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Kato T, Nakayama K, Li Y, Wang Z, Sugawara K, Tanaka K, Takahashi T, Yao Y, Sato T. Quasi-Homoepitaxial Growth of Highly Strained Alkali-Metal Ultrathin Films on Kagome Superconductors. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2024:e2309003. [PMID: 38828764 DOI: 10.1002/advs.202309003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2024] [Revised: 04/12/2024] [Indexed: 06/05/2024]
Abstract
Applying lattice strain to thin films, a critical factor to tailor their properties such as stabilizing a structural phase unstable at ambient pressure, generally necessitates heteroepitaxial growth to control the lattice mismatch with substrate. Therefore, while homoepitaxy, the growth of thin film on a substrate made of the same material, is a useful method to fabricate high-quality thin films, its application to studying strain-induced structural phases is limited. Contrary to this general belief, here the quasi-homoepitaxial growth of Cs and Rb thin films is reported with substantial in-plane compressive strain. This is achieved by utilizing the alkali-metal layer existing in bulk crystal of kagome metals AV3Sb5 (A = Cs and Rb) as a structural template. The angle-resolved photoemission spectroscopy measurements reveal the formation of metallic quantum well states and notable thickness-dependent quasiparticle lifetime. Comparison with density functional theory calculations suggests that the obtained thin films crystalize in the face-centered cubic structure, which is typically stable only under high pressure in bulk crystals. These findings provide a useful approach for synthesizing highly strained thin films by quasi-homoepitaxy, and pave the way for investigating many-body interactions in Fermi liquids with tunable dimensionality.
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Affiliation(s)
- Takemi Kato
- Department of Physics, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan
| | - Kosuke Nakayama
- Department of Physics, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan
| | - Yongkai Li
- Centre for Quantum Physics, Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE), School of Physics, Beijing Institute of Technology, Beijing, 100081, P. R. China
- Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems, Beijing Institute of Technology, Beijing, 100081, P. R. China
- Material Science Center, Yangtze Delta Region Academy of Beijing Institute of Technology, Jiaxing, 314011, P. R. China
| | - Zhiwei Wang
- Centre for Quantum Physics, Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE), School of Physics, Beijing Institute of Technology, Beijing, 100081, P. R. China
- Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems, Beijing Institute of Technology, Beijing, 100081, P. R. China
- Material Science Center, Yangtze Delta Region Academy of Beijing Institute of Technology, Jiaxing, 314011, P. R. China
| | - Katsuaki Sugawara
- Department of Physics, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan
- Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency (JST), Tokyo, 102-0076, Japan
- Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Sendai, 980-8577, Japan
| | - Kiyohisa Tanaka
- UVSOR Synchrotron Facility, Institute for Molecular Science, Okazaki, 444-8585, Japan
- School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI), Okazaki, 444-8585, Japan
| | - Takashi Takahashi
- Department of Physics, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan
| | - Yugui Yao
- Centre for Quantum Physics, Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE), School of Physics, Beijing Institute of Technology, Beijing, 100081, P. R. China
- Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems, Beijing Institute of Technology, Beijing, 100081, P. R. China
| | - Takafumi Sato
- Department of Physics, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan
- Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Sendai, 980-8577, Japan
- Center for Science and Innovation in Spintronics (CSIS), Tohoku University, Sendai, 980-8577, Japan
- International Center for Synchrotron Radiation Innovation Smart (SRIS), Tohoku University, Sendai, 980-8577, Japan
- Mathematical Science Center for Co-creative Society (MathCCS), Tohoku University, Sendai, 980-8578, Japan
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2
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Chang K, Hu M, Lin H, Liu J, Xue QK, Chen X, Ji SH. Oscillation of Electronic-Band-Gap Size Induced by Crystalline Symmetry Change in Ultrathin PbTe Films. PHYSICAL REVIEW LETTERS 2023; 131:016202. [PMID: 37478437 DOI: 10.1103/physrevlett.131.016202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2022] [Accepted: 06/09/2023] [Indexed: 07/23/2023]
Abstract
For the semiconductors of atomic length scales, even one atom layer difference could modify crystal symmetry and lead to a significant change in electronic structure, which is essential for modern electronics. However, the experimental exploration of such effect has not been achieved due to challenges in sample fabrication and characterization with atomic-scale precision. Here, we report the discovery of crystal symmetry alternation induced band-gap oscillation in atomically thin PbTe films by scanning tunneling microscopy. As the thickness of PbTe films is reduced from an 18- to 2-atomic layer, the band-gap size not only expands from 0.19 eV to 1.06 eV by 5.6 fold, but also exhibits an even-odd-layer oscillation, which is attributed to the alternating crystal symmetries between P4/mmm and P4/nmm. Our work sheds new light on electronic structure engineering of semiconductors at atomic scale for next-generation nanoelectronics.
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Affiliation(s)
- Kai Chang
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
- Beijing Academy of Quantum Information Sciences, Beijing 100193, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100084, China
| | - Mengli Hu
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | - Haicheng Lin
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100084, China
| | - Junwei Liu
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | - Qi-Kun Xue
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
- Beijing Academy of Quantum Information Sciences, Beijing 100193, China
- Frontier Science Center for Quantum Information, Beijing 100084, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100084, China
| | - Xi Chen
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
- Frontier Science Center for Quantum Information, Beijing 100084, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100084, China
| | - Shuai-Hua Ji
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
- Frontier Science Center for Quantum Information, Beijing 100084, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100084, China
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3
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Zhang H, Weinert M, Li L. Giant Periodic Pseudomagnetic Fields in Strained Kagome Magnet FeSn Epitaxial Films on SrTiO 3(111) Substrate. NANO LETTERS 2023; 23:2397-2404. [PMID: 36912449 PMCID: PMC10037333 DOI: 10.1021/acs.nanolett.3c00345] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/09/2023] [Revised: 03/08/2023] [Indexed: 06/18/2023]
Abstract
Quantum materials, particularly Dirac materials with linearly dispersing bands, can be effectively tuned by strain-induced lattice distortions leading to a pseudomagnetic field that strongly modulates their electronic properties. Here, we grow kagome magnet FeSn films, consisting of alternatingly stacked Sn2 honeycomb (stanene) and Fe3Sn kagome layers, on SrTiO3(111) substrates by molecular beam epitaxy. Using scanning tunneling microscopy/spectroscopy, we show that the Sn honeycomb layer can be periodically deformed by epitaxial strain for a film thickness below 10 nm, resulting in differential conductance peaks consistent with Landau levels generated by a pseudomagnetic field greater than 1000 T. Our findings demonstrate the feasibility of strain engineering the electronic properties of topological magnets at the nanoscale.
