Techniques in Transmission Electron Microscopy

Development of a Novel and Quantitative Approach to Phase Imaging with Applications to Functional Nanomaterials
Transmission electron microscope (TEM) images represent the collective amplitudes of electrons in the form of intensities. It is also possible to detect phase shifts of electron waves, albeit through indirect means. Electron holography is capable of performing such measurements using modified TEMs and there have been successful quantitative phase maps reported in the recent literature.
Alternatively, phase information can be encoded in images by imposing controllable aberrations in the TEM, such as focus variations. Extraction of phase information buried in recorded intensities is known as 'phase retrieval'. The 'transport of intensity equation' (TIE) analytically relates defocus-induced intensity variations to spatial gradients in the electron phase. Paganin and Nugent [1] recently developed an efficient algorithm for solving this differential equation, which requires knowledge of an experimental through-focus derivative image and in-focus image.

In this project, we aim to use the Paganin-Nugent solution [1] of the TIE to develop phase retrieval for the TEM. Our industrial aims are to detect subtle dopant variations in transistor type specimens on the nano-scale, which are difficult to sense by other means. We have demonstrated [2] that such information can be inferred from retrieved phase maps.

Collaborators: Dr Vicki Keast (University of Newcastle), (ACMM, The University of Sydney), Dr Steven Duvall (formerly Intel Corporation, Australia), Dr Kevin Johnson (Intel Corporation, Oregon, USA), Prof. Keith Nugent (University of Melbourne).

[1] D. Paganin and K. A. Nugent, Phys. Rev. Lett. 80 (1998) 2586-2589.
[2] T. C. Petersen, V. J. Keast, K. Johnson, S. Duvall, Phil. Mag., 87 (2007) 3565 – 3578.

3-D Characterisation of Nanostructured Materials by Electron Tomography
The broad aim of this project is to develop a world-leading scientific capability at the University of Sydney in quantitative electron tomography. Our will meet this ambitious goal by combining advanced microscopy with sophisticated computational approaches to data analysis. The specific aims of this work are to:

  • acquire nanometre-resolution tomographic data from new microporous (greater than 2 nm pore diameters) and mesoporous (2-50 nm pore diameters) materials - for brevity, 'nanoporous' materials;
  • develop the computational and analytical approaches required to extract fully-quantitative parameters from the 3-D reconstructions, including measures of wall thickness, pore volume-fraction, pore geometry, the location of catalytic sites in ‘doped’ mesoporous systems etc.; and
  • apply this unprecedented information to the rational design of new nanoporous materials.

Investigators: ,
Collaborator: Prof. Thomas Maschmeyer, School of Chemistry, University of Sydney.