Abstract
Nowadays ptychographic tomography in the hard x-ray regime, i.e., at energies above about 2 keV, is a well-established measurement technique. At the Paul Scherrer Institut, currently two instruments are available: one is measuring at room temperature and atmospheric pressure, and the other, the so-called OMNY (tOMography Nano crYo) instrument, is operating at ultra-high vacuum and offering cryogenic sample temperatures down to 10 K. In this manuscript, we present the sample mounts that were developed for these instruments. Aside from excellent mechanical stability and thermal conductivity, they also offer highly reproducible mounting. Various types were developed for different kinds of samples and are presented in detail, including examples of how specimens can be mounted on these holders. We also show the first hard x-ray ptychographic tomography measurements of high-pressure frozen biological samples, in the present case Chlamydomonas cells, the related sample pins and preparation steps. For completeness, we present accessories such as transportation containers for both room temperature and cryogenic samples and a gripper mechanism for automatic sample changing. The sample mounts are not limited to x-ray tomography or hard x-ray energies, and we believe that they can be very useful for other instrumentation projects.
Highlights
X-ray computed tomography (CT) is widely used in imaging as it allows three-dimensional visualization of specimens non-destructively.1 For a measurement, many projections of a specimen are acquired from different sample orientations and reconstructed into a three-dimensional dataset
As an example of a technical challenge resolved by these pins, we further show a demonstration of nanotomography of high pressure frozen Chlamydomonas cells with a resolution of about 100 nm in 3D
While in the case of Ref. 23, the sample was transferred to the vacuum chamber of OMNY at room temperature, the cryogenic samples of Ref. 27 required cryogenic sample transfer
Summary
X-ray computed tomography (CT) is widely used in imaging as it allows three-dimensional visualization of specimens non-destructively. For a measurement, many projections of a specimen are acquired from different sample orientations and reconstructed into a three-dimensional dataset. As an example of a technical challenge resolved by these pins, we further show a demonstration of nanotomography of high pressure frozen Chlamydomonas cells with a resolution of about 100 nm in 3D We expect that such pin designs can be used in other setups aiming for highresolution nanotomography or pre-aligned sample exposure both for room and cryogenic temperatures. The conical shape has proven to be mechanically stable; projection measurements with sub-10 nm resolution have been successfully performed, and an isotropic 3D resolution below 15 nm has been demonstrated in the instrument measuring at room temperature.16,17 These results were limited in resolution by mechanical stability of the entire setup and available photon flux, not by the sample pin. This keeps the possibility to look at a sample again at a later point
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