Transmission Electron Tomography: Imaging Nanostructures in 3D

  • Author / Creator
    Wang, Xiongyao
  • In studies of nanoscale materials, electron tomography (ET) can be used to obtain three dimensional information on the morphology and spatial distribution of nanoparticles. Electron tomography records a tilt series of projected images of an object and then mathematically reconstructs a 3D map of the object from the recorded images. Filtered back-projection (FBP), which is based on spatial Fourier transforms, and simultaneous iterative reconstruction techniques (SIRT), which are purely algebraic, are the two common reconstruction methods used to generate a tomographic "3D matrix" from the recorded images. Three aspects of ET were investigated in this thesis: the reconstruction and visualization, experimental considerations, and practical applications. First, to quantify the quality of the reconstruction and the selection of visualization threshold was discussed. The quality of the reconstruction by FBP and SIRT methods was evaluated by root mean square (RMS) difference frequency analysis, a quantitative description of similarity between the original test and its reconstruction. A quality index (QI) method was proposed and successfully applied to set the visualization threshold for volume rendering of tomographic reconstructions. Setting the threshold according to a priori known space-filling volume fraction of nanoparticles was found not to be a suitable parameter for visualization. The effect of the filter used in FBP was examined. On the experimental front of electron tomography, a new ET sample preparation method was developed. The new method combines standard thin film deposition techniques and focused ion beam (FIB) milling. The proposed method minimized the effect of the projected thickness and missing wedge by controlling the thickness of the thin film and the width of the bar. Furthermore, the new method reduces gallium implantation problems and is suitable for tomographic sample preparation of samples in solution. Finally, the tomographic results of latex nanoparticles, Au nanocrystal multilayer, and Si nanocrystals embedded in silica glass were examined. A new method was developed by combining high angle annular dark-field (HAADF) and energy-filtered STEM techniques simultaneously to obtain parallel recording of 3D tomographic data from two different types of nanoparticles. This method was successfully applied to investigate the Er doped Si nanocrystals system.

  • Subjects / Keywords
  • Graduation date
    Fall 2012
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.