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Aliyar T, Ma H, Krishnan R, Singh G, Chong BQ, Wang Y, Verzhbitskiy I, Yu Wong CP, Johnson Goh KE, Shen ZX, Koh TS, Rahman R, Weber B. Symmetry Breaking and Spin-Orbit Coupling for Individual Vacancy-Induced In-Gap States in MoS 2 Monolayers. Nano Lett 2024; 24:2142-2148. [PMID: 38323571 DOI: 10.1021/acs.nanolett.3c03681] [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] [Indexed: 02/08/2024]
Abstract
Spins confined to point defects in atomically thin semiconductors constitute well-defined atomic-scale quantum systems that are being explored as single-photon emitters and spin qubits. Here, we investigate the in-gap electronic structure of individual sulfur vacancies in molybdenum disulfide (MoS2) monolayers using resonant tunneling scanning probe spectroscopy in the Coulomb blockade regime. Spectroscopic mapping of defect wave functions reveals an interplay of local symmetry breaking by a charge-state-dependent Jahn-Teller lattice distortion that, when combined with strong (≃100 meV) spin-orbit coupling, leads to a locking of an unpaired spin-1/2 magnetic moment to the lattice at low temperature, susceptible to lattice strain. Our results provide new insights into the spin and electronic structure of vacancy-induced in-gap states toward their application as electrically and optically addressable quantum systems.
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Affiliation(s)
- Thasneem Aliyar
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
| | - Hongyang Ma
- School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
| | - Radha Krishnan
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
| | - Gagandeep Singh
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
| | - Bi Qi Chong
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
| | - Yitao Wang
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
| | - Ivan Verzhbitskiy
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore 138634, Singapore
| | - Calvin Pei Yu Wong
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore 138634, Singapore
| | - Kuan Eng Johnson Goh
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore 138634, Singapore
| | - Ze Xiang Shen
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
| | - Teck Seng Koh
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
| | - Rajib Rahman
- School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
| | - Bent Weber
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
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Ziesen A, Hassler F. Low-energy in-gap states of vortices in superconductor-semiconductor heterostructures. J Phys Condens Matter 2021; 33:294001. [PMID: 33971638 DOI: 10.1088/1361-648x/abff93] [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: 03/18/2021] [Accepted: 05/10/2021] [Indexed: 06/12/2023]
Abstract
The recent interest in the low-energy states in vortices of semiconductor-superconductor heterostructures are mainly fuelled by the prospects of using Majorana zero modes for quantum computation. The knowledge of low-lying states in the vortex core is essential as they pose a limitation on the topological computation with these states. Recently, the low-energy spectra of clean heterostructures, for superconducting-pairing profiles that vary slowly on the scale of the Fermi wavelength of the semiconductor, have been analytically calculated. In this work, we formulate an alternative method based on perturbation theory to obtain concise analytical formulas to predict the low-energy states including explicit magnetic-field and gap profiles. We provide results for both a topological insulator (with a linear spectrum) as well as for a conventional electron gas (with a quadratic spectrum). We discuss the spectra for a wide range of parameters, including both the size of the vortex and the chemical potential of the semiconductor, and thereby provide a tool to guide future experimental efforts. We compare these findings to numerical results.
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Affiliation(s)
- Alexander Ziesen
- JARA Institute for Quantum Information, RWTH Aachen University, Aachen, Germany
| | - Fabian Hassler
- JARA Institute for Quantum Information, RWTH Aachen University, Aachen, Germany
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Baeumer C, Funck C, Locatelli A, Menteş TO, Genuzio F, Heisig T, Hensling F, Raab N, Schneider CM, Menzel S, Waser R, Dittmann R. In-Gap States and Band-Like Transport in Memristive Devices. Nano Lett 2019; 19:54-60. [PMID: 30241437 DOI: 10.1021/acs.nanolett.8b03023] [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] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Point defects such as oxygen vacancies cause emergent phenomena such as resistive switching in transition-metal oxides, but their influence on the electron-transport properties is far from being understood. Here, we employ direct mapping of the electronic structure of a memristive device by spectromicroscopy. We find that oxygen vacancies result in in-gap states that we use as input for single-band transport simulations. Because the in-gap states are situated below the Fermi level, they do not contribute to the current directly but impact the shape of the conduction band. Accordingly, we can describe our devices with band-like transport and tunneling across the Schottky barrier at the interface.
