Browsing by Author "Tsao, Che-Wei"

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Dielectric property determination of hybrid Al2O3-filled MWCNT buckypaper by the rectangular cavity perturbation technique
(2015-04-01)
Miao, Hsin-Yuan
;
Liu, Jih-Hsin
;
Saravanan, L.
;
Tsao, Che-Wei
;
Pan, Jui-Wen
This study investigated the complex dielectric permittivity of freestanding multiwalled carbon nanotube buckypaper (MWCNT-BP) and a synthesized hybrid alumina-filled buckypaper (Al2O3-BP) composite with different alumina loadings (5-30 wt%). The non-destructive microwave transmission technique for complex permittivity determination involving cavity perturbation was employed to characterize a set of Al2O3-BP sheets. This was done by filling a rectangular cavity resonator with a standard dielectric Teflon sample and then performing permittivity measurements for the buckypaper (BP) samples in the X-band frequency range (7-12 GHz). Field-emission scanning electron microscopy (FESEM) was used to analyze the morphology of the MWCNT-BP and the alumina-loaded BP composites. DC electrical resistivity measurements clearly demonstrated conductor-insulator transition. The effect of alumina loadings on the dielectric properties of the synthesized hybrid Al2O3-BP sheet is discussed.
Efficiency evaluation of a hybrid miniaturized concentrated photovoltaic for harvesting direct/diffused solar light
(2019-03-01)
Tsao, Wei-Chen
;
Zeng, Qiu-Chun
;
Yeh, Yu-Hsiang
;
Tsai, Chih-Hung
;
Hong, Hwen-Fen
In this paper, a miniaturized concentrator photovoltaic (CPV) system is experimentally demonstrated based on a hot embossing silicone lens array with a size of 2 cm x 2 cm. Owing to the small size of the lens array, the total track of the CPV system can be as small as 4 cm. Consequently, the weight of the CPV system can be much lower than conventional bulky CPV system. For harvesting the diffuse solar radiation, perovskite solar cells are mounted adjacent to a multi junction solar cell. Theoretically, the short-circuit current of the CPV system can be enhanced from 48.1 to 85.5 mA for gamma = 0.7. The enhancement can be much higher for off-normal incident light. This kind of hybrid CPV system will be useful for cloudy weather and also useful for compensating the loss caused by the miss-alignment of the tracking module.
High quality factor nonpolar GaN photonic crystal nanocavities
(2013-05-13)
Wu, Tzeng-Tsong
;
Lo, Sheng-Yun
;
Huang, Huei-Min
;
Tsao, Che-Wei
;
Lu, Tien-Chang
High quality factor a-plane nonpolar GaN two-dimensional photonic crystal (PC) nanocavities on r-plane sapphire substrates have been demonstrated. Nonpolar GaN PC nanocavities on a thin membrane structure were realized by using e-beam lithography to define the PC patterns and focused-ion beam milling to fabricate the suspended thin membrane. A dominant resonant mode at 388 nm with a high quality factor of approximately 4300 has been demonstrated at 77K by the micro-photoluminescence system. Moreover, the degree of polarization of the emission from the non-polar GaN PC nanocavity was measured to be 64% along the m crystalline direction. (C) 2013 AIP Publishing LLC.
Light emission characteristics of nonpolar a-plane GaN-based photonic crystal defect cavities
(2015-01-01)
Kao, Tsung Sheng
;
Wu, Tzeng-Tsong
;
Tsao, Che-Wei
;
Lin, Jyun-Hao
;
Lin, Da-Wei
In this paper, nonpolar a-plane GaN-based photonic crystals (PCs) with different defect cavities have been demonstrated. By using a micro-photoluminescence (mu-PL) system operated at 77 K, the dominant resonant modes of the GaN-based PC defect cavities show high quality factor (Q) values in the light emission performance which can be up to 4.3x10(3). Moreover, the degree of polarization (DOP) of the light emission from the nonpolar GaN-based PC defect cavities was measured to achieve around 64 % along the m crystalline direction.
Light Emission Characteristics of Nonpolar a-Plane GaN-Based Photonic Crystal Defect Cavities
(2016-09)
Kao, Tsung Sheng
;
Wu, Tzeng-Tsong
;
Tsao, Che-Wei
;
Lin, Jyun-Hao
;
Lin, Da-Wei
In this paper, the light emission performance from nonpolar a-plane gallium nitride (GaN)-based photonic crystal (PC) slabs with line-type defect cavities has been investigated. Via the focused ion beam milling technique, thin membrane structures of the nonpolar GaN PC defect cavities were engineered, exhibiting one dominated resonant mode occurred at 419.3 nm with a high quality factor of 1.9 x 10(3) in the photoluminescence emission characterizations. In the far-field region, light emission performance shows a high polarization degree of 50% with the beam direction perpendicular to the defect cavity. Compared with the PC defect cavity patterns fabricated on c-axial oriented GaN materials, the a-plane PC defect cavities display not only the linear light output-input power dependence, but also an invariant resonant mode of constant light emission behavior with increasing the injection carriers, therefore providing a new perspective for the future development of promising optoelectronic devices.
Microwave Absorption Properties of Silver Doped MWCNT Buckypaper
(2013)
Tsao, Che-Wei
;
Saravanan, L.
;
Liu, Jih-Hsin
;
Miao, Hsin-Yuan
;
Wang, Li-Chih
Microwave absorbing property of composites containing Ag nanoparticles filled multiwalled carbon nanotube buckypaper (Ag-BP) has been investigated. Buckypaper doped with silver was prepared by direct dispersion and filtration method. From the low temperature resistivity measurement it was found that increasing doping level decreases the electrical conductivity of the buckypaper. 30 wt. % and 40 wt. % of Ag-BP samples shows the maximum transmission coefficient, with very high conductivity. The results demonstrate that microwave absorption of Ag-BP was attributed only due to the dielectric loss rather than other losses. The absorption peak frequency of the Ag/MWCNTs-BP can be controlled easily in the presence of Ag nanoparticles into the CNT mats.
NONPOLAR GAN TWO DIMENSIONAL PHOTONIC CRYSTAL H2 HIGH QUALITY FACTOR NANOCAVITIES
(2013-01-01)
Lu, Tien-Chang
;
Wu, Tzeng-Tsong
;
Lo, Sheng-Yun
;
Tsao, Che-Wei
;
Huang, Huei-Min
Nonpolar GaN two-dimensional photonic crystal (PC) H2 nanocavities have been realized and investigated. One dominated resonant mode was demonstrated at 388 nm with quality factor of approximately 4300 at 77K. Moreover, the degree of polarization of the emission from the non-polar GaN PC nanocavity was measured to be 64% along the m crystalline direction.