We investigated the surface morphology changes in a 2 inch-diameter, c-plane, free-standing GaN wafer using X-ray diffraction topography in a grazing-incidence geometry.
Plans to construct surface-analysis equipment which will be placed on beamline BL24XU of SPring-8 are presented. There are three experimental hutches in BL24XU, which are available simultaneously by using diamond monochromators as beam splitters. The purpose of the surface-analysis equipment is the simultaneous measurement of fluorescent and diffracted X-rays in grazing-incidence geometry. The instrument is equipped with a solid-state detector (SSD) and a flat position-sensitive proportional counter (PSPC) combined with analysing crystals for X-ray fluorescence (XRF) analysis. A curved PSPC and the goniometer that mounts the SSD used for XRF are also installed for X-ray diffraction. X-ray fluorescence holography and polarized X-ray emission spectroscopy modes are available, so three-dimensional images of atomic configurations and also the anisotropic structure of materials will be studied.
The Göbel mirror allows parallelization of the divergent X-ray beam leading to its higher intensity. Perfectly collimated (parallel) beam radically decreases errors of determined peak position in diffraction experiments. In the present work the Göbel mirror was applied for stress measurements using grazing incidence geometry.
Grazing incidence geometry, called MGID-sin2y, was applied to measure surface stresses in very thin layers (depth of a few mm) of Al-Mg alloy samples subjected to different thermal and mechanical treatments. The Göbel mirror was used to parallelize the incident X-ray beam. Perfect collimation of the beam significantly increases accuracy of determined peak position and consequently allows to measure low stresses in surface layers.
An X-ray prism for the extraction of a specific harmonic of undulator radiation is proposed. By using the prism in a grazing incidence geometry, the beam axes of fundamental and harmonics of undulator radiation are separated with large angles over 10 µrad, which enables the selection of a specific harmonic with the help of apertures, while keeping a high photon flux. The concept of the harmonic separation was experimentally confirmed using X-ray beams from the X-ray free-electron laser SACLA.
Surface morphology smoothing of a 2 inch-diameter GaN homoepitaxial layer observed by X-ray diffraction topography