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Affiliation(s)
- Christoph Baeumer
- Peter Gruenberg Institute , Forschungszentrum Juelich GmbH and JARA-FIT , 52425 Juelich , Germany
| | - Carsten Funck
- Institute for Electronic Materials, IWE2 , RWTH Aachen University , 52074 Aachen , Germany
| | - Andrea Locatelli
- Elettra - Sincrotrone Trieste S.C.p.A., S.S. 14 km - 163,5 in AREA Science Park , I-34149 Basovizza , Trieste , Italy
| | - Tevfik Onur Menteş
- Elettra - Sincrotrone Trieste S.C.p.A., S.S. 14 km - 163,5 in AREA Science Park , I-34149 Basovizza , Trieste , Italy
| | - Francesca Genuzio
- Elettra - Sincrotrone Trieste S.C.p.A., S.S. 14 km - 163,5 in AREA Science Park , I-34149 Basovizza , Trieste , Italy
| | - Thomas Heisig
- Peter Gruenberg Institute , Forschungszentrum Juelich GmbH and JARA-FIT , 52425 Juelich , Germany
| | - Felix Hensling
- Peter Gruenberg Institute , Forschungszentrum Juelich GmbH and JARA-FIT , 52425 Juelich , Germany
| | - Nicolas Raab
- Peter Gruenberg Institute , Forschungszentrum Juelich GmbH and JARA-FIT , 52425 Juelich , Germany
| | - Claus M Schneider
- Peter Gruenberg Institute , Forschungszentrum Juelich GmbH and JARA-FIT , 52425 Juelich , Germany
| | - Stephan Menzel
- Peter Gruenberg Institute , Forschungszentrum Juelich GmbH and JARA-FIT , 52425 Juelich , Germany
| | - Rainer Waser
- Peter Gruenberg Institute , Forschungszentrum Juelich GmbH and JARA-FIT , 52425 Juelich , Germany
- Institute for Electronic Materials, IWE2 , RWTH Aachen University , 52074 Aachen , Germany
| | - Regina Dittmann
- Peter Gruenberg Institute , Forschungszentrum Juelich GmbH and JARA-FIT , 52425 Juelich , Germany
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Abstract
Colloidal quantum dots exhibit various defects and deviations from ideal structures due to kinetic processes, although their band gap frequently remains open and clean. In this Letter, we computationally investigate intrinsic defects in a real-size PbS quantum dot passivated with realistic Cl-ligands. We show that the colloidal intrinsic defects are ionic in nature. Unlike previous computational results, we find that even nonideal, atomically nonstoichiometric quantum dots have a clean band gap without in-gap-states provided that quantum dots satisfy electronic stoichiometry.
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Affiliation(s)
- Danylo Zherebetskyy
- Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | - Yingjie Zhang
- Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
- Applied Science and Technology Graduate Program, University of California at Berkeley , Berkeley, California 94720, United States
| | - Miquel Salmeron
- Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | - Lin-Wang Wang
- Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
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Zhang Y, Zherebetskyy D, Bronstein ND, Barja S, Lichtenstein L, Alivisatos AP, Wang LW, Salmeron M. Molecular Oxygen Induced in-Gap States in PbS Quantum Dots. ACS Nano 2015; 9:10445-10452. [PMID: 26402255 DOI: 10.1021/acsnano.5b04677] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Artificial solids composed of semiconductor quantum dots (QDs) are being developed for large-area electronic and optoelectronic applications, but these materials often have defect-induced in-gap states (IGS) of unknown chemical origin. Here we performed scanning probe based spectroscopic analysis and density functional theory calculations to determine the nature of such states and their electronic structure. We found that IGS near the valence band occur frequently in the QDs except when treated with reducing agents. Calculations on various possible defects and chemical spectroscopy revealed that molecular oxygen is most likely at the origin of these IGS. We expect this impurity-induced deep IGS to be a common occurrence in ionic semiconductors, where the intrinsic vacancy defects either do not produce IGS or produce shallow states near band edges. Ionic QDs with surface passivation to block impurity adsorption are thus ideal for high-efficiency optoelectronic device applications.
