1
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Li Y, Chan YH, Hlevyack JA, Bowers JW, Chou MY, Chiang TC. Topological Quantum Well States in Pb/Sb Thin-Film Heterostructures. ACS Nano 2024; 18:10243-10248. [PMID: 38530641 PMCID: PMC11008363 DOI: 10.1021/acsnano.4c00724] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2024] [Revised: 03/12/2024] [Accepted: 03/21/2024] [Indexed: 03/28/2024]
Abstract
Composite topological heterostructures, wherein topologically protected states are electronically tuned due to their proximity to other matter, are key avenues for exploring emergent physical phenomena. Particularly, pairing a topological material with a superconductor such as Pb is a promising means for generating a topological superconducting phase with exotic Majorana quasiparticles, but oft-neglected is the emergence of bulklike spin-polarized states that are quite relevant to applications. Using high-resolution photoemission spectroscopy and first-principles calculations, we report the emergence of bulk-like spin-polarized topological quantum well states with long coherence lengths in Pb films grown on the topological semimetal Sb. The results establish Pb/Sb heterostructures as topological superconductor candidates and advance the current understanding of topological coupling effects required for realizing emergent physics and for designing advanced spintronic device architectures.
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Affiliation(s)
- Yao Li
- Department
of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois Urbana−Champaign; Urbana, Illinois 61801, United States
| | - Yang-hao Chan
- Institute
of Atomic and Molecular Sciences, Academia
Sinica, Taipei 10617, Taiwan
- Physics
Division, National Center for Theoretical
Sciences, Taipei 10617, Taiwan
| | - Joseph A. Hlevyack
- Department
of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois Urbana−Champaign; Urbana, Illinois 61801, United States
| | - John W. Bowers
- Department
of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois Urbana−Champaign; Urbana, Illinois 61801, United States
| | - Mei-Yin Chou
- Institute
of Atomic and Molecular Sciences, Academia
Sinica, Taipei 10617, Taiwan
- Department
of Physics, National Taiwan University, Taipei 10617, Taiwan
| | - Tai-Chang Chiang
- Department
of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois Urbana−Champaign; Urbana, Illinois 61801, United States
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2
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Liu RY, Huang A, Sankar R, Hlevyack JA, Su CC, Weng SC, Lin MK, Chen P, Cheng CM, Denlinger JD, Mo SK, Fedorov AV, Chang CS, Jeng HT, Chuang TM, Chiang TC. Dirac Nodal Line in Hourglass Semimetal Nb 3SiTe 6. Nano Lett 2023; 23:380-388. [PMID: 36382909 DOI: 10.1021/acs.nanolett.2c03293] [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: 06/16/2023]
Abstract
Glide-mirror symmetry in nonsymmorphic crystals can foster the emergence of novel hourglass nodal loop states. Here, we present spectroscopic signatures from angle-resolved photoemission of a predicted topological hourglass semimetal phase in Nb3SiTe6. Linear band crossings are observed at the zone boundary of Nb3SiTe6, which could be the origin of the nontrivial Berry phase and are consistent with a predicted glide quantum spin Hall effect; such linear band crossings connect to form a nodal loop. Furthermore, the saddle-like Fermi surface of Nb3SiTe6 observed in our results helps unveil linear band crossings that could be missed. In situ alkali-metal doping of Nb3SiTe6 also facilitated the observation of other band crossings and parabolic bands at the zone center correlated with accidental nodal loop states. Overall, our results complete the system's band structure, help explain prior Hall measurements, and suggest the existence of a nodal loop at the zone center of Nb3SiTe6.
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Affiliation(s)
- Ro-Ya Liu
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois61801, United States
- Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois61801, United States
- Institute of Physics, Academia Sinica, Taipei11529, Taiwan
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California94720, United States
- National Synchrotron Radiation Research Center, Hsinchu30076, Taiwan
| | - Angus Huang
- Department of Physics, National Tsing Hua University, Hsinchu30013, Taiwan
| | - Raman Sankar
- Institute of Physics, Academia Sinica, Taipei11529, Taiwan
| | - Joseph Andrew Hlevyack
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois61801, United States
- Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois61801, United States
| | - Chih-Chuan Su
- Institute of Physics, Academia Sinica, Taipei11529, Taiwan
| | - Shih-Chang Weng
- National Synchrotron Radiation Research Center, Hsinchu30076, Taiwan
| | - Meng-Kai Lin
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois61801, United States
- Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois61801, United States
| | - Peng Chen
- Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science and Shanghai Center for Complex Physics, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai200240, China
| | - Cheng-Maw Cheng
- National Synchrotron Radiation Research Center, Hsinchu30076, Taiwan
| | - Jonathan D Denlinger
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California94720, United States
| | - Sung-Kwan Mo
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California94720, United States
| | - Alexei V Fedorov
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California94720, United States
| | | | - Horng-Tay Jeng
- Institute of Physics, Academia Sinica, Taipei11529, Taiwan
- Department of Physics, National Tsing Hua University, Hsinchu30013, Taiwan
- Physics Division, National Center for Theoretical Sciences, Taipei10617, Taiwan
| | | | - Tai-Chang Chiang
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois61801, United States
- Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois61801, United States
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3
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Lin MK, Chen GH, Ho CL, Chueh WC, Hlevyack JA, Kuo CN, Fu TY, Lin JJ, Lue CS, Chang WH, Takagi N, Arafune R, Chiang TC, Lin CL. Tip-Mediated Bandgap Tuning for Monolayer Transition Metal Dichalcogenides. ACS Nano 2022; 16:14918-14924. [PMID: 36036754 DOI: 10.1021/acsnano.2c05841] [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: 06/15/2023]
Abstract
Monolayer transition metal dichalcogenides offer an appropriate platform for developing advanced electronics beyond graphene. Similar to two-dimensional molecular frameworks, the electronic properties of such monolayers can be sensitive to perturbations from the surroundings; the implied tunability of electronic structure is of great interest. Using scanning tunneling microscopy/spectroscopy, we demonstrated a bandgap engineering technique in two monolayer materials, MoS2 and PtTe2, with the tunneling current as a control parameter. The bandgap of monolayer MoS2 decreases logarithmically by the increasing tunneling current, indicating an electric-field-induced gap renormalization effect. Monolayer PtTe2, by contrast, exhibits a much stronger gap reduction, and a reversible semiconductor-to-metal transition occurs at a moderate tunneling current. This unusual switching behavior of monolayer PtTe2, not seen in bulk semimetallic PtTe2, can be attributed to its surface electronic structure that can readily couple to the tunneling tip, as demonstrated by theoretical calculations.
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Affiliation(s)
- Meng-Kai Lin
- Department of Physics, National Central University, Taoyuan 32001, Taiwan
| | - Guan-Hao Chen
- Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
- Research Center for Applied Sciences, Academia Sinica, Taipei 11529, Taiwan
| | - Ciao-Lin Ho
- Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
| | - Wei-Chen Chueh
- Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
| | - Joseph Andrew Hlevyack
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
- Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Chia-Nung Kuo
- Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan
- Taiwan Consortium of Emergent Crystalline Materials, National Science and Technology Council, Taipei 106, Taiwan
| | - Tsu-Yi Fu
- Department of Physics, National Taiwan Normal University, Taipei 11677, Taiwan
| | - Juhn-Jong Lin
- Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
- Center for Emergent Functional Matter Science (CEFMS), National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
| | - Chin Shan Lue
- Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan
- Taiwan Consortium of Emergent Crystalline Materials, National Science and Technology Council, Taipei 106, Taiwan
| | - Wen-Hao Chang
- Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
- Research Center for Applied Sciences, Academia Sinica, Taipei 11529, Taiwan
- Center for Emergent Functional Matter Science (CEFMS), National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
| | - Noriaki Takagi
- Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501, Japan
| | - Ryuichi Arafune
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Ibaraki 304-0044, Japan
| | - Tai-Chang Chiang
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
- Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Chun-Liang Lin
- Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
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4
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Lu Q, Cook J, Zhang X, Chen KY, Snyder M, Nguyen DT, Reddy PVS, Qin B, Zhan S, Zhao LD, Kowalczyk PJ, Brown SA, Chiang TC, Yang SA, Chang TR, Bian G. Realization of unpinned two-dimensional dirac states in antimony atomic layers. Nat Commun 2022; 13:4603. [PMID: 35933407 PMCID: PMC9357080 DOI: 10.1038/s41467-022-32327-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2022] [Accepted: 07/26/2022] [Indexed: 11/24/2022] Open
Abstract
Two-dimensional (2D) Dirac states with linear dispersion have been observed in graphene and on the surface of topological insulators. 2D Dirac states discovered so far are exclusively pinned at high-symmetry points of the Brillouin zone, for example, surface Dirac states at \documentclass[12pt]{minimal}
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\begin{document}$$\overline{{{\Gamma }}}$$\end{document}Γ¯ in topological insulators Bi2Se(Te)3 and Dirac cones at K and \documentclass[12pt]{minimal}
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\begin{document}$$K^{\prime}$$\end{document}K′ points in graphene. The low-energy dispersion of those Dirac states are isotropic due to the constraints of crystal symmetries. In this work, we report the observation of novel 2D Dirac states in antimony atomic layers with phosphorene structure. The Dirac states in the antimony films are located at generic momentum points. This unpinned nature enables versatile ways such as lattice strains to control the locations of the Dirac points in momentum space. In addition, dispersions around the unpinned Dirac points are highly anisotropic due to the reduced symmetry of generic momentum points. The exotic properties of unpinned Dirac states make antimony atomic layers a new type of 2D Dirac semimetals that are distinct from graphene. In graphene and on the surfaces of many topological insulators, the Dirac cones are pinned to high symmetry points in reciprocal space. Here, the authors report that the Dirac cones in atomically-thin Sb layers occur at generic reciprocal-space points which can be tuned by lattice strain.
