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Boora M, Lin YC, Chen C, Trainor N, Robinson JA, Redwing JM, Suh JY. Low-Frequency Raman Study of Large-Area Twisted Bilayers of WS 2 Stacked by an Etchant-Free Transfer Method. ACS APPLIED MATERIALS & INTERFACES 2024; 16:2902-2911. [PMID: 38166373 DOI: 10.1021/acsami.3c14708] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2024]
Abstract
Monolayer transition metal dichalcogenides have strong intracovalent bonding. When stacked in multilayers, however, weak van der Waals interactions dominate interlayer mechanical coupling and, thus, influence their lattice vibrations. This study presents the frequency evolution of interlayer phonons in twisted WS2 bilayers, highly subject to the twist angle. The twist angle between the layers is controlled to modulate the spacing between the layers, which, in turn, affects the interlayer coupling that is probed by Raman spectroscopy. The shifts of high-frequency E2g1 (Γ) and A1g (Γ) phonon modes and their frequency separations are dependent on the twist angle, reflecting the correlation between the interlayer mechanical coupling and twist angle. In this work, we fabricated large-area, twisted bilayer WS2 with a clean interface with controlled twist angles. Polarized Raman spectroscopy identified new interlayer modes, which were not previously reported, depending on the twist angle. The appearance of breathing modes in Raman phonon spectra provides evidence of strong interlayer coupling in bilayer structures. We confirm that the twist angle can alter the exciton and trion dynamics of bilayers as indicated by the photoluminescence peak shift. These large-area controlled twist angle samples have practical applications in optoelectronic device fabrication and twistronics.
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Affiliation(s)
- Manpreet Boora
- Department of Physics, Michigan Technological University, Houghton, Michigan 49931, United States
| | - Yu-Chuan Lin
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- Department of Materials Science and Engineering, National Yang Ming Chiao Tung University, Hsinchu City 300093, Taiwan
| | - Chen Chen
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Nicholas Trainor
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Joshua A Robinson
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- 2D Crystal Consortium Materials Innovation Platform, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- Department of Chemistry and Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Joan M Redwing
- Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
- 2D Crystal Consortium Materials Innovation Platform, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Jae Yong Suh
- Department of Physics, Michigan Technological University, Houghton, Michigan 49931, United States
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2
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Upadhyay B, Sharma R, Maity D, Narayan TN, Pal SK. Ultrafast carrier dynamics in vanadium-doped MoS 2 alloys. NANOSCALE 2023; 15:16344-16353. [PMID: 37786388 DOI: 10.1039/d3nr03337f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/04/2023]
Abstract
Substitutional doping is a most promising approach to manipulate the electronic and optical properties of two-dimensional (2D) transition metal dichalcogenides (TMDCs). In addition to inducing magnetism, vanadium (V) doping can lead to semiconductor-metal transition in TMDCs. However, the dynamics of charge carriers that governs the optoelectronic properties of doped TMDCs has been rarely revealed. In this work, we have investigated the dynamics of photocarriers in pristine and V-doped monolayer (ML) MoS2. Comparison of the transient absorption (TA) spectra of ML MoS2 with lightly (≤1%) and heavily (3.62%) V-doped MoS2 infers the induction of additional energy states in the doped materials giving rise to new low energy bleach features in the TA spectra. The quasiparticle band structure of MoS2 is found to disappear at sufficiently high V doping due to the presence of impurity bands. An attempt has also been made to study the manipulation of the carrier lifetime with V doping in MoS2. Our TA kinetic measurements suggest that the decay kinetics of the carriers becomes slower with increasing doping percentage and at a higher doping level the carriers survive for a much longer time compared to pristine MoS2. Furthermore, we have identified a new electronic transition (NET) in heavily V-doped MoS2 at high pump fluences.
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Affiliation(s)
- Bhuvan Upadhyay
- School of Physical Sciences, Indian Institute of Technology Mandi, Kamand, Mandi, Himachal Pradesh, 175075, India.
