1
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Pan CR, Chou MY. Energetically Favored 2D to 3D Transition: Why Silicene Cannot Be Grown on Ag(111). Nano Lett 2024; 24:4172-4177. [PMID: 38502098 PMCID: PMC11010229 DOI: 10.1021/acs.nanolett.4c00140] [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: 01/11/2024] [Revised: 03/10/2024] [Accepted: 03/13/2024] [Indexed: 03/20/2024]
Abstract
Silicene, a two-dimensional (2D) Si monolayer with properties similar to those of graphene, has attracted considerable attention because of its compatibility with existing technology. Most growth efforts to date have focused on the Ag(111) substrate, with a 3 × 3 phase widely reported below one monolayer (ML). As the coverage increases, a √3 × √3 pattern frequently emerges, which has been proposed by various experimental investigations as a Si ( 111 ) - 3 × 3 - Ag reconstructed structure. We report first-principles calculations to understand this series of observations. A major finding from our energetics studies is that Si growth on Ag(111) beyond one ML will switch to the Volmer-Weber mode, forming three-dimensional sp3 films. Combining with the condition that the 3 × 3 monolayer on Ag(111) does not have the correct buckling pattern of freestanding silicene, we conclude that silicene cannot be grown on Ag(111) and that a 2D to 3D transition is energetically favored beyond one ML.
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Affiliation(s)
- Chi-Ruei Pan
- School
of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
- Institute
of Atomic and Molecular Sciences, Academia
Sinica, Taipei 11529, Taiwan
| | - Mei-Yin Chou
- School
of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
- Institute
of Atomic and Molecular Sciences, Academia
Sinica, Taipei 11529, Taiwan
- Department
of Physics, National Taiwan University, Taipei 10617, Taiwan
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2
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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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3
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Chen CJ, Chou MY, Huang YL, Hsiao SM. [Practice Barriers for Nurse Practitioners in Rural Hospitals]. Hu Li Za Zhi 2023; 70:47-55. [PMID: 37469319 DOI: 10.6224/jn.202308_70(4).07] [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] [Subscribe] [Scholar Register] [Indexed: 07/21/2023]
Abstract
BACKGROUND Nurse practitioners (NPs) are regarded as part of the primary healthcare professional team in rural hospitals, which often faced difficulties in hiring doctors. Only a few studies have been conducted that assess the barriers to practice for NPs in rural hospitals in Taiwan. PURPOSE This study was designed to explore the barriers of practice for NPs working in rural hospitals. METHODS A qualitative research approach was used in this study, and participants were recruited using purposive sampling. Data on barriers to clinical practice were collected using face-to-face, in-depth interviews. RESULTS A total of 10 NPs participated in this study. The three barriers identified were patient safety concerns, the impact of limited medical resources and the demands and heavy workload on NPs, and the difficulties of balancing the interests of profit-oriented hospitals and patients' personal medical insurance rights. CONCLUSIONS / IMPLICATIONS FOR PRACTICE To reduce barriers to practice, NPs require additional training from the government to strengthen their clinical knowledge and skills. In addition, when facing insufficient support from the Department of Health, these NPs may leverage online hospital marketing and crowdfunding platforms to obtain necessary software/hardware resources for their rural hospitals. If universal health insurance and personal medical insurance are misused within a hospital, NPs should have the moral courage to speak up and should be provided with adequate protection under rules and regulations that allow them to report cheating, illegal behaviors, and other activities that waste / misdirect healthcare resources.
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Affiliation(s)
- Chen-Ju Chen
- MSN, RN, NP, Department of Nursing, Chaozhou Antai Hospital, Taiwan, ROC
| | - Mei-Yin Chou
- BSN, RN, NP, Department of Nursing, Chaozhou Antai Hospital, Taiwan, ROC
| | - Yen-Ling Huang
- MSN, RN, NP, Department of Nursing, Zuoying Branch of Kaohsiung Armed Forces General Hospital, Taiwan, ROC
| | - Szu-Mei Hsiao
- PhD, RN, Assistant Professor, Department of Nursing, National Chi Nan University, Taiwan, ROC.
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4
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Holbrook M, Chen Y, Kim H, Frammolino L, Liu M, Pan CR, Chou MY, Zhang C, Shih CK. Creating a Nanoscale Lateral Junction in a Semiconductor Monolayer with a Large Built-in Potential. ACS Nano 2023; 17:6966-6972. [PMID: 36946518 DOI: 10.1021/acsnano.3c01082] [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: 06/18/2023]
Abstract
The ability to engineer atomically thin nanoscale lateral junctions is critical to lay the foundation for future two-dimensional (2D) device technology. However, the traditional approach to creating a heterojunction by direct growth of a heterostructure of two different materials constrains the available band offsets, and it is still unclear if large built-in potentials are attainable for 2D materials. The electronic properties of atomically thin semiconducting transition metal dichalcogenides (TMDs) are not static, and their exciton binding energy and quasiparticle band gap depend strongly on the proximal environment. Recent studies have shown that this effect can be harnessed to engineer the lateral band profile of a monolayer TMD to create a lateral electronic junction. Here we demonstrate the synthesis of a nanoscale lateral junction in monolayer MoSe2 by intercalating Se at the interface of an hBN/Ru(0001) substrate. The Se intercalation creates a spatially abrupt modulation of the local hBN/Ru work function, which is imprinted directly onto an overlying MoSe2 monolayer to create a lateral junction with a large built-in potential of 0.83 ± 0.06 eV. We spatially resolve the MoSe2 band profile and work function using scanning tunneling spectroscopy to map out the nanoscale depletion region. The Se intercalation also modifies the dielectric environment, influencing the local band gap renormalization and increasing the MoSe2 band gap by ∼0.26 ± 0.1 eV. This work illustrates that environmental proximity engineering provides a robust method to indirectly manipulate the band profile of 2D materials outside the limits of their intrinsic properties.
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Affiliation(s)
- Madisen Holbrook
- Department of Physics, The University of Texas, Austin, Texas 78712, United States
| | - Yuxuan Chen
- Department of Physics, The University of Texas, Austin, Texas 78712, United States
| | - Hyunsue Kim
- Department of Physics, The University of Texas, Austin, Texas 78712, United States
| | - Lisa Frammolino
- Department of Physics, The University of Texas, Austin, Texas 78712, United States
| | - Mengke Liu
- Department of Physics, The University of Texas, Austin, Texas 78712, United States
| | - Chi-Ruei Pan
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - Mei-Yin Chou
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - Chengdong Zhang
- School of Physics and Technology, Wuhan University, Wuhan 430072, China
| | - Chih-Kang Shih
- Department of Physics, The University of Texas, Austin, Texas 78712, United States
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5
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Wang J, Gao J, Chou MY, Landman U. Structure Relaxation and Liquidlike Enhanced Cu Diffusion at the Surface of β-Cu 2S Chalcocite. Nano Lett 2021; 21:8895-8900. [PMID: 34617776 DOI: 10.1021/acs.nanolett.1c03504] [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] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The hitherto unexplored surface structural and dynamical properties of the thermoelectric material β-Cu2S chalcocite, are uncovered using ab initio molecular dynamics simulations at 450 K. The material exhibits a hybrid crystalline-liquid behavior, with the liquidlike dynamics of the Cu atoms and the crystalline order of the sulfur sublattice. The topmost nanoscale region of the material is predicted to undergo significant structural relaxation, resulting in a ∼10% increase in the distance between the topmost S-layers accompanied by an increased Cu density. Cu diffusion in the interlayer regions of the surface S-sublattice is enhanced (doubled) compared to the bulk value, and an underlying microscopic mechanism, entailing marked emergent surface-induced softening of the S-sublattice vibrational dynamics, is described.
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Affiliation(s)
- Jing Wang
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430, United States
| | - Jianping Gao
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430, United States
| | - Mei-Yin Chou
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430, United States
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan
| | - Uzi Landman
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430, United States
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6
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Siao MD, Lin YC, He T, Tsai MY, Lee KY, Chang SY, Lin KI, Lin YF, Chou MY, Suenaga K, Chiu PW. Embedment of Multiple Transition Metal Impurities into WS 2 Monolayer for Bandstructure Modulation. Small 2021; 17:e2007171. [PMID: 33711202 DOI: 10.1002/smll.202007171] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2020] [Revised: 02/12/2021] [Indexed: 06/12/2023]
Abstract
Band structure by design in 2D layered semiconductors is highly desirable, with the goal to acquire the electronic properties of interest through the engineering of chemical composition, structure, defect, stacking, or doping. For atomically thin transition metal dichalcogenides, substitutional doping with more than one single type of transition metals is the task for which no feasible approach is proposed. Here, the growth of WS2 monolayer is shown codoped with multiple kinds of transition metal impurities via chemical vapor deposition controlled in a diffusion-limited mode. Multielement embedment of Cr, Fe, Nb, and Mo into the host lattice is exemplified. Abundant impurity states thus generate in the bandgap of the resultant WS2 and provide a robust switch of charging/discharging states upon sweep of an electric filed. A profound memory window exists in the transfer curves of doped WS2 field-effect transistors, forming the basis of binary states for robust nonvolatile memory. The doping technique presented in this work brings one step closer to the rational design of 2D semiconductors with desired electronic properties.