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Affiliation(s)
- Huimin Zhang
- Department
of Physics and Astronomy, West Virginia
University, Morgantown, West Virginia 26506, United States
- State
Key Laboratory of Structural Analysis, Optimization and CAE Software
for Industrial Equipment, Dalian University
of Technology, Dalian, 116024, China
| | - Michael Weinert
- Department
of Physics, University of Wisconsin, Milwaukee, Wisconsin 53201, United States
| | - Lian Li
- Department
of Physics and Astronomy, West Virginia
University, Morgantown, West Virginia 26506, United States
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4
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Liu C, Zhao C, Zhong S, Chen C, Zhang Z, Jia Y, Wang J. Equally Spaced Quantum States in van der Waals Epitaxy-Grown Nanoislands. NANO LETTERS 2021; 21:9285-9292. [PMID: 34677982 DOI: 10.1021/acs.nanolett.1c03423] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Pursuing the confinement of linearly dispersive relativistic Fermions is of interest in both fundamental physics and potential applications. Here, we report strong STM evidence for the equally spaced, strikingly sharp, and densely distributed quantum well states (QWSs) near Fermi energy in Pb(111) nanoislands, van der Waals epitaxially grown on graphitized 6H-SiC(0001). The observations can be explained as the quantized energies of confined linearly dispersive [111] electrons, which essentially "simulate" the out-of-plane relativistic quasiparticles. The equally spaced QWSs with an origin of confined relativistic electrons are supported by phenomenological simulations and Fabry-Pérot fittings based on the relativistic Fermions. First-principles calculations further reveal that the spin-orbit coupling strengthens the relativistic nature of electrons near Fermi energy. Our finding uncovers the unique equally spaced quantum states in electronic systems beyond Landau levels and may inspire future studies on confined relativistic quasiparticles in flourishing topological materials and applications in structurally simpler quantum cascade laser.
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Affiliation(s)
- Chaofei Liu
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
| | - Chunxiang Zhao
- International Laboratory for Quantum Functional Materials of Henan, and School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450001, China
| | - Shan Zhong
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
| | - Cheng Chen
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
| | - Zhenyu Zhang
- International Center for Quantum Design of Functional Materials (ICQD), Hefei National Laboratory for Physical Sciences at Microscale, and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
| | - Yu Jia
- International Laboratory for Quantum Functional Materials of Henan, and School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450001, China
| | - Jian Wang
- International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
- CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China
- Beijing Academy of Quantum Information Sciences, Beijing 100193, China
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5
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Measuring the Electron–Phonon Interaction in Two-Dimensional Superconductors with He-Atom Scattering. CONDENSED MATTER 2020. [DOI: 10.3390/condmat5040079] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Helium-atom scattering (HAS) spectroscopy from conducting surfaces has been shown to provide direct information on the electron–phonon interaction, more specifically the mass-enhancement factor λ from the temperature dependence of the Debye–Waller exponent, and the mode-selected electron–phonon coupling constants λQν from the inelastic HAS intensities from individual surface phonons. The recent applications of the method to superconducting ultra-thin films, quasi-1D high-index surfaces, and layered transition-metal and topological pnictogen chalcogenides are briefly reviewed.
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6
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Späth T, Popp M, Hoffmann-Vogel R. Film Thickness of Pb Islands on the Si(111) Surface. PHYSICAL REVIEW LETTERS 2020; 124:016101. [PMID: 31976694 DOI: 10.1103/physrevlett.124.016101] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2018] [Revised: 08/27/2019] [Indexed: 06/10/2023]
Abstract
We analyze topographic scanning force microscopy images together with Kelvin probe images obtained on Pb islands and on the wetting layer on Si(111) for variable annealing times. Within the wetting layer we observe negatively charged Si-rich areas. We show evidence that these Si-rich areas result from islands that have disappeared by coarsening. We argue that the islands are located on Si-rich areas inside the wetting layer such that the Pb/Si interface of the islands is in line with the top of the wetting layer rather than with its interface to the substrate. We propose that the Pb island heights are one atomic layer smaller than previously believed. For the quantum size effect bilayer oscillations of the work function observed in this system, we conclude that for film thicknesses below 9 atomic layers large values of the work function correspond to even numbers of monolayers instead of odd ones. The atomically precise island height is important to understand ultrafast "explosive" island growth in this system.
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Affiliation(s)
- Th Späth
- Physikalisches Institut, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany
| | - M Popp
- Physikalisches Institut, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany
| | - R Hoffmann-Vogel
- Department of Physics, University of Konstanz, Universitätsstrasse 10, 78464 Konstanz, Germany
- Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, 14476 Potsdam, Germany
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7
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Trang CX, Shimamura N, Nakayama K, Souma S, Sugawara K, Watanabe I, Yamauchi K, Oguchi T, Segawa K, Takahashi T, Ando Y, Sato T. Conversion of a conventional superconductor into a topological superconductor by topological proximity effect. Nat Commun 2020; 11:159. [PMID: 31919356 PMCID: PMC6952357 DOI: 10.1038/s41467-019-13946-0] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2019] [Accepted: 12/10/2019] [Indexed: 12/03/2022] Open
Abstract
Realization of topological superconductors (TSCs) hosting Majorana fermions is a central challenge in condensed-matter physics. One approach is to use the superconducting proximity effect (SPE) in heterostructures, where a topological insulator contacted with a superconductor hosts an effective p-wave pairing by the penetration of Cooper pairs across the interface. However, this approach suffers a difficulty in accessing the topological interface buried deep beneath the surface. Here, we propose an alternative approach to realize topological superconductivity without SPE. In a Pb(111) thin film grown on TlBiSe2, we discover that the Dirac-cone state of substrate TlBiSe2 migrates to the top surface of Pb film and obtains an energy gap below the superconducting transition temperature of Pb. This suggests that a Bardeen-Cooper-Schrieffer superconductor is converted into a TSC by the topological proximity effect. Our discovery opens a route to manipulate topological superconducting properties of materials. Realizing topological superconductivity is essential for applicable fault-tolerant quantum computation. Here, Trang et al. report migration of Dirac-cone from TlBiSe2 substrate to top surface of superconducting Pb film due to topological proximity effect, suggesting realization of topological superconductivity.
