1
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Huang S, Griffin E, Cai J, Xin B, Tong J, Fu Y, Kravets V, Peeters FM, Lozada-Hidalgo M. Gate-controlled suppression of light-driven proton transport through graphene electrodes. Nat Commun 2023; 14:6932. [PMID: 37907470 PMCID: PMC10618495 DOI: 10.1038/s41467-023-42617-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2023] [Accepted: 10/17/2023] [Indexed: 11/02/2023] Open
Abstract
Recent experiments demonstrated that proton transport through graphene electrodes can be accelerated by over an order of magnitude with low intensity illumination. Here we show that this photo-effect can be suppressed for a tuneable fraction of the infra-red spectrum by applying a voltage bias. Using photocurrent measurements and Raman spectroscopy, we show that such fraction can be selected by tuning the Fermi energy of electrons in graphene with a bias, a phenomenon controlled by Pauli blocking of photo-excited electrons. These findings demonstrate a dependence between graphene's electronic and proton transport properties and provide fundamental insights into molecularly thin electrode-electrolyte interfaces and their interaction with light.
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Affiliation(s)
- S Huang
- Department of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK
- National Graphene Institute, The University of Manchester, Manchester, M13 9PL, UK
| | - E Griffin
- Department of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK.
- National Graphene Institute, The University of Manchester, Manchester, M13 9PL, UK.
| | - J Cai
- Department of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK
- College of Advanced Interdisciplinary Studies, National University of Defence Technology, Changsha, Hunan, 410073, China
| | - B Xin
- Department of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK
- National Graphene Institute, The University of Manchester, Manchester, M13 9PL, UK
| | - J Tong
- Department of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK
- National Graphene Institute, The University of Manchester, Manchester, M13 9PL, UK
| | - Y Fu
- Department of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK
- National Graphene Institute, The University of Manchester, Manchester, M13 9PL, UK
| | - V Kravets
- Department of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK
| | - F M Peeters
- Departamento de Fisica, Universidade Federal do Ceara, 60455-900, Fortaleza, Ceara, Brazil
- Departement Fysica, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020, Antwerp, Belgium
| | - M Lozada-Hidalgo
- Department of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK.
- National Graphene Institute, The University of Manchester, Manchester, M13 9PL, UK.
- Research and Innovation Center for graphene and 2D materials (RIC2D), Khalifa University, PO Box 127788, Abu Dhabi, United Arab Emirates.
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2
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Wahab OJ, Daviddi E, Xin B, Sun PZ, Griffin E, Colburn AW, Barry D, Yagmurcukardes M, Peeters FM, Geim AK, Lozada-Hidalgo M, Unwin PR. Proton transport through nanoscale corrugations in two-dimensional crystals. Nature 2023; 620:782-786. [PMID: 37612394 PMCID: PMC10447238 DOI: 10.1038/s41586-023-06247-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2023] [Accepted: 05/23/2023] [Indexed: 08/25/2023]
Abstract
Defect-free graphene is impermeable to all atoms1-5 and ions6,7 under ambient conditions. Experiments that can resolve gas flows of a few atoms per hour through micrometre-sized membranes found that monocrystalline graphene is completely impermeable to helium, the smallest atom2,5. Such membranes were also shown to be impermeable to all ions, including the smallest one, lithium6,7. By contrast, graphene was reported to be highly permeable to protons, nuclei of hydrogen atoms8,9. There is no consensus, however, either on the mechanism behind the unexpectedly high proton permeability10-14 or even on whether it requires defects in graphene's crystal lattice6,8,15-17. Here, using high-resolution scanning electrochemical cell microscopy, we show that, although proton permeation through mechanically exfoliated monolayers of graphene and hexagonal boron nitride cannot be attributed to any structural defects, nanoscale non-flatness of two-dimensional membranes greatly facilitates proton transport. The spatial distribution of proton currents visualized by scanning electrochemical cell microscopy reveals marked inhomogeneities that are strongly correlated with nanoscale wrinkles and other features where strain is accumulated. Our results highlight nanoscale morphology as an important parameter enabling proton transport through two-dimensional crystals, mostly considered and modelled as flat, and indicate that strain and curvature can be used as additional degrees of freedom to control the proton permeability of two-dimensional materials.
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Affiliation(s)
- O J Wahab
- Department of Chemistry, University of Warwick, Coventry, UK
| | - E Daviddi
- Department of Chemistry, University of Warwick, Coventry, UK
| | - B Xin
- Department of Physics and Astronomy, The University of Manchester, Manchester, UK
- National Graphene Institute, The University of Manchester, Manchester, UK
| | - P Z Sun
- Department of Physics and Astronomy, The University of Manchester, Manchester, UK
- National Graphene Institute, The University of Manchester, Manchester, UK
| | - E Griffin
- Department of Physics and Astronomy, The University of Manchester, Manchester, UK
- National Graphene Institute, The University of Manchester, Manchester, UK
| | - A W Colburn
- Department of Chemistry, University of Warwick, Coventry, UK
| | - D Barry
- Department of Physics and Astronomy, The University of Manchester, Manchester, UK
| | - M Yagmurcukardes
- Department of Photonics, Izmir Institute of Technology, Urla, Turkey
| | - F M Peeters
- Departement Fysica, Universiteit Antwerpen, Antwerp, Belgium
- Departamento de Fisica, Universidade Federal do Ceara, Fortaleza, Brazil
| | - A K Geim
- Department of Physics and Astronomy, The University of Manchester, Manchester, UK.
- National Graphene Institute, The University of Manchester, Manchester, UK.
| | - M Lozada-Hidalgo
- Department of Physics and Astronomy, The University of Manchester, Manchester, UK.
- National Graphene Institute, The University of Manchester, Manchester, UK.
| | - P R Unwin
- Department of Chemistry, University of Warwick, Coventry, UK.
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3
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Javdani Z, Hassani N, Faraji F, Zhou R, Sun C, Radha B, Neyts E, Peeters FM, Neek-Amal M. Clogging and Unclogging of Hydrocarbon-Contaminated Nanochannels. J Phys Chem Lett 2022; 13:11454-11463. [PMID: 36469310 DOI: 10.1021/acs.jpclett.2c03016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
The recent advantages of the fabrication of artificial nanochannels enabled new research on the molecular transport, permeance, and selectivity of various gases and molecules. However, the physisorption/chemisorption of the unwanted molecules (usually hydrocarbons) inside nanochannels results in the alteration of the functionality of the nanochannels. We investigated contamination due to hydrocarbon molecules, nanochannels made of graphene, hexagonal boron nitride, BC2N, and molybdenum disulfide using molecular dynamics simulations. We found that for a certain size of nanochannel (i.e., h = 0.7 nm), as a result of the anomalous hydrophilic nature of nanochannels made of graphene, the hydrocarbons are fully adsorbed in the nanochannel, giving rise to full uptake. An increasing temperature plays an important role in unclogging, while pressure does not have a significant role. The results of our pioneering work contribute to a better understanding and highlight the important factors in alleviating the contamination and unclogging of nanochannels, which are in good agreement with the results of recent experiments.
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Affiliation(s)
- Z Javdani
- Department of Physics, Shahid Rajaee Teacher Training University, 16875-163 Lavizan, 1678815811Tehran, Iran
| | - N Hassani
- Department of Physics, Shahid Rajaee Teacher Training University, 16875-163 Lavizan, 1678815811Tehran, Iran
- Department of Chemistry, Razi University, Kermanshah67149, Iran
| | - F Faraji
- PLASMANT, Department of Chemistry, University of Antwerp, Universiteitsplein 1, 2610Antwerp, Belgium
| | - R Zhou
- State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, Xi'an710049, China
| | - C Sun
- State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, Xi'an710049, China
| | - B Radha
- Department of Physics and Astronomy, School of Natural Sciences, The University of Manchester and National Graphene Institute, Oxford Road, ManchesterM13 9PL, U.K
| | - E Neyts
- PLASMANT, Department of Chemistry, University of Antwerp, Universiteitsplein 1, 2610Antwerp, Belgium
| | - F M Peeters
- Department of Physics, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020Antwerpen, Belgium
- Departamento de Física, Universidade Federal do Ceará, 60455-760Fortaleza, Ceará, Brazil
| | - M Neek-Amal
- Department of Physics, Shahid Rajaee Teacher Training University, 16875-163 Lavizan, 1678815811Tehran, Iran
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4
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Miranda LP, da Costa DR, Peeters FM, Costa Filho RN. Vacancy clustering effect on the electronic and transport properties of bilayer graphene nanoribbons. Nanotechnology 2022; 34:055706. [PMID: 36322965 DOI: 10.1088/1361-6528/ac9f50] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2022] [Accepted: 11/01/2022] [Indexed: 06/16/2023]
Abstract
Experimental realizations of two-dimensional materials are hardly free of structural defects such as e.g. vacancies, which, in turn, modify drastically its pristine physical defect-free properties. In this work, we explore effects due to point defect clustering on the electronic and transport properties of bilayer graphene nanoribbons, for AA and AB stacking and zigzag and armchair boundaries, by means of the tight-binding approach and scattering matrix formalism. Evident vacancy concentration signatures exhibiting a maximum amplitude and an universality regardless of the system size, stacking and boundary types, in the density of states around the zero-energy level are observed. Our results are explained via the coalescence analysis of the strong sizeable vacancy clustering effect in the system and the breaking of the inversion symmetry at high vacancy densities, demonstrating a similar density of states for two equivalent degrees of concentration disorder, below and above the maximum value.
