10 results on '"Weimin Chen"'
Search Results
2. Dilute nitrides-based nanowires—a promising platform for nanoscale photonics and energy technology
- Author
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Irina Buyanova and Weimin Chen
- Subjects
Nanostructure ,Fabrication ,Materials science ,business.industry ,Mechanical Engineering ,Nanowire ,Nanophotonics ,Bioengineering ,Nanotechnology ,02 engineering and technology ,General Chemistry ,Nitride ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Epitaxy ,01 natural sciences ,0104 chemical sciences ,Mechanics of Materials ,General Materials Science ,Electrical and Electronic Engineering ,Photonics ,0210 nano-technology ,business ,Molecular beam epitaxy - Abstract
Dilute nitrides are novel III-V-N semiconductor alloys promising for a great variety of applications ranging from nanoscale light emitters and solar cells to energy production via photoelectrochemical reactions and to nano-spintronics. These alloys have become available in the one-dimensional geometry only most recently, thanks to the advances in the nanowire (NW) growth utilizing molecular beam epitaxy. In this review we will summarize growth approaches currently utilized for the fabrication of such novel dilute nitride-based NWs, discuss their structural, defect-related and optical properties, as well as provide several examples of their potential applications.
- Published
- 2019
3. Molecular beam epitaxial growth of dilute nitride GaNAs and GaInNAs nanowires
- Author
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Fumitaro Ishikawa, Weimin Chen, T. Mita, Irina Buyanova, Naoki Tsuda, J. Natsui, Yumiko Shimizu, Mattias Jansson, Ryo Fujiwara, Mitsuki Yukimune, and R M Balagula
- Subjects
Materials science ,Nanostructure ,Silicon ,Nanowire ,chemistry.chemical_element ,Bioengineering ,Crystal growth ,02 engineering and technology ,Nitride ,010402 general chemistry ,Epitaxy ,01 natural sciences ,Scanning transmission electron microscopy ,General Materials Science ,Electrical and Electronic Engineering ,nanowire ,GaAs ,dilute nitrides ,molecular beam epitaxy ,business.industry ,Mechanical Engineering ,General Chemistry ,Condensed Matter Physics ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,chemistry ,Mechanics of Materials ,Optoelectronics ,0210 nano-technology ,business ,Den kondenserade materiens fysik ,Molecular beam epitaxy - Abstract
We report the growth of dilute nitride GaNAs and GaInNAs core-multishell nanowires (NWs) using molecular beam epitaxy assisted by a plasma source. Using the self-catalyst vapor-liquid-solid growth mode, these NWs were grown on Si(111) and silicon on insulator substrates. The GaNAs and GaInNAs shells contain nitrogen up to 3%. Axial cross-sectional scanning transmission electron microscopy measurements and energy-dispersive x-ray spectrometry confirm the formation of the core-multishell NW structure. We obtained high-quality GaNAs NWs with nitrogen compositions up to 2%. On the other hand, GaNAs containing 3% nitrogen, and GaInNAs NWs, show distorted structures; moreover, the optical emissions seem to be related to defects. Further optimisations of the growth conditions will improve these properties, promising future applications in nanoscale optoelectronics. Funding Agencies|KAKENHI by the Japan Society for the Promotion of Science [16H05970]; Swedish Energy Agency [P40119-1]
- Published
- 2019
4. Three-dimensional SnO2/carbon on Cu foam for high-performance lithium ion battery anodes
- Author
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Wenyong Wang, Weimin Chen, and Scott Maloney
- Subjects
Materials science ,Mechanical Engineering ,chemistry.chemical_element ,Bioengineering ,Nanotechnology ,02 engineering and technology ,General Chemistry ,Chemical vapor deposition ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrochemistry ,01 natural sciences ,Lithium-ion battery ,0104 chemical sciences ,Anode ,chemistry ,Chemical engineering ,Mechanics of Materials ,Electrode ,General Materials Science ,Electrical and Electronic Engineering ,0210 nano-technology ,Porosity ,Carbon ,Current density - Abstract
SnO2 is an attractive anode material for lithium-ion batteries (LIBs) due to its high theoretical specific capacity (1491 mAh g(-1)), low cost, and environmental benignity. The main challenges for SnO2 anodes are their low intrinsic conductivity and poor cycling stability associated with their large volume changes during the charge and discharge process. Here, we present a simple chemical vapor deposition method to fabricate three-dimensional SnO2/carbon on Cu foam electrodes for LIBs. Such a three-dimensional electrode combines multiple advantages, including a continuous electrically conductive network, short pathways for electron transport and ion diffusion, and porous space to allow for the volume expansion of SnO2 nanoparticles. With this anode, superior electrochemical performance is achieved with a high reversible specific capacity of 1171 mAh g(-1) at a current density of 100 mA g(-1). A stable cycling performance as well as an excellent rate capability is also achieved. These outstanding lithium-storage properties suggest the strategy is a reliable approach for fabricating high-performance LIB electrodes.