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Affiliation(s)
- C X Trang
- Department of Physics, Tohoku University, Sendai, 980-8578, Japan
| | - N Shimamura
- Department of Physics, Tohoku University, Sendai, 980-8578, Japan
| | - K Nakayama
- Department of Physics, Tohoku University, Sendai, 980-8578, Japan.,Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency (JST), Tokyo, 102-0076, Japan
| | - S Souma
- Center for Spintronics Research Network, Tohoku University, Sendai, 980-8577, Japan.,WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai, 980-8577, Japan
| | - K Sugawara
- Department of Physics, Tohoku University, Sendai, 980-8578, Japan.,Center for Spintronics Research Network, Tohoku University, Sendai, 980-8577, Japan.,WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai, 980-8577, Japan
| | - I Watanabe
- Department of Physics, Tohoku University, Sendai, 980-8578, Japan
| | - K Yamauchi
- Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka, 567-0047, Japan
| | - T Oguchi
- Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka, 567-0047, Japan
| | - K Segawa
- Department of Physics, Kyoto Sangyo University, Kyoto, 603-8555, Japan
| | - T Takahashi
- Department of Physics, Tohoku University, Sendai, 980-8578, Japan.,Center for Spintronics Research Network, Tohoku University, Sendai, 980-8577, Japan.,WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai, 980-8577, Japan
| | - Yoichi Ando
- Institute of Physics II, University of Cologne, Köln, 50937, Germany
| | - T Sato
- Department of Physics, Tohoku University, Sendai, 980-8578, Japan. .,Center for Spintronics Research Network, Tohoku University, Sendai, 980-8577, Japan. .,WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai, 980-8577, Japan.
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8
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Li BH, Zhang GH, Liang Y, Hao QQ, Sun JL, Zhou CY, Tao YT, Yang XM, Ren ZF. Femtosecond time-resolved spectroscopic photoemission electron microscopy for probing ultrafast carrier dynamics in heterojunctions. CHINESE J CHEM PHYS 2019. [DOI: 10.1063/1674-0068/cjcp1903044] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Affiliation(s)
- Bo-han Li
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Guan-hua Zhang
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
| | - Yu Liang
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
- Key Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials (IAM), Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University, Nanjing 211816, China
| | - Qun-qing Hao
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
| | - Ju-long Sun
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
| | - Chuan-yao Zhou
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
| | - You-tian Tao
- Key Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials (IAM), Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University, Nanjing 211816, China
| | - Xue-ming Yang
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
- Department of Chemistry, Southern University of Science and Technology, Shenzhen 518055, China
| | - Ze-feng Ren
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
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9
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Benedek G, Miret-Artés S, Toennies JP, Manson JR. Electron-Phonon Coupling Constant of Metallic Overlayers from Specular He Atom Scattering. J Phys Chem Lett 2018; 9:76-83. [PMID: 29240430 DOI: 10.1021/acs.jpclett.7b03047] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
He atom scattering has been shown to be a sensitive probe of electron-phonon interaction properties at surfaces. Here it is shown that measurements of the thermal attenuation of the specular He atom diffraction peak (the Debye-Waller effect) can determine the electron-phonon coupling constant, λ, for ultrathin films of metal overlayers on various close-packed metal substrates. Values of λ obtained for single and multiple monolayers of alkali metals, and for Pb layers on Cu(111), extrapolated to large thicknesses, agree favorably with known bulk values. This demonstrates that He atom scattering can measure the electron-phonon coupling strength as a function of film thickness on a layer-by-layer basis.
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Affiliation(s)
- G Benedek
- Donostia International Physics Center (DIPC) , Paseo Manuel de Lardizabal, 4, 20018 Donostia-San Sebastian, Spain
- Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca , Via Cozzi 53, 20125 Milano, Italy
| | - Salvador Miret-Artés
- Donostia International Physics Center (DIPC) , Paseo Manuel de Lardizabal, 4, 20018 Donostia-San Sebastian, Spain
- Instituto de Física Fundamental, Consejo Superior de Investigaciones Científicas , Serrano 123, 28006 Madrid, Spain
| | - J P Toennies
- Max Planck Institüt für Dynamik und Selbstorganisation , Am Fassberg 17, 37077 Göttingen, Germany
| | - J R Manson
- Donostia International Physics Center (DIPC) , Paseo Manuel de Lardizabal, 4, 20018 Donostia-San Sebastian, Spain
- Department of Physics and Astronomy, Clemson University , Clemson, South Carolina 29634, United States
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10
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Formation of Surface and Quantum-Well States in Ultra Thin Pt Films on the Au(111) Surface. MATERIALS 2017; 10:ma10121409. [PMID: 29232833 PMCID: PMC5744344 DOI: 10.3390/ma10121409] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/21/2017] [Revised: 12/05/2017] [Accepted: 12/07/2017] [Indexed: 12/22/2022]
Abstract
The electronic structure of the Pt/Au(111) heterostructures with a number of Pt monolayers n ranging from one to three is studied in the density-functional-theory framework. The calculations demonstrate that the deposition of the Pt atomic thin films on gold substrate results in strong modifications of the electronic structure at the surface. In particular, the Au(111) s-p-type Shockley surface state becomes completely unoccupied at deposition of any number of Pt monolayers. The Pt adlayer generates numerous quantum-well states in various energy gaps of Au(111) with strong spatial confinement at the surface. As a result, strong enhancement in the local density of state at the surface Pt atomic layer in comparison with clean Pt surface is obtained. The excess in the density of states has maximal magnitude in the case of one monolayer Pt adlayer and gradually reduces with increasing number of Pt atomic layers. The spin-orbit coupling produces strong modification of the energy dispersion of the electronic states generated by the Pt adlayer and gives rise to certain quantum states with a characteristic Dirac-cone shape.
