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lattices are related by the definitions (11). When the crystal is rotated, both the direct lattice and
the reciprocal lattice are rotated. Vectors in the lattice have dimensions of [length]; vectors in the
reciprocal lattice have the dimensions of [length]-1. The crystal lattice is a lattice in real or
ordinary space; the reciprocal lattice is a lattice in the associated Fourier space. A helpful tool for
drawing the diffracted pattern is the Ewald's construction shown in Figure 12.
21H
The spots on the right hand side and the reciprocal lattice rods represent the diffraction pattern in
the reciprocal lattice space. The vector K is drawn in the direction of the incident electron beam
and it terminates at any reciprocal point. A sphere is drawn with a radius equal to k=2π/λ about
the origin of K. The diffracted beam will be formed if this sphere intersects any other point in the
reciprocal lattice. The sphere as drawn intercepts a point connected with the end of K by a
reciprocal lattice vector G. The diffracted beam is in the direction Ki=K+∆k where ∆k= G. The
construction was demonstrated by P.P.Ewald [17]. This is because after the completion of the
growth the sample is smooth and uniform causing 2-dimensional diffraction to occur. The
diffraction spots in the reciprocal lattice space are therefore close to each other and appear in the
form of rods or streaks on the screen.
The RHEED patterns are therefore a symbolic representation of the surface morphology
of a crystal. These patterns need to be recorded to observe and record the crystal growth pattern.
These pictures can then be used for future studies to grow required semiconductor materials.
First a single sample can be grown and the RHEED images can be recorded. When it is required
to start mass production of the same semiconductor material these RHEED images can be used
to compare and predict the growth of the crystals being grown. If the samples under mass
production have RHEED images different from the earlier recorded ones, these can be discarded
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