Browsing by Author "Tzeng, Yu-Fen"

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Carbon nanobeads as an anode material on high rate capability lithium ion batteries
(2009-11-30)
Chang, Jian-Chia
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Tzeng, Yu-Fen
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Chen, Jin-Ming
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Chiu, Hsin-Tien
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Lee, Chi-Young
Carbon nanobeads (CNBs) were prepared by reacting cyclohexachlorobenzene with dispersed sodium metal at 200 degrees C for 4 h. The CNBs prepared in this manner formed uniform nanobeads, with sizes ranging from 100 to 300 nm. Heating resulted in a reduction in the size of the CNBs, and improvements in their degree of crystallinity. The nanosized carbon materials considerably increased the surface area of the powder, reducing the distance of the intercalation/deintercalation pathway, substantially improving the charge capacity of the lithium ion battery at a high charging rate. The charge capacity of CNBs was found to be 238 mAh g(-1), while that of commercial MCMB reached only 36 mAh g(-1), when the charging rate was 1C (372 mAh g(-1)). As the charging rate was further increased to 2C (744 mAh g(-1)) and 3C (1116 mAh g(-1)), the charge capacities of CNBs dropped to 173 and 111 mAh g(-1), respectively. The cyclic performance of the CNBs was measured and found to be significantly improved in comparison to other carbonaceous materials, for up to 100 cycles. Although cyclic performance did result in a gradual reduction in capacity, the CNBs still greatly exceeded the capacity of MCMB. These results clearly demonstrate the potential role of CNBs as anodes for high capacity Li ion batteries for use in the automobile industry. (C) 2009 Elsevier Ltd. All rights reserved.
Electron field emission properties on ultra-nano-crystalline diamond coated silicon nanowires
(2008-07-01)
Tzeng, Yu-Fen
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Lee, Chi-Young
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Chiu, Hsin-Tien
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Tai, Nyan-Hwa
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Lin, I-Nan
Ultra-nano-crystal line diamond (UNCD) nano-emitters were prepared by coating UNCD films on the tip of silicon nanowire (SiNW) templates by microwave plasma-enhanced chemical vapor deposition process. The electron field emission properties of the UNCD/SiNW nano-emitters varied markedly with the pre-seeding process for the SiNW-templates. The direct ultrasonication process is more efficient in the formation of the diamond nuclei than the carburization/ultrasonication process, yielding UNCD/SiNWs nano-emitters with better electron field emission properties. The electron field emission can be turned on at (E(0))(UNCD/SiNW4)= 3.75 V/mu m, yielding a large electron field emission current density of (Je)(UNCD/SiNW4)= 11.22 mA/cm(2) at an applied field of 9.75 V/mu m. These characteristics are significantly better than those of bare SiNWs or planar UNCD films. (C) 2008 Elsevier B.V. All rights reserved.
Electron field emission properties on UNCD coated Si-nanowires
(2008-04-01)
Tzeng, Yu-Fen
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Lee, Yen-Chih
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Lee, Chi-Young
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Chiu, Hsin-Tien
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Lin, I-Nan
The electron field emission (EFE) properties of Si-nanowires (SiNW) were improved by coating a UNCD films on the SiNWs. The SiNWs were synthesized by an electroless metal deposition (EMD) process, whereas the UNCD films were deposited directly on bare SiNW templates using Ar-plasma based microwave plasma enhanced chemical vapor deposition (MPE-CVD) process. The electron field emission properties of thus made nano-emitters increase with MPE-CVD time interval for coating the UNCD films, attaining small turn-on field (E(0)=6.4 V/mu m) and large emission current density (J(e)=6.0 mA/cm(2) at 12.6 V/mu m). This is presumably owing to the higher UNCD granulation density and better UNCD-to-Si electrical contact on SiNWs. The electron field emission behavior of these UNCD nanowires emitters is significantly better than the bare SiNW ((E(0))(SiNWs)=8.6 V/mu m and (J(e))(SiNWs)<0.01 mA/cm(2) at the same applied field) and is comparable to those for carbon nanotubes. (C) 2008 Elsevier B.V. All rights reserved.