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Affiliation(s)
- L P Miranda
- Departamento de Física, Universidade Federal do Ceará, Campus do Pici, Fortaleza, Ceará, Brazil
| | - D R da Costa
- Departamento de Física, Universidade Federal do Ceará, Campus do Pici, Fortaleza, Ceará, Brazil
- Key Laboratory for Micro/Nano Optoelectronic Devices of Ministry of Education & Hunan Provincial Key Laboratory of Low-Dimensional Structural Physics and Devices, School of Physics and Electronics, Hunan University, Changsha 410082, People's Republic of China
| | - F M Peeters
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - R N Costa Filho
- Departamento de Física, Universidade Federal do Ceará, Campus do Pici, Fortaleza, Ceará, Brazil
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5
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Cai J, Griffin E, Guarochico-Moreira VH, Barry D, Xin B, Yagmurcukardes M, Zhang S, Geim AK, Peeters FM, Lozada-Hidalgo M. Wien effect in interfacial water dissociation through proton-permeable graphene electrodes. Nat Commun 2022; 13:5776. [PMID: 36182944 PMCID: PMC9526707 DOI: 10.1038/s41467-022-33451-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2022] [Accepted: 09/20/2022] [Indexed: 11/09/2022] Open
Abstract
Strong electric fields can accelerate molecular dissociation reactions. The phenomenon known as the Wien effect was previously observed using high-voltage electrolysis cells that produced fields of about 107 V m-1, sufficient to accelerate the dissociation of weakly bound molecules (e.g., organics and weak electrolytes). The observation of the Wien effect for the common case of water dissociation (H2O [Formula: see text] H+ + OH-) has remained elusive. Here we study the dissociation of interfacial water adjacent to proton-permeable graphene electrodes and observe strong acceleration of the reaction in fields reaching above 108 V m-1. The use of graphene electrodes allows measuring the proton currents arising exclusively from the dissociation of interfacial water, while the electric field driving the reaction is monitored through the carrier density induced in graphene by the same field. The observed exponential increase in proton currents is in quantitative agreement with Onsager's theory. Our results also demonstrate that graphene electrodes can be valuable for the investigation of various interfacial phenomena involving proton transport.
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Affiliation(s)
- J Cai
- National Graphene Institute, The University of Manchester, Manchester, M13 9PL, UK.,Department of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK.,College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha, Hunan, 410073, China
| | - E Griffin
- National Graphene Institute, The University of Manchester, Manchester, M13 9PL, UK.,Department of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK
| | - V H Guarochico-Moreira
- National Graphene Institute, The University of Manchester, Manchester, M13 9PL, UK.,Department of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK.,Escuela Superior Politécnica del Litoral, ESPOL, Facultad de Ciencias Naturales y Matemáticas, P.O. Box 09-01-5863, Guayaquil, Ecuador
| | - D Barry
- Department of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK
| | - B Xin
- National Graphene Institute, The University of Manchester, Manchester, M13 9PL, UK.,Department of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK
| | - M Yagmurcukardes
- Departement Fysica, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020, Antwerp, Belgium.,Department of Photonics, Izmir Institute of Technology, 35430, Izmir, Urla, Turkey
| | - S Zhang
- Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China
| | - A K Geim
- National Graphene Institute, The University of Manchester, Manchester, M13 9PL, UK.,Department of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK.,Centre for Advanced 2D Materials, National University of Singapore, Singapore, 117546, Singapore
| | - F M Peeters
- Departement Fysica, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020, Antwerp, Belgium
| | - M Lozada-Hidalgo
- National Graphene Institute, The University of Manchester, Manchester, M13 9PL, UK. .,Department of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK.
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6
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Yagmurcukardes M, Sozen Y, Baskurt M, Peeters FM, Sahin H. Interface-dependent phononic and optical properties of GeO/MoSO heterostructures. Nanoscale 2022; 14:865-874. [PMID: 34985489 DOI: 10.1039/d1nr06534c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
The interface-dependent electronic, vibrational, piezoelectric, and optical properties of van der Waals heterobilayers, formed by buckled GeO (b-GeO) and Janus MoSO structures, are investigated by means of first-principles calculations. The electronic band dispersions show that O/Ge and S/O interface formations result in a type-II band alignment with direct and indirect band gaps, respectively. In contrast, O/O and S/Ge interfaces give rise to the formation of a type-I band alignment with an indirect band gap. By considering the Bethe-Salpeter equation (BSE) on top of G0W0 approximation, it is shown that different interfaces can be distinguished from each other by means of the optical absorption spectra as a consequence of the band alignments. Additionally, the low- and high-frequency regimes of the Raman spectra are also different for each interface type. The alignment of the individual dipoles, which is interface-dependent, either weakens or strengthens the net dipole of the heterobilayers and results in tunable piezoelectric coefficients. The results indicate that the possible heterobilayers of b-GeO/MoSO asymmetric structures possess various electronic, optical, and piezoelectric properties arising from the different interface formations and can be distinguished by means of various spectroscopic techniques.
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Affiliation(s)
- M Yagmurcukardes
- Department of Photonics, Izmir Institute of Technology, 35430, Izmir, Turkey.
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
- NANOlab Center of Excellence, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - Y Sozen
- Department of Photonics, Izmir Institute of Technology, 35430, Izmir, Turkey.
| | - M Baskurt
- Department of Photonics, Izmir Institute of Technology, 35430, Izmir, Turkey.
| | - F M Peeters
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
- NANOlab Center of Excellence, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - H Sahin
- Department of Photonics, Izmir Institute of Technology, 35430, Izmir, Turkey.
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7
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Alihosseini M, Ghasemi S, Ahmadkhani S, Alidoosti M, Esfahani DN, Peeters FM, Neek-Amal M. Electronic Properties of Oxidized Graphene: Effects of Strain and an Electric Field on Flat Bands and the Energy Gap. J Phys Chem Lett 2022; 13:66-74. [PMID: 34958221 DOI: 10.1021/acs.jpclett.1c03286] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
A multiscale modeling and simulation approach, including first-principles calculations, ab initio molecular dynamics simulations, and a tight binding approach, is employed to study band flattening of the electronic band structure of oxidized monolayer graphene. The width of flat bands can be tuned by strain, the external electric field, and the density of functional groups and their distribution. A transition to a conducting state is found for monolayer graphene with impurities when it is subjected to an electric field of ∼1.0 V/Å. Several parallel impurity-induced flat bands appear in the low-energy spectrum of monolayer graphene when the number of epoxy groups is changed. The width of the flat band decreases with an increase in tensile strain but is independent of the electric field strength. Here an alternative and easy route for obtaining band flattening in thermodynamically stable functionalized monolayer graphene is introduced. Our work discloses a new avenue for research on band flattening in monolayer graphene.
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Affiliation(s)
- M Alihosseini
- Department of Physics, Shahid Rajaee University, Lavizan, Tehran 16785-136, Iran
| | - S Ghasemi
- Department of Physics, Shahid Rajaee University, Lavizan, Tehran 16785-136, Iran
| | - S Ahmadkhani
- Department of Physics, Shahid Rajaee University, Lavizan, Tehran 16785-136, Iran
| | - M Alidoosti
- Pasargad Institute for Advanced Innovative Solutions (PIAIS), Tehran 1991633357, Iran
| | - D Nasr Esfahani
- Pasargad Institute for Advanced Innovative Solutions (PIAIS), Tehran 1991633357, Iran
- Department of Converging Technologies, Khatam University, Tehran 1991633357, Iran
| | - F M Peeters
- Departement Fysica, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
| | - M Neek-Amal
- Department of Physics, Shahid Rajaee University, Lavizan, Tehran 16785-136, Iran
- Departement Fysica, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
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8
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Abstract
Two-dimensional materials composed of transition metal carbides and nitrides (MXenes) are poised to revolutionize energy conversion and storage. In this work, we used density functional theory (DFT) to investigate the adsorption of Mg and Na adatoms on five M2CS2 monolayers (where M = Mo, Nb, Ti, V, and Zr) for battery applications. We assessed the stability of the adatom (i.e. Na and Mg)-monolayer systems by calculating adsorption and formation energies, as well as voltages as a function of surface coverage. For instance, we found that Mo2CS2 cannot support a full layer of Na nor even a single Mg atom. Na and Mg exhibit the strongest binding on Zr2CS2, followed by Ti2CS2, Nb2CS2 and V2CS2. Using the nudged elastic band method (NEB), we computed promising diffusion barriers for both dilute and nearly full ion surface coverage cases. In the dilute ion adsorption case, a single Mg and Na atom on Ti2CS2 experience ∼0.47 eV and ∼0.10 eV diffusion barriers between the lowest energy sites, respectively. For a nearly full surface coverage, a Na ion moving on Ti2CS2 experiences a ∼0.33 eV energy barrier, implying a concentration-dependent diffusion barrier. Our molecular dynamics results indicate that the three (one) layers (layer) of the Mg (Na) ion on both surfaces of Ti2CS2 remain stable at T = 300 K. While, according to voltage calculations, Zr2CS2 can store Na up to three atomic layers, our MD simulations predict that the outermost layers detach from the Zr2CS2 monolayer due to the weak interaction between Na ions and the monolayer. This suggests that MD simulations are essential to confirm the stability of an ion-electrode system - an insight that is mostly absent in previous studies.
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Affiliation(s)
- G Chaney
- Department of Physics, University of Maryland Baltimore County, 1000 Hilltop Cir, Baltimore, MD 21250, USA.
| | - D Çakır
- Department of Physics and Astrophysics, University of North Dakota, Grand Forks, North Dakota 58202, USA.
| | - F M Peeters
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerpen, Belgium
| | - C Ataca
- Department of Physics, University of Maryland Baltimore County, 1000 Hilltop Cir, Baltimore, MD 21250, USA.
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9
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Wang Q, Lin S, Liu X, Xu W, Xiao Y, Liang C, Ding L, Peeters FM. Photoluminescence and electronic transition behaviors of single-stranded DNA. Phys Rev E 2021; 104:034412. [PMID: 34654201 DOI: 10.1103/physreve.104.034412] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2021] [Accepted: 08/31/2021] [Indexed: 11/07/2022]
Abstract
Due to the potential application of DNA for biophysics and optoelectronics, the electronic energy states and transitions of this genetic material have attracted a great deal of attention recently. However, the fluorescence and corresponding physical process of DNA under optical excitation with photon energies below ultraviolet are still not fully clear. In this work, we experimentally investigate the photoluminescence (PL) properties of single-stranded DNA (ssDNA) samples under near-ultraviolet (NUV) and visible excitations (270∼440 nm). Based on the dependence of the PL peak wavelength (λ_{em}) upon the excitation wavelength (λ_{ex}), the PL behaviors of ssDNA can be approximately classified into two categories. In the relatively short excitation wavelength regime, λ_{em} is nearly constant due to exciton-like transitions associated with delocalized excitonic states and excimer states. In the relatively long excitation wavelength range, a linear relation of λ_{em}=Aλ_{ex}+B with A>0 or A<0 can be observed, which comes from electronic transitions related to coupled vibrational-electronic levels. Moreover, the transition channels in different excitation wavelength regimes and the effects of strand length and base type can be analyzed on the basis of these results. These important findings not only can give a general description of the electronic energy states and transitional behaviors of ssDNA samples under NUV and visible excitations, but also can be the basis for the application of DNA in nanoelectronics and optoelectronics.