- Advanced Materials Research Center, Indian Institute of Technology Mandi, Kamand, Mandi, Himachal Pradesh, 175075, India
| | - Rahul Sharma
- Tata Institute of Fundamental Research-Hyderabad, Sy. No. 36/P, Gopanapally Village, Serilingampally Mandal, Hyderabad-500046, India
- Department of Physics and Astronomy, Uppsala University, 75236, Uppsala, Sweden
| | - Dipak Maity
- Tata Institute of Fundamental Research-Hyderabad, Sy. No. 36/P, Gopanapally Village, Serilingampally Mandal, Hyderabad-500046, India
| | - Tharangattu N Narayan
- Tata Institute of Fundamental Research-Hyderabad, Sy. No. 36/P, Gopanapally Village, Serilingampally Mandal, Hyderabad-500046, India
| | - Suman Kalyan Pal
- School of Physical Sciences, Indian Institute of Technology Mandi, Kamand, Mandi, Himachal Pradesh, 175075, India.
- Advanced Materials Research Center, Indian Institute of Technology Mandi, Kamand, Mandi, Himachal Pradesh, 175075, India
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3
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Pelaez-Fernandez M, Lin YC, Suenaga K, Arenal R. Optoelectronic Properties of Atomically Thin Mo xW (1-x)S 2 Nanoflakes Probed by Spatially-Resolved Monochromated EELS. NANOMATERIALS (BASEL, SWITZERLAND) 2021; 11:3218. [PMID: 34947566 PMCID: PMC8708971 DOI: 10.3390/nano11123218] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/03/2021] [Revised: 11/10/2021] [Accepted: 11/16/2021] [Indexed: 11/17/2022]
Abstract
Band gap engineering of atomically thin two-dimensional (2D) materials has attracted a huge amount of interest as a key aspect to the application of these materials in nanooptoelectronics and nanophotonics. Low-loss electron energy loss spectroscopy has been employed to perform a direct measurement of the band gap in atomically thin MoxW(1-x)S2 nanoflakes. The results show a bowing effect with the alloying degree, which fits previous studies focused on excitonic transitions. Additional properties regarding the Van Hove singularities in the density of states of these materials, as well as high energy excitonic transition, have been analysed as well.
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Affiliation(s)
- Mario Pelaez-Fernandez
- Instituto de Nanociencia y Materiales de Aragon (INMA), CSIC-U. de Zaragoza, Calle Pedro Cerbuna 12, 50009 Zaragoza, Spain;
- Laboratorio de Microscopias Avanzadas, Universidad de Zaragoza, Calle Mariano Esquillor, 50018 Zaragoza, Spain
| | - Yung-Chang Lin
- National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8565, Japan;
| | - Kazu Suenaga
- The Institute of Scientific and Industrial Research (ISIR-SANKEN), Osaka University, Osaka 567-0047, Japan;
| | - Raul Arenal
- Instituto de Nanociencia y Materiales de Aragon (INMA), CSIC-U. de Zaragoza, Calle Pedro Cerbuna 12, 50009 Zaragoza, Spain;
- Laboratorio de Microscopias Avanzadas, Universidad de Zaragoza, Calle Mariano Esquillor, 50018 Zaragoza, Spain
- ARAID Fundation, 50018 Zaragoza, Spain
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4
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Liang X, Qin C, Gao Y, Han S, Zhang G, Chen R, Hu J, Xiao L, Jia S. Reversible engineering of spin-orbit splitting in monolayer MoS 2via laser irradiation under controlled gas atmospheres. NANOSCALE 2021; 13:8966-8975. [PMID: 33970179 DOI: 10.1039/d1nr00019e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Monolayer transition metal dichalcogenides, manifesting strong spin-orbit coupling combined with broken inversion symmetry, lead to coupling of spin and valley degrees of freedom. These unique features make them highly interesting for potential spintronic and valleytronic applications. However, engineering spin-orbit coupling at room temperature as demanded after device fabrication is still a great challenge for their practical applications. Here we reversibly engineer the spin-orbit coupling of monolayer MoS2 by laser irradiation under controlled gas environments, where the spin-orbit splitting has been effectively regulated within 140 meV to 200 meV. Furthermore, the photoluminescence intensity of the B exciton can be reversibly manipulated over 2 orders of magnitude. We attribute the engineering of spin-orbit splitting to the reduction of binding energy combined with band renormalization, originating from the enhanced absorption coefficient of monolayer MoS2 under inert gases and subsequently the significantly boosted carrier concentrations. Reflectance contrast spectra during the engineering stages provide unambiguous proof to support our interpretation. Our approach offers a new avenue to actively control the spin-orbit splitting in transition metal dichalcogenide materials at room temperature and paves the way for designing innovative spintronic devices.