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Affiliation(s)
- Ming-Deng Siao
- Department of Electrical Engineering, National Tsing Hua University, Hsinchu, 30013, Taiwan
| | - Yung-Chang Lin
- National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, 305-8565, Japan
| | - Tao He
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan
| | - Meng-Yu Tsai
- Department of Electrical Engineering, National Tsing Hua University, Hsinchu, 30013, Taiwan
- Department of Physics, National Chung Hsing University, Taichung, 40227, Taiwan
| | - Kuei-Yi Lee
- Graduate Institute of Electro-Optical Engineering, National Taiwan University of Science and Technology, Taipei, 10607, Taiwan
| | - Shou-Yi Chang
- Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, 30013, Taiwan
| | - Kuang-I Lin
- Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan, 70101, Taiwan
| | - Yen-Fu Lin
- Department of Physics, National Chung Hsing University, Taichung, 40227, Taiwan
| | - Mei-Yin Chou
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan
- Department of Physics, National Taiwan University, Taipei, 10617, Taiwan
| | - Kazu Suenaga
- National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, 305-8565, Japan
| | - Po-Wen Chiu
- Department of Electrical Engineering, National Tsing Hua University, Hsinchu, 30013, Taiwan
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan
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7
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Zhang H, Holbrook M, Cheng F, Nam H, Liu M, Pan CR, West D, Zhang S, Chou MY, Shih CK. Epitaxial Growth of Two-Dimensional Insulator Monolayer Honeycomb BeO. ACS Nano 2021; 15:2497-2505. [PMID: 33481561 DOI: 10.1021/acsnano.0c06596] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The emergence of two-dimensional (2D) materials launched a fascinating frontier of flatland electronics. Most crystalline atomic layer materials are based on layered van der Waals materials with weak interlayer bonding, which naturally leads to thermodynamically stable monolayers. We report the synthesis of a 2D insulator composed of a single atomic sheet of honeycomb structure BeO (h-BeO), although its bulk counterpart has a wurtzite structure. The h-BeO is grown by molecular beam epitaxy (MBE) on Ag(111) thin films that are also epitaxially grown on Si(111) wafers. Using scanning tunneling microscopy and spectroscopy (STM/S), the honeycomb BeO lattice constant is determined to be 2.65 Å with an insulating band gap of 6 eV. Our low-energy electron diffraction measurements indicate that the h-BeO forms a continuous layer with good crystallinity at the millimeter scale. Moiré pattern analysis shows the BeO honeycomb structure maintains long-range phase coherence in atomic registry even across Ag steps. We find that the interaction between the h-BeO layer and the Ag(111) substrate is weak by using STS and complementary density functional theory calculations. We not only demonstrate the feasibility of growing h-BeO monolayers by MBE, but also illustrate that the large-scale growth, weak substrate interactions, and long-range crystallinity make h-BeO an attractive candidate for future technological applications. More significantly, the ability to create a stable single-crystalline atomic sheet without a bulk layered counterpart is an intriguing approach to tailoring 2D electronic materials.
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Affiliation(s)
- Hui Zhang
- Department of Physics, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Madisen Holbrook
- Department of Physics, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Fei Cheng
- Department of Physics, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Hyoungdo Nam
- Department of Physics, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Mengke Liu
- Department of Physics, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Chi-Ruei Pan
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
| | - Damien West
- Department of Physics, Rensselaer Polytechnic Institute, Troy, New York 12180, United States
| | - Shengbai Zhang
- Department of Physics, Rensselaer Polytechnic Institute, Troy, New York 12180, United States
| | - Mei-Yin Chou
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - Chih-Kang Shih
- Department of Physics, The University of Texas at Austin, Austin, Texas 78712, United States
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8
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Abstract
A van der Waals bonded moiré bilayer formed by sequential growth of TiSe2 and TiTe2 monolayers exhibits emergent electronic structure as evidenced by angle-resolved photoemission band mapping. The two monolayers adopt the same lattice orientation but incommensurate lattice constants. Despite the lack of translational symmetry, sharp dispersive bands are observed. The dispersion relations appear distinct from those for the component monolayers alone. Theoretical calculations illustrate the formation of composite bands by coherent electronic coupling despite the weak interlayer bonding, which leads to band renormalization and energy shifts.
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Affiliation(s)
- 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
| | - Tao He
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - 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
| | - 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, Shanghai 200240, China
| | - Sung-Kwan Mo
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, 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
| | - T-C 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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9
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Abstract
Contact engineering has been the central issue in the context of high-performance field-effect transistors (FETs) made of atomic thin transition metal dichalcogenides (TMDs). Conventional metal contacts on TMDs have been made on top via a lithography process, forming a top-bonded contact scheme with an appreciable contact barrier. To provide a more efficient pathway for charge injection, an end-bonded contact scheme has been proposed, in which covalent bonds are formed between the contact metal and channel edges. Yet, little efforts have been made to realize this contact configuration. Here, we bridge this gap and demonstrate seeded growth of end-bonded contact with different TMDs by means of chemical vapor deposition (CVD). Monolayer WSe2 FETs with a CVD-grown channel and end contacts exhibit improved performance metrics, including an on-current density of 30 μA/μm, a hole mobility of 90 cm2/V·s, and a subthreshold swing of 94 mV/dec, an order of magnitude superior than those of top-contact FET counterparts that share the same channel material. A fundamental NOT logic gate constructed using top-gated and end-bonded WSe2 and MoS2 FETs is also demonstrated. Calculations using density functional theory indicate that the superior device performance stems mainly from the stronger metal-TMD hybridization and substantial gap states in the end-contact configuration.
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Affiliation(s)
- Chun-Hao Chu
- Department of Electrical Engineering , National Tsing Hua University , Hsinchu 30013 , Taiwan
| | - Ho-Chun Lin
- Institute of Atomic and Molecular Sciences , Academia Sinica , Taipei 10617 , Taiwan
- Department of Physics , National Taiwan University , Taipei 10617 , Taiwan
| | - Chao-Hui Yeh
- Department of Electrical Engineering , National Tsing Hua University , Hsinchu 30013 , Taiwan
| | - Zheng-Yong Liang
- Department of Electrical Engineering , National Tsing Hua University , Hsinchu 30013 , Taiwan
| | - Mei-Yin Chou
- Institute of Atomic and Molecular Sciences , Academia Sinica , Taipei 10617 , Taiwan
- Department of Physics , National Taiwan University , Taipei 10617 , Taiwan
| | - Po-Wen Chiu
- Department of Electrical Engineering , National Tsing Hua University , Hsinchu 30013 , Taiwan
- Institute of Atomic and Molecular Sciences , Academia Sinica , Taipei 10617 , Taiwan
- Frontier Research Center on Fundamental and Applied Science of Matters , National Tsing Hua University , Hsinchu 30013 , Taiwan
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10
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Wei PC, Bhattacharya S, Liu YF, Liu F, He J, Tung YH, Yang CC, Hsing CR, Nguyen DL, Wei CM, Chou MY, Lai YC, Hung TL, Guan SY, Chang CS, Wu HJ, Lee CH, Li WH, Hermann RP, Chen YY, Rao AM. Thermoelectric Figure-of-Merit of Fully Dense Single-Crystalline SnSe. ACS Omega 2019; 4:5442-5450. [PMID: 31459709 PMCID: PMC6648424 DOI: 10.1021/acsomega.8b03323] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2018] [Accepted: 02/14/2019] [Indexed: 05/26/2023]
Abstract
Single-crystalline SnSe has attracted much attention because of its record high figure-of-merit ZT ≈ 2.6; however, this high ZT has been associated with the low mass density of samples which leaves the intrinsic ZT of fully dense pristine SnSe in question. To this end, we prepared high-quality fully dense SnSe single crystals and performed detailed structural, electrical, and thermal transport measurements over a wide temperature range along the major crystallographic directions. Our single crystals were fully dense and of high purity as confirmed via high statistics 119Sn Mössbauer spectroscopy that revealed <0.35 at. % Sn(IV) in pristine SnSe. The temperature-dependent heat capacity (C p) provided evidence for the displacive second-order phase transition from Pnma to Cmcm phase at T c ≈ 800 K and a small but finite Sommerfeld coefficient γ0 which implied the presence of a finite Fermi surface. Interestingly, despite its strongly temperature-dependent band gap inferred from density functional theory calculations, SnSe behaves like a low-carrier-concentration multiband metal below 600 K, above which it exhibits a semiconducting behavior. Notably, our high-quality single-crystalline SnSe exhibits a thermoelectric figure-of-merit ZT ∼1.0, ∼0.8, and ∼0.25 at 850 K along the b, c, and a directions, respectively.
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Affiliation(s)
- Pai-Chun Wei
- Institute of Physics, Academia Sinica, Taipei 11529, Taiwan, Republic of China
- Computer, Electrical, and Mathematical Sciences and Engineering
Division, King Abdullah University of Science
and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
| | - Sriparna Bhattacharya
- Department
of Physics and Astronomy, Clemson Nanomaterials Institute, Clemson University, Clemson 29634-0978, United States
| | - Yu-Fei Liu
- Department
of Physics and Astronomy, Clemson Nanomaterials Institute, Clemson University, Clemson 29634-0978, United States
| | - Fengjiao Liu
- Department
of Physics and Astronomy, Clemson Nanomaterials Institute, Clemson University, Clemson 29634-0978, United States
| | - Jian He
- Department
of Physics and Astronomy, Clemson Nanomaterials Institute, Clemson University, Clemson 29634-0978, United States
| | - Yung-Hsiang Tung
- Department of Physics, Chung Yuan Christian University, Chung-Li 32023, Taiwan, Republic of China
| | - Chun-Chuen Yang
- Department of Physics, Chung Yuan Christian University, Chung-Li 32023, Taiwan, Republic of China
| | - Cheng-Rong Hsing
- Institute
of Atomic and Molecular Sciences, Academia
Sinica, Taipei 10617, Taiwan, Republic of China
| | - Duc-Long Nguyen
- Institute
of Atomic and Molecular Sciences, Academia
Sinica, Taipei 10617, Taiwan, Republic of China
- Department of Physics, National Central University, Taoyuan
City 32001, Taiwan, Republic of China
- Molecular Science and Technology
Program, Taiwan International Graduate Program, Academia Sinica, Taipei 11529, Taiwan, Republic of China
| | - Ching-Ming Wei
- Institute
of Atomic and Molecular Sciences, Academia
Sinica, Taipei 10617, Taiwan, Republic of China
| | - Mei-Yin Chou
- Institute
of Atomic and Molecular Sciences, Academia
Sinica, Taipei 10617, Taiwan, Republic of China
| | - Yen-Chung Lai
- National Synchrotron Radiation Research
Center, Hsin-Chu 30076, Taiwan, Republic of China
| | - Tsu-Lien Hung
- Institute of Physics, Academia Sinica, Taipei 11529, Taiwan, Republic of China
| | - Syu-You Guan
- Institute of Physics, Academia Sinica, Taipei 11529, Taiwan, Republic of China
- Department of Physics, National
Taiwan University, Taipei 10617, Taiwan, Republic of China
| | - Chia-Seng Chang
- Institute of Physics, Academia Sinica, Taipei 11529, Taiwan, Republic of China
- Department of Physics, National
Taiwan University, Taipei 10617, Taiwan, Republic of China
| | - Hsin-Jay Wu
- Department
of Materials Science and Engineering, National
Chiao Tung University, Hsinchu 30010, Taiwan, Republic of China
| | - Chi-Hung Lee
- Department of Physics, National Central University, Taoyuan
City 32001, Taiwan, Republic of China
| | - Wen-Hsien Li
- Department of Physics, National Central University, Taoyuan
City 32001, Taiwan, Republic of China
| | - Raphael P. Hermann
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Yang-Yuan Chen
- Institute of Physics, Academia Sinica, Taipei 11529, Taiwan, Republic of China
| | - Apparao M. Rao
- Department
of Physics and Astronomy, Clemson Nanomaterials Institute, Clemson University, Clemson 29634-0978, United States
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11
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Yeh CH, Chen HC, Lin HC, Lin YC, Liang ZY, Chou MY, Suenaga K, Chiu PW. Ultrafast Monolayer In/Gr-WS 2-Gr Hybrid Photodetectors with High Gain. ACS Nano 2019; 13:3269-3279. [PMID: 30790512 DOI: 10.1021/acsnano.8b09032] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [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
One of the primary limitations of previously reported two-dimensional (2D) photodetectors is a low frequency response (≪ 1 Hz) for sensitive devices with gain. Yet, little efforts have been devoted to improve the temporal response of photodetectors while maintaining high gain and responsivity. Here, we demonstrate a gain of 6.3 × 103 electrons per photon and a responsivity of 2.6 × 103 A/W while simultaneously exhibiting an ultrafast response time of 40-65 μs in a hybrid photodetector that consists of graphene-WS2-graphene junctions covered with indium (In) adatoms atop. The resultant responsivity is 6 orders of magnitude higher than that of conventional photodetectors comprising solely of a Au-WS2-Au junction. The photogain is provided mainly by the adsorbed In adatoms, from which photogenerated electrons can be transferred to the WS2 channel, while holes remain trapped in In adatoms, leading to a photogating effect as electrons are recirculating during the residence of holes in In adatoms. At a gate voltage near the Dirac point of graphene, a detectivity of D* = 2.2 × 1012 Jones and an ON/OFF ratio of 104 are achieved. The enhanced performance of the device can be attributed partly to the transparent graphene/WS2 contact and partly to the strong capacitive coupling of the In adatoms with the WS2 channel, which enables ultrafast carrier dynamics.
