field ion microscope abbr., FIM (rus. микроскопия, полевая ионная abbr., ПИМ) — microscopy technique used to image the surface of a needle-shaped specimen with the help of field desorption of atoms of an "imaging" gas that are adsorbed by the examined surface .

Description

Field ion microscopy was invented by E. Muller in 1951. A field ion microscopy assembly is depicted in Fig. 1a. Its key elements include a specimen in the shape of sharp needle with positive potential of 1-10 keV applied to it and a fluorescent screen that has been replaced in modern assemblies by a microchannel plate, both placed in a vacuum chamber. The chamber is backfilled with an imaging gas, usually helium or neon, at pressure of 10-5 to 10-3 torr. The specimen is cooled to very low temperatures (~20–80 К).

The imaging technique is illustrated in Fig. 1b. Imaging gas around the tip is polarised in an electric field, and while the field is not uniform, polarised atoms are attracted to the needle surface. Adsorbed atoms may become ionised due to the tunnelling of electrons into the tip, and the ions are accelerated by the field in the direction of the screen, creating an image of the emitting surface on it. A field ion microscope’s resolution depends on the thermal speed of imaging ion and may reach 0.1 nm (i.e., atomic resolution) when the tip is cooled to very low temperatures (see Fig. 2).

Tip material limitations are the same as those of the field emission microscope. Hence, most research activities involving field ion microscopes are conducted on metals with high melting points (W, Mo, Pt, Ir). The most interesting results obtained using the field ion microscopy technique are associated with the study of the dynamical behaviour of surfaces and the behaviour of atoms on surfaces. The problems studied include adsorption and desorption, surface diffusion of atoms and clusters, step motion, equilibrium crystal shape, etc.

Illustrations

Fig. 1. а — Field ion microscopy trial plant; b — schematic diagram depicting the microscope im
Fig. 1. а — Field ion microscopy trial plant; b — schematic diagram depicting the microscope imaging process [2].
Fig. 2. Field ion microscope image of a tungsten tip with the radius of ~12 nm obtained at the
Fig. 2. Field ion microscope image of a tungsten tip with the radius of ~12 nm obtained at the temperature of 21 K [3].

Authors

  • Zotov Andrey V.
  • Saranin Alexander A.

Sources

  1. Oura K. et al. Surface Science: An Introduction // Springer, 2010 - 452 pp.
  2. Tsong T. T., Chen C. Dynamics and diffusion of atoms at stepped surfaces // The chemical physics of solid surfaces. — Amsterdam: Elsevier, 1997. V. 8: Growth and properties of ultrathin epitaxial layers / Ed. by D.A. King, D. P. Woodruff. P. 102–148.
  3. Tsong T. T., Sweeney J. Direct observation of the atomic structure of W(100) surface // Solid State Commun. 1979. V. 30, №7. P. 767–770.

Contact us