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Affiliation(s)
- Qiangsheng Lu
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
| | - Jacob Cook
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
| | - Xiaoqian Zhang
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
| | - Kyle Y Chen
- Rock Bridge High School, Columbia, MO, 65203, USA
| | - Matthew Snyder
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
| | - Duy Tung Nguyen
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
| | | | - Bingchao Qin
- School of Materials Science and Engineering, Beihang University, Beijing, 100191, China
| | - Shaoping Zhan
- School of Materials Science and Engineering, Beihang University, Beijing, 100191, China
| | - Li-Dong Zhao
- School of Materials Science and Engineering, Beihang University, Beijing, 100191, China
| | - Pawel J Kowalczyk
- Department of Solid State Physics, Faculty of Physics and Applied Informatics, University of Lodz, 90-236 Lodz, Pomorska, 149/153, Poland.
| | - Simon A Brown
- The MacDiarmid Institute for Advanced Materials and Nanotechnology, School of Physical and Chemical Sciences, University of Canterbury, Private Bag 4800, Christchurch, 8140, New Zealand
| | - Tai-Chang Chiang
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL, 61801-3080, USA.,Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, 104 South Goodwin Avenue, Urbana, IL, 61801-2902, USA
| | - Shengyuan A Yang
- Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore, 487372, Singapore
| | - Tay-Rong Chang
- Department of Physics, National Cheng Kung University, Tainan, 701, Taiwan
| | - Guang Bian
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA.
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5
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Lu Q, Le C, Zhang X, Cook J, He X, Zarenia M, Vaninger M, Miceli PF, Singh DJ, Liu C, Qin H, Chiang TC, Chiu CK, Vignale G, Bian G. Dirac Fermion Cloning, Moiré Flat Bands, and Magic Lattice Constants in Epitaxial Monolayer Graphene. Adv Mater 2022; 34:e2200625. [PMID: 35446987 DOI: 10.1002/adma.202200625] [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: 01/20/2022] [Revised: 04/14/2022] [Indexed: 06/14/2023]
Abstract
Tuning interactions between Dirac states in graphene has attracted enormous interest because it can modify the electronic spectrum of the 2D material, enhance electron correlations, and give rise to novel condensed-matter phases such as superconductors, Mott insulators, Wigner crystals, and quantum anomalous Hall insulators. Previous works predominantly focus on the flat band dispersion of coupled Dirac states from different twisted graphene layers. In this work, a new route to realizing flat band physics in monolayer graphene under a periodic modulation from substrates is proposed. Graphene/SiC heterostructure is taken as a prototypical example and it is demonstrated experimentally that the substrate modulation leads to Dirac fermion cloning and, consequently, the proximity of the two Dirac cones of monolayer graphene in momentum space. Theoretical modeling captures the cloning mechanism of the Dirac states and indicates that moiré flat bands can emerge at certain magic lattice constants of the substrate, specifically when the period of modulation becomes nearly commensurate with the ( 3 × 3 ) R 30 o \[(\sqrt 3 \; \times \;\sqrt 3 )R{30^o}\] supercell of graphene. The results show that epitaxial single monolayer graphene on suitable substrates is a promising platform for exploring exotic many-body quantum phases arising from interactions between Dirac electrons.
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Affiliation(s)
- Qiangsheng Lu
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
| | - Congcong Le
- RIKEN Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS), Wako, Saitama, 351-0198, Japan
| | - Xiaoqian Zhang
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
- Department of Physics, Southern University of Science and Technology, Shenzhen, 518055, China
| | - Jacob Cook
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
| | - Xiaoqing He
- Electron Microscopy Core Facility, University of Missouri, Columbia, MO, 65211, USA
- Department of Mechanical and Aerospace Engineering, University of Missouri, Columbia, MO, 65211, USA
| | - Mohammad Zarenia
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
| | - Mitchel Vaninger
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
| | - Paul F Miceli
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
| | - David J Singh
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
| | - Chang Liu
- Department of Physics, Southern University of Science and Technology, Shenzhen, 518055, China
| | - Hailang Qin
- Department of Physics, Southern University of Science and Technology, Shenzhen, 518055, China
| | - Tai-Chang Chiang
- Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, IL, 61801-3080, USA
- Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, 104 South Goodwin Avenue, Urbana, IL, 61801-2902, USA
| | - Ching-Kai Chiu
- RIKEN Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS), Wako, Saitama, 351-0198, Japan
| | - Giovanni Vignale
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
| | - Guang Bian
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
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6
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Li Y, Bowers JW, Hlevyack JA, Lin MK, Chiang TC. Emergent and Tunable Topological Surface States in Complementary Sb/Bi 2Te 3 and Bi 2Te 3/Sb Thin-Film Heterostructures. ACS Nano 2022; 16:9953-9959. [PMID: 35699943 PMCID: PMC9245572 DOI: 10.1021/acsnano.2c04639] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2022] [Accepted: 06/09/2022] [Indexed: 06/15/2023]
Abstract
Epitaxial thin-film heterostructures offer a versatile platform for realizing topological surface states (TSSs) that may be emergent and/or tunable by tailoring the atomic layering in the heterostructures. Here, as an experimental demonstration, Sb and Bi2Te3 thin films with closely matched in-plane lattice constants are chosen to form two complementary heterostructures: Sb overlayers on Bi2Te3 (Sb/Bi2Te3) and Bi2Te3 overlayers on Sb (Bi2Te3/Sb), with the overlayer thickness as a tuning parameter. In the bulk form, Sb (a semimetal) and Bi2Te3 (an insulator) both host TSSs with the same topological order but substantially different decay lengths and dispersions, whereas ultrathin Sb and Bi2Te3 films by themselves are fully gapped trivial insulators. Angle-resolved photoemission band mappings, aided by theoretical calculations, confirm the formation of emergent TSSs in both heterostructures. The energy position of the topological Dirac point varies as a function of overlayer thickness, but the variation is non-monotonic, indicating nontrivial effects in the formation of topological heterostructure systems. The results illustrate the rich physics of engineered composite topological systems that may be exploited for nanoscale spintronics applications.
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Affiliation(s)
- Yao Li
- Department
of Physics, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
- Frederick
Seitz Materials Research Laboratory, University
of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
| | - John W. Bowers
- Department
of Physics, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
- Frederick
Seitz Materials Research Laboratory, University
of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
| | - Joseph A. Hlevyack
- Department
of Physics, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
- Frederick
Seitz Materials Research Laboratory, University
of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
| | - Meng-Kai Lin
- Department
of Physics, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
- Frederick
Seitz Materials Research Laboratory, University
of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
- Department
of Physics, National Central University, Taoyuan 32001, Taiwan
| | - Tai-Chang Chiang
- Department
of Physics, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
- Frederick
Seitz Materials Research Laboratory, University
of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
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7
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Märkl T, Salehitaleghani S, Le Ster M, Kowalczyk PJ, Wang X, Wang P, Snyder M, Bian G, Chiang TC, Brown SA. Antimony oxide nanostructures in the monolayer limit: self-assembly of van der Waals-bonded molecular building blocks. Nanotechnology 2021; 32:125701. [PMID: 33271514 DOI: 10.1088/1361-6528/abd059] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Antimony oxide nanostructures have been identified as candidates for a range of electronic and optoelectronic applications. Here we demonstrate the growth of 2-dimensional antimony oxide nanostructures on various substrates, including highly oriented pyrolytic graphite (HOPG), MoS2 and α-Bi(110) nanoislands. Using scanning tunneling microscopy (STM) we show that the nanostructures formed are exclusively highly crystalline α-Sb2O3(111) monolayers with a lattice constant of 796 pm ± 7 pm. The nanostructures are triangular with lateral dimensions of up to ∼30 nm. Even though elemental antimony nanostructures are grown simultaneously mixed phases are not observed and both materials exhibit their own distinct growth modes. Moiré patterns are also observed and simulated, allowing confirmation of the atomic unit cell and an understanding of the orientation of the Sb2O3 structures with respect to the supporting materials. As in the bulk, the Sb2O3 nanostructures are formed from Sb4O6 molecules that are weakly interacting through van der Waals forces. This allows physical modification of the nanostructures with the STM tip. Scanning tunnelling spectroscopy reveals a wide band gap of at least 3.5 eV. Finally, we show that possible alternative structures that have unit cells comparable to those observed can be excluded based on our DFT calculations. The considered structures are a 2 × 2 reconstruction of β-Sb with one vacancy per unit cell and a van der Waals solid composed of Sb4 clusters. Previous reports have predominantly demonstrated Sb2O3 structures with much larger thicknesses.
