Study of the Surface Morphology and Inclusions of Heavy Metals in Basal-Faceted Sapphire Ribbons Using In-Line X-Ray Phase-Contrast Imaging

Abstract

This study presents the results of research concerning microsteps on the surface and the inclusions of heavy metals in the volume of sapphire ribbons grown using Stepanov’s method. Basal-faceted sapphire ribbons exhibit a low density of steps, which are caused by small changes in the orientation of the growth surface or the thickness of the ribbon. Phase contrast imaging using synchrotron radiation is employed to study the defects. It is shown for the first time that the height of a step of 1 µm can be determined directly from the image. An analytical solution for the intensity distribution of the step in the case of fully coherent X-ray radiation is obtained. When the phase shift is small, there is a direct proportionality between contrast and step height, and the inverse problem is easily solved. The height obtained using the phase-contrast-imaging method is confirmed by measurements using atomic force microscopy. To analyze microinclusions, a computer simulation program is used, which allows for assessment of their sizes. We find that the experimental contrast matches the theoretical calculations only if the calculated intensity profile is convolved with a Gaussian function. The full width at half maximum of the Gaussian is independently obtained from preliminary measurements.