Radiation Damage of TiC and TiN during Microanalysis in the Electron Microscope

Cluckie, Mary M (1990) Radiation Damage of TiC and TiN during Microanalysis in the Electron Microscope. PhD thesis, University of Glasgow.

Abstract

The work presented in this thesis is concerned with the preferential mass loss observed during high spatial resolution micro-analysis of ceramic materials such as TiC and TiN. Electron energy loss spectroscopy (EELS) was used to investigate the preferential loss of the light elements as a function of dose incident upon the specimen. This thesis is primarily concerned with the characterisation of the knock-on displacement damage mechanism thought to be responsible for the mass loss. Chapter 1 gives a general introduction to these knock-on damage processes with particular emphasis on radiation damage observed in the electron microscope. To perform quantitative EELS microanalysis without the use of standard specimens it is necessary to have an accurate knowledge of the cross-sections relevant to the inelastic scattering of electrons. Chapter 2 outlines the development of partial cross-sections required for EELS analysis and discusses other processes which may contribute to the EELS spectrum. Chapter 3 develops two radiation damage mechanisms as possible explanations for the depletion of the light elements in Tic and TiN during electron irradiation: a forward knock-on displacement model and an isotropic radiation induced diffusion model. In chapter 4 a brief description is given of the scanning transmission electron microscope (STEM) used to carry out the high current density radiation damage experiments described in this thesis. The discussion includes a description of two specimen preparation techniques developed to provide electron transparent samples with a plentiful supply of uniform thin areas, suitable for radiation damage experiments. The reduced dose rate incident upon the specimen during radiation damage experiments results in statistically poor EEL spectra. Often, the accuracy with which quantitative data can be extracted from these "noisy" spectra is limited by the accuracy of the background stripping routines. Chapter 5 compares and contrast three such background fitting routines using both experimental and theoretically generated spectra in an attempt to assess which, if any, is more reliable in the presence of noise. The experimental results are presented in chapter 6 and 7 for the TiC and TiN materials. Comparison of the rate of loss of C and N with respect to dose at various specimen thicknesses is carried out to establish which, if either, of the two radiation damage mechanisms considered in chapter 3 is applicable to the data. Other considerations such as dose rate effects, channeling effects and the loss of Ti from the sample are considered in more detail in chapter 7 and their effect on the measured rate of loss of N is established. Some high angle ADF images are presented in chapter 6 as a possible method of following the radiation damage process and to highlight the inhomogeneous nature of the damage processes in TiC and TiN.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Condensed matter physics, Nuclear physics and radiation, Materials science
• Date of Award: 1990
• Depositing User: Enlighten Team
• Unique ID: glathesis:1990-78143
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 28 Feb 2020 12:09
• Last Modified: 28 Feb 2020 12:09
• URI: https://theses.gla.ac.uk/id/eprint/78143