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Affiliation(s)
- Xilong Liang
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan, Shanxi 030006, China. and Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China
| | - Chengbing Qin
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan, Shanxi 030006, China. and Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China
| | - Yan Gao
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan, Shanxi 030006, China. and Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China and Department of Physics, Shanxi Datong University, Datong, 037009, China
| | - Shuangping Han
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan, Shanxi 030006, China. and Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China
| | - Guofeng Zhang
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan, Shanxi 030006, China. and Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China
| | - Ruiyun Chen
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan, Shanxi 030006, China. and Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China
| | - Jianyong Hu
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan, Shanxi 030006, China. and Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China
| | - Liantuan Xiao
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan, Shanxi 030006, China. and Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China
| | - Suotang Jia
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan, Shanxi 030006, China. and Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China
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Wines D, Ersan F, Ataca C. Engineering the Electronic, Thermoelectric, and Excitonic Properties of Two-Dimensional Group-III Nitrides through Alloying for Optoelectronic Devices (B 1-xAl xN, Al 1-xGa xN, and Ga 1-xIn xN). ACS APPLIED MATERIALS & INTERFACES 2020; 12:46416-46428. [PMID: 32942852 DOI: 10.1021/acsami.0c11124] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Recently, two-dimensional (2D) group-III nitride semiconductors such as h-BN, h-AlN, h-GaN, and h-InN have attracted attention because of their exceptional electronic, optical, and thermoelectric properties. It has also been demonstrated, theoretically and experimentally, that properties of 2D materials can be controlled by alloying. In this study, we performed density functional theory (DFT) calculations to investigate 2D B1-xAlxN, Al1-xGaxN, and Ga1-xInxN alloyed structures. We also calculated the thermoelectric properties of these structures using Boltzmann transport theory based on DFT and the optical properties using the GW method and the Bethe-Salpeter equation. We find that by changing the alloying concentration, the band gap and exciton binding energies of each structure can be tuned accordingly, and for certain concentrations, a high thermoelectric performance is reported with strong dependence on the effective mass of the given alloyed monolayer. In addition, the contribution of each e-h pair is explained by investigating the e-h coupling strength projected on the electronic band structure, and we find that the exciton binding energy decreases with increase in sequential alloying concentration. With the ability to control such properties by alloying 2D group-III nitrides, we believe that this work will play a crucial role for experimentalists and manufacturers focusing on next-generation electronic, optoelectronic, and thermoelectric devices.
