Growth of dislocation-free silicon crystals in the 〈110〉 direction for use as neutron monochromators

Abstract

Silicon crystals are hot-pressed for obtaining increased mosaicity to achieve higher neutron reflectivities. It has been noticed that an even mosaic distribution is obtained by pressing dislocation-free Si crystals grown in the 〈110〉 direction. A new method has been proposed to grow dislocation-free Si crystals in the 〈110〉 direction in a reproducible manner. Several flared up bulges introduced into the stem are mainly responsible for getting rid of the dislocations effectively. The plausible mechanisms responsible for the diversion of axial dislocations and for eliminating them are discussed in the light of earlier studies. Study of the plastic deformation of these crystals using in-situ γ-ray diffractometry revealed that the mosaic distribution is very even, which results in higher neutron reflectivity. Thus, Si crystals grown in the 〈110〉 direction without dislocations are good starting materials for the preparation of efficient neutron monochromators.