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Di Bernardo I, Blyth J, Watson L, Xing K, Chen YH, Chen SY, Edmonds MT, Fuhrer MS. Defects, band bending and ionization rings in MoS 2. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 34:174002. [PMID: 35081526 DOI: 10.1088/1361-648x/ac4f1d] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2021] [Accepted: 01/26/2022] [Indexed: 06/14/2023]
Abstract
Chalcogen vacancies in transition metal dichalcogenides are widely acknowledged as both donor dopants and as a source of disorder. The electronic structure of sulphur vacancies in MoS2however is still controversial, with discrepancies in the literature pertaining to the origin of the in-gap features observed via scanning tunneling spectroscopy (STS) on single sulphur vacancies. Here we use a combination of scanning tunnelling microscopy and STS to study embedded sulphur vacancies in bulk MoS2crystals. We observe spectroscopic features dispersing in real space and in energy, which we interpret as tip position- and bias-dependent ionization of the sulphur vacancy donor due to tip induced band bending. The observations indicate that care must be taken in interpreting defect spectra as reflecting in-gap density of states, and may explain discrepancies in the literature.
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Affiliation(s)
- Iolanda Di Bernardo
- Australian Research Council Centre of Excellence in Future Low-Energy Electronics Technologies, Monash University, Clayton, 3800, VIC, Australia
- School of Physics and Astronomy, Monash University, Clayton, 3800, VIC, Australia
| | - James Blyth
- Australian Research Council Centre of Excellence in Future Low-Energy Electronics Technologies, Monash University, Clayton, 3800, VIC, Australia
- School of Physics and Astronomy, Monash University, Clayton, 3800, VIC, Australia
| | - Liam Watson
- Australian Research Council Centre of Excellence in Future Low-Energy Electronics Technologies, Monash University, Clayton, 3800, VIC, Australia
- School of Physics and Astronomy, Monash University, Clayton, 3800, VIC, Australia
| | - Kaijian Xing
- School of Physics and Astronomy, Monash University, Clayton, 3800, VIC, Australia
| | - Yi-Hsun Chen
- Australian Research Council Centre of Excellence in Future Low-Energy Electronics Technologies, Monash University, Clayton, 3800, VIC, Australia
- School of Physics and Astronomy, Monash University, Clayton, 3800, VIC, Australia
| | - Shao-Yu Chen
- Australian Research Council Centre of Excellence in Future Low-Energy Electronics Technologies, Monash University, Clayton, 3800, VIC, Australia
- School of Physics and Astronomy, Monash University, Clayton, 3800, VIC, Australia
| | - Mark T Edmonds
- Australian Research Council Centre of Excellence in Future Low-Energy Electronics Technologies, Monash University, Clayton, 3800, VIC, Australia
- School of Physics and Astronomy, Monash University, Clayton, 3800, VIC, Australia
- Monash Centre for Atomically Thin Materials, Monash University, Clayton, 3800, VIC, Australia
| | - Michael S Fuhrer
- Australian Research Council Centre of Excellence in Future Low-Energy Electronics Technologies, Monash University, Clayton, 3800, VIC, Australia
- School of Physics and Astronomy, Monash University, Clayton, 3800, VIC, Australia
- Monash Centre for Atomically Thin Materials, Monash University, Clayton, 3800, VIC, Australia
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Fu M, Liang L, Zou Q, Nguyen GD, Xiao K, Li AP, Kang J, Wu Z, Gai Z. Defects in Highly Anisotropic Transition-Metal Dichalcogenide PdSe 2. J Phys Chem Lett 2020; 11:740-746. [PMID: 31880944 DOI: 10.1021/acs.jpclett.9b03312] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The atomic and electronic structures of pristine PdSe2 as well as various intrinsic vacancy defects in PdSe2 are studied comprehensively by combining scanning tunneling microscopy, spectroscopy, and density functional theory calculations. Other than the topmost Se atoms, sublayer Pd atoms and the intrinsic Pd and Se vacancy defects are identified. Both VSe and VPd defects induce defect states near the Fermi level. As a result, the vacancy defects can be negatively charged by a tip gating effect. At negative sample bias, the screened Coulomb interaction between the scanning tunneling microscopy (STM) tip and the charged vacancies creates a disk-like protrusion around the VPd and crater-like features around VSe. The magnification effect of the long-range charge localization at the charged defect site makes sublayer defects as deep as 1 nm visible even in STM images. This result proves that by gating the probe, scanning probe microscopy can be used as an easy tool for characterizing sublayer defects in a nondestructive way.
