Browsing by Author "Wu, Chih-Yu"

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Direct Formation of Wafer Scale Graphene Thin Layers on Insulating Substrates by Chemical Vapor Deposition
(2011-09-01)
Su, Ching-Yuan
;
Lu, Ang-Yu
;
Wu, Chih-Yu
;
Li, Yi-Te
;
Liu, Keng-Ku
Direct formation of high-quality and wafer scale graphene thin layers on insulating gate dielectrics such as SiO(2) is emergent for graphene electronics using Si-wafer compatible fabrication. Here, we report that in a chemical vapor deposition process the carbon species dissociated on Cu surfaces not only result in graphene layers on top of the catalytic Cu thin films but also diffuse through Cu grain boundaries to the interface between Cu and underlying dielectrics. Optimization of the process parameters leads to a continuous and large-area graphene thin layers directly formed on top of the dielectrics. The bottom-gated transistor characteristics for the graphene films have shown quite comparable carrier mobility compared to the top-layer graphene. The proposed method allows us to achieve wafer-sized graphene on versatile insulating substrates without the need of graphene transfer.
Efficient reduction of graphene oxide catalyzed by copper
(2012)
Lin, Yu-Chuan
;
Liu, Keng-Ku
;
Wu, Chih-Yu
;
Chu, Chih-Wei
;
Wang, Jacob Tse-Wei
We report that copper thin films deposited on top of graphene oxide (GO) serve as an effective catalyst to reduce GO sheets in a diluted hydrogen environment at high temperature. The reduced GO (rGO) sheets exhibit higher effective field-effect hole mobility, up to 80 cm(2) V-1 s(-1), and lower sheet resistance (13 k Omega square(-1)) compared with those reduced by reported methods such as hydrazine and thermal annealing. Raman and XPS characterizations are addressed to study the reduction mechanism on graphene oxide underneath copper thin films. The level of reduction in rGO sheets is examined by Raman spectroscopy and it is well correlated with hole mobility values. The conductivity enhancement is attributed to the growth of the graphitic domain size. This method is not only suitable for reduction of single GO sheets but also applicable to lower the sheet resistance of Langmuir-Blodgett assembled GO films.
Growth selectivity of hexagonal-boron nitride layers on Ni with various crystal orientations
(2012)
Lee, Yi-Hsien
;
Liu, Keng-Ku
;
Lu, Ang-Yu
;
Wu, Chih-Yu
;
Lin, Cheng-Te
Layered hexagonal-boron nitride (h-BN) films were synthesized by chemical vapor deposition (CVD) on Ni foils using ammonia borane as a precursor. Confocal Raman spectroscopy and electron backscatter diffraction (EBSD) were used to probe the effect of underlying Ni crystals with various orientations on growth behaviors of h-BN layers. The growth of the h-BN layers strongly depends on the Ni crystal orientations, where the growth rate of h-BN is larger on Ni(100)-like crystal surfaces but the growth on Ni(111)-like surfaces is not detectable, suggesting that Ni (100)-like facets are likely to promote the growth of h-BN compared with Ni (111)-like surfaces. The observation is in clear contrast to the reported growth of h-BN on Ni(111) in an ultrahigh vacuum environment. The as-grown CVD h-BN films on Ni exhibit a layered structure as revealed by atomic force microscopy (AFM). Thin h-BN layers are found on the Ni domain with a low growth rate. The observation of h-BN growth on various Ni grains may provide insights for the control of thickness, size and morphology of CVD h-BN films.
Multifunctional nanoparticles with controllable dimensions and tripled orthogonal reactivity
(2017-10-21)
Wu, Chih-Yu
;
Chang, Chun-Wei
;
Yuan, Ruei-Hung
;
Chiang, Yu-Chih
;
Chen, Jiun-Tai
Multifunctional nanoparticles featuring three distinct and orthogonal functionalities for performing catalyst-free click reactions of azide-alkyne and maleimide-thiol and atom transfer radical polymerization (ATRP) are fabricated using a simple chemical vapor deposition copolymerization approach with the flexibility to control the particle size and geometry.
Simple bridge-type AC/DC converters with natural input-current-shaper
(2006)
Liu, Hsing-Fu
;
Wu, Chih-Yu
;
Sun, Chin
;
Chang, Lon-Kou
;
電控工程研究所
This paper presents a new design for bridge-type AC/DC converters with natural input current shaper. They have a fast output voltage regulation in full range input (85V similar to 265V/AC). An additional winding in main transformer can naturally modify a line current. Further, the additional winding reduces an input inductance, so the weight and size of magnetic material are significantly reduced. The total harmonic distortion (THD) of the line current complies with IEC61000-3-2 class D. Furthermore, the proposed converters use current sensorless control and they can employ a conventional voltage-fed controller to simply the control circuit.