98 results on '"Cheng Maw Cheng"'
Search Results
2. Three-dimensional ultrafast charge-density-wave dynamics in CuTe
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Nguyen Nhat Quyen, Wen-Yen Tzeng, Chih-En Hsu, I-An Lin, Wan-Hsin Chen, Hao-Hsiang Jia, Sheng-Chiao Wang, Cheng-En Liu, Yu-Sheng Chen, Wei-Liang Chen, Ta-Lei Chou, I-Ta Wang, Chia-Nung Kuo, Chun-Liang Lin, Chien-Te Wu, Ping-Hui Lin, Shih-Chang Weng, Cheng-Maw Cheng, Chang-Yang Kuo, Chien-Ming Tu, Ming-Wen Chu, Yu-Ming Chang, Chin Shan Lue, Hung-Chung Hsueh, and Chih-Wei Luo
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Science - Abstract
Abstract Charge density waves (CDWs) involved with electronic and phononic subsystems simultaneously are a common quantum state in solid-state physics, especially in low-dimensional materials. However, CDW phase dynamics in various dimensions are yet to be studied, and their phase transition mechanism is currently moot. Here we show that using the distinct temperature evolution of orientation-dependent ultrafast electron and phonon dynamics, different dimensional CDW phases are verified in CuTe. When the temperature decreases, the shrinking of c-axis length accompanied with the appearance of interchain and interlayer interactions causes the quantum fluctuations (QF) of the CDW phase until 220 K. At T
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- 2024
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3. Determination of optical nonlinearity with photothermal effect within a layered bismuth telluride
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Jia-Chi Lan, Te-Yuan Chung, Cheng-Maw Cheng, Jung-Chun-Andrew Huang, and Chao-Kuei Lee
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Photothermal nonlinearity ,Optical nonlinearity ,Photothermal effect ,Nonlinear refractive index ,Z-scan ,Mining engineering. Metallurgy ,TN1-997 - Abstract
In this work, the photothermal nonlinearity within a layered bismuth telluride (Bi2Te3) is studied in detail. The dynamics of the optical nonlinearity with increasing photothermal effect are investigated via pump-probe spectroscopy. The difference between the thermally-induced and photon-induced nonlinearities was clarified and the entire photothermal nonlinearity was therefore sketched. Furthermore, by removing the thermally-induced background signal, the n2 without accumulated heat can then be estimated. For example, the n2 value is 2.80 × 10−8 cm2/W at a peak intensity of 12.81 MW/cm2. The results are compared with those obtained from another measurement to validate the reliability of the estimation. The working range of the n2 value is also discussed. To provide further validation of the feasibility of the proposed method, the photothermal nonlinearity within monolayer graphene is provided and discussed. This work provides an alternative method to deal with optical nonlinearity measurements that are subject to the photothermal effect, paving the way toward further related research.
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- 2023
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4. Kondo interaction in FeTe and its potential role in the magnetic order
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Younsik Kim, Min-Seok Kim, Dongwook Kim, Minjae Kim, Minsoo Kim, Cheng-Maw Cheng, Joonyoung Choi, Saegyeol Jung, Donghui Lu, Jong Hyuk Kim, Soohyun Cho, Dongjoon Song, Dongjin Oh, Li Yu, Young Jai Choi, Hyeong-Do Kim, Jung Hoon Han, Younjung Jo, Ji Hoon Shim, Jungpil Seo, Soonsang Huh, and Changyoung Kim
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Science - Abstract
Abstract Finding d-electron heavy fermion states has been an important topic as the diversity in d-electron materials can lead to many exotic Kondo effect-related phenomena or new states of matter such as correlation-driven topological Kondo insulator. Yet, obtaining direct spectroscopic evidence for a d-electron heavy fermion system has been elusive to date. Here, we report the observation of Kondo lattice behavior in an antiferromagnetic metal, FeTe, via angle-resolved photoemission spectroscopy, scanning tunneling spectroscopy and transport property measurements. The Kondo lattice behavior is represented by the emergence of a sharp quasiparticle and Fano-type tunneling spectra at low temperatures. The transport property measurements confirm the low-temperature Fermi liquid behavior and reveal successive coherent-incoherent crossover upon increasing temperature. We interpret the Kondo lattice behavior as a result of hybridization between localized Fe 3dxy and itinerant Te 5pz orbitals. Our observations strongly suggest unusual cooperation between Kondo lattice behavior and long-range magnetic order.
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- 2023
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5. Author Correction: Kondo interaction in FeTe and its potential role in the magnetic order
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Younsik Kim, Min-Seok Kim, Dongwook Kim, Minjae Kim, Minsoo Kim, Cheng-Maw Cheng, Joonyoung Choi, Saegyeol Jung, Donghui Lu, Jong Hyuk Kim, Soohyun Cho, Dongjoon Song, Dongjin Oh, Li Yu, Young Jai Choi, Hyeong-Do Kim, Jung Hoon Han, Younjung Jo, Ji Hoon Shim, Jungpil Seo, Soonsang Huh, and Changyoung Kim
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Science - Published
- 2024
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6. Formation of surface states on Pb(111) by Au adsorption
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Wei-Chuan Chen, Chin-Hsuan Chen, Angus Huang, Kaweng Lei, David Mikolas, Ming-kwan Dai, Je-Ming Kuo, Dai-Shien Lin, Cheng-Maw Cheng, H.-T. Jeng, and S.-J. Tang
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Medicine ,Science - Abstract
Abstract Using low-energy electron diffraction and angle-resolved photoemission spectroscopy, we investigated the lattice and electronic structures of the Pb(111) surface upon the adsorption of Au atoms at the low temperature T = 40 K. Unlike earlier results showing the formation of PbAu-alloy layers at room temperature, we found that Au atoms form a ultra-thin superstructure, Au/Pb(111)-3 × 3, on top of the Pb(111) surface. Moreover, three surface-state bands, S1, S2, and S3, are induced within and immediately adjacent to the Pb bulk projected band gap centered at the surface zone boundary $${\overline{\text{M}}}_{Pb(111)}$$ M ¯ P b ( 111 ) at the energies of − 0.02, − 1.05, and − 2.56 eV, respectively. First-principles calculation based on Au/Pb(111)-3 × 3 confirms the measured surface-state bands among which the most interesting are the S1 and S3 surface states. They are derived from surface resonances in Pb(111). Moreover, S1, which disperses across Fermi level, exhibits a large anisotropic Rashba splitting with α of 1.0 and 3.54 eVÅ in the two symmetry directions centered at $${\overline{\text{M}}}_{Pb(111)}$$ M ¯ P b ( 111 ) . The corresponding Rashba splitting of S1 bands in Cu/Pb(111)-3 × 3 and Ag/Pb(111)-3 × 3 was calculated for comparison.
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- 2023
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7. Efficient Hydrogen Evolution Reaction in 2H-MoS2 Basal Planes Enhanced by Surface Electron Accumulation
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Vimal Krishnamoorthy, Hemanth Kumar Bangolla, Chi-Yang Chen, Yu-Ting Huang, Cheng-Maw Cheng, Rajesh Kumar Ulaganathan, Raman Sankar, Kuei-Yi Lee, He-Yun Du, Li-Chyong Chen, Kuei-Hsieh Chen, and Ruei-San Chen
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molybdenum disulfide ,surface electron accumulation ,hydrogen evolution reaction ,overpotential ,Tafel slope ,Chemical technology ,TP1-1185 ,Chemistry ,QD1-999 - Abstract
An innovative strategy has been developed to activate the basal planes in molybdenum disulfide (MoS2) to improve their electrocatalytic activity by controlling surface electron accumulation (SEA) through aging, annealing, and nitrogen-plasma treatments. The optimal hydrogen evolution reaction (HER) performance was obtained on the surface treated with nitrogen-plasma for 120 s. An overpotential of 0.20 V and a Tafel slope of 120 mV dec−1 were achieved for the optimized condition. The angle-resolved photoemission spectroscopy measurement confirmed the HER efficiency enhanced by the SEA conjugated with the sulfur vacancy active sites in the MoS2 basal planes. This study provides new insight into optimizing MoS2 catalysts for energy applications.
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- 2024
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8. The Singularity Paramagnetic Peak of Bi0.3Sb1.7Te3 with p-type Surface State
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Shiu-Ming Huang, Pin-Cing Wang, Pin-Cyuan Chen, Jai-Long Hong, Cheng-Maw Cheng, Hao-Lun Jian, You-Jhih Yan, Shih-Hsun Yu, and Mitch M. C. Chou
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Paramagnetic susceptibility peak ,Topological material ,Dirac point ,Surface state ,Materials of engineering and construction. Mechanics of materials ,TA401-492 - Abstract
Abstract The magnetization measurement was performed in the Bi0.3Sb1.7Te3 single crystal. The magnetic susceptibility revealed a paramagnetic peak independent of the experimental temperature variation. It is speculated to be originated from the free-aligned spin texture at the Dirac point. The ARPES reveals that the Fermi level lies below the Dirac point. The Fermi wavevector extracted from the de Haas–van Alphen oscillation is consistent with the energy dispersion in the ARPES. Our experimental results support that the observed paramagnetic peak in the susceptibility curve does not originate from the free-aligned spin texture at the Dirac point.
