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Teaching transmission electron microscopy (TEM) in Inorganic Chemistry
Teaching transmission electron microscopy (TEM) in Inorganic Chemistry
A group-based activity designed to introduce TEM and enable students to interpret low-resolution TEM images. This activity assumes familiarity with atomic structure, crystal structure, and diffraction. It followed a prior discussion about powder X-ray diffraction.
Two models are presented illustrating how electrons could interact with matter, as follows:
Based on these models, small groups were first asked the following question.
1. What properties of a nanoparticle sample would make it more likely that an electron's path would be deflected causing a darker image?
1. What properties of a nanoparticle sample would make it more likely that an electron's path would be deflected causing a darker image?
Each group was asked to offer a property until all of the following were identified:
Greater scattering due to higher nuclear charge.
Greater scattering due to more atoms, that could result from a thicker or more dense sample.
Greater diffraction due to more crystallinity.
Greater diffraction due to better orientation with respect to the beam.
While students readily recognized that more charge would induce more scattering, they needed to be pushed to relate this to actual properties such as sample thickness. Furthermore, while crystallinity was readily recognized as a cause of electron deflection, orientation was not immediately recognized.
After this more general discussion, a specific set of images was shown and small groups were asked to interpret them. These copyrighted images were taken from de Nijs and Zhaochuan Fan and Frans D Tichelaar and Daniël Vanmaekelbergh and Alfons van Blaaderen and Thijs J H Vlugt and Marijn A van Huis and Henny W Zandbergen, A. O. Y. A. B. Nanotechnology 2014, 25 (5), 055601; copyrighted at IOP and shown on ResearchGate).
2. Without any chemical context, give all of the possible explanations you can think of for why some nanocubes in Figure 2a appear darker than others.
2. Without any chemical context, give all of the possible explanations you can think of for why some nanocubes in Figure 2a appear darker than others.
Each group was asked to offer an explanation until all of the following reason were identified. Darker cubes might be...
Thicker (although the similar size makes it unlikely that this is the case).
Have a different chemical composition that consists of higher atomic masses.
Be more crystalline.
Have a crystalline orientation that better deflects electrons.
3. Without any chemical context, give all of the possible explanations you can think of for why some nanocubes in Figure 2b have centers that are darker than the outer area.
3. Without any chemical context, give all of the possible explanations you can think of for why some nanocubes in Figure 2b have centers that are darker than the outer area.
Each group was asked to offer an explanation until all of the following reason were identified. The darker center of the cubes might be caused by...
A more crystalline center.
A center that has heavier atoms or is denser.
Development of this material was supported by the National Science Foundation (CHE-1724948)
http://iopscience.iop.org/article/10.1088/0957-4484/25/5/055601/pdf
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