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Affiliation(s)
- Mingming Fu
- Fujian Provincial Key Laboratory of Semiconductors and Applications, Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Department of Physics , Xiamen University , Xiamen , Fujian Province 361005 , P.R. China
- Center for Nanophase Materials Sciences , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
| | - Liangbo Liang
- Center for Nanophase Materials Sciences , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
| | - Qiang Zou
- Center for Nanophase Materials Sciences , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
| | - Giang D Nguyen
- Center for Nanophase Materials Sciences , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
| | - Kai Xiao
- Center for Nanophase Materials Sciences , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
| | - An-Ping Li
- Center for Nanophase Materials Sciences , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
| | - Junyong Kang
- Fujian Provincial Key Laboratory of Semiconductors and Applications, Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Department of Physics , Xiamen University , Xiamen , Fujian Province 361005 , P.R. China
| | - Zhiming Wu
- Fujian Provincial Key Laboratory of Semiconductors and Applications, Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Department of Physics , Xiamen University , Xiamen , Fujian Province 361005 , P.R. China
| | - Zheng Gai
- Center for Nanophase Materials Sciences , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
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Correlated impurity complex in the asymmetric tunneling contact: an ideal system to observe negative tunneling conductivity. Sci Rep 2019; 9:15974. [PMID: 31685867 PMCID: PMC6828695 DOI: 10.1038/s41598-019-52095-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2019] [Accepted: 10/11/2019] [Indexed: 11/09/2022] Open
Abstract
We studied theoretically electron transport through the impurity complex localized between the tunneling contact leads by means of the generalized Keldysh diagram technique. The formation of multiple well pronounced regions with negative tunneling conductivity in the I-V characteristics was revealed. The appearance of negative tunneling conductivity is caused by the presence of both strong Coulomb correlations and the asymmetry of tunneling rates, which lead to the blockade of the electron transport through the system for a certain values of applied bias. The developed theory and obtained results may be useful for the application of impurity (dopant) atoms as a basic elements in modern nanoelectronic circuits.
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Hu Z, Niu T, Guo R, Zhang J, Lai M, He J, Wang L, Chen W. Two-dimensional black phosphorus: its fabrication, functionalization and applications. NANOSCALE 2018; 10:21575-21603. [PMID: 30457619 DOI: 10.1039/c8nr07395c] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Phosphorus, one of the most abundant elements in the Earth (∼0.1%), has attracted much attention in the last five years since the rediscovery of two-dimensional (2D) black phosphorus (BP) in 2014. The successful scaling down of BP endows this 'old material' with new vitality, resulting from the intriguing semiconducting properties in the atomic scale limit, i.e. layer-dependent bandgap that covers from the visible light to mid-infrared light spectrum as well as hole-dominated ambipolar transport characteristics. Intensive research effort has been devoted to the fabrication, characterization, functionalization and application of BP and other phosphorus allotropes. In this review article, we summarize the fundamental properties and fabrication techniques of BP, with particular emphasis on the recent progress in molecular beam epitaxy growth of 2D phosphorus. Subsequently, we highlight recent progress in BP (opto)electronic device applications achieved via customized manipulation methods, such as interface, defect and bandgap engineering as well as forming Lego-like stacked heterostructures.