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Affiliation(s)
- Yingjie Zhang
- Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | - Danylo Zherebetskyy
- Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | | | - Sara Barja
- Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | - Leonid Lichtenstein
- Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | - A Paul Alivisatos
- Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
- Kavli Energy NanoScience Institute , Berkeley, California 94720, United States
| | - Lin-Wang Wang
- Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | - Miquel Salmeron
- Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
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Zhang Y, Zherebetskyy D, Bronstein ND, Barja S, Lichtenstein L, Schuppisser D, Wang LW, Alivisatos AP, Salmeron M. Charge percolation pathways guided by defects in quantum dot solids. Nano Lett 2015; 15:3249-3253. [PMID: 25844919 DOI: 10.1021/acs.nanolett.5b00454] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Charge hopping and percolation in quantum dot (QD) solids has been widely studied, but the microscopic nature of the percolation process is not understood or determined. Here we present the first imaging of the charge percolation pathways in two-dimensional PbS QD arrays using Kelvin probe force microscopy (KPFM). We show that under dark conditions electrons percolate via in-gap states (IGS) instead of the conduction band, while holes percolate via valence band states. This novel transport behavior is explained by the electronic structure and energy level alignment of the individual QDs, which was measured by scanning tunneling spectroscopy (STS). Chemical treatments with hydrazine can remove the IGS, resulting in an intrinsic defect-free semiconductor, as revealed by STS and surface potential spectroscopy. The control over IGS can guide the design of novel electronic devices with impurity conduction, and photodiodes with controlled doping.
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Affiliation(s)
- Yingjie Zhang
- †Applied Science and Technology Graduate Program, University of California at Berkeley, Berkeley, California 94720, United States
- ‡Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Danylo Zherebetskyy
- ‡Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Noah D Bronstein
- §Department of Chemistry, University of California at Berkeley, Berkeley, California 94720, United States
| | - Sara Barja
- ‡Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Leonid Lichtenstein
- ‡Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - David Schuppisser
- ‡Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Lin-Wang Wang
- ‡Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - A Paul Alivisatos
- ‡Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
- §Department of Chemistry, University of California at Berkeley, Berkeley, California 94720, United States
- ∥Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, United States
- ⊥Kavli Energy NanoScience Institute, Berkeley, California 94720, United States
| | - Miquel Salmeron
- ‡Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
- ∥Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, United States
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Downie RA, Popuri SR, Ning H, Reece MJ, Bos JG. Effect of Spark Plasma Sintering on the Structure and Properties of Ti 1-xZr xNiSn Half-Heusler Alloys. Materials (Basel) 2014; 7:7093-104. [PMID: 28788234 DOI: 10.3390/ma7107093] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/10/2014] [Revised: 10/06/2014] [Accepted: 10/09/2014] [Indexed: 11/27/2022]
Abstract
XNiSn (X = Ti, Zr and Hf) half-Heusler alloys have promising thermoelectric properties and are attracting enormous interest for use in waste heat recovery. In particular, multiphase behaviour has been linked to reduced lattice thermal conductivities, which enables improved energy conversion efficiencies. This manuscript describes the impact of spark plasma sintering (SPS) on the phase distributions and thermoelectric properties of Ti0.5Zr0.5NiSn based half-Heuslers. Rietveld analysis reveals small changes in composition, while measurement of the Seebeck coefficient and electrical resistivities reveals that all SPS treated samples are electron doped compared to the as-prepared samples. The lattice thermal conductivities fall between 4 W·m−1·K−1 at 350 K and 3 W·m−1·K−1 at 740 K. A maximum ZT = 0.7 at 740 K is observed in a sample with nominal Ti0.5Zr0.5NiSn composition.
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