The TEM provides the user with advantages over the light microscope in three key areas:

1. Resolution at high magnification. Resolution can be defined as the smallest distance between two closely opposed points, at which they may be recognised as two separate entities. The best resolution possible in a light microscope is about 200 nm whereas a typical TEM has a resolution of better than 1 nm. This enables visualisation of features in crystal lattices, such as defects and dislocations, as well as sub-cellular structures such as organelles and molecular machinery.

Dislocations in an additively manufactured Ni-based superalloy. Credit: Zibin Chen and Bryan Lim, University of Sydney.

Structures within a chloroplast. Credit: Ian Kaplin, University of Sydney.

2. Structural information through diffraction. If the material being viewed has a periodic structure, like that in a crystal, then the beam can interact with that structure in such a way that it diffracts. The ability to form diffraction patterns of this kind is unique to the TEM, and provides information on crystal structure, symmetry and orientation of the crystal being viewed.

Diffraction pattern from crystalline specimen taken on a major zone axis. Image courtesy of Roger Wepf, University of Queensland.

Quantitative convergent beam electron diffraction pattern. Image courtesy Andy Johnson, University of Western Australia.

3. Microanalysis. Analysis of sample elemental composition can be performed in the TEM. This is also possible in the SEM, but not at the high resolutions possible in TEM.

Energy dispersive spectroscopy imaging of the interface between BiFeO3 and SiTiO3. Image courtesy of Jiangtao Qu, University of Sydney.