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Jadczak J, Andrzejewski J, Debus J, Ho CH, Bryja L. Resonant Exciton Scattering Reveals Raman Forbidden Phonon Modes in Layered GeS. J Phys Chem Lett 2023; 14:3986-3994. [PMID: 37083310 PMCID: PMC10165653 DOI: 10.1021/acs.jpclett.3c00783] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Germanium monosulfide with an anisotropic puckered crystalline structure has recently attracted much attention due to its unique optical and electronic properties; however, exciton-phonon interactions were only superficially elucidated. We study the resonant Raman scattering and the photoluminescence of the optically active Γ-exciton in layered GeS flakes and evaluate the exciton and phonon responses on variations in the excitation energy, laser-light and emission polarizations, temperature, and laser power. A double-resonance mechanism allows for observing Raman forbidden (dark) first- and second-order longitudinal-optical phonon modes whose symmetries and energies are moreover calculated by density functional perturbation theory. For (quasi)-resonant exciton excitation, the selection rules become relaxed so that a fourth-order Fröhlich intraband process is mediated by the scattering of the electron with a longitudinal-optical and an acoustic phonon. Our results demonstrate considerable coupling between phonons and photogenerated carriers in GeS flakes and the high efficiency of multiorder scattering in optical processes.
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Affiliation(s)
- Joanna Jadczak
- Department of Experimental Physics, Wroclaw University of Science and Technology, 50-370 Wroclaw, Poland
| | - Janusz Andrzejewski
- Department of Experimental Physics, Wroclaw University of Science and Technology, 50-370 Wroclaw, Poland
| | - Joerg Debus
- Department of Physics, TU Dortmund University, 44227 Dortmund, Germany
| | - Ching-Hwa Ho
- Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei, 106, Taiwan
| | - Leszek Bryja
- Department of Experimental Physics, Wroclaw University of Science and Technology, 50-370 Wroclaw, Poland
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Sun Y, Jiao Z, Zandvliet HJW, Bampoulis P. Strong Fermi-Level Pinning in GeS-Metal Nanocontacts. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2022; 126:11400-11406. [PMID: 35865793 PMCID: PMC9289947 DOI: 10.1021/acs.jpcc.2c02827] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Germanium sulfide (GeS) is a layered monochalcogenide semiconductor with a band gap of about 1.6 eV. To verify the suitability of GeS for field-effect-based device applications, a detailed understanding of the electronic transport mechanisms of GeS-metal junctions is required. In this work, we have used conductive atomic force microscopy (c-AFM) to study charge carrier injection in metal-GeS nanocontacts. Using contact current-voltage spectroscopy, we identified three dominant charge carrier injection mechanisms: thermionic emission, direct tunneling, and Fowler-Nordheim tunneling. In the forward-bias regime, thermionic emission is the dominating current injection mechanism, whereas in the reverse-bias regime, the current injection mechanism is quantum mechanical tunneling. Using tips of different materials (platinum, n-type-doped silicon, and highly doped p-type diamond), we found that the Schottky barrier is almost independent of the work function of the metallic tip, which is indicative of a strong Fermi-level pinning. This strong Fermi-level pinning is caused by charged defects and impurities.
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Sutter E, Wang J, Sutter P. Lateral Heterostructures of Multilayer GeS and SnS van der Waals Crystals. ACS NANO 2020; 14:12248-12255. [PMID: 32886477 DOI: 10.1021/acsnano.0c05978] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Engineered heterostructures derive distinct properties from materials integration and interface formation. Two-dimensional crystals have been combined to form vertical stacks and lateral heterostuctures with covalent line interfaces. While thicker vertical stacks have been realized, lateral heterostructures from multilayer van der Waals crystals, which could bring the benefits of high-quality interfaces to bulk-like layered materials, have remained much less explored. Here, we demonstrate the integration of anisotropic layered Sn and Ge monosulfides into complex heterostructures with seamless lateral interfaces and tunable vertical design using a two-step growth process. The anisotropic lattice mismatch at the lateral interfaces between GeS and SnS is relaxed via dislocations and interfacial alloying. Nanoscale optoelectronic measurements by cathodoluminescence spectroscopy show the characteristic light emission of joined high-quality van der Waals crystals. Spectroscopy across the lateral interface indicates valley-selective luminescence in the bulk SnS component that arises due to anisotropic electron transfer across the interface. The results demonstrate the ability to realize high-quality lateral heterostructures of multilayer van der Waals crystals for diverse applications, e.g., in optoelectronics or valleytronics.
