SNAPCAT · Scanning probe energy loss spectroscopy of Nanoscale Alloy Particles for heterogeneous CATalysis

Scanning probe energy loss spectroscopy of Nanoscale Alloy Particles for heterogeneous CATalysis

Most heterogeneous catalysts take the form of catalytically active nanoparticles dispersed over a support medium. To improve catalytic function and reduce waste requires improving the homogeneity of these nanoparticles, whether it be their size, shape or composition. Measurements of individual nanoparticles require access to expensive instrumentation such as a scanning transmission electron microscope (STEM). The project applies a novel and relatively inexpensive technique, scanning probe energy loss spectroscopy (SPELS), to study the composition, size and shape of individual size-selected Pt-based alloy nanoparticles, deposited using an inert gas-aggregation source, with a view to better understanding and improving their catalytic performance. The study is timely given the current interest in developing clean energy alternatives to fossil fuels. New methodologies and fundamental insights in this area can lead to significant economic and environmental impact. The overall objectives of the project have been: RO1 To quantify the sensitivity and resolution of SPELS by mapping plasmons on well-defined Ag nanostructures. RO2 To investigate Pt alloys formed on single crystal surfaces. RO3 To produce size-selected nanoparticles of Pt alloys. RO4 To measure the composition of individual alloy nanoparticles with SPEL. RO5 To identify target materials and optimise deposition parameters for alloy nanoparticle production. Due to the early termination of the project not all of the anticipated research objectives were reached. However, many valuable insights have been gained from the work done. Using a home-built retarding field analyser, it was possible to detect the plasmon loss feature at 2.6 eV on the Au(111) surface with SPELS. Field-induced roughening of the Au surface was also observed. SPELS was used to image size-selected Pt and Au nanoparticles in both constant field emission current (CFEC) mode and backscattered electron (BSE) mode. Nanoparticles appear as protrusions in constant field emission current images and as troughs in the corresponding backscattered electron images. A small lateral offset was found between the field emission and backscattered electron images that is independent of the scan direction. This can be ascribed to the fact that backscattered electrons are not detected from the region directly under the tip apex due to field suppression. This is the first experimental demonstration of this effect and also represents the highest imaging resolution obtained with SPELS to date.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз