Transmission electron and scanning transmission electron tomography, techniques for the three-dimensional characterization of microstructural features at a nanometer length scale, make use of the fact that, despite their limited thickness, thin foils do have a third dimension. This limited thickness has traditionally caused difficulties in quantifying features observed in TEM micrographs which are projections of the three-dimensions. Such difficulties, including well-known phenomena such as the Holmes effect (i.e., overprojection) and particle truncation [1-3], make traditional 2-D stereological procedures such as volume fraction, difficult or impossible. However, the same third dimension (i.e., foil thickness) which renders traditional stereological methods impractical makes electron tomography possible.

Tomography is a technique where images are recorded from a specimen in as many viewing directions as possible. Thus, tomography is the integration of data collected from a series of images in which the orientation of the specimen relative to the incident beam is progressively varied, and the series then reconstructed. Traditionally in the TEM this has meant recording a series of TEM images at different tilt-angles, typically with a CCD camera and over the range of -70° to +70° at regular tilt intervals of approximately 1° or 2°. This approach has been applied successfully in life science for already more than decade [4-7]. In many cases it is possible to record data series by hand – though it is a very tedious process involving precise tilting, image shifting (one of the most important aspects of tomography to minimize information loss through variation in imaging area), focusing, imaging, and tilting. Researchers performing this manually can only process a very limited number of samples in a given timeframe, resulting in an increase in cost, both operationally (e.g., microscope time) and from an opportunity cost perspective.

At this time, the equipment and software required to perform experiments within CAMM have not been delivered. In the future, we intend to characterize various features exhibited in Ti-alloy systems, including the representation and quantification of secondary a, isothermal and athermal w, and ultrafine dispersions of second phase intermetallics, including Ti5Si3, Ti5Ge3, and Ti3Al. Similarly, for the Ni-based superalloys, it includes the representation and quantification of tertiary g’. These nanometer scale precipitates are known to significantly impact the mechanical properties and subsequent phase transformations of a large number of alloys.

Example Results

1. L.M. Cruz-Orive, Journal of Microscopy, Vol. 131 (3), September 1983, pp. 265-290.
2. R.E. Miles, Journal of Microscopy, Vol. 107, (3), August 1976, pp. 227-233.
3. J.E. Hilliard, Transactions of the Metallurgical Society of AIME, Vol 224, October 1962, pp. 906-917.
4. Koster, A. J., et al., Perspectives of molecular and cellular electron tomography. J. Struct. Biol.(1997) 120 (3), 276.
5. Baumeister,W., Grimm, R. & Walz, J. 1999. Electron tomography of molecules and cells. Trends Cell Biol 9, 81–85.
6. McEwen, B.F. & Marko, M. 2001. The emergence of electron tomography as an important tool for investigating cellular ultrastructure. J Histochem Cytochem 49, 553–563.
7. McIntosh, J.R. 2001. Electron microscopy of cells: A new beginning for a new century. J Cell Biol 153, F25–F32.

Relevant Papers published within CAMM

            None Currently Available – New area of research

Other References of interest available in the literature

1. Buseck, P.R., Dunin-Borkowksi, R.E. Devouard, B., Frankel, R.B., McCartney, M.R., Midgley, P.A., Pósfai, M., Weyland, M., “Magnetite morphology and life on Mars”. Proceedings of the National Academy of Sciences 98, (24), 13490-13495, (2001).
2. Gilbert, P., “Iterative methods for the three-dimensional reconstruction of an object from projections”. Journal of Theoretical Biology, 36, 10-5-117, (1972).
3. Gordon, R., Bender., Herman, G.T., “Algebraic Reconstruction Techniques (ART) for three-dimensional electron microscopy and X-ray photography”. Journal of Theoretical Biology, 29, 471-481, (1970).
4. Midgley, P.A., Weyland, M., Thomas, J.M., Johnson B.F.G., “Z-contrast tomography: a technique in three-dimensional nanostructural analysis based on Rutherford scattering”. Chemical Communications, 18, 907-908, (2001).
5. Midgley, P.A., Weyland, M., “3D electron microscopy in the physical sciences: the development of Z-contrast and EFTEM tomography”. Ultramicroscopy, in press. (2003)
6. Otten, M.T., “High-Angle Annular Dark-Field Imaging on a TEM/STEM System”. Journal of Electron Microscopy Technique, 17, 221-230, (1991).
7. Radermacher, M., “3-Dimensional reconstruction of single particles from random and nonrandom tilt series”. Journal of Electron Microscopy Technique, 9, 359-394, (1988).
8. Radermacher, M., Weighted back-projection methods. In Frank, J. (ed.) Electron Tomography. Three-dimensional imaging with the Transmission Electron Microscopy. Plenum Press, 91-115, (1992).
9. Skoglund, U., Ofverstedt, L.G., Burnett, R.M., Bricogne, G., “Maximum-entropy three-dimensional reconstruction with deconvolution of the contrast transfer function: a test
10. application with adenovirus”. Journal of Structural Biology, 117 (3) 173-188, (1996).
11. Weyland, M., “Electron tomography of catalysts”. Topics in Catalysis, 21 (4), 173-83, (2002).
12. Weyland, M., Midgley, P.A., “Extending Energy Filtered Transmission Electron Microscopy (EFTEM) in three dimensions using electron tomography”. Microscopy & Microanalysis, in press, (2003).
13. U. Ziese, A.H. Janssen, J.L. Murk, W.J.C. Geerts, T. Krift, A.J. Verkleij, A.J. Koster, “Automated high-throughput electron tomography by pre-calibration of image shifts”, J. Microscopy, 205:2 (2002)187-200.