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Affiliation(s)
- Daniel Wines
- Department of Physics, University of Maryland Baltimore County, Baltimore, Maryland 21250, United States
| | - Fatih Ersan
- Department of Physics, University of Maryland Baltimore County, Baltimore, Maryland 21250, United States
- Department of Physics, Aydin Adnan Menderes University, Aydin 09100, Turkey
| | - Can Ataca
- Department of Physics, University of Maryland Baltimore County, Baltimore, Maryland 21250, United States
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6
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Riche F, Bragança H, Qu F, Lopez-Richard V, Xie SJ, Dias AC, Marques GE. Robust room temperature emissions of trion in darkish WSe 2monolayers: effects of dark neutral and charged excitonic states. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:365702. [PMID: 32365339 DOI: 10.1088/1361-648x/ab8fd4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2020] [Accepted: 05/04/2020] [Indexed: 06/11/2023]
Abstract
Owing to nonzero charge and spin degrees of freedom, trions offer unprecedented tunability and open new paths for applications in devices based on 2D semiconductors. However, in monolayer WSe2, the trion photoluminescence is commonly detected only at low temperatures and vanishes at room temperature, which undermines practical applications. To unveil how to overcome this obstacle, we have developed a comprehensive theory to probe the impact of different excitonic channels on the trion emission in WSe2monolayers, which combinesab initiotight-binding formalism, Bethe-Salpeter equation and a set of coupled rate equations to describe valley dynamics of excitonic particles. Through a systematic study in which new scattering channels are progressively included, we found that, besides the low electron density, strong many-body correlations between bright and dark excitonic states quenches the trion emission in WSe2. Therefore, the reduction of scatterings from bright to dark states is required to achieve trion emission at room temperature for experimentally accessible carrier concentrations.
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Affiliation(s)
- Flavio Riche
- Instituto de Física, Universidade de Brasília, Brasília-DF, Brazil
| | - Helena Bragança
- Departamento de Física, Universidade Federal de Ouro Preto, Ouro Preto-MG, Brazil
- Departamento de Física, Universidade Federal de São Carlos, São Carlos-SP, Brazil
| | - Fanyao Qu
- Instituto de Física, Universidade de Brasília, Brasília-DF, Brazil
| | - Victor Lopez-Richard
- Departamento de Física, Universidade Federal de São Carlos, São Carlos-SP, Brazil
| | - S J Xie
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan, People's Republic of China
| | - A C Dias
- Instituto de Física, Universidade de Brasília, Brasília-DF, Brazil
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7
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Adnan M, Baumberg JJ, Vijaya Prakash G. Linear and nonlinear optical probing of various excitons in 2D inorganic-organic hybrid structures. Sci Rep 2020; 10:2615. [PMID: 32054972 PMCID: PMC7018830 DOI: 10.1038/s41598-020-59457-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2019] [Accepted: 11/27/2019] [Indexed: 11/10/2022] Open
Abstract
Nonlinear optical properties, such as two-(or multi-) photon absorption (2PA), are of special interest for technologically important applications in fast optical switching, in vivo imaging and so on. Highly intense infrared ultrashort pulses probe deep into samples and reveal several underlying structural perturbations (inter-layer distortions, intra-layer crumpling) and also provide information about new excited states and their relaxation. Naturally self-assembled inorganic-organic multiple quantum wells (IO-MQWs) show utility from room-temperature exciton emission features (binding energies ~200–250 meV). These Mott type excitons are highly sensitive to the self-assembly process, inorganic network distortions, thickness and inter-layer distortions of these soft two-dimensional (2D) and weak van der Waal layered hybrids. We demonstrate strong room-temperature nonlinear excitation intensity dependent two-photon absorption induced exciton photoluminescence (2PA-PL) from these IO-MQWs, excited by infrared femtosecond laser pulses. Strongly confined excitons show distinctly different one- and two-photon excited photoluminescence energies: from free-excitons (2.41 eV) coupled to the perfectly aligned MQWs and from energy down-shifted excitons (2.33 eV) that originate from the locally crumpled layered architecture. High intensity femtosecond induced PL from one-photon absorption (1PA-PL) suggests saturation of absorption and exciton-exciton annihilation, with typical reduction in PL radiative relaxation times from 270 ps to 190 ps upon increasing excitation intensities. From a wide range of IR excitation tuning, the origin of 2PA-PL excitation is suggested to arise from exciton dark states which extend below the bandgap. Observed two-photon absorption coefficients (β ~75 cm/GW) and two-photon excitation cross-sections (η2σ2 ~ 110GM), further support the evidence for 2PA excitation origin. Both 1PA- and 2PA-PL spatial mappings over large areas of single crystal platelets demonstrate the co-existence of both free and deep-level crumpled excitons with some traces of defect-induced trap state emission. We conclude that the two-photon absorption induced PL is highly sensitive to the self-assembly process of few to many mono layers, the crystal packing and deep level defects. This study paves a way to tailor the nonlinear properties of many 2D material classes. Our results thus open new avenues for exploring fundamental phenomena and novel optoelectronic applications using layered inorganic-organic and other metal organic frameworks.
