The Electron Microscope as an Illustration of the （电子显微镜的插图）.pdf

Science Teachers’ Workshop 2000 The Electron Microscope as an Illustration of the Wave Nature of the Electron Professor David R McKenzie University of Sydney (mckenzie@physics.usyd.edu.au) Introduction The transmission electron microscope uses principles that originated in light microscopy and which therefore rely on the properties of waves. We will illustrate these principles using the electron microscope. The Wave Nature of the Electron Light has been shown to have particle like properties when it is absorbed, as for example, in the photoelectric effect. Electrons, which are normally thought of as particles, have a wave-like character in their propagation and show all of the phenomena normally associated with waves. Wavelike phenomena include interference and diffraction. The electron microscope provides an ideal opportunity to illustrate the wave-like character of the electron. In fact, the very operation of the electron microscope relies on the properties of waves. The Electron Lens The electron is one of a family of particles called the Leptons. Leptons are fundamental particles which do not appear to be made up of other constituent particles. In this respect they are different to the particle family called Baryons, which includes the neutron and the proton. The neutron and the proton have a fine structure which is made out of quarks and gluons. The electron is a negatively charged lepton. The negative charge of the electron enables us to focus a parallel beam of electrons to a point and thereby produce a lens. An electron lens is shown in Figure 1. Figure 1. The Illustration on the left shows how a magnetic field (B) deflects an electron travelling with velocity (v) by means of the magnetic force (F). Note that the plane containing the optical axis and the electron trajectory is rotated a