Electron Microscopy
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Electron microscopy (EM) (Author: Prof. Dr. Goerg Hannes Michler)
Introduction
The diverse structures and morphology of plastics have been studied using electron microscopy for several decades. With the development of microscopic techniques and methods, structural details ranging from macroscopic sizes down to approximately 0.1 nm (= 10-10 m) can be imaged (Table 1). Alternative techniques are scattering methods (SALS – Small Angle Light Scattering; SAXS, WAXS – Small and Wide Angle X-ray Scattering; SANS – Small Angle Neutron Scattering), as scattering methods and microscopic techniques often provide complementary results.
Table 1: Size of structural details of plastics, resolutions and magnifications that can be obtained with the various microscopic techniques and scattering methods
Overview of methods
Electron microscopy (EM) can be divided into the techniques of transmission electron microscopy (TEM) and scanning electron microscopy (SEM). A leap forward in the investigation of nanostructures (see also: micromechanics & nanomechanics) in particular came with the development of scanning probe microscopy and, in particular, atomic force microscopy (AFM), a method that is important for plastics. The different types of microscopy can be classified in general terms according to whether an image is obtained by irradiation, as with a ‘lamp’, or by scanning the surface (see: fracture surface) as with a “finger” or a “needle” – see Fig. 1 [1–3]:
| Fig. 1: | Schematic diagram of the principles of the different types of microscopy (see text) [1–3] |
Type 1 – Transmission: A beam of light or electrons passes through a thin sample or test piece in a light microscope (LM) or transmission electron microscope (TEM); thin (LM) or ultra-thin samples (TEM) are required
Type 2 – Reflection: A stationary beam is reflected by the sample; compact samples can be examined
Type 3 – Scanning beam: A focused beam (laser light or electron beam) is scanned across the sample and reflected (in confocal laser scanning microscopy) or generates secondary and backscattered electrons (in scanning electron microscopy)
Type 4 – A focused scanning beam penetrates a thin sample (scanning transmission electron microscope)
Type 5 – Scanning tip: A mechanical tip is scanned over the sample and interacts with it due to various physical properties (in atomic force microscopy or scanning tunnelling microscopy for conductive samples).
The various techniques can be used to examine the surfaces of compact plastics and their interiors – see diagram in Fig. 2 above. Surface structures can be examined directly using scanning electron microscopy (SEM, ESEM), atomic force microscopy (AFM) and indirectly using the imprint technique with transmission electron microscopy (TEM). Ultra-thin and semi-thin sections of the interior are examined using TEM, and thicker sections using AFM. To compare the results that can be achieved with the various techniques, the figure below shows the typical cross-hatched morphology of commercial isotactic polypropylene (abbreviation: iPP) in individual images.
Numerous reviews cover the details of light microscopy [4, 5], electron microscopy [1, 6–11, 14] and atomic force microscopy [1, 3, 12, 13].
| Fig. 2: | oben: Use of various microscopic techniques to examine surfaces and the interior below: Comparison of the results of various microscopic techniques for α-iPP: a) SEM image after permanganate etching b) TEM image after chemical contrasting c) AFM image |
Acknowledgements
The editors of the lexicon would like to thank Prof. Dr. rer. nat. habil. Goerg Hannes Michler, Martin Luther University Halle-Wittenberg and Polymer Service GmbH Merseburg for their guest contribution.
See also
- Scanning electron microscopy (SEM)
- Atomic force microscopy (AFM)
- Environmental-SEM (ESEM)
- Transmission electron microscopy
- In-situ tensile test in ESEM with AE
- Microtomy
References
| [1] | Michler, G. H.: Electron Microscopy of Polymers. Springer, Berlin Heidelberg (2008) (ISBN 978-3-54036350-7; see AMK-Library under F 1) |
| [2] | Michler, G. H., Balta-Calleja, F. J.: Nano- and Micromechanics of Polymers: Structure Modification and Improvement of Properties. Carl Hanser, Munich (2012) (ISBN 978-3-446-42767-9; see AMK-Library under F 13) |
| [3] | Michler, G. H.: Atlas of Polymer Morphology. Morphology, Deformation and Fracture Structures. Carl Hanser, Munich (2016) (ISBN 978-1-56990-557-9; E-Book ISBN 978-1-56990-558-6; see AMK-Library under F 14) |
| [4] | Kern, M., Trempler, J.: Observation and Measurement Microscopy in Material Science. Brünne-Verlag, Berlin Heidelberg (2008) (ISBN 978-3-9809-8489-8) |
| [5] | Wu, J., Chan, Ch.-M., Mai, Y.-W.: in Polymer Blends and Alloys; Shonaike, G. O.; Simon, G. P. (Eds.) Chapter 18, pp. 505 – 548 |
| [6] | Michler, G. H., Lebek, W.: Ultramikrotomie in der Materialforschung. Carl Hanser, Munich (2004) (ISBN 3-446-22721-0; see AMK-Library under F 5) |
| [7] | Michler, G. H.: New possibilities of electron microscopical determination of the morphology polymers. Ultramicroscopy 15 (1984) 81–100 |
| [8] | Bethge, H., Heydenreich, J.: (Eds.) Electron Microscopy in Solid State Physics. Elsevier Sci. Publ. Amsterdam (1987) |
| [9] | Goodhew, P. J., Humphreys, F. J., Beanland, R.: Electron Microscopy and Analysis. 3rd Edition., Taylor & Francis, London (2000) (ISBN 0-7484-0968-8) |
| [10] | Zhang, X.-F., Zhang, Z.: (Eds.) Progress in Transmission Electron Microscopy. 1: Concepts and Techniques. Springer, Berlin (2001) (ISBN 3-540-67680-5) |
| [11] | Li, Zh. R.: (Ed.) Industrial Application of Electron Microscopy. Marcel Dekker Inc., New York (2003) |
| [12] | Magonov, S. N.: In: Meyers, R. A. (Ed.) Encyclopedia of Analytical Chemistry. Wiley, Chichester, UK (2000) (ISBN 978-0-4719-7670-7) |
| [13] | Schönherr, H., Vancso, G. J.: Scanning Force Microscopy of Polymers. Springer, Berlin Heidelberg (2010) (ISBN 978-3-642-01231-0) |
| [14] | Michler, G. H.: Elektronenmikroskopie in Halle (Saale) – Stand, Perspektiven, Anwendungen. [Heinz-Bethge-Stiftung für angewandte Elektronenmikroskopie] (2017) (see AMK-Library under F 20) |
Additional references
- Picht, J., Heydenreich, I.: Einführung in die Elektronenmikroskopie. Verlag Technik (1966) (see AMK-Library under F 32)