In-plane-aligned membranes of carbon nanotubes D.A. Walters, M.J. Casavant, X.C. Qin, C.B. Human, P.J. Boul, L.M. Ericson, E.H. Haroz, M.J. O'Connell, K. Smith, D.T. Colbert * , R.E. Smalley Departments of Chemistry and Physics, The Center for Nanoscale Science and Technology, Rice University, MS-100, P.O. Box 1892, Houston, TX 77251-1892, USA Received 15 October 2000 Abstract Wehaveproducedthe®rstmacroscopicobjectscomprisedofhighlyalignedsingle-wallcarbonnanotubesSWNTs). TheseobjectsarethinmembranespreparedbyproducingasuspensionofSWNTsegments,introducingthesuspension toastrongmagnetic®eldtoalignthesegments,and®lteringthesuspensioninthemagnetic®eldtoproduceanaligned membrane of SWNT. These membranes exhibited natural cleavage planes parallel to the magnetic ®eld. This prepa- ration of macroscopic samples of aligned single-wall nanotubes permits exploitation of their highly anisotropic properties,andwillenablemeasurementoftheelectronic,thermal,magnetic,mechanical,andopticalpropertiesofbulk nanotube materials. Ó 2001 Elsevier Science B.V. All rights reserved. 1. Introduction Single-wall carbon nanotubes SWNTs) are prized for their mechanical, electrical, thermal, and chemical properties. Early theoretical predic- tions of these properties have been substantially veri®edexperimentallyashighqualitymaterialhas become available. Macroscopic materials com- prising large number of nanotubes in crystalline alignment with one another would constitute highly anisotropic material with a wide range of potential applications. We report here the ®rst realization of a macroscopic sample comprising substantially aligned SWNT. The aligned nanotube sample produced in the present experiment was created by aligning sus- pendedSWNTsegmentsinastrongmagnetic®eld and ®ltering them out of suspension while they remainalignedbythemagnetic®eld.SWNTshave been predicted to have an anisotropic magnetic susceptibility[1].Thelowestenergyorientationfor all SWNT types is parallel to the ®eld, B. Appli- cationofasucientlystrongmagnetic®eldshould thereforeorientnanotubesthatarefreetorotatein a liquid suspension [1]; a process similar to the magnetic orientation of liquid crystals [2]. Mag- neticalignmenthasalreadybeendemonstratedfor small quantities of multi-wall nanotubes [3]. Cal- culations reveal that metallic SWNTs such as the n; n variety)areparamagneticinthedirectionof their long axes, and tend to align parallel to the ambient magnetic ®eld. The other varieties of SWNT are diamagnetic, but their diamagnetic susceptibilities are most negative in the direction perpendicular to the tube axis, causing them to also align parallel to the direction of an ambient ®eld. The alignment energies for both the para- magnetic and diamagnetic varieties of SWNT are 13 April 2001 Chemical Physics Letters 338 2001) 14±20 www.elsevier.nl/locate/cplett * Corresponding author. Fax: +1-713-285-5320. E-mail address: colbert@rice.edu D.T. Colbert). 0009-2614/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0009-261401)00072-0