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Su WB, Lu SM, Jeng HT, Chan WY, Chang HH, Pai WW, Liu HL, Chang CS. Observing quantum trapping on MoS 2 through the lifetimes of resonant electrons: revealing the Pauli exclusion principle. NANOSCALE ADVANCES 2020; 2:5848-5856. [PMID: 36133857 PMCID: PMC9418783 DOI: 10.1039/d0na00682c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/19/2020] [Accepted: 11/11/2020] [Indexed: 06/16/2023]
Abstract
We demonstrate that the linewidth of the field emission resonance (FER) observed on the surface of MoS2 using scanning tunneling microscopy can vary by up to one order of magnitude with an increasing electric field. This phenomenon originates from quantum trapping, in which the electron relaxed from a resonant electron in the FER is momentarily trapped in a potential well on the MoS2 surface due to its wave nature. Because the relaxed electron and the resonant electron have the same spin, through the action of the Pauli exclusion principle, the lifetimes of the resonant electrons can be substantially prolonged when the relaxed electrons engage in resonance trapping. The linewidth of the FER is thus considerably reduced to as narrow as 12 meV. The coexistence of the resonant electron and the relaxed electron requires the emission of two electrons, which can occur through the exchange interaction.
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Affiliation(s)
- Wei-Bin Su
- Institute of Physics, Academia Sinica Nankang Taipei 11529 Taiwan
| | - Shin-Ming Lu
- Institute of Physics, Academia Sinica Nankang Taipei 11529 Taiwan
| | - Horng-Tay Jeng
- Department of Physics, National Tsing Hua University Hsinchu 30013 Taiwan
- Institute of Physics, Academia Sinica Nankang Taipei 11529 Taiwan
- Physics Division, National Center for Theoretical Sciences Hsinchu 30013 Taiwan
| | - Wen-Yuan Chan
- Institute of Physics, Academia Sinica Nankang Taipei 11529 Taiwan
| | - Ho-Hsiang Chang
- Institute of Physics, Academia Sinica Nankang Taipei 11529 Taiwan
| | - Woei Wu Pai
- Center for Condensed Matter Sciences, National Taiwan University Taipei 10617 Taiwan
| | - Hsiang-Lin Liu
- Department of Physics, National Taiwan Normal University Taipei 11677 Taiwan
| | - Chia-Seng Chang
- Institute of Physics, Academia Sinica Nankang Taipei 11529 Taiwan
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Liu X, Wang CZ. Interplay between quantum confinement and surface effects in thickness selective stability of thin Ag and Eu films. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:185504. [PMID: 28272026 DOI: 10.1088/1361-648x/aa6556] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Using first-principles calculations, we show that both face-centered cubic (fcc) Ag (1 1 0) ultrathin films and body-centered cubic (bcc) Eu(1 1 0) ultrathin films exhibit thickness selective stability. However, the origin of such thickness selection is different. While the thickness selective stability in fcc Ag(1 1 0) films is mainly due to the well-known quantum well states ascribed to the quantum confinement effects in free-electron-like metal films, the thickness selection in bcc Eu(1 1 0) films is more complex and also strongly correlated with the occupation of the surface and surface resonance states.
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Affiliation(s)
- Xiaojie Liu
- Center for Quantum Sciences and School of Physics, Northeast Normal University, Changchun 130117, People's Republic of China
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Chan WY, Lu SM, Su WB, Liao CC, Hoffmann G, Tsai TR, Chang CS. Sharpness-induced energy shifts of quantum well states in Pb islands on Cu(111). NANOTECHNOLOGY 2017; 28:095706. [PMID: 28135205 DOI: 10.1088/1361-6528/aa583a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We elucidate that the tip sharpness in scanning tunneling microscopy (STM) can be characterized through the number of field-emission (FE) resonances. A higher number of FE resonances indicates higher sharpness. We observe empty quantum well (QW) states in Pb islands on Cu(111) under different tip sharpness levels. We found that QW states observed by sharper tips always had lower energies, revealing negative energy shifts. This sharpness-induced energy shift originates from an inhomogeneous electric field in the STM gap. An increase in sharpness increases the electric field inhomogeneity, that is, enhances the electric field near the tip apex, but weakens the electric field near the sample. As a result, higher sharpness can increase the electronic phase in vacuum, causing the lowering of QW state energies. Moreover, the behaviors of negative energy shift as a function of state energy are entirely different for Pb islands with a thickness of two and nine atomic layers. This thickness-dependent behavior results from the electrostatic force in the STM gap decreasing with increasing tip sharpness. The variation of the phase contributed from the expansion deformation induced by the electrostatic force in a nine-layer Pb island is significantly greater, sufficient to effectively negate the increase of electronic phase in vacuum.
