ABSTRACT
This chapter details the description of the principles of operation, design aspects, performances, and ion beam characteristics of the gas field ionization source (GFIS) and liquid-metal ion source (LMIS). The GFIS requires the use of gaseous feed materials, while the field evaporation ion source utilizes molten materials for generation of high-brightness ion beams; the latter source is commonly referred to as a liquid-metal ion source LMIS. The field ionization process usually requires fields of the order of 108 V/cm. The basic mechanisms of the field emission and field ionization processes are essentially the same and involve the tunneling of electrons from the metal into the vacuum or electrons from the atom or molecule into the surface. The LMIS utilizes either a needle or capillary that serves as the conduit for a liquid metal having a high surface tension and a low vapor pressure at its melting point.
