INSTITUTE OF PHYSICS PUBLISHING NANOTECHNOLOGY Nanotechnology 15 (2004) 1047–1053 PII: S0957-4484(04)77526-1 Constructing, connecting and soldering nanostructures by environmental electron beam deposition Kristian Mølhave 1 , Dorte Nørgaard Madsen, Søren Dohn and Peter Bøggild MikroelektronikCentret, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark E-mail: krm@mic.dtu.dk Received 9 March 2004 Published 21 June 2004 Online at stacks.iop.org/Nano/15/1047 doi:10.1088/0957-4484/15/8/033 Abstract Highly conductive nanoscale deposits with solid gold cores can be made by electron beam deposition in an environmental scanning electron microscope (ESEM), suggesting the method to be used for constructing, connecting and soldering nanostructures. This paper presents a feasibility study for such applications. We identify several issues related to contamination and unwanted deposition, relevant for deposition in both vacuum (EBD) and environmental conditions (EEBD). We study relations between scan rate, deposition rate, angle and line width for three-dimensional structures. Furthermore, we measure the conductivity of deposits containing gold cores, and find these structures to be highly conductive, approaching the conductivity of solid gold and capable of carrying high current densities. Finally, we study the use of the technique for soldering nanostructures such as carbon nanotubes. Based on the presented results we are able to estimate limits for the applicability of the method for the various applications, but also demonstrate that it is a versatile and powerful tool for nanotechnology within these limits. M This article features online multimedia enhancements 1. Introduction The investigation of electron beam deposition (EBD) as a technique for serial writing of three-dimensional nanostructures started in the 1980s. EBD has been used to make functional structures, such as field emission devices [1], thermal sensors [2], nanotweezers [3, 4] and tools for manipulating DNA [5]. In combination with in situ nanomanipulation equipment, EBD is capable of forming mechanically strong attachments of carbon nanotubes for strain measurements [6] and decreasing the contact resistance of contacts to nanotubes [7]. Conductive nanostructures are deposited by using metal-containing source gasses. The conductivity can be increased by decreasing the amount of amorphous carbon included in the structure [8, 9]. Environmental electron beam deposition (EEBD), where a 1 Author to whom any correspondence should be addressed. background gas such as water is present in an environmental electron microscope, was demonstrated by Folch et al [10]. Their results indicated that a high metal content could be achieved by EEBD. Our investigations have shown that it is possible to form a core of solid gold in EEBD structures [11]. Figures 1(a) and (b) show typical apexes of tips deposited in nitrogen and water, respectively. A gold core is clearly present in the tip deposited in water, while the tip deposited in nitrogen contains nanocrystals in an amorphous carbon matrix. The solid gold structures appear to be highly conductive and EEBD can be used to solder carbon nanotubes to electrodes obtaining low contact resistances [12]. Over the last decade a range of promising three- dimensional devices have been achieved with EBD, but relatively little has been reported regarding the limitations of the technique for such structures. Koops et al [13] studied growth rate and inclination of free standing EBD lines versus 0957-4484/04/081047+07$30.00 © 2004 IOP Publishing Ltd Printed in the UK 1047