Browsing by Author "Yu, Shih-Ying"

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Cobalt silicide nanocables grown on Co films: synthesis and physical properties
(2010-12-03)
Hsin, Cheng-Lun
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Yu, Shih-Ying
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Wu, Wen-Wei
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材料科學與工程學系
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Department of Materials Science and Engineering
Single-crystalline cobalt silicide/SiO(x) nanocables have been grown on Co thin films on an SiO(2) layer by a self-catalysis process via vapor-liquid-solid mechanism. The nanocables consist of a core of CoSi nanowires and a silicon oxide shell with a length of several tens of micrometers. In the confined space in the oxide shell, the CoSi phase is stable and free from agglomeration in samples annealed in air ambient at 900 degrees C for 1 h. The nanocable structure came to a clear conclusion that the thermal stability of the silicide nanowires can be resolved by the shell encapsulation. Cobalt silicide nanowires were obtained from the nanocable structure. The electrical properties of the CoSi nanowires have been found to be compatible with their thin film counterpart and a high maximum current density of the nanowires has been measured. One way to obtain silicate nanowires has been demonstrated. The silicate compound, which is composed of cobalt, silicon and oxygen, was achieved. The Co silicide/oxide nanocables are potentially useful as a key component of silicate nanowires, interconnects and magnetic units in nanoelectronics.
Growth and properties of single-crystalline Ge nanowires and germanide/Ge nano-heterostructures
(2012)
Tsai, Cheng-Yu
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Yu, Shih-Ying
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Hsin, Cheng-Lun
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Huang, Chun-Wei
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Wang, Chun-Wen
Single-crystalline Ge nanowires have been synthesized on Au-coated Si substrates through a thermal evaporation, condensation method and vapor-liquid-solidmechanism. The [111] growth direction of the Ge nanowires was analyzed using HRTEM and fast Fourier transform diffraction patterns. Global back-gated Ge nanowire field-effect transistors (FETs) on the Si3N4 dielectrics were fabricated and studied, showing p-type behavior and a field effect hole mobility of 44.3 cm(2) V-1 s(-1). The Ge channel length could be well controlled through the annealing process. After a rapid thermal annealing (RTA) process, Ni2Ge/Ge/Ni2Ge nano-heterostructures were formed. The electrical transport properties were effectively improved by the heterojunction rather than the metal contact. The epitaxial relationship between Ge and orthorhombic Ni2Ge was Ge [110]//Ni2Ge[110] and Ge(-11-1)//Ni2Ge(1-1-2). From electrical transport properties, the measured resistivity of the Ge nanowires was much lower than intrinsic bulk Ge material. A room temperature photoluminescence spectrum of the Ge nanowires possessed a broad blue emission with a peak at 462 nm in wavelength, which was attributed to the oxide-related defect states. Due to the existence of the defects, a Ge nanowire FET was able to detect visible light and serve as a nanowire photodetector.
Growth of single-crystalline cobalt silicide nanowires with excellent physical properties
(2011-10-01)
Liang, Yu-Hsin
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Yu, Shih-Ying
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Hsin, Cheng-Lun
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Huang, Chun-Wei
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Wu, Wen-Wei
With the miniaturization of electron devices, the minuscule structures are important to state-of-the-art science and technology. Therefore, the growth methods and properties of nanomaterials have been extensively studied recently. Here, we use chemical vapor transport (CVT) methods to synthesize single-crystalline cobalt silicide nanowires (NWs) by using (CoCl(2)center dot 6H(2)O) as a single-source precursor. By changing reaction temperature and ambient pressure, we can obtain different morphology of cobalt silicide NWs under the appropriate concentration of silicon and cobalt. The field emission measurement of CoSi NWs shows low turn-on field (5.02 V/mu m) and it is outstanding for magnetic properties that differ from the bulk CoSi. The CoSi nanowires with different diameters have diversemagnetic saturation (Ms) and coercive force (Hc). (C) 2011 American Institute of Physics. [doi:10.1063/1.3643007]
High-yield synthesis of ZnO nanowire arrays and their opto-electrical properties
(2012)
Kao, Chen-Yen
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Hsin, Cheng-Lun
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Huang, Chun-Wei
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Yu, Shih-Ying
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Wang, Chun-Wen
In this article, ZnO nanostructures were synthesized via the hydrothermal method which used ZnCl2 and HMTA mixed solution as the precursor. A multistep growth was adopted to improve the growth restriction of a closed system, not only the length but also the aspect ratio were increased with steps of growth, and the shape of nanorods maintained integrity. Furthermore, photoluminescence spectra which have the near-band-edge-emission (similar to 3.37 eV) and defect-related emission show the optical properties of ZnO nanostructures. The defect-related emission intensity was greatly enhanced with the increasing surface area of ZnO nanowires. The level of the OH group was attributed to the yellow-light emission (similar to 580 nm) and the red-shift phenomenon. In addition, we fabricated two types of ultraviolet photodetectors: a single nanowire device and a nanowire-array device, operating at a low bias (less than 5 mV). With the lower energy consumption and the weaker persistent photoconductive effect, our ultraviolet photodetectors have better performance, exhibiting a short response time and higher sensitivity.
