 However, unlike in a LEED experiment where the sampled surface area is some square millimeters, one inserts the illumination and the beam aperture into the beam path while imaging a surface and thus reduces the size of the sampled surface area.The chosen area ranges from a fraction of a square micrometer to square micrometers.If the surface is not homogeneous, a diffraction pattern obtained from LEED experiment appears convoluted and is therefore hard to analyze.