Reconciling structure prediction of alloyed, ultrathin nanowires with spectroscopy

Abstract

A number of complementary, synergistic advances are reported herein. First, we describe the ‘first-time’ synthesis of ultrathin Ru₂Co₁ nanowires (NWs) possessing average diameters of 2.3 ± 0.5 nm using a modified surfactant-mediated protocol. Second, we utilize a combination of quantitative EDS, EDS mapping (along with accompanying line-scan profiles), and EXAFS spectroscopy results to probe the local atomic structure of not only novel Ru₂Co₁ NWs but also ‘control’ samples of analogous ultrathin Ru₁Pt₁, Au₁Ag₁, Pd₁Pt₁, and Pd₁Pt₉ NWs. We demonstrate that ultrathin NWs possess an atomic-level geometry that is fundamentally dependent upon their intrinsic chemical composition. In the case of the PdPt NW series, EDS mapping data are consistent with the formation of a homogeneous alloy, a finding further corroborated by EXAFS analysis. By contrast, EXAFS analysis results for both Ru₁Pt₁ and Ru₂Co₁ imply the generation of homophilic structures in which there is a strong tendency for the clustering of ‘like’ atoms; associated EDS results for Ru₁Pt₁ convey the same conclusion, namely the production of a heterogeneous structure. Conversely, EDS mapping data for Ru₂Co₁ suggests a uniform distribution of both elements. In the singular case of Au₁Ag₁, EDS mapping results are suggestive of a homogeneous alloy, whereas EXAFS analysis pointed to Ag segregation at the surface and an Au-rich core, within the context of a core–shell structure. These cumulative outcomes indicate that only a combined consideration of both EDS and EXAFS results can provide for an accurate representation of the local atomic structure of ultrathin NW motifs.