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11
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Imboden M, Han H, Stark T, Bishop D. Cryogenic Fab-on-a-Chip Sticks the Landing. ACS NANO 2017; 11:8707-8716. [PMID: 28759197 DOI: 10.1021/acsnano.7b01808] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Using a microelectromechanical systems (MEMS)-based Fab-on-a-Chip, we quench-condense lead thin-films. Suppressing the formation of lead islands makes it possible to grow a homogeneous and continuous film as thin as 2 nm, without the use of an adhesion layer. Thermal cycling from 3 K to as low as 10 K reveals irreversible annealing of the thin-film characteristic of a metastable state. The transition to the stable state is smooth and is completed by cycling the temperature above ∼42 K, where a distinctive resistance minimum is observed. This resistive minimum is accompanied by an unexpected peak in the superconducting transition temperature. After further thermal cycling, the standard metallic/superconductive behavior is established. The MEMS-based approach yields a platform for systematic studies of quench-condensed thin-film materials, making an intriguing parameter space of mesoscopic physics experimentally accessible.
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Affiliation(s)
- Matthias Imboden
- École Polytechnique Fédérale de Lausanne , Neuchâtel NE 2002, Switzerland
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12
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Observation of enhanced superconductivity in the vicinity of Ar-induced nano-cavities in Pb(111). Sci Rep 2017; 7:12177. [PMID: 28939806 PMCID: PMC5610268 DOI: 10.1038/s41598-017-12505-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Accepted: 09/11/2017] [Indexed: 11/24/2022] Open
Abstract
Local variations of superconductivity have been studied using scanning tunneling microscopy around nano-cavities formed by Ar ions embedded in Pb(111). Various factors including the density of states at Fermi energy, electron–phonon couplings, and quantum well states, which are known to affect superconductivity, have been examined. We show that the superconductivity is enhanced near the nano-cavities and propose that quantum effects such as quantum confinement, proximity effect and multi-gap effect are possibly involved in determining the superconducting gap of this system. These results have important implications for the characterization and understanding of superconductivity at a nanometer scale.
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13
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Späth T, Popp M, Pérez León C, Marz M, Hoffmann-Vogel R. Near-equilibrium measurement of quantum size effects using Kelvin probe force microscopy. NANOSCALE 2017; 9:7868-7874. [PMID: 28555693 DOI: 10.1039/c7nr01874f] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
In nano-structures such as thin films electron confinement results in the quantization of energy levels in the direction perpendicular to the film. The discretization of the energy levels leads to the oscillatory dependence of many properties on the film thickness due to quantum size effects. Pb on Si(111) is a specially interesting system because a particular relationship between the Pb atomic layer thickness and its Fermi wavelength leads to a periodicity of the oscillation of two atomic layers. Here, we demonstrate how the combination of scanning force microscopy (SFM) and Kelvin probe force microscopy (KPFM) provides a reliable method to monitor the quantum oscillations in the work function of Pb ultra-thin film nano-structures on Si(111). Unlike other techniques, with SFM/KPFM we directly address single Pb islands, determine their height while suppressing the influence of electrostatic forces, and, in addition, simultaneously evaluate their local work function by measurements close to equilibrium, without current-dependent and non-equilibrium effects. Our results evidence even-odd oscillations in the work function as a function of the film thickness that decay linearly with the film thickness, proving that this method provides direct and precise information on the quantum states.
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Affiliation(s)
- Thomas Späth
- Physikalisches Institut, Karlsruhe Institute of Technology (KIT), Wolfgang-Gaede-Str. 1, 76128 Karlsruhe, Germany.
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14
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Li C, Yi S, Xia C, Cui P, Niu C, Cho JH, Jia Y, Zhang Z. Dimensionality and Valency Dependent Quantum Growth of Metallic Nanostructures: A Unified Perspective. NANO LETTERS 2016; 16:6628-6635. [PMID: 27685453 DOI: 10.1021/acs.nanolett.6b03351] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Quantum growth refers to the phenomena in which the quantum mechanically confined motion of electrons in metallic wires, islands, and films determines their overall structural stability as well as their physical and chemical properties. Yet to date, there has been a lack of a unified understanding of quantum growth with respect to the dimensionality of the nanostructures as well as the valency of the constituent atoms. Based on a first-principles approach, we investigate the stability of nanowires, nanoislands, and ultrathin films of prototypical metal elements. We reveal that the Friedel oscillations generated at the edges (or surfaces) of the nanostructures cause corresponding oscillatory behaviors in their stability, leading to the existence of highly preferred lengths (or thicknesses). Such magic lengths of the nanowires are further found to depend on both the number of valence electrons and the radial size, with the oscillation period monotonously increasing for alkali and group IB metals, and monotonously decreasing for transition and group IIIA-VA metals. When the radial size of the nanowires increases to reach ∼10 Å, the systems equivalently become nanosize islands, and the oscillation period saturates to that of the corresponding ultrathin films. These findings offer a generic perspective of quantum growth of different classes of metallic nanostructures.
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Affiliation(s)
- Chenhui Li
- International Laboratory for Quantum Functional Materials of Henan, and School of Physics and Engineering, Zhengzhou University , Zhengzhou 450001, China
| | - Seho Yi
- Department of Physics and Research Institute for Natural Sciences, Hanyang University , 17 Haengdang-Dong, Seongdong-Ku, Seoul 133-791, Korea
| | - Congxin Xia
- College of Physics and Materials Science, Henan Normal University , Xinxiang 453000, China
| | - Ping Cui
- International Center for Quantum Design of Functional Materials (ICQD), Hefei National Laboratory for Physical Sciences at the Microscale, and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China , Hefei, Anhui 230026, P. R. China
| | - Chunyao Niu
- International Laboratory for Quantum Functional Materials of Henan, and School of Physics and Engineering, Zhengzhou University , Zhengzhou 450001, China
| | - Jun-Hyung Cho
- International Laboratory for Quantum Functional Materials of Henan, and School of Physics and Engineering, Zhengzhou University , Zhengzhou 450001, China
- Department of Physics and Research Institute for Natural Sciences, Hanyang University , 17 Haengdang-Dong, Seongdong-Ku, Seoul 133-791, Korea
- International Center for Quantum Design of Functional Materials (ICQD), Hefei National Laboratory for Physical Sciences at the Microscale, and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China , Hefei, Anhui 230026, P. R. China
| | - Yu Jia
- International Laboratory for Quantum Functional Materials of Henan, and School of Physics and Engineering, Zhengzhou University , Zhengzhou 450001, China
- Key Laboratory for Special Functional Materials of Ministry of Education, and School of Physics and Electronics, Henan University , Kaifeng 475004, China
| | - Zhenyu Zhang
- International Center for Quantum Design of Functional Materials (ICQD), Hefei National Laboratory for Physical Sciences at the Microscale, and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China , Hefei, Anhui 230026, P. R. China
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15
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Manson JR, Benedek G, Miret-Artés S. Electron-Phonon Coupling Strength at Metal Surfaces Directly Determined from the Helium Atom Scattering Debye-Waller Factor. J Phys Chem Lett 2016; 7:1016-1021. [PMID: 26927966 DOI: 10.1021/acs.jpclett.6b00139] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
A new quantum-theoretical derivation of the elastic and inelastic scattering probability of He atoms from a metal surface, where the energy and momentum exchange with the phonon gas can occur only through the mediation of the surface free-electron density, shows that the Debye-Waller exponent is directly proportional to the electron-phonon mass coupling constant λ. The comparison between the values of λ extracted from existing data on the Debye-Waller factor for various metal surfaces and the λ values known from literature indicates a substantial agreement, which opens the possibility of directly extracting the electron-phonon coupling strength in quasi-2D conducting systems from the temperature or incident energy dependence of the elastic helium atom scattering intensities.
