Inorganic Replication in Electron Microscopy

Abstract

Contrast and resolution in electron micrographs from thin replica films are determined by the geometrical relationships between the directions of incidence of the condensing atom beam and the local surface normal, during film formation by evaporation in vacuo, and the direction of incidence of the electron beam, during subsequent exposure in the microscope. Replica films may be formed of any material suitable for vacuum evaporation. Metal atoms in general tend to stick where they strike, moving only short distances, 100 Å or less, to nucleating centers where they form small crystallites. Oxides such as silica and silicon monoxide, and also the semi‐metal germanium, form amorphous films. A portion of the incident material, about 50% in the case of silica, migrates large distances, 5000 Å or more, before finally condensing; the remainder sticks where it first strikes the surface. The existence of a minimum perceptible mass thickness difference, about 0.7 μg/cm2 for 50 kv electrons, results in an optimum replica mass thickness of about 10 μg/cm2. The resolution of the replica film is proportional to its linear thickness and hence is inversely proportional to its density. Micrographs of silica, chromium, gold‐manganin, aluminum, aluminum‐platinum‐chromium and germanium replicas are shown. The importance of stereoscopic methods in interpretation of micrographs is discussed.

Theoretical calculation of layer geometry in rotary shadowed models of membrane‐associated particles

“…In unidirectional shadowing, heavy metal accumulates on the specimen in a layer whose thickness as measured along the line of the incident metal-ion beam is constant over the whole specimen (Muller, 1942;Calbick, 1951;Moor, 1959;Misra & Das Gupta, 1965;Smith & Kistler, 1977). Figure 1 shows the relation between T (metal thickness along the incident beam), d, (thickness of the layer on a horizontal plane) and a thickness d2 (thickness of the layer on a vertical plane) which is dependent on the angle a (angle of the incident beam).…”

Carbon Replication of Particulates and Ultramicroscopic Crystals

“…Carbon replication (1) of surfaces for electron microscopy is a useful, convenient technique with wide application; it may be adapted to mount small particle dispersions for electron microscopy or to replicate the single tiny particles and crystals of such specimens. Finely divided powders have not been replicated extensively by any process, although Calbick in particular has used silica replicas in the study of size and shape of crystalline particulates in alkaline earth carbonate powders (3)(4)(5).…”