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Platinum/iridium/carbon: a high‐resolution shadowing material for TEM, STM and SEM of biological macromolecular structures
Author(s) -
Wepf Roger,
Amrein Matthias,
Bürkli Urs,
Gross Heinz
Publication year - 1991
Publication title -
journal of microscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0022-2720
DOI - 10.1111/j.1365-2818.1991.tb03159.x
Subject(s) - scanning electron microscope , materials science , resolution (logic) , transmission electron microscopy , iridium , macromolecule , layer (electronics) , analytical chemistry (journal) , carbon fibers , nanotechnology , chemistry , chromatography , composite material , organic chemistry , biochemistry , artificial intelligence , composite number , computer science , catalysis
SUMMARY Thin Pt/Ir/C coating films (1.5 nm) show a fine granularity and provide a high structural resolution in the transmission electron microscope (TEM) when applied to freeze‐dried biological macromolecules. They keep their structure when exposed to atmospheric conditions, without the need of an additional stabilizing carbon layer, in contrast to conventional high‐resolution shadowing materials such as Ta/W and Pt/C. However, the correct ratio of the components has turned out to be crucial. When evaporating Pt/Ir/C from the source electrode in an electron‐beam‐heated evaporator, the ratio of the three elements changes progressively, and, consequently, the properties of such films depend strongly on the mass that has been pre‐evaporated. In this paper we present a quantitative analysis of the composition of Pt/Ir/C films by wavelength‐dispersive X‐ray analysis (WDX) undertaken in association with TEM experiments. We applied Pt/Ir/C shadowing to two regular biological test specimens, the phage T4 type III polyhead and the HPI‐layer of Deinococcus radiodurans. It turns out that Pt/Ir/C films containing at least 25% C are three‐dimensionally stable on the freeze‐dried macromolecular samples. By the dramatically improved resolution power of the latest scanning electron microscopes (SEM) and the invention of the scanning tunnelling microscope (STM), two new surface‐sensitive tools for the investigation of biological macromolecular structures became available. The Pt/Ir/C coating has proved to be well suited for STM and SEM imaging of freeze‐dried biological structures because of its good electrical conductivity and its direct three‐dimensional stability. We compare STM, SEM and TEM images of freeze‐dried and Pt/Ir/C‐coated polyheads.