Page 158 - Introduction to Colloid and Surface Chemistry

The solid-gas interface 147

Fluorescent
screen
Observation
window

Electron gun
(monoenergetic
Crystal
collimated
source
UHV
chamber
Grids

Figure 5.18 Schematic illustration of a LEED apparatus

tional to the spacings between the scattering sources. The resulting
LEED pattern (as with any other diffraction pattern), therefore,
shows the surface net in 'reciprocal space' rather than directly, as
illustrated in Figure 5.21.
The C (2 x 2) surface layer shown in Figure 5.21b is, in effect, two
slightly displaced (2 x 2) surface layers, the first as shown and the

Incident Scattered
electrons
electrons

Figure 5,19 Diffraction by a row of atoms for normal incidence