Abstract
This note reports a study of the coating of a crystal with `ice' at temperatures below 45 K during single-crystal in-house diffraction experiments when using an open-flow helium cryostat. The `ice' consists mainly of crystalline oxygen and nitrogen. This suggests completely different techniques for avoiding this type of icing compared with water icing. With appropriate choices of crystal mount, crystal position with respect to the nozzle and gas flow conditions, it is possible to avoid detectable condensation. However, sometimes this cannot be achieved in practice (poor diffraction from a smaller crystal, necessity of positioning the crystal in certain orientations to achieve desired data completeness, need to reduce helium consumption etc.). The problem of icing seems to be less common for powder experiments where the laminar gas flow is parallel to the capillary containing the sample, and for synchrotron experiments where the sample is comparatively small and almost continuously rotated, which facilitates the ice covering being removed by the gas flow. This last technique can in principle also be applied to single-crystal X-ray diffraction using laboratory diffractometers – periodic rapid rotation of the crystal can help to minimize any icing, but this technique will not work when the condensation rate is comparable to or faster than one frame of data collection. The coating around a sample crystal reduces the quality of the diffraction data, and the temperature at the sample below the coating may differ significantly from that at the cryostat nozzle reported by the instrument.
Funder
Ministry of Science and Higher Education of the Russian Federation
Universität Wien
Austrian Science Fund
Novosibirsk State Technical University
Publisher
International Union of Crystallography (IUCr)
Subject
General Biochemistry, Genetics and Molecular Biology
Cited by
1 articles.
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