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Affiliation(s)
- Tobias Märkl
- The MacDiarmid Institute for Advanced Materials and Nanotechnology, School of Physical and Chemical Sciences, University of Canterbury, Christchurch, New Zealand
| | - Sara Salehitaleghani
- The MacDiarmid Institute for Advanced Materials and Nanotechnology, School of Physical and Chemical Sciences, University of Canterbury, Christchurch, New Zealand
| | - Maxime Le Ster
- The MacDiarmid Institute for Advanced Materials and Nanotechnology, School of Physical and Chemical Sciences, University of Canterbury, Christchurch, New Zealand
| | - Pawel J Kowalczyk
- Department of Solid State Physics, Faculty of Physics and Applied Informatics, University of Lodz, Lodz, Poland
| | - Xiaoxiong Wang
- College of Science, Nanjing University of Science and Technology, Nanjing 210094, People's Republic of China
| | - Peng Wang
- College of Electronic Communication and Physics, Shandong University of Science and Technology, Qingdao 266590, People's Republic of China
| | - Matthew Snyder
- Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, United States of America
| | - Guang Bian
- Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, United States of America
| | - Tai-Chang Chiang
- Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, IL 61801-3080, United States of America
| | - Simon A Brown
- The MacDiarmid Institute for Advanced Materials and Nanotechnology, School of Physical and Chemical Sciences, University of Canterbury, Christchurch, New Zealand
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8
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Kowalczyk PJ, Brown SA, Maerkl T, Lu Q, Chiu CK, Liu Y, Yang SA, Wang X, Zasada I, Genuzio F, Menteş TO, Locatelli A, Chiang TC, Bian G. Realization of Symmetry-Enforced Two-Dimensional Dirac Fermions in Nonsymmorphic α-Bismuthene. ACS Nano 2020; 14:1888-1894. [PMID: 31971774 DOI: 10.1021/acsnano.9b08136] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Two-dimensional (2D) Dirac-like electron gases have attracted tremendous research interest ever since the discovery of free-standing graphene. The linear energy dispersion and nontrivial Berry phase play a pivotal role in the electronic, optical, mechanical, and chemical properties of 2D Dirac materials. The known 2D Dirac materials are gapless only within certain approximations, for example, in the absence of spin-orbit coupling (SOC). Here, we report a route to establishing robust Dirac cones in 2D materials with nonsymmorphic crystal lattice. The nonsymmorphic symmetry enforces Dirac-like band dispersions around certain high-symmetry momenta in the presence of SOC. Through μ-ARPES measurements, we observe Dirac-like band dispersions in α-bismuthene. The nonsymmorphic lattice symmetry is confirmed by μ-low-energy electron diffraction and scanning tunneling microscopy. Our first-principles simulations and theoretical topological analysis demonstrate the correspondence between nonsymmorphic symmetry and Dirac states. This mechanism can be straightforwardly generalized to other nonsymmorphic materials. The results enlighten the search of symmetry-enforced Dirac fermions in the vast uncharted world of nonsymmorphic 2D materials.
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Affiliation(s)
- Pawel J Kowalczyk
- Department of Solid State Physics, Faculty of Physics and Applied Informatics , University of Lodz , 90-236 Lodz , Pomorska 149/153, Poland
| | - Simon A Brown
- The MacDiarmid Institute for Advanced Materials and Nanotechnology, School of Physical and Chemical Sciences , University of Canterbury , Private Bag 4800 , Christchurch 8140 , New Zealand
| | - Tobias Maerkl
- The MacDiarmid Institute for Advanced Materials and Nanotechnology, School of Physical and Chemical Sciences , University of Canterbury , Private Bag 4800 , Christchurch 8140 , New Zealand
| | - Qiangsheng Lu
- Department of Physics and Astronomy , University of Missouri , Columbia , Missouri 65211 , United States
| | - Ching-Kai Chiu
- Kavli Institute for Theoretical Sciences , University of Chinese Academy of Sciences , Beijing 100190 , China
| | - Ying Liu
- Research Laboratory for Quantum Materials , Singapore University of Technology and Design , Singapore 487372
| | - Shengyuan A Yang
- Research Laboratory for Quantum Materials , Singapore University of Technology and Design , Singapore 487372
| | - Xiaoxiong Wang
- College of Science , Nanjing University of Science and Technology , Nanjing 210094 , China
| | - Ilona Zasada
- Department of Solid State Physics, Faculty of Physics and Applied Informatics , University of Lodz , 90-236 Lodz , Pomorska 149/153, Poland
| | - Francesca Genuzio
- Elettra - Sincrotrone Trieste S.C.p.A. , Basovizza, I-34149 Trieste , Italy
| | - Tevfik Onur Menteş
- Elettra - Sincrotrone Trieste S.C.p.A. , Basovizza, I-34149 Trieste , Italy
| | - Andrea Locatelli
- Elettra - Sincrotrone Trieste S.C.p.A. , Basovizza, I-34149 Trieste , Italy
| | - Tai-Chang Chiang
- Department of Physics , University of Illinois at Urbana-Champaign , 1110 West Green Street , Urbana , Illinois 61801-3080 , United States
- Frederick Seitz Materials Research Laboratory , University of Illinois at Urbana-Champaign , 104 South Goodwin Avenue , Urbana , Illinois 61801-2902 , United States
| | - Guang Bian
- Department of Physics and Astronomy , University of Missouri , Columbia , Missouri 65211 , United States
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9
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Chen P, Chen YT, Liu RY, Chen HD, Lin D, Fedorov AV, Chiang TC. Atomic-Scale Chemical Conversion of Single-Layer Transition Metal Dichalcogenides. ACS Nano 2019; 13:5611-5615. [PMID: 30987421 DOI: 10.1021/acsnano.9b00756] [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: 06/09/2023]
Abstract
Chemical conversion by atomic substitution offers a powerful route toward the creation of unusual structures and functionalities. Here, we demonstrate the progressive transformation of single-layer TiTe2 into TiSe2 by reaction with a Se flux in vacuum. Angle-resolved photoemission spectroscopy and scanning tunneling microscopy reveal intriguing reaction patterns involving TiSe2 island ingrowth starting from the TiTe2 island edges, while the band structure and core level signatures of TiSe2 grow in intensity at the expense of those corresponding to TiTe2. Lattice mismatch between TiTe2 and TiSe2 results in misfit holes and lattice distortions over a distance behind a seamless fingerlike reaction front. The regions of TiSe2 and TiTe2 are distinguished by a height difference and a charge density wave (CDW) at different transition temperatures. The method of in situ chemical conversion offers opportunities for atomic-scale engineering of layered transition metal dichalcogenides that host useful properties arising from CDW, Dirac, Weyl, superconducting, spin-valley, and magnetic structures.
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Affiliation(s)
- Peng Chen
- Department of Physics , University of Illinois at Urbana-Champaign , 1110 West Green Street , Urbana , Illinois 61801-3080 , United States
- Frederick Seitz Materials Research Laboratory , University of Illinois at Urbana-Champaign , 104 South Goodwin Avenue , Urbana , Illinois 61801-2902 , United States
- Advanced Light Source , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States
| | - Yun-Ting Chen
- Department of Physics , National Tsing Hua University , Hsinchu 30013 , Taiwan
| | - Ro-Ya Liu
- Department of Physics , University of Illinois at Urbana-Champaign , 1110 West Green Street , Urbana , Illinois 61801-3080 , United States
- Frederick Seitz Materials Research Laboratory , University of Illinois at Urbana-Champaign , 104 South Goodwin Avenue , Urbana , Illinois 61801-2902 , United States
- Advanced Light Source , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States
- Institute of Physics , Academia Sinica , Taipei 11529 , Taiwan
| | - Han-De Chen
- Department of Physics , National Tsing Hua University , Hsinchu 30013 , Taiwan
| | - Dengsung Lin
- Department of Physics , National Tsing Hua University , Hsinchu 30013 , Taiwan
| | - Alexei V Fedorov
- Advanced Light Source , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States
| | - Tai-Chang Chiang
- Department of Physics , University of Illinois at Urbana-Champaign , 1110 West Green Street , Urbana , Illinois 61801-3080 , United States
- Frederick Seitz Materials Research Laboratory , University of Illinois at Urbana-Champaign , 104 South Goodwin Avenue , Urbana , Illinois 61801-2902 , United States
- Department of Physics , National Taiwan University , Taipei 10617 , Taiwan
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10
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Flötotto D, Bai Y, Chan YH, Chen P, Wang X, Rossi P, Xu CZ, Zhang C, Hlevyack JA, Denlinger JD, Hong H, Chou MY, Mittemeijer EJ, Eckstein JN, Chiang TC. In Situ Strain Tuning of the Dirac Surface States in Bi 2Se 3 Films. Nano Lett 2018; 18:5628-5632. [PMID: 30109804 DOI: 10.1021/acs.nanolett.8b02105] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [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
Elastic strain has the potential for a controlled manipulation of the band gap and spin-polarized Dirac states of topological materials, which can lead to pseudomagnetic field effects, helical flat bands, and topological phase transitions. However, practical realization of these exotic phenomena is challenging and yet to be achieved. Here we show that the Dirac surface states of the topological insulator Bi2Se3 can be reversibly tuned by an externally applied elastic strain. Performing in situ X-ray diffraction and in situ angle-resolved photoemission spectroscopy measurements during tensile testing of epitaxial Bi2Se3 films bonded onto a flexible substrate, we demonstrate elastic strains of up to 2.1% and quantify the resulting changes in the topological surface state. Our study establishes the functional relationship between the lattice and electronic structures of Bi2Se3 and, more generally, demonstrates a new route toward momentum-resolved mapping of strain-induced band structure changes.
