New X-Ray Topographic Technique for Detection of Small Defects in Highly Perfect Crystals

A new topographic method is described to obtain kinematical images of small defects in highly perfect crystals. In this method, x rays diffracted by strain fields around defects are recorded separate from those by perfect regions of crystals. The capability of the method is demonstrated by observing some small defects in a dislocation-free Si crystal which cannot be revealed by Lang and Borrmann topographic techniques. The observed images are due to defects which are revealed as shallow pits by the Sirtl etching. By assuming that the defects are dislocation loops, their sizes are roughly estimated: the majority of the defects is less than 5000 Å in size. It is concluded that the present technique is capable of detecting short-range strains in crystals which are very small compared with extinction distances.