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- 2022
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9. Author Correction: Formation of surface states on Pb(111) by Au adsorption
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Wei‑Chuan Chen, Chin‑Hsuan Chen, Angus Huang, Kaweng Lei, David Mikolas, Ming‑kwan Dai, Je‑Ming Kuo, Dai‑Shien Lin, Cheng‑Maw Cheng, H.‑T. Jeng, and S.‑J. Tang
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Medicine ,Science - Published
- 2023
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10. Robust charge-density wave strengthened by electron correlations in monolayer 1T-TaSe2 and 1T-NbSe2
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Yuki Nakata, Katsuaki Sugawara, Ashish Chainani, Hirofumi Oka, Changhua Bao, Shaohua Zhou, Pei-Yu Chuang, Cheng-Maw Cheng, Tappei Kawakami, Yasuaki Saruta, Tomoteru Fukumura, Shuyun Zhou, Takashi Takahashi, and Takafumi Sato
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Science - Abstract
Monolayer transition metal dechalcogenides are a promising platform to study the interplay of low-dimensionality and electron correlations. Here, the authors report a Mott insulator state in monolayer 1T-TaSe2, that survives far above room temperature and is robust against external perturbations.
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- 2021
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11. Direct observation of kink evolution due to Hund’s coupling on approach to metal-insulator transition in NiS2−x Se x
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Bo Gyu Jang, Garam Han, Ina Park, Dongwook Kim, Yoon Young Koh, Yeongkwan Kim, Wonshik Kyung, Hyeong-Do Kim, Cheng-Maw Cheng, Ku-Ding Tsuei, Kyung Dong Lee, Namjung Hur, Ji Hoon Shim, Changyoung Kim, and Gabriel Kotliar
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Science - Abstract
A decisive spectroscopic evidence of the Hund’s coupling energy scale in multi-orbital correlated systems has been lacking. Here, the authors identify a kink feature due to Hund´s coupling in the spectral function of NiS2x Se x as they track its evolution across the Mott-insulator transition.
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- 2021
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12. Dirac Nodal Line in Hourglass Semimetal Nb3SiTe6
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Ro-Ya Liu, Angus Huang, Raman Sankar, Joseph Andrew Hlevyack, Chih-Chuan Su, Shih-Chang Weng, Meng-Kai Lin, Peng Chen, Cheng-Maw Cheng, Jonathan D. Denlinger, Sung-Kwan Mo, Alexei V. Fedorov, Chia-Seng Chang, Horng-Tay Jeng, Tien-Ming Chuang, and Tai-Chang Chiang
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Mechanical Engineering ,General Materials Science ,Bioengineering ,General Chemistry ,Condensed Matter Physics - Published
- 2022
13. Epitaxial Growth and Structural Characterizations of MnBi2Te4 Thin Films in Nanoscale
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Shu-Hsuan Su, Jen-Te Chang, Pei-Yu Chuang, Ming-Chieh Tsai, Yu-Wei Peng, Min Kai Lee, Cheng-Maw Cheng, and Jung-Chung Andrew Huang
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MnBi2Te4 ,topological insulators ,antiferromagnetic order ,molecular beam epitaxy ,Chemistry ,QD1-999 - Abstract
The intrinsic magnetic topological insulator MnBi2Te4 has attracted much attention due to its special magnetic and topological properties. To date, most reports have focused on bulk or flake samples. For material integration and device applications, the epitaxial growth of MnBi2Te4 film in nanoscale is more important but challenging. Here, we report the growth of self-regulated MnBi2Te4 films by the molecular beam epitaxy. By tuning the substrate temperature to the optimal temperature for the growth surface, the stoichiometry of MnBi2Te4 becomes sensitive to the Mn/Bi flux ratio. Excessive and deficient Mn resulted in the formation of a MnTe and Bi2Te3 phase, respectively. The magnetic measurement of the 7 SL MnBi2Te4 film probed by the superconducting quantum interference device (SQUID) shows that the antiferromagnetic order occurring at the Néel temperature 22 K is accompanied by an anomalous magnetic hysteresis loop along the c-axis. The band structure measured by angle-resolved photoemission spectroscopy (ARPES) at 80 K reveals a Dirac-like surface state, which indicates that MnBi2Te4 has topological insulator properties in the paramagnetic phase. Our work demonstrates the key growth parameters for the design and optimization of the synthesis of nanoscale MnBi2Te4 films, which are of great significance for fundamental research and device applications involving antiferromagnetic topological insulators.
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- 2021
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14. Germanene structure enhancement by adjacent insoluble domains of lead
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Ting-Yu Chen, David Mikolas, Santosh Chiniwar, Angus Huang, Chung-Huang Lin, Cheng-Maw Cheng, Chung-Yu Mou, H.-T. Jeng, Woei Wu Pai, and S.-J. Tang
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Physics ,QC1-999 - Abstract
Growth of Xene, referred to as the analog of graphene made of atoms other than carbon, with higher lattice quality and more intrinsic electronic structures, is an important challenge to the development of two-dimensional (2D) materials. We report an approach using Pb-atom deposition to striped-phase (SP) germanene grown on Ag(111) to trigger it to a quasifreestanding phase (QP). Using low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM), we demonstrate that the 2D monatomic Pb layer, instead of being on top, grows side-by-side with QP germanene, not only driving the SP-to-QP transition but further enhancing the lattice order of QP as revealed by the dramatic evolution of LEED-spot shape and uniform STM-imaged array of moiré patterns. Originally oriented at 30° to Ag(111), the QP germanene transits first to a narrow distribution of rotations then to two sharp domains at ±3° from 30°, while the monoatomic Pb domains twist from ±4.3° to ±9.5° with respect to Ag(111). The analysis of higher-order coincidence for both layers on Ag(111) is in complete agreement with LEED results and reveals a picture of two insoluble monatomic layers driving each other to a more optimal configuration. Moreover, the corresponding density of states measured by scanning tunneling spectroscopy for quality-enhanced QP germanene exhibits a clear V-shape distribution at the energy ∼0.4 eV above Fermi level, indicating the Fermi-Dirac cone, which agrees with our density functional theory calculation.
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- 2021
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15. Enhance high harmonic generation (HHG) efficiency via compact multi-plate continuum post-compression for time-resolved angle-resolved photoemission spectroscopy
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Hao-Hsiang Jia, Tien-Tien Yeh, Cheng-Maw Cheng, Chih-Wei Luo, Ming-Chang Chen, and Ping-Hui Lin
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Instrumentation - Abstract
Time-resolved angle-resolved photoemission spectroscopy (Tr-APRES) gives direct insight into electron dynamics by providing temporal-, energy-, and momentum-resolved information in one experiment. A major obstacle to using high harmonic generation (HHG) probe pulses for photoemission spectroscopy is the low conversion efficiency, that is, the low flux of probe photons. We use a Yb-KGW based duo-laser source with an oscillator to pump two separate amplifiers and generate two synchronized pulsed laser sources with average energies of 7.5 and 6 W. By using the multiplate continuum method and chirped mirrors, the resulting flux of HHG photons at 33–70 eV can be increased 50-fold (up to 1011 photons/s) by using post-compressed 30 fs pulses compared with the photon flux generated by the fundamental 190 fs pulses. Moreover, pulses from the 6 W amplifier are used to pump an optical parametric amplifier that can vary the wavelengths for photoexcitation. The system performance is demonstrated by applying Tr-ARPES to single-crystal graphite. The front tilt broadening is significantly suppressed by the off-plane mounted conical grating, leading to a 184 fs temporal resolution that is mainly limited by the pump pulse. The energy resolution is 176 meV.
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- 2023
16. Enhanced Ferromagnetic Interaction in Modulation-Doped GaMnN Nanorods
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Yuan-Ting Lin, Paritosh Vilas Wadekar, Hsiang-Shun Kao, Yu-Jung Zheng, Quark Yung-Sung Chen, Hui-Chun Huang, Cheng-Maw Cheng, New-Jin Ho, and Li-Wei Tu
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A1. Characterization ,A1. Doping ,A3. Molecular beam epitaxy ,B1. Nanomaterials ,B1. Nitrides ,B2. Magnetic materials ,Materials of engineering and construction. Mechanics of materials ,TA401-492 - Abstract
Abstract In this report, ferromagnetic interactions in modulation-doped GaMnN nanorods grown on Si (111) substrate by plasma-assisted molecular beam epitaxy are investigated with the prospect of achieving a room temperature ferromagnetic semiconductor. Our results indicate the thickness of GaN layer in each GaN/MnN pair, as well as Mn-doping levels, are essential for suppressing secondary phases as well as enhancing the magnetic moment. For these optimized samples, structural analysis by high-resolution X-ray diffractometry and Raman spectroscopy verifies single-crystalline modulation-doped GaMnN nanorods with Ga sites substituted by Mn atoms. Energy dispersive X-ray spectrometry shows that the average Mn concentration can be raised from 0.4 to 1.8% by increasing Mn fluxes without formation of secondary phases resulted in a notable enhancement of the saturation magnetization as well as coercive force in these nanorods.
