Ion Beam Source
Most widespread are instruments using liquid-metal ion sources (LMIS), especially gallium ion sources. Ion sources based on elemental gold and iridium are also available. In a gallium LMIS, gallium metal is placed in contact with a tungsten needle and heated gallium wets the tungsten and flows to the tip of the needle where the opposing forces of surface tension and electric field form the gallium into a cusp shaped tip called a Taylor cone. The tip radius of this cone is extremely small (~2 nm). The huge electric field at this small tip (greater than 1 x 108 volts per centimeter) causes ionization and field emission of the gallium atoms.
Source ions are then generally accelerated to an energy of 1–50 keV (kiloelectronvolts), and focused onto the sample by electrostatic lenses. LMIS produce high current density ion beams with very small energy spread. A modern FIB can deliver tens of nanoamperes of current to a sample, or can image the sample with a spot size on the order of a few nanometers.
Read more about this topic: Focused Ion Beam
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