Towards new methods for investigating soft and soft-hard hybrid materials in the electron microscope

Understanding and controlling materials stability under the irradiation of an electron beam is one of the big challenges in electron microscopy. Beam damage thresholds have been studied in many hard and biological materials, but there are several classes of soft and soft-hard hybrid materials which have barely been investigated up until now. Beam effects are not comprehensively understood even in more intensively studied materials. For example, an electron beam can give rise to subtle effects such as the generation of electric potentials or plasmons and thus induce reactions with the environment far below the radiation threshold for materials damage. In biological materials, contrast formation in SEM may be influenced by electric surface potentials. Electric potentials can be modified by gas environments in ESEM and ETEM, however, the effect of gas species on sample stability and induced surface reactions are not well understood. Recent experiments show that the application of external potentials can even suppress undesired electrochemical processes and thus enhance the stability of materials in electron microscopes. Other strategies for stabilization involve sample cooling and reduced electron energies.

This proposed project aims to develop strategies for performing high quality electron microscopy studies on soft and soft-hard hybrid systems. Because the tactics developed for hard materials are often diametric to those needed for soft materials, investigating interfaces between soft and hard materials in an electron microscope presents an exceptional challenge. Our general approach is to perform systematic studies on carefully selected model material systems where the results can be easily transferred and applied to a broad class of soft and soft-hard hybrids. We envision a strategy based on the following systematic approaches: (i) Determination of radiation thresholds for the selected model material systems and simulation of electron scattering. (ii) Comparison of effects of total electron dose to electron flux. (iii) Measurement of beam induced electric potentials and currents. (iv) Testing of different approaches for sample stabilization such as gas environments, sample cooling, varying beam energy, applying external electric potentials. The selected model systems will include spores and dried cells, wood and polymer materials, and immobilized molecular catalysts on surfaces. Beam induced excitations will be studied by EBIC and low loss EELS. Careful study of sample stability and irreversible changes will be performed by SEM, TEM, ADF imaging, EELS, and X-ray spectroscopy, in both controlled atmospheres (environmental TEM and SEM) and at low temperatures (Cryo SEM and TEM).

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Contact

Identity

Prof. Christian Jooss

eMail

jooss@ump.gwdg.de