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- 2017
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17. Epitaxially ferroelectric hexagonal boron nitride on graphene
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Chung-Lin Wu, Sheng-Shong Wong, Zhen-You Lin, Sheng-Zhu Ho, Chin-En Hsu, Ping-Hung Li, Ching-Yu Chen, Yen-Fu Huang, Chia-Hao Chen, Yi-Chun Chen, Hung-Chung Hsueh, and Cheng-Maw Cheng
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Ferroelectricity in two-dimensional (2D) van der Waals (vdW) layers has revolutionized our understanding of the vdW layered coupling, and has been introduced in the domains of moiré superlattice patterns generated by interlayer twisting or sliding. In the smallest limit of thickness, untwisted and epitaxial vdW stacking layers exhibiting ferroelectricity would clearly serve as building blocks for realizing 2D devices with nonvolatile and reconfigurable functionalities. In this study, we grew ferroelectric hexagonal boron nitride (h-BN) films on single-crystal graphene synthesized on a SiC (0001) substrate using nitrogen plasma-assisted molecular beam epitaxy (PA-MBE). Systematic angle-resolved photoemission spectroscopy (ARPES) studies and first-principles calculations revealed that the epitaxial mono-, bi-, and tri-layer h-BN films exhibit layer-number-dependent µ-band dispersions due to an AB stacking sequence on a Bernal-stacked graphene substrate. Furthermore, our piezoelectric force microscopy (PFM) confirmed the coexistence of robust moiré and sliding ferroelectricity at the well-aligned h-BN/graphene heterojunction and in multilayered h-BN films, respectively. In principle, as-developed epitaxially ferroelectric h-BN is limited only by the size of the crystalline graphene substrate, thereby providing a versatile and scalable 2D ferroelectric platform with promising exotic physics and vdW device applications down to a few atomic layers.
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- 2023
18. Evolution of optical nonlinearity within a graphene/Bi2Te3 heterostructure
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Jia-Chi Lan, Chan-Shan Yang, Chun-Hu Chen, Cheng-Maw Cheng, Hong Liu, and Chao-Kuei Lee
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Materials Chemistry ,General Chemistry - Abstract
Effect of passive Q-switched solid-state laser for different absorption behaviours of absorbers.
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- 2022
19. Robust charge-density wave strengthened by electron correlations in monolayer 1T-TaSe2 and 1T-NbSe2
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Cheng Maw Cheng, Takashi Takahashi, Shuyun Zhou, Changhua Bao, Tomoteru Fukumura, Ashish Chainani, Katsuaki Sugawara, Hirofumi Oka, Takafumi Sato, Pei Yu Chuang, Shaohua Zhou, Yuki Nakata, Yasuaki Saruta, and Tappei Kawakami
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Materials science ,Science ,General Physics and Astronomy ,FOS: Physical sciences ,Electron ,General Biochemistry, Genetics and Molecular Biology ,Condensed Matter - Strongly Correlated Electrons ,Condensed Matter::Materials Science ,Phase (matter) ,Condensed Matter::Superconductivity ,Monolayer ,Superconductivity ,Condensed Matter::Quantum Gases ,Condensed Matter - Materials Science ,Multidisciplinary ,Condensed matter physics ,Electronic correlation ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed Matter::Other ,Transition temperature ,Materials Science (cond-mat.mtrl-sci) ,General Chemistry ,Photoexcitation ,Condensed Matter::Strongly Correlated Electrons ,Charge density wave - Abstract
Combination of low-dimensionality and electron correlation is vital for exotic quantum phenomena such as the Mott-insulating phase and high-temperature superconductivity. Transition-metal dichalcogenide (TMD) 1T-TaS2 has evoked great interest owing to its unique nonmagnetic Mott-insulator nature coupled with a charge-density-wave (CDW). To functionalize such a complex phase, it is essential to enhance the CDW-Mott transition temperature TCDW-Mott, whereas this was difficult for bulk TMDs with TCDW-Mott 2. Furthermore, the electron correlation derived lower Hubbard band survives under external perturbations such as carrier doping and photoexcitation, in contrast to the bulk counterpart. The enhanced Mott-Hubbard and CDW gaps for monolayer TaSe2 compared to NbSe2, originating in the lattice distortion assisted by strengthened correlations and disappearance of interlayer hopping, suggest stabilization of a likely nonmagnetic CDW-Mott insulator phase well above the room temperature. The present result lays the foundation for realizing monolayer CDW-Mott insulator based devices operating at room temperature.
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- 2021
20. Spin-to-Charge Conversion Manipulated by Fine-Tuning the Fermi Level of Topological Insulator (Bi1–xSbx)2Te3
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Cheong-Wei Chong, Jung-Chun-Andrew Huang, Yi-Chun Chen, Pei-Yu Chuang, Jung-Chuan Lee, Zong Mou Lin, Ya Wen Li, Shu Hsuan Su, and Cheng-Maw Cheng
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symbols.namesake ,Fine-tuning ,Materials science ,Condensed matter physics ,Topological insulator ,Fermi level ,Materials Chemistry ,Electrochemistry ,symbols ,Charge (physics) ,Electronic, Optical and Magnetic Materials ,Spin-½ - Published
- 2021
21. Direct observation of kink evolution due to Hund’s coupling on approach to metal-insulator transition in NiS2−x Se x
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Gabriel Kotliar, Ji Hoon Shim, Yoon Young Koh, Hyeong-Do Kim, Cheng Maw Cheng, Wonshik Kyung, Garam Han, Ina Park, Namjung Hur, Ku Ding Tsuei, Dong-Wook Kim, Changyoung Kim, Yeongkwan Kim, Bo Gyu Jang, and Kyung Dong Lee
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Physics ,Multidisciplinary ,Condensed matter physics ,Science ,General Physics and Astronomy ,Angle-resolved photoemission spectroscopy ,02 engineering and technology ,General Chemistry ,Electron ,021001 nanoscience & nanotechnology ,01 natural sciences ,General Biochemistry, Genetics and Molecular Biology ,Coupling (physics) ,0103 physical sciences ,Coulomb ,Density functional theory ,Condensed Matter::Strongly Correlated Electrons ,Fermi liquid theory ,Metal–insulator transition ,010306 general physics ,0210 nano-technology ,Characteristic energy - Abstract
Understanding characteristic energy scales is a fundamentally important issue in the study of strongly correlated systems. In multiband systems, an energy scale is affected not only by the effective Coulomb interaction but also by the Hund’s coupling. Direct observation of such energy scale has been elusive so far in spite of extensive studies. Here, we report the observation of a kink structure in the low energy dispersion of NiS2−xSex and its characteristic evolution with x, by using angle resolved photoemission spectroscopy. Dynamical mean field theory calculation combined with density functional theory confirms that this kink originates from Hund’s coupling. We find that the abrupt deviation from the Fermi liquid behavior in the electron self-energy results in the kink feature at low energy scale and that the kink is directly related to the coherence-incoherence crossover temperature scale. Our results mark the direct observation of the evolution of the characteristic temperature scale via kink features in the spectral function, which is the hallmark of Hund’s physics in the multiorbital system.
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- 2021
22. Role of carrier-transfer in the optical nonlinearity of graphene/Bi2Te3 heterojunctions
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Chao-Kuei Lee, Hong Liu, Junpeng Qiao, Shi-Hsin Lin, Meng-Yu Wu, Cheng-Maw Cheng, Ren-Huai Jhang, Wei-Heng Sung, Chun-Hu Chen, Jia-Chi Lan, Li-Wei Tu, Gengchiau Liang, and Li-Ren Ng
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Materials science ,business.industry ,Graphene ,Pulse duration ,Heterojunction ,Saturable absorption ,02 engineering and technology ,Electron ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Laser ,01 natural sciences ,0104 chemical sciences ,law.invention ,Amplitude modulation ,law ,Topological insulator ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business - Abstract
Two-dimensional (2D) topological insulators (TIs) have attracted a lot of attention owing to their striking optical nonlinearity. However, the ultra-low saturable intensity (SI) of TIs resulting from the bulk conduction band limits their applications, such as in mode-locking solid-state lasers. In this work, through fabricating a graphene/Bi2Te3 heterojunction which combines monolayer graphene and a Bi2Te3 nanoplate, the optical nonlinearities are analyzed. Moreover, the thickness-dependent characteristics are also investigated by varying the thickness of the Bi2Te3 when synthesizing the heterojunctions. Furthermore, with the aid of the estimated junction electron escape time, a model of the photo-excited carrier-transfer mechanism is proposed and used to describe the phenomena of depression of ultra-low saturable absorption (SA) from the Bi2Te3 bulk band. The increased modulation depth of the graphene/Bi2Te3 heterojunction can accordingly be realized in more detail. In addition, a Q-switched solid-state laser operating at 1064 nm with heterojunction saturable absorbers is built up and characterized for validating the proposed model. The laser performance with varied Bi2Te3 thickness, such as pulse duration and repetition rate, agrees quite well with our proposed model. Our work demonstrates the functionality of optical nonlinear engineering by tuning the thickness of the graphene/Bi2Te3 heterojunction and demonstrates its potential for applications.