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Affiliation(s)
- Qiujin Wang
- School of Physics and Astronomy and Key Lab of Quantum Information of Yunnan Province, Yunnan University, Kunming 650091, China
| | - Shuo Lin
- School of Physics and Astronomy and Key Lab of Quantum Information of Yunnan Province, Yunnan University, Kunming 650091, China
| | - Xuan Liu
- School of Physics and Astronomy and Key Lab of Quantum Information of Yunnan Province, Yunnan University, Kunming 650091, China
| | - Wen Xu
- School of Physics and Astronomy and Key Lab of Quantum Information of Yunnan Province, Yunnan University, Kunming 650091, China.,Micro Optical Instruments Inc., 518118 Shenzhen, China.,Key Laboratory of Material Physics, Institute of Solid State Physics, Chinese Academy of Science, Hefei 230031, China
| | - Yiming Xiao
- School of Physics and Astronomy and Key Lab of Quantum Information of Yunnan Province, Yunnan University, Kunming 650091, China
| | - Changneng Liang
- School of Physics and Astronomy and Key Lab of Quantum Information of Yunnan Province, Yunnan University, Kunming 650091, China
| | - Lan Ding
- School of Physics and Astronomy and Key Lab of Quantum Information of Yunnan Province, Yunnan University, Kunming 650091, China
| | - F M Peeters
- School of Physics and Astronomy and Key Lab of Quantum Information of Yunnan Province, Yunnan University, Kunming 650091, China.,Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
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10
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Dong HM, Tao ZH, Duan YF, Li LL, Huang F, Peeters FM. Substrate dependent terahertz magneto-optical properties of monolayer WS 2. Opt Lett 2021; 46:4892-4895. [PMID: 34598227 DOI: 10.1364/ol.435055] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2021] [Accepted: 08/31/2021] [Indexed: 06/13/2023]
Abstract
Terahertz (THz) magneto-optical (MO) properties of monolayer (ML) tungsten disulfide (WS2), placed on different substrates and subjected to external magnetic fields, are studied using THz time-domain spectroscopy (TDS). We find that the THz MO conductivity exhibits a nearly linear response in a weak magnetic field, while a distinctly nonlinear/oscillating behavior is found in strong magnetic fields owing to strong substrate-induced random impurity scattering and interactions. The THz MO response of ML WS2 depends sensitively on the choice of the substrates, which we trace back to electronic localization and the impact of the substrates on the Landau level (LL) spectrum. Our results provide an in-depth understanding of the THz MO properties of ML WS2/substrate systems, especially the effect of substrates, which can be utilized to realize atomically thin THz MO nano-devices.
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11
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Lavor IR, da Costa DR, Covaci L, Milošević MV, Peeters FM, Chaves A. Zitterbewegung of Moiré Excitons in Twisted MoS_{2}/WSe_{2} Heterobilayers. Phys Rev Lett 2021; 127:106801. [PMID: 34533367 DOI: 10.1103/physrevlett.127.106801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Accepted: 06/28/2021] [Indexed: 06/13/2023]
Abstract
The moiré pattern observed in stacked noncommensurate crystal lattices, such as heterobilayers of transition metal dichalcogenides, produces a periodic modulation of their band gap. Excitons subjected to this potential landscape exhibit a band structure that gives rise to a quasiparticle dubbed the moiré exciton. In the case of MoS_{2}/WSe_{2} heterobilayers, the moiré trapping potential has honeycomb symmetry and, consequently, the moiré exciton band structure is the same as that of a Dirac-Weyl fermion, whose mass can be further tuned down to zero with a perpendicularly applied field. Here we show that, analogously to other Dirac-like particles, the moiré exciton exhibits a trembling motion, also known as Zitterbewegung, whose long timescales are compatible with current experimental techniques for exciton dynamics. This promotes the study of the dynamics of moiré excitons in van der Waals heterostructures as an advantageous solid-state platform to probe Zitterbewegung, broadly tunable by gating and interlayer twist angle.
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Affiliation(s)
- I R Lavor
- Departamento de Física, Universidade Federal do Ceará, 60455-760 Fortaleza, Ceará, Brazil
- Instituto Federal de Educação, Ciência e Tecnologia do Maranhão, KM-04, Enseada, 65200-000 Pinheiro, Maranhão, Brazil
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - D R da Costa
- Departamento de Física, Universidade Federal do Ceará, 60455-760 Fortaleza, Ceará, Brazil
| | - L Covaci
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - M V Milošević
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - F M Peeters
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - A Chaves
- Departamento de Física, Universidade Federal do Ceará, 60455-760 Fortaleza, Ceará, Brazil
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
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12
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Deily Nazar N, Vazifehshenas T, Ebrahimi MR, Peeters FM. Strong anisotropic optical properties of 8- Pmmn borophene: a many-body perturbation study. Phys Chem Chem Phys 2021; 23:16417-16422. [PMID: 34318830 DOI: 10.1039/d1cp01910d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Using first-principles many-body perturbation theory, we investigate the optical properties of 8-Pmmn borophene at two levels of approximations; the GW method considering only the electron-electron interaction and the GW in combination with the Bethe-Salpeter equation including electron-hole coupling. The band structure exhibits anisotropic Dirac cones with semimetallic character. The optical absorption spectra are obtained for different light polarizations and we predict strong optical absorbance anisotropy. The absorption peaks undergo a global redshift when the electron-hole interaction is taken into account due to the formation of bound excitons which have an anisotropic excitonic wave function.
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Affiliation(s)
- N Deily Nazar
- Department of Physics, Shahid Beheshti University, G. C., Evin, Tehran 1983969411, Iran.
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13
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Lavor IR, da Costa DR, Chaves A, Sena SHR, Farias GA, Van Duppen B, Peeters FM. Effect of zitterbewegung on the propagation of wave packets in ABC-stacked multilayer graphene: an analytical and computational approach. J Phys Condens Matter 2021; 33:095503. [PMID: 33232944 DOI: 10.1088/1361-648x/abcd7f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The time evolution of a low-energy two-dimensional Gaussian wave packet in ABC-stacked n-layer graphene (ABC-NLG) is investigated. Expectation values of the position (x, y) of center-of-mass and the total probability densities of the wave packet are calculated analytically using the Green's function method. These results are confirmed using an alternative numerical method based on the split-operator technique within the Dirac approach for ABC-NLG, which additionally allows to include external fields and potentials. The main features of the zitterbewegung (trembling motion) of wave packets in graphene are demonstrated and are found to depend not only on the wave packet width and initial pseudospin polarization, but also on the number of layers. Moreover, the analytical and numerical methods proposed here allow to investigate wave packet dynamics in graphene systems with an arbitrary number of layers and arbitrary potential landscapes.
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Affiliation(s)
- I R Lavor
- Instituto Federal de Educação, Ciência e Tecnologia do Maranhão, KM-04, Enseada, 65200-000, Pinheiro, Maranhão, Brazil
- Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, Campus do Pici, 60455-900 Fortaleza, Ceará, Brazil
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - D R da Costa
- Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, Campus do Pici, 60455-900 Fortaleza, Ceará, Brazil
| | - Andrey Chaves
- Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, Campus do Pici, 60455-900 Fortaleza, Ceará, Brazil
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - S H R Sena
- Instituto de Ciências Exatas e da Natureza, Universidade da Integração Internacional da Lusofonia Afro-Brasileira, Centro, 62790-000 Redenção, Ceará, Brasil
| | - G A Farias
- Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, Campus do Pici, 60455-900 Fortaleza, Ceará, Brazil
| | - B Van Duppen
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - F M Peeters
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
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14
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González-García A, López-Pérez W, González-Hernández R, Bacaksiz C, Šabani D, Milošević MV, Peeters FM. Transition-metal adatoms on 2D-GaAs: a route to chiral magnetic 2D materials by design. J Phys Condens Matter 2021; 33:145803. [PMID: 33503605 DOI: 10.1088/1361-648x/abe077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Accepted: 01/27/2021] [Indexed: 06/12/2023]
Abstract
Using relativistic density-functional calculations, we examine the magneto-crystalline anisotropy and exchange properties of transition-metal atoms adsorbed on 2D-GaAs. We show that single Mn and Mo atom (Co and Os) strongly bind on 2D-GaAs, and induce local out-of-plane (in-plane) magnetic anisotropy. When a pair of TM atoms is adsorbed on 2D-GaAs in a close range from each other, magnetisation properties change (become tunable) with respect to concentrations and ordering of the adatoms. In all cases, we reveal presence of strong Dzyaloshinskii-Moriya interaction. These results indicate novel pathways towards two-dimensional chiral magnetic materials by design, tailored for desired applications in magneto-electronics.
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Affiliation(s)
- A González-García
- Grupo de Investigación en Física Aplicada, Departamento de Física, Universidad del Norte, Barranquilla, Colombia
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - W López-Pérez
- Grupo de Investigación en Física Aplicada, Departamento de Física, Universidad del Norte, Barranquilla, Colombia
| | - R González-Hernández
- Grupo de Investigación en Física Aplicada, Departamento de Física, Universidad del Norte, Barranquilla, Colombia
| | - C Bacaksiz
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
- NANOlab Center of Excellence, University of Antwerp, Belgium
- Bremen Center for Computational Material Science (BCCMS), Bremen D-28359, Germany
- Computational Science Research Center, Beijing and Computational Science and Applied Research Institute Shenzhen, Shenzhen, People's Republic of China
| | - D Šabani
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
- NANOlab Center of Excellence, University of Antwerp, Belgium
| | - M V Milošević
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
- NANOlab Center of Excellence, University of Antwerp, Belgium
| | - F M Peeters
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
- NANOlab Center of Excellence, University of Antwerp, Belgium
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15
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Jalali H, Ghorbanfekr H, Hamid I, Neek-Amal M, Rashidi R, Peeters FM. Out-of-plane permittivity of confined water. Phys Rev E 2020; 102:022803. [PMID: 32942431 DOI: 10.1103/physreve.102.022803] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2019] [Accepted: 07/01/2020] [Indexed: 06/11/2023]
Abstract
The dielectric properties of confined water is of fundamental interest and is still controversial. For water confined in channels with height smaller than h=8Å, we found a commensurability effect and an extraordinary decrease in the out-of-plane dielectric constant down to the limit of the dielectric constant of optical water. Spatial resolved polarization density data obtained from molecular dynamics simulations are found to be antisymmetric across the channel and are used as input in a mean-field model for the dielectric constant as a function of the height of the channel for h>15Å. Our results are in excellent agreement with a recent experiment [L. Fumagalli et al., Science 360, 1339 (2018)SCIEAS0036-807510.1126/science.aat4191].