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Affiliation(s)
- Zehua Hu
- School of Physics and Optoelectronic Engineering, Nanjing University of Information Science & Technology, Nanjing 210044, China and Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore.
| | - Tianchao Niu
- Herbert Gleiter Institute of Nanoscience, College of Materials Science and Engineering, Nanjing University of Science and Technology, No. 200 Xiaolingwei, Nanjing 210094, China.
| | - Rui Guo
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543, Singapore
| | - Jialin Zhang
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543, Singapore
| | - Min Lai
- School of Physics and Optoelectronic Engineering, Nanjing University of Information Science & Technology, Nanjing 210044, China
| | - Jun He
- School of Physics and Electronics, Central South University, 932 Lushan Road, Changsha 100083, China
| | - Li Wang
- Institute for Advanced Study and Department of Physics, Nanchang University, 999 Xue Fu Da Dao, Nanchang 330000, China
| | - Wei Chen
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore. and Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543, Singapore and National University of Singapore (Suzhou) Research Institute, 377 Lin Quan Street, Suzhou Industrial Park, Suzhou 215123, China
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5
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Nguyen GD, Liang L, Zou Q, Fu M, Oyedele AD, Sumpter BG, Liu Z, Gai Z, Xiao K, Li AP. 3D Imaging and Manipulation of Subsurface Selenium Vacancies in PdSe_{2}. PHYSICAL REVIEW LETTERS 2018; 121:086101. [PMID: 30192587 DOI: 10.1103/physrevlett.121.086101] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2018] [Indexed: 05/12/2023]
Abstract
Two-dimensional materials such as layered transition-metal dichalcogenides (TMDs) are ideal platforms for studying defect behaviors, an essential step towards defect engineering for novel material functions. Here, we image the 3D lattice locations of selenium-vacancy V_{Se} defects and manipulate them using a scanning tunneling microscope (STM) near the surface of PdSe_{2}, a recently discovered pentagonal layered TMD. The V_{Se} show a characterisitc charging ring in a spatially resolved conductance map, based on which we can determine its subsurface lattice location precisely. Using the STM tip, not only can we reversibly switch the defect states between charge neutral and charge negative, but also trigger migrations of V_{Se} defects. This allows a demonstration of direct "writing" and "erasing" of atomic defects and tracing the diffusion pathways. First-principles calculations reveal a small diffusion barrier of V_{Se} in PdSe_{2}, which is much lower than S vacancy in MoS_{2} or an O vacancy in TiO_{2}. This finding opens an opportunity of defect engineering in PdSe_{2} for such as controlled phase transformations and resistive-switching memory device application.
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Affiliation(s)
- Giang D Nguyen
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Liangbo Liang
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Qiang Zou
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Mingming Fu
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Akinola D Oyedele
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
- Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville, Tennessee 37996, USA
| | - Bobby G Sumpter
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
- Oak Ridge National Laboratory, Computational Sciences and Engineering Division, Oak Ridge, Tennessee 37831, USA
| | - Zheng Liu
- Center for Programmable Materials, School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore
| | - Zheng Gai
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Kai Xiao
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - An-Ping Li
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
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6
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Qiu Z, Fang H, Carvalho A, Rodin AS, Liu Y, Tan SJR, Telychko M, Lv P, Su J, Wang Y, Castro Neto AH, Lu J. Resolving the Spatial Structures of Bound Hole States in Black Phosphorus. NANO LETTERS 2017; 17:6935-6940. [PMID: 29035538 DOI: 10.1021/acs.nanolett.7b03356] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Understanding the local electronic properties of individual defects and dopants in black phosphorus (BP) is of great importance for both fundamental research and technological applications. Here, we employ low-temperature scanning tunnelling microscope (LT-STM) to probe the local electronic structures of single acceptors in BP. We demonstrate that the charge state of individual acceptors can be reversibly switched by controlling the tip-induced band bending. In addition, acceptor-related resonance features in the tunnelling spectra can be attributed to the formation of Rydberg-like bound hole states. The spatial mapping of the quantum bound states shows two distinct shapes evolving from an extended ellipse shape for the 1s ground state to a dumbbell shape for the 2px excited state. The wave functions of bound hole states can be well-described using the hydrogen-like model with anisotropic effective mass, corroborated by our theoretical calculations. Our findings not only provide new insight into the many-body interactions around single dopants in this anisotropic two-dimensional material but also pave the way to the design of novel quantum devices.
