Short Communication Scanning electron microscopy investigation of Cu-TCNQ micro/nanostructures synthesized via vapor-induced reaction method

AbstractMicro/nanostructures based on the metal–organic complex Cu–TCNQ were successfully synthesized by a novel method: vapor-inducedreaction. Scanning electron microscopy was used to investigate the morphology on the three different parts of the substrate: the hot reactionarea, a transitional reaction area and an induced reaction area. The results show that the morphology of the as-grown structures evolves frommicrostructures to nanostructures. The formation mechanism of these different structures may be understood from electrochemical principlesand the decreasing concentration of TCNQ.q 2005 Elsevier Ltd. All rights reserved. PACS: 68.65; 61.46; 81.10.DnKeywords: Cu–TCNQ; Vapor-induced reaction; Morphologies; Micro/nanostuctures; SEM 1. IntroductionOne-dimensional (1D) nanostructures have recentlybecome the focus of intensive research owing to theirunique chemical, physical and mechanical properties, andhave proven to be key components in the fabrication ofnanoscale devices (Cui et al., 2001; Xia et al., 2003; Wang,2003). So far, 1D nanostructures have been widely achievedin various materials, such as metals, semiconductors andoxides. In addition, various routes have been developed tomake an ideal 1D nanostructure, for instance vapor-phasemethod (Yuan et al., 1996; Yang et al., 1997), vapor–liquid–solid method (Duan et al., 2000 a,b), solution–liquid–solidmethod (Trentler et al., 1997; Markowitz et al., 2001),solvothermal method (Wang et al., 2002), solution-phasemethod (Sun et al., 2002 a,b), template-mediated growth(Han et al., 1997) and microwave-assisted synthesis (Liuet al., 2004).Functional charge-transfer metal–organic complexessuch as Cu, Ag–TCNQ (where TCNQ stands for tetra-cyanoquinodimethane) have attracted extensive attentionsince the 1970s. They can be used as memories or switchesin molecular electronics, due to the p-orbital overlapping ofneighbor molecules. Electrical switches and memoryelements made from their thin films have been reported(Potember et al., 1979; Wan et al., 2000; Sun et al., 1998).Recently the growth mechanism, the electrical switchingand memory effect of single Ag–TCNQ nanowire syn-thesized by vacuum vapor-transport reaction were reported(Ye et al., 2004; Fan et al., 2003). Other micro/nano-structures of Ag–TCNQ have been synthesized by solutionreaction, such as tubes, rods and dentrites (Cao et al., 2005).However, 1D micro/nanostructures of Cu–TCNQ haveseldom been reported.