ULTRAHIGH-VACUUM FACILITY FOR HIGH-RESOLUTION GRAZING-ANGLE X-RAY-DIFFRACTION AT A VERTICAL WIGGLER SOURCE OF SYNCHROTRON-RADIATION

A versatile ultrahigh-vacuum chamber has been designed for grazing ang le X-ray standing-wave and diffraction experiments at the vertical wig gler source of the Photon Factory. Unlike at other sources, the vertic ally polarized X-rays from the wiggler favour the use of a horizontal scattering geometry. The X-ray chamber is equipped with a hemispherica l beryllium window, which allows any scattering angle to be attained a nd secondary emissions to be measured. The chamber is of a compact des ign, sitting on a precision rotary table which is rotated for scans. S amples are introduced from a portable vessel. The whole procedure can be performed in a vacuum better than 10(-7) Pa. The system has success fully been applied to a grazing-angle X-ray standing-wave experiment, which determined the dimer bond length and the domain structure of Si( 001) surfaces deposited with monolayer arsenic.