The present status of the ESRF diffraction topography beamline: new experimental results

The source characteristics of third-generation synchrotron radiation machines lead to enhanced possibilities for diffraction topographic techniques: real-time observations, high-resolution experiments, investigation of heavy or bulky materials using short wavelengths and the possibility of using large sample environments. We describe the instrumentation of the ESRF ID19 'Topography and High Resolution Diffraction Beamline', which has been designed to take advantage of these new experimental possibilities. Experiments performed, in white and monochromatic beam, on two other beamlines of the ESRF illustrate these new possibilities. They show that (i) typical exposure times for white-beam topography (down to about 10 -2 s) are about 10 2 -10 3 times shorter than at other synchrotron radiation topographic set-ups, (ii) the divergence of the diffracted beam is small enough to retain good spatial resolution when placing the film far (up to 1 m) from the sample, (iii) with short wavelengths (about 10 pm and less) it is possible to carry out topographical investigations of bulky or heavy samples or to detect weak long-range deformation fields of defects and (iv) 'low-divergent wave' or 'weak-beam' monochromatic beam topographs can be recorded in a few seconds. Sample-heating effects are observed in white-beam topography even for materials that are not highly absorbing or thermally insulating. A simple criterion for observation of these effects is presented and tested.