Some experimental artifacts in low energy electron diffraction studies of phase transitions

Low energy electron diffraction (LEED) is an important experimental technique for the study of continuous order—disorder phase transitions. Extraction of the critical exponents and their associated amplitudes requires an accurate determination of the single-scattering intensity versus the parallel component of the scattering vector. Interpretation of measured intensities is complicated by multiple scattering, variation of the scattering factor, and thermal vibrations. These can cause the measured intensity profiles to be skewed and can add substantial intensity which is peaked at the Brillouin zone center. An example of a subsidiary structure induced by multiple scattering is given for Au(110). The effects on the measured critical exponents β,ϒ, and v are shown to be small in most cases. However, the amplitudes associated with these exponents, such as the correlation length can be seriously affected. Some of these effects also occur in other diffraction methods.