Ultrathin Gold Nanowires with the Polytetrahedral Structure of Bulk Manganese

Abstract

Despite the intensive interest in thin gold nanowires for a variety of technologically important applications, key details of the mechanism of their formation and atomic-scale structure remain unknown. Here we synthesize highly uniform, very long, and ultrathin gold nanowires in a liquid-phase environment and study their nucleation and growth using in situ high-energy synchrotron X-ray diffraction. By controlling the type of solvents, reducing agents, and gold precursor concentration, it is shown that the nucleation and growth of gold nanowires involve the emergence and self-assembly of transient linear gold complexes, respectively. In sharp contrast with the face-centered-cubic bulk gold, the evolved nanowires are found to possess a tetrahedrally close packed structure incorporating distorted icosahedra and larger size coordination polyhedra of the type observed with the room-temperature phase of bulk manganese. We relate the complexes to synergistic effects between the selected precursor and reducing agents that become appreciable over a narrow range of their molar ratios. We attribute the unusual structural state of gold nanowires to geometrical frustration effects arising from the conflicting tendencies of assemblies of metal atoms to evolve toward attaining high atomic packing density while keeping the atomic-level stresses low, ultimately favoring the growth of cylindrical nanowires with a well-defined diameter and atomically smooth surface. Our work provides a roadmap for comprehensive characterization and, hence, better understanding of 1D metallic nanostructures with an unusual atomic arrangement and may have important implications for their synthesis and performance in practical applications.

Imaging Beam‐Sensitive Materials by Electron Microscopy

“…The characterizations of various defects and partial disorder is difficult, especially at nanoscopic or even atomic scale. EM imaging is widely used to probe such local structures, such as defects and partial disorder 135,393,394. Similar difficulty appears when the defective materials are beam sensitive, which can be tackled by diverse dose‐efficient EM imaging techniques.…”

There's no place like real-space: elucidating size-dependent atomic structure of nanomaterials using pair distribution function analysis

“…[71][72][73] While widely applied for fully amorphous and disordered crystalline materials, this approach has been less used for nanomaterials, although recent examples have shown its application to nanoparticles. [74][75][76] Independent of the approach to modelling, the quality of a t to a PDF is oen analyzed through the R w -factor, which is a measure of the difference between the calculated (G calc ) and experimental PDF (G obs ) that is calculated as:…”

“…It was found that a-Mn, which closely resembles a tcp structure, provided the best t to the data. 76,125 The nanowires are formed from particle assembly in solution and it was suggested that they adapt the tcp-like structure in order to maintain close atomic packing while avoiding the strain introduced by the high surface area of the nanowires.…”

The role of pre-nucleation clusters in the crystallization of gold nanoparticles

“…[39][40][41] By varying the OY concentration, it is also possible to prepare ultrasmall nanospheres by the same method and, interestingly, regardless of their shapes both kinds of particles synthesized at room temperature exhibit an atomic structure different from the fcc structure of bulk Au. 42 In this paper, we present a detailed description of the role of OY in the nucleation/growth mechanism of Au NPs relying on in situ XAS, SAXS and high-energy X-ray diffraction (HE-XRD) studies performed during syntheses carried out with different OY concentrations. Only a few experimental studies were devoted to the nucleation and growth mechanism of NPs prepared by these methods, and exclusively to nanowires characterized using in situ techniques, SAXS, 43,44 DLS, 45 or a combination of XAS and SAXS.…”

“…Syntheses of Au nanospheres and nanowires were performed by reduction of HAuCl 4 •3H 2 O by TIPS in a solution of OY in hexane following the procedures described in ref. 42. For all syntheses, the final nominal concentration of Au and TIPS in hexane was kept constant at 20 mM and 1 M, respectively.…”