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Affiliation(s)
- Chao-Hui Yeh
- Department of Electrical Engineering , National Tsing Hua University , Hsinchu 30013 , Taiwan
| | - Hsiang-Chieh Chen
- Department of Electrical Engineering , National Tsing Hua University , Hsinchu 30013 , Taiwan
| | - Ho-Chun Lin
- Institute of Atomic and Molecular Sciences, Academia Sinica , Taipei 10617 , Taiwan
- Department of Physics , National Taiwan University , Taipei 10617 , Taiwan
| | - Yung-Chang Lin
- National Institute of Advanced Industrial Science and Technology (AIST) , Tsukuba 305-8565 , Japan
| | - Zheng-Yong Liang
- Department of Electrical Engineering , National Tsing Hua University , Hsinchu 30013 , Taiwan
| | - Mei-Yin Chou
- Institute of Atomic and Molecular Sciences, Academia Sinica , Taipei 10617 , Taiwan
- Department of Physics , National Taiwan University , Taipei 10617 , Taiwan
| | - Kazu Suenaga
- National Institute of Advanced Industrial Science and Technology (AIST) , Tsukuba 305-8565 , Japan
| | - Po-Wen Chiu
- Department of Electrical Engineering , National Tsing Hua University , Hsinchu 30013 , Taiwan
- Institute of Atomic and Molecular Sciences, Academia Sinica , Taipei 10617 , Taiwan
- Frontier Research Center on Fundamental and Applied Science of Matters , National Tsing Hua University , Hsinchu 30013 , Taiwan
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12
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Lin YC, Yeh CH, Lin HC, Siao MD, Liu Z, Nakajima H, Okazaki T, Chou MY, Suenaga K, Chiu PW. Stable 1T Tungsten Disulfide Monolayer and Its Junctions: Growth and Atomic Structures. ACS Nano 2018; 12:12080-12088. [PMID: 30525432 DOI: 10.1021/acsnano.8b04979] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [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
Transition-metal dichalcogenides in the 1T phase have been a subject of increasing interest, which is partly due to their fascinating physical properties and partly to their potential applications in the next generation of electronic devices, including supercapacitors, electrocatalytic hydrogen evolution, and phase-transition memories. The primary method for obtaining 1T WS2 or MoS2 has been using ion intercalation in combination with solution-based exfoliation. The resulting flakes are small in size and tend to aggregate upon deposition, forming an intercalant-TMD complex with small 1T and 1T' patches embedded in the 2H matrix. Existing growth methods have, however, produced WS2 or MoS2 solely in the 2H phase. Here, we have refined the growth approach to obtain monolayer 1T WS2 up to 80 μm in size based on chemical vapor deposition. With the aid of synergistic catalysts (iron oxide and sodium chloride), 1T WS2 can nucleate in the infant stage of the growth, forming special butterfly-like single crystals with the 1T phase in one wing and the 2H phase in the other. Distinctive types of phase boundaries are discovered at the 1T-2H interface. The 1T structure thus grown is thermodynamically stable over time and even persists at a high temperature above 800 °C, allowing for a stepwise edge epitaxy of lateral 1T heterostructures. Atomic images show that the 1T WS2-MoS2 heterojunction features a coherent and defectless interface with a sharp atomic transition. The stable 1T phase represents a missing piece of the puzzle in the research of atomic thin van der Waals crystals, and our growth approach provides an accessible way of filling this gap.
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Affiliation(s)
| | - Chao-Hui Yeh
- Department of Electrical Engineering , National Tsing Hua University , Hsinchu 30013 , Taiwan
| | - Ho-Chun Lin
- Institute of Atomic and Molecular Sciences , Academia Sinica , Taipei 10617 , Taiwan
| | - Ming-Deng Siao
- Department of Electrical Engineering , National Tsing Hua University , Hsinchu 30013 , Taiwan
| | - Zheng Liu
- Inorganic Functional Materials Research Institute , National Institute of Advanced Industrial Science and Technology (AIST) , Nagoya 463-8560 , Japan
| | | | | | - Mei-Yin Chou
- Institute of Atomic and Molecular Sciences , Academia Sinica , Taipei 10617 , Taiwan
| | - Kazu Suenaga
- Department of Mechanical Engineering , The University of Tokyo , Tokyo 113-8656 , Japan
| | - Po-Wen Chiu
- Department of Electrical Engineering , National Tsing Hua University , Hsinchu 30013 , Taiwan
- Institute of Atomic and Molecular Sciences , Academia Sinica , Taipei 10617 , Taiwan
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13
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Abstract
To date, almost all of the discussions on topological insulators (TIs) have focused on two- and three-dimensional systems. One-dimensional (1D) TIs manifested in real materials, in which localized spin states may exist at the end or near the junctions, have largely been unexplored. Previous studies have considered the system of gapped graphene nanoribbons (GNRs) possessing spatial symmetries (e.g., inversion) with only termination patterns commensurate with inversion- or mirror-symmetric unit cells. In this work, we prove that a symmetry-protected [Formula: see text] topological classification exists for any type of termination. In these cases the Berry phase summed up over all occupied bands turns out to be π-quantized in the presence of the chiral symmetry. However, it does not always provide the correct corresponding [Formula: see text] as one would have expected. We show that only the origin-independent part of the Berry phase gives the correct bulk-boundary correspondence by its π-quantized values. The resulting [Formula: see text] invariant depends on the choice of the 1D unit cell (defined by the nanoribbon termination) and is shown to be connected to the symmetry eigenvalues of the wave functions at the center and boundary of the Brillouin zone. Using the cove-edged GNRs as examples, we demonstrate the existence of localized states at the end of some GNR segments and at the junction between two GNRs based on a topological analysis. The current results are expected to shed light on the design of electronic devices based on GNRs as well as the understanding of the topological features in 1D systems.
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Affiliation(s)
- Kuan-Sen Lin
- Department of Physics , National Taiwan University , Taipei 10617 , Taiwan
- Department of Physics , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801-3080 , United States
- Institute of Atomic and Molecular Sciences , Academia Sinica , Taipei 10617 , Taiwan
| | - Mei-Yin Chou
- Department of Physics , National Taiwan University , Taipei 10617 , Taiwan
- Institute of Atomic and Molecular Sciences , Academia Sinica , Taipei 10617 , Taiwan
- School of Physics , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States
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14
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Chen P, Pai WW, Chan YH, Madhavan V, Chou MY, Mo SK, Fedorov AV, Chiang TC. Unique Gap Structure and Symmetry of the Charge Density Wave in Single-Layer VSe_{2}. Phys Rev Lett 2018; 121:196402. [PMID: 30468619 DOI: 10.1103/physrevlett.121.196402] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2018] [Indexed: 06/09/2023]
Abstract
Single layers of transition metal dichalcogenides (TMDCs) are excellent candidates for electronic applications beyond the graphene platform; many of them exhibit novel properties including charge density waves (CDWs) and magnetic ordering. CDWs in these single layers are generally a planar projection of the corresponding bulk CDWs because of the quasi-two-dimensional nature of TMDCs; a different CDW symmetry is unexpected. We report herein the successful creation of pristine single-layer VSe_{2}, which shows a (sqrt[7]×sqrt[3]) CDW in contrast to the (4×4) CDW for the layers in bulk VSe_{2}. Angle-resolved photoemission spectroscopy from the single layer shows a sizable (sqrt[7]×sqrt[3]) CDW gap of ∼100 meV at the zone boundary, a 220 K CDW transition temperature twice the bulk value, and no ferromagnetic exchange splitting as predicted by theory. This robust CDW with an exotic broken symmetry as the ground state is explained via a first-principles analysis. The results illustrate a unique CDW phenomenon in the two-dimensional limit.
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Affiliation(s)
- P Chen
- Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080, USA
- Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, 104 South Goodwin Avenue, Urbana, Illinois 61801-2902, USA
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Woei Wu Pai
- Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan
- Department of Physics, National Taiwan University, Taipei 10617, Taiwan
| | - Y-H Chan
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - V Madhavan
- Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080, USA
- Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, 104 South Goodwin Avenue, Urbana, Illinois 61801-2902, USA
| | - M Y Chou
- Department of Physics, National Taiwan University, Taipei 10617, Taiwan
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
| | - S-K Mo
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - A-V Fedorov
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - T-C Chiang
- Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080, USA
- Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, 104 South Goodwin Avenue, Urbana, Illinois 61801-2902, USA
- Department of Physics, National Taiwan University, Taipei 10617, Taiwan
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15
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Zhang Q, Yu J, Ebert P, Zhang C, Pan CR, Chou MY, Shih CK, Zeng C, Yuan S. Tuning Band Gap and Work Function Modulations in Monolayer hBN/Cu(111) Heterostructures with Moiré Patterns. ACS Nano 2018; 12:9355-9362. [PMID: 30107116 DOI: 10.1021/acsnano.8b04444] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The moiré pattern formed between a two-dimensional (2D) material and the substrate has played a crucial role in tuning the electronic structure of the 2D material. Here, by using scanning tunneling microscopy and spectroscopy, we found a moiré-pattern-dependent band gap and work function modulation in hexagonal boron nitride (hBN)/Cu(111) heterostructures, whose amplitudes increase with the moiré pattern wavelength. Moreover, the work function modulation shifts agree well with the conduction band edge shifts, indicating a spatially constant electron affinity for the hBN layer. Density functional theory calculations showed that these observations in hBN/Cu(111) heterostructures mainly originated from the hybridization of the N 3p z orbital and Cu 4s orbital in different atomic configurations. Our results show that the twist-angle dependence of moiré patterns in hBN/Cu(111) heterostructures can be used to tailor the electronic properties including band gap and work function.