Fabrication of an ultra-nanocrystalline diamond-coated silicon wire array with enhanced field-emission performance
(2007-10-31)
Tzeng, Yu-Fen
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Liu, Kao-Hsiang
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Lee, Yen-Chih
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Lin, Sue-Jian
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Lin, I-Nan
Large- area ultra- nanocrystalline diamond- coated silicon nanowire ( UNCD/ SiNW) field- emitter arrays were prepared by the deposition of ultra- nanocrystalline diamond ( UNCD) on the tips of arrays of silicon nanowires ( SiNWs) with uniform diameters. The electron field- emission ( EFE) behavior of UNCD/ SiNW arrays as well as that of the SiNW arrays has been observed. The SiNWs exhibit good electron field- emission properties with turn- on fields ( E0) of about 7.6 V mu m- 1, which is superior to the EFE properties of planar- silicon materials. The turn- on fields are related to the diameter of the SiNWs. Coating the SiNWs with a UNCD film further improves their EFE properties. The threshold field for attaining J(e) = 0.1 mAcm(-2) EFE current density is 16.0 V mu m(-1) for bare SiNWs and 10.2 V mu m(-1) for UNCD/ SiNWs. The improvement in EFE properties due to the UNCD coating is presumably due to the lower work function of field emission of the UNCD materials, compared to that of the silicon materials.
On the enhancement of field emission performance of ultrananocrystalline diamond coated nanoemitters
(2007-08-06)
Tzeng, Yu-Fen
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Lee, Yen-Chih
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Lee, Chi-Young
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Lin, I.-Nan
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Chiu, Hsin-Tien
Ultrananocrystalline diamond (UNCD) nanoemitters were synthesized by a microwave plasma enhanced chemical vapor deposition process using silicon nanowires (SiNWs) as the template. Preseeding markedly enhances the nucleation of diamond on the SiNW templates, resulting in UNCD grains of smaller size and uniform distribution, which leads to significantly improved electron field emission (EFE) properties. The EFE for UNCD nanoemitters can be turned on at (E(0))(UNCD-NE)=4.4 V/mu m, achieving large EFE current density, (J(e))(UNCD-NE)=13.9 mA/cm(2) at an applied field of 12 V/mu m, which is comparable with that of carbon nanotubes, but with much better processing reliability. (c) 2007 American Institute of Physics.
Stacked Silicon Nanowires with Improved Field Enhancement Factor
(2010-02-01)
Tzeng, Yu-Fen
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Wu, Hung-Chi
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Sheng, Pei-Sun
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Tai, Nyan-Hwa
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Chiu, Hsin Tien
This work describes newly structured stacked silicon nanowires (s-SiNWs), consisting of nanosized silicon wires on top of silicon microrods (SiMRs) and exhibiting pronouncedly superior electron held emission (EFE) characteristics to the conventional SiNWs, by using a two-step electroless metal deposition process. Experimental results indicate that for these s-SiNWs, the electrostatic "screen effect" is markedly suppressed and the held enhancement factor (beta-value) is significantly increased ((beta)(s-SiNWs) = 2533). Additionally, the turn-on held (Eo) for triggering the EFE process is reduced to a level comparable with that of carbon nanotubes, viz. (E(0))(s-SiNWs) = 2.0 V/mu m. This simple and robust modified electroless metal deposition approach does not require either a high temperature or an expensive photolithographic process and possesses great potential for applications.
Ti5Si3 nanowire and its field emission property
(2008-04-08)
Lin, Huang-Kai
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Tzeng, Yu-Fen
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Wang, Chia-Hsin
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Tai, Nyan-Hwa
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Lin, I-Nan