Control of radiation damage in the TEM.

Contrast has traditionally been produced in electron-microscopy of weak phase objects by simply defocusing the objective lens. There now is renewed interest, however, in using devices that apply a uniform quarter-wave phase shift to the scattered electrons relative to the unscattered beam, or that generate in-focus image contrast in some other way. Renewed activity in making an electron-optical equivalent of the familiar “phase-contrast” light microscope is based in part on the improved possibilities that are now available for device microfabrication. There is also a better understanding that it is important to take full advantage of contrast that can be had at low spatial frequency when imaging large, macromolecular objects. In addition, a number of conceptually new phase-plate designs have been proposed, thus increasing the number of options that are available for development. The advantages, disadvantages, and current status of each of these options is now compared and contrasted. Experimental results that are, indeed, superior to what can be accomplished with defocus-based phase contrast have been obtained recently with two different designs of phase-contrast aperture. Nevertheless, extensive work also has shown that fabrication of such devices is inconsistent, and that their working lifetime is short. The main limitation, in fact, appears to be electrostatic charging of any device that is placed into the electron diffraction pattern. The challenge in fabricating phase plates that are practical to use for routine work in electron microscopy thus may be more in the area of materials science than in the area of electron optics.

/pdf/invited-review-article-methods-for-imaging-weak-phase-49fkbjae9p.pdf

Invited Review Article: Methods for imaging weak-phase objects in electron microscopy

Choice of operating voltage for a transmission electron microscope.

https://hal.archives-ouvertes.fr/hal-01922227/document

Demonstration of a 2 × 2 programmable phase plate for electrons

Phase plates are a new technique in the field of cryo-electron microscopy. They provide improved contrast and signal-to-noise ratio in images of radiation sensitive specimens. Thin film phase plates are being tested in biological applications and have demonstrated benefits for single particle analysis and cryo-tomography. There are still unsolved problems, such as reliability of manufacturing and deterioration of performance with time. Several other types of phase plates are currently under development and may become available for cryo-microscopy in near future. Presented is a short overview of the current state of the field as well as ideas for the future directions. Also included is a detailed description of the instrumentation requirements and the experimental procedures for phase plate application.

W.K. Hsieh

Papers

Imaging of soft and hard materials using a Boersch phase plate in a transmission electron microscope