New Possibilities of Diffraction Topography at Third Generation Synchrotron Radiation Facilities

Abstract

Third generation synchrotron radiation (SR) facilities like the ESRF provide new experimental possibilities for diffraction topography. Some of them are straightforward; the high energy photons (50–120 keV) allow the investigation of heavy and/or bulky samples in transmission, and the photon flux is such that real-time experiments at the 0.01 s time scale are feasible. However the availability of high energy photons and the brilliance of the source have additional consequences. The high energy photons are associated with a small intrinsic diffraction width, and consequently with the possibility of studying defects inducing very weak distortion fields. On the other hand, the high brilliance corresponds to a small source size with dimensions in the 0.1 mm range for the ESRF ID19 wiggler ‘topography’ beamline, devoted to imaging and high resolution diffraction. The ID19 experimental station is relatively far away from the source, at 145 m, to compensate for the small opening angle of the radiation (Baruchel, Draperi and Zontone 1993. The “geometrical” resolution of topographs d×S /D (S being the source size, D the source-to-sample and d the sample-to-detector distances) is thus greatly improved compared with the topographic stations at older SR machines. Practically, this enhanced geometrical resolution allows observation of details in the topographs with an acceptable resolution (less than 10 µm) at distances as great as one meter from the sample, and consequently the use, as a new parameter, of the crystal to detector distance to characterize a given defect.