Browsing by Author "Luo, RC"

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Carbon nanotubes grown using cobalt silicide as catalyst and hydrogen pretreatment
(2005-12-01)
Wen, HC
;
Yang, KH
;
Ou, KL
;
Wu, WF
;
Luo, RC
Cobalt catalytic-layers 25 mn were deposited by sputtering on silicon substrates. At the pretreatments, hydrogen plasma was conducted for 4-16 min at 600 degrees C in a MPCVD system. Pretreated samples were characterized using SEM and AFM. Surface morphologies of catalytic-layers were changed after hydrogen plasma pretreatments. The cobalt layers became discontinuous and some nanoparticles were formed. With pretreatments for a long time, nanoparticles tended to agglomerate to reduce surface energy and larger nanoparticles were observed. It is believed that the optimum pretreatment condition for the growth of carbon nanotubes could be achieved because relatively high growth failure and nanofibers (> 100 nm) was observed for shorter and longer than 12 min pretreatment, respectively. It is found that the hydrogen pretreatment is a crucial step for the making of nucleation sites in the synthesis of carbon nanotubes using cobalt silicide as catalyst on Si substrates. After the pretreatment, mixture gases of hydrogen and methane were then flowed into the chamber for 12 min, samples were characterized using SEM, TEM and Raman spectrum. Carbon atoms were adsorbed on the islands of catalysts, and then diffused into the edge of nanotubes. Cobalt silicides were formed due to high processing temperature, and cobalt atoms tended to diffuse and stay on the silicon substrates, which enhance carbon nanotubes to grow under the root growth mechanism. (c) 2005 Elsevier B.V. All rights reserved.
Effects of ammonia plasma treatment on the surface characteristics of carbon fibers
(2006-02-24)
Wen, HC
;
Yang, K
;
Ou, KL
;
Wu, WF
;
Chou, CP
Carbon fibers were grown from cobalt catalysts with larger size (> 100 nm), and the size distribution can be controlled by pretreatment. Pretreated cobalt catalytic-layers were observed as islands, which can enhance the growth of carbon fibers. The carbon fibers were treated by ammonia plasma in a PECVD system. High-energy ammonia plasma not only can cause damage but also adsorb on carbon fibers. The ammonia plasma treatment resulted in the etching effect. It is also observed that the more treatment time, the more disorder in structures of carbon fibers. The N-H functional groups were found on the surfaces of ammonia plasma treated carbon fibers and this observation can be further investigated to develop chemical sensor application. (c) 2005 Elsevier B.V. All rights reserved.