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Affiliation(s)
- Zhizhan Qiu
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
- NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore , 28 Medical Drive, Singapore 117456
| | - Hanyan Fang
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
| | - Alexandra Carvalho
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
| | - A S Rodin
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
| | - Yanpeng Liu
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
| | - Sherman J R Tan
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
- NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore , 28 Medical Drive, Singapore 117456
| | - Mykola Telychko
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
| | - Pin Lv
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
| | - Jie Su
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
| | - Yewu Wang
- Department of Physics & State Key Laboratory of Silicon Materials, Zhejiang University , Hangzhou 310027, P. R. China
| | - A H Castro Neto
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
- Department of Physics, National University of Singapore , 3 Science Drive 2, Singapore 117542
| | - Jiong Lu
- Department of Chemistry, National University of Singapore , 3 Science Drive 3, Singapore 117543
- Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , Singapore 117546
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7
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Kiraly B, Hauptmann N, Rudenko AN, Katsnelson MI, Khajetoorians AA. Probing Single Vacancies in Black Phosphorus at the Atomic Level. NANO LETTERS 2017; 17:3607-3612. [PMID: 28481547 PMCID: PMC5474690 DOI: 10.1021/acs.nanolett.7b00766] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Revised: 05/04/2017] [Indexed: 05/26/2023]
Abstract
Utilizing a combination of low-temperature scanning tunneling microscopy/spectroscopy (STM/STS) and electronic structure calculations, we characterize the structural and electronic properties of single atomic vacancies within several monolayers of the surface of black phosphorus. We illustrate, with experimental analysis and tight-binding calculations, that we can depth profile these vacancies and assign them to specific sublattices within the unit cell. Measurements reveal that the single vacancies exhibit strongly anisotropic and highly delocalized charge density, laterally extended up to 20 atomic unit cells. The vacancies are then studied with STS, which reveals in-gap resonance states near the valence band edge and a strong p-doping of the bulk black phosphorus crystal. Finally, quasiparticle interference generated near these vacancies enables the direct visualization of the anisotropic band structure of black phosphorus.
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8
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Rashidi M, Burgess JAJ, Taucer M, Achal R, Pitters JL, Loth S, Wolkow RA. Time-resolved single dopant charge dynamics in silicon. Nat Commun 2016; 7:13258. [PMID: 27782125 PMCID: PMC5095180 DOI: 10.1038/ncomms13258] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Accepted: 09/08/2016] [Indexed: 11/09/2022] Open
Abstract
As the ultimate miniaturization of semiconductor devices approaches, it is imperative that the effects of single dopants be clarified. Beyond providing insight into functions and limitations of conventional devices, such information enables identification of new device concepts. Investigating single dopants requires sub-nanometre spatial resolution, making scanning tunnelling microscopy an ideal tool. However, dopant dynamics involve processes occurring at nanosecond timescales, posing a significant challenge to experiment. Here we use time-resolved scanning tunnelling microscopy and spectroscopy to probe and study transport through a dangling bond on silicon before the system relaxes or adjusts to accommodate an applied electric field. Atomically resolved, electronic pump-probe scanning tunnelling microscopy permits unprecedented, quantitative measurement of time-resolved single dopant ionization dynamics. Tunnelling through the surface dangling bond makes measurement of a signal that would otherwise be too weak to detect feasible. Distinct ionization and neutralization rates of a single dopant are measured and the physical process controlling those are identified. Probing individual impurities will become increasingly important as devices shrink towards the nanoscale. Here Rashidi et al., introduce a method based on time-resolved scanning tunnelling spectroscopy of surface dangling bonds to investigate the dynamics of individual dopants in silicon.
