereby affecting the low-energy valley excitations ($K$-valley polarization) in a strained $\mathrm{ML}\text{\ensuremath{-}}\mathrm{Mo}{\mathrm{S}}_{2}$ lattice. The quantum origin of this decoherent valley arises from the differences in the Bloch orbital wave functions of electron and hole states at the exciton band edges and their deformation under strain. A higher drift (g1.5 times) is noticed when strain is along the zigzag (ZZ) axis relative to the armchair (AC) axis, which is attributed to a faster decline in Young's modulus and Poisson's ratio (PR) along the ZZ direction. A similar valley drift only in the VBM of uniaxially strained $\mathrm{ML}\text{\ensuremath{-}}\mathrm{Mo}{\mathrm{S}}_{2}$ was reported in an earlier local density approximation (LDA) based density functional theory (DFT) study [Q. Zhang et al., Phys. Rev. B 88, 245447 (2013)], where a massive valley drift occurring at the CBM was fully overlooked. Moreover, the giant VBM drift reported therein is 6 times the drift observed in our DFT studies based on spin-orbit coupling (SOC) and Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA) functionals. The physical origin of valley drift has been ascertained in our thorough investigations. The robustness of our approach is substantiated as follows. With progressive increase in strain magnitude (0--10%), the band gap remains direct up to 2% uniaxial tensile strain, under SOC, which accurately reproduces the experimental strain-induced direct-to-indirect band gap transitions occurring at \ensuremath{\sim}2% strain. Based on LDA-DFT [Q. Zhang et al., Phys. Rev. B 88, 245447 (2013)], this crossover in band gap has been incorrectly reported to occur at a higher value of uniaxial strain of 4%. Moreover, the direct SOC band gap shows a linear redshift at a rate of 51--53 meV/(% of strain), under uniaxial tensile strain, which is in excellent quantitative agreement with experimentally observed rates in the redshift of direct excitonic transitions measured in several optical absorption and photoluminescence (PL) spectroscopy experiments. In addition, the Berry curvature \textohm{}($k$) of electron/hole bands gets significantly modulated in strained $\mathrm{ML}\text{\ensuremath{-}}\mathrm{Mo}{\mathrm{S}}_{2}$, where the intensity of the flux profile increases as a function of the magnitude of strain with an opposite drift around $K/K'$, when strained along the ZZ/AC direction. A strong strain-valley coupling leads to an enhancement in the strength of spin-orbit induced spin splitting of bands at VBM/CBM, which is sizably enhanced (\ensuremath{\sim}7 meV) simply by the strain-controlled orbital motions. Our findings are of prime importance in the valley physics of $\mathrm{Mo}{\mathrm{S}}_{2}$. Besides, the important theoretical insights emerging from this work will trigger further experimental investigations on $\mathrm{ML}\text{\ensuremath{-}}\mathrm{Mo}{\mathrm{S}}_{2}$ to realize its novel technological potential in nanoelectronics, spintronics, and valleytronics.
- Published
- 2019
48. 2D HfN2/graphene interface based Schottky device: Unmatched controllability in electrical contacts and carrier concentration via electrostatic gating and out-of-plane strain
- Author
-
Manish Kumar Mohanta and Abir De Sarkar
- Subjects
Materials science ,business.industry ,Graphene ,Schottky barrier ,Doping ,General Physics and Astronomy ,Schottky diode ,Heterojunction ,02 engineering and technology ,Surfaces and Interfaces ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Electrical contacts ,0104 chemical sciences ,Surfaces, Coatings and Films ,law.invention ,law ,Optoelectronics ,Field-effect transistor ,0210 nano-technology ,business ,Ohmic contact - Abstract
Graphene-based van der Waals heterostructure (vdWH) comprising of HfN2 monolayer stacked over graphene has been designed and studied based on density functional theory. The vdWH forms a n-type Schottky contact with a Schottky barrier height (SBH) of 0.67 eV, while it exhibits p-type SBH of 0.93 eV. The response of SBH and electrical contact properties to external perturbation, such as, vertical strain and electric field has been investigated thoroughly. Under the application of strain and normal electric field within range of ±0.3 V/A, the type of electrical contacts, i.e., n/p type Schottky or Ohmic, is found to be interconvertible, while electron/hole doping in graphene is tunable by a doping carrier concentration of up to ~1013 cm−2, which lies between experimentally observed molecular doping (~1012 cm−2) and electrolytic gating (~1014 cm−2). Such an extremely high tunability in electrical contacts, doping carrier concentration along with its excellent optical response in the visible light region shows unrivalled potential of this vdWH in high performance graphene-based futuristic Schottky transistors with high on/off ratio, ultrathin phototransistor with high gain, low-power multivalued optical non volatile memory devices, and nanoelectronics.
