Soldering of Nanotubes onto Microelectrodes Dorte Nørgaard Madsen, † Kristian Mølhave, † Ramona Mateiu, † Anne Marie Rasmussen, ‡ Michael Brorson, ‡ Claus J. H. Jacobsen, ‡ and Peter Bøggild* ,† Mikroelektronik Centret, Technical UniVersity of Denmark, DK-2800 Kgs. Lyngby, Denmark, and Haldor Topsøe A/S, NymølleVej 55, DK-2800 Lyngby, Denmark Received September 17, 2002; Revised Manuscript Received November 6, 2002 ABSTRACT Suspended bridges of individual multiwalled carbon nanotubes were fabricated inside a scanning electron microscope by soldering the nanotube onto microelectrodes with highly conducting gold-carbon material. By the decomposition of organometallic vapor with the electron beam, metal-containing solder bonds were formed at the intersection of the nanotube and the electrodes. Current-voltage curves indicated metallic conduction of the nanotubes, with resistances in the range of 9-29 kΩ. Bridges made entirely of the soldering material exhibited resistances on the order of 100 Ω, and the solder bonds were consistently found to be mechanically stronger than the carbon nanotubes. Carbon nanotubes have been proposed as prototypical nanoscale building blocks because of their unique mechanical and electrical properties. 1 To explore their potential in physics, chemistry, and biology, a number of methods have been employed to form electrical and mechanical connections to devices and nanostructures. 2-5 We present an in situ method for the highly conductive attachment of nanoscale components by the use of a gold-carbon composite soldering material deposited by a focused electron beam. This method does not require electrical contact to the electrodes or the component and allows for the assembly of 3D structures. We used a Philips XL30 ESEM-FEG environmental scanning electron microscope, operating at a water vapor pressure of 100 Pa. Dimethylacetylacetonate gold(III), which has a vapor pressure of 1 Pa at 25 °C, was placed in a container with a narrow bore tube to control the diffusion of organometallic vapor onto the sample. The electron beam locally decomposes the organometallic compound and thereby deposits a material with metallic content. 6 Using a 2-mm- long tube with a diameter of 0.8 mm, we obtained a growth rate of 500 nm/min. Tips with lengths of more than 10 μm could be grown without a significant decrease in the growth rate. All depositions were made at room temperature. A nanomanipulator stage inside the chamber was used to move a silicon chip with two cantilever microelectrodes. 7 The electrodes were connected to a DC voltage source, and the current was monitored continuously (see Figure 1a). Samples of free-standing multiwalled carbon nanotubes (MWNTs) were prepared 8 and characterized by transmission electron * Corresponding author. E-mail: pb@mic.dtu.dk. ² Technical University of Denmark. ‡ Haldor Topsøe A/S. Figure 1. (a) Illustration of two microelectrodes positioned close to a multiwalled nanotube (1) extending from a catalyst particle on a substrate. Organometallic molecules decomposed by the electron beam (2) are deposited to form a cross-shaped solder bond (3) and a protective bond (4) near the edge of the electrode. (b) ESEM image of a carbon nanotube across two electrodes, connected by soldering bonds and protective bonds (top). When the electrode pair is withdrawn, the nanotube breaks at the protective bonds (bottom). NANO LETTERS 2003 Vol. 3, No. 1 47-49 10.1021/nl0257972 CCC: $25.00 © 2003 American Chemical Society Published on Web 11/27/2002