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Affiliation(s)
- H Jalali
- Department of Physics, University of Zanjan, 45195-313, Zanjan, Iran
- Department of Physics, Shahid Rajaee Teacher Training University, 16875-163, Lavizan, Tehran, Iran
| | - H Ghorbanfekr
- Department of Physics, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
| | - Ilyar Hamid
- Department of Physics, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
| | - M Neek-Amal
- Department of Physics, Shahid Rajaee Teacher Training University, 16875-163, Lavizan, Tehran, Iran
- Department of Physics, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
| | - R Rashidi
- Department of Physics, Shahid Rajaee Teacher Training University, 16875-163, Lavizan, Tehran, Iran
| | - F M Peeters
- Department of Physics, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
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16
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Bafekry A, Akgenc B, Ghergherehchi M, Peeters FM. Strain and electric field tuning of semi-metallic character WCrCO 2MXenes with dual narrow band gap. J Phys Condens Matter 2020; 32:355504. [PMID: 32348966 DOI: 10.1088/1361-648x/ab8e88] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2020] [Accepted: 04/29/2020] [Indexed: 06/11/2023]
Abstract
Motivated by the recent successful synthesis of double-M carbides, we investigate structural and electronic properties of WCrC and WCrCO2monolayers and the effects of biaxial and out-of-plane strain and electric field using density functional theory. WCrC and WCrCO2monolayers are found to be dynamically stable. WCrC is metallic and WCrCO2display semi-metallic character with narrow band gap, which can be controlled by strain engineering and electric field. WCrCO2monolayer exhibits a dual band gap which is preserved in the presence of an electric field. The band gap of WCrCO2monolayer increases under uniaxial strain while it becomes metallic under tensile strain, resulting in an exotic 2D double semi-metallic behavior. Our results demonstrate that WCrCO2is a new platform for the study of novel physical properties in two-dimensional Dirac materials and which may provide new opportunities to realize high-speed low-dissipation devices.
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Affiliation(s)
- A Bafekry
- Department of Physics, University of Guilan, 41335-1914 Rasht, Iran
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - B Akgenc
- Department of Physics, Kirklareli University, Kirklareli, Turkey
| | - M Ghergherehchi
- College of Electronic and Electrical Engineering, Sungkyun kwan University, Suwon, Korea
| | - F M Peeters
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
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17
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Abstract
By means of density functional theory based first-principles calculations, the structural, vibrational, and electronic properties of 1H- and 1T-phases of single-layer CaX2 (X = F, Cl, Br, or I) structures are investigated. Our results reveal that both the 1H- and 1T-phases are dynamically stable in terms of their phonon band dispersions with the latter being the energetically favorable phase for all single-layers. In both phases of single-layer CaX2 structures, significant phonon softening occurs as the atomic radius increases. In addition, each structural phase exhibits distinctive Raman active modes that enable one to characterize either the phase or the structure via Raman spectroscopy. The electronic band dispersions of single-layer CaX2 structures reveal that all structures are indirect bandgap insulators with a decrease in bandgaps from fluorite to iodide crystals. Furthermore, the calculated linear elastic constants, in-plane stiffness, and Poisson ratio indicate the ultra-soft nature of CaX2 single-layers, which is quite important for their nanoelastic applications. Overall, our study reveals that with their dynamically stable 1T- and 1H-phases, single-layers of CaX2 crystals can be alternative ultra-thin insulators.
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Affiliation(s)
- M Baskurt
- Department of Photonics, Izmir Institute of Technology, Izmir, Turkey
| | - M Yagmurcukardes
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - F M Peeters
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
| | - H Sahin
- Department of Photonics, Izmir Institute of Technology, Izmir, Turkey
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18
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Lavor IR, da Costa DR, Chaves A, Farias GA, Macêdo R, Peeters FM. Magnetic field induced vortices in graphene quantum dots. J Phys Condens Matter 2020; 32:155501. [PMID: 31860873 DOI: 10.1088/1361-648x/ab6463] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The energy spectrum and local current patterns in graphene quantum dots (QD) are investigated for different geometries in the presence of an external perpendicular magnetic field. Our results demonstrate that, for specific geometries and edge configurations, the QD exhibits vortex and anti-vortex patterns in the local current density, in close analogy to the vortex patterns observed in the probability density current of semiconductor QD, as well as in the order parameter of mesoscopic superconductors.
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Affiliation(s)
- I R Lavor
- Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, Campus do Pici, 60455-900 Fortaleza, Ceará, Brazil
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19
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González-García A, López-Pérez W, González-Hernández R, Rivera-Julio J, Espejo C, Milośević MV, Peeters FM. Two-dimensional hydrogenated buckled gallium arsenide: an ab initio study. J Phys Condens Matter 2020; 32:145502. [PMID: 31822645 DOI: 10.1088/1361-648x/ab6043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
First-principles calculations have been carried out to investigate the stability, structural and electronic properties of two-dimensional (2D) hydrogenated GaAs with three possible geometries: chair, zigzag-line and boat configurations. The effect of van der Waals interactions on 2D H-GaAs systems has also been studied. These configurations were found to be energetic and dynamic stable, as well as having a semiconducting character. Although 2D GaAs adsorbed with H tends to form a zigzag-line configuration, the energy differences between chair, zigzag-line and boat are very small which implies the metastability of the system. Chair and boat configurations display a [Formula: see text]-[Formula: see text] direct bandgap nature, while pristine 2D-GaAs and zigzag-line are indirect semiconductors. The bandgap sizes of all configurations are also hydrogen dependent, and wider than that of pristine 2D-GaAs with both PBE and HSE functionals. Even though DFT-vdW interactions increase the adsorption energies and reduce the equilibrium distances of H-GaAs systems, it presents, qualitatively, the same physical results on the stability and electronic properties of our studied systems with PBE functional. According to our results, 2D buckled gallium arsenide is a good candidate to be synthesized by hydrogen surface passivation as its group III-V partners 2D buckled gallium nitride and boron nitride. The hydrogenation of 2D-GaAs tunes the bandgap of pristine 2D-GaAs, which makes it a potential candidate for optoelectronic applications in the blue and violet ranges of the visible electromagnetic spectrum.
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Affiliation(s)
- A González-García
- Grupo de Investigación en Física Aplicada, Departamento de Física, Universidad del Norte, Barranquilla, Colombia. Departement Fysica, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
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20
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Wang Z, Wang YB, Yin J, Tóvári E, Yang Y, Lin L, Holwill M, Birkbeck J, Perello DJ, Xu S, Zultak J, Gorbachev RV, Kretinin AV, Taniguchi T, Watanabe K, Morozov SV, Anđelković M, Milovanović SP, Covaci L, Peeters FM, Mishchenko A, Geim AK, Novoselov KS, Fal’ko VI, Knothe A, Woods CR. Composite super-moiré lattices in double-aligned graphene heterostructures. Sci Adv 2019; 5:eaay8897. [PMID: 32064323 PMCID: PMC6989342 DOI: 10.1126/sciadv.aay8897] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2019] [Accepted: 10/22/2019] [Indexed: 05/30/2023]
Abstract
When two-dimensional (2D) atomic crystals are brought into close proximity to form a van der Waals heterostructure, neighbouring crystals may influence each other's properties. Of particular interest is when the two crystals closely match and a moiré pattern forms, resulting in modified electronic and excitonic spectra, crystal reconstruction, and more. Thus, moiré patterns are a viable tool for controlling the properties of 2D materials. However, the difference in periodicity of the two crystals limits the reconstruction and, thus, is a barrier to the low-energy regime. Here, we present a route to spectrum reconstruction at all energies. By using graphene which is aligned to two hexagonal boron nitride layers, one can make electrons scatter in the differential moiré pattern which results in spectral changes at arbitrarily low energies. Further, we demonstrate that the strength of this potential relies crucially on the atomic reconstruction of graphene within the differential moiré super cell.
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Affiliation(s)
- Zihao Wang
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - Yi Bo Wang
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - J. Yin
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- Institute of Nano Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
| | - E. Tóvári
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - Y. Yang
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - L. Lin
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - M. Holwill
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - J. Birkbeck
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - D. J. Perello
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - Shuigang Xu
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - J. Zultak
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - R. V. Gorbachev
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- Henry Royce Institute for Advanced Materials, Oxford Road, Manchester M13 9PL, UK
| | - A. V. Kretinin
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- Department of Materials, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - T. Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - K. Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - S. V. Morozov
- Institute of Microelectronics Technology RAS, Chernogolovka 142432, Russia
| | - M. Anđelković
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, Antwerp, Belgium
| | - S. P. Milovanović
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, Antwerp, Belgium
| | - L. Covaci
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, Antwerp, Belgium
| | - F. M. Peeters
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, Antwerp, Belgium
| | - A. Mishchenko
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - A. K. Geim
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - K. S. Novoselov
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- Centre for Advanced 2D Materials, National University of Singapore, Singapore 117546, Singapore
- Chongqing 2D Materials Institute, Liangjiang New Area, Chongqing 400714, China
| | - Vladimir I. Fal’ko
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- Henry Royce Institute for Advanced Materials, Oxford Road, Manchester M13 9PL, UK
| | - Angelika Knothe
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - C. R. Woods
- Department of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Oxford Road, Manchester M13 9PL, UK
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21
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Shah NA, Li LL, Mosallanejad V, Peeters FM, Guo GP. Transport characteristics of multi-terminal pristine and defective phosphorene systems. Nanotechnology 2019; 30:455705. [PMID: 31390597 DOI: 10.1088/1361-6528/ab3961] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Atomic vacancies and nanopores act as local scattering centers and modify the transport properties of charge carriers in phosphorene nanoribbons (PNRs). We investigate the influence of such atomic defects on the electronic transport of multi-terminal PNR. We use the non-equilibrium Green's function approach within the tight-binding framework to calculate the transmission coefficient and the conductance. Terminals induce band mixing resulting in oscillations in the conductance. In the presence of atomic vacancies and nanopores the conductance between non-axial terminals exhibit constructive scattering, which is in contrast to mono-axial two-terminal systems where the conductance exhibits destructive scattering. This can be understood from the spatial local density of states of the transport modes in the system. Our results provide fundamental insights into the electronic transport in PNR-based multi-terminal systems and into the ability of atomic defects and nanopores through tuning the transport properties.