- Published
- 2021
49. Dual response of graphene-based ultra-small molecular junctions to defect engineering
- Author
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Xiao-Xiao Fu, Kun-Peng Dou, Abir De Sarkar, and Ruiqin Zhang
- Subjects
Materials science ,Condensed matter physics ,Dopant ,Graphene ,Fermi level ,Doping ,Molecular electronics ,Fermi energy ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,law.invention ,symbols.namesake ,law ,Molecular conductance ,symbols ,General Materials Science ,Density functional theory ,Electrical and Electronic Engineering ,0210 nano-technology - Abstract
It has been reported that N and B doping induce a quasi-bound state that suppresses the conduction in graphene nanoribbon (GNR)-based junctions, while an H defect or a pyridine-like N-atom (PN) substitution at the edge of the GNR does not affect the transmission close to the Fermi energy. However, these results may vary when the size of the functional unit of the GNR junction decreases to a molecular level. In this study, a defect is introduced to a test-bed architecture consisting of a polyacene bridging two zigzag GNR electrodes, which changes the molecular state alignment and coupling to the electrode states, and varies the equivalence between two eigen-channels at the Fermi level. It is revealed that B and N atom substitution, and H defects play a dual role in the molecular conductance, whereas the PN substitution acts as an ineffective dopant. The results obtained from density functional theory combined with the non-equilibrium Green’s function method aid in determining the optimal design for the GNR-based ultra-small molecular devices via defect engineering.
- Published
- 2016
50. Influence of Boron Substitution on Conductance of Pyridine- and Pentane-Based Molecular Single Electron Transistors: First-Principles Analysis
- Author
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Anurag Srivastava, Md. Shahzad Khan, K. S. Kaur, Mohd. Shahid Khan, Vikash Sharma, Madura Marathe, Abir De Sarkar, and Boddepalli SanthiBhushan
- Subjects
010302 applied physics ,Ab initio ,Coulomb blockade ,Conductance ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Pentane ,chemistry.chemical_compound ,chemistry ,Computational chemistry ,0103 physical sciences ,Pyridine ,Materials Chemistry ,Molecule ,Physical chemistry ,Density functional theory ,Electrical and Electronic Engineering ,0210 nano-technology ,Boron - Abstract
We have investigated the modeling of boron-substituted molecular single-electron transistor (SET), under the influence of a weak coupling regime of Coulomb blockade between source and drain metal electrodes. The SET consists of a single organic molecule (pyridine/pentane/1,2-azaborine/butylborane) placed over the dielectric, with boron (B) as a substituent. The impact of B-substitution on pyridine and pentane molecules in isolated, as well as SET, environments has been analyzed by using density functional theory-based ab initio packages Atomistix toolkit-Virtual NanoLab and Gaussian03. The performance of proposed SETs was analyzed through charging energies, total energy as a function of gate potential and charge stability diagrams. The analysis confirms that the B-substituted pentane (butylborane) and the boron-substituted pyridine (1,2-azaborine) show remarkably improved conductance in SET environment in comparison to simple pyridine and pentane molecules.
- Published
- 2016
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