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Affiliation(s)
- Mohammad Rashidi
- Department of Physics, University of Alberta, Edmonton, Alberta, Canada T6G 2J1.,National Institute for Nanotechnology, National Research Council of Canada, Edmonton, Alberta, Canada T6G 2M9
| | - Jacob A J Burgess
- Max Planck Institute for the Structure and Dynamics of Matter, 22761 Hamburg, Germany.,Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany
| | - Marco Taucer
- Department of Physics, University of Alberta, Edmonton, Alberta, Canada T6G 2J1.,National Institute for Nanotechnology, National Research Council of Canada, Edmonton, Alberta, Canada T6G 2M9
| | - Roshan Achal
- Department of Physics, University of Alberta, Edmonton, Alberta, Canada T6G 2J1
| | - Jason L Pitters
- National Institute for Nanotechnology, National Research Council of Canada, Edmonton, Alberta, Canada T6G 2M9
| | - Sebastian Loth
- Max Planck Institute for the Structure and Dynamics of Matter, 22761 Hamburg, Germany.,Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany
| | - Robert A Wolkow
- Department of Physics, University of Alberta, Edmonton, Alberta, Canada T6G 2J1.,National Institute for Nanotechnology, National Research Council of Canada, Edmonton, Alberta, Canada T6G 2M9
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Lee D, Gohlke D, Benjamin A, Gupta JA. Influence of the local environment on Mn acceptors in GaAs. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:154202. [PMID: 25782688 DOI: 10.1088/0953-8984/27/15/154202] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
As transistors continue to shrink toward nanoscale dimensions, their characteristics are increasingly dependent on the statistical variations of impurities in the semiconductor material. The scanning tunneling microscope (STM) can be used to not only study prototype devices with atomically precise placement of impurity atoms, but can also probe how the properties of these impurities depend on the local environment. Tunneling spectroscopy of Mn acceptors in GaAs indicates that surface-layer Mn act as a deep acceptor, with a hole binding energy that can be tuned by positioning charged defects nearby. Band bending induced by the tip or by these defects can also tune the ionization state of the acceptor complex, evident as a ring-like contrast in STM images. The interplay of these effects is explored over a wide range of defect distances, and understood using iterative simulations of tip-induced band bending.
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10
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Zheng H, Weismann A, Berndt R. Tuning the electron transport at single donors in zinc oxide with a scanning tunnelling microscope. Nat Commun 2015; 5:2992. [PMID: 24390611 DOI: 10.1038/ncomms3992] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2013] [Accepted: 11/22/2013] [Indexed: 11/09/2022] Open
Abstract
In devices like the single-electron transistor the detailed transport properties of a nanostructure can be measured by tuning its energy levels with a gate voltage. The scanning tunnelling microscope in contrast usually lacks such a gate electrode. Here we demonstrate tuning of the levels of a donor in a scanning tunnelling microscope without a third electrode. The potential and the position of the tip are used to locally control band bending. Conductance maps in this parameter space reveal Coulomb diamonds known from three-terminal data from single-electron transistors and provide information on charging transitions, binding energies and vibrational excitations. The analogy to single-electron transistor data suggests a new way of extracting these key quantities without making any assumptions about the unknown shape of the scanning tunnelling microscope tip.
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Affiliation(s)
- Hao Zheng
- Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, D-24098 Kiel, Germany
| | - Alexander Weismann
- Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, D-24098 Kiel, Germany
| | - Richard Berndt
- Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, D-24098 Kiel, Germany
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Mahani MR, Pertsova A, Canali CM. Trend of the magnetic anisotropy for individual Mn dopants near the (1 1 0) GaAs surface. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:394006. [PMID: 25212432 DOI: 10.1088/0953-8984/26/39/394006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Using a microscopic finite-cluster tight-binding model, we investigate the trend of the magnetic anisotropy energy as a function of the cluster size for an individual Mn impurity positioned in the vicinity of the (1 1 0) GaAs surface. We present results of calculations for large cluster sizes containing approximately 10(4) atoms, which have not been investigated so far. Our calculations demonstrate that the anisotropy energy of a Mn dopant in bulk GaAs, found to be non-zero in previous tight-binding calculations, is purely a finite size effect that vanishes with inverse cluster size. In contrast to this, we find that the splitting of the three in-gap Mn acceptor energy levels converges to a finite value in the limit of the infinite cluster size. For a Mn in bulk GaAs this feature is related to the nature of the mean-field treatment of the coupling between the impurity and its nearest neighbor atoms. We also calculate the trend of the anisotropy energy in the sublayers as the Mn dopant is moved away from the surface towards the center of the cluster. Here the use of large cluster sizes allows us to position the impurity in deeper sublayers below the surface, compared to previous calculations. In particular, we show that the anisotropy energy increases up to the fifth sublayer and then decreases as the impurity is moved further away from the surface, approaching its bulk value. The present study provides important insights for experimental control and manipulation of the electronic and magnetic properties of individual Mn dopants at the semiconductor surface by means of advanced scanning tunneling microscopy techniques.