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Affiliation(s)
- Qiang Zhang
- International Center for Quantum Design of Functional Materials (ICQD), Hefei National Laboratory for Physical Sciences at the Microscale, and Synergetic Innovation Center of Quantum Information and Quantum Physics , University of Science and Technology of China , Hefei , Anhui 230026 , China
- CAS Key Laboratory of Strongly-Coupled Quantum Matter Physics, and Department of Physics , University of Science and Technology of China , Hefei , Anhui 230026 , China
- Department of Physics , University of Texas at Austin , Austin , Texas 78712 , United States
| | - Jin Yu
- Beijing Computational Science Research Center , Beijing 100084 , China
- Theory of Condensed Matter , Radboud University , Nijmegen 6525 , AJ , The Netherlands
| | - Philipp Ebert
- Peter Grünberg Institut , Forschungszentrum Jülich GmbH , 52425 Jülich , Germany
| | - Chendong Zhang
- Department of Physics , University of Texas at Austin , Austin , Texas 78712 , United States
- School of Physics and Technology , Wuhan University , Wuhan 430072 , China
| | - Chi-Ruei Pan
- School of Physics , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States
| | - Mei-Yin Chou
- School of Physics , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States
- Institute of Atomic and Molecular Sciences , Academia Sinica , Taipei 10617 , Taiwan
| | - Chih-Kang Shih
- Department of Physics , University of Texas at Austin , Austin , Texas 78712 , United States
| | - Changgan Zeng
- International Center for Quantum Design of Functional Materials (ICQD), Hefei National Laboratory for Physical Sciences at the Microscale, and Synergetic Innovation Center of Quantum Information and Quantum Physics , University of Science and Technology of China , Hefei , Anhui 230026 , China
- CAS Key Laboratory of Strongly-Coupled Quantum Matter Physics, and Department of Physics , University of Science and Technology of China , Hefei , Anhui 230026 , China
| | - Shengjun Yuan
- Beijing Computational Science Research Center , Beijing 100084 , China
- School of Physics and Technology , Wuhan University , Wuhan 430072 , China
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16
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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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17
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Chen P, Pai WW, Chan YH, Sun WL, Xu CZ, Lin DS, Chou MY, Fedorov AV, Chiang TC. Large quantum-spin-Hall gap in single-layer 1T' WSe 2. Nat Commun 2018; 9:2003. [PMID: 29784909 PMCID: PMC5962594 DOI: 10.1038/s41467-018-04395-2] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [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: 02/07/2018] [Accepted: 04/24/2018] [Indexed: 12/04/2022] Open
Abstract
Two-dimensional (2D) topological insulators (TIs) are promising platforms for low-dissipation spintronic devices based on the quantum-spin-Hall (QSH) effect, but experimental realization of such systems with a large band gap suitable for room-temperature applications has proven difficult. Here, we report the successful growth on bilayer graphene of a quasi-freestanding WSe2 single layer with the 1T′ structure that does not exist in the bulk form of WSe2. Using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy/spectroscopy (STM/STS), we observe a gap of 129 meV in the 1T′ layer and an in-gap edge state located near the layer boundary. The system′s 2D TI characters are confirmed by first-principles calculations. The observed gap diminishes with doping by Rb adsorption, ultimately leading to an insulator–semimetal transition. The discovery of this large-gap 2D TI with a tunable band gap opens up opportunities for developing advanced nanoscale systems and quantum devices. The current known two-dimensional topological insulators with small band gaps limit the potential for room temperature applications. Here, Chen et al. observe a sizable gap of 129 meV in a 1T'-WSe2 single layer grown on bilayer graphene with in-gap edge state near the layer boundary.
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Affiliation(s)
- P Chen
- 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. .,Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
| | - Woei Wu Pai
- Center for Condensed Matter Sciences, National Taiwan University, Taipei, 10617, Taiwan.,Department of Physics, National Taiwan University, Taipei, 10617, Taiwan.,Center of Atomic Initiative for New Materials, National Taiwan University, Taipei, 6 10617, Taiwan
| | - Y-H Chan
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan
| | - W-L Sun
- Department of Physics, National Tsing Hua University, Hsinchu, 30013, Taiwan
| | - C-Z Xu
- 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
| | - D-S Lin
- Department of Physics, National Tsing Hua University, Hsinchu, 30013, Taiwan
| | - M Y Chou
- Department of Physics, National Taiwan University, Taipei, 10617, Taiwan.,Center of Atomic Initiative for New Materials, National Taiwan University, Taipei, 6 10617, Taiwan.,School of Physics, Georgia Institute of Technology, Atlanta, GA, 30332, USA
| | - A-V Fedorov
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - T-C 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. .,Department of Physics, National Taiwan University, Taipei, 10617, Taiwan.
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18
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Tsai Y, Chu Z, Han Y, Chuu CP, Wu D, Johnson A, Cheng F, Chou MY, Muller DA, Li X, Lai K, Shih CK. Tailoring Semiconductor Lateral Multijunctions for Giant Photoconductivity Enhancement. Adv Mater 2017; 29:1703680. [PMID: 28891108 DOI: 10.1002/adma.201703680] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2017] [Revised: 07/24/2017] [Indexed: 06/07/2023]
Abstract
Semiconductor heterostructures have played a critical role as the enabler for new science and technology. The emergence of transition-metal dichalcogenides (TMDs) as atomically thin semiconductors has opened new frontiers in semiconductor heterostructures either by stacking different TMDs to form vertical heterojunctions or by stitching them laterally to form lateral heterojunctions via direct growth. In conventional semiconductor heterostructures, the design of multijunctions is critical to achieve carrier confinement. Analogously, successful synthesis of a monolayer WS2 /WS2(1-x) Se2x /WS2 multijunction lateral heterostructure via direct growth by chemical vapor deposition is reported. The grown structures are characterized by Raman, photoluminescence, and annular dark-field scanning transmission electron microscopy to determine their lateral compositional profile. More importantly, using microwave impedance microscopy, it is demonstrated that the local photoconductivity in the alloy region can be tailored and enhanced by two orders of magnitude over pure WS2 . Finite element analysis confirms that this effect is due to the carrier diffusion and confinement into the alloy region. This work exemplifies the technological potential of atomically thin lateral heterostructures in optoelectronic applications.
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Affiliation(s)
- Yutsung Tsai
- Department of Physics, Center for Complex Quantum Systems, The University of Texas at Austin, Austin, TX, 78712, USA
| | - Zhaodong Chu
- Department of Physics, Center for Complex Quantum Systems, The University of Texas at Austin, Austin, TX, 78712, USA
| | - Yimo Han
- School of Applied and Engineering Physics, Cornell University Ithaca, Ithaca, NY, 14853, USA
| | - Chih-Piao Chuu
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan
- Physics Division, National Center for Theoretical Sciences, Hsinchu, 300, Taiwan
| | - Di Wu
- Department of Physics, Center for Complex Quantum Systems, The University of Texas at Austin, Austin, TX, 78712, USA
| | - Alex Johnson
- Department of Physics, Center for Complex Quantum Systems, The University of Texas at Austin, Austin, TX, 78712, USA
| | - Fei Cheng
- Department of Physics, Center for Complex Quantum Systems, The University of Texas at Austin, Austin, TX, 78712, USA
| | - Mei-Yin Chou
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan
- School of Physics, Georgia Institute of Technology, Atlanta, GA, 30332, USA
| | - David A Muller
- School of Applied and Engineering Physics, Cornell University Ithaca, Ithaca, NY, 14853, USA
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, 14853, USA
| | - Xiaoqin Li
- Department of Physics, Center for Complex Quantum Systems, The University of Texas at Austin, Austin, TX, 78712, USA
| | - Keji Lai
- Department of Physics, Center for Complex Quantum Systems, The University of Texas at Austin, Austin, TX, 78712, USA
| | - Chih-Kang Shih
- Department of Physics, Center for Complex Quantum Systems, The University of Texas at Austin, Austin, TX, 78712, USA
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19
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Lu AY, Zhu H, Xiao J, Chuu CP, Han Y, Chiu MH, Cheng CC, Yang CW, Wei KH, Yang Y, Wang Y, Sokaras D, Nordlund D, Yang P, Muller DA, Chou MY, Zhang X, Li LJ. Janus monolayers of transition metal dichalcogenides. Nat Nanotechnol 2017; 12:744-749. [PMID: 28507333 DOI: 10.1038/nnano.2017.100] [Citation(s) in RCA: 522] [Impact Index Per Article: 74.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2016] [Accepted: 04/20/2017] [Indexed: 05/22/2023]
Abstract
Structural symmetry-breaking plays a crucial role in determining the electronic band structures of two-dimensional materials. Tremendous efforts have been devoted to breaking the in-plane symmetry of graphene with electric fields on AB-stacked bilayers or stacked van der Waals heterostructures. In contrast, transition metal dichalcogenide monolayers are semiconductors with intrinsic in-plane asymmetry, leading to direct electronic bandgaps, distinctive optical properties and great potential in optoelectronics. Apart from their in-plane inversion asymmetry, an additional degree of freedom allowing spin manipulation can be induced by breaking the out-of-plane mirror symmetry with external electric fields or, as theoretically proposed, with an asymmetric out-of-plane structural configuration. Here, we report a synthetic strategy to grow Janus monolayers of transition metal dichalcogenides breaking the out-of-plane structural symmetry. In particular, based on a MoS2 monolayer, we fully replace the top-layer S with Se atoms. We confirm the Janus structure of MoSSe directly by means of scanning transmission electron microscopy and energy-dependent X-ray photoelectron spectroscopy, and prove the existence of vertical dipoles by second harmonic generation and piezoresponse force microscopy measurements.
