8 results on '"Cheng-Maw Cheng"'
Search Results
2. 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
3. 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
4. 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
5. 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
6. 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
7. 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
8. 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
- Subjects
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
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