Abstract
The research of this thesis is an investigation of interference effects in wide-angle incident X-ray waveguides. Usually, the conventional waveguides make an incident X-ray beam couple into a waveguide from the side or the front of a waveguide at grazing or normal incident condition. However, this incident geometry cannot be applied to cases involving a large-angle incident X-ray beam. For solving this problem, here we propose to use a surface diffraction beam of (113) reflection to guide X-rays at wide-angle incidence. Using the micro-electronic lithographic process, we etched a 4-inch [001] silicon wafer with a stripe structure along [110]. Each stripe was 250μm in height, 2cm in length, and the width varying from 5μm to 100μm. The etched wafer was then plated with gold by thermal evaporation to about 300nm in thickness on the top and bottom sides of the crystal. The stripe surrounded by gold films acted as an X-ray waveguide. In the diffraction experiment, we guided the 8878eV photons at the incident angle of 50.48 deg. into the waveguide via the (113) surface reflection. The surface diffracted (113) beam then propagated in the [110] direction. Subsequently, 2θscans of the (113) at the exit of waveguide were performed and X-ray interference fringes coming from the waveguide were detected for the photon energies ranging 8878eV ± 350eV.For theoretical analysis, we used the dynamical theory of X-ray diffraction in a Cartesian coordinate system to calculate mode of wave-propagation, wavevectors, wavefield amplitudes, and intensities. We found that when the photon energy increased, the intensity ratio between the zeroth-order maximum (the central bright band) and the first-order maximum decreased and the interference effect became more pronounced. This result was qualitatively in good agreement with the experiment. The physical mechanism is that in this Au-Si-Au sandwich waveguide structure the diffraction beam of (113) consists of two modes of wave-propagation dominant in the waveguide and the interaction of the two modes gives the interference patterns observed in the experiment. Moreover, the tunable photon energy range of this kind X-ray waveguides is 8878eV ± 350eV.