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University of Melbourne

1. Lugg, Nathan R. Atomic-resolution imaging using inelastically scattered electrons.

Degree: 2011, University of Melbourne

Transmission electron microscopy (TEM) is a powerful technique for studying matter at the atomic scale. In this thesis we theoretically investigate how images in several imaging modes are formed using electrons that have scattered inelastically within a specimen. Understanding how both the channelling of the incident electron probe and the inelastic transition potentials within the specimen combine to generate the inelastically scattered wave is fundamental in understanding how an inelastic image is formed. We demonstrate that the atomic-resolution chemical mapping of elements within a specimen can be achieved using energy-filtered transmission electron microscopy (EFTEM) based on inner-shell ionisation. We show how the approach based on calculating the elastic wavefunction and individual inelastic (ionisation) transition potentials can provide insight as to when direct interpretation may and may not be possible. This is demonstrated by a comparison between experimental data and simulation for the EFTEM image of the La N4,5 edge in LaB6 in which direct interpretation of the location of the La columns is possible. Chemical mapping of the atoms in a specimen using scanning transmission electron microscopy (STEM) based on electron energy-loss spectroscopy (EELS) has recently been demonstrated using known test specimens. In this thesis we present the first applications of this novel technique to the compositional determination of a technologically important Ce/Zr mixed oxide (Ce2Zr2O8) catalytic nanocrystal. Full quantum mechanical calculations are an essential part of the analysis and are used to identify perturbations in the chemical composition from that of the ideal Ce2Zr2O8 ordered nanocrystal structure. To date standard TEM operating voltages (≥ 100 kV) have been used in STEM. These high accelerating voltages lead to radiation damage, especially in specimens containing light elements. Recent technological advances in aberration correction have enabled high-resolution imaging at lower incident energies where knock-on damage is less problematic. With the amelioration of this problem in mind, we will discuss theoretically the advantages and disadvantages of moving to the low accelerating voltage regime with respect to electron channelling and the inelastic probe-specimen interactions that take place within the specimen. High angle annular dark field (HAADF) STEM, STEM EELS imaging and annular bright field (ABF) STEM imaging are all considered. We find that, in general, elastic channelling along columns is favoured by high accelerating voltages and that, in contrast, lower accelerating voltages provide more favourable inelastic interactions. The recently developed technique of ABF STEM, which is based on both elastic and inelastic (thermal) scattering, has shown much potential in directly imaging atoms as light as Li and H, which are…

Subjects/Keywords: transmission electron microscopy (TEM); scanning transmission electron microscopy; (STEM); energy-filtered transmission electron microscopy (EFTEM); electron energy-loss spectroscopy (EELS); atomic-resolution imaging; low accelerating voltage

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Lugg, N. R. (2011). Atomic-resolution imaging using inelastically scattered electrons. (Doctoral Dissertation). University of Melbourne. Retrieved from http://hdl.handle.net/11343/37069

Chicago Manual of Style (16th Edition):

Lugg, Nathan R. “Atomic-resolution imaging using inelastically scattered electrons.” 2011. Doctoral Dissertation, University of Melbourne. Accessed August 21, 2019. http://hdl.handle.net/11343/37069.

MLA Handbook (7th Edition):

Lugg, Nathan R. “Atomic-resolution imaging using inelastically scattered electrons.” 2011. Web. 21 Aug 2019.

Vancouver:

Lugg NR. Atomic-resolution imaging using inelastically scattered electrons. [Internet] [Doctoral dissertation]. University of Melbourne; 2011. [cited 2019 Aug 21]. Available from: http://hdl.handle.net/11343/37069.

Council of Science Editors:

Lugg NR. Atomic-resolution imaging using inelastically scattered electrons. [Doctoral Dissertation]. University of Melbourne; 2011. Available from: http://hdl.handle.net/11343/37069

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