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Affiliation(s)
- Ang-Yu Lu
- Physical Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Saudi Arabia
| | - Hanyu Zhu
- NSF Nanoscale Science and Engineering Center, University of California, Berkeley, California 94720, USA
| | - Jun Xiao
- NSF Nanoscale Science and Engineering Center, University of California, Berkeley, California 94720, USA
| | - Chih-Piao Chuu
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - Yimo Han
- School of Applied &Engineering Physics, Cornell University, Ithaca, New York 14850, USA
| | - Ming-Hui Chiu
- Physical Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Saudi Arabia
| | - Chia-Chin Cheng
- Research Center for Applied Sciences, Academia Sinica, Taipei 10617, Taiwan
- Department of Material Science and Engineering, National Chiao Tung University, Hsinchu 300, Taiwan
| | - Chih-Wen Yang
- Physical Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Saudi Arabia
| | - Kung-Hwa Wei
- Department of Material Science and Engineering, National Chiao Tung University, Hsinchu 300, Taiwan
| | - Yiming Yang
- Department of Chemistry, University of California, Berkeley, California 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Yuan Wang
- NSF Nanoscale Science and Engineering Center, University of California, Berkeley, California 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Dimosthenis Sokaras
- SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - Dennis Nordlund
- SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - Peidong Yang
- Department of Chemistry, University of California, Berkeley, California 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - David A Muller
- School of Applied &Engineering Physics, Cornell University, Ithaca, New York 14850, USA
- Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853, USA
| | - Mei-Yin Chou
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
- Department of Physics, National Taiwan University, Taipei 10617, Taiwan
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
| | - Xiang Zhang
- NSF Nanoscale Science and Engineering Center, University of California, Berkeley, California 94720, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Lain-Jong Li
- Physical Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Saudi Arabia
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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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Zhang C, Chuu CP, Ren X, Li MY, Li LJ, Jin C, Chou MY, Shih CK. Interlayer couplings, Moiré patterns, and 2D electronic superlattices in MoS 2/WSe 2 hetero-bilayers. Sci Adv 2017; 3:e1601459. [PMID: 28070558 PMCID: PMC5218515 DOI: 10.1126/sciadv.1601459] [Citation(s) in RCA: 194] [Impact Index Per Article: 27.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Accepted: 11/28/2016] [Indexed: 05/19/2023]
Abstract
By using direct growth, we create a rotationally aligned MoS2/WSe2 hetero-bilayer as a designer van der Waals heterostructure. With rotational alignment, the lattice mismatch leads to a periodic variation of atomic registry between individual van der Waals layers, exhibiting a Moiré pattern with a well-defined periodicity. By combining scanning tunneling microscopy/spectroscopy, transmission electron microscopy, and first-principles calculations, we investigate interlayer coupling as a function of atomic registry. We quantitatively determine the influence of interlayer coupling on the electronic structure of the hetero-bilayer at different critical points. We show that the direct gap semiconductor concept is retained in the bilayer although the valence and conduction band edges are located at different layers. We further show that the local bandgap is periodically modulated in the X-Y direction with an amplitude of ~0.15 eV, leading to the formation of a two-dimensional electronic superlattice.
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Affiliation(s)
- Chendong Zhang
- Department of Physics, University of Texas at Austin, Austin, TX 78712, USA
| | - Chih-Piao Chuu
- Institute of Atomic and Molecular Sciences, Academia Sinica, P.O. Box 23-166, Taipei 10617, Taiwan
| | - Xibiao Ren
- State Key Laboratory of Silicon Materials and School of Materials Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, People’s Republic of China
| | - Ming-Yang Li
- Physical Science and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
- Research Center for Applied Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - Lain-Jong Li
- Physical Science and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
- Research Center for Applied Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - Chuanhong Jin
- State Key Laboratory of Silicon Materials and School of Materials Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, People’s Republic of China
| | - Mei-Yin Chou
- Institute of Atomic and Molecular Sciences, Academia Sinica, P.O. Box 23-166, Taipei 10617, Taiwan
- School of Physics, Georgia Institute of Technology, Atlanta, GA 30332, USA
- Department of Physics, National Taiwan University, Taipei 10617, Taiwan
| | - Chih-Kang Shih
- Department of Physics, University of Texas at Austin, Austin, TX 78712, USA
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22
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Chen P, Chan YH, Wong MH, Fang XY, Chou MY, Mo SK, Hussain Z, Fedorov AV, Chiang TC. Dimensional Effects on the Charge Density Waves in Ultrathin Films of TiSe 2. Nano Lett 2016; 16:6331-6336. [PMID: 27648493 DOI: 10.1021/acs.nanolett.6b02710] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Charge density wave (CDW) formation in solids is a critical phenomenon involving the collective reorganization of the electrons and atoms in the system into a wave structure, and it is expected to be sensitive to the geometric constraint of the system at the nanoscale. Here, we study the CDW transition in TiSe2, a quasi-two-dimensional layered material, to determine the effects of quantum confinement and changing dimensions in films ranging from a single layer to multilayers. Of key interest is the characteristic length scale for the transformation from a two-dimensional case to the three-dimensional limit. Angle-resolved photoemission spectroscopy (ARPES) measurements of films with thicknesses up to six layers reveal substantial variations in the energy structure of discrete quantum well states; however, the temperature-dependent band gap renormalization converges at just three layers. The results indicate a layer-dependent mixture of two transition temperatures and a very-short-range CDW interaction within a three-dimensional framework.
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Affiliation(s)
- P 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
| | - Y-H Chan
- Institute of Atomic and Molecular Sciences, Academia Sinica , Taipei 10617, Taiwan
| | - M-H Wong
- 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
| | - X-Y Fang
- 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 Y 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
| | - S-K Mo
- Advanced Light Source, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | - Z Hussain
- Advanced Light Source, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | - A-V Fedorov
- Advanced Light Source, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
| | - T-C 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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23
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Alikhani M, Alyami B, Lee IS, Almoammar S, Vongthongleur T, Alikhani M, Alansari S, Sangsuwon C, Chou MY, Khoo E, Boskey A, Teixeira CC. Saturation of the biological response to orthodontic forces and its effect on the rate of tooth movement. Orthod Craniofac Res 2016; 18 Suppl 1:8-17. [PMID: 25865529 DOI: 10.1111/ocr.12090] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/02/2014] [Indexed: 01/16/2023]
Abstract
OBJECTIVES Investigate the expression and activity of inflammatory markers in response to different magnitudes of orthodontic forces and correlate this response with other molecular and cellular events during orthodontic tooth movement. SETTING AND SAMPLE POPULATION CTOR Laboratory; 245 Sprague Dawley male rats. METHODS AND MATERIALS Control, sham, and 5 different experimental groups received different magnitudes of force on the right maxillary first molar using a coil spring. In the sham group, the spring was not activated. Control group did not receive any appliance. At days 1, 3, 7, 14, and 28, the maxillae were collected for RNA and protein analysis, immunohistochemistry, and micro-CT. RESULTS There was a linear relation between the force and the level of cytokine expression at lower magnitudes of force. Higher magnitudes of force did not increase the expression of cytokines. Activity of CCL2, CCL5, IL-1, TNF-α, RANKL, and number of osteoclasts reached a saturation point in response to higher magnitudes of force, with unchanged rate of tooth movement. CONCLUSION After a certain magnitude of force, there is a saturation in the biological response, and higher forces do not increase inflammatory markers, osteoclasts, nor the amount of tooth movement. Therefore, higher forces to accelerate the rate of tooth movement are not justified.
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Affiliation(s)
- M Alikhani
- Consortium for Translational Orthodontic Research, New York University College of Dentistry, New York, NY, USA; Department of Orthodontics, New York University College of Dentistry, New York, NY, USA; Department of Developmental Biology, Harvard School of Dental Medicine, Boston, MA, USA
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24
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Chen P, Chan YH, Fang XY, Zhang Y, Chou MY, Mo SK, Hussain Z, Fedorov AV, Chiang TC. Charge density wave transition in single-layer titanium diselenide. Nat Commun 2015; 6:8943. [PMID: 26568512 PMCID: PMC4660365 DOI: 10.1038/ncomms9943] [Citation(s) in RCA: 73] [Impact Index Per Article: 8.1] [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: 07/21/2015] [Accepted: 10/19/2015] [Indexed: 11/18/2022] Open
Abstract
A single molecular layer of titanium diselenide (TiSe2) is a promising material for advanced electronics beyond graphene—a strong focus of current research. Such molecular layers are at the quantum limit of device miniaturization and can show enhanced electronic effects not realizable in thick films. We show that single-layer TiSe2 exhibits a charge density wave (CDW) transition at critical temperature TC=232±5 K, which is higher than the bulk TC=200±5 K. Angle-resolved photoemission spectroscopy measurements reveal a small absolute bandgap at room temperature, which grows wider with decreasing temperature T below TC in conjunction with the emergence of (2 × 2) ordering. The results are rationalized in terms of first-principles calculations, symmetry breaking and phonon entropy effects. The observed Bardeen-Cooper-Schrieffer (BCS) behaviour of the gap implies a mean-field CDW order in the single layer and an anisotropic CDW order in the bulk. Single molecular layers of TiSe2 are promising for advanced electronic applications, and it is therefore important to characterize their phases. Here, the authors use ARPES to detect a charge density wave transition without Fermi surface nesting and that takes place at a temperature higher than in bulk.
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Affiliation(s)
- P Chen
- Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080, USA.,Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, 104 South Goodwin Avenue, Urbana, Illinois 61801-2902, USA.,Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Y-H Chan
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - X-Y Fang
- Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080, USA.,Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, 104 South Goodwin Avenue, Urbana, Illinois 61801-2902, USA
| | - Y Zhang
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.,National Laboratory of Solid State Microstructures, School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.,Stanford Institute of Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
| | - M Y 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
| | - S-K Mo
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Z Hussain
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - A-V Fedorov
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - T-C Chiang
- Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080, USA.,Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, 104 South Goodwin Avenue, Urbana, Illinois 61801-2902, USA.,Department of Physics, National Taiwan University, Taipei 10617, Taiwan
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25
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Chiu MH, Zhang C, Shiu HW, Chuu CP, Chen CH, Chang CYS, Chen CH, Chou MY, Shih CK, Li LJ. Determination of band alignment in the single-layer MoS2/WSe2 heterojunction. Nat Commun 2015; 6:7666. [PMID: 26179885 PMCID: PMC4518320 DOI: 10.1038/ncomms8666] [Citation(s) in RCA: 219] [Impact Index Per Article: 24.3] [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: 03/27/2015] [Accepted: 05/29/2015] [Indexed: 12/23/2022] Open
Abstract
The emergence of two-dimensional electronic materials has stimulated proposals of novel electronic and photonic devices based on the heterostructures of transition metal dichalcogenides. Here we report the determination of band offsets in the heterostructures of transition metal dichalcogenides by using microbeam X-ray photoelectron spectroscopy and scanning tunnelling microscopy/spectroscopy. We determine a type-II alignment between MoS2 and WSe2 with a valence band offset value of 0.83 eV and a conduction band offset of 0.76 eV. First-principles calculations show that in this heterostructure with dissimilar chalcogen atoms, the electronic structures of WSe2 and MoS2 are well retained in their respective layers due to a weak interlayer coupling. Moreover, a valence band offset of 0.94 eV is obtained from density functional theory, consistent with the experimental determination.