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Affiliation(s)
- J R Manson
- Department of Physics and Astronomy, Clemson University , Clemson, South Carolina 29634, United States
- Donostia International Physics Center (DIPC) , Paseo Manuel de Lardizabal, 4 20018 Donostia-San Sebastian, Spain
| | - G Benedek
- Donostia International Physics Center (DIPC) , Paseo Manuel de Lardizabal, 4 20018 Donostia-San Sebastian, Spain
- Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca , Via Cozzi 53, 20125 Milano, Italy
| | - Salvador Miret-Artés
- Donostia International Physics Center (DIPC) , Paseo Manuel de Lardizabal, 4 20018 Donostia-San Sebastian, Spain
- Instituto de Física Fundamental , Consejo Superior de Investigaciones Científicas, Serrano 123, 28006 Madrid, Spain
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16
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Schackert M, Märkl T, Jandke J, Hölzer M, Ostanin S, Gross EKU, Ernst A, Wulfhekel W. Local measurement of the Eliashberg function of Pb islands: enhancement of electron-phonon coupling by quantum well states. PHYSICAL REVIEW LETTERS 2015; 114:047002. [PMID: 25679904 DOI: 10.1103/physrevlett.114.047002] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Indexed: 06/04/2023]
Abstract
Inelastic tunneling spectroscopy of Pb islands on Cu(111) obtained by scanning tunneling microscopy below 1 K provides a direct access to the local Eliashberg function of the islands with high energy resolution. The Eliashberg function describes the electron-phonon interaction causing conventional superconductivity. The measured Eliashberg function strongly depends on the local thickness of the Pb nanostructures and shows a sharp maximum when quantum well states of the Pb islands come close to the Fermi energy. Ab initio calculations reveal that this is related to enhanced electron-phonon coupling at these thicknesses.
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Affiliation(s)
- Michael Schackert
- Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Straße 1, 76131 Karlsruhe, Germany
| | - Tobias Märkl
- Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Straße 1, 76131 Karlsruhe, Germany
| | - Jasmin Jandke
- Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Straße 1, 76131 Karlsruhe, Germany
| | - Martin Hölzer
- Max-Planck Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle, Germany
| | - Sergey Ostanin
- Max-Planck Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle, Germany
| | - Eberhard K U Gross
- Max-Planck Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle, Germany
| | - Arthur Ernst
- Max-Planck Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle, Germany and Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie, Universität Leipzig, Linnéstraße 2, 04103 Leipzig, Germany
| | - Wulf Wulfhekel
- Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Straße 1, 76131 Karlsruhe, Germany
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17
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Wójcik P, Zegrodnik M. Quantum size effect on the paramagnetic critical field in free-standing superconducting nanofilms. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:455302. [PMID: 25318561 DOI: 10.1088/0953-8984/26/45/455302] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The quantum size effect on the in-plane paramagnetic critical field in Pb(1 1 1) free-standing nanofilms is investigated with the use of the spin-generalized Bogoliubov-de Gennes equations. It is shown that the critical field oscillates as a function of the nanofilm thickness with the period ∼ 2 ML (even-odd oscillations), modulated by the beating effect. The calculated values of the critical field for different nanofilm thicknesses are analyzed in the context of the Clogston-Chandrasekhar limit. It is found that the critical field for superconducting nanofilms differs from this limit. This phenomena is explained in terms of quantization of the electron energy caused by the confinement of electron motion in a direction perpendicular to the film. The thermal effect and thickness-dependence of electron-phonon coupling on the value of the critical magnetic field are also studied.
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Affiliation(s)
- P Wójcik
- AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, al. A. Mickiewicza 30, Kraków, Poland
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18
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Ligges M, Sandhofer M, Sklyadneva I, Heid R, Bohnen KP, Freutel S, Rettig L, Zhou P, Echenique PM, Chulkov EV, Bovensiepen U. Electron-phonon coupling in quantum-well states of the Pb/Si(1 1 1) system. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:352001. [PMID: 25115690 DOI: 10.1088/0953-8984/26/35/352001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The electron-phonon coupling parameters in the vicinity of the Γ point, λ(Γ), for electronic quantum well states in epitaxial lead films on a Si(1 1 1) substrate are measured using 5, 7 and 12 ML films and femtosecond laser photoemission spectroscopy. The λ (Γ) values in the range of 0.6-0.9 were obtained by temperature-dependent line width analysis of occupied quantum well states and found to be considerably smaller than the momentum averaged electron-phonon coupling at the Fermi level of bulk lead, (λ = 1.1-1.7). The results are compared to density functional theory calculations of the lead films with and without interfacial stress. It is shown that the discrepancy can not be explained by means of confinement effects or simple structural modifications of the Pb films and, thus, is attributed to the influence of the substrate on the Pb electronic and vibrational structures.
