This paper reviews four major equipment developed at the National Physical Laboratory for growth and perfection evaluation of single crystals, namely (i) a crystal puller for growth of nearly perfect crystals by the Czochralski method; (ii) a microfocus x-ray generator; (iii) an x-ray diffraction topography camera; and (iv) a triple crystal x-ray diffractometer. The crystal puller can provide smooth, uniform and variable pulling rates. The maximum length of pull is nearly 60 cm. Efforts have been made to isolate vibrations. Nearly perfect single crystals of KCI, KBr and NaC1 with maximum diameter of ~ 60 mm have been grown. The crystals give diffraction curves with half width in the range of 10-30 sec of arc. In the projection topographs, dislocations can be resolved and characterized. The microfocus xray generator is a demountable continuously evacuated system with specially designed electron gun and anode assembly. The vacuum is continuously monitored for ease of maintenance. In the point focus mode the spot size is 40/zm on the anode. X-ray topography system is a versatile equipment used for projection and section topography. It can provide 360 ° rotations to the specimen disc around an axis perpendicular to it. Rotations of a few se¢ of arc can be given to the specimen around a vertical axis. Typical diffraction curves of a dislocation-free crystal and a crystal with boundaries are shown. Well-resolved images of dislocations are shown in a topograph as an illustration. In the triple crystal x-ray diffractometer a highly collimated and monochromated K~1 exploring x-ray beam is obtained by combining microfocus source, a special collimator and crystal monochromators of Bonse-Hart type. With this beam very narrow diffraction curves with half width of about 5 sec of arc can be recorded. Typical results of measurement of diffuse x-ray scattering (Dxs) on nearly perfect silicon single crystals are discussed. It has been observed that the contribution of phonons to the DXS is negligible. The DXS is mainly due to point defect aggregates.
