X-ray-interferometric determination of angstrom-scale lattice shifts at the surface of silicon crystals - the analogue to light-optical interference microscopy

摘要

The paper presents a new imaging method based on a refined and better stabilised X-ray Michelson interferometer [APPEL, BONSE]. Interference fringes are detected which mark local Angstrom-scale shifts of the lattice at the surface of the interferometer's phase-shifter crystal. Conventional double-crystal topography (DCT), lacking phase information of the beam reflected by the specimen crystal, does not detect mere lattice shifts. The new method appears to be also more sensitive to any combined lattice strain delta = Delta d/d + cot theta(B) Delta theta (theta(B): Bragg angle, d: lattice parameter) present in the crystal layer contributing to the surface Bragg reflection. delta is known to be the dominant part of the DCT image [BONSE, 1958; BONSE, HARTMANN]. The technique presented here is the X-ray analogue to the well known light-optical interference microscope. A possible application is the testing of silicon crystals for minute lattice imperfections causing lattice-incoherent positions of atoms in a surface layer of typical 1 to 10 mu m thickness. For instance striations, which under certain conditions arise during crystal growth, cause such incoherence. [References: 18]