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Affiliation(s)
- David Flötotto
- Department of Physics , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
- Frederick Seitz Materials Research Laboratory , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
| | - Yang Bai
- Department of Physics , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
- Frederick Seitz Materials Research Laboratory , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
| | - Yang-Hao Chan
- Institute of Atomic and Molecular Sciences , Academia Sinica , Taipei 10617 , Taiwan
| | - Peng Chen
- Department of Physics , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
- Frederick Seitz Materials Research Laboratory , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
- Advanced Light Source , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States
| | - Xiaoxiong Wang
- College of Science , Nanjing University of Science and Technology , Nanjing 210094 , China
| | - Paul Rossi
- Max Planck Institute for Intelligent Systems , Heisenbergstraße 3 , D-70569 Stuttgart , Germany
| | - Cai-Zhi Xu
- Department of Physics , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
- Frederick Seitz Materials Research Laboratory , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
| | - Can Zhang
- Department of Physics , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
- Frederick Seitz Materials Research Laboratory , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
| | - Joseph A Hlevyack
- Department of Physics , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
- Frederick Seitz Materials Research Laboratory , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
| | - Jonathan D Denlinger
- Advanced Light Source , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States
| | - Hawoong Hong
- Advanced Photon Source , Argonne National Laboratory , Argonne , Illinois 60439 , United States
| | - Mei-Yin Chou
- Institute of Atomic and Molecular Sciences , Academia Sinica , Taipei 10617 , Taiwan
- School of Physics , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States
- Department of Physics , National Taiwan University , Taipei 10617 , Taiwan
| | - Eric J Mittemeijer
- Max Planck Institute for Intelligent Systems , Heisenbergstraße 3 , D-70569 Stuttgart , Germany
- Institute for Materials Science , University of Stuttgart , Germany
| | - James N Eckstein
- Department of Physics , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
- Frederick Seitz Materials Research Laboratory , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
| | - Tai-Chang Chiang
- Department of Physics , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
- Frederick Seitz Materials Research Laboratory , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States
- Department of Physics , National Taiwan University , Taipei 10617 , Taiwan
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11
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Flötotto D, Ota Y, Bai Y, Zhang C, Okazaki K, Tsuzuki A, Hashimoto T, Eckstein JN, Shin S, Chiang TC. Superconducting pairing of topological surface states in bismuth selenide films on niobium. Sci Adv 2018; 4:eaar7214. [PMID: 29719866 PMCID: PMC5922797 DOI: 10.1126/sciadv.aar7214] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/2017] [Accepted: 03/09/2018] [Indexed: 05/21/2023]
Abstract
A topological insulator film coupled to a simple isotropic s-wave superconductor substrate can foster helical pairing of the Dirac fermions associated with the topological surface states. Experimental realization of such a system is exceedingly difficult, however using a novel "flip-chip" technique, we have prepared single-crystalline Bi2Se3 films with predetermined thicknesses in terms of quintuple layers (QLs) on top of Nb substrates fresh from in situ cleavage. Our angle-resolved photoemission spectroscopy (ARPES) measurements of the film surface disclose superconducting gaps and coherence peaks of similar magnitude for both the topological surface states and bulk states. The ARPES spectral map as a function of temperature and film thickness up to 10 QLs reveals key characteristics relevant to the mechanism of coupling between the topological surface states and the superconducting Nb substrate; the effective coupling length is found to be much larger than the decay length of the topological surface states.
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Affiliation(s)
- David Flötotto
- Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, IL 61801, USA
| | - Yuichi Ota
- Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba, Japan
| | - Yang Bai
- Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, IL 61801, USA
| | - Can Zhang
- Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, IL 61801, USA
| | - Kozo Okazaki
- Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba, Japan
| | - Akihiro Tsuzuki
- Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba, Japan
| | - Takahiro Hashimoto
- Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba, Japan
| | - James N. Eckstein
- Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, IL 61801, USA
| | - Shik Shin
- Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba, Japan
| | - Tai-Chang Chiang
- Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, IL 61801, USA
- Corresponding author.
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12
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Lin CL, Arafune R, Liu RY, Yoshimura M, Feng B, Kawahara K, Ni Z, Minamitani E, Watanabe S, Shi Y, Kawai M, Chiang TC, Matsuda I, Takagi N. Visualizing Type-II Weyl Points in Tungsten Ditelluride by Quasiparticle Interference. ACS Nano 2017; 11:11459-11465. [PMID: 29061038 DOI: 10.1021/acsnano.7b06179] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Weyl semimetals (WSMs) are classified into two types, type I and II, according to the topology of the Weyl point, where the electron and hole pockets touch each other. Tungsten ditelluride (WTe2) has garnered a great deal of attention as a strong candidate to be a type-II WSM. However, the Weyl points for WTe2 are located above the Fermi level, which has prevented us from identifying the locations and the connection to the Fermi arc surface states by using angle-resolved photoemission spectroscopy. Here, we present experimental proof that WTe2 is a type-II WSM. We measured energy-dependent quasiparticle interference patterns with a cryogenic scanning tunneling microscope, revealing the position of the Weyl point and its connection with the Fermi arc surface states, in agreement with prior theoretical predictions. Our results provide an answer to this crucial question and stimulate further exploration of the characteristics of WSMs.
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Affiliation(s)
- Chun-Liang Lin
- Department of Advanced Materials Science, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
| | - Ryuichi Arafune
- International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science , 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
| | - Ro-Ya Liu
- Institute for Solid State Physics, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
| | - Masato Yoshimura
- Department of Advanced Materials Science, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
| | - Baojie Feng
- Institute for Solid State Physics, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
| | - Kazuaki Kawahara
- Department of Advanced Materials Science, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
| | - Zeyuan Ni
- Department of Materials Engineering, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Emi Minamitani
- Department of Materials Engineering, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Satoshi Watanabe
- Department of Materials Engineering, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Youguo Shi
- Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China
| | - Maki Kawai
- Department of Advanced Materials Science, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
| | - Tai-Chang Chiang
- Department of Physics, University of Illinois , Urbana, Illinois 61801, United States
| | - Iwao Matsuda
- Institute for Solid State Physics, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
| | - Noriaki Takagi
- Department of Advanced Materials Science, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
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13
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Liu RY, Ogawa Y, Chen P, Ozawa K, Suzuki T, Okada M, Someya T, Ishida Y, Okazaki K, Shin S, Chiang TC, Matsuda I. Femtosecond to picosecond transient effects in WSe 2 observed by pump-probe angle-resolved photoemission spectroscopy. Sci Rep 2017; 7:15981. [PMID: 29167479 PMCID: PMC5700159 DOI: 10.1038/s41598-017-16076-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2017] [Accepted: 11/06/2017] [Indexed: 11/30/2022] Open
Abstract
Time-dependent responses of materials to an ultrashort optical pulse carry valuable information about the electronic and lattice dynamics; this research area has been widely studied on novel two-dimensional materials such as graphene, transition metal dichalcogenides (TMDs) and topological insulators (TIs). We report herein a time-resolved and angle-resolved photoemission spectroscopy (TRARPES) study of WSe2, a layered semiconductor of interest for valley electronics. The results for below-gap optical pumping reveal energy-gain and -loss Floquet replica valence bands that appear instantaneously in concert with the pump pulse. Energy shift, broadening, and complex intensity variation and oscillation at twice the phonon frequency for the valence bands are observed at time scales ranging from the femtosecond to the picosecond and beyond. The underlying physics is rich, including ponderomotive interaction, dressing of the electronic states, creation of coherent phonon pairs, and diffusion of charge carriers - effects operating at vastly different time domains.
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Affiliation(s)
- Ro-Ya Liu
- Institute for Solid State Physics, the University of Tokyo, Kashiwa, Chiba, 277-8581, Japan
| | - Yu Ogawa
- Institute for Solid State Physics, the University of Tokyo, Kashiwa, Chiba, 277-8581, Japan
| | - Peng Chen
- Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois, 61801-3080, USA
| | - Kenichi Ozawa
- Department of Chemistry, Tokyo Institute of Technology, Meguro-ku, Tokyo, 152-8551, Japan
| | - Takeshi Suzuki
- Institute for Solid State Physics, the University of Tokyo, Kashiwa, Chiba, 277-8581, Japan
| | - Masaru Okada
- Institute for Solid State Physics, the University of Tokyo, Kashiwa, Chiba, 277-8581, Japan
| | - Takashi Someya
- Institute for Solid State Physics, the University of Tokyo, Kashiwa, Chiba, 277-8581, Japan
| | - Yukiaki Ishida
- Institute for Solid State Physics, the University of Tokyo, Kashiwa, Chiba, 277-8581, Japan
| | - Kozo Okazaki
- Institute for Solid State Physics, the University of Tokyo, Kashiwa, Chiba, 277-8581, Japan
| | - Shik Shin
- Institute for Solid State Physics, the University of Tokyo, Kashiwa, Chiba, 277-8581, Japan
| | - Tai-Chang Chiang
- Institute for Solid State Physics, the University of Tokyo, Kashiwa, Chiba, 277-8581, Japan.
- Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois, 61801-3080, USA.
| | - Iwao Matsuda
- Institute for Solid State Physics, the University of Tokyo, Kashiwa, Chiba, 277-8581, Japan.