- Published
- 2020
23. Unravelling the effect of sulfur vacancies on the electronic structure of the MoS2 crystal
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Xutang Tao, Xinru Li, Jia-Chi Lan, Shanpeng Wang, Jie Qiao, Xixia Zhang, Cheng-Maw Cheng, and Chao-Kuei Lee
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Materials science ,Condensed matter physics ,Photoemission spectroscopy ,business.industry ,General Physics and Astronomy ,chemistry.chemical_element ,Angle-resolved photoemission spectroscopy ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,Sulfur ,Crystal ,chemistry.chemical_compound ,Semiconductor ,chemistry ,0103 physical sciences ,Density functional theory ,Physical and Theoretical Chemistry ,010306 general physics ,0210 nano-technology ,business ,Molybdenum disulfide - Abstract
Molybdenum disulfide (MoS2) is one of the two-dimensional layered semiconductor transition metal dichalcogenides (TMDCs) with great potential in electronics, optoelectronics, and spintronic devices. Sulfur vacancies in MoS2 are the most prevalent defects. However, the effect of sulfur vacancies on the electronic structure of MoS2 is still in dispute. Here we experimentally and theoretically investigated the effect of sulfur vacancies in MoS2. The vacancies were intentionally introduced by thermal annealing of MoS2 crystals in a vacuum environment. Angle-resolved photoemission spectroscopy (ARPES) was used directly to observe the electronic structure of the MoS2 single crystals. The experimental result distinctly revealed the appearance of an occupied defect state just above the valence band maximum (VBM) and an upward shift of the VBM after creating sulfur vacancies. In addition, density functional theory (DFT) calculations also confirmed the existence of the occupied defect state close to the VBM as well as two deep unoccupied states induced by the sulfur vacancies. Our results provide evidence to contradict that sulfur vacancies indicate the origin of n-type behaviour in MoS2. This work provides a rational strategy for tuning the electronic structures of MoS2.
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- 2020
24. Topological Proximity-Induced Dirac Fermion in Two-Dimensional Antimonene
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Shu Hsuan Su, Hsin Yu Chen, Chao-Kuei Lee, Chih-Wei Luo, Shih Hsun Yu, Tay-Rong Chang, Ku Ding Tsuei, Shih-Chang Weng, Mitch M.C. Chou, Horng-Tay Jeng, Wei Chuan Chen, Pei Yu Chuang, Cheng Maw Cheng, Li-Wei Tu, Jung Chun Andrew Huang, and Chien Ming Tu
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Physics ,Texture (cosmology) ,Band gap ,Fermi level ,Dirac (software) ,General Engineering ,General Physics and Astronomy ,Topology ,symbols.namesake ,Dirac fermion ,Topological insulator ,symbols ,General Materials Science ,Proximity effect (atomic physics) ,Spin-½ - Abstract
Antimonene is a promising two-dimensional (2D) material that is calculated to have a significant fundamental bandgap usable for advanced applications such as field-effect transistors, photoelectric devices, and the quantum-spin Hall (QSH) state. Herein, we demonstrate a phenomenon termed topological proximity effect, which occurs between a 2D material and a three-dimensional (3D) topological insulator (TI). We provide strong evidence derived from hydrogen etching on Sb2Te3 that large-area and well-ordered antimonene presents a 2D topological state. Delicate analysis with a scanning tunneling microscope of the evolutionary intermediates reveals that hydrogen etching on Sb2Te3 resulted in the formation of a large area of antimonene with a buckled structure. A topological state formed in the antimonene/Sb2Te3 heterostructure was confirmed with angle-resolved photoemission spectra and density-functional theory calculations; in particular, the Dirac point was located almost at the Fermi level. The results reveal that Dirac fermions are indeed realized at the interface of a 2D normal insulator (NI) and a 3D TI as a result of strong hybridization between antimonene and Sb2Te3. Our work demonstrates that the position of the Dirac point and the shape of the Dirac surface state can be tuned by varying the energy position of the NI valence band, which modifies the direction of the spin texture of Sb-BL/Sb2Te3via varying the Fermi level. This topological phase in 2D-material engineering has generated a paradigm in that the topological proximity effect at the NI/TI interface has been realized, which demonstrates a way to create QSH systems in 2D-material TI heterostructures.
- Published
- 2021
25. Germanene structure enhancement by adjacent insoluble domains of lead
- Author
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Shu-Jung Tang, David Mikolas, Cheng-Maw Cheng, Horng-Tay Jeng, Santosh Chiniwar, Ting-Yu Chen, Chung-Huang Lin, Woei Wu Pai, Chung-Yu Mou, and Angus Huang
- Subjects
Physics ,Germanene ,Condensed matter physics ,Fermi level ,Scanning tunneling spectroscopy ,law.invention ,symbols.namesake ,law ,Lattice (order) ,symbols ,Density of states ,Density functional theory ,Twist ,Scanning tunneling microscope - Abstract
Growth of Xene, referred to as the analog of graphene made of atoms other than carbon, with higher lattice quality and more intrinsic electronic structures, is an important challenge to the development of two-dimensional (2D) materials. We report an approach using Pb-atom deposition to striped-phase (SP) germanene grown on Ag(111) to trigger it to a quasifreestanding phase (QP). Using low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM), we demonstrate that the 2D monatomic Pb layer, instead of being on top, grows side-by-side with QP germanene, not only driving the SP-to-QP transition but further enhancing the lattice order of QP as revealed by the dramatic evolution of LEED-spot shape and uniform STM-imaged array of moir\'e patterns. Originally oriented at 30\ifmmode^\circ\else\textdegree\fi{} to Ag(111), the QP germanene transits first to a narrow distribution of rotations then to two sharp domains at \ifmmode\pm\else\textpm\fi{}3\ifmmode^\circ\else\textdegree\fi{} from 30\ifmmode^\circ\else\textdegree\fi{}, while the monoatomic Pb domains twist from \ifmmode\pm\else\textpm\fi{}4.3\ifmmode^\circ\else\textdegree\fi{} to \ifmmode\pm\else\textpm\fi{}9.5\ifmmode^\circ\else\textdegree\fi{} with respect to Ag(111). The analysis of higher-order coincidence for both layers on Ag(111) is in complete agreement with LEED results and reveals a picture of two insoluble monatomic layers driving each other to a more optimal configuration. Moreover, the corresponding density of states measured by scanning tunneling spectroscopy for quality-enhanced QP germanene exhibits a clear V-shape distribution at the energy \ensuremath{\sim}0.4 eV above Fermi level, indicating the Fermi-Dirac cone, which agrees with our density functional theory calculation.
- Published
- 2021
26. Role of carrier-transfer in the optical nonlinearity of graphene/Bi
- Author
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Jia-Chi, Lan, Junpeng, Qiao, Wei-Heng, Sung, Chun-Hu, Chen, Ren-Huai, Jhang, Shi-Hsin, Lin, Li-Ren, Ng, Gengchiau, Liang, Meng-Yu, Wu, Li-Wei, Tu, Cheng-Maw, Cheng, Hong, Liu, and Chao-Kuei, Lee
- Abstract
Two-dimensional (2D) topological insulators (TIs) have attracted a lot of attention owing to their striking optical nonlinearity. However, the ultra-low saturable intensity (SI) of TIs resulting from the bulk conduction band limits their applications, such as in mode-locking solid-state lasers. In this work, through fabricating a graphene/Bi
- Published
- 2020
27. Direct observation of kink evolution due to Hund's coupling on approach to metal-insulator transition in NiS
- Author
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Bo Gyu, Jang, Garam, Han, Ina, Park, Dongwook, Kim, Yoon Young, Koh, Yeongkwan, Kim, Wonshik, Kyung, Hyeong-Do, Kim, Cheng-Maw, Cheng, Ku-Ding, Tsuei, Kyung Dong, Lee, Namjung, Hur, Ji Hoon, Shim, Changyoung, Kim, and Gabriel, Kotliar
- Subjects
Electronic structure ,Electronic properties and materials ,Phase transitions and critical phenomena ,Article - Abstract
Understanding characteristic energy scales is a fundamentally important issue in the study of strongly correlated systems. In multiband systems, an energy scale is affected not only by the effective Coulomb interaction but also by the Hund’s coupling. Direct observation of such energy scale has been elusive so far in spite of extensive studies. Here, we report the observation of a kink structure in the low energy dispersion of NiS2−xSex and its characteristic evolution with x, by using angle resolved photoemission spectroscopy. Dynamical mean field theory calculation combined with density functional theory confirms that this kink originates from Hund’s coupling. We find that the abrupt deviation from the Fermi liquid behavior in the electron self-energy results in the kink feature at low energy scale and that the kink is directly related to the coherence-incoherence crossover temperature scale. Our results mark the direct observation of the evolution of the characteristic temperature scale via kink features in the spectral function, which is the hallmark of Hund’s physics in the multiorbital system., A decisive spectroscopic evidence of the Hund’s coupling energy scale in multi-orbital correlated systems has been lacking. Here, the authors identify a kink feature due to Hund´s coupling in the spectral function of NiS2xSex as they track its evolution across the Mott-insulator transition.
