Influence of beam coherence on measurements of roughness in film growth

Diffracted intensity oscillations in epitaxial growth are discussed in terms of the existing roughness scale on the surface and the coherence length of the radiation used to measure them. It is shown that for systems with unbounded interface width growth, the greater the coherence length, the more rapidly the oscillations damp out. On the other hand, oscillations can occur and be persistent if the coherence length of the beam is much shorter than the characteristic horizontal length scale for roughness, even in the case where unbounded growth is present. This behavior is governed by the magnitude of the coherence length of the beam, relative to the lateral length scale that characterizes the surface structure.