Electrical transport properties of individual gold nanowires

S. Karim, W. Ensinger, C. Hassel, T. W. Cornelius, J. L. Duan, R. Neumann Physics Division, PINSTECH, Islamabad, Pakistan; Darmstadt University of Technology, Darmstadt, Germany; Department of physics, University of Duisburg-Essen, Germany; GSI, Darmstadt, Germany; IMP, CAS Lanzhou, P R China Metallic nanowires are regarded as essential components for the development of nanoelectronic devices. Their electrical resistivity, being one of the most important properties in electrical applications, is the subject of intense theoretical and experimental investigations [1]. When the object size becomes comparable to the electronic mean free path, finite-size effects are expected to occur, leading to additional scattering of the conduction electrons at both the surface [2] and the inner grain boundaries [3]. These scattering processes increase the electrical resistivity. Here, we present our first results on the resistivity of single cylindrical gold nanowires, electrically contacted by means of electron beam lithography (EBL). In a first step, we prepared ensembles of polycrystalline gold nanowires by electrochemical deposition in etched ion track templates [4]. The wires were freed from the polymeric host by dissolving the matrix in dichloromethane. The solvent was exchanged several times to obtain clean nanowires which were subsequently detached from the bottom support by placing the vessel in an ultrasonic bath. Finally, these polymer-free nanowires were dispersed on a GaAs substrate by spreading some drops of the solution on the wafer. The GaAs substrate carrying the wires was transferred to a scanning electron microscope (SEM) for contact processing by EBL. In order to fabricate macroscopic bonding pads to one of the wires, which were randomly distributed on the sample, a sufficiently long and wellseparated wire was chosen. Based on the contact layout adequate for the selected wire, a polymethylmethacrylate (PMMA) layer was spun onto the substrate and the sample was retransferred into the SEM. Then, the layout was exposed to the electron beam, and the PMMA was developed in a mixture of isopropanol and methylisobutylketone. Subsequently, the gold contacts were deposited by thermal evaporation, and the lift-off process took place in a hot acetone bath leaving the wire contacted with 200nm thick gold leads. For the electrical measurements, we used a four-point contact geometry by applying currents of typically 1 μA. Temperature dependent measurements were done in a He-bath cryostat where the temperature was varied down to few K.