Synthesis of Pt–Containing Metals Alloy and Hybrid Nanowires and Investigation of Electronic Structure Using Synchrotron-Based X-Ray Absorption Techniques

Abstract

Platinum–containing bimetallic nanomaterials have shown different electronic structures from their monometallic counterparts, bringing exotic properties to various catalytic and magnetic applications. The synthesis and shape–dependent properties of bimetallic cubes, truncated cubes, dendrites, and hollow structures, have been intensively studied. One dimensional (1D) Pt–containing nanostructure has attracted special interest, although synthetic challenges in the fine control over morphology arising from unfavorable anisotropic growth of symmetric cubic lattice structures from Pt metal and alloys (Ahmadi et al., 1996; Cozzoli & Manna, 2005; Xia et al., 2003). The electronic structure of bimetallic nanowires is associated with their heterogeneous structural diversity strongly, such as phase segregation (Zhong & Maye, 2001), intermetallic alloy (Casado-Rivera et al., 2004), random alloy (Shibata, et al., 2002) and near surface alloy (NSA) (Greeley & Mavrikakis, 2006; Knudsen, et al., 2007) (See Scheme). Therefore, detailed studies of bimetallic heterogeneous structures are essential for their applications. The structural characterization of bimetallic nanomaterials is not trivial, partly due to the complexity of heterogeneous nature imposed by nanoscale system. X–ray absorption fine spectroscopy (XAS) is a well established tool for investigating the element–resolved structure of bimetallic nanomaterials, since the local environment and electronic properties of atoms of each resonant element can be studied separately by tuning the X–ray energy to the absorbing edge of each metal. XAS has been successfully used to study bonding habit, geometry, electronic and surface structure of many bimetallic nanoparticles (e.g., Pt/Ru, Pt/Au, Pd/Au and Pt/Ir) (Nashner et al., 1997). When the short range order information extracted from XAS analysis is combined with the knowledge of the long range order and average compositional distribution obtained by complementary techniques, actual heterogeneous structure and electronic state of nanomaterials can be quantitatively analyzed. In this chapter, we intend to focus on our recent results on the synthesis and electronic structures of ultrathin PtAu alloy nanowires, Pt/Au phase–segregated hybrid nanowires.