MS-1-P-2349 Atomic-scale Defects Leading to Lattice Strain in Single-crystal Ultrafine Gold Nanowires

Gold nanowires of molecular scale dimension are of fundamental as well as technological interest owing to their tunable electrical transport characteristics leading to ballistic conduction. This implies single electron sensitivity making them potentially active material for catalysis and molecule sensing. This demands a large scale production of the wires in pristine form for applicability and a detailed atomic structure study to interprete their properties different from the bulk. Although the chemical synthesis route has been reported and electrical transport studies have been carried out recently on the single crystal 2 nm gold wires of large aspect ratio (approx. 500 or more), the structural investigation is not done so far. HRTEM combined with image simulation and exit wave reconstruction can provide information on the local atomic structure, however, with aberration corrected microscopes and advanced analytical methods one can analyse the structure with picometer precision. This method is limited to atomically thin samples. Quantitative HAADF-STEM is a technique to analyse the structure of even few tens of nanometer thick samples and it allows us to determine atom positions in the lattice and determine elemental composition of the atomic columns. Aberration corrected electron microscopy, therefore, combined with advanced quantification methods is a state of the art technique to extract information atom-by-atom ¹. Here we present our investigation on these ultrafine gold nanowires to determine their atomic structure by low dose aberration corrected high resolution (S)TEM. Quantification reveals patterned strain in the crystals which increases at the surface layer of atoms and that the wires are faceted with irregular atomic scale surface steps ². These structural aspects can be related to their unique electrical features and makes them potential candidates for catalysis and sensorics. Besides, from the HRSTEM image, atom counts in the atomic columns in viewing direction is obtained and a 3D visualization of the wire atomic structure could also be deduced. Further, we looked into the atom dynamics due to interaction with the electron beam at higher dose which gives an insight to its mechanical behaviour and stability. Figure 1. provides an overview of the lattice strain and the atom counting analysis.

¹ G. V. Tendeloo et al. Adv. Mater. 24, 5655-5675 (2012)
² P. Kundu et al. ACS Nano 8, 599-606 (2014)