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Affiliation(s)
- Nayyar Abbas Shah
- CAS Key Laboratory of Quantum Information, and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Chinese Academy of Sciences, Hefei 230026, People's Republic of China
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22
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Mogg L, Hao GP, Zhang S, Bacaksiz C, Zou YC, Haigh SJ, Peeters FM, Geim AK, Lozada-Hidalgo M. Atomically thin micas as proton-conducting membranes. Nat Nanotechnol 2019; 14:962-966. [PMID: 31477802 DOI: 10.1038/s41565-019-0536-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Accepted: 07/24/2019] [Indexed: 06/10/2023]
Abstract
Monolayers of graphene and hexagonal boron nitride (hBN) are highly permeable to thermal protons1,2. For thicker two-dimensional (2D) materials, proton conductivity diminishes exponentially, so that, for example, monolayer MoS2 that is just three atoms thick is completely impermeable to protons1. This seemed to suggest that only one-atom-thick crystals could be used as proton-conducting membranes. Here, we show that few-layer micas that are rather thick on the atomic scale become excellent proton conductors if native cations are ion-exchanged for protons. Their areal conductivity exceeds that of graphene and hBN by one to two orders of magnitude. Importantly, ion-exchanged 2D micas exhibit this high conductivity inside the infamous gap for proton-conducting materials3, which extends from ∼100 °C to 500 °C. Areal conductivity of proton-exchanged monolayer micas can reach above 100 S cm-2 at 500 °C, well above the current requirements for the industry roadmap4. We attribute the fast proton permeation to ~5-Å-wide tubular channels that perforate micas' crystal structure, which, after ion exchange, contain only hydroxyl groups inside. Our work indicates that there could be other 2D crystals5 with similar nanometre-scale channels, which could help close the materials gap in proton-conducting applications.
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Affiliation(s)
- L Mogg
- National Graphene Institute, The University of Manchester, Manchester, UK
- School of Physics and Astronomy, The University of Manchester, Manchester, UK
| | - G-P Hao
- National Graphene Institute, The University of Manchester, Manchester, UK.
- State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian, China.
| | - S Zhang
- National Graphene Institute, The University of Manchester, Manchester, UK
- Key Laboratory for Green Chemical Technology of Ministry of Education, Collaborative Innovation Center of Chemical Science and Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin, China
| | - C Bacaksiz
- Departement Fysica, Universiteit Antwerpen, Antwerp, Belgium
| | - Y-C Zou
- School of Materials, The University of Manchester, Manchester, UK
| | - S J Haigh
- School of Materials, The University of Manchester, Manchester, UK
| | - F M Peeters
- Departement Fysica, Universiteit Antwerpen, Antwerp, Belgium
| | - A K Geim
- National Graphene Institute, The University of Manchester, Manchester, UK.
- School of Physics and Astronomy, The University of Manchester, Manchester, UK.
| | - M Lozada-Hidalgo
- National Graphene Institute, The University of Manchester, Manchester, UK.
- School of Physics and Astronomy, The University of Manchester, Manchester, UK.
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23
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González-García A, López-Pérez W, González-Hernández R, Rodríguez JA, Milośević MV, Peeters FM. Tunable 2D-gallium arsenide and graphene bandgaps in a graphene/GaAs heterostructure: an ab initio study. J Phys Condens Matter 2019; 31:265502. [PMID: 30840939 DOI: 10.1088/1361-648x/ab0d70] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The bandgap behavior of 2D-GaAs and graphene have been investigated with van der Waals heterostructured into a yet unexplored graphene/GaAs bilayer, under both uniaxial stress along c axis and different planar strain distributions. The 2D-GaAs bandgap nature changes from [Formula: see text]-K indirect in isolated monolayer to [Formula: see text]-[Formula: see text] direct in graphene/GaAs bilayer. In the latter, graphene exhibits a bandgap of 5 meV. The uniaxial stress strongly affects the graphene electronic bandgap, while symmetric in-plane strain does not open the bandgap in graphene. Nevertheless, it induces remarkable changes on the GaAs bandgap-width around the Fermi level. However, when applying asymmetric in-plane strain to graphene/GaAs, the graphene sublattice symmetry is broken, and the graphene bandgap is open at the Fermi level to a maximum width of 814 meV. This value is much higher than that reported for just graphene under asymmetric strain. The [Formula: see text]-[Formula: see text] direct bandgap of GaAs remains unchanged in graphene/GaAs under different types of applied strain. The analyses of phonon dispersion and the elastic constants yield the dynamical and mechanical stability of the graphene/GaAs system, respectively. The calculated mechanical properties for bilayer heterostructure are better than those of their constituent monolayers. This finding, together with the tunable graphene bandgap not only by the strength but also by the direction of the strain, enhance the potential for strain engineering of ultrathin group-III-V electronic devices hybridized by graphene.
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Affiliation(s)
- A González-García
- Grupo de Investigación en Física Aplicada, Departamento de Física, Universidad del Norte, Barranquilla, Colombia. Departement Fysica, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
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Rivera-Julio J, González-García A, González-Hernández R, López-Pérez W, Peeters FM, Hernández-Nieves AD. Vibrational properties of germanane and fluorinated germanene in the chair, boat, and zigzag-line configurations. J Phys Condens Matter 2019; 31:075301. [PMID: 30523897 DOI: 10.1088/1361-648x/aaf45f] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The electronic and vibrational properties of germanane and fluorinated germanene are studied within density functional theory (DFT) and density functional perturbation theory frameworks. Different structural configurations of germanane and fluorinated germanene are investigated. The energy difference between the different configurations are consistently smaller than the energy of thermal fluctuations for all the analyzed DFT functionals LDA, GGA, and hybrid functionals, which implies that, in principle, it is possible to find these different configurations in different regions of the sample as minority phases or local defects. We calculate the Raman and infrared spectra for these configurations by using ab initio calculations and compare it with available experimental spectra for germanane. Our results show the presence of minority phases compatible with the configurations analyzed in this work. As these low energy configurations are metastable the present work shows that the synthesis of these energy competing phases is feasible by selectively changing the synthesis conditions, which is an opportunity to expand in this way the availability of new two-dimensional compounds.
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Affiliation(s)
- J Rivera-Julio
- Condensed matter theory group, Centro Atomico Bariloche and CONICET, S. C. de Bariloche, 8400 S. C. de Bariloche, Argentina. Departement Fysica, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
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Nakhaee M, Yagmurcukardes M, Ketabi SA, Peeters FM. Single-layer structures of a100- and b010-Gallenene: a tight-binding approach. Phys Chem Chem Phys 2019; 21:15798-15804. [DOI: 10.1039/c9cp02515d] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Using the simplified linear combination of atomic orbitals (LCAO) method in combination with ab initio calculations, we construct a tight-binding (TB) model for two different crystal structures of monolayer gallium: a100- and b010-Gallenene.
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Affiliation(s)
- M. Nakhaee
- Department of Physics
- University of Antwerp
- Groenenborgerlaan 171
- B-2020 Antwerp
- Belgium
| | - M. Yagmurcukardes
- Department of Physics
- University of Antwerp
- Groenenborgerlaan 171
- B-2020 Antwerp
- Belgium
| | | | - F. M. Peeters
- Department of Physics
- University of Antwerp
- Groenenborgerlaan 171
- B-2020 Antwerp
- Belgium
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Abstract
When confined between graphene layers, water in the presence of additional hydronium and hydroxide ions exhibits distinct properties such as ion layering structure determined by the channel size, disruption of the ion solvation shell, and slower ion recombination rate as compared to bulk water.
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Affiliation(s)
| | | | - M. Neek-Amal
- Department of Physics
- Shahid Rajaee Teacher Training University
- Lavizan
- Iran
| | - F. M. Peeters
- Department of Physics
- Universiteit Antwerpen
- B-2020 Antwerpen
- Belgium
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Abdullah HM, Bahlouli H, Peeters FM, Van Duppen B. Confined states in graphene quantum blisters. J Phys Condens Matter 2018; 30:385301. [PMID: 30102244 DOI: 10.1088/1361-648x/aad9c7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Bilayer graphene samples may exhibit regions where the two layers are locally delaminated forming a so-called quantum blister in the graphene sheet. Electron and hole states can be confined in this graphene quantum blisters (GQB) by applying a global electrostatic bias. We scrutinize the electronic properties of these confined states under the variation of interlayer bias, coupling, and blister's size. The spectra display strong anti-crossings due to the coupling of the confined states on upper and lower layers inside the blister. These spectra are layer localized where the respective confined states reside on either layer or equally distributed. For finite angular momentum, this layer localization can be at the edge of the blister and corresponds to degenerate modes of opposite momenta. Furthermore, the energy levels in GQB exhibit electron-hole symmetry that is sensitive to the electrostatic bias. Finally, we demonstrate that confinement in GQB persists even in the presence of a variation in the inter-layer coupling.
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Affiliation(s)
- H M Abdullah
- Department of Physics, King Fahd University of Petroleum and Minerals, 31261 Dhahran, Saudi Arabia. Saudi Center for Theoretical Physics, PO Box 32741, Jeddah 21438, Saudi Arabia. Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
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Dong HM, Xu W, Peeters FM. Electrical generation of terahertz blackbody radiation from graphene. Opt Express 2018; 26:24621-24626. [PMID: 30469575 DOI: 10.1364/oe.26.024621] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2018] [Accepted: 08/28/2018] [Indexed: 06/09/2023]
Abstract
Recent experimental work on the application of graphene for novel illumination motivated us to present a theoretical study of the blackbody radiation emission from a freely suspended graphene driven by a dc electric field. Strong terahertz (THz) emission, with intensity up to mW/cm2, can be generated with increasing electric field strength due to the heating of electrons in graphene. We show that the intensity of the THz emission generated electrically from graphene depends rather sensitively on the lattice temperature in relatively weak electric fields, whereas it is less sensitive to the lattice temperature in relative strong electric fields. Our study highlights the practical application of graphene as intense THz source where the radiation is generated electrically.