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14
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Xu CZ, Chan YH, Chen Y, Chen P, Wang X, Dejoie C, Wong MH, Hlevyack JA, Ryu H, Kee HY, Tamura N, Chou MY, Hussain Z, Mo SK, Chiang TC. Elemental Topological Dirac Semimetal: α-Sn on InSb(111). Phys Rev Lett 2017; 118:146402. [PMID: 28430465 DOI: 10.1103/physrevlett.118.146402] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Indexed: 05/20/2023]
Abstract
Three-dimensional (3D) topological Dirac semimetals (TDSs) are rare but important as a versatile platform for exploring exotic electronic properties and topological phase transitions. A quintessential feature of TDSs is 3D Dirac fermions associated with bulk electronic states near the Fermi level. Using angle-resolved photoemission spectroscopy, we have observed such bulk Dirac cones in epitaxially grown α-Sn films on InSb(111), the first such TDS system realized in an elemental form. First-principles calculations confirm that epitaxial strain is key to the formation of the TDS phase. A phase diagram is established that connects the 3D TDS phase through a singular point of a zero-gap semimetal phase to a topological insulator phase. The nature of the Dirac cone crosses over from 3D to 2D as the film thickness is reduced.
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Affiliation(s)
- Cai-Zhi Xu
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
- Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Yang-Hao Chan
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - Yige Chen
- Department of Physics, University of Toronto, Toronto, Ontario M5S 1A7, Canada
| | - Peng Chen
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
- Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Xiaoxiong Wang
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
- Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
- College of Science, Nanjing University of Science and Technology, Nanjing 210094, China
| | - Catherine Dejoie
- Structure of Materials Group, ESRF-The European Synchrotron CS40220, 38043 Grenoble Cedex 9, France
| | - Man-Hong Wong
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
- Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - Joseph Andrew Hlevyack
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
- Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - Hyejin Ryu
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Hae-Young Kee
- Department of Physics, University of Toronto, Toronto, Ontario M5S 1A7, Canada
| | - Nobumichi Tamura
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Mei-Yin Chou
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
- Department of Physics, National Taiwan University, Taipei 10617, Taiwan
| | - Zahid Hussain
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Sung-Kwan Mo
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Tai-Chang Chiang
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
- Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
- Department of Physics, National Taiwan University, Taipei 10617, Taiwan
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15
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Feng B, Sugino O, Liu RY, Zhang J, Yukawa R, Kawamura M, Iimori T, Kim H, Hasegawa Y, Li H, Chen L, Wu K, Kumigashira H, Komori F, Chiang TC, Meng S, Matsuda I. Dirac Fermions in Borophene. Phys Rev Lett 2017; 118:096401. [PMID: 28306312 DOI: 10.1103/physrevlett.118.096401] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2016] [Indexed: 05/12/2023]
Abstract
Honeycomb structures of group IV elements can host massless Dirac fermions with nontrivial Berry phases. Their potential for electronic applications has attracted great interest and spurred a broad search for new Dirac materials especially in monolayer structures. We present a detailed investigation of the β_{12} sheet, which is a borophene structure that can form spontaneously on a Ag(111) surface. Our tight-binding analysis revealed that the lattice of the β_{12} sheet could be decomposed into two triangular sublattices in a way similar to that for a honeycomb lattice, thereby hosting Dirac cones. Furthermore, each Dirac cone could be split by introducing periodic perturbations representing overlayer-substrate interactions. These unusual electronic structures were confirmed by angle-resolved photoemission spectroscopy and validated by first-principles calculations. Our results suggest monolayer boron as a new platform for realizing novel high-speed low-dissipation devices.
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Affiliation(s)
- Baojie Feng
- Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | - Osamu Sugino
- Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | - Ro-Ya Liu
- Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | - Jin Zhang
- Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Ryu Yukawa
- Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan
| | - Mitsuaki Kawamura
- Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | - Takushi Iimori
- Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | - Howon Kim
- Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | - Yukio Hasegawa
- Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | - Hui Li
- Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Lan Chen
- Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Kehui Wu
- Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
| | - Hiroshi Kumigashira
- Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan
| | - Fumio Komori
- Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | - Tai-Chang Chiang
- Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
- Department of Physics, University of Illinois, Urbana, Illinois 61801, USA
| | - Sheng Meng
- Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
| | - Iwao Matsuda
- Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
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16
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Bian G, Wang Z, Wang XX, Xu C, Xu S, Miller T, Hasan MZ, Liu F, Chiang TC. Engineering Electronic Structure of a Two-Dimensional Topological Insulator Bi(111) Bilayer on Sb Nanofilms by Quantum Confinement Effect. ACS Nano 2016; 10:3859-3864. [PMID: 26932368 DOI: 10.1021/acsnano.6b00987] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We report on the fabrication of a two-dimensional topological insulator Bi(111) bilayer on Sb nanofilms via a sequential molecular beam epitaxy growth technique. Our angle-resolved photoemission measurements demonstrate the evolution of the electronic band structure of the heterostructure as a function of the film thickness and reveal the existence of a two-dimensional spinful massless electron gas within the top Bi bilayer. Interestingly, our first-principles calculation extrapolating the observed band structure shows that, by tuning down the thickness of the supporting Sb films into the quantum dimension regime, a pair of isolated topological edge states emerges in a partial energy gap at 0.32 eV above the Fermi level as a consequence of quantum confinement effect. Our results and methodology of fabricating nanoscale heterostructures establish the Bi bilayer/Sb heterostructure as a platform of great potential for both ultra-low-energy-cost electronics and surface-based spintronics.
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Affiliation(s)
- Guang Bian
- Joseph Henry Laboratory, Department of Physics, Princeton University , Princeton, New Jersey 08544, United States
- Department of Physics, University of Illinois at Urbana-Champaign , 1110 West Green Street, Urbana, Illinois 61801-3080, United States
| | - Zhengfei Wang
- Department of Materials Science and Engineering, University of Utah , Salt Lake City, Utah 84122, United States
| | - Xiao-Xiong Wang
- College of Science, Nanjing University of Science and Technology , Nanjing 210094, China
| | - Caizhi Xu
- Department of Physics, University of Illinois at Urbana-Champaign , 1110 West Green Street, Urbana, Illinois 61801-3080, United States
- Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign , 104 South Goodwin Avenue, Urbana, Illinois 61801-2902, United States
| | - SuYang Xu
- Joseph Henry Laboratory, Department of Physics, Princeton University , Princeton, New Jersey 08544, United States
| | - Thomas Miller
- Department of Physics, University of Illinois at Urbana-Champaign , 1110 West Green Street, Urbana, Illinois 61801-3080, United States
- Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign , 104 South Goodwin Avenue, Urbana, Illinois 61801-2902, United States
| | - M Zahid Hasan
- Joseph Henry Laboratory, Department of Physics, Princeton University , Princeton, New Jersey 08544, United States
| | - Feng Liu
- Department of Materials Science and Engineering, University of Utah , Salt Lake City, Utah 84122, United States
- Collaborative Innovation Center of Quantum Matter , Beijing 100084, China
| | - Tai-Chang Chiang
- Department of Physics, University of Illinois at Urbana-Champaign , 1110 West Green Street, Urbana, Illinois 61801-3080, United States
- Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign , 104 South Goodwin Avenue, Urbana, Illinois 61801-2902, United States
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17
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Ren J, Fu L, Bian G, Su J, Zhang H, Velury S, Yukawa R, Zhang L, Wang T, Zha G, Guo R, Miller T, Hasan MZ, Chiang TC. An Effective Approach to Improving Cadmium Telluride (111)A Surface by Molecular-Beam-Epitaxy Growth of Tellurium Monolayer. ACS Appl Mater Interfaces 2016; 8:726-735. [PMID: 26672795 DOI: 10.1021/acsami.5b09863] [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: 06/05/2023]
Abstract
The surface cleansing treatment of non-natural cleavage planes of semiconductors is usually performed in vacuum using ion sputtering and subsequent annealing. In this Research Article, we report on the evolution of surface atomic structure caused by different ways of surface treatment as monitored by in situ core-level photoemission measurements of Cd-4d and Te-4d atomic levels and reflection high-energy electron diffraction (RHEED). Sputtering of surface increases the density of the dangling bonds by 50%. This feature and the less than ideal ordering can be detrimental to device applications. An effective approach is employed to improve the quality of this surface. One monolayer (ML) of Te grown by the method of molecular beam epitaxy (MBE) on the target surface with heating at 300 °C effectively improves the surface quality as evidenced by the improved sharpness of RHEED pattern and a reduced diffuse background in the spectra measured by high-resolution ultraviolet photoemission spectroscopy (HRUPS). Calculations have been performed for various atomic geometries by employing first-principles geometry optimization. In conjunction with an analysis of the core level component intensities in terms the layer-attenuation model, we propose a "vacancy site" model of the modified 1 ML-Te/CdTe(111)A (2 × 2) surface.
