Multidimensional Characterisation of Inorganic Nanoparticles Using Scanning Transmission Electron Microscopy

Abstract

In this thesis, an electron fluence efficient method for the 3D chemical imaging of inorganic nanoparticles have been explored through the use of scanning transmission electron microscopy (STEM), high angle annular dark field image (HAADF) and energy dispersive X-ray spectroscopy (EDS). The method, termed as spectroscopic single particle reconstruction (SPR), assumes nanoparticles are identical but randomly orientated on a support. Thus by expose each nanoparticle to electron beam only once, a collection of nanoparticles viewed at different orientations can be obtained to perform 3D reconstruction. Unlike tilt-series electron tomography (TS-ET) which images the same specimen multiple times, spectroscopic single particle reconstruction disperses total dose budget to all imaged particles thus not only enables the ability to imaging beam sensitive nanoparticles in 3D, but also increase the EDS counts for better EDS quantification. The presumption of nanoparticle population homogeneity can be eased to that only a subset of the whole population are all identical. By applying selection criterion such as thresholding nanoparticle compositions, platinum-nickel (PtNi) nanoparticles contain 45-55 at% Pt and 55-65 at% Pt were characterised by spectroscopic single particle reconstruction approach and found they show similar 3D elemental segregation behaviour. The 3D elemental segregation results not only agree with previous reports to show Ni-enriched facets, but also find new evidence for the importance of considering effect of crystallographic vertices and surface facets on local elemental distribution. An additional advantage of spectroscopic SPR for 3D imaging is that no high angle tilt is needed, which opens the possibility to perform 3D structural and chemical imaging for nanoparticles in-situ using all ranges of commercial in-situ holders without special requirement for high tilt to do TS-ET. This opportunity is explored using an in-situ heating holder to reconstruct the 3D structure transformation of PtNi at different temperatures.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Rob Lindsay (Supervisor) & Sarah Haigh (Supervisor)