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Affiliation(s)
- Ming-Hui Chiu
- Institute of Atomic and Molecular Sciences, Academia Sinica, No. 1, Roosevelt Road, Sec. 4, Taipei 10617, Taiwan
| | - Chendong Zhang
- Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA
| | - Hung-Wei Shiu
- National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
| | - Chih-Piao Chuu
- Institute of Atomic and Molecular Sciences, Academia Sinica, No. 1, Roosevelt Road, Sec. 4, Taipei 10617, Taiwan
| | - Chang-Hsiao Chen
- Institute of Atomic and Molecular Sciences, Academia Sinica, No. 1, Roosevelt Road, Sec. 4, Taipei 10617, Taiwan
| | - Chih-Yuan S. Chang
- Institute of Atomic and Molecular Sciences, Academia Sinica, No. 1, Roosevelt Road, Sec. 4, Taipei 10617, Taiwan
| | - Chia-Hao Chen
- National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
| | - Mei-Yin Chou
- Institute of Atomic and Molecular Sciences, Academia Sinica, No. 1, Roosevelt Road, Sec. 4, Taipei 10617, Taiwan
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
- Deapartment of Physics, National Taiwan University, Taipei 10617, Taiwan
| | - Chih-Kang Shih
- Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA
| | - Lain-Jong Li
- Institute of Atomic and Molecular Sciences, Academia Sinica, No. 1, Roosevelt Road, Sec. 4, Taipei 10617, Taiwan
- Physical Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
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26
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Zhang W, Chuu CP, Huang JK, Chen CH, Tsai ML, Chang YH, Liang CT, Chen YZ, Chueh YL, He JH, Chou MY, Li LJ. Ultrahigh-gain photodetectors based on atomically thin graphene-MoS2 heterostructures. Sci Rep 2014; 4:3826. [PMID: 24451916 PMCID: PMC3899643 DOI: 10.1038/srep03826] [Citation(s) in RCA: 321] [Impact Index Per Article: 32.1] [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: 11/06/2013] [Accepted: 01/03/2014] [Indexed: 12/22/2022] Open
Abstract
Due to its high carrier mobility, broadband absorption, and fast response time, the semi-metallic graphene is attractive for optoelectronics. Another two-dimensional semiconducting material molybdenum disulfide (MoS2) is also known as light- sensitive. Here we show that a large-area and continuous MoS2 monolayer is achievable using a CVD method and graphene is transferable onto MoS2. We demonstrate that a photodetector based on the graphene/MoS2 heterostructure is able to provide a high photogain greater than 108. Our experiments show that the electron-hole pairs are produced in the MoS2 layer after light absorption and subsequently separated across the layers. Contradictory to the expectation based on the conventional built-in electric field model for metal-semiconductor contacts, photoelectrons are injected into the graphene layer rather than trapped in MoS2 due to the presence of a perpendicular effective electric field caused by the combination of the built-in electric field, the applied electrostatic field, and charged impurities or adsorbates, resulting in a tuneable photoresponsivity.
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Affiliation(s)
- Wenjing Zhang
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 11529, Taiwan
| | - Chih-Piao Chuu
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 11529, Taiwan
| | - Jing-Kai Huang
- 1] Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 11529, Taiwan [2] Department of Photonics, National Chiao Tung University, HsinChu 300, Taiwan
| | - Chang-Hsiao Chen
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 11529, Taiwan
| | - Meng-Lin Tsai
- Graduate Institute of Photonics and Optoelectronics, and Department of ElectricalEngineering, National Taiwan University, Taipei, Taiwan
| | - Yung-Huang Chang
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 11529, Taiwan
| | - Chi-Te Liang
- Department of Physics, National Taiwan University, Taipei, Taiwan
| | - Yu-Ze Chen
- Department of Materials Science and Engineering, National Tsing-Hua University, Hsinchu, 300, Taiwan
| | - Yu-Lun Chueh
- Department of Materials Science and Engineering, National Tsing-Hua University, Hsinchu, 300, Taiwan
| | - Jr-Hau He
- Graduate Institute of Photonics and Optoelectronics, and Department of ElectricalEngineering, National Taiwan University, Taipei, Taiwan
| | - Mei-Yin Chou
- 1] Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 11529, Taiwan [2] Department of Physics, National Taiwan University, Taipei, Taiwan [3] School of Physics, Georgia Institute of Technology, Atlanta, GA 30332, USA
| | - Lain-Jong Li
- 1] Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 11529, Taiwan [2] Department of Physics, National Tsing Hua University, HsinChu 300, Taiwan [3] Department of Medical Research, China Medical University Hospital, Taichung, Taiwan
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27
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Abstract
The low-energy quasiparticles in graphene can be described by a Dirac-Weyl Hamiltonian for massless fermions, hence graphene has been proposed to be an effective medium to study exotic phenomena originally predicted for relativistic particle physics, such as Klein tunneling and Zitterbewegung. In this work, we show that another important particle-physics phenomenon, the neutrino oscillation, can be studied and observed in a particular graphene system, namely, twisted bilayer graphene. It has been found that graphene layers grown epitaxially on SiC or by the chemical vapor deposition method on metal substrates display a stacking pattern with adjacent layers rotated by an angle with respect to each other. The quasiparticle states in two distinct graphene layers act as neutrinos with two flavors, and the interlayer interaction between them induces an appreciable coupling between these two "flavors" of massless fermions, leading to neutrino-like oscillations. In addition, our calculation shows that anisotropic transport properties manifest in a specific energy window, which is accessible experimentally in twisted bilayer graphene. Combining two graphene layers enables us to probe the rich physics involving multiple interacting Dirac fermions.
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Affiliation(s)
- Lede Xian
- School of Physics, Georgia Institute of Technology , Atlanta, Georgia 30332, United States
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28
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Abstract
Various surface passivations for silicon nanowires have previously been investigated to extend their stability and utility. However, the fundamental mechanisms by which such passivations alter the electronic properties of silicon nanowires have not been clearly understood thus far. In this work, we address this issue through first-principles calculations on fluorine, methyl and hydrogen passivated [110] and [111] silicon nanowires. Comparing these results, we explain how passivations may alter the electronic structure through quantum confinement and strain and demonstrate how silicon nanowires may be modelled by an infinite circular quantum well. We also discuss why [110] nanowires are more strongly influenced by their surface passivation than [111] nanowires.
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Affiliation(s)
- Keenan Zhuo
- School of physics, Georgia Institute of Technology, Atlanta, GA 30332-0430, USA
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Berrut G, Andrieu S, Araujo de Carvalho I, Baeyens JP, Bergman H, Cassim B, Cerreta F, Cesari M, Cha HB, Chen LK, Cherubini A, Chou MY, Cruz-Jentoft AJ, De Decker L, Du P, Forette B, Forette F, Franco A, Guimaraes R, Guttierrez-Robledo LM, Jauregui J, Khavinson V, Lee WJ, Peng LN, Perret-Guillaume C, Petrovic M, Retornaz F, Rockwood K, Rodriguez-Manas L, Sieber C, Spatharakis G, Theou O, Topinkova E, Vellas B, Benetos A. Promoting access to innovation for frail old persons. IAGG (International Association of Gerontology and Geriatrics), WHO (World Health Organization) and SFGG (Société Française de Gériatrie et de Gérontologie) Workshop--Athens January 20-21, 2012. J Nutr Health Aging 2013; 17:688-93. [PMID: 24097023 DOI: 10.1007/s12603-013-0039-2] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
UNLABELLED Frailty tends to be considered as a major risk for adverse outcomes in older persons, but some important aspects remain matter of debate. OBJECTIVES The purpose of this paper is to present expert's positions on the main aspects of the frailty syndrome in the older persons. PARTICIPANTS Workshop organized by International Association of Gerontology and Geriatrics (IAGG), World Health Organization (WHO) and Société Française de Gériatrie et de Gérontologie (SFGG). RESULTS Frailty is widely recognized as an important risk factor for adverse health outcomes in older persons. This can be of particular value in evaluating non-disabled older persons with chronic diseases but today no operational definition has been established. Nutritional status, mobility, activity, strength, endurance, cognition, and mood have been proposed as markers of frailty. Another approach calculates a multidimensional score ranging from "very fit" to "severely frail", but it is difficult to apply into the medical practice. Frailty appears to be secondary to multiple conditions using multiple pathways leading to a vulnerability to a stressor. Biological (inflammation, loss of hormones), clinical (sarcopenia, osteoporosis etc.), as well as social factors (isolation, financial situation) are involved in the vulnerability process. In clinical practice, detection of frailty is of major interest in oncology because of the high prevalence of cancer in older persons and the bad tolerance of the drug therapies. Presence of frailty should also be taken into account in the definition of the cardiovascular risks in the older population. The experts of the workshop have listed the points reached an agreement and those must to be a priority for improving understanding and use of frailty syndrome in practice. CONCLUSION Frailty in older adults is a syndrome corresponding to a vulnerability to a stressor. Diagnostic tools have been developed but none can integrate at the same time the large spectrum of factors and the simplicity asked by the clinical practice. An agreement with an international common definition is necessary to develop screening and to reduce the morbidity in older persons.
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Affiliation(s)
- G Berrut
- Pr Athanase Benetos, MD, PhD, Département de Médecine Gériatrique, CHU de Nancy, Avenue de Bourgogne, BP 217, 54511 Vandoeuvre-les-Nancy, France,
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30
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Abstract
We have performed calculations of adsorption energetics on the graphene surface using the state-of-the-art diffusion quantum Monte Carlo method. Two types of configurations are considered in this work: the adsorption of a single O, F, or H atom on the graphene surface and the H-saturated graphene system (graphane). The adsorption energies are compared with those obtained from density functional theory with various exchange-correlation functionals. The results indicate that the approximate exchange-correlation functionals significantly overestimate the binding of O and F atoms on graphene, although the preferred adsorption sites are consistent. The energy errors are much less for atomic hydrogen adsorbed on the surface. We also find that a single O or H atom on graphene has a higher energy than in the molecular state, while the adsorption of a single F atom is preferred over the gas phase. In addition, the energetics of graphane is reported. The calculated equilibrium lattice constant turns out to be larger than that of graphene, at variance with a recent experimental suggestion.
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Affiliation(s)
- C R Hsing
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
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31
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Abstract
The Hofstadter butterfly spectrum for Landau levels in a two-dimensional periodic lattice is a rare example exhibiting fractal properties in a truly quantum system. However, the observation of this physical phenomenon in a conventional material will require a magnetic field strength several orders of magnitude larger than what can be produced in a modern laboratory. It turns out that for a specific range of rotational angles twisted bilayer graphene serves as a special system with a fractal energy spectrum under laboratory accessible magnetic field strengths. This unique feature arises from an intriguing electronic structure induced by the interlayer coupling. Using a recursive tight-binding method, we systematically map out the spectra of these Landau levels as a function of the rotational angle. Our results give a complete description of LLs in twisted bilayer graphene for both commensurate and incommensurate rotational angles and provide quantitative predictions of magnetic field strengths for observing the fractal spectra in these graphene systems.
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Affiliation(s)
- Z F Wang
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
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32
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Abstract
Graphene is believed to be an excellent candidate material for next-generation electronic devices. However, one needs to take into account the nontrivial effect of metal contacts in order to precisely control the charge injection and extraction processes. We have performed transport calculations for graphene junctions with wetting metal leads (metal leads that bind covalently to graphene) using nonequilibrium Green's functions and density functional theory. Quantitative information is provided on the increased resistance with respect to ideal contacts and on the statistics of current fluctuations. We find that charge transport through the studied two-terminal graphene junction with Ti contacts is pseudo-diffusive up to surprisingly high energies.
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Affiliation(s)
- Salvador Barraza-Lopez
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, United States.
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33
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Abstract
We have performed first-principles calculations to study the lattice vibrational modes and their Raman activities in silicon nanowires (SiNWs). Two types of characteristic vibrational modes are examined: high-frequency optical modes and low-frequency confined modes. Their frequencies have opposite size dependence with a red shift for the optical modes and a blue shift for the confined modes as the diameter of SiNWs decreases. In addition, our calculations show that these vibrational modes can be detected by Raman scattering measurements, providing an efficient way to estimate the size of SiNWs.
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Affiliation(s)
- Li Yang
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430, United States
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34
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Lee CM, Lee RCH, Ruan WY, Chou MY. Energy spectra of a single-electron magnetic dot using the massless Dirac-Weyl equation. J Phys Condens Matter 2010; 22:355501. [PMID: 21403291 DOI: 10.1088/0953-8984/22/35/355501] [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: 05/30/2023]
Abstract
In this paper, we study the low-lying energy spectra of a two-dimensional (2D) graphene-based magnetic dot in a perpendicular and radially inhomogeneous magnetic field with the use of the massless Dirac-Weyl equation. Numerical calculations are performed using 2D harmonic basis states for direct diagonalization. Effects of both the dot size and the magnetic field on the low-lying energy spectra are discussed.
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Affiliation(s)
- C M Lee
- Newtech Computer (HK) Ltd, Unit P, 6/F., Kaiser Estate, Phase 3, 11 Hok Yuen Street, Hunghom, Hong Kong.
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35
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Barraza-Lopez S, Vanević M, Kindermann M, Chou MY. Effects of metallic contacts on electron transport through graphene. Phys Rev Lett 2010; 104:076807. [PMID: 20366907 DOI: 10.1103/physrevlett.104.076807] [Citation(s) in RCA: 16] [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: 12/04/2009] [Indexed: 05/29/2023]
Abstract
We report on a first-principles study of the conductance through graphene suspended between Al contacts as a function of junction length, width, and orientation. The charge transfer at the leads and into the freestanding section gives rise to an electron-hole asymmetry in the conductance and in sufficiently long junctions induces two conductance minima at the energies of the Dirac points for suspended and clamped regions, respectively. We obtain the potential profile along a junction caused by doping and provide parameters for effective model calculations of the junction conductance with weakly interacting metallic leads.
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36
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Abstract
We have systematically investigated the effect of oxidation on the structural and electronic properties of graphene based on first-principles calculations. Energetically favorable atomic configurations and building blocks are identified, which contain epoxide and hydroxyl groups in close proximity with each other. Different arrangements of these units yield a local-density approximation band gap over a range of a few eV. These results suggest the possibility of creating and tuning the band gap in graphene by varying the oxidation level and the relative amount of epoxide and hydroxyl functional groups on the surface.
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Affiliation(s)
- Jia-An Yan
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430, USA
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37
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Miller T, Chou MY, Chiang TC. Phase relations associated with one-dimensional shell effects in thin metal films. Phys Rev Lett 2009; 102:236803. [PMID: 19658957 DOI: 10.1103/physrevlett.102.236803] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2009] [Indexed: 05/28/2023]
Abstract
The physical and chemical properties of thin metal films show damped oscillations as a function of film thickness (one-dimensional shell effects). While the oscillation period, determined by subband crossings of the Fermi level, is the same for all properties, the phases can be different. Specifically, oscillations in the work function and surface energy are offset by 1/4 of a period. For Pb(111) films, this offset is approximately 0.18 monolayers, a seemingly very small effect. However, aliasing caused by the discrete atomic layer structure leads to striking out-of-phase beating patterns displayed by these two quantities.
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Affiliation(s)
- T Miller
- Department of Physics, University of Illinois, Urbana, Illinois 61801-3080, USA
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38
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Yvon K, Renaudin G, Wei CM, Chou MY. Hydrogenation-induced insulating state in the intermetallic compound LaMg2Ni. Phys Rev Lett 2005; 94:066403. [PMID: 15783759 DOI: 10.1103/physrevlett.94.066403] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2004] [Indexed: 05/24/2023]
Abstract
Hydrogenation-induced metal-semiconductor transitions usually occur in simple systems based on rare earths and/or magnesium, accompanied by major reconstructions of the metal host (atom shifts >2 A). We report on the first such transition in a quaternary system based on a transition element. Metallic LaMg2Ni absorbs hydrogen near ambient conditions, forming the nonmetallic hydride LaMg2NiH7 which has a nearly unchanged metal host structure (atom shifts <0.7 A). The transition is induced by a charge transfer of conduction electrons into tetrahedral [NiH4]4- complexes having closed-shell electron configurations.
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Affiliation(s)
- K Yvon
- Laboratory of Crystallography, University of Geneva, 1211 Geneva 4, Switzerland
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39
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Huang CR, Lin SS, Chou MY, Ho CC, Wang L, Lee YL, Chen CS, Yang CC. Demonstration of different modes of cell death upon herpes simplex virus 1 infection in different types of oral cells. Acta Virol 2005; 49:7-15. [PMID: 15929393] [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: 05/02/2023]
Abstract
The effects of Herpes simplex virus 1 (HSV-1) infection on five different types of oral cancerous cells (neck metastasis of gingival carcinoma (GNM) cells and tongue squamous cells of carcinoma (TSCCa) and non-cancerous cells (buccal mucosal fibroblasts (BF), gingival fibroblasts (GF), oral submucosal fibrosis cells (OSF)) and one type of non-oral cancerous cells (KB cells) were investigated. In HSV-1-infected cells the cell viability, CPE, viral antigens accumulation, caspase-3 activity, annexin V binding and DNA fragmentation were estimated. Three different forms or pathways of cell death were considered: apoptosis (the presence or rise of caspase-3 activity, DNA fragmentation and annexin V binding), slow cell death (the presence or rise of DNA fragmentation, the absence or decline of caspase-3 activity and annexin V binding), and necrosis (the absence of decline of caspase-3 activity, DNA fragmentation and annexin V binding). The viability of all cell types, except for KB cells, was reduced by the infection. CPE and viral antigens data demonstrated that all six types of cells could be infected with HSV-1. Upon HSV-1 infection there occurred (i) a classical apoptosis in GF cells, (ii) apoptosis in the early phase of infection and necrosis in the late phase of infection in GNM and TSCCa cells, (iii) slow cell death followed by necrosis in BF and OSF cells (however, these cells showed a different type of CPE), (iv) a classical slow cell death in KB cells. It is hypothesized that HSV-1 infection has a potential to induce several distinct pathways leading to cell death or several forms of cell death. Moreover, more than one pathway may be involved in the death of particular cell type. As HSV-1 was demonstrated to infect different oral and non-oral cells and cause different pathways or forms of cell death, the safety of using HSV-1 as a vector for gene therapy should be re-considered.
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Affiliation(s)
- C R Huang
- Institute of Immunology, Chung Shan Medical University Hospital, Taichung, Taiwan, Republic of China
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40
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Abstract
The atomic geometry, electronic structure, and magnetic moment of 4d transition-metal clusters with 13 atoms are studied by pseudopotential density-functional calculations. We find a new buckled biplanar structure with a C(2v) symmetry stabilized by enhanced s-d hybridization. It has a lower energy than the close-packed icosahedral or cuboctahedral structure for elements with more than half-filled d shells. The magnetic moments of this buckled biplanar structure are found to be smaller than those of the icosahedral structure and closer to available experimental results.
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Affiliation(s)
- C M Chang
- Department of Physics, National Dong Hwa University, Hualien 974, Taiwan, Republic of China
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41
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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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42
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Abstract
We investigate the structural, electronic, and optical properties of hydrogen-passivated silicon nanowires along [110] and [111] directions with diameter d up to 4.2 nm from first principles. The size and orientation dependence of the band gap is investigated and the local-density gap is corrected with the GW approximation. Quantum confinement becomes significant for d<2.2 nm, where the dielectric function exhibits strong anisotropy and new low-energy absorption peaks start to appear in the imaginary part of the dielectric function for polarization along the wire axis.
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Affiliation(s)
- Xinyuan Zhao
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430, USA
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43
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Hong H, Wei CM, Chou MY, Wu Z, Basile L, Chen H, Holt M, Chiang TC. Alternating layer and island growth of Pb on Si by spontaneous quantum phase separation. Phys Rev Lett 2003; 90:076104. [PMID: 12633252 DOI: 10.1103/physrevlett.90.076104] [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] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2002] [Indexed: 05/24/2023]
Abstract
Real-time in situ x-ray studies of continuous Pb deposition on Si(111)-(7x7) at 180 K reveal an unusual growth behavior. A wetting layer forms first to cover the entire surface. Then islands of a fairly uniform height of about five monolayers form on top of the wetting layer and grow to fill the surface. The growth then switches to a layer-by-layer mode upon further deposition. This behavior of alternating layer and island growth can be attributed to spontaneous quantum phase separation based on a first-principles calculation of the system energy.
