Field-emission microscopy

[3] In FEM, the phenomenon of field electron emission was used to obtain an image on the detector based on the difference in work function of the various crystallographic planes on the surface.

A field-emission microscope consists of a metallic sample shaped like a sharp tip and a fluorescent screen enclosed within an ultrahigh vacuum chamber.

[4] The sample is held at a large negative potential (1–10 kV) relative to the fluorescent screen, which generates an electric field near the tip apex of 2-7 x 109 V/m.

The field-emitted electrons travel along the field lines and produce bright and dark patches on the fluorescent screen, exhibiting a one-to-one correspondence with the crystal planes of the hemispherical emitter.

[5] This situation can be achieved by utilizing single-molecule electron emitters,[6] and it is possible to observe molecular orbitals in single fullerene molecules using FEM.

For these reasons, refractory metals with high melting temperatures (e.g., W, Mo, Pt, Ir) are conventional objects for FEM experiments.