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Kandemir A, Peeters FM, Sahin H. Monitoring the effect of asymmetrical vertical strain on Janus single layers of MoSSe via vibrational spectrum. J Chem Phys 2018; 149:084707. [PMID: 30193504 DOI: 10.1063/1.5043207] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- A. Kandemir
- Department of Materials Science and Engineering, Izmir Institute of Technology, 35430 Izmir, Turkey
| | - F. M. Peeters
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
| | - H. Sahin
- Department of Photonics, Izmir Institute of Technology, 35430 Izmir, Turkey
- ICTP-ECAR Eurasian Center for Advanced Research, Izmir Institute of Technology, 35430 Izmir, Turkey
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Zarenia M, Hamilton AR, Peeters FM, Neilson D. Multiband Mechanism for the Sign Reversal of Coulomb Drag Observed in Double Bilayer Graphene Heterostructures. Phys Rev Lett 2018; 121:036601. [PMID: 30085815 DOI: 10.1103/physrevlett.121.036601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Indexed: 06/08/2023]
Abstract
Coupled 2D sheets of electrons and holes are predicted to support novel quantum phases. Two experiments of Coulomb drag in electron-hole (e-h) double bilayer graphene (DBLG) have reported an unexplained and puzzling sign reversal of the drag signal. However, we show that this effect is due to the multiband character of DBLG. Our multiband Fermi liquid theory produces excellent agreement and captures the key features of the experimental drag resistance for all temperatures. This demonstrates the importance of multiband effects in DBLG: they have a strong effect not only on superfluidity, but also on the drag.
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Affiliation(s)
- M Zarenia
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
- Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211, USA
| | - A R Hamilton
- ARC Centre of Excellence for Future Low Energy Electronics Technologies, School of Physics, The University of New South Wales, Sydney, New South Wales 2052, Australia
| | - F M Peeters
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
| | - D Neilson
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
- Physics Division, Science & Technology School, University of Camerino, 62032 Camerino, Italy
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Simchi H, Simchi M, Fardmanesh M, Peeters FM. Phase transition and field effect topological quantum transistor made of monolayer MoS 2. J Phys Condens Matter 2018; 30:235303. [PMID: 29697056 DOI: 10.1088/1361-648x/aac050] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We study topological phase transitions and topological quantum field effect transistor in monolayer molybdenum disulfide (MoS2) using a two-band Hamiltonian model. Without considering the quadratic (q 2) diagonal term in the Hamiltonian, we show that the phase diagram includes quantum anomalous Hall effect, quantum spin Hall effect, and spin quantum anomalous Hall effect regions such that the topological Kirchhoff law is satisfied in the plane. By considering the q 2 diagonal term and including one valley, it is shown that MoS2 has a non-trivial topology, and the valley Chern number is non-zero for each spin. We show that the wave function is (is not) localized at the edges when the q 2 diagonal term is added (deleted) to (from) the spin-valley Dirac mass equation. We calculate the quantum conductance of zigzag MoS2 nanoribbons by using the nonequilibrium Green function method and show how this device works as a field effect topological quantum transistor.
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Affiliation(s)
- H Simchi
- Department of Physics, Iran University of Science and Technology, Narmak, Tehran 16844, Iran. Semiconductor Technology Center, PO Box 19575-199, Tehran, Iran
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Hu S, Gopinadhan K, Rakowski A, Neek-Amal M, Heine T, Grigorieva IV, Haigh SJ, Peeters FM, Geim AK, Lozada-Hidalgo M. Transport of hydrogen isotopes through interlayer spacing in van der Waals crystals. Nat Nanotechnol 2018; 13:468-472. [PMID: 29556005 DOI: 10.1038/s41565-018-0088-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2017] [Accepted: 02/06/2018] [Indexed: 06/08/2023]
Abstract
Atoms start behaving as waves rather than classical particles if confined in spaces commensurate with their de Broglie wavelength. At room temperature this length is only about one ångström even for the lightest atom, hydrogen. This restricts quantum-confinement phenomena for atomic species to the realm of very low temperatures1-5. Here, we show that van der Waals gaps between atomic planes of layered crystals provide ångström-size channels that make quantum confinement of protons apparent even at room temperature. Our transport measurements show that thermal protons experience a notably higher barrier than deuterons when entering van der Waals gaps in hexagonal boron nitride and molybdenum disulfide. This is attributed to the difference in the de Broglie wavelengths of the isotopes. Once inside the crystals, transport of both isotopes can be described by classical diffusion, albeit with unexpectedly fast rates comparable to that of protons in water. The demonstrated ångström-size channels can be exploited for further studies of atomistic quantum confinement and, if the technology can be scaled up, for sieving hydrogen isotopes.
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Affiliation(s)
- S Hu
- National Graphene Institute, The University of Manchester, Manchester, UK.
| | - K Gopinadhan
- School of Physics and Astronomy, The University of Manchester, Manchester, UK
| | - A Rakowski
- School of Materials, The University of Manchester, Manchester, UK
| | - M Neek-Amal
- National Graphene Institute, The University of Manchester, Manchester, UK
- Departement Fysica, Universiteit Antwerpen, Antwerpen, Belgium
- Department of Physics, Shahid Rajaee Teacher Training University, Tehran, Iran
| | - T Heine
- Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie, Universität Leipzig, Leipzig, Germany
| | - I V Grigorieva
- School of Physics and Astronomy, The University of Manchester, Manchester, UK
| | - S J Haigh
- School of Materials, The University of Manchester, Manchester, UK
| | - F M Peeters
- Departement Fysica, Universiteit Antwerpen, Antwerpen, Belgium
| | - A K Geim
- National Graphene Institute, The University of Manchester, Manchester, UK.
- School of Physics and Astronomy, The University of Manchester, Manchester, UK.
| | - M Lozada-Hidalgo
- National Graphene Institute, The University of Manchester, Manchester, UK.
- School of Physics and Astronomy, The University of Manchester, Manchester, UK.
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Conti S, Perali A, Peeters FM, Neilson D. Multicomponent Electron-Hole Superfluidity and the BCS-BEC Crossover in Double Bilayer Graphene. Phys Rev Lett 2017; 119:257002. [PMID: 29303331 DOI: 10.1103/physrevlett.119.257002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Indexed: 06/07/2023]
Abstract
Superfluidity in coupled electron-hole sheets of bilayer graphene is predicted here to be multicomponent because of the conduction and valence bands. We investigate the superfluid crossover properties as functions of the tunable carrier densities and the tunable energy band gap E_{g}. For small band gaps there is a significant boost in the two superfluid gaps, but the interaction-driven excitations from the valence to the conduction band can weaken the superfluidity, even blocking the system from entering the Bose-Einstein condensate (BEC) regime at low densities. At a given larger density, a band gap E_{g}∼80-120 meV can carry the system into the strong-pairing multiband BCS-BEC crossover regime, the optimal range for realization of high-T_{c} superfluidity.
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Affiliation(s)
- S Conti
- Dipartimenti di Fisica e di Farmacia, Università di Camerino, 62032 Camerino (MC), Italy
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
| | - A Perali
- Dipartimenti di Fisica e di Farmacia, Università di Camerino, 62032 Camerino (MC), Italy
| | - F M Peeters
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
| | - D Neilson
- Dipartimenti di Fisica e di Farmacia, Università di Camerino, 62032 Camerino (MC), Italy
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
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Bekaert J, Bignardi L, Aperis A, van Abswoude P, Mattevi C, Gorovikov S, Petaccia L, Goldoni A, Partoens B, Oppeneer PM, Peeters FM, Milošević MV, Rudolf P, Cepek C. Free surfaces recast superconductivity in few-monolayer MgB 2: Combined first-principles and ARPES demonstration. Sci Rep 2017; 7:14458. [PMID: 29089566 PMCID: PMC5663715 DOI: 10.1038/s41598-017-13913-z] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2017] [Accepted: 10/02/2017] [Indexed: 11/08/2022] Open
Abstract
Two-dimensional materials are known to harbour properties very different from those of their bulk counterparts. Recent years have seen the rise of atomically thin superconductors, with a caveat that superconductivity is strongly depleted unless enhanced by specific substrates, intercalants or adatoms. Surprisingly, the role in superconductivity of electronic states originating from simple free surfaces of two-dimensional materials has remained elusive to date. Here, based on first-principles calculations, anisotropic Eliashberg theory, and angle-resolved photoemission spectroscopy (ARPES), we show that surface states in few-monolayer MgB2 make a major contribution to the superconducting gap spectrum and density of states, clearly distinct from the widely known, bulk-like σ- and π-gaps. As a proof of principle, we predict and measure the gap opening on the magnesium-based surface band up to a critical temperature as high as ~30 K for merely six monolayers thick MgB2. These findings establish free surfaces as an unavoidable ingredient in understanding and further tailoring of superconductivity in atomically thin materials.
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Affiliation(s)
- J Bekaert
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020, Antwerp, Belgium.
| | - L Bignardi
- Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747AG, Groningen, The Netherlands
- Elettra Sincrotrone Trieste, Strada Statale 14 km.163.5, I-34149, Trieste, Italy
| | - A Aperis
- Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20, Uppsala, Sweden
| | - P van Abswoude
- Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747AG, Groningen, The Netherlands
| | - C Mattevi
- IOM-CNR, Laboratorio TASC, Strada Statale 14 km.163.5, I-34149, Trieste, Italy
- Department of Materials, Imperial College London, Exhibition road, SW7 2AZ, London, United Kingdom
| | - S Gorovikov
- Elettra Sincrotrone Trieste, Strada Statale 14 km.163.5, I-34149, Trieste, Italy
- Canadian Light Source Inc., 44 Innovation Blvd, Saskatoon, SK S7N 2V3, Canada
| | - L Petaccia
- Elettra Sincrotrone Trieste, Strada Statale 14 km.163.5, I-34149, Trieste, Italy
| | - A Goldoni
- Elettra Sincrotrone Trieste, Strada Statale 14 km.163.5, I-34149, Trieste, Italy
| | - B Partoens
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020, Antwerp, Belgium
| | - P M Oppeneer
- Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20, Uppsala, Sweden
| | - F M Peeters
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020, Antwerp, Belgium
| | - M V Milošević
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020, Antwerp, Belgium.
| | - P Rudolf
- Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747AG, Groningen, The Netherlands.
| | - C Cepek
- IOM-CNR, Laboratorio TASC, Strada Statale 14 km.163.5, I-34149, Trieste, Italy
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Abdullah HM, Van Duppen B, Zarenia M, Bahlouli H, Peeters FM. Quantum transport across van der Waals domain walls in bilayer graphene. J Phys Condens Matter 2017; 29:425303. [PMID: 28737500 DOI: 10.1088/1361-648x/aa81a8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Bilayer graphene can exhibit deformations such that the two graphene sheets are locally detached from each other resulting in a structure consisting of domains with different van der Waals inter-layer coupling. Here we investigate how the presence of these domains affects the transport properties of bilayer graphene. We derive analytical expressions for the transmission probability, and the corresponding conductance, across walls separating different inter-layer coupling domains. We find that the transmission can exhibit a valley-dependent layer asymmetry and that the domain walls have a considerable effect on the chiral tunnelling properties of the charge carriers. We show that transport measurements allow one to obtain the strength with which the two layers are coupled. We perform numerical calculations for systems with two domain walls and find that the availability of multiple transport channels in bilayer graphene significantly modifies the conductance dependence on inter-layer potential asymmetry.
