Direct synthesis of self-aligned single-walled carbon nanotubes on paper Qin Zhou a, * , Kaihui Liu b , Shaomin Xiong c , Feng Wang b , Liwei Lin a a Berkeley Sensor and Actuator Center, Department of Mechanical Engineering, University of California, Berkeley, CA 94720, USA b Department of Physics, University of California, Berkeley, CA 94720, USA c Department of Mechanical Engineering, University of California, Berkeley, CA 94720, USA ARTICLE INFO Article history: Received 27 May 2011 Accepted 19 October 2011 Available online 25 October 2011 ABSTRACT A technique of micro chemical vapor deposition (lCVD) is reported for the direct synthesis of self-aligned SWCNTs on various substrates including plastics and paper. With the guid- ance of micro flow channels, self-aligned SWCNTs up to hundreds of microns in length have been collected. Both Raman spectral and transmission electron microscopy have val- idated the high quality of these SWCNTs. In conclusion, lCVD could be a versatile method to synthesize pristine SWCNTs for various applications. Published by Elsevier Ltd. 1. Introduction The integration of nanomaterials with flexible substrates has drawn great interests targeting low-cost and lightweight appli- cations [1–5]. Among various nanomaterials, single-walled car- bon nanotubes (SWCNTs) have a unique set of specific properties including high electronic mobility [6], high electrical current carrying capability [7,8], and ballistic electron trans- port phenomenon at room temperature [9,10]. These break- through demonstrations of SWCNTs, however, have all been based on the direct growth of SWCNTs in high temperature chambers without post-assembly processes to avoid possible degradations during the transfer processes [11–19]. Specifi- cally, two types of transfer processes have been commonly em- ployed for one-dimensional nanostructures. The solution-cast approach starts with the dispersion of SWCNTs with liquid to form a nanotube ink, which is later deposited onto a target sub- strate and dried [14–18]. Nanotubes deposited by this method usually exhibit degraded electrical performance due to random alignment [15,18], ultrasonic agitation [20], and/or electrical property modifications from the SWCNT–solvent interactions [21,22]. The second approach starts with the synthesis of well-aligned SWCNTs with the aid of electrical field [23], gas flow [24,25], or crystal lattice orientation on the growth sub- strate [26]. Afterwards, a transfer layer (usually polymer) is deposited and SWCNTs are attached to the transfer layer and relocated to a target substrate [27,28]. The transfer layer is later dissolved or etched away, leaving aligned SWCNTs on the tar- get substrate. This approach preserves the originally well- aligned patterns but various chemicals used in the process could affect the electrical properties of SWCNTs due to chem- ical doping and surface adsorption [21]. Here we describe a dif- ferent approach without the transfer process to allow as-grown SWCNTs to be directly placed onto arbitrary substrates with self-aligned patterns such as glass, ceramics and tempera- ture-sensitive substrates including plastics and papers. 2. Experimental 2.1. Concept and setup Fig. 1 illustrates the basic principle and the setup of the syn- thesis process. Briefly, micro chemical vapor deposition (lCVD) system which is part of the suspended cantilever microstructure [29], is built by means of silicon micromachin- ing processes. Adequate heat transfer design limits the high 0008-6223/$ - see front matter Published by Elsevier Ltd. doi:10.1016/j.carbon.2011.10.032 * Corresponding author. E-mail address: zhouqin@berkeley.edu (Q. Zhou). CARBON 50 (2012) 1179 – 1185 Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon