Electron loss spectroscopy as an adjunct to imaging has added elemental and chemical analysis to the high resolution imaging capabilities of electron microscopy. The development of monochromator and spectrometers that give meV energy resolution has revolutionized spectroscopy in the electron microscope. Now we can probe vibrations with peaks in the IR region1, optical absorption from defects, as well as the UV and soft X-ray excitations that have been the traditional area of interest in electron loss spectroscopy. Theoretical analysis showed that CH, NH, NH2 and OH vibrations would give a strong signal2 and that they could be excited from distances of up to 100 nm. It was predicted by Cohen et al3 that it would be possible to use an aloof beam to minimize specimen damage. This has been used in our recent demonstration of “damage-free” spectroscopy of guanine fish scales4. Furthermore, theory predicts that there should also be a high resolution signal, possibly even atomic resolution 2,5, and more detailed analysis is defining the necessary microscope operating conditions.
It is not just electron spectroscopy where theory has shown the way forward. Simple theoretical analysis showed that it would be possible to image beam sensitive biological specimens with low radiation exposure using annular dark field STEM, if the detector inner cut off were small enough5. This has been experimentally realized in the cryo STEM work of Wolf et al 6. Further development of the theory has shown that it will be possible to map out the contents of small prokaryotic cells at about 2 nm spatial resolution in 3D using cryo-STEM tomography.
- O.L. Krivanek et al, Nature, 514, 20-212, (2014)
- P. Rez, Microsc. Microanal. 20, 671-677, (2014)
- H. Cohen et al, Phys. Rev. Lett, 782-785, (1998)
- P. Rez et al, Nature Commun, (2016)
- C. Dwyer, Phys. Rev. B 89, 054103, (2014)
- P. Rez, Ultramicr. 96, 117-124, (2003)
- S.G. Wolf, L. Houben and M. Elbaum, Nature Methods, 11, 423 (2014)
