Periodic Reporting for period 1 - SNAPCAT (Scanning probe energy loss spectroscopy of Nanoscale Alloy Particles for heterogeneous CATalysis)
Reporting period: 2016-05-01 to 2018-04-30
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.
WP2 SPELS measurements on epitaxial alloy films: Task 1 – build a temperature programmed desorption setup. Due to the need to design and assemble a working electron energy analyser, building the temperature programmed desorption was put on hold. Task 2 – SPELS measurements on epitaxial thin films. SPELS measurments were performed on the Au(111) surface where the characteristic plasmon loss feature at 2.6 eV was observed. A home-built electron beam evaporator was assembled and tested for in-situ thin film deposition. Task 3 – microfabrication of co-axial tips. No co-axial tips were microfabricated during the reporting period.
WP3 SPELS on nanoparticles: Task 1 – Produce size-selected Pt clusters. Pt923, Au923 and Pt147 nanoparticles were deposited onto graphite substrates using the inert gas aggregation source. Task 2 – Produce alloy nanoparticles. Co-deposition of Pt and Au nanoparticles produced PtAu nanostructures. Task 3 – SPELS of alloy nanoparticles. The BSE signal from the nanoparticles was lower than that obtained from the surrounding graphite substrate.The Pt and Au could not be distinguished in BSE images due to their similar atomic numbers. A small offset was observed between the same nanoparticle features in simultaneously acquired CFEC and BSE images, which was independent of the scan direction. This confirms that the BSE are detected from a probe area adjacent to the tip, and not from the region directly under the tip apex due to field suppression. Preliminary SPELS measurements of the energy loss spectrum of the PtAu nanostructures could not resolve the plasmon loss feature attributed to Au. Task 4 – optimise magnetron targets for producing homogeneous nanoparticle ensembles. This work was not completed due to the early termination of the project.
WP4 Training & Dissemination activities: Task 1 – Website. A website related to the project has been established at http://snapcatweb.wordpress.com. Task 2 – Public outreach. Dr. Murphy established a profile on ResearchGate with details of the project and relevant publications. Task 3 – Training & secondment. Dr. Murphy received some training in the operation of the gas aggregation cluster source. He has also learned some programming in Python in order to process the SPELS data. He attended several seminars by invited speakers who are experts in the field of nanoparticle synthesis and characterisation and microscopy. Task 4 – Conference. Dr. Murphy has recently attended the Microscience and Microscopy Congress (mmc2017) in Manchester. Task 5 – Papers. A paper reporting the preliminary results on imaging size-selected nanoparticles with SPELS is in preparation.
Dr. Murphy has started a new permanent position as a lecturer at the Institute of Technology Tallaght (ITT), Ireland. He is being supported by the University of Birmingham through an equipment loan that will allow him to continue the work begun during his fellowship with a view to completing the workplan outlined in the project.