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Affiliation(s)
- M Ligges
- Fakultät für Physik und Zentrum für Nanointegration (CENIDE), Universität Duisburg-Essen, Lotharstr. 1, 47048 Duisburg, Germany
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19
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Huang GQ, Yang J. Surface lattice dynamics and electron-phonon interaction in ultrathin Bi(111) film. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:175004. [PMID: 23552259 DOI: 10.1088/0953-8984/25/17/175004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The surface phonon and electron-phonon interactions in the two-dimensional topological insulator Bi(111) film are calculated, including the spin-orbit coupling from density-functional perturbation theory. By analyzing the zone-center phonons, an anomalous phonon hardening of two Raman modes, Eg and A1g, in ultrathin films is found and is explained by considering the redistribution of the charge density on the surface of the semimetallic Bi. Surface phonon band structures and the surface phonon density of states are given, and we find that softening and hardening of surface phonon modes occur simultaneously in ultrathin Bi film, but the softening may dominate over the hardening. The calculated electron-phonon coupling constant λ for Bi(111) film is much larger than that for the bulk, which might induce surface-localized superconductivity in this two-dimensional topological insulator.
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Affiliation(s)
- G Q Huang
- Department of Physics and Institute of Theoretical Physics, Nanjing Normal University, Nanjing 210023, People's Republic of China
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20
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Altfeder I, Matveev KA, Voevodin AA. Imaging the electron-phonon interaction at the atomic scale. PHYSICAL REVIEW LETTERS 2012; 109:166402. [PMID: 23215098 DOI: 10.1103/physrevlett.109.166402] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2012] [Indexed: 06/01/2023]
Abstract
Thin Pb films epitaxially grown on 7×7 reconstructed Si(111) represent an ideal model system for studying the electron-phonon interaction at the metal-insulator interface. For this system, using a combination of scanning tunneling microscopy and inelastic electron tunneling spectroscopy, we performed direct real-space imaging of the electron-phonon coupling parameter. We found that λ increases when the electron scattering at the Pb/Si(111) interface is diffuse and decreases when the electron scattering is specular. We show that the effect is driven by transverse redistribution of the electron density inside a quantum well.
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Affiliation(s)
- Igor Altfeder
- Nanoelectronic Materials Branch, Air Force Research Laboratory, Wright Patterson AFB, Ohio 45433, USA.
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21
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Tong C, Yoon SF, Wang L. Large size self-assembled quantum rings: quantum size effect and modulation on the surface diffusion. NANOSCALE RESEARCH LETTERS 2012; 7:520. [PMID: 23006618 PMCID: PMC3502451 DOI: 10.1186/1556-276x-7-520] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/23/2012] [Accepted: 09/18/2012] [Indexed: 06/01/2023]
Abstract
We demonstrate experimentally the submicron size self-assembled (SA) GaAs quantum rings (QRs) by quantum size effect (QSE). An ultrathin In0.1 Ga0.9As layer with different thickness is deposited on the GaAs to modulate the surface nucleus diffusion barrier, and then the SA QRs are grown. It is found that the density of QRs is affected significantly by the thickness of inserted In0.1 Ga0.9As, and the diffusion barrier modulation reflects mainly on the first five monolayer . The physical mechanism behind is discussed. The further analysis shows that about 160 meV decrease in diffusion barrier can be achieved, which allows the SA QRs with density of as low as one QR per 6 μm2. Finally, the QRs with diameters of 438 nm and outer diameters of 736 nm are fabricated using QSE.
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Affiliation(s)
- Cunzhu Tong
- State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun, 130033, China
| | - Soon Fatt Yoon
- School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, 639798, Singapore
| | - Lijun Wang
- State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun, 130033, China
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22
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Qi Y, Eskelsen JR, Mazur U, Hipps KW. Fabrication of graphene with CuO islands by chemical vapor deposition. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:3489-3493. [PMID: 22233199 DOI: 10.1021/la2048163] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Graphene prepared on Cu foil by chemical vapor deposition was studied as a function of post growth cooling conditions. CuO islands embedded in the graphene film were discovered and studied by scanning electron microscopy, atomic force microscopy, and X-ray photoemission spectroscopy. It is shown that nanostructured holes can be formed within a graphene film by reduction using hydrogen cooling immediately after film growth. We also observe the formation of symmetrical oxide islands in these holes. This study provides an easy way to fabricate a graphene + CuO composite, and the method may be extended to other graphene based structures.
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Affiliation(s)
- Yun Qi
- Materials Science and Engineering Program and Department of Chemistry, Washington State University, Pullman, Washington 99164-4630, USA.
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23
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Pan S, Liu Q, Ming F, Wang K, Xiao X. Interface effects on the quantum well states of Pb thin films. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:485001. [PMID: 22034437 DOI: 10.1088/0953-8984/23/48/485001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Using scanning tunneling spectroscopy, we have studied the interface effect on quantum well states of Pb thin films grown on various metal-terminated (Pb, Ag, and Au) n-type Si(111) surfaces and on two different p-type Si(111) surfaces. The dispersion relation E(k) of the electrons of the Pb film and the phase shift at the substrate interface were determined by applying the quantization rule to the measured energy positions of the quantum well states. Characteristic features in the phase shift versus energy curves were identified and were correlated to the directional conduction band of the silicon substrate and to the Schottky barrier formed between the metal film and the semiconductor. A model involving the band structure of the substrate, the Schottky barrier, and the effective thickness of the interface was introduced to qualitatively but comprehensively explain all the observed features of the phase shift at the substrate interface. Our physical understanding of the phase shift is critically important for using interface modification to control the quantum well states.
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Affiliation(s)
- Shuan Pan
- Department of Physics, The Chinese University of Hong Kong, Shatin, NT, Hong Kong
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24
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Liu Y, Miller T, Chiang TC. Electronic structure and trilayer growth of indium films on Si(111): a photoemission study. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:365302. [PMID: 21865634 DOI: 10.1088/0953-8984/23/36/365302] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We report on the preferred trilayer growth of indium films on Si(111) studied by angle-resolved photoemission spectroscopy. By employing an interfactant and optimized annealing conditions, the kinetic constraint on the In atoms due to the substrate is greatly reduced and 'electronic growth'-where film morphology is controlled by the quantized electronic structure of the film-can be achieved at low coverage. Our photoemission spectra reveal that films of 4 ML (monolayers) and 7 ML thicknesses are energetically favored due to a lower surface energy, as confirmed by theoretical calculations. A detailed comparison of the photoemission spectra between In films grown on the In-√3 × √3/Si(111) surface and those on the Si(111) 7 × 7 surface shows that the √3 × √3 interfactant is a better template for growing In films at low coverage and effectively reduces the electronic coupling between the film and the substrate. In addition, the observed band structures of In films are in reasonable agreement with first-principles calculations and suggest that In films grown on the √3 × √3 interfactant might already be close to the bulk-like body-centered tetragonal structure at around 10 ML.
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Affiliation(s)
- Y Liu
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801-3080, USA
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25
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Bose S, García-García AM, Ugeda MM, Urbina JD, Michaelis CH, Brihuega I, Kern K. Observation of shell effects in superconducting nanoparticles of Sn. NATURE MATERIALS 2010; 9:550-554. [PMID: 20512156 DOI: 10.1038/nmat2768] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2010] [Accepted: 04/16/2010] [Indexed: 05/29/2023]
Abstract
In a zero-dimensional superconductor, quantum size effects (QSE) not only set the limit to superconductivity, but are also at the heart of new phenomena such as shell effects, which have been predicted to result in large enhancements of the superconducting energy gap. Here, we experimentally demonstrate these QSE through measurements on single, isolated Pb and Sn nanoparticles. In both systems superconductivity is ultimately quenched at sizes governed by the dominance of the quantum fluctuations of the order parameter. However, before the destruction of superconductivity, in Sn nanoparticles we observe giant oscillations in the superconducting energy gap with particle size leading to enhancements as large as 60%. These oscillations are the first experimental proof of coherent shell effects in nanoscale superconductors. Contrarily, we observe no such oscillations in the gap for Pb nanoparticles, which is ascribed to the suppression of shell effects for shorter coherence lengths. Our study paves the way to exploit QSE in boosting superconductivity in low-dimensional systems.
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26
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Hu Z, Yang Y, Sun B, Shao X, Wang W, Zhang P. Quantum oscillations in adsorption energetics of atomic oxygen on Pb(111) ultrathin films: A density-functional theory study. J Chem Phys 2010; 132:024703. [DOI: 10.1063/1.3277674] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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27
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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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28
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Wang J, Ma XC, Qi Y, Fu YS, Ji SH, Lu L, Xie XC, Jia JF, Chen X, Xue QK. An unusual magnetoresistance effect in the heterojunction structure of an ultrathin single-crystal Pb film on silicon substrate. NANOTECHNOLOGY 2008; 19:475708. [PMID: 21836289 DOI: 10.1088/0957-4484/19/47/475708] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Superconductor films on semiconductor substrates have drawn much attention recently since the derived superconductor-based electronics have been shown to be promising for future data processing and storage technologies. By growing atomically uniform single-crystal epitaxial Pb films of several nanometers thick on Si wafers to form a sharp superconductor-semiconductor heterojunction, we have obtained an unusual magnetoresistance effect when the Pb film is superconducting. In addition to the large fundamental interest in this effect, the simple structure, and compatibility and scalability with current Si-based semiconductor technology offer a great opportunity for integrating superconducting circuits and detectors in a single chip.
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Affiliation(s)
- Jian Wang
- Institute of Physics, Chinese Academy of Sciences, Beijing 100080, People's Republic of China. The Center for Nanoscale Science and Department of Physics, Pennsylvania State University, University Park, PA 16802-6300, USA
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29
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Zhang Z, Zhang Y, Fu Q, Zhang H, Yao Y, Ma T, Tan D, Xue Q, Bao X. Modulation of surface reactivity via electron confinement in metal quantum well films: O2 adsorption on Pb∕Si(111). J Chem Phys 2008; 129:014704. [DOI: 10.1063/1.2919992] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
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30
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Yndurain F, Jigato MP. First principles calculation of localized surface phonons and electron-phonon interaction at pb(111) thin films. PHYSICAL REVIEW LETTERS 2008; 100:205501. [PMID: 18518552 DOI: 10.1103/physrevlett.100.205501] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2007] [Indexed: 05/26/2023]
Abstract
A first principles calculation of the vibrational modes of Pb(111) thin films of thickness up to 14 layers reveals the existence of localized vibrational modes at the slab's surface. Both longitudinal and transverse surface modes localized a few atomic layers are found at energies above the bulk bands. The frequency of these modes presents a bilayer oscillatory behavior. The electron-phonon interaction of the slab's quantum well states is also calculated. We find a large (small) deformation potential for the lowest unoccupied (highest occupied) quantum well state. Its absolute value is also oscillatory with the number of layers.
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Affiliation(s)
- Felix Yndurain
- Departamento de Física de la Materia Condensada and Instituto de Ciencia de Materiales Nicolás Cabrera, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain.
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31
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Yang Y, Zhou G, Wu J, Duan W, Xue QK, Gu BL, Jiang P, Ma X, Zhang SB. The adsorption of O2 on Pb films and the effect of quantum modulation: A first-principles prediction. J Chem Phys 2008; 128:164705. [DOI: 10.1063/1.2905210] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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32
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Fu YS, Ji SH, Chen X, Ma XC, Wu R, Wang CC, Duan WH, Qiu XH, Sun B, Zhang P, Jia JF, Xue QK. Manipulating the Kondo resonance through quantum size effects. PHYSICAL REVIEW LETTERS 2007; 99:256601. [PMID: 18233541 DOI: 10.1103/physrevlett.99.256601] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2007] [Indexed: 05/25/2023]
Abstract
Manipulating the Kondo effect by quantum confinement has been achieved by placing magnetic molecules on silicon-supported nanostructures. The Kondo resonance of individual manganese phthalocyanine (MnPc) molecules adsorbed on the top of Pb islands was studied by scanning tunneling spectroscopy. Oscillating Kondo temperatures as a function of film thickness were observed and attributed to the formation of the thickness-dependent quantum-well states in the host Pb islands. The present approach provides a technologically feasible way for single spin manipulation by precise thickness control of thin films.