- Published
- 2020
28. Surface-dominant transport properties in MoSe2 nanosheets
- Author
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Chi Yang Chen, Tsu Yi Fu, Kuei Yi Lee, Cheng Maw Cheng, Yu Wen Chu, Hung Ru Chen, Chin Jung Ho, Ruei-San Chen, Yu Shin Chang, Manickam Anandan, and Liang Chiun Chao
- Subjects
Materials science ,business.industry ,Photoconductivity ,Electron ,Carrier lifetime ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Responsivity ,Light intensity ,chemistry.chemical_compound ,Band bending ,chemistry ,Molybdenum diselenide ,Optoelectronics ,Electric current ,business - Abstract
The electronic transport and photoconduction properties of the molybdenum diselenide (MoSe2 ) nanosheets were investigated. The transfer length method analysis suggests the electric current following an anomalously two-dimensional (2D) flow rather than the general 3D mode. The 2D current implies a higher electron concentration and downward band bending at the surface. A broad spectral photoresponse from ultraviolet to near-infrared wavelengths was also observed for the MoSe 2 nanosheets. The optimal responsivity and photoconductive gain respectively at 58 A/W and 179 under the wavelengths at 405 nm were achieved. A surface-controlled photoconduction mechanism based on the surface band bending and electron accumulation is proposed to explain the long carrier lifetime and its dependence of light intensity and environment in MoSe 2 nanostructures .
- Published
- 2022
29. Anti-site defect effect on the electronic structure of a Bi2Te3 topological insulator
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Cheong Wei Chong, Yaw Wen Yang, Yucheng Wu, Yi-Kang Lan, Chih-Kai Yang, Ku Ding Tsuei, Wei Chuan Chen, Shu Hsuan Su, Yi Fan Chen, Shih-Chang Weng, Yen Fa Liao, Shen Lin Chang, H. L. Su, Jyh-Fu Lee, Chi Hsuan Lee, Chia Hsin Wang, Pei Yu Chuang, Cheng Maw Cheng, Yu Heng Chou, and Jung-Chun Andrew Huang
- Subjects
Materials science ,Spintronics ,Condensed matter physics ,Extended X-ray absorption fine structure ,General Chemical Engineering ,Fermi level ,Angle-resolved photoemission spectroscopy ,02 engineering and technology ,General Chemistry ,Electronic structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,symbols.namesake ,Topological insulator ,0103 physical sciences ,symbols ,Thin film ,010306 general physics ,0210 nano-technology ,Surface states - Abstract
Tuning the Fermi level (EF) in Bi2Te3 topological-insulator (TI) films is demonstrated on controlling the temperature of growth with molecular-beam epitaxy (MBE). Angle-resolved photoemission spectra (ARPES) reveal that EF of Bi2Te3 thin films shifts systematically with the growth temperature (Tg). The key role that a Bi-on-Te(1) (BiTe1) antisite defect plays in the electronic structure is identified through extended X-ray-absorption fine-structure (EXAFS) spectra at the Bi L3-edge. Calculations of electronic structure support the results of fitting the EXAFS, indicating that the variation of EF is due to the formation and suppression of BiTe1 that is tunable with the growth temperature. Our findings provide not only insight into the correlation between the defect structure and electronic properties but also a simple route to control the intrinsic topological surface states, which could be useful for applications in TI-based advanced electronic and spintronic devices.
- Published
- 2018
30. Single-crystalline silver films on mica
- Author
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Ku Ding Tsuei, Chia Hsin Wang, Cheng Maw Cheng, Yaw Wen Yang, Dah An Luh, and Chen Wei Liu
- Subjects
Materials science ,Annealing (metallurgy) ,Metals and Alloys ,Analytical chemistry ,Mineralogy ,02 engineering and technology ,Surfaces and Interfaces ,021001 nanoscience & nanotechnology ,01 natural sciences ,Spectral line ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,Electron diffraction ,Sputtering ,law ,0103 physical sciences ,Materials Chemistry ,Thermal stability ,Mica ,Scanning tunneling microscope ,010306 general physics ,0210 nano-technology ,Single crystal - Abstract
Highly ordered Ag films grown on cleaved mica with a two-step procedure were characterized in detail with several techniques for surface analysis, including low-energy electron diffraction, X-ray photoemission spectra, a scanning tunneling microscope and angle-resolved photoemission spectra. Silver films of a thickness ≥ 100 nm were deposited on mica substrates at 300 K and stored under ambient conditions. The Ag/mica films became atomically flat and free of contamination when they were transferred into ultra-high vacuum and prepared with sputtering and annealing. The experimental results indicate that the surfaces of the cleaned Ag/mica films have structural and electronic properties resembling those of a Ag(111) single crystal with ordered domains aligned over a macroscopic region, but the surfaces of the Ag/mica films became rough on annealing above 623 K. On the rough surfaces, the surface steps tended to bunch together, yielding flat terraces bound with steps of large heights. With the decreased thermal stability in mind, the Ag/mica film is adoptable as a cheap platform alternative to a Ag(111) single crystal for the growth of highly ordered overlayers.
- Published
- 2018
31. Corrigendum: Significantly enhanced giant Rashba splitting in a thin film of binary alloy (2015 New J. Phys. 17 083015)
- Author
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Wei-Chuan Chen, Tay-Rong Chang, Sun-Ting Tsai, Sh Yamamoto, Je-Ming Kuo, Cheng-Maw Cheng, Ku-Ding Tsuei, Koichiro Yaji, Hsin Lin, H-T Jeng, Chung-Yu Mou, Iwao Matsuda, and S-J Tang
- Subjects
Science ,Physics ,QC1-999 - Published
- 2015
- Full Text
- View/download PDF
32. Significantly enhanced giant Rashba splitting in a thin film of binary alloy
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Wei-Chuan Chen, Tay-Rong Chang, Sun-Ting Tsai, S Yamamoto, Je-Ming Kuo, Cheng-Maw Cheng, Ku-Ding Tsuei, Koichiro Yaji, Hsin Lin, H-T Jeng, Chung-Yu Mou, Iwao Matsuda, and S-J Tang
- Subjects
giant Rashba splitting ,binary alloy ,Pb and Au ,Science ,Physics ,QC1-999 - Abstract
Dirac cones in a two-dimensional environment have attracted much attention not only because of the massless Dirac fermions but also due to their capability to lock the spin direction with the momentum. Here we demonstrate that the Rashba effect within a single layer of a binary alloy composed of heavy atoms, Pb and Au, can be driven by and even tweaked with the adjacent top and bottom layers to yield cone-like structures and further enhance the Rashba coupling strength. Two cones are observed at the surface zone center $\bar{\Gamma }$ with giant Rashba parameters 1.53 and 4.45 eVÅ; an anisotropic giant Rashba splitting at the surface zone boundary $\bar{M}$ has a great value, 6.26 eVÅ, inferring the critical role of p - d hybridization between Pb and Au. Our results reveal not only an interesting natural phenomenon but also a feasible method of tweaking the Rashba effect of a two-dimensional system.
- Published
- 2015
- Full Text
- View/download PDF
33. Selective Hydrogen Etching Leads to 2D Bi(111) Bilayers on Bi2Se3: Large Rashba Splitting in Topological Insulator Heterostructure
- Author
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Chia Hsin Wang, Hsin Lin, Yaw Wen Yang, Shu Hsuan Su, Tay-Rong Chang, Pei Yu Chuang, Cheng Maw Cheng, Ku Ding Tsuei, H. L. Su, Hsin Yu Chen, Sheng Wen Chen, Wei Chuan Chen, Wu Yucheng, Jung Chun Andrew Huang, Yi Tung, and Horng-Tay Jeng
- Subjects
Condensed matter physics ,Chemistry ,General Chemical Engineering ,chemistry.chemical_element ,Angle-resolved photoemission spectroscopy ,Heterojunction ,02 engineering and technology ,General Chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Bismuth ,law.invention ,symbols.namesake ,X-ray photoelectron spectroscopy ,law ,Topological insulator ,0103 physical sciences ,Materials Chemistry ,symbols ,Density functional theory ,Scanning tunneling microscope ,van der Waals force ,010306 general physics ,0210 nano-technology - Abstract
Ultrathin bilayers (BLs) of bismuth have been predicated to be a two-dimensional (2D) topological insulator. Here we report on a new route to manufacture the high-quality Bi bilayers from a 3D topological insulator, a top-down approach to prepare large-area and well-ordered Bi(111) BL with deliberate hydrogen etching on epitaxial Bi2Se3 films. With scanning tunneling microscopy (STM) and X-ray photoelectron spectra (XPS) in situ, we confirm that the removal of Se from the top of a quintuple layer (QL) is the key factor, leading to a uniform formation of Bi(111) BL in the van der Waals gap between the first and second QL of Bi2Se3. The angle resolved photoemission spectroscopy (ARPES) in situ and complementary density functional theory (DFT) calculations show a giant Rashba splitting with a coupling constant of 4.5 eV A in the Bi(111) BL on Bi2Se3. Moreover, the thickness of Bi BLs can be tuned by the amount of hydrogen exposure. Our ARPES and DFT study indicated that the Bi hole-like bands increase with i...