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Affiliation(s)
- H M Abdullah
- Department of Physics, King Fahd University of Petroleum and Minerals, 31261 Dhahran, Saudi Arabia. Saudi Center for Theoretical Physics, 31261 Dhahran, Saudi Arabia. Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
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Berdiyorov GR, Milošević MV, Hernández-Nieves AD, Peeters FM, Domínguez D. Microfluidic manipulation of magnetic flux domains in type-I superconductors: droplet formation, fusion and fission. Sci Rep 2017; 7:12129. [PMID: 28935888 PMCID: PMC5608719 DOI: 10.1038/s41598-017-11659-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2017] [Accepted: 08/21/2017] [Indexed: 11/09/2022] Open
Abstract
The magnetic flux domains in the intermediate state of type-I superconductors are known to resemble fluid droplets, and their dynamics in applied electric current is often cartooned as a "dripping faucet". Here we show, using the time-depended Ginzburg-Landau simulations, that microfluidic principles hold also for the determination of the size of the magnetic flux-droplet as a function of the applied current, as well as for the merger or splitting of those droplets in the presence of the nanoengineered obstacles for droplet motion. Differently from fluids, the flux-droplets in superconductors are quantized and dissipative objects, and their pinning/depinning, nucleation, and splitting occur in a discretized form, all traceable in the voltage measured across the sample. At larger applied currents, we demonstrate how obstacles can cause branching of laminar flux streams or their transformation into mobile droplets, as readily observed in experiments.
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Affiliation(s)
- G R Berdiyorov
- Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University, Qatar Foundation, Doha, Qatar
| | - M V Milošević
- Departement Fysica, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020, Antwerpen, Belgium
| | - A D Hernández-Nieves
- Centro Atomico Bariloche and Instituto Balseiro, 8400, San Carlos de Bariloche, Rio Negro, Argentina
| | - F M Peeters
- Departement Fysica, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020, Antwerpen, Belgium.
| | - D Domínguez
- Centro Atomico Bariloche and Instituto Balseiro, 8400, San Carlos de Bariloche, Rio Negro, Argentina
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de Araújo JLB, Munarin FF, Farias GA, Peeters FM, Ferreira WP. Structure and reentrant percolation in an inverse patchy colloidal system. Phys Rev E 2017; 95:062606. [PMID: 28709279 DOI: 10.1103/physreve.95.062606] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2016] [Indexed: 11/07/2022]
Abstract
Two-dimensional systems of inverse patchy colloids modeled as disks with a central charge and having their surface decorated with oppositely pointlike charged patches are investigated using molecular dynamics simulations. The self-assembly of the patchy colloids leads to diverse ground state configurations ranging from crystalline arrangements of monomers to linear clusters, ramified linear clusters and to percolated configurations. Two structural phase diagrams are constructed: (1) as a function of the net charge and area fraction, and (2) as a function of the net charge and the range of the pair interaction potential. An interesting reentrant percolation transition is obtained as a function of the net charge of the colloids. We identify distinct mechanisms that lead to the percolation transition.
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Affiliation(s)
- J L B de Araújo
- Department of Physics, Federal University of Ceará, Fortaleza, Ceará 60.455-970, Brazil
| | - F F Munarin
- Department of Academic and Technological Integration, Federal University of Ceará, Fortaleza, Ceará 60.455-900, Brazil
| | - G A Farias
- Department of Physics, Federal University of Ceará, Fortaleza, Ceará 60.455-970, Brazil
| | - F M Peeters
- Department of Physics, University of Antwerp, Groenenborgerlaan 171,B-2020 Antwerpen, Belgium
| | - W P Ferreira
- Department of Physics, Federal University of Ceará, Fortaleza, Ceará 60.455-970, Brazil
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38
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da Costa DR, Chaves A, Farias GA, Peeters FM. Valley filtering in graphene due to substrate-induced mass potential. J Phys Condens Matter 2017; 29:215502. [PMID: 28437252 DOI: 10.1088/1361-648x/aa6b24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The interaction of monolayer graphene with specific substrates may break its sublattice symmetry and results in unidirectional chiral states with opposite group velocities in the different Dirac cones (Zarenia et al 2012 Phys. Rev. B 86 085451). Taking advantage of this feature, we propose a valley filter based on a transversal mass kink for low energy electrons in graphene, which is obtained by assuming a defect region in the substrate that provides a change in the sign of the substrate-induced mass and thus creates a non-biased channel, perpendicular to the kink, for electron motion. By solving the time-dependent Schrödinger equation for the tight-binding Hamiltonian, we investigate the time evolution of a Gaussian wave packet propagating through such a system and obtain the transport properties of this graphene-based substrate-induced quantum point contact. Our results demonstrate that efficient valley filtering can be obtained, provided: (i) the electron energy is sufficiently low, i.e. with electrons belonging mostly to the lowest sub-band of the channel, and (ii) the channel length (width) is sufficiently long (narrow). Moreover, even though the transmission probabilities for each valley are significantly affected by impurities and defects in the channel region, the valley polarization in this system is shown to be robust against their presence.
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Affiliation(s)
- D R da Costa
- Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, Campus do Pici, 60455-900 Fortaleza, Ceará, Brazil. Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
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Petrović MD, Milovanović SP, Peeters FM. Scanning gate microscopy of magnetic focusing in graphene devices: quantum versus classical simulation. Nanotechnology 2017; 28:185202. [PMID: 28304284 DOI: 10.1088/1361-6528/aa677a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We compare classical versus quantum electron transport in recently investigated magnetic focusing devices (Bhandari et al 2016 Nano Lett. 16 1690) exposed to the perturbing potential of a scanning gate microscope (SGM). Using the Landauer-Büttiker formalism for a multi-terminal device, we calculate resistance maps that are obtained as the SGM tip is scanned over the sample. There are three unique regimes in which the scanning tip can operate (focusing, repelling, and mixed regime) which are investigated. Tip interacts mostly with electrons with cyclotron trajectories passing directly underneath it, leaving a trail of modified current density behind it. Other (indirect) trajectories become relevant when the tip is placed near the edges of the sample, and current is scattered between the tip and the edge. We point out that, in contrast to SGM experiments on gapped semiconductors, the STM tip can induce a pn junction in graphene, which improves contrast and resolution in SGM. We also discuss possible explanations for spatial asymmetry of experimentally measured resistance maps, and connect it with specific configurations of the measuring probes.
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Peelaers H, Durgun E, Partoens B, Bilc DI, Ghosez P, Van de Walle CG, Peeters FM. Ab initio study of hydrogenic effective mass impurities in Si nanowires. J Phys Condens Matter 2017; 29:095303. [PMID: 28059776 DOI: 10.1088/1361-648x/aa5768] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The effect of B and P dopants on the band structure of Si nanowires is studied using electronic structure calculations based on density functional theory. At low concentrations a dispersionless band is formed, clearly distinguishable from the valence and conduction bands. Although this band is evidently induced by the dopant impurity, it turns out to have purely Si character. These results can be rigorously analyzed in the framework of effective mass theory. In the process we resolve some common misconceptions about the physics of hydrogenic shallow impurities, which can be more clearly elucidated in the case of nanowires than would be possible for bulk Si. We also show the importance of correctly describing the effect of dielectric confinement, which is not included in traditional electronic structure calculations, by comparing the obtained results with those of G0W0 calculations.
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Affiliation(s)
- H Peelaers
- Materials Department, University of California, Santa Barbara, CA 93106-5050, United States of America. Departement Fysica, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
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Li LL, Moldovan D, Xu W, Peeters FM. Electric- and magnetic-field dependence of the electronic and optical properties of phosphorene quantum dots. Nanotechnology 2017; 28:085702. [PMID: 28045010 DOI: 10.1088/1361-6528/aa55e8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Recently, black phosphorus quantum dots were fabricated experimentally. Motivated by these experiments, we theoretically investigate the electronic and optical properties of rectangular phosphorene quantum dots (RPQDs) in the presence of an in-plane electric field and a perpendicular magnetic field. The energy spectra and wave functions of RPQDs are obtained numerically using the tight-binding approach. We find edge states within the band gap of the RPQD which are well separated from the bulk states. In an undoped RPQD and for in-plane polarized light, due to the presence of well-defined edge states, we find three types of optical transitions which are between the bulk states, between the edge and bulk states, and between the edge states. The electric and magnetic fields influence the bulk-to-bulk, edge-to-bulk, and edge-to-edge transitions differently due to the different responses of bulk and edge states to these fields.
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Affiliation(s)
- L L Li
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium. Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
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Abstract
The effects of strain, induced by a Gaussian bump, on the magnetic field dependent transport properties of a graphene Hall bar are investigated. The numerical simulations are performed using both classical and quantum mechanical transport theory and we found that both approaches exhibit similar characteristic features. The effects of the Gaussian bump are manifested by a decrease of the bend resistance, R B, around zero-magnetic field and the occurrence of side-peaks in R B. These features are explained as a consequence of bump-assisted scattering of electrons towards different terminals of the Hall bar. Using these features we are able to give an estimate of the size of the bump. Additional oscillations in R B are found in the quantum description that are due to the population/depopulation of Landau levels. The bump has a minor influence on the Hall resistance even for very high values of the pseudo-magnetic field. When the bump is placed outside the center of the Hall bar valley polarized electrons can be collected in the leads.