- Published
- 2016
5. Passivation effects on quantum dots prepared by successive ionic layer adsorption and reaction
- Author
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Wenyong Wang, Qilin Dai, Uma Poudyal, Scott Maloney, and Weimin Chen
- Subjects
Materials science ,Passivation ,Ionic bonding ,Bioengineering ,Nanotechnology ,02 engineering and technology ,engineering.material ,010402 general chemistry ,01 natural sciences ,law.invention ,Colloid ,chemistry.chemical_compound ,Adsorption ,Coating ,law ,Oleylamine ,Solar cell ,General Materials Science ,Electrical and Electronic Engineering ,Mechanical Engineering ,technology, industry, and agriculture ,General Chemistry ,equipment and supplies ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,chemistry ,Chemical engineering ,Mechanics of Materials ,Quantum dot ,engineering ,0210 nano-technology - Abstract
ZnS is typically used to passivate semiconductor quantum dots (QDs) prepared by the successive ionic layer adsorption and reaction (SILAR) method for solar cell applications, while for colloidal QDs, organic ligands are usually used for this passivation purpose. In this study we utilized oleylamine and oleic acid ligands, besides ZnS, to passivate QDs prepared by the SILAR approach, and investigated their effects on the incident photon-to-current efficiency (IPCE) performance of the solar cells. It was observed that oleylamine passivation decreased device performance, while oleic acid passivation improved the IPCE of the cells. Redshift of the IPCE onset wavelength was also observed after oleic acid coating, which was attributed to the delocalization of excitons in the CdS QDs.
- Published
- 2016
6. Ultrafast growth of large-area monolayer MoS2film via gold foil assistant CVD for a highly sensitive photodetector
- Author
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Yu Leyong, Xingzhan Wei, Haofei Shi, Changbin Nie, Weimin Chen, Jun Shen, Shuanglong Feng, and Wenqiang Lu
- Subjects
Materials science ,Silicon dioxide ,Band gap ,Mechanical Engineering ,Bioengineering ,Nanotechnology ,02 engineering and technology ,General Chemistry ,Substrate (electronics) ,Chemical vapor deposition ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,Thermal conductivity ,chemistry ,Mechanics of Materials ,Monolayer ,General Materials Science ,Electrical and Electronic Engineering ,0210 nano-technology ,Molybdenum disulfide ,FOIL method - Abstract
Two-dimensional molybdenum disulfide (MoS2) is a promising material for ultrasensitive photodetectors owing to its tunable band gap and high absorption coefficient. However, controlled synthesis of high-quality, large-area monolayer molybdenum disulfide (MoS2) is still a challenge in practical application. In this work, we report a gold foil assistant chemical vapor deposition method for the synthesis of large-size (>400 μm) single-crystal MoS2 film on a silicon dioxide (SiO2) substrate. The influence of Au foil in enlarging the size of single-crystal MoS2 is investigated systemically using thermal simulation in Ansys workbench 16.0, including thermal conductivity, temperature difference and thermal relaxation time of the interface of SiO2 substrate and Au foil, which indicate that Au foil can increase the temperature of the SiO2 substrate rapidly and decrease the temperature difference between the oven and substrate. Finally, the properties of the monolayer MoS2 film are further confirmed using back-gated field-effect transistors: a high photoresponse of 15.6 A W−1 and a fast photoresponse time of 100 ms. The growth techniques described in this study could be beneficial for the development of other atomically thin two-dimensional transition metal dichalcogenide materials.
- Published
- 2017
7. Defect properties of ZnO nanowires revealed from an optically detected magnetic resonance study
- Author
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N. Koteeswara Reddy, Charles W. Tu, Weimin Chen, Stanislav Filippov, Jan Eric Stehr, Irina Buyanova, Shula Chen, and M. Devika
- Subjects
Photoluminescence ,Materials science ,Magnetic Resonance Spectroscopy ,Thermal chemical vapor deposition ,Optical Phenomena ,Nanowires ,Mechanical Engineering ,Analytical chemistry ,Zno nanowires ,Bioengineering ,General Chemistry ,Conductivity ,Nuclear magnetic resonance ,Effective mass (solid-state physics) ,Mechanics of Materials ,Magnetic resonance study ,General Materials Science ,Electrical and Electronic Engineering ,Zinc Oxide - Abstract
Optically detected magnetic resonance (ODMR) complemented by photoluminescence measurements is used to evaluate optical and defect properties of ZnO nanowires (NWs) grown by rapid thermal chemical vapor deposition. By monitoring visible emissions, several grown-in defects are revealed and attributed to Zn vacancies, shallow (but not effective mass) donor and exchange-coupled pairs of Zn vacancies and Zn interstitials. It is also found that the intensity of the donor-related ODMR signals is substantially lower in the NWs compared with that in bulk ZnO. This may indicate that formation of native donors is suppressed in NWs, which is beneficial for achieving p-type conductivity.