- Published
- 2017
34. Substrate-mediated umklapp scattering at the incommensurate interface of a monatomic alloy layer
- Author
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Ting-Yu Chen, Angus Huang, Cheng-Maw Cheng, Ching-Ming Wei, Santosh Chiniwar, Cheng-Rong Hsing, Wei-Chuan Chen, Shu-Jung Tang, Horng-Tay Jeng, Woei Wu Pai, and Chung-Huang Lin
- Subjects
Physics ,Image (category theory) ,Nuclear Theory ,Alloy ,Substrate (electronics) ,Single band ,engineering.material ,Umklapp scattering ,Monatomic ion ,Crystallography ,Atomic radius ,Atom ,engineering ,Nuclear Experiment - Abstract
Ultrathin Pb and Ge films deposited on Ag(111) surfaces have been investigated and compared. We found that at 1/3 ML, both films formed surface alloys, ${\mathrm{Ag}}_{2}\mathrm{Pb}$ and ${\mathrm{Ag}}_{2}\mathrm{Ge}$, with $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}R{30}^{\ensuremath{\circ}}$ and $\frac{19}{20}\sqrt{3}\ifmmode\times\else\texttimes\fi{}\frac{19}{20}\sqrt{3}R{30}^{\ensuremath{\circ}}$ structures on Ag(111) but the surface electronic structures exhibit a most evident difference at the Ag(111) surface zone boundary ${\overline{M}}_{\mathrm{Ag}(111)}$, where the single band and the splitting ones were observed, respectively. Up to 1 ML, ${\mathrm{Ag}}_{2}\mathrm{Ge}$ subsequently develops into germanene with a striped phase and then a quasifreestanding phase, as previously reported [Lin et al., Phys. Rev. Mater. 2, 024003 (2018)], while ${\mathrm{Ag}}_{2}\mathrm{Pb}$ evolves to a dense Pb(111) phase that also reveals splitting bands at ${\overline{M}}_{\mathrm{Ag}(111)}$. We discover that the larger (smaller) atomic size of a Pb (Ge) atom with respect to an Ag atom causes the commensurate (incommensurate) interfaces and further demonstrate that the splitting bands of ${\mathrm{Ag}}_{2}\mathrm{Ge}$ surface alloy and 1-ML Pb film originated from the commonly incommensurate interface with Ag(111), which mediates umklapp scattering by inducing the mirror image of the pristine ${\mathrm{Ag}}_{2}\mathrm{Ge}$ and Pb(111) bands relative to ${\overline{M}}_{\mathrm{Ag}(111)}.$
- Published
- 2019
35. Probing the Origin of Extreme Magnetoresistance in Pr/Sm Mono-Antimonides/Bismuthides
- Author
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Tai-Chang Chiang, Fan Wu, Cheng-Maw Cheng, Zhe Sun, Huiqiu Yuan, Peng Li, Yang Liu, Chao Cao, Zhongzheng Wu, Chunyu Guo, and Yi Liu
- Subjects
Electron mobility ,Condensed Matter - Materials Science ,Materials science ,Magnetoresistance ,Condensed matter physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,Photoemission spectroscopy ,Quantum oscillations ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,02 engineering and technology ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,01 natural sciences ,Transition point ,Hall effect ,0103 physical sciences ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Electronic band structure ,Surface states - Abstract
Combining angle-resolved photoemission spectroscopy and magneto-transport measurements, we systematically investigated the possible origin of the extreme magnetoresistance in Pr/Sm mono-antimonides/bismuthides (PrSb, SmSb, PrBi, SmBi). Our photoemission measurements reveal that the bulk band inversion and surface states are absent (present) in Pr/Sm antimonides (bismuthides), implying that topological surface states are unlikely to play an important role for the observed extreme magnetoresistance. We found that the electron-hole compensation is well satisfied in all these compounds and the bulk band structure exhibits no obvious temperature dependence from 10 K up to 150 K. Simultaneous fittings of the magnetoresistance and Hall coefficient reveal that the carrier mobility is dramatically enhanced at low temperature, which naturally explains the suppression of extreme magnetoresistance at high temperatures. Our results therefore show that the extreme magnetoresistance in these compounds can be well accounted for by the two-band model with good electron-hole compensation. Finally, we found that both PrSb and SmSb exhibit highly linear bulk bands near the X point and lie close to the transition point between a topologically trivial and nontrivial phase, which might be relevant for the observed anomalous quantum oscillations., 6 figures
- Published
- 2019
36. Rashba effect within the space–charge layer of a semiconductor
- Author
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Chung-Huang Lin, Tay-Rong Chang, Ro-Ya Liu, Cheng-Maw Cheng, Ku-Ding Tsuei, H -T Jeng, Chung-Yu Mou, Iwao Matsuda, and S -J Tang
- Subjects
semiconductor band edges ,space–charge layer ,Rashba effect ,Science ,Physics ,QC1-999 - Abstract
The observed heavy-hole, light-hole and split-off band edges of a semiconductor are the well known consequence of two physical processes: atomic spin–orbital interaction and solid-state band–band anticrossing. In this work, we examined the four band-edge-like bands in great detail within the Ge space–charge layer with either Pb/Ge(111)- $\sqrt{3}\times \sqrt{3}$ R30° or a 2 ML Pb film on Ge(111). Our results reveal that the conventional picture of band edges for a semiconductor is actually crude. In addition, momentum-dependent Rashba splitting effect can be included to explain the observed non-split-off band, indicating the Rashba effect as an intrinsic property near a semiconductor surface.
- Published
- 2014
- Full Text
- View/download PDF
37. Twenty-First NSRRC Users' Meeting and Workshops
- Author
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Ming-Tzu Shih, Der-Hsin Wei, and Cheng-Maw Cheng
- Subjects
Nuclear and High Energy Physics ,Engineering ,business.industry ,Photon source ,Library science ,Center (algebra and category theory) ,business ,Atomic and Molecular Physics, and Optics ,Research center - Abstract
The Twenty-First NSRRC Users' Meeting was held at the Activity Center of the National Synchrotron Radiation Research Center (NSRRC) in Taiwan from September 9 to 10, 2015. At the same time, celebration of the first light of the Taiwan Photon Source (TPS), achieved at the end of 2014, highlighted the prospective scientific frontiers marked by the TPS storage ring. Jointly organized by the UEC Chair Ying-Hao Chu (National Chiao Tung Univ.) and Cheng-Maw Cheng (NSRRC), the meeting consisted of two plenary sessions and three featured workshops. Nearly 30 distinguished scholars, both domestic and international, were invited to present their research achievements. This highly anticipated event attracted an enthusiastic crowd of more than 370 synchrotron experts, users, and potential users.
- Published
- 2016
38. Tight-binding parameters of graphite determined with angle-resolved photoemission spectra
- Author
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Jian-Lun Peng, Ching-Hung Chen, Cheng-Maw Cheng, Ku-Ding Tsuei, Jih-Young Yuh, and Chia-Jen Hsu
- Subjects
Materials science ,Binding energy ,Oxide ,Analytical chemistry ,General Physics and Astronomy ,Cleavage (crystal) ,Angle-resolved photoemission spectroscopy ,Surfaces and Interfaces ,General Chemistry ,Condensed Matter Physics ,Spectral line ,Surfaces, Coatings and Films ,chemistry.chemical_compound ,Tight binding ,chemistry ,Graphite ,Electronic band structure - Abstract
An exfoliated Kish graphite sample on a heavily n-doped Si substrate covered with native oxide was prepared with a conventional micromechanical cleavage method. From angle-resolved photoemission spectra (ARPES), we measured the band structure of graphite over photon energies from 28 eV to 116 eV. The inner potential V0 = 17.25 eV is determined with a period from the band dispersion in the KH direction. A set of parameters in the tight-binding method and the SWMcC model for graphite is extracted from the fitted results. A comparison of constant-energy mapping results at large binding energy indicates the reliability of the tight-binding parameters extracted from the ARPES results.
