The contrast of inclusions compared with that of micropipes in back-reflection synchrotron white-beam topographs of SiC

Images of inclusions in synchrotron white-beam back-reflection X-ray topographs appear as spots of light contrast surrounded by darker rings, resembling images of micropipes, which appear as distinct white circles surrounded by dark rings. Section topographs taken across the centers of micropipes gave vertically displaced two-tailed images, arising from the helical tilt of the reflecting planes about the micropipes' screw dislocation axes. Section topographs taken across the inclusions showed no vertical displacement, only dark bars bracketing a region of depleted contrast, arising from the convex bulge of the reflecting planes lying above the inclusion. The features of the inclusion images could be reproduced in computer simulations based on the elastic displacement function of a spherical inclusion in a semi-infinite solid, and compared with others based on the displacement function of a screw dislocation in an infinite solid.