CTFFIND4: Fast and accurate defocus estimation from electron micrographs.

https://journals.iucr.org/m/issues/2020/02/00/fq5009/fq5009.pdf

Estimation of high-order aberrations and anisotropic magnification from cryo-EM data sets in RELION-3.1.

RNA-Induced Conformational Switching and Clustering of G3BP Drive Stress Granule Assembly by Condensation

The molecular organization of eukaryotic nuclear volumes remains largely unexplored. Here we combined recent developments in cryo-electron tomography (cryo-ET) to produce three-dimensional snapshots of the HeLa cell nuclear periphery. Subtomogram averaging and classification of ribosomes revealed the native structure and organization of the cytoplasmic translation machinery. Analysis of a large dynamic structure-the nuclear pore complex-revealed variations detectable at the level of individual complexes. Cryo-ET was used to visualize previously elusive structures, such as nucleosome chains and the filaments of the nuclear lamina, in situ. Elucidation of the lamina structure provides insight into its contribution to metazoan nuclear stiffness.

https://science.sciencemag.org/content/sci/351/6276/969.full.pdf

Visualizing the molecular sociology at the HeLa cell nuclear periphery

We describe a phase plate for transmission electron microscopy taking advantage of a hitherto-unknown phenomenon, namely a beam-induced Volta potential on the surface of a continuous thin film. The Volta potential is negative, indicating that it is not caused by beam-induced electrostatic charging. The film must be heated to ∼200 °C to prevent contamination and enable the Volta potential effect. The phase shift is created “on the fly” by the central diffraction beam eliminating the need for precise phase plate alignment. Images acquired with the Volta phase plate (VPP) show higher contrast and unlike Zernike phase plate images no fringing artifacts. Following installation into the microscope, the VPP has an initial settling time of about a week after which the phase shift behavior becomes stable. The VPP has a long service life and has been used for more than 6 mo without noticeable degradation in performance. The mechanism underlying the VPP is the same as the one responsible for the degradation over time of the performance of thin-film Zernike phase plates, but in the VPP it is used in a constructive way. The exact physics and/or chemistry behind the process causing the Volta potential are not fully understood, but experimental evidence suggests that radiation-induced surface modification combined with a chemical equilibrium between the surface and residual gases in the vacuum play an important role.

https://www.pnas.org/content/pnas/111/44/15635.full.pdf

Volta potential phase plate for in-focus phase contrast transmission electron microscopy

A compact electron microscope uses a removable sample holder having walls that form a part of the vacuum region in which the sample resides. By using the removable sample holder to contain the vacuum, the volume of air requiring evacuation before imaging is greatly reduced and the microscope can be evacuated rapidly. In a preferred embodiment, a sliding vacuum seal allows the sample holder to be positioned under the electron column, and the sample holder is first passed under a vacuum buffer to remove air in the sample holder.

Compact scanning electron microscope

The invention relates to an environmental cell for use in e.g. an electron microscope. The environmental cell shows an aperture (15) for passing the beam produced by the electron microscope to a sample (6) placed inside the environmental cell. The environmental cell according to the invention is characterized in that a part of the environmental cell (14) is transparent to secondary radiation such as back-scattered electrons or X-rays. This enables the detection of this radiation by a detector placed outside the environmental cell and thus a much simpler construction of the cell.

Environmental cell for a particle-optical apparatus

Design of a hybrid double-sideband/single-sideband (schlieren) objective aperture suitable for electron microscopy

Particle-optical apparatus are normally embodied with a magnetic or electrostatic lens so as to focus a beam 1 of charged particles onto a sample 8. It is desirable to be able to use these apparatus at different beam energies. It is, however, undesirable that the focus position 9 of the beam, as a result hereof, should shift with respect to the sample 8. Use of a permanent-magnetic material 6 in a magnetic lens has advantages as regards compact construction, but is normally avoided because it is not easily possible to adjust the lens power to match varying beam energies. The invention shows how it is possible to keep constant the focus position 9, independent of the energy of the particles in the beam 1, by combining a magnetic lens - that has been furnished with permanent-magnetic material - with an electrostatic lens. The electrostatic lens is embodied in that case as an accelerating lens.

Bart Buijsse

Papers

Volta potential phase plate for in-focus phase contrast transmission electron microscopy

Compact scanning electron microscope

Environmental cell for a particle-optical apparatus

Design of a hybrid double-sideband/single-sideband (schlieren) objective aperture suitable for electron microscopy

Particle-optical apparatus with a permanent-magnetic lens and an electrostatic lens