Plenary Lecture: HIGH RESOLUTION ELECTRON ENERGY-LOSS SPECTROSCOPY FOR THE STUDY OF ORGANIC AND BIOLOGICAL SYSTEMS IN THE SCANNING TRANSMISSION ELECTRON MICROSCOPE

The need to characterize chemistry, structure and bonding with high spatial resolution has driven the exciting developments in electron energy-loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) over the last two decades, including development of high-performance electron monochromators, improved spectrometers and new detectors with a high detector quantum efficiency (DQE). [1] Without monochromation, energy resolution (ΔE) in the range 0.5-0.8eV as measured by the full width half maximum (FWHM) of the zero-loss peak is typical. Introduction of a commercially available monochromated instrument at the turn of the century enabled ΔE

One of the most exciting, and challenging, research opportunities for high resolution STEM-EELS is to probe the spatial distribution of functional groups in organic/ biological systems. This can be achieved by investigation of both electronic and vibrational excitations. Pioneering work in the study of vibrational excitations has been conducted on systems such as guanine crystals and amino acids. [4,5] Molecular materials, such molecular magnets [6] and organic photovoltaics [7], and polymer materials [8] have been the focus of electronic excitations in high resolution EELS investigations. In this contribution, I will discuss recent results in high resolution STEM-EELS from the literature as well as from my own research activities, focusing on how these capabilities have the potential to provide new insights in the study of organic, hybrid (organic-inorganic) and biological materials.

[1] M.J. Lagos et al, Microscopy, 2022, 71(S1), i174–i199

[2] P. Tiemeijer et al, (2002), Microsc. Microanal. 8: 70–71.

[3] O.L. Krivanek et al, (2009) Philos. Trans. R. Soc. London, Ser. A 367: 3683–3697.

[4] P. Rez et al (2016) Nat. Commun. 7: 10945.

[5] J.A. Hachtel et al (2019) Science 8: 525–528.

[6] A.H. Trout, D.W. McComb et al, (2022) “Probing the Structure of Vanadium Tetracyanoethylene using Electron Energy-loss Spectroscopy” (submitted)

[7] J.A. Alexander, D. W. McComb et al, Ultramicroscopy 180 (2017) ‏ ‏ 125-132

[8] R. Colby, B. Ford, R.E.A. Williams & D.W. McComb, (2022) “High resolution EELS of polymers” 2022 (submitted)

[9] The author acknowledges financial support from a number of sources over the last two decades including Defense Advanced Research Projects Agency (DARPA), the Center for Emergent Materials at The Ohio State University, an NSF MRSEC (DMR- 2011876), the Air Force Research Laboratory (AFRL), the Air Force Office of Scientific Research (AFOSR) and the Engineering and Physical Sciences Research Council (EPSRC), as well as support from numerous industrial collaborators.