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Affiliation(s)
- Jie Ren
- State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University , Xi'an 710072, China
- Department of Physics, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801-3080, United States
| | - Li Fu
- State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University , Xi'an 710072, China
| | - Guang Bian
- Joseph Henry Laboratory and Department of Physics, Princeton University , Princeton, New Jersey 08544, United States
| | - Jie Su
- State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University , Xi'an 710072, China
| | - Hao Zhang
- State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University , Xi'an 710072, China
| | - Saavanth Velury
- Department of Physics, University of California , Berkeley, California 94720, United States
| | - Ryu Yukawa
- Institute for Solid State Physics, University of Tokyo , Kashiwanoha, Chiba 277-8581, Japan
| | - Longxiang Zhang
- Department of Physics, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801-3080, United States
| | - Tao Wang
- State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University , Xi'an 710072, China
| | - Gangqiang Zha
- State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University , Xi'an 710072, China
| | - Rongrong Guo
- State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University , Xi'an 710072, China
| | - Tom Miller
- Department of Physics, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801-3080, United States
| | - M Zahid Hasan
- Joseph Henry Laboratory and Department of Physics, Princeton University , Princeton, New Jersey 08544, United States
| | - Tai-Chang Chiang
- Department of Physics, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801-3080, United States
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Liu Y, Miller T, Chiang TC. Electronic structure and trilayer growth of indium films on Si(111): a photoemission study. J Phys Condens Matter 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] [What about the content of this article? (0)] [Affiliation(s)] [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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Tang SJ, Lee CY, Huang CC, Chang TR, Cheng CM, Tsuei KD, Jeng HT, Yeh V, Chiang TC. Electronic versus lattice match for metal-semiconductor epitaxial growth: Pb on Ge(111). Phys Rev Lett 2011; 107:066802. [PMID: 21902356 DOI: 10.1103/physrevlett.107.066802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2011] [Indexed: 05/31/2023]
Abstract
Lattice match is important for epitaxial growth. We show that a competing mechanism, electronic match, can dominate at small film thicknesses for metal-semiconductor systems, where quantum confinement and symmetry requirements may favor a different growth pattern. For Pb(111) on Ge(111), an accidental lattice match leads to a √3 × √3 configuration involving a 30° in-plane rotation at large film thicknesses, but it gives way to an incommensurate (1 × 1) configuration at small film thickness. The transformation follows an approximately inverse-film-thickness dependence with superimposed bilayer oscillations.
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Affiliation(s)
- S-J Tang
- Department of Physics, National Tsing Hua University, Hsinchu, Taiwan.
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20
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Affiliation(s)
- Tai-Chang Chiang
- Department of Physics and the Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, IL 61801, USA.
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Upton MH, Wei CM, Chou MY, Miller T, Chiang TC. Thermal stability and electronic structure of atomically uniform Pb films on Si(111). Phys Rev Lett 2004; 93:026802. [PMID: 15323937 DOI: 10.1103/physrevlett.93.026802] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2003] [Indexed: 05/24/2023]
Abstract
Atomically uniform Pb films are successfully prepared on Si(111), despite a large lattice mismatch. Angle-resolved photoemission measurements of the electronic structure show layer-resolved quantum well states which can be correlated with dramatic variations in thermal stability. The odd film thicknesses N = 5, 7, and 9 monolayers show sharp quantum well states. The even film thicknesses N = 6 and 8 do not, but are much more stable than the odd film thicknesses. This correlation is discussed in terms of a total energy calculation and Friedel-like oscillations in properties.
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Affiliation(s)
- M H Upton
- Frederick Seitz Materials Research Laboratory, Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801-2902, USA
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Abstract
Chlorine termination of mixed Ge/Si(100) surfaces substantially enhances the contrast between Ge and Si sites in scanning tunneling microscopy observations. This finding enables a detailed investigation of the spatial distribution of Ge atoms deposited on Si(100) by atomic layer epitaxy. The results are corroborated by photoemission measurements aided by an unusually large chemical shift between Cl adsorbed on Si and Ge. Adsorbate-substrate atomic exchange during growth is shown to be important. The resulting interface is thus graded, but characterized by a very short length scale of about one monolayer.
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Affiliation(s)
- D S Lin
- Institute of Physics, National Chiao-Tung University, 1001 Ta-Hsueh Road, Hsinchu 300, Taiwan, Republic of China
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Abstract
We have studied the structural stability of thin silver films with thicknesses of N = 1 to 15 monolayers, deposited on an Fe(100) substrate. Photoemission spectroscopy results show that films of N = 1, 2, and 5 monolayer thicknesses are structurally stable for temperatures above 800 kelvin, whereas films of other thicknesses are unstable and bifurcate into a film with N +/- 1 monolayer thicknesses at temperatures around 400 kelvin. The results are in agreement with theoretical predictions that consider the electronic energy of the quantum well associated with a particular film thickness as a significant contribution to the film stability.
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Affiliation(s)
- D A Luh
- Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, IL 61801-3080, USA
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Abstract
The charge-density-wave transition in TiSe (2), which results in a commensurate (2x2x2) superlattice at temperatures below approximately 200 K, presumably involves softening of a zone-boundary phonon mode. For the first time, this phonon-softening behavior has been examined over a wide temperature range by synchrotron x-ray thermal diffuse scattering.
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Affiliation(s)
- M Holt
- Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080, USA
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Abstract
Gene imprinting is an epigenetic mechanism for accomplishing persistent change in gene expression. In this brief paper, we explore the mechanisms for imprinting genes and present data showing that the synthetic estrogen, diethylstilbestrol (DES) can developmentally imprint genes by changing the pattern of DNA methylation. We further discuss the implications of this and other findings for non-mutagenic aspects of developmental toxicology, and suggest ways to use this concept in modifying in vitro screening for developmental toxicants.
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Affiliation(s)
- J A McLachlan
- Environmental Endocrinology Laboratory, Center for Bioenvironmental Research, Tulane and Xavier Universities, 1340 Tulane Avenue, New Orleans, LA 70112, USA.
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Li S, Chiang TC, Davis GR, Williams RM, Wilson VP, McLachlan JA. Decreased expression of Wnt7a mRNA is inversely associated with the expression of estrogen receptor-alpha in human uterine leiomyoma. J Clin Endocrinol Metab 2001; 86:454-7. [PMID: 11232041 DOI: 10.1210/jcem.86.1.7276] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Wnt-7a gene not only guides the development of the anterior-posterior axis in the female reproductive tract, but also plays a critical role in uterine smooth muscle pattering and maintenance of adult uterine function. This gene is also responsive to changes in the levels of sex steroid hormone in the female reproductive tract. To explore the molecular mechanisms underlying the pathogenesis of uterine leiomyoma, the expression of Wnt7a mRNA in the leiomyoma has been assessed. RT-PCR was performed on uterine leiomyomas and the adjacent myometria. Of 30 cases of leiomyomas studied, 67% showed a decreased mRNA level as compared to the paired myometria. On the other hand, estrogen receptor-alpha (ER-alpha) mRNA is hyper-expressed in 67% of the leiomyomas as compared to their paired myometrium. An inverse association at mRNA expression was found between Wnt7a and ER-alpha. Miller et alhas shown that fetal exposure of DES results in de-regulation of Wnt7a during uterine morphogenesis. Referring to their results, we have postulated that hypersensitivity of leiomyoma cells to estrogen may deregulate the Wnt7a expression. Decreased expression of Wnt7a may lead to loss of control in patterning of the myometrium and result in development of leiomyoma
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Affiliation(s)
- S Li
- Center for Bioenvironmental Research and Department of Pharmacology, Tulane/Xavier Universities, New Orleans, Louisiana 70112-2699, USA.
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27
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Burow ME, Weldon CB, Chiang TC, Tang Y, Collins-Burow BM, Rolfe K, Li S, McLachlan JA, Beckman BS. Differences in protein kinase C and estrogen receptor alpha, beta expression and signaling correlate with apoptotic sensitivity of MCF-7 breast cancer cell variants. Int J Oncol 2000; 16:1179-87. [PMID: 10811993 DOI: 10.3892/ijo.16.6.1179] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Widespread use of MCF-7 human breast cancer cells as a model system for breast cancer has lead to variations in these cells between different laboratories. Although several reports have addressed these differences in terms of proliferation and estrogenic response, differences in sensitivity to apoptosis have just begun to be described. Based on the possible differences in apoptotic sensitivity that may arise due to the existence of MCF-7 cell variants, we determined the relative sensitivity of MCF-7 cell variants from three established laboratories (designated M, L and N) to known inducers of apoptosis. Consistent with our previous studies we demonstrate that differences exist among these variants in regards to tumor necrosis factor alpha (TNF)-induced cell death and inhibition of proliferation in a dose-dependent manner. To establish if the difference in apoptotic susceptibility was specific to TNF, the three MCF-7 cell variants were tested for their response to other known inducers of apoptosis: okadaic acid, staurosporine and 4-hydroxy-tamoxifen. Viability and DNA fragmentation analysis revealed a similar pattern of resistance to apoptosis by all agents in the MCF-7 M variant. The MCF-7 L variant was resistant to okadaic acid and 4-hydroxy-tamoxifen but not staurosporine. In contrast, MCF-7 N cells were sensitive to induction of apoptosis by all agents. The role of both protein kinase C (PKC) and estrogen signaling in the regulation of cell survival prompted investigation of these pathways as a mechanism for differential sensitivity of MCF-7 cell variants to apoptosis. While both estrogen receptor alpha (ERalpha) and ERbeta were expressed in MCF-7 M and N cells, the absence of ERbeta in MCF-7 L cells correlated with decreased estrogen responsiveness of the L variant. Variations in estrogenic responsiveness and PKC isoform expression may account for the enhanced susceptibility of both the L and N variants to staurosporine.