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Affiliation(s)
- Wen-Yuan Chan
- Institute of Physics, Academia Sinica, Nankang, Taipei 11529, Taiwan, Republic of China
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Saha SK, Manna S, Stepanyuk VS, Kirschner J. Visualizing Non-abrupt Transition of Quantum Well States at Stepped Silver Surfaces. Sci Rep 2015; 5:12847. [PMID: 26243639 PMCID: PMC4525284 DOI: 10.1038/srep12847] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2015] [Accepted: 07/10/2015] [Indexed: 11/09/2022] Open
Abstract
We use scanning tunneling spectroscopy (STS) experiments and first-principles density functional theory (DFT) calculations to address a fundamental question of how quantum well (QW) states for electrons in a metal evolve spatially in the lateral direction when there is a surface step that changes the vertical confinement thickness. This study reveals a clear spatially dependent, nearly continuous trend in the energetic shifts of quantum well (QW) states of thin Ag(111) film grown on Cu(111) substrate, showing the strongest change near the step edge. A large energetic shift equaling up to ~200 meV with a lateral extension of the QW states of the order of ~20 Å is found, even though the step-edge is atomically sharp as evidenced by a line scan. The observed lateral extension and the nearly smooth transition of QW states are understood within the context of step-induced charge oscillation, and Smoluchowski-type charge spreading and smoothing.
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Affiliation(s)
| | - Sujit Manna
- Max-Planck-Institut für Mikrostrukturphysik, 06120 Halle, Germany
| | | | - Jürgen Kirschner
- 1] Max-Planck-Institut für Mikrostrukturphysik, 06120 Halle, Germany [2] Martin-Luther-Universität Halle-Wittenberg, 06120 Halle, Germany
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Chan WY, Huang HS, Su WB, Lin WH, Jeng HT, Wu MK, Chang CS. Field-induced expansion deformation in Pb islands on Cu(111): evidence from energy shift of empty quantum-well states. PHYSICAL REVIEW LETTERS 2012; 108:146102. [PMID: 22540808 DOI: 10.1103/physrevlett.108.146102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2011] [Indexed: 05/31/2023]
Abstract
We use scanning tunneling microscopy and spectroscopy to measure the energy shift of empty quantum-well (QW) states in Pb islands on the Cu(111) surface. It is found that, with an increase of the electric field, the behavior of the energy shift can be grouped into two different modes for most QW states. In the first mode, the state energy moves toward high energy monotonically. In the second mode, the state energy shifts to a lower energy initially and then turns around to a higher energy. Moreover, we have observed that the QW states of higher energy behave in preference to the first mode, but they gradually change to the second mode as the Pb island becomes thicker. This thickness-dependent behavior reflects the existence of local expansion in the Pb islands, due to the electric field, and that the expansion is larger for a thicker island. QW states can thus be used for studying the localized lattice deformation in the nanometer scale.
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Affiliation(s)
- W Y Chan
- Institute of Physics, Academia Sinica, Nankang, Taipei 115, Taiwan
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Yang MC, Lin CL, Su WB, Lin SP, Lu SM, Lin HY, Chang CS, Hsu WK, Tsong TT. Phase contribution of image potential on empty quantum well States in pb islands on the cu(111) surface. PHYSICAL REVIEW LETTERS 2009; 102:196102. [PMID: 19518977 DOI: 10.1103/physrevlett.102.196102] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2009] [Indexed: 05/27/2023]
Abstract
We use scanning tunneling spectroscopy to explore the quantum well states in the Pb islands grown on a Cu(111) surface. Our observation demonstrates that the empty quantum well states, whose energy levels lie beyond 1.2 eV above the Fermi level, are significantly affected by the image potential. As the quantum number increases, the energy separation between adjacent states is shrinking rather than widening, contrary to the prediction for a square potential well. By simply introducing a phase factor to reckon the effect of the image potential, the shrinking behavior of the energy separation can be reasonably explained with the phase accumulation model. The model also reveals that there exists a quantum regime above the Pb surface in which the image potential is vanished. Moreover, the quasi-image-potential state in the tunneling gap is quenched because of the existence of the quantum well states.
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Affiliation(s)
- M C Yang
- Institute of Physics, Academia Sinica, Nankang, Taipei 115, Taiwan, ROC
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Chulkov EV, Borisov AG, Gauyacq JP, Sanchez-Portal D, Silkin VM, Zhukov VP, Echenique PM. Electronic Excitations in Metals and at Metal Surfaces. Chem Rev 2006; 106:4160-206. [PMID: 17031983 DOI: 10.1021/cr050166o] [Citation(s) in RCA: 208] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- E V Chulkov
- Departamento de Física de Materiales and Centro Mixto CSIC-UPV/EHU, Facultad de Ciencias Químicas, Universidad del País Vasco UPV/EHU, Apdo. 1072, 20080 San Sebastian/Donostia, Basque Country, Spain.
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Corriol C, Silkin VM, Sánchez-Portal D, Arnau A, Chulkov EV, Echenique PM, von Hofe T, Kliewer J, Kröger J, Berndt R. Role of elastic scattering in electron dynamics at ordered alkali overlayers on Cu(111). PHYSICAL REVIEW LETTERS 2005; 95:176802. [PMID: 16383854 DOI: 10.1103/physrevlett.95.176802] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2005] [Indexed: 05/05/2023]
Abstract
Scanning tunneling spectroscopy of p(2 x 2) Cs and Na ordered overlayers on Cu(111) reveals similar line widths of quasi-two-dimensional quantum well states despite largely different binding energies. Detailed calculations show that 50% of the line widths are due to electron-phonon scattering while inelastic electron-electron scattering is negligible. The mechanism of enhanced elastic scattering due to Brillouin zone backfolding contributes the remaining width.
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Affiliation(s)
- C Corriol
- Donostia International Physics Center, Paseo Manuel de Lardizabal 4, San Sebastian 20018, Spain
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