Soldering of Carbon Nanotube Bridges using Electron Beam Deposited Gold
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Soldering of Carbon Nanotube Bridges using Electron Beam Deposited Gold Søren Dohn, Kristian Mølhave, Dorte Nørgaard Madsen, Ramona Mateiu, Peter Bøggild, Anne Marie Rasmussen1, Michael Brorson1 and Claus J.H. Jacobsen1 MIC, Technical University of Denmark, Building 345 east, DK-2800 Kgs. Lyngby, Denmark 1 Haldor Topsøe A/S, Nymøllevej 55, DK-2800 Kgs. Lyngby, Denmark ABSTRACT We have formed suspended bridges of carbon nanotubes between microcantilevers using electron beam dissociation of metal-organic vapours. By electron beam exposure of a surface in the presence of gold-carbon molecules emitted inside an environmental scanning electron microscope, we are able to form tips and other freestanding nanostructures of high metallic content. Suspended bridges made entirely of this material exhibit resistances less than 50 times that of pure gold, and consist of dense metallic cores surrounded by a crust of nanoparticles. We used standard microfabrication techniques to produce silicon chips with multiple microcantilevers extending over the edge. Individual multiwalled carbon nanotubes grown catalyticcally by chemical vapour deposition, were positioned across two cantilevers using in-situ nanomanipulation tools. Drawing a cross-shaped gold-carbon bond on each end of the carbon nanotube consistently resulted in electrical contact with resistances in the range 1-90 kΩ and linear current-voltage characteristics. We found that soldering bonds having a line width down to 10-15 nm form connections and last for days in ambient conditions. INTRODUCTION Since the discovery of the carbon nanotube (CNT) in 1991 by S. Iijima [1], the CNT has been foretold a great future in electronic devices and as reinforcement in various materials due to the unique mechanical and electrical properties. To gain insight as well as to fabricate prototype devices it is therefore of paramount importance to obtain electrical connections to CNT. In practice, studies of the electrical properties generally require the nanotubes to be interfaced to measurement equipment via microelectrodes. This is often done by dispersing CNT on a surface and subsequently manipulating the nanotubes towards electrodes [2] or alternatively, locating the positions of the nanotubes for subsequent lithographic deposition of electrodes [3]. Although these methods have proven excellent for investigations of the electrical properties alone, the interplay of mechanical and electrical properties is more accessible from studies of suspended nanotube bridges that allow electrical measurement during mechanical deformation. Such bridges have been formed by underetching devices after deposition of electrodes [4], and by growth from prepositioned catalytic material. Finally, nanomanipulators equipped with sharp tips have been used inside scanning electron microscopes (SEM) to mechanically bend and pull nanotubes while monitoring their electrical conductance [5]. In these experiments, none of the methods used appear to offer strong mechanical connection combined with low-resistance
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