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Affiliation(s)
- M R Mahani
- Department of Physics and Electrical Engineering, Linnæus University, Norra Vägen 49, 391 82, Kalmar, Sweden
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12
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Lu CP, Li G, Mao J, Wang LM, Andrei EY. Bandgap, mid-gap states, and gating effects in MoS2. NANO LETTERS 2014; 14:4628-4633. [PMID: 25004377 DOI: 10.1021/nl501659n] [Citation(s) in RCA: 123] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The discovery of graphene has put the spotlight on other layered materials including transition metal dichalcogenites (TMD) as building blocks for novel heterostructures assembled from stacked atomic layers. Molybdenum disulfide, MoS2, a semiconductor in the TMD family, with its remarkable thermal and chemical stability and high mobility, has emerged as a promising candidate for postsilicon applications such as switching, photonics, and flexible electronics. Because these rely on controlling the position of the Fermi energy (EF), it is crucial to understand its dependence on doping and gating. To elucidate these questions we carried out gated scanning tunneling microscopy (STM) and spectroscopy (STS) measurements and compared them with transport measurements in a field effect transistor (FET) device configuration. This made it possible to measure the bandgap and the position of EF in MoS2 and to track its evolution with gate voltage. For bulk samples, the measured bandgap (∼ 1.3 eV) is comparable to the value obtained by photoluminescence, and the position of EF (∼ 0.35 eV) below the conduction band, is consistent with N-doping reported in this material. We show that the N-doping in bulk samples can be attributed to S vacancies. In contrast, the significantly higher N-doping observed in thin MoS2 films deposited on SiO2 is dominated by charge traps at the sample-substrate interface.
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Affiliation(s)
- Chih-Pin Lu
- Department of Physics, National Taiwan University , Taipei, 10617 Taiwan, Republic of China
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Lin W, Foley A, Alam K, Wang K, Liu Y, Chen T, Pak J, Smith AR. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2014; 85:043702. [PMID: 24784613 DOI: 10.1063/1.4870276] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without breaking vacuum, and convenient visual access to the sample and tip inside a superconducting magnet cryostat. A sample/tip handling system is optimized for both the molecular beam epitaxy growth system and the scanning tunneling microscope system. The sample/tip handing system enables in situ STM studies on epitaxially grown samples, and tip exchange in the superconducting magnet cryostat. The hybrid molecular beam epitaxy and low temperature scanning tunneling microscopy system is capable of growing semiconductor-based hetero-structures with controlled accuracy down to a single atomic-layer and imaging them down to atomic resolution.