- Published
- 2015
39. Construction of a manipulator with six degrees of freedom and a rotary platform differentially pumped via retractable welded bellows
- Author
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Cheng-Maw Cheng and Jih-Young Yuh
- Subjects
Materials science ,Rotation around a fixed axis ,Mechanical engineering ,Welding ,Condensed Matter Physics ,Surfaces, Coatings and Films ,law.invention ,Bellows ,Manipulator system ,Sputtering ,law ,Six degrees of freedom ,Vacuum chamber ,Instrumentation - Abstract
Photoelectron spectra (PES) have played an important role since the beginning of research in surface and material science. When these techniques are applied for the analysis of a more complicated system such as: highly correlated, surface-interface, transition-metal-oxide, samples are maneuvered between UHV chambers for sputtering, deposition or cleavage with a multiple-degree-of-freedom manipulator that consists of an x-y-z translational stage as well as rotation about these three axis. After these processes, a sample surface must be annealed to re-crystallize or cooled to its critical temperature before studying; control of temperature over a wide range is thus also an essential capability of a manipulator system. To integrate all above functions, a sample manipulator was constructed featuring control of temperature over a wide range -- 20 K to 1000 K, six degrees of freedom for sample positioning, sample transfer with exchangeable sample-mounting modules to fulfill varied experimental needs. Another special feature of our design is a retractable welded bellows to replace the formed bellows that connects to the differentially pumped rotary platform (DPRP) that provide the rotational motion of the sample in polar angular directions. This modification prevents the long formed bellows connected to its pumping system from dangling around the analysis vacuum chamber and interfering with other instruments.
- Published
- 2015
40. Epitaxial growth of Cu on Ag(1 1 1) studied with angle-resolved photoemission spectroscopy
- Author
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Chih Hao Huang, Dah An Luh, Cheng Maw Cheng, and Ku Ding Tsuei
- Subjects
Crystallography ,Materials science ,Annealing (metallurgy) ,General Physics and Astronomy ,Angle-resolved photoemission spectroscopy ,Surfaces and Interfaces ,General Chemistry ,Metallic thin films ,Condensed Matter Physics ,Epitaxy ,Spectral line ,Surfaces, Coatings and Films ,Surface states - Abstract
The growth of Cu on Ag(1 1 1) under varied growth conditions was investigated with angle-resolved photoemission spectra. The evolution of Cu/Ag(1 1 1) during annealing was characterized on monitoring its surface states. The surface morphology of a Cu film on Ag(1 1 1) depends on the temperature and the Cu coverage. Islands or crystalline films develop when Cu is deposited at ∼300 K. Defects in the Cu films penetrate deeply into the Ag(1 1 1) substrate and expose the Ag(1 1 1) surface. The deposition of Cu at a low temperature results in disordered films. On annealing, the films become ordered with defects. Our results show the segregation of Ag on the Cu surface, which occurs at 300 K and becomes accelerated significantly at ∼380 K. After being annealed above 430 K, all islands and films of Cu are fully covered with Ag, showing a (9 × 9) reconstruction. Our results indicate also that the segregation of Ag on the Cu surface occurs only after the Ag(1 1 1) surface is exposed, indicating that Ag atoms migrate to the Cu(1 1 1) surface, not through bulk Cu, but along the walls of the islands and the defects in the films.
- Published
- 2015
41. Intrinsic ferromagnetism and anomalous Hall effect in GaN thin film by Mn delta doping
- Author
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Li-Wei Tu, Che-Min Lin, Yuan-Ting Lin, Tsan-Chuen Leung, Cheng-Maw Cheng, P.V. Wadekar, Quark Y. Chen, and Ching-Wen Chang
- Subjects
Materials science ,Gallium nitride ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,Transition metal ,Hall effect ,Condensed Matter::Superconductivity ,Materials Chemistry ,Spintronics ,Condensed matter physics ,Mechanical Engineering ,Doping ,Metals and Alloys ,Heterojunction ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Ferromagnetism ,chemistry ,Mechanics of Materials ,Condensed Matter::Strongly Correlated Electrons ,0210 nano-technology ,Molecular beam epitaxy - Abstract
Compound semiconductors doped with magnetically active transition metals (TM) are actively pursued for semiconductor spintronics. Herein we report that delta doping (δ-doping) has been used to incorporate manganese (Mn) into the gallium nitride (GaN) matrix resulting in phase pure highly crystalline heteroepitaxial thin films of (Ga,Mn)N on c-plane sapphire (Al2O3) by plasma-assisted molecular beam epitaxy. Magnetotransport measurements reveal the anomalous Hall effect (AHE) while magnetic measurements show the existence of ferromagnetic ordering. Density functional theory calculations show that δ-doping of Mn atom enables exchange interactions between the Mn 3d states and N 2p states thereby resulting in spin polarized holes in the valence band giving rise to observed AHE and ferromagnetism. This work opens new avenues for incorporating spin polarized carriers in III-nitrides based semiconductors by creating magnetically active Mn layers in heterostructures for spintronics applications.
- Published
- 2020
42. Tunable electronic structure and surface states in rare-earth monobismuthides with partially filled f shell
- Author
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Deng-Sung Lin, Yi Wu, Tai-Chang Chiang, Chunyu Guo, Huiqiu Yuan, Zhongzheng Wu, Frank Steglich, Cheng-Maw Cheng, Chao Cao, Yi Liu, Zhe Sun, Peng Li, Yang Liu, and Fan Wu
- Subjects
Surface (mathematics) ,Physics ,Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed matter physics ,Magnetism ,Photoemission spectroscopy ,Shell (structure) ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,02 engineering and technology ,Electronic structure ,Electron ,021001 nanoscience & nanotechnology ,01 natural sciences ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,0103 physical sciences ,010306 general physics ,0210 nano-technology ,Electronic band structure ,Surface states - Abstract
Here we report the evolution of bulk band structure and surface states in rare earth mono-bismuthides with partially filled f shell. Utilizing synchrotron-based photoemission spectroscopy, we determined the three-dimensional bulk band structure and identified the bulk band inversions near the X points, which, according to the topological theory, could give rise to nontrivial band topology with odd number of gapless topological surface states. Near the surface Gamma bar point, no clear evidence for predicted gapless topological surface state is observed due to its strong hybridization with the bulk bands. Near the M bar point, the two surface states, due to projections from two inequivalent bulk band inversions, interact and give rise to two peculiar sets of gapped surface states. The bulk band inversions and corresponding surface states can be tuned substantially by varying rare earth elements, in good agreement with density-functional theory calculations assuming local f electrons. Our study therefore establishes rare earth mono-bismuthides as an interesting class of materials possessing tunable electronic properties and magnetism, providing a promising platform to search for novel properties in potentially correlated topological materials., Comment: 7 figures
- Published
- 2018
43. Single-layer dual germanene phases on Ag(111)
- Author
-
Tai-Chang Chiang, Horng-Tay Jeng, Cheng Maw Cheng, Ryu Yukawa, Woei Wu Pai, Shu-Jung Tang, Tay-Rong Chang, Ting-Yu Chen, Angus Huang, Iwao Matsuda, Chung-Yu Mou, Wei Chuan Chen, and C.-H. Lin
- Subjects
Germanene ,Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Silicene ,Graphene ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,law.invention ,Lattice constant ,Quantum spin Hall effect ,law ,0103 physical sciences ,Stanene ,General Materials Science ,Scanning tunneling microscope ,010306 general physics ,0210 nano-technology - Abstract
Two-dimensional (2D) honeycomb lattices beyond graphene promise new physical properties such as quantum spin Hall effect. While there have been claims of growth of such lattices (silicene, germanene, stanene), their existence needs further support and their preparation and characterization remain a difficult challenge. Our findings suggest that two distinct phases associated with germanene, the analog of graphene made of germanium (Ge) instead of carbon, can be grown on Ag(111) as observed by scanning tunneling microscopy, low-energy electron diffraction, and angle-resolved photoemission spectroscopy. One such germanene exhibits an atom-resolved alternatively buckled full honeycomb lattice, which is tensile strained and partially commensurate with the substrate to form a striped phase (SP). The other, a quasifreestanding phase (QP), is also consistent with a honeycomb lattice with a lattice constant incommensurate with the substrate but very close to the theoretical value for freestanding germanene. The SP, with a lower atomic density, can be driven into the QP and coexist with the QP by additional Ge deposition. Band mapping and first-principles calculations with proposed SP and QP models reveal an interface state exists only in the SP but the characteristic \ensuremath{\sigma} band of freestanding germanene emerges only in the QP---this leads to an important conclusion that adlayer-substrate commensurability plays a key role to affect the electronic structure of germanene. The evolution of the dual germanene phases manifests the competitive formation of Ge-Ge covalent and Ge-Ag interfacial bonds.
- Published
- 2018
44. Helicity-dependent terahertz emission spectroscopy of topological insulator Sb2Te3 thin films
- Author
-
Yi Cheng Chen, Jung Chun A. Huang, Ping Huang, Chien Ming Tu, Jiunn-Yuan Lin, Takayoshi Kobayashi, Pei Yu Chuang, Cheng Maw Cheng, Jenh-Yih Juang, Ming Yu Lin, Way-Faung Pong, Kaung Hsiung Wu, and Chih-Wei Luo
- Subjects
Physics ,Condensed matter physics ,Spintronics ,Terahertz radiation ,Physics::Optics ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Helicity ,symbols.namesake ,Dirac fermion ,Topological insulator ,0103 physical sciences ,symbols ,Emission spectrum ,010306 general physics ,0210 nano-technology ,Excitation ,Surface states - Abstract
We report on helicity-dependent terahertz emissions that originate from the helicity-dependent photocurrents in topological insulator $\mathrm{S}{\mathrm{b}}_{2}\mathrm{T}{\mathrm{e}}_{3}$ thin films due to ultrafast optical excitation. The polarity of the emitted terahertz radiation is controlled by both the incident angle and the helicity of optical pulses. Using an unprecedented decomposition-recombination procedure in the time domain, the signals of the Dirac fermions are fully separated from bulk contributions. These results provide insights into the optical coupling of topological surface states and open up opportunities for applying helicity-dependent terahertz emission spectroscopy in spintronics.
