title: Paraxial charge compensator for electron cryomicroscopy.
abstract: We describe a multi-hole condenser aperture for the production of several electron beams in the transmission electron microscope (TEM) making it possible to simultaneously image and irradiate spatially separated regions of a specimen. When the specimen is a thin film of vitreous ice suspended over a holey carbon film, simultaneous irradiation of the adjacent carbon support with the off-axis beam compensates for some of the effects of charging in the image formed by a beam irradiating only the ice. Because the intervening region is not irradiated, charge-neutralization of frozen-hydrated specimens can occur by a through-space mechanism such as the emission of secondary electrons from a grounded carbon support film. We use paraxial charge compensation (PCC) to control the amount of charge build-up on the specimen and observe the effects of charge on images. The multi-hole aperture thus provides a tool for investigating the mechanism of charging and charge mitigation during the imaging of radiation sensitive biological specimens by cryomicroscopy.
authors.affiliation: Division of Physical Biochemistry, MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London, NW7 1AA, United Kingdom.
authors.forename: John A
authors.initials: JA
authors.lastname: Berriman
authors.forename: Peter B
authors.initials: PB
authors.lastname: Rosenthal
mesh_terms: D002244:Carbon; D020285:Cryoelectron Microscopy / Q000295:instrumentation*; D007053:Ice; D046529:Microscopy, Electron, Transmission; D013048:Specimen Handling
chemical_list: D007053:Ice; D002244:Carbon