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Affiliation(s)
- M E Burow
- Molecular and Cellular Biology Program, Tulane University School of Medicine, New Orleans, LA, USA
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Chiang TC, Kok VK, Tu HH, Su YM, Yeh CH, Chung MT. Surgical treatment of bronchiectasis: 10 years' experience. Zhonghua Yi Xue Za Zhi (Taipei) 1999; 62:690-4. [PMID: 10533298] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/14/2023]
Abstract
BACKGROUND Since antibiotic therapy and vaccination have been widely used in medical practice, the incidence of bronchiectasis has decreased steadily. The principal role of surgery associated with this disease is for the treatment of complications. We present an analysis of surgical results during a 10-year period. METHODS The medical records of bronchiectasis patients who were surgically treated were retrospectively reviewed from July, 1987, to March, 1998. The surgical indications, complications and recurrences of bronchiectasis were evaluated. RESULTS A total of 41 bronchiectasis patients underwent surgical treatment from 1987 to 1998 at our hospital. There were 18 males (mean age, 37.8 +/- 15.3 years; range, 16-73 years), and 23 females (mean age, 33 +/- 7.1 years; range, 21-46 years). The indications for surgery were hemoptysis in 30, failed medical treatment in eight, suspected neoplasm in two and retention of a foreign body in one patient. Anatomic resections of the diseased sites were carried out more frequently on the left lower lobes of the lungs. In total, there were 20 left lower lobes, five right lower lobes, 10 left lingular lobes, five right middle lobes, four left upper lobes and one right upper lobe that required surgery. Surgical complications included hemorrhage in one patient, bronchopleural fistula in one and galactorrhea in one patient. The follow-up intervals were from two to 131 months (mean, 72.5 +/- 37.6 months; median, 74 months). There were two cases of recurrent symptoms and six cases of recurrent hemoptysis; all were easily controlled by medication. There were no mortalities. CONCLUSIONS Surgical treatment of bronchiectasis yields immediate resolution of symptoms, better quality of life and no mortalities. Cessation of smoking, avoiding air pollution and careful medical follow-up are mandatory.
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Affiliation(s)
- T C Chiang
- Department of Surgery, Cardinal Tien Hospital, Hsientien, Taipei, Taiwan, ROC
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Chiang TC, Wang CY. Dead-on-arrival patients in Panchiao, Taipei. Zhonghua Yi Xue Za Zhi (Taipei) 1999; 62:509-13. [PMID: 10462827] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/13/2023]
Abstract
BACKGROUND The present emergency medical service (EMS) system in the Panchiao area includes operations in Panchiao, Sulin, Sunshia, Chung Ho and Touchen, which is in the early developmental stage. Educational programs such as emergency medical technician (EMT)-I, and -II have been provided for less than 25% of firefighters in that area. Several mass educational programs in cardiopulmonary resuscitation (CPR) were also provided for the inhabitants of the area. The purpose of this study was to establish a database of dead-on-arrival (DOA) patients during this early stage of the EMS system development so that comparisons of EMS performance could be assessed to identify any future needs of the EMS system in the Panchiao area. METHODS A patient was verified as DOA if there was no pulse nor a response to stimulation. For every DOA patient, several parameters were recorded in a registration book, which began January 1, 1995, and included the following: name, gender, age, mode of transportation, time to hospitalization, on-scene CPR, prehospital basic life support, possible etiology, response to advanced cardiac life support (ACLS), disposition and outcome. The registration book was reviewed and a follow-up study was designed, which covered the entire year of 1995. RESULTS There were 292 DOA patients brought to the emergency room of the Far Eastern Memorial Hospital in Panchiao, Taipei, between January 1, 1995, and December 31, 1995. The study population comprised 190 (65.1%) men and 102 (34.9%) women. The mean age of the men was 51.8 +/- 22.3 years (mean +/- standard deviation). The mean age of the women was 59.8 +/- 24.4 years. Emergency service ambulances transported most DOA patients, though a few were transported by private ambulance from nursing homes. There were only two incidents in which prehospital CPR was conducted. The time to hospitalization varied from five to 170 minutes and averaged 38.3 minutes. Following ACLS, 244 (83.6%) patients were pronounced dead in the emergency room. Cardiovascular and respiratory problems were the leading etiologies and trauma was the second. There were 48 patients (16.4%) who responded to ACLS, but only eight (2.7%) survived until hospital discharge. CONCLUSIONS Delayed initiation of the EMS system resulted in an average time to hospitalization of 38.3 minutes. Cardiovascular collapse was the leading etiology in DOA patients. There were only two patients who received prehospital CPR, suggesting that layperson CPR and EMT education cannot be overemphasized.
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Affiliation(s)
- T C Chiang
- Department of Emergency Medicine, Cardinal Tein Hospital, Hsientien, Taiwan, ROC
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30
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Liang KC, Tsui KY, Tyan YM, Chiang TC. Buspirone impaired acquisition and retention in avoidance tasks: involvement of the hippocampus. CHINESE J PHYSIOL 1998; 41:33-44. [PMID: 9629480] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
This study investigated the effects of buspirone on acquisition as well as formation and expression of memory in three different types of avoidance tasks. Rats were trained and tested on a one-trial inhibitory avoidance task, an 8-trial active avoidance task or the Morris water maze. Buspirone (5.0 mg/kg) was administered subcutaneously 30 min before training, immediately after training or 30 min before testing. Retention was tested at various times after training. In the inhibitory avoidance task, pretraining injections of buspirone produced a marked impairing effect on retention, posttraining injections of buspirone produced a moderate but time-dependent memory deficit. Pretest injections of buspirone suppressed retention performance. Such an effect was more pronounced in the 1-day test than in the 21-day test. Intra-hippocampal infusion of buspirone (5.0 micrograms) before testing suppressed expression of the 1-day, but not the 21-day, memory. In the active avoidance task and the Morris water maze, an injection of buspirone before training or testing also impaired acquisition or suppressed retention performance. These findings suggest that buspirone given at various times could compromise acquisition, consolidation and retrieval of affective memory and the hippocampus was involved in the retrieval effect.
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Affiliation(s)
- K C Liang
- Department of Psychology, National Taiwan University, Taipei, ROC
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31
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Affiliation(s)
- I Hertz-Picciotto
- Department of Epidemiology, CB 7400, University of North Carolina, Chapel Hill 27599, USA
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Abstract
OBJECTIVES Roller-type scanners can be used to digitize radiographs. This study evaluated the physical performance of a roller-type scanner with regard to dynamic range, scan reproducibility, and homogeneity. METHODS A VXR-12 (Vidar System Corp., Herndon, Va.) roller-type scanner with imaging editing software Paint Shop Pro (JASC Inc., Minnetonka, Minn.) was used to digitize a step tablet image on Kodak T-MAT G films (Kodak, Rochester, N.Y.). The step tablet image was scanned at various locations and with different scanning settings. The pixel values of the resulting image were analyzed. The step tablet image was also scanned by a Wellhofer WD 102 Filmdensitometer (Wellhofer Dosimetrie, Schwarzenbruck, Germany) to measure the optical densities of the steps on the film for comparison. RESULTS With the use of the default scanning settings the digitized images had pixel values distributed in a similar dynamic range to that of the film densitometer. This scanner produced consistent images with different scanning positions, different orientation of the images, and different power states of the scanner. CONCLUSIONS This roller-type scanner has a similar dynamic range to that of the film densitometer. The operating condition of the scanner is stable, and the resulting image is not significantly affected by the scanning positions. This type of scanner should be suitable for digitizing dental x-ray films, although the limiting scanning resolution might not be sufficient for some diagnostic purposes.
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Affiliation(s)
- S K Chen
- Division of Oral and Maxillofacial Imaging, School of Dentistry, College of Medicine, National Taiwan University, Taipei
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Wang TC, Wu CM, Sun LS, Chiang TC. [Giant cystic hygroma: a case report]. Zhonghua Yi Xue Za Zhi (Taipei) 1993; 51:479-481. [PMID: 8281498] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Cystic hygromas are congenital malformations of the lymphatic system appearing as single or multiloculated, fluid-filled cavities found mainly in the neck and axilla region. Antenatal ultrasound examination done in this case showed a suspicious giant cystic mass over the neck and chest area. At birth, the mass turned out to be a rare giant cystic hygroma measuring about 25cm x 26cm covering neck, anterior chest, axilla, proximal right upper limb, upper abdomen and upper back area. Because of some compromise to the infant's breathing, an emergency resection was done, and the infant tolerated the procedure well. Pathology report confirmed the diagnosis.
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Affiliation(s)
- T C Wang
- Department of Pediatreics, Far Eastern Memorial Hospital
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Chiang TC, Kok VK, Wong YK. Boerhaave's syndrome--successful treatment of a late case. Zhonghua Yi Xue Za Zhi (Taipei) 1991; 47:50-3. [PMID: 1848463] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
A case of spontaneous rupture of the esophagus (Boerhaave's Syndrome) underwent medical treatment as acute myocardial infarction as initial impression, delay diagnosed 16 days after acute event, and subsequently treated successfully, is presented. Because the patient was critically ill, a conservative management was approached, i.e., NG tube decompression, tube thoracostomy, gastrostomy, broad spectrum antibiotics, TPN to jejunostomy enteral feeding. The patient was salvaged successfully and recovered without complication. The initial unawareness of mediastinal emphysema on chest film resulted in delayed diagnosis.