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Affiliation(s)
- Hawoong Hong
- Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, 104 S. Goodwin Avenue, Urbana, Illinois 61801-2902, USA
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44
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Kidd TE, Miller T, Chou MY, Chiang TC. Electron-hole coupling and the charge density wave transition in TiSe2. Phys Rev Lett 2002; 88:226402. [PMID: 12059437 DOI: 10.1103/physrevlett.88.226402] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2001] [Indexed: 05/23/2023]
Abstract
Angle-resolved photoemission is employed to measure the band structure of TiSe2 in order to clarify the nature of the ( 2 x 2 x 2) charge density wave transition. The results show a very small indirect gap in the normal phase transforming into a larger indirect gap at a different location in the Brillouin zone. Fermi surface topology is irrelevant in this case. Instead, electron-hole coupling together with a novel indirect Jahn-Teller effect drives the transition.
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Affiliation(s)
- T E Kidd
- Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080, USA
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45
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Chou MY, Yang CH, Lu FI, Lin HC, Hwang PP. Modulation of calcium balance in tilapia larvae (Oreochromis mossambicus) acclimated to low-calcium environments. J Comp Physiol B 2002; 172:109-14. [PMID: 11916107 DOI: 10.1007/s00360-001-0231-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
This study examined how developing fish larvae regulate their Ca2+ balance for acclimation to low ambient Ca2+. Calcium balance in newly hatched larvae was examined individually. Developing larvae not only increased Ca2+ influx but also decreased Ca2+ efflux when they were acclimated to low-Ca2+ environments. After acclimation for 8 days, the influx and efflux of the low-Ca2+ (0.02 mM) group were about 106% and 43%, respectively, compared to those of the high-Ca2+ (1.0 mM) group. Sensitivity and response to low-Ca2+ environments are age-dependent. Upon acute exposure to low Ca2+. newly hatched (H0) larvae increased both Ca2+ influx (from 24% to 67% of high-Ca2+) and net uptake (from 5% to 69%) within 64 h, while 3-day-posthatching (H3) larvae managed to reach the levels of the control within 38 h. Declining Ca2+ efflux in H3 larvae occurred 14 h after exposure, much faster than those in H0 larvae (38 h). It is suggested that modulation of Ca2+-balance mechanisms in developing larvae is dependent upon the levels of Ca2+ in the larval body.
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Affiliation(s)
- M Y Chou
- Department of Biology, Tunghai University, Taichung, Taiwan, ROC
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46
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Abstract
The antibacterial effects of various types of widely used endodontic sealers have not been compared systematically on facultative or obligate anaerobic endodontic pathogens. The aim of this study was to evaluate the antimicrobial properties of four commonly used endodontic sealers: two epoxy-resin-based sealers (AH26, AH plus), one zinc-oxide eugenol-based sealer (N2), and one calcium hydroxide-based sealer (Sealapex). The testing microbes were four facultative anaerobic species (Streptococcus mutans, Streptococcus sanguis, Escherichia coli, and Staphylococcus aureus) and four obligate anaerobic species (Porphyromonas gingivalis, Porphyromonas endodontalis, Fusobacterium nucleatum, and Prevotella intermedia). The freshly mixed sealers were placed into the prepared wells of agar plates inoculated with the test microorganisms. After varying periods of incubation (2 days for facultative anaerobic species and 7 days for obligate anaerobic species), the zones of growth inhibition were observed and measured. All the sealers were distinctly different from each other in their antimicrobial activity. The sealers showed different inhibitory effects depending on the types and bacterial strains. N2 containing formaldehyde and eugenol proved to be the most effective against the microorganisms. The extreme antimicrobial potency of this root canal sealer must be weighted against its pronounced tissue toxic effect.
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Affiliation(s)
- C C Lai
- Institute of Stomatology, Chung Shan Medical and Dental College Taichung, Taiwan
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47
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Abstract
The purpose of the study was to evaluate the presence of alteration of the tumor suppressor gene p16 and to correlate these changes with the clinical status of the patients in oral squamous cell carcinoma. Forty-eight oral squamous cell carcinomas were included in the analyses. Deletion analysis was performed by the polymerase chain reaction (PCR). Mutation analysis was restricted to exon 1 and exon 2 of the p16 gene, previously shown to have a high incidence of mutations. The sequences containing exon 1 and exon 2 were amplified by PCR and screened with a single-strand conformation polymorphism (SSCP) technique. Samples showing band shifts in SSCP were sequenced by PCR direct sequencing. Western blots were used to detect the protein expression of the p16 gene, and the results were evaluated with regard to their biological relevance in correlation with clinicopathological factors. Seven (14.6%) deletions were found; 5 (10.4%) mutations were discovered and located in different codons; 26 (54%) specimens had no p16 protein expression; in 11 specimens with p16 deletion or mutation, p16 protein could not be detected. One mutation was non-sense. The p16 gene alterations showed no relationship with location and clinical stage of cancer; however, a close relationship between p16 alterations and cancer metastasis to neck lymph node was found. The alteration rate gradually elevated from well to poorly differentiated grades. We perceive two results. First, the alterations of the p16 gene are common in oral squamous cell carcinoma. Second, the alterations of the p16 gene may attribute to the metastatic behavior or histological grade of cancer cells.
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Affiliation(s)
- C H Tsai
- Pathology Department, Chung Shan Medical and Dental College Hospital, 110, Sec. 1 Chien Kuo N. Road, Taichung 402, Taiwan, ROC
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48
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Chang YC, Huang FM, Tai KW, Chou MY. The effect of sodium hypochlorite and chlorhexidine on cultured human periodontal ligament cells. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001; 92:446-50. [PMID: 11598582 DOI: 10.1067/moe.2001.116812] [Citation(s) in RCA: 122] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
OBJECTIVE The objective of this study was to examine the effects of sodium hypochlorite (NaOCl) and chlorhexidine (CHx) on cultured human periodontal ligament (PDL) cells in vitro. STUDY DESIGN The effects of irrigation solutions on human PDL cells were evaluated by propidium iodide fluorescence cytotoxicity assay, protein synthesis assay, and mitochondrial activity. RESULTS Both NaOCl and CHx were cytotoxic to human PDL cells in a concentration- and contact time-dependent manner. In addition, CHx inhibited protein synthesis in human PDL cells. Although NaOCl displayed cellular cytotoxicity, it showed no protein inhibition in the PDL cells. Furthermore, both NaOCl and CHx exhibited an inhibitory effect on mitochondrial activity on human PDL cells. CONCLUSIONS This study suggests that these irrigation fluids may cause detrimental effects on vital tissues. Its clinical significance, however, needs to be evaluated further because concentration used, exposure time to the agent, and exposure surface area are important factors affecting the resulting effect.
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Affiliation(s)
- Y C Chang
- School of Dentistry, Chung Shan Medical and Dental College, Taichung, Taiwan
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49
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Abstract
Areca quid chewing has been linked to oral submucous fibrosis and oral cancer. Arecoline, a major areca nut alkaloid, is considered to be the most important etiologic factor in the areca nut. In order to elucidate the pathobiological effects of arecoline, cytotoxicity assays, cellular glutathione S-transferase (GST) activity and lipid peroxidation assay were employed to investigate cultured human buccal mucosal fibroblasts. To date, there is a large proportion of areca quid chewers who are also smokers. Furthermore, nicotine, the major product of cigarette smoking, was added to test how it modulated the cytotoxicity of arecoline. At a concentration higher than 50 microg/ml, arecoline was shown to be cytotoxic to human buccal fibroblasts in a dose-dependent manner by the alamar blue dye colorimetric assay (P<0.05). In addition, arecoline significantly decreased GST activity in a dose-dependent manner (P<0.05). At concentrations of 100 microg/ml and 400 microg/ml, arecoline reduced GST activity about 21% and 46%, respectively, during a 24 h incubation period. However, arecoline at any test dose did not increase lipid peroxidation in the present human buccal fibroblast test system. The addition of extracellular nicotine acted synergistically on the arecoline-induced cytotoxicity. Arecoline at a concentration of 50 microg/ml caused about 30% of cell death over the 24 h incubation period. However, 2.5 mM nicotine enhanced the cytotoxic response and caused about 50% of cell death on 50 microg/ml arecoline-induced cytotoxicity. Taken together, arecoline may render human buccal mucosal fibroblasts more vulnerable to other reactive agents in cigarettes via GST reduction. The compounds of tobacco products may act synergistically in the pathogenesis of oral mucosal lesions in areca quid chewers. The data presented here may partly explain why patients who combined the habits of areca quid chewing and cigarette smoking are at greater risk of contracting oral cancer.
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Affiliation(s)
- Y C Chang
- Department of Dentistry, Chung Shan Medical and Dental College Hospital, Taichung, Taiwan
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50
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Liao PH, Lee TL, Yang LC, Yang SH, Chen SL, Chou MY. Adenomatous polyposis coli gene mutation and decreased wild-type p53 protein expression in oral submucous fibrosis: a preliminary investigation. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001; 92:202-7. [PMID: 11505268 DOI: 10.1067/moe.2001.116816] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
OBJECTIVE The purpose of this study was to identify the adenomatous polyposis coli (APC) tumor suppressor gene mutation and level of wild-type p53 protein expression in patients with oral submucous fibrosis (OSF). STUDY DESIGN Cells from OSF and control subjects were cultured in Dulbecco modified Eagle medium with 10% fetal bovine serum at 37 degrees C. Genomic DNA was extracted from cultured cells and used as a template for polymerase chain reaction amplification of the APC tumor suppressor gene. The presence of wild-type p53 protein in cell lysates of cultured cells was analyzed by Western blot. Data were analyzed by the sign test for nonparametric samples and by analysis of variance. RESULTS The results showed that the APC gene of explant cultured cells from OSF patients (8/8) had a CGA-to-GGA transition mutation at codon 498 that resulted in an Arg-to-Gly missense mutation (P <.01). All (8/8) normal HGF cultures revealed expression of the wild-type APC protein. Cells cultured from 7 of 8 OSF patients were also found to have a single nucleotide deletion at nucleotide 1494 that resulted in creating a stop codon (TGA) at codon 504 (P <.01). This created a premature signal for the endpoint of translation and thus resulted in the generation of a truncated protein product that encodes a polypeptide of 503 amino acid residue. It was found that wild- type p53 protein in human gingival fibroblast cell cultures was significantly higher than in OSF cells (P <.01). CONCLUSION Alterations of the APC and wild-type p53 tumor suppressor genes in OSF may imply a risk for progression to oral cancer.
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Affiliation(s)
- P H Liao
- Departmnent of Dentistry, Chung Shan Medical and Dental College, Taichung, Taiwan, ROC
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