Field-emission microscopy

Microscopy techniques are utilized to generate magnified real-space images of the surface of a tip apex. Typically, microscopy information pertains to the surface crystallography (i.e., how the atoms are arranged at the surface) and surface morphology (i.e., the shape and size of topographic features making the surface). Field-emission microscopy (FEM) was invented by Erwin Müller in 1936. 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. ==Setup and working principle==

A field-emission microscope consists of a metallic sample shaped like a sharp tip and a fluorescent screen enclosed within an ultrahigh vacuum chamber. Typically, the tip radius used in this microscope is on the order of 100 nm, and it is made of a metal with a high melting point, such as tungsten. This situation can be achieved by utilizing single-molecule electron emitters, and it is possible to observe molecular orbitals in single fullerene molecules using FEM. Application of FEM is limited by the materials that can be fabricated in the shape of a sharp tip and can tolerate high electrostatic fields. For these reasons, refractory metals with high melting temperatures (e.g., W, Mo, Pt, Ir) are conventional objects for FEM experiments. In addition, the FEM has also been used to study adsorption and surface diffusion processes, making use of the work-function change associated with the adsorption process. ==See also==