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Affiliation(s)
- T C Chiang
- Department of Surgery, Far Eastern Memorial Hospital, Taipei, R.O.C
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35
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Liao W, Smith WD, Chiang TC, Williams LR. Rapid, low-cost cleanup procedure for determination of semivolatile organic compounds in human and bovine adipose tissues. J Assoc Off Anal Chem 1988; 71:742-7. [PMID: 3417593] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
A gas chromatographic/mass spectrometric (GC/MS) method is described for determination of organic environmental pollutants in human and bovine adipose tissues. Compounds such as organochlorine pesticides, polychlorinated biphenyls, polynuclear aromatic hydrocarbons, polychlorinated aromatics, and brominated aromatics are extracted with organic solvents and separated from coextracted lipids on a Florisil column. The eluate is concentrated and compounds are identified and quantitated by GC/MS analysis. The method was evaluated in a single laboratory for ability to recover compounds of environmental and regulatory importance. Except for a few more polar compounds, such as phthalates and phosphates, recoveries averaged about 85%. The elution system maximized recovery and allowed minimal coelution of lipid materials. Detection limits for most compounds studied were in the range of 5-50 ng/g (ppb).
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Affiliation(s)
- W Liao
- Lockheed Engineering and Management Services Co., Inc., Environmental Programs, Las Vegas, NV 89119
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Sato K, Hotta M, Kageyama J, Chiang TC, Hu HY, Dong MH, Ling N. Synthesis and in vitro bioactivity of human growth hormone-releasing factor analogs substituted with a single D-amino acid. Biochem Biophys Res Commun 1987; 149:531-7. [PMID: 3122736 DOI: 10.1016/0006-291x(87)90400-1] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Fifty-four analogs of human growth hormone-releasing factor (hGRF) substituted with a single D-amino acid were synthesized by solid phase methodology. Their capacity to release growth hormone was tested on rat anterior pituitary cells in monolayer culture. Among the series of 28 analogs, which had the amino acid at each position of hGRF (1-29)NH2, except glycine at position 15, substituted by the corresponding D-isomer, [D-Ala2]-, [D-Asp3]-, [D-Asn8]-, [D-Tyr10]-, [D-Asp25]-, [D-Met27]-, [D-Ser28]-, and [D-Arg29]hGRF(1-29)NH2 were as potent as hGRF(1-29)NH2, while [D-Ile5]-, [D-Phe6]-, [D-Thr7]-, and [D-Val13]hGRF(1-29)NH2 showed quite low potencies. Effects of substitution with other D-amino acids in positions 2,3,8,9,10 and 11 were also studied. In most cases, the resulting analogs showed decreased potency, but still retained high intrinsic activity. Only [D-Arg2]hGRF(1-29)NH2 showed very low intrinsic activity and some antagonistic property.
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Affiliation(s)
- K Sato
- Laboratories for Neuroendocrinology, Salk Institute, La Jolla, CA 92037
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Chiang TC, Liao W, Williams LR. Use of solid phase Florisil cartridges to separate fat from semivolatile organic compounds in adipose tissue. J Assoc Off Anal Chem 1987; 70:100-2. [PMID: 3031005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
A quick method for separation of semivolatile organic compounds from fat in adipose tissue has been developed. This method uses commercially available solid phase cartridges for sample cleanup. The results indicate that the recoveries, from hexane-extracted fat, of 4 representative classes of organic compounds range from 86.2 to 116%. The solid phase cartridges provide excellent separations of the fat from the analytes; no extraneous interference peaks were detected in the gas chromatograms. The method requires only 0.1 g sample and is quick and simple to use. Although results are reported for samples containing 1-14 ppm, the final extract can be concentrated to a volume allowing detection between 10 and 100 ppb.
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38
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Chan YS, Chiang TC, Cheng YY, Tai KF, Chang HM. [Choleretic effects of acetophenone derivatives and analogues on rats]. Zhongguo Yao Li Xue Bao 1986; 7:443-7. [PMID: 2954420] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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39
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Ling N, Baird A, Wehrenberg WB, Ueno N, Munegumi T, Chiang TC, Regno M, Brazeau P. Synthesis and in vitro bioactivity of human growth hormone-releasing factor analogs substituted at position-1. Biochem Biophys Res Commun 1984; 122:304-10. [PMID: 6430292 DOI: 10.1016/0006-291x(84)90475-3] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Eight position-1 analogs of the 40-amino acid fragment and two position-1 analogs of human growth hormone-releasing factor were synthesized by solid phase methodology and their capacity to release growth hormone was determined using rat anterior pituitary cells in monolayer culture. Relative to hGRF(1-40)OH, which was arbitrarily assigned a potency value of 1, [D-Tyr1]hGRF(1-40)OH, [Phe1]hGRF(1-40)OH, [Trp1]hGRF(1-40)OH, [His1]hGRF(1-40)OH, [Ala1]hGRF(1-40)OH, [(-Ac)Tyr1]hGRF(1-40)OH, Arg0-hGRF(1-40)OH and Ala0-hGRF(1-40)OH have potencies of 0.022, 0.038, 0.003, 0.351, 0.010, 0.032, 0.002 and 0.007 respectively. Relative to hGRF(1-44)NH2 = 1, [(3-Me)His1]hGRF(1-44)NH2 and [(O-Me)Tyr1]hGRF(1-44)NH2 have potencies of 0.132 and 0.001 respectively. These results demonstrate the prerequisite for an aromatic residue at position-1 for potent biological activity and also suggest that the capacity for hydrogen bond formation with the first residue is required for full receptor-ligand interaction.
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40
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Chiang TC, Chang HM, Mak TC. New Oleanene-type Triterpenes from Abrus precatorius and X-ray Crystal Structure of Abrusgenic Acid-Methanol 1:1 Solvate. Planta Med 1983; 49:165-9. [PMID: 17405042 DOI: 10.1055/s-2007-969840] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
From ABRUS PRECATORIUS Abl. triterpenoids abruslactone, methyl abrusgenate and abrusgenic acid were isolated and elucidated by spectroscopic and X-ray techniques.
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Affiliation(s)
- T C Chiang
- Department of Chemistry and Chinese Medicinal Materials Research Centre, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong
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Affiliation(s)
- M P Wong
- Department of Chemistry and Chinese Medicinal Materials Research Centre, The Chinese University of Hong Kong
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42
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Affiliation(s)
- S M Wong
- Department of Chemistry and Chinese Medicinal Materials Research Centre The Chinese University of Hong Kong
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43
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Abstract
After hydrolysis of the saponin fraction of the roots of Abrus cantoniensis, a new triterpenoid sapogenol, cantoniensistriol, was isolated together with sophoradiol, soyasapogenol B and soyasapogenol A. The structures of cantoniensistriol and sophoradiol were elucidated by spectroscopic methods. On the basis of the relation between cantoniensistriol and soyasapogenol A, the steric assignment of the C-21 and C-22 hydroxyl groups of the latter was discussed.
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Affiliation(s)
- T C Chiang
- Chinese Medicinal Material Research Centre, The Chinese University of Hong Kong
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Abstract
A rapid and sensitive method of analysis for retinoic acid in human blood has been developed using gas chromatography-mass spectrometry for separation and detection. The retinoic acid is isolated by solvent extraction into petroleum ether, and converted to methyl retinoate by reacting with dimethylformamide dimethylacetal. The method has been applied to the study of retinoic acid in human blood after subtotal inunction, total inunction and intravenous injection of retinoic acid. The sensitivity limit of 1 ng/ml blood is realized with a 10-ml blood sample.
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45
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Ho BL, Chiang TC. [A study for treadmill exercise protocols for Chinese males (author's transl)]. Taiwan Yi Xue Hui Za Zhi 1980; 79:491-9. [PMID: 6934254] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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46
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Chiang TC, Culbert H, Wyman B, Cohen L, Ovadia J. The half field technique of radiation therapy for the cancers of head and neck. Int J Radiat Oncol Biol Phys 1979; 5:1899-901. [PMID: 528255 DOI: 10.1016/0360-3016(79)90580-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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47
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Ho BL, Wang DJ, Lee YT, Chiang TC, Wang SP, Liu CM. [A study of differences in interpretation of exercise electrocardiogram (author's transl)]. Taiwan Yi Xue Hui Za Zhi 1978; 77:859-67. [PMID: 284095] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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48
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Abstract
The site of origin, the histology, the morphology, the extent, and the T category of the primary carcinoma of nasopharynx and their correlations, including incidence of cervical lymph node metastasis, of 159 consecutive cases seen in a period of four years are studied.
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49
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Sharett T, Fine L, Chiang TC. Rapid afterloading with guide fixation of radioactive sources in cancer of the oral cavity. Am J Roentgenol Radium Ther Nucl Med 1974; 120:182-7. [PMID: 4810296 DOI: 10.2214/ajr.120.1.182] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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50
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Lin TM, Chen KP, Lin CC, Hsu MM, Tu SM, Chiang TC, Jung PF, Hirayama T. Retrospective study on nasopharyngeal carcinoma. J Natl Cancer Inst 1973; 51:1403-8. [PMID: 4762926 DOI: 10.1093/jnci/51.5.1403] [Citation(s) in RCA: 62] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
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