“Especially impressed by the highly precise goniometer”

Sun, 07.05.2023

It is planned that the department for Chemical Crystallography and Electron Microscopy, which today offers as a service a wide range of techniques for the analysis of solid compounds such as SC-XRD, PXRD, SEM and TEM, will also host by then the electron diffractometer.

On the occasion of the negotiations, Professor Christian Lehmann gave ELDICO an interview about his perspectives for the development of electron diffraction as upcoming analytical method in crystallography, how his institute may use the ED-1 for, and where he sees strengths of the instrument:

ELDICO: In your department, you offer a wide range of techniques for the analysis of solid compounds such as SC-XRD, PXRD, SEM and TEM. Now you are planning to complement your capabilities with a dedicated electron diffractometer from ELDICO Scientific, the ELDICO ED-1. What research areas do you expect to support with it and for which analytical questions – which were perhaps not so easily accessible before?

Professor Christian Lehmann: At our institute, we are working in the research fields of heterogenic catalysis, organo-catalysis, organometallic chemistry, and organic chemistry. All our research areas will benefit from the ELDICO ED-1 as they all need crystal structure analysis. Even more so, when often only minute amounts of samples of a few milligrams or even micrograms will be available from synthesis experiments. Consequently, the amounts available for subsequent crystallization are therefore smaller. In the end, structural data on an atomic level is much more suitable to obtain from single crystal analysis. As the crystals are inevitably very small, we will need the new instrument.

The ELDICO ED-1 is designed to be an efficient analytical tool – easy to use and generating fast results suitable for a Service Center like yours. What are your plans on how to operate the machine and let many other colleagues benefit from it?

We have established processes in our service center and the ELDICO ED-1 supports those processes. Therefore, we are happy that our experts can seamlessly integrate the ELDICO ED-1 into their existing workflow.

Currently, we provide as a service center completely solved crystal structures to our internal colleagues. If later, we plan to involve external colleagues in the upstream data processing, the flexible data format of the ED-1 will be highly beneficial. Our colleagues can continue working with the data with whatever software they regard as most suitable for their specific topics.

Therefore, we are happy that the DECTRIS Quadro® detector in the ELDICO ED-1 provides the frames in CBF format. We have been used to working with that format for a long time and we have several software tools already at hand for that format.

In your view, what makes the ELDICO ED-1 stand out and what features will you put emphasis on?

Coming from working with a TEM, I am especially impressed by the highly precise goniometer which has been newly developed for that purpose. Also by the octagon and the capabilities, freedom and space to operate that it offers. Furthermore, the nanometer-precise localization of the sample in the rotational axis is an important feature, and last, but not least the very precise mechanism that keeps the sample in the beam is remarkable.

Regarding the goniometer, I think it is clever to define the rotational axis via the detector coordinates. That is a well-probed approach in SC-XRD, and we are happy to find it again in ED-1. For the goniometers which are usually found in electron microscopes, no specific emphasis was put on rotational precision.

Also, the decision to renounce all electron optical elements between the sample and the detector gives us unprecedented precision – not interfered with distortions. And though that restricts users from measuring very large unit cells, the fixed camera length in ED-1 and the resulting unit cell seems to be a good compromise for most of the targeted users in our view.

Electron crystallography is an evolving scientific area. What are your ideas to advance the progress in the field, and how can ELDICO support you with that?

For chemists, the discrepancy between the R-values from SC-XRD versus ED data will probably be a certain drawback, as low R-values are perceived as a sign of quality. This can be a problem in publications, for example, if structural data from ED are not accepted because of high R-values. Dynamical Refinement is a step in the right direction to address this problem and these solutions get better and better.

Perhaps the high R-values due to dynamic scattering are an inherent problem that people should accept. In exchange, they will gain more information in an easier way about light atoms in a crystal structure. As an example, electron diffraction has the potential to provide additional information about hydrogen even easier than it would be with X-ray.

We will be curious to see what further instrumentation we can build together onto the octagon or the sample holder making use of the large space around. For the octagon, I think of an EDX of course. And for the sample holder, I have in mind all kinds of MEMS holders for in-situ/operando experiments.

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