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Affiliation(s)
- Wenzhi Lin
- Department of Physics and Astronomy, Nanoscale and Quantum Phenomena Institute, Ohio University, Athens, Ohio 45701, USA
| | - Andrew Foley
- Department of Physics and Astronomy, Nanoscale and Quantum Phenomena Institute, Ohio University, Athens, Ohio 45701, USA
| | - Khan Alam
- Department of Physics and Astronomy, Nanoscale and Quantum Phenomena Institute, Ohio University, Athens, Ohio 45701, USA
| | - Kangkang Wang
- Department of Physics and Astronomy, Nanoscale and Quantum Phenomena Institute, Ohio University, Athens, Ohio 45701, USA
| | - Yinghao Liu
- Department of Physics and Astronomy, Nanoscale and Quantum Phenomena Institute, Ohio University, Athens, Ohio 45701, USA
| | - Tianjiao Chen
- Department of Physics and Astronomy, Nanoscale and Quantum Phenomena Institute, Ohio University, Athens, Ohio 45701, USA
| | - Jeongihm Pak
- Department of Physics and Astronomy, Nanoscale and Quantum Phenomena Institute, Ohio University, Athens, Ohio 45701, USA
| | - Arthur R Smith
- Department of Physics and Astronomy, Nanoscale and Quantum Phenomena Institute, Ohio University, Athens, Ohio 45701, USA
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Schnedler M, Weidlich P, Portz V, Weber D, Dunin-Borkowski R, Ebert P. Correction of nonlinear lateral distortions of scanning probe microscopy images. Ultramicroscopy 2014; 136:86-90. [DOI: 10.1016/j.ultramic.2013.08.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2013] [Revised: 08/01/2013] [Accepted: 08/08/2013] [Indexed: 10/26/2022]
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15
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Münnich G, Donarini A, Wenderoth M, Repp J. Fixing the energy scale in scanning tunneling microscopy on semiconductor surfaces. PHYSICAL REVIEW LETTERS 2013; 111:216802. [PMID: 24313511 DOI: 10.1103/physrevlett.111.216802] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2013] [Indexed: 06/02/2023]
Abstract
In scanning tunneling experiments on semiconductor surfaces, the energy scale within the tunneling junction is usually unknown due to tip-induced band bending. Here, we experimentally recover the zero point of the energy scale by combining scanning tunneling microscopy with Kelvin probe force spectroscopy. With this technique, we revisit shallow acceptors buried in GaAs. Enhanced acceptor-related conductance is observed in negative, zero, and positive band-bending regimes. An Anderson-Hubbard model is used to rationalize our findings, capturing the crossover between the acceptor state being part of an impurity band for zero band bending and the acceptor state being split off and localized for strong negative or positive band bending, respectively.
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Affiliation(s)
- Gerhard Münnich
- Institute of Experimental and Applied Physics, University of Regensburg, 93053 Regensburg, Germany
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16
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Krebs O, Lemaître A. Optically induced coupling of two magnetic dopant spins by a photoexcited hole in a Mn-doped InAs/GaAs quantum dot. PHYSICAL REVIEW LETTERS 2013; 111:187401. [PMID: 24237560 DOI: 10.1103/physrevlett.111.187401] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2013] [Revised: 08/06/2013] [Indexed: 06/02/2023]
Abstract
We report evidence of a photoinduced coupling between two spins provided by Mn dopants in their neutral acceptor state A(0) in a single InAs/GaAs quantum dot. The coupling occurs due to simultaneous exchange interactions between each of the two dopant spins and a photocreated hole. Microphotoluminescence spectroscopy achieved both in longitudinal and perpendicular magnetic fields reveals the splitting of the four spin configurations |J(1) = ± 1,J(2) = ± 1} due to the 2A(0)-hole exchange interaction. We obtain a comprehensive interpretation of the experimental data with a simplified spin Hamiltonian model, which more specifically shows that the hole-mediated coupling is similar to a ε(12)-70 μeV exchange interaction between both A(0) spins.
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Affiliation(s)
- O Krebs
- CNRS-Laboratoire de Photonique et de Nanostructures, Route de Nozay, 91460 Marcoussis, France
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17
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Lee DH, Gupta JA. Tunable control over the ionization state of single Mn acceptors in GaAs with defect-induced band bending. NANO LETTERS 2011; 11:2004-2007. [PMID: 21524100 DOI: 10.1021/nl2003686] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
A scanning tunneling microscope was used to study the ionization of single Mn acceptors in GaAs(110). The ionization state switches when the GaAs valence band is bent across a Mn acceptor level. This produces a ringlike feature in STM images, whose diameter depends on the tunneling conditions and distance to charged arsenic vacancies. By varying the latter, we could tune the ionization switching, as well as quantify the contributions from tip- and vacancy-induced band bending.