- Published
- 2012
8. Spin injection in lateral InAs quantum dot structures by optical orientation spectroscopy
- Author
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S Suraprapapich, Weimin Chen, Irina Buyanova, Charles W. Tu, and Jan Beyer
- Subjects
Materials science ,Exciton ,Bioengineering ,Electron ,Microscopy, Atomic Force ,Indium ,Arsenicals ,Condensed Matter::Materials Science ,Quantum Dots ,Nanotechnology ,General Materials Science ,Electrical and Electronic Engineering ,Photoluminescence ,Spin-½ ,Condensed matter physics ,Spins ,Quantum dots ,Mechanical Engineering ,Spectrum Analysis ,Exchange interaction ,Relaxation (NMR) ,General Chemistry ,Condensed Matter Physics ,Mechanics of Materials ,Quantum dot ,Quantum dot laser ,Condensed Matter::Strongly Correlated Electrons ,Den kondenserade materiens fysik - Abstract
Optical spin injection is studied in novel laterally-arranged self-assembled InAs/GaAs quantum dot structures, by using optical orientation measurements in combination with tunable laser spectroscopy. It is shown that spins of uncorrelated free carriers are better conserved during the spin injection than the spins of correlated electrons and holes in an exciton. This is attributed to efficient spin relaxation promoted by the electron–hole exchange interaction of the excitons. Our finding suggests that separate carrier injection, such as that employed in electrical spin injection devices, can be advantageous for spin conserving injection. It is also found that the spin injection efficiency decreases for free carriers with high momentum, due to the acceleration of spin relaxation processes. Original Publication:Jan Beyer, Irina A Buyanova, Suwaree Suraprapapich, Charles Tu and Weimin Chen, Spin injection in lateral InAs quantum dot structures by optical orientation spectroscopy, 2009, Nanotechnology, (20), 37, 375401.http://dx.doi.org/10.1088/0957-4484/20/37/375401Copyright: Institute of Physicshttp://www.iop.org/
- Published
- 2009
9. The Hanle effect and electron spin polarization in InAs/GaAs quantum dots up to room temperature
- Author
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S Suraprapapich, Jan Beyer, Charles W. Tu, Irina Buyanova, and Weimin Chen
- Subjects
Hanle effect ,Materials science ,Spin polarization ,Condensed matter physics ,Mechanical Engineering ,Bioengineering ,General Chemistry ,Electron ,Atmospheric temperature range ,Condensed Matter Physics ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Mechanics of Materials ,Quantum dot ,Naturvetenskap ,General Materials Science ,Spin-flip ,Electrical and Electronic Engineering ,Natural Sciences ,Spin (physics) ,Den kondenserade materiens fysik ,Wetting layer - Abstract
Hanle effect in InAs/GaAs quantum dots (QDs) is studied under optical orientation as a function of temperature over the range of 150-300 K, with the aim to understand the physical mechanism responsible for the observed sharp increase of electron spin polarization with increasing temperature. The deduced spin lifetime Ts of positive trions in the QDs is found to be independent of temperature, and is also insensitive to excitation energy and density. It is argued that the measured Ts is mainly determined by the longitudinal spin flip time (T1) and the spin dephasing time (T2 *) of the studied QD ensemble, of which both are temperatureindependent over the studied temperature range and the latter makes a larger contribution. The observed sharply rising of the QD spin polarization degree with increasing temperature, on the other hand, is shown to be induced by an increase in spin injection efficiency from the barrier/wetting layer and also by a moderate increase in spin detection efficiency of the QD. funding agencies|Swedish Research Council| 621-2011-4254
- Published
- 2012
10. Three-dimensional SnO2/carbon on Cu foam for high-performance lithium ion battery anodes.
- Author
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Weimin Chen, Scott Maloney, and Wenyong Wang
- Subjects
- *
ELECTRICAL properties of tin oxides , *LITHIUM-ion batteries , *ELECTRIC conductivity , *CHEMICAL vapor deposition , *ELECTRON transport - Abstract
SnO2 is an attractive anode material for lithium-ion batteries (LIBs) due to its high theoretical specific capacity (1491 mAh g−1), low cost, and environmental benignity. The main challenges for SnO2 anodes are their low intrinsic conductivity and poor cycling stability associated with their large volume changes during the charge and discharge process. Here, we present a simple chemical vapor deposition method to fabricate three-dimensional SnO2/carbon on Cu foam electrodes for LIBs. Such a three-dimensional electrode combines multiple advantages, including a continuous electrically conductive network, short pathways for electron transport and ion diffusion, and porous space to allow for the volume expansion of SnO2 nanoparticles. With this anode, superior electrochemical performance is achieved with a high reversible specific capacity of 1171 mAh g−1 at a current density of 100 mA g−1. A stable cycling performance as well as an excellent rate capability is also achieved. These outstanding lithium-storage properties suggest the strategy is a reliable approach for fabricating high-performance LIB electrodes. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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