Synchrotron-radiation plane-wave GID topography (abstract)

Abstract

X-ray-diffraction topography is a traditional tool for investigating the real structure of crystals and provides high sensitivity to lattice constant variations with good space resolution. However, recent advances in technology and the growing importance of surface regions of single-crystal and multilayer systems require new approaches to this method, which are made possible by the high brightness and wide tunability of synchrotron radiation. In this work the SR plane-wave grazing-incidence diffraction (GID) topography is discussed as an effective tool for depth-resolved investigations of near-surface defect structures in single crystals and epitaxial layers. The favorable properties of synchrotron radiation enable one to avoid the usual limitations on applicability of this diffraction geometry and investigate all classes of defects in real materials. The experiments were performed at the beamlines ROEMO1 and CEMO of HASYLAB, using double-crystal Ge/asymmetric Si monochromators. The image formation of near-surface dislocations and the effects of refraction on rough surfaces were investigated. Oblique diffraction planes were used to compare the topography in skew incoplanar and coplanar geometries. The latter is shown to be more effective, as it utilizes the wavelength tunability of SR and allows one to vary the diffraction conditions in a wide range from usual highly asymmetric to grazing incidence below the critical angle of total external reflection (and the penetration depth from hundreds to tens of nanometers) without off-plane rotations and provides pictures free of complicated geometrical distortions. The dislocation images at different diffraction conditions proved to be qualitatively the same for near-surface defects, while the structure distortions, produced by the defects in the underlying layers, become invisible at grazing incidence, due to both depth resolution of the method and inevitable loss of lattice-parameter resolution. This might be a substantial advantage for characterization of films on substrates with a low perfection. Thus SR based plane-wave GID topography provides all the features of usual asymmetric topography and has substantial advantages for surface defect analysis.