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Affiliation(s)
- Eli Sutter
- Department of Mechanical & Materials Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
| | - Jia Wang
- Department of Mechanical & Materials Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
| | - Peter Sutter
- Department of Electrical & Computer Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
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Fan X, Su L, Zhang F, Huang D, Sang DK, Chen Y, Li Y, Liu F, Li J, Zhang H, Xie H. Layer-Dependent Properties of Ultrathin GeS Nanosheets and Application in UV-Vis Photodetectors. ACS APPLIED MATERIALS & INTERFACES 2019; 11:47197-47206. [PMID: 31763823 DOI: 10.1021/acsami.9b14663] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Two-dimensional germanium sulfide (GeS), an analogue of phosphorene, has attracted broad attention owing to its excellent environmental stabilities, fascinating electronic and optical properties, and applications in various nanodevices. In spite of the current achievements on 2D GeS, the report of ultrathin few-layer GeS nanosheets within 5 nm is still lacking. Here in this contribution, we have achieved preparation of ultrathin few-layer GeS nanosheets with thicknesses of 1.3 ± 0.1 nm [approximately three layers (∼3L)], 3.2 ± 0.2 nm (∼6L), and 4.2 ± 0.3 nm (∼8L) via a typical liquid-phase exfoliation (LPE) method. Based on various experimental characterizations and first-principles calculations, the layer-dependent electronic, transport, and optical properties are investigated. For the few-layer GeS nanosheets, enhanced light absorption in the UV-vis region and superior photoresponse behavior with increasing layer number is observed, while for the thin films above 10 nm, the properties degenerate to the bulk feature. In addition, the as-prepared ultrathin nanosheets manifest great potential in the applications of photoelectrochemical (PEC)-type photodetectors, exhibiting excellent and stable periodic photoresponse behavior under the radiation of white light. The ∼8L GeS-based photodetector exhibits superior performance than the thinner GeS nanosheets (<4 nm), even better as compared to the bulk or film (above 10 nm) counterparts in terms of higher photoresponsivity along with remarkable photodetection performance in the UV-vis region. This work not only provides direct and solid evidence of the layer-number evolutionary band structure, mobility, and optical properties of ultrathin 2D GeS nanosheets but also promotes the foreseeable applications of 2D GeS as energy-related photoelectric devices.
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Peng J, Li W, Wang Y, Yu X, Liu J, He Q. Pressure-induced improvement in symmetry and change in electronic properties of SnSe. J Mol Model 2017; 23:319. [PMID: 29063282 DOI: 10.1007/s00894-017-3494-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2017] [Accepted: 10/04/2017] [Indexed: 11/27/2022]
Abstract
To explore the structural and electronic properties of SnSe under pressure, we applied hydrostatic pressure from 0 to 8 GPa to a fully relaxed SnSe cell sample based on plane-wave pseudopotential density functional theory. The calculated results indicate that the structure of SnSe changes gradually from an irregular zigzag structure with low symmetry to a B1-like structure with regular arrangement and high symmetry under pressure. The lattice parameters and cell volume of SnSe decrease monotonically as the applied pressure increases. The energy band gap of SnSe becomes narrow under pressure and is finally closed at 6.1 GPa. Moreover, we found that SnSe exhibits non-magnetic and semi-metallic features based on analyzing its electronic state density and spin state density. This can be attributed to the decrease in the lattices constants and the enhancement of the Sn-Se bond interaction under pressure, which causes the density of electronic states to increase near the Fermi surface. Finally, the charge distribution between Se-Sn-Se along the c-axis changes gradually from asymmetric to symmetric as the pressure is increased to 6.1 GPa and beyond. This implies that enhancement of the structure symmetry of SnSe can lead to a symmetrical distribution of charges, which further affects the bonding characteristics of the Sn-Se bond.
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Affiliation(s)
- Jingjing Peng
- Guangdong Engineering Technology Research Center of Efficient Green Energy and Environment Protection Materials, South China Normal University, Guangzhou, 510006, China
- School of Physics and Telecommunication Engineering, Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou, 510006, China
| | - Wei Li
- Guangdong Engineering Technology Research Center of Efficient Green Energy and Environment Protection Materials, South China Normal University, Guangzhou, 510006, China.
