Scanning Electron Microscopy

Abstract

Scanning electron microscopy (SEM) has a history almost as old as TEM, but the development of a commercial product took much longer. (1938) built the first SEM, and (1942) produced an SEM with a 50-nm probe. A group in Cambridge, England headed by Oatley began work in 1948 that led to the first commercial SEM (the Cambridge Stereoscan) in 1965. (1963) achieved a beam diameter of 5nm, which resulted in 10-nm resolution. With the introduction of the Cambridge Stereoscan in 1965, the biological Community immediately began exploiting the tool to examine numerous tissues and cells. During the 1970s, resolution was improved to 5–6 nm, microprobe analysis (EDS) was applied to SEMs, freeze-fracture methods were explored (Haggis, 1972), and magnifications of over 100,000 × became a reality. The 1980s saw the introduction of FEGs in commercially produced SEMs offered by Hitachi and then JEOL, which allowed lower accelerating voltages and increased magnification and resolution (under 1 nm) and which were immediately adopted by materials scientists. A major technological advance occurred in 1986, when Cambridge Instruments introduced the first digital SEM. This allowed images to be stored and transmitted as digital files, allowed several independently captured images to be averaged to minimize charging artifacts, and led to the contemporary assortment of SEMs operated through a Microsoft Windows™ environment, which has provided a user platform that is accessible to most scientists at work today. By the late 1980s, biologists had discovered FEG instruments and were examining tissues and cells at low voltages with high magnifications previously possible only with sectioned material viewed with a TEM (Ris, 1991). The 1980s and 1990s also saw improvements in probe diameters for microanalysis along with better instrument sensitivity, allowing recognition of elements with lower Z-numbers than previously possible (see Chapter 14).