LEED: Principle of operation:

The eqn. for λ provides the values of 2.74 - 0.87 Å for the energy range 20 to 200 eV. This is seen to be comparable with atomic spacing, suitable for diffraction condition associated with the atomic structure.

Let us consider a one dimensional chain of atoms as shown in Figure 7.02 separated by a distance a and the electron beam incident normal to the chain.

Figure 7.02: Schematic of lattice and e-beam incident.

For the constructive interference, the path difference between the wave fronts scattered by the two nearest atoms must be equal to the integral multiple of wavelengths.

where, asinθ is the path difference between two scattered waves.