Single crystals of Al-Mn superlattice were grown by molecular-beam epitaxy (MBE) . The superlattice structure was examined by x-ray diffraction technique, while novel surface structures were observed in situ by reflection high-energy electron diffraction (RHEED) . Annealing experiment of Al (fcc) -Mn (fcc) superlattice was carried out and it was found that the concept of competition among some local structures could be applied to the atomic diffusion process.
Ni-contaminated surfaces of coverages less than 0.1 ML (monolayer) were studied by low-energy electron diffraction (LEED), Auger-electron spectroscopy (AES) and ion channeling and blocking spectroscopy with varying surface heat treatment. The reconstructed structures of Ni-contaminated surfaces of Si vary with the Ni-concentration in the surface, which changes depending on the heat treatment. The surface reconstructed structures on Ni-contaminated surfaces for Si (110), (100) and (111) have been discussed on the basis of our experimental results of LEED with referring to other results of scanning tunneling microscopy (STM) .
We describe the experimental method and some of the results of our recent structural studies for expanded fluids. The energy-dispersive X-ray diffraction measurements for fluid Hg have been carried out for the first time in the density range from 13.55 to 8.78 g/cm3 including the metal-nonmetal transition region. It was found that the volume expansion of liquid Hg in the metallic region, to the reduced density of about 10 g/cm3, is not accompanied by a uniform increase of interatomic distance r1 but mainly caused by a decrease of coordination number N1. When the transition region is approached the decrease of N1 becomes rather small and rl starts to elongate.