- Published
- 2017
45. The Density of States and the Transport Effective Mass in a Highly Oriented Semiconducting Polymer: Electronic Delocalization in 1D
- Author
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Lei Ying, Byoung Hoon Lee, Chan Luo, Alan J. Heeger, Jessica Sherman, Ben B. Y. Hsu, Shrayesh N. Patel, Jean-Luc Brédas, Guillermo C. Bazan, Haitao Sun, Cheng Zhong, Ming Wang, Cheng Maw Cheng, and Michael L. Chabinyc
- Subjects
chemistry.chemical_classification ,Materials science ,Polymers ,business.industry ,Mechanical Engineering ,Electrons ,Polymer ,Electron ,Semiconducting polymer ,Delocalized electron ,Effective mass (solid-state physics) ,Semiconductor ,Semiconductors ,Solubility ,chemistry ,Mechanics of Materials ,Chemical physics ,Computational chemistry ,Thiadiazoles ,Density of states ,General Materials Science ,business ,Electronic band structure - Abstract
The determination of the band structure along k parallel to the chain direction demonstrates significant electronic delocalization. The small effective mass [m* = 0.106mo ] is consistent with the high measured mobility.
- Published
- 2015
46. Adsorption and desorption of thermally generated hydrogen atoms on Au(111) and Ag/Au(111)
- Author
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Chia Hsin Wang, Cheng Maw Cheng, Yaw Wen Yang, Kun Rong Li, Dah An Luh, Ren Yu Huang, Ku Ding Tsuei, and Ching Hung Chen
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Hydrogen ,Annealing (metallurgy) ,Chemistry ,Analytical chemistry ,chemistry.chemical_element ,Angle-resolved photoemission spectroscopy ,Surfaces and Interfaces ,Condensed Matter Physics ,Spectral line ,Surfaces, Coatings and Films ,Metal ,Adsorption ,visual_art ,Desorption ,Materials Chemistry ,visual_art.visual_art_medium ,Chemical composition - Abstract
To explore the possibility of employing thermally generated H atoms to determine the chemical composition of a metallic surface, we investigated the adsorption and desorption of H atoms generated with a thermal cracker on surfaces Au(111) and Ag/Au(111). Angle-resolved photoemission spectra showed that the noble-metallic surfaces deteriorated upon exposure to a flux of H atoms at ~ 100 K. Upon subsequent annealing, the order of the surfaces was mostly recovered when H atoms on the surfaces desorbed, but the recovery was incomplete even with annealing at a temperature much higher than that at which H atoms desorb. X-ray photoemission spectra showed that O-containing contaminants existed on the surfaces after the H dosing. The evolution of O 1s during annealing indicated that the O-containing contaminants were H 2 O and its moieties generated during thermal cracking; the disturbances of the surfaces remaining above the desorption temperature of H atoms were likely caused by chemisorbed O. Our results show that it is possible to employ thermally generated H atoms to determine the chemical composition of a metallic surface, but a small proportion of H 2 O in a H 2 gas line might be unavoidable; precautions against possible O contamination are required when a thermal cracker is employed.
- Published
- 2015
47. Alkali-metal induced band structure deformation investigated by angle-resolved photoemission spectroscopy and first-principles calculations
- Author
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Shu-Jung Tang, Masaki Taniguchi, Takushi Iimori, Fumio Komori, Akari Takayama, Iwao Matsuda, W. C. Chen, Hirofumi Namatame, Cheng-Maw Cheng, Suguru Ito, Takao Someya, Baojie Feng, and Masashi Arita
- Subjects
Condensed Matter - Materials Science ,Materials science ,Photoemission spectroscopy ,chemistry.chemical_element ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Angle-resolved photoemission spectroscopy ,02 engineering and technology ,Deformation (meteorology) ,021001 nanoscience & nanotechnology ,Alkali metal ,Elementary charge ,01 natural sciences ,Molecular physics ,Bismuth ,Condensed Matter::Materials Science ,Adsorption ,chemistry ,Condensed Matter::Superconductivity ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Electronic band structure - Abstract
Alkali-metal adsorption on the surface of materials is widely used for in situ surface electron doping, particularly for observing unoccupied band structures by angle-resolved photoemission spectroscopy (ARPES). However, the effects of alkali-metal atoms on the resulting band structures have yet to be fully investigated, owing to difficulties in both experiments and calculations. Here, we combine ARPES measurements on cesium-adsorbed ultrathin bismuth films with first-principles calculations of the electronic charge densities and demonstrate a simple method to evaluate alkali-metal induced band deformation. We reveal that deformation of bismuth surface bands is directly correlated with vertical charge-density profiles at each electronic state of bismuth. In contrast, a change in the quantized bulk bands is well described by a conventional rigid-band-shift picture. We discuss these two aspects of the band deformation holistically, considering spatial distributions of the electronic states and cesium-bismuth hybridization, and provide a prescription for applying alkali-metal adsorption to a wide range of materials., Comment: 8 pages, 7 figures
- Published
- 2017
- Full Text
- View/download PDF
48. Robustness of a Topologically Protected Surface State in a Sb2Te2Se Single Crystal
- Author
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Li-Wei Tu, Chao-Kuei Lee, Shih Hsun Yu, Ching-Wen Chang, Marin Gospodinov, Shih-Chang Weng, Mitch M.C. Chou, Ku Ding Tsuei, Chih-Wei Luo, Cheng Maw Cheng, Wei Chuan Chen, and Hung-Duen Yang
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Multidisciplinary ,Materials science ,Condensed matter physics ,Spintronics ,Scattering ,business.industry ,Doping ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter::Materials Science ,Semiconductor ,Topological insulator ,0103 physical sciences ,Thermoelectric effect ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,business ,Single crystal - Abstract
A topological insulator (TI) is a quantum material in a new class with attractive properties for physical and technological applications. Here we derive the electronic structure of highly crystalline Sb2Te2Se single crystals studied with angle-resolved photoemission spectra. The result of band mapping reveals that the Sb2Te2Se compound behaves as a p-type semiconductor and has an isolated Dirac cone of a topological surface state, which is highly favored for spintronic and thermoelectric devices because of the dissipation-less surface state and the decreased scattering from bulk bands. More importantly, the topological surface state and doping level in Sb2Te2Se are difficult to alter for a cleaved surface exposed to air; the robustness of the topological surface state defined in our data indicates that this Sb2Te2Se compound has a great potential for future atmospheric applications.
- Published
- 2016
49. THz Generation and Detection on Dirac Fermions in Topological Insulators
- Author
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Helmuth Berger, Ching Hung Chen, Hsueh Ju Chen, Wen Yen Tzeng, Shin An Ku, Takayoshi Kobayashi, Kaung-Hsiung Wu, Chia Ching Lee, Jenh-Yih Juang, H. J. Wang, Raman Sankar, Meng Chi Chiang, Tien Tien Yeh, Chih-Wei Luo, Jiunn-Yuan Lin, Wei Chen Chu, Cheng Maw Cheng, Fangcheng Chou, Chien Ming Tu, Ku Ding Tsuei, and Hung-Duen Yang
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Physics ,chemistry.chemical_compound ,symbols.namesake ,Condensed matter physics ,Web of science ,chemistry ,Dirac fermion ,Terahertz radiation ,Topological insulator ,symbols ,Bismuth selenide ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials - Abstract
Reference EPFL-ARTICLE-195580doi:10.1002/adom.201300221View record in Web of Science Record created on 2014-01-09, modified on 2017-05-12
- Published
- 2013
50. Helicity-dependent terahertz radiation from topological insulator Sb2Te3 thin film by femtosecond optical excitation
- Author
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Ming-Yu Lin, Chih-Wei Luo, Ping Huang, Yi Cheng Chen, Jiunn-Yuan Lin, Pei-Yu Chuang, Chien Ming Tu, Way-Faung Pong, Takayoshi Kobayashi, Cheng-Maw Cheng, and Jung-Chun Huang
- Subjects
0301 basic medicine ,Photocurrent ,Materials science ,Condensed Matter::Other ,business.industry ,Terahertz radiation ,Photoconductivity ,Physics::Optics ,Optical polarization ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Helicity ,03 medical and health sciences ,030104 developmental biology ,Topological insulator ,Femtosecond ,Optoelectronics ,Thin film ,business - Abstract
We report on terahertz radiation from topological insulator (TI) Sb 2 Te 3 thin film under ultrafast optical excitation with different helicity. Polarity-reversals of the emitted THz radiation were observed as the helicity of optical pulses reversed. The observed phenomena are coincident with the characteristics of the helicity-dependent photocurrent on TIs. Our work demonstrates the potential applications of surface photocurrents on TIs for opto-spintronics devices.
- Published
- 2016
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