title: Minimizing electrostatic charging of an aperture used to produce in-focus phase contrast in the TEM.
abstract: Microfabricated devices designed to provide phase contrast in the transmission electron microscope must be free of phase distortions caused by unexpected electrostatic effects. We find that such phase distortions occur even when a device is heated to 300 °C during use in order to avoid the formation of polymerized, carbonaceous contamination. Remaining factors that could cause unwanted phase distortions include patchy variations in the work function of a clean metal surface, radiation-induced formation of a localized oxide layer, and creation of a contact potential between an irradiated area and the surround due to radiation-induced structural changes. We show that coating a microfabricated device with evaporated carbon apparently eliminates the problem of patchy variation in the work function. Furthermore, we show that a carbon-coated titanium device is superior to a carbon-coated gold device, with respect to radiation-induced electrostatic effects. A carbon-coated, hybrid double-sideband/single-sideband aperture is used to record in-focus, cryo-EM images of monolayer crystals of streptavidin. Images showing no systematic phase error due to charging are achievable under conditions of low-dose data collection. The contrast in such in-focus images is sufficient that one can readily see individual streptavidin tetramer molecules. Nevertheless, these carbon-coated devices perform well for only a limited length of time, and the cause of failure is not yet understood.
authors.affiliation: Life Sciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720, USA. Electronic address: rmglaeser@lbl.gov.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Glaeser
authors.forename: Simone
authors.initials: S
authors.lastname: Sassolini
authors.forename: Rossana
authors.initials: R
authors.lastname: Cambie
authors.forename: Jian
authors.initials: J
authors.lastname: Jin
authors.forename: Stefano
authors.initials: S
authors.lastname: Cabrini
authors.forename: Andreas K
authors.initials: AK
authors.lastname: Schmid
authors.forename: Radostin
authors.initials: R
authors.lastname: Danev
authors.forename: Bart
authors.initials: B
authors.lastname: Buijsse
authors.forename: Roseann
authors.initials: R
authors.lastname: Csencsits
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Downing
authors.forename: David M
authors.initials: DM
authors.lastname: Larson
authors.forename: Dieter
authors.initials: D
authors.lastname: Typke
authors.forename: B G
authors.initials: BG
authors.lastname: Han
mesh_terms: D002244:Carbon / Q000737:chemistry; D046529:Microscopy, Electron, Transmission / Q000295:instrumentation* / Q000379:methods*; D055616:Microtechnology; D011487:Protein Conformation; D055672:Static Electricity; D019809:Streptavidin / Q000737:chemistry
chemical_list: D002244:Carbon; D019809:Streptavidin
keywords: Charging; Cryo-EM; Phase contrast; Phase plate