| Comments |
"Transmission electron microscopy at present affords a resolving power of about 0.2 nanometer, roughly 500,000 times greater than that of the human eye. This is about twice the diameter of a hydrogen atom. Although the resolving power of the scanning electron microscope is only about 10 nanometers, this instrument has become a valuable tool for biologists." See Lodish et al., Molecular Cell Biology fifth edition 2004 p.190 right column 2nd paragraph: "Alternatively, the scanning electron microscope allows investigators to view the surfaces of unsectioned metal-coated specimens. An intense electron beam inside the microscope scans rapidly over the sample. Molecules in the coating are excited and release secondary electrons that are focused onto a scintillation detector the resulting signal is displayed on a cathode-ray tube (see Figure 5-50, right). Because the number of secondary electrons produced by any one point on the sample depends on the angle of the electron beam in relation to the surface, the scanning electron micrograph has a three-dimensional appearance (Figure 5-53). The resolving power of scanning electron microscopes, which is limited by the thickness of the metal coating, is only about 10 nm, much less than that of transmission instruments." See BNID 101469 |