Characterization of Metallic Nanoparticles by X-ray Spectroscopy: Introduction and Application of High-resolution X-ray Absorption and Emission Spectrocsopy

In almost all areas of technology, metallic nanoparticles (NPs) are of interest due to their special properties, mainly arising due to their small size that implies the relevance of quantum effects as well as the significance of the surface. However, the identification of the property inducing surface-to-volume interactions is a difficult task, as the small size inhibits a lot of standard techniques to be applicable. Here X-ray absorption spectroscopy (XAS) is a favorable tool for the characterization of NPs, independent on size, degree of crystallinity and shape/condition of the surface. Using standard XAS, a tempered nanosized cobalt-platinum catalyst have been investigated and its outstanding properties in a fuel cell have been revealed. One drawback remains though, as the properties found are a superposition of all different chemical environments of the chosen element. Here, additional opportunities are provided by high-resolution fluorescence-detected XAS, which is chemical sensitive and therefore allows for site-selective investigations. For a system of 6 nm sized cobalt NPs, this technique have granted access to the properties of the NPs' interior and outer shell separately.