- School of Physics and Telecommunication Engineering, Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou, 510006, China.
| | - Yu Wang
- Guangdong Engineering Technology Research Center of Efficient Green Energy and Environment Protection Materials, South China Normal University, Guangzhou, 510006, China
- School of Physics and Telecommunication Engineering, Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou, 510006, China
| | - Xiaoyan Yu
- Guangdong Engineering Technology Research Center of Efficient Green Energy and Environment Protection Materials, South China Normal University, Guangzhou, 510006, China
- School of Physics and Telecommunication Engineering, Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou, 510006, China
| | - Junming Liu
- Laboratory of Solid State Microstructures and Innovative Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, China
| | - Qinyu He
- Guangdong Engineering Technology Research Center of Efficient Green Energy and Environment Protection Materials, South China Normal University, Guangzhou, 510006, China.
- School of Physics and Telecommunication Engineering, Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou, 510006, China.
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Agostino A, Bonometti E, Castiglioni M, Lausarot PM. Preparation Of Germanium Monosulfide Particles By Microwave Assisted Sublimation. ACTA ACUST UNITED AC 2016. [DOI: 10.1080/14328917.2004.11784825] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Structural phase transition of SnSe under uniaxial stress and hydrostatic pressure: an ab initio study. J Mol Model 2011; 17:2989-94. [PMID: 21360183 DOI: 10.1007/s00894-011-1019-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2010] [Accepted: 02/09/2011] [Indexed: 10/18/2022]
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A new phase of solid iodine with different molecular covalent bonds. Proc Natl Acad Sci U S A 2008; 105:4999-5001. [PMID: 18367667 DOI: 10.1073/pnas.0801280105] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
There is a great interest in the behavior of diatomic molecular solids under extremely high-pressure conditions that lead to pressure-induced metallization, molecular dissociation, and formation of atomic phase. The consensus has been that the phase-transition sequence that happened in both solid bromine and iodine is from a molecular phase (phase I), to an incommensurate phase (phase V), and then to an atomic phase (phase II), with increasing pressure. However, a puzzle remains unresolved for both solids: pressure-induced X and Y bands were observed in the Raman spectra in the molecular phase at low pressures, even before the onset of phase V. Here, we suggest a phase for solid iodine in such a low-pressure range (designated as phase I') in which two different covalent intramolecular bonds coexist, based on first-principles calculations and later corroborated by x-ray diffraction experiments. The pressure dependence of the X and Y bands and other vibrational frequencies measured experimentally can be explained nicely by combining the vibrational modes of phase I and phase I'. These results help improve our understanding on the pressure-induced molecular dissociation and metallization in diatomic solids and may shed some light on the investigation of similar phenomena in solid H(2).
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Clark SJ, Adam CJ, Hsueh HC, Pu F, Crain J. Vibrational Properties of Liquid Crystal Molecules from AB Initio Computer Simulation. ACTA ACUST UNITED AC 2006. [DOI: 10.1080/10587259708041859] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- S. J. Clark
- a Department of Physics and Astronomy , The University of Edinburgh , Mayfield Road, EH9 352 , Scotland
| | - C. J. Adam
- a Department of Physics and Astronomy , The University of Edinburgh , Mayfield Road, EH9 352 , Scotland
| | - H. C. Hsueh
- a Department of Physics and Astronomy , The University of Edinburgh , Mayfield Road, EH9 352 , Scotland
| | - F. Pu
- a Department of Physics and Astronomy , The University of Edinburgh , Mayfield Road, EH9 352 , Scotland
- b Institute of High Temperature and Pressure Physics, Chengdu University of Science and Technology , P. R. China
| | - J. Crain
- a Department of Physics and Astronomy , The University of Edinburgh , Mayfield Road, EH9 352 , Scotland
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Siddick MM, Ackland GJ, Morrison CA. Constrained dynamics and extraction of normal modes fromab initiomolecular dynamics: Application to ammonia. J Chem Phys 2006; 125:64707. [PMID: 16942305 DOI: 10.1063/1.2218848] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We present a methodology for extracting phonon data from ab initio Born-Oppenheimer molecular dynamics calculations of molecular crystals. Conventional ab initio phonon methods based on perturbations are difficult to apply to lattice modes because the perturbation energy is dominated by intramolecular modes. We use constrained molecular dynamics to eliminate the effect of bond bends and stretches and then show how trajectories can be used to isolate and define in particular, the eigenvalues and eigenvectors of modes irrespective of their symmetry or wave vector. This is done by k-point and frequency filtering and projection onto plane wave states. The method is applied to crystalline ammonia: the constrained molecular dynamics allows a significant speed-up without affecting structural or vibrational modes. All Gamma point lattice modes are isolated: the frequencies are in agreement with previous studies; however, the mode assignments are different.
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Affiliation(s)
- M M Siddick
- School of Physics, The University of Edinburgh, Mayfield Road, Edinburgh EH9 3JZ, United Kingdom
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