Synthesis and Structural Characterization of Ultra-thin Flexible Au Nanowires
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1206-M16-29
Synthesis and Structural Characterization of Ultra-thin Flexible Au Nanowires
Alexandre Kisner,1 Marc Heggen,2 Karsten Tillmann,2 Yulia Mourzina1 and Andreas Offenhäusser1 1 Institute of Bio- and Nanosystems and CNI - Center of Nanoelectronic Systems for Information Technology, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany. 2 Institute of Solid State Research and Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons (ER-C), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany. ABSTRACT Au nanowires (AuNWs) were produced by electroless reduction of HAuCl4 in a micellar structure formed by oleylamine and investigated by means of high-resolution transmission electron microscopy (HRTEM). Micrometer long ultra-thin flexible AuNWs with 1—2 nm diameter and AuNWs with about 12 nm diameter and a few hundred nm length were produced. Their extremities show a characteristic bulging. In contradiction with previous work, the bodies of the 12 nm nanowires are defect-free along the axial direction, their extremities, however, show the presence of twin boundaries. Ultra-thin AuNWs were often found as bundles presenting lengths of few micrometers. Although they are stable in solution for months, they were found to be quite sensitive to electron beam irradiation during HRTEM experiments, with a tendency to break up into face centered cubic (fcc) Au droplets. It is proposed that the micellar configuration of oleylamine plays a fundamental role in the atomic arrangement of nanowires. Finally, we anticipate our results to be a starting point for a more realistic experimental investigation of surface effects on the mechanical properties of ultra-thin nanowires with high aspect ratio, which have been only widely exploited theoretically.
INTRODUCTION
Au nanowires are one of the most fundamental building blocks for the fabrication of nanodevices [1-3]. The atomic structure of these nanowires plays a crucial role regarding their electromechanical properties [4-7]. For instance, atomic simulation shows that surface steps promoted by surface reconstruction along the [111] axial orientation of a 5 nm diameter Au nanowire lower the tensile yield strength by 38 % [6]. In another remarkable study, Dunn et al. showed through a modified embedded atom method that depending on the initial crystallographic orientation, AuNWs with a cross-sectional area below 4 nm2 can undergo phase transformations [7]. Despite these and several other theoretical analyses which also have made novel predictions concerning the atomic structure of ultra-thin metal nanowires, a more basic question still remains challenging, that is, the synthesis of stable high aspect ratio ultra-thin Au nanowires with highly oriented structure [8-10]. A promising and pioneer successful wet chemical approach to produce micrometer long ultrathin Au nanowires was recently demonstrated by Ravishankar et al., and subsequently by others in similar attempts [11-16]. However, a more detailed investigation of the atomic structure of those nanowires has not been sho
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