Copper (Cu) and Cobalt (Co) with remarkable difference in the catalytic activity for the growth of carbon nanotubes (CNTs) have been used to prepare metal-nanowire/CNT heterojunctions. The ordered arrays of Cu nanowire/CNT (CuNW/CNT) and Co nanowire/CNT (CoNW/CNT) heterojunctions were prepared by combining electrochemical deposition and chemical vapor deposition. The interfaces between CNTs and Cu or Co nanowires have been examined and compared. At the interface of CuNW/CNT heterojunction, the tip of CuNW is encapsulated by carbon material (named "cap") and connected the CNT consisting of amorphous carbon (a-C). Two-segment CuNW/amorphous CNT (CuNW/a-CNT) hybrid nanostructure was obtained for the CuNW/CNT heterojunctions due to low catalytic activity of Cu. It is also interesting that a hollow gap was observed between the "cap" and the CuNW. By contrast with the case of Cu, multi-walled CNT (MWCNT) was achieved and no hollow gap was observed at the interface of CoNW/CNT heterojunctions. Threesegment CoNW/MWCNT/a-CNT hybrid nanostructure was observed for the CoNW/CNT heterojunctions because of high catalytic activity of Co. Because no stable copper carbides are observed, we infer that the growth mechanism of CuNW/CNT heterojunctions is different from that of CoNW/CNT. Possible growth models of CuNW/CNT and CoNW/CNT heterojunctions are proposed based on experimental results, respectively.
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