Field Emission Microscope (FEM)
The field emission microscope was invented by Erwin Mueller in 1936.
This instrument approached, for the first time, to view a surface on
a scale of atomic dimensions and yet simultaneously allowed one to
follow
rapid changes at the surface.
In its simplest form, FEM consit of a shap needle emitter and a
fluorecent
screen as shown in Fig. 1. By appling negative field to the emitter,
electrons are emitted from the surface of the emitter to the direction
of the screen. The image contrast appears due to the difference in
current densities of electron, which originated from the difference in
work functions and electric field on the emitter surface
(Fowler-Nordheim
relation).
An example of a FEM image is shown is Fig. 2 together with a FIM image
from the identical surface. While FIM prives atomic image of the
surface,
FEM provide current density variation emitted form the surface.
Fig. 2 FEM and FIM images of a clean Ni surface. Both images were
obtained
from the identical surface of a Ni tip. (Curtsy of K. Hono, NRIM)
General References
-
R. Gomer, Field Emission and Field Ion Microscopy, Harvard
University Press,
(1961).
-
E. W. Mueller, Modern diffraction and imaging techniques in materials
science, eds. S. Amelinckx, R. Gevers, G. Remault and J. Van Landuyt,
North Holland, Amsterdam.