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Affiliation(s)
- S P Milovanović
- Departement Fysica, Universiteit Antwerpen Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
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Abstract
A theoretical and experimental study of the work function of few-layer graphene is reported. The influence of the number of layers on the work function is investigated in the presence of a substrate, a molecular dipole layer, and combinations of the two. The work function of few-layer graphene is almost independent of the number of layers with only a difference between monolayer and multilayer graphene of about 60 meV. In the presence of a charge-donating substrate the charge distribution is found to decay exponentially away from the substrate and this is directly reflected in the work function of few-layer graphene. A dipole layer changes the work function only when placed in between the substrate and few-layer graphene through a change of the charge transfer between the two.
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Affiliation(s)
- O Leenaerts
- Departement Fysica, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
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Kiymaz D, Yagmurcukardes M, Tomak A, Sahin H, Senger RT, Peeters FM, Zareie HM, Zafer C. Controlled growth mechanism of poly (3-hexylthiophene) nanowires. Nanotechnology 2016; 27:455604. [PMID: 27727143 DOI: 10.1088/0957-4484/27/45/455604] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Synthesis of 1D-polymer nanowires by a self-assembly method using marginal solvents is an attractive technique. While the formation mechanism is poorly understood, this method is essential in order to control the growth of nanowires. Here we visualized the time-dependent assembly of poly (3-hexyl-thiophene-2,5-diyl) (P3HT) nanowires by atomic force microscopy and scanning tunneling microscopy. The assembly of P3HT nanowires was carried out at room temperature by mixing cyclohexanone (CHN), as a poor solvent, with polymer solution in 1,2-dichlorobenzene (DCB). Both π-π stacking and planarization, obtained at the mix volume ratio of P3HT (in DCB):CHN (10:7), were considered during the investigation. We find that the length of nanowires was determined by the ordering of polymers in the polymer repetition direction. Additionally, our density functional theory calculations revealed that the presence of DCB and CHN molecules that stabilize the structural distortions due to tail group of polymers was essential for the core-wire formation.
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Affiliation(s)
- D Kiymaz
- Solar Energy Institute, Ege University, 35100 Izmir, Turkey
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Ackerman ML, Kumar P, Neek-Amal M, Thibado PM, Peeters FM, Singh S. Anomalous Dynamical Behavior of Freestanding Graphene Membranes. Phys Rev Lett 2016; 117:126801. [PMID: 27689288 DOI: 10.1103/physrevlett.117.126801] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2016] [Indexed: 06/06/2023]
Abstract
We report subnanometer, high-bandwidth measurements of the out-of-plane (vertical) motion of atoms in freestanding graphene using scanning tunneling microscopy. By tracking the vertical position over a long time period, a 1000-fold increase in the ability to measure space-time dynamics of atomically thin membranes is achieved over the current state-of-the-art imaging technologies. We observe that the vertical motion of a graphene membrane exhibits rare long-scale excursions characterized by both anomalous mean-squared displacements and Cauchy-Lorentz power law jump distributions.
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Affiliation(s)
- M L Ackerman
- Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA
| | - P Kumar
- Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA
| | - M Neek-Amal
- Department of Physics, Shahid Rajaee Teacher Training University, 16875-163 Lavizan, Tehran, Iran
| | - P M Thibado
- Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA
| | - F M Peeters
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
| | - Surendra Singh
- Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA
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Tomak A, Bacaksiz C, Mendirek G, Sahin H, Hur D, Görgün K, Senger RT, Birer Ö, Peeters FM, Zareie HM. Structural changes in a Schiff base molecular assembly initiated by scanning tunneling microscopy tip. Nanotechnology 2016; 27:335601. [PMID: 27378765 DOI: 10.1088/0957-4484/27/33/335601] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We report the controlled self-organization and switching of newly designed Schiff base (E)-4-((4-(phenylethynyl) benzylidene) amino) benzenethiol (EPBB) molecules on a Au (111) surface at room temperature. Scanning tunneling microscopy and spectroscopy (STM/STS) were used to image and analyze the conformational changes of the EPBB molecules. The conformational change of the molecules was induced by using the STM tip while increasing the tunneling current. The switching of a domain or island of molecules was shown to be induced by the STM tip during scanning. Unambiguous fingerprints of the switching mechanism were observed via STM/STS measurements. Surface-enhanced Raman scattering was employed, to control and identify quantitatively the switching mechanism of molecules in a monolayer. Density functional theory calculations were also performed in order to understand the microscopic details of the switching mechanism. These calculations revealed that the molecular switching behavior stemmed from the strong interaction of the EPBB molecules with the STM tip. Our approach to controlling intermolecular mechanics provides a path towards the bottom-up assembly of more sophisticated molecular machines.
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Affiliation(s)
- A Tomak
- Department of Materials Science and Engineering, Izmir Institute of Technology, Izmir 35430, Turkey
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Sivek J, Sahin H, Partoens B, Peeters FM. Giant magnetic anisotropy in doped single layer molybdenum disulfide and fluorographene. J Phys Condens Matter 2016; 28:195301. [PMID: 27073191 DOI: 10.1088/0953-8984/28/19/195301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Stable monolayer materials based on existing, well known and stable two-dimensional crystal fluorographene and molybdenum disulfide are predicted to exhibit a huge magnetocrystalline anisotropy when functionalized with adsorbed transition metal atoms at vacant sides. Ab initio calculations within the density-functional theory formalism were performed to investigate the adsorption of the transitional metals in a single S (or F) vacancy of monolayer molybdenum disulfide (or fluorographene). We found strong bonding of the transitional metal atoms to the vacant sites with binding energies ranging from 2.5 to 5.2 eV. Our calculations revealed that these systems with adsorbed metal atoms exhibit a magnetic anisotropy, specifically the structures including Os and Ir show a giant magnetocrystalline anisotropy energy of 31-101 meV. Our results demonstrate the possibility of obtaining stable monolayer materials with huge magnetocrystalline anisotropy based on preexisting, well known and stable two-dimensional crystals: fluorographene and molybdenum disulfide. We believe that the results obtained here are useful not only for deeper understanding of the origin of magnetocrystalline anisotropy but also for the design of monolayer optoelectronic devices with novel functionalities.
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Affiliation(s)
- J Sivek
- Departement Fysica, Universiteit Antwerpen, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
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Čukarić NA, Partoens B, Tadić MŽ, Arsoski VV, Peeters FM. The 30-band k ⋅ p theory of valley splitting in silicon thin layers. J Phys Condens Matter 2016; 28:195303. [PMID: 27093609 DOI: 10.1088/0953-8984/28/19/195303] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The valley splitting of the conduction-band states in a thin silicon-on-insulator layer is investigated using the 30-band k ⋅ p theory. The system composed of a few nm thick [Formula: see text] layer embedded within thick SiO2 layers is analyzed. The valley split states are found to cross periodically with increasing quantum well width, and therefore the energy splitting is an oscillatory function of the quantum well width, with period determined by the wave vector K 0 of the conduction band minimum. Because the valley split states are classified by parity, the optical transition between the ground hole state and one of those valley split conduction band states is forbidden. The oscillations in the valley splitting energy decrease with electric field and with smoothing of the composition profile between the well and the barrier by diffusion of oxygen from the SiO2 layers to the Si quantum well. Such a smoothing also leads to a decrease of the interband transition matrix elements. The obtained results are well parametrized by the effective two-valley model, but are found to disagree from previous 30-band calculations. This discrepancy could be traced back to the fact that the basis for the numerical solution of the eigenproblem must be restricted to the first Brillouin zone in order to obtain quantitatively correct results for the valley splitting.
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Affiliation(s)
- Nemanja A Čukarić
- School of Electrical Engineering, University of Belgrade, PO Box 35-54, 11120 Belgrade, Serbia
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Zarenia M, Perali A, Peeters FM, Neilson D. Large gap electron-hole superfluidity and shape resonances in coupled graphene nanoribbons. Sci Rep 2016; 6:24860. [PMID: 27108968 PMCID: PMC4843006 DOI: 10.1038/srep24860] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2015] [Accepted: 04/06/2016] [Indexed: 11/09/2022] Open
Abstract
We predict enhanced electron-hole superfluidity in two coupled electron-hole armchair-edge terminated graphene nanoribbons separated by a thin insulating barrier. In contrast to graphene monolayers, the multiple subbands of the nanoribbons are parabolic at low energy with a gap between the conduction and valence bands, and with lifted valley degeneracy. These properties make screening of the electron-hole interaction much weaker than for coupled electron-hole monolayers, thus boosting the pairing strength and enhancing the superfluid properties. The pairing strength is further boosted by the quasi one-dimensional quantum confinement of the carriers, as well as by the large density of states near the bottom of each subband. The latter magnifies superfluid shape resonances caused by the quantum confinement. Several superfluid partial condensates are present for finite-width nanoribbons with multiple subbands. We find that superfluidity is predominately in the strongly-coupled BEC and BCS-BEC crossover regimes, with large superfluid gaps up to 100 meV and beyond. When the gaps exceed the subband spacing, there is significant mixing of the subbands, a rounding of the shape resonances, and a resulting reduction in the one-dimensional nature of the system.
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Affiliation(s)
- M Zarenia
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
| | - A Perali
- Dipartimenti di Fisica e di Farmacia, Università di Camerino, 62032 Camerino, Italy
| | - F M Peeters
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
| | - D Neilson
- Dipartimenti di Fisica e di Farmacia, Università di Camerino, 62032 Camerino, Italy
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Milovanović SP, Peeters FM. Characterization of the size and position of electron-hole puddles at a graphene p-n junction. Nanotechnology 2016; 27:105203. [PMID: 26866679 DOI: 10.1088/0957-4484/27/10/105203] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The effect of an electron-hole puddle on the electrical transport when governed by snake states in a bipolar graphene structure is investigated. Using numerical simulations we show that information on the size and position of the electron-hole puddle can be obtained using the dependence of the conductance on magnetic field and electron density of the gated region. The presence of the scatterer disrupts snake state transport which alters the conduction pattern. We obtain a simple analytical formula that connects the position of the electron-hole puddle with features observed in the conductance. The size of the electron-hole puddle is estimated from the magnetic field and gate potential that maximizes the effect of the puddle on the electrical transport.
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