Multishell EXAFS Fitting Analysis of a Compositionally Precise Thiolate-Gold Nanocluster
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Multishell EXAFS Fitting Analysis of a Compositionally Precise Thiolate-Gold Nanocluster Daniel M. Chevrier1, Amares Chatt1, Peng Zhang1, Chenjie Zeng2, and Rongchao Jin2 1
Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada
2
Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
ABSTRACT Thiolate-gold nanoclusters exhibit unique optical, magnetic and chiral properties, which are attractive for novel applications in nanotechnology. A fundamental challenge facing these nanomaterials is being able to study and understand their physical properties in various experimental conditions. To overcome this, extended X-ray absorption fine structure (EXAFS) spectroscopy can be employed to probe the Au local structure of thiolate-gold nanoclusters in a variety of conditions, providing valuable structural information from multiple bonding environments (i.e. metal-metal and metal-ligand interactions). This study discusses a methodology for conducting a multishell EXAFS fitting analysis that can be implemented for thiolate-gold nanocluster systems. Specifically, experimental and simulated EXAFS data for Au36(SR)24 nanoclusters are examined with a total of 5 scattering paths fitted to the experimental data. INTRODUCTION Thiolate-protected gold nanoparticles (Au-SR NPs) are inarguably some of the most widely studied materials in nanotechnology because of their robust properties, high stability and functional surface environment [1,2]. The properties of Au-SR NPs are largely dependent on the particle size, which can be tailored with established protocols [3]. As the size of the Au-SR NP reaches 1-2 nm in diameter, however, the electronic and structural properties of the Au-SR NP are unlike their larger counterparts. Nanoparticles in this size regime are more commonly known as nanoclusters (NCs) and are composed of only a few atoms to hundreds of atoms [4]. As a result of these ultra-small nanoparticles, the electronic and structural properties deviate from the bulk, becoming highly sensitive to the exact composition of the Au-SR NC. Recent synthetic achievements have also enabled researchers to obtain single-sized Au-SR NC products with defined molecular formulae [4]. For this reason, the Aun(SR)m (n is the number of Au atoms and m is the number of thiolate ligands) terminology has been adopted. For many years the structural environment of Aun(SR)m NCs remained elusive. It was not until 2007 when Jadzinsky et al. reported the first crystal structure of a Au102(SR)44 NC that revealed a non-face centered cubic core structure (non-fcc) and short Au(I)-SR oligomer units protecting the core in what are known as staple-like motifs [5]. Since this breakthrough, the number of newly isolated or crystalized Aun(SR)m NC species has grown significantly [6]. A number of promising applications for Aun(SR)m NC materials have been proposed based on their unique optical, magnetic and chiral properties [4]. Nonetheless, one of the primary challenges preventing the advancement of Au
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