Electron Microscopy Quotes

It is pathetic to watch the endless efforts—equipped with microscopy and chemistry, with mathematics and electronics—to reproduce a single violin of the kind the half-literate Stradivari turned out as a matter of routine more than 200 years ago.

Long before the idea of scanning specimens with a small spot of light produced confocal light microscopy, the idea of using a small spot of electrons to scan surfaces had been around for as long as electron microscopy itself. A surface demarcates the boundary of a solid, and is the site of interaction with the surrounding environment, from a ball bearing to a living cell. In the mechanical world, adhesion, friction, wear, and corrosion are all dependent upon surface properties. The smooth surface of a ball bearing is crucial in the reduction of friction, but its efficiency may well be compromised by wear or corrosion.

It has been estimated that a career electron microscopist who spends his working days preparing, sectioning and staining, observing, and recording biological material will get through the equivalent of one cubic millimetre of tissue in a forty-year working lifetime.

So far we have considered the effects of varying the type of illumination, so at this point we can sum up how one specimen can be imaged in four separate ways. In a conventional microscope with bright field illumination, contrast comes from absorbance of light by the sample (Figure 7a). Using dark field illumination, contrast is generated by light scattered from the sample (Figure 7b). In phase contrast, interference between different path lengths produces contrast (Figure 7c), and in polarizing microscopy it is the rotation of polarized light produced by the specimen between polarizer and analyser (Figure 7d). This is ‘converted’ into an image that has colour and a three dimensional appearance by the use of Wollaston prisms in differential interference microscopy. For virtually any specimen, hard or soft, isotropic or anisotropic, organic or inorganic, biological, metallurgical, or manufactured, there will be a variety of imaging modes that will produce complementary information. Some of the types of light microscopy we have looked at above have direct parallels in electron microscopy (Chapter 4).

The advent of low temperature scanning EM led to a study by Bill Wergin and colleagues from NASA in which they collected samples from different types of snow cover found in the prairies, taiga (snow forest), and alpine environments. With snow depths up to a metre, various layers occurred in which the crystals underwent a change in their microscopic shape from the original freshly fallen crystals, to the development of flat faces and sharp edges. It is this metamorphosis of lying snow that determines the likelihood of avalanches, which can be predicted from the crystal structures at various depths. Although scanning EM (electron microscopy) is hardly available as a routine assay in distant mountain regions, this work helped in the use of microwave radiology investigation of the snow water equivalent in the snow pack, as large snow crystals scatter passive microwave more than small crystals. Smaller and more rounded crystals of snow do not interlock, and can slide more easily over each other, increasing the risk of avalanches.