Field-ion Microscope

Name:
Field-ion Microscope
Detailed information:
A type of microscope whose unique feature is that it has no lens system. Invented by Muller in 1951, it is capable of resolving metal atoms 2–3 Å in diameter. Its essential components are an evacuated glass chamber through which runs a wire carrying an electric impulse of 30,000 volts that establishes a field strength of 500 million volts/cm. A specimen of the metal to be observed, which is machined to an extremely fine tip and is positively charged, is connected to the wire. An inert gas such as helium or neon is then admitted. The positively charged tip of the specimen attracts electrons from the helium atoms, creating positive helium ions. These are strongly repelled by the metal atoms and stream to the negatively charged fluorescent screen, producing an image of the individual atoms of the metal. Magnifications of one million times or more have been obtained of atoms of indium, tungsten, and others.See Electron Microscope.