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Affiliation(s)
- Ying-Shuang Fu
- Department of Physics, Tsinghua University, Beijing 100084, China
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33
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Ma X, Jiang P, Qi Y, Jia J, Yang Y, Duan W, Li WX, Bao X, Zhang SB, Xue QK. Experimental observation of quantum oscillation of surface chemical reactivities. Proc Natl Acad Sci U S A 2007; 104:9204-8. [PMID: 17517632 PMCID: PMC1874227 DOI: 10.1073/pnas.0611024104] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Here we present direct observation of a quantum reactivity with respect to the amounts of O(2) adsorbed and the rates of surface oxidation as a function of film thickness on ultrathin (2-6 nm) Pb mesas by scanning tunneling microscopy. Simultaneous spectroscopic measurements on the electronic structures reveal a quantum oscillation that originates from quantum well states of the mesas, as a generalization of the Fabry-Pérot modes of confined electron waves. We expect the quantum reactivity to be a general phenomenon for most ultrathin metal films with broad implications, such as nanostructure tuning of surface reactivities and rational design of heterogeneous catalysts.
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Affiliation(s)
- Xucun Ma
- Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China
| | - Peng Jiang
- Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China
| | - Yun Qi
- Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China
| | - Jinfeng Jia
- Department of Physics, Tsinghua University, Beijing 100084, China
| | - Yu Yang
- Department of Physics, Tsinghua University, Beijing 100084, China
| | - Wenhui Duan
- Department of Physics, Tsinghua University, Beijing 100084, China
| | - Wei-Xue Li
- Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China; and
| | - Xinhe Bao
- Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China; and
| | - S. B. Zhang
- National Renewable Energy Laboratory, Golden, CO 80401
| | - Qi-Kun Xue
- Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China
- Department of Physics, Tsinghua University, Beijing 100084, China
- To whom correspondence should be addressed: E-mail:
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34
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Ma LY, Tang L, Guan ZL, He K, An K, Ma XC, Jia JF, Xue QK, Han Y, Huang S, Liu F. Quantum size effect on adatom surface diffusion. PHYSICAL REVIEW LETTERS 2006; 97:266102. [PMID: 17280431 DOI: 10.1103/physrevlett.97.266102] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2006] [Indexed: 05/13/2023]
Abstract
Using scanning tunneling microscopy, we demonstrate that the nucleation density of Fe islands on the surface of nanoscale Pb films oscillates with the film thickness, providing a direct manifestation of the quantum size effect on surface diffusion. The Fe adatom diffusion barriers were derived to be 204+/-5 and 187+/-5 meV on a 21 and 26 monolayer (ML) Pb film, respectively, by matching the kinetic Monte Carlo simulations to the experimental island densities. The effect is further illustrated by the growth of Fe islands on wedged Pb films, where the Fe island density is consistently higher on the odd-layer films than on the even-layer films in the thickness range of 11 to 15 ML.
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Affiliation(s)
- Li-Ying Ma
- Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China
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35
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Mathias S, Wiesenmayer M, Aeschlimann M, Bauer M. Quantum-well wave-function localization and the electron-phonon interaction in thin Ag nanofilms. PHYSICAL REVIEW LETTERS 2006; 97:236809. [PMID: 17280230 DOI: 10.1103/physrevlett.97.236809] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2006] [Revised: 10/20/2006] [Indexed: 05/13/2023]
Abstract
The electron-phonon interaction in thin Ag nanofilms epitaxially grown on Cu(111) is investigated by temperature-dependent and angle-resolved photoemission from silver quantum-well states. Clear oscillations in the electron-phonon coupling parameter as a function of the silver film thickness are observed. Different from other thin film systems where quantum oscillations are related to the Fermi-level crossing of quantum-well states, we can identify a new mechanism behind these oscillations, based on the wave-function localization of the quantum-well states in the film.
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Affiliation(s)
- S Mathias
- Department of Physics, University of Kaiserslautern, 67663 Kaiserslautern, Germany
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36
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Wu YZ, Schmid AK, Qiu ZQ. Spin-dependent quantum interference from epitaxial MgO thin films on Fe(001). PHYSICAL REVIEW LETTERS 2006; 97:217205. [PMID: 17155772 DOI: 10.1103/physrevlett.97.217205] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2006] [Indexed: 05/12/2023]
Abstract
Spin-dependent electron reflection from MgO thin films grown on Fe(001) was measured using spin-polarized low energy electron microscopy. The electron reflectivity exhibits quantum interference from which two MgO energy bands with Delta1 symmetry were determined in experiment. We found that a bulklike MgO energy gap is fully established for MgO film thicker than 3 atomic monolayers and that the electron reflectivity from the MgO/Fe interface exhibits a spin-dependent amplitude and a spin-independent phase change.
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Affiliation(s)
- Y Z Wu
- Surface Physics Laboratory (National Key Laboratory), Fudan University, Shanghai 200433, China.
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37
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Ricci DA, Miller T, Chiang TC. Controlling the thermal stability of thin films by interfacial engineering. PHYSICAL REVIEW LETTERS 2005; 95:266101. [PMID: 16486372 DOI: 10.1103/physrevlett.95.266101] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2005] [Indexed: 05/06/2023]
Abstract
The quantized electronic structure in Pb films on Si(111) varies substantially as the film thickness increases. The changes in electronic energy cause the thermal stability of the films to oscillate with an approximate bilayer period. The phase of the oscillations can be controlled by interfacial engineering. Comparison of Pb films prepared on Si(111) terminated by In, Au, and Pb as interfactants reveals a phase reversal. For , films made of odd numbers of atomic layers (5, 7, and 9) are more stable than the even ones. This trend is reversed for the other two cases.
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Affiliation(s)
- D A Ricci
- Department of Physics, University of Illinois at Urbana-Champaign, 61801-3080, USA
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38
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Bao XY, Zhang YF, Wang Y, Jia JF, Xue QK, Xie XC, Zhao ZX. Quantum size effects on the perpendicular upper critical field in ultrathin lead films. PHYSICAL REVIEW LETTERS 2005; 95:247005. [PMID: 16384412 DOI: 10.1103/physrevlett.95.247005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/05/2005] [Indexed: 05/05/2023]
Abstract
We report the thickness-dependent (in terms of atomic layers) oscillation behavior of the perpendicular upper critical field Hc2perpendicular in the ultrathin lead films at the reduced temperature (t = T/Tc). Distinct oscillations of the normal-state resistivity as a function of film thickness have also been observed. Compared with the Tc oscillation, the Hc2perpendicular shows a considerable large oscillation amplitude and a pi phase shift. The oscillatory mean free path caused by the quantum size effect plays a role in Hc2perpendicular oscillation.
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Affiliation(s)
- Xin-Yu Bao
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China
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