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Affiliation(s)
- Dong-Hun Lee
- Department of Physics, Ohio State University, Columbus, Ohio 43210, United States
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18
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Abstract
The sensitive dependence of a semiconductor's electronic, optical and magnetic properties on dopants has provided an extensive range of tunable phenomena to explore and apply to devices. Recently it has become possible to move past the tunable properties of an ensemble of dopants to identify the effects of a solitary dopant on commercial device performance as well as locally on the fundamental properties of a semiconductor. New applications that require the discrete character of a single dopant, such as single-spin devices in the area of quantum information or single-dopant transistors, demand a further focus on the properties of a specific dopant. This article describes the huge advances in the past decade towards observing, controllably creating and manipulating single dopants, as well as their application in novel devices which allow opening the new field of solotronics (solitary dopant optoelectronics).
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Affiliation(s)
- Paul M Koenraad
- COBRA Inter-University Research Institute, Department of Applied Physics, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands.
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19
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Strandberg TO, Canali CM, MacDonald AH. Chern number spins of Mn acceptor magnets in GaAs. PHYSICAL REVIEW LETTERS 2011; 106:017202. [PMID: 21231770 DOI: 10.1103/physrevlett.106.017202] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2010] [Indexed: 05/30/2023]
Abstract
We determine the effective total spin J of local moments formed from acceptor states bound to Mn ions in GaAs by evaluating their magnetic Chern numbers. When individual Mn atoms are close to the sample surface, the total spin changes from J=1 to J=2, due to quenching of the acceptor orbital moment. For Mn pairs in bulk, the total J depends on pair orientation in the GaAs lattice and on the separation between the Mn atoms. We point out that Berry curvature variation as a function of local moment orientation can profoundly influence the quantum-spin dynamics of these magnetic entities.
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Affiliation(s)
- T O Strandberg
- School of Computer Science, Physics and Mathematics, Linnæus University, 39233 Kalmar-Sweden
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20
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Lee DH, Gupta JA. Tunable Field Control Over the Binding Energy of Single Dopants by a Charged Vacancy in GaAs. Science 2010; 330:1807-10. [DOI: 10.1126/science.1197434] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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21
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Celebi C, Garleff JK, Silov AY, Yakunin AM, Koenraad PM, Van Roy W, Tang JM, Flatté ME. Surface induced asymmetry of acceptor wave functions. PHYSICAL REVIEW LETTERS 2010; 104:086404. [PMID: 20366956 DOI: 10.1103/physrevlett.104.086404] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2009] [Indexed: 05/29/2023]
Abstract
Measurements of the local density of states of individual acceptors in III-V semiconductors show that the symmetry of the acceptor states strongly depends on the depth of the atom below a (110) surface. Tight-binding calculations performed for a uniformly strained bulk material demonstrate that strain induced by the surface relaxation is responsible for the observed depth-dependent symmetry breaking of acceptor wave functions. As this effect is strongest for weakly bound acceptors, it explains within a unified approach the commonly observed triangular shapes of shallow acceptors and the crosslike shapes of deeply bound acceptor states in III-V materials.
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Affiliation(s)
- C Celebi
- COBRA Inter-University Research Institute, Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, NL-5600 MB Eindhoven, The Netherlands
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22
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Jancu JM, Girard JC, Nestoklon MO, Lemaître A, Glas F, Wang ZZ, Voisin P. STM images of subsurface Mn atoms in GaAs: evidence of hybridization of surface and impurity states. PHYSICAL REVIEW LETTERS 2008; 101:196801. [PMID: 19113292 DOI: 10.1103/physrevlett.101.196801] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2008] [Indexed: 05/27/2023]
Abstract
We show that scanning tunneling microscopy (STM) images of subsurface Mn atoms in GaAs are formed by hybridization of the impurity state with intrinsic surface states. They cannot be interpreted in terms of bulk-impurity wave-function imaging. Atomic-resolution images obtained using a low-temperature apparatus are compared with advanced, parameter-free tight-binding simulations accounting for both the buckled (110) surface and vacuum electronic properties. Splitting of the acceptor state due to buckling is shown to play a prominent role.
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Affiliation(s)
- J-M Jancu
- CNRS-Laboratoire de Photonique et de Nanostructures, route de Nozay, F-91460, Marcoussis, France
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