In Situ TEM and Energy Dispersion Spectrometer Analysis of Chemical Composition Change in ZnO Nanowire Resistive Memories
(2013-04-16)
Huang, Yu-Ting
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Yu, Shih-Ying
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Hsin, Cheng-Lun
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Huang, Chun-Wei
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Kang, Chen-Fang
Resistive random-access memory (ReRAM) has been of wide interest for its potential to replace flash memory in the next-generation nonvolatile memory roadmap. In this study, we have fabricated the Au/ZnO-nanowire/Au nanomemory device by electron beam lithography and, subsequently, utilized in situ transmission electron microscopy (TEM) to observe the atomic structure evolution from the initial state to the low-resistance state (LRS) in the ZnO nanowire. The element mapping of LRS showing that the nanowire was zinc dominant indicating that the oxygen vacancies were introduced after resistance switching. The results provided direct evidence, suggesting that the resistance change resulted from oxygen migration.
Single-crystalline Ge nanowires and Cu3Ge/Ge nano-heterostructures
(2012)
Hsu, Shan-Chun
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Hsin, Cheng-Lun
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Huang, Chun-Wei
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Yu, Shih-Ying
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Wang, Chun-Wen
Single-crystalline germanium nanowires were synthesized via vapor-liquid-solid mechanism. The characteristics of the Ge nanowires were investigated by a transmission electron microscope to identify the [111] growth direction. The Ge nanowire-based field-effect-transistors on Si3N4 dielectrics were fabricated, showing a p-type semiconducting behavior with hole mobility of 47.03 cm(2) V-1 s(-1). The formation of Cu3Ge/Ge/Cu3Ge nanoheterostructures was demonstrated with the reaction between copper contacts and Ge nanowires by rapid thermal annealing. The diameter-dependent electrical transport property of Ge nanowires indicates that with diameters of more than 80 nm, the resistivity of Ge nanowires decreased with diameter decrease, while with diameters of less than 80 nm, it increased. With multiple annealing processes, the channel length of the Ge nanowire transistors can be successfully controlled. From electrical measurements of each annealing step, the electrical transport property was significantly improved by sequential formation of Cu3Ge contacts. The gradual formation of the germanide structure reduces Fermi level pinning effect and increases the Ohmic behavior of electrical transportation.
Well-aligned ZnO nanowires with excellent field emission and photocatalytic properties
(2012)
Chu, Fu-Hsuan
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Huang, Chun-Wei
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Hsin, Cheng-Lun
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Wang, Chun-Wen
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Yu, Shih-Ying
Well-aligned ZnO nanowires (NWs) were successfully synthesized on Si(100) by the process of carbothermal reduction and vapor-liquid-solid method. Scanning electron microscopy and transmission electron microscopy results confirmed that ZnO NWs were single crystalline wurtzite structures and grew along the [0001] direction. The influences of substrate temperature and total pressure on the growth were discussed. The well-aligned ZnO NWs show good field emission properties, and the emitter constructed of pencil-like ZnO NWs exhibited a low turn-on field (3.82 V mu m(-1)) and a high field enhancement factor (beta 2303). Finally, we demonstrated that the as-prepared ZnO NWs with small diameter on the substrate have good photocatalytic activity toward degradation of methylene blue. Using ZnO NWs with Au nanoparticles (NPs) would decrease the recombination rate of hole-electron pairs due to the great shift of the Fermi level to the conduction band. Hence, adding Au NPs was a promising method to enhance the photocatalytic performance of ZnO NWs. It is significant that photocatalyst fabricated by ZnO NWs can apply to the degradation of organic pollution, and solve the environmental issues.