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Affiliation(s)
- Mohammad Adnan
- Nanophotonics Lab, Department of Physics, Indian Institute of Technology Delhi, New Delhi, 110016, India
| | - Jeremy J Baumberg
- Nanophotonics Centre, Cavendish Laboratory, University of Cambridge, Cambridge, CB3 0HE, United Kingdom
| | - G Vijaya Prakash
- Nanophotonics Lab, Department of Physics, Indian Institute of Technology Delhi, New Delhi, 110016, India.
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Adnan M, Rao KN, Acharyya JN, Kumar D, Dehury KM, Prakash GV. Synthesis, Structural, Linear, and Nonlinear Optical Studies of Inorganic-Organic Hybrid Semiconductors (R-C 6H 4CHCH 3NH 3) 2PbI 4, (R = CH 3, Cl). ACS OMEGA 2019; 4:19565-19572. [PMID: 31788586 PMCID: PMC6881839 DOI: 10.1021/acsomega.9b01704] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/10/2019] [Accepted: 10/30/2019] [Indexed: 06/10/2023]
Abstract
Synthesis, crystal structure, and optical properties of two-dimensional (2D) layered structurally slightly different inorganic-organic (IO) hybrid semiconductors (R-C6H4C2H4NH3)2PbI4 (R = CH3, Cl) are presented. They are naturally self-assembled systems where two (RNH3)+ moieties are sandwiched between two infinitely extended 2D layers of the [PbI6]4- octahedral network and treated as natural IO multiple quantum wells. While the former compound crystallizes into an orthorhombic system in the Cmc21 space group, the latter crystallizes into a monoclinic system in the space group P21/c. As a thin film, they are well-oriented along the (l00) direction. Both single crystals and thin films show strong room-temperature Mott type exciton features that are highly sensitive to the self-assembly and crystal packing. Linear (one-photon) and nonlinear (two-photon) optical probing of single crystals for exciton photoluminescence imaging and spectral spatial mapping provide deep insight into the layered re-arrangement and structural crumpling due to organic conformation. The strongly confined excitons, within the lowest band gap of inorganic, show distinctly different one- and two-photon excited photoluminescence peaks: free excitons from perfectly aligned 2D self-assembly and energy down-shifted excitons originated from the locally crumpled layered arrangement. Their structural aspects are successfully presented with proper correlation that emphasize various differences in physical and optical properties associated between these novel IO hybrids.
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Affiliation(s)
- Mohammad Adnan
- Nanophotonics
Lab, Department of Physics and Department of Chemistry, Indian Institute of Technology Delhi, New Delhi 110016, New Delhi, India
| | - Kotla Nageswara Rao
- Nanophotonics
Lab, Department of Physics and Department of Chemistry, Indian Institute of Technology Delhi, New Delhi 110016, New Delhi, India
| | - Jitendra Nath Acharyya
- Nanophotonics
Lab, Department of Physics and Department of Chemistry, Indian Institute of Technology Delhi, New Delhi 110016, New Delhi, India
| | - Dinesh Kumar
- Nanophotonics
Lab, Department of Physics and Department of Chemistry, Indian Institute of Technology Delhi, New Delhi 110016, New Delhi, India
| | - Kshetra Mohan Dehury
- Nanophotonics
Lab, Department of Physics and Department of Chemistry, Indian Institute of Technology Delhi, New Delhi 110016, New Delhi, India
| | - G. Vijaya Prakash
- Nanophotonics
Lab, Department of Physics and Department of Chemistry, Indian Institute of Technology Delhi, New Delhi 110016, New Delhi, India
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