Surface Science Letters 281 (1993) L335-L340 North-Holland surface science letters Surface Science Letters Characterization of carbon nanotubes by scanning probe microscopy Mark J. Gallagher, Dong Chen, Bruce P. Jacobsen, Dror Sarid Optical Sciences Center, University of Arizona, Tucson, A Z 85721, USA Lowell D. Lamb, Frank A. Tinker, Jun Jiao, Donald R. Huffman Department of Physics, University of Arizona, Tucson, AZ 85721, USA Supapan Seraphin and Dan Zhou Department of Materials Science and Engineering, University of Arizona, Tucson, AZ 85721, USA Received 23 October 1992; accepted for publication 17 November 1992 Carbon nanotubes, fabricated by the Ebbesen-Ajayan method, were imaged using scanning tunneling microscopy(STM) and atomic force microscopy (AFM) in air and were compared to images obtained with high-resolution transmission electron microscopy(HRTEM). The HRTEM images revealed an abundance of elongated structures ranging in diameter from 3.0 to 30 nm, and with lengths of up to 0.8/xm. Many of the structures possessed several graphitic shells as if the tubes were nested one in the other. Reproducible images of the tubular structures, typically 20 nm in diameter and with a large variation in length, were obtained with both STM and AFM when the nanotubes were deposited on hydrogen-terminatedSi(111), confirmingthat the nested structures observed with HRTEM do indeed have a tubular morphology.No single-walled, bare nanotubes or spherical fullerenes (typical of the Kriitschmer-Huffman process) were observed. 1. Introduction Prompted by the discovery of a method for mass production [1], the last two years have seen an extensive effort directed toward the explo- ration of the properties of the roughly spherical, one-nanometer-sized fullerenes (e.g., C60 and C70). Recently, Ebbesen and Ajayan [2] reported a new process for the synthesis of large quantities of another novel class of carbon structures, so- called nanotubes. These are thought to consist of one or more shells of hexagonally patterned sheets of carbon atoms, with the ends of the nanotubes capped by fullerene-like hemispheres [2-4]. They typically vary in diameter from 2 to 20 nm, and can have lengths of several micrometers. Even before Ebbesen and Ajayan's report, several the- oretical studies of these structures appeared in the literature [4-9]. The electrical conductivity of nanotubes has been of particular interest; for instance, Hamada et al. have predicted [5] that for nanotubes with a single wall, the electronic- transport properties can vary from semiconduct- ing to metallic, depending on the diameter of the structure and the degree of helicity in the ar- rangement of the carbon hexagons. Although the images of nanotubes reported so far [2,3] are quite striking, it is not possible to completely determine the morphology of these structures using HRTEM alone. With STM and AFM, how- ever, it is possible to directly observe the three- dimensional nature of the nanotubes, probing both their topography and electronic structure. We present here the first STM and AFM images 0039-6028/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved