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This chapter provides an introduction to field emission, field ionization, and field desorption. The application of a sufficiently high electric field to a solid surface will result in the emission of electrons or ions. Field electron emission occurs when a negative electric field of 3···6 V/nm is applied to a metal or semiconductor surface. Although field emission from solids into liquids has been observed, the most widely studied cases involve emission from a solid surface into a vacuum. Field emission relies on the quantum-mechanical process of electron tunneling for which there is no classical analog. Field ion emission results when a positive electric field, approximately an order of magnitude larger than electron emission fields, is applied to a solid in the presence of a background gas. The applied electric field ionizes atoms of the background gas and projects them away from the surface. As in the case of field emission, the field ionization process involves quantum-mechanical tunneling, but in field ionization the electron tunneling is in the reverse direction. Field desorption refers to the process in which an applied positive field causes ionization and desorption of surface atom. If the desorbed ions originate from surface atoms of the sample material, the process is often referred to as field evaporation. One distinction between field ionization and field desorption (or evaporation) is related to the region where ionization takes place. |
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