Structural characterization of monomethylurea single crystals grown by solution methods

Monomethylurea single crystals grown by mechanical dimension limitation and top seed solution growth methods have been characterized by X-ray topograp hy and high resolution X-ray diffraction techniques. The samples showed a r elatively low defect content with typical values of the full width at half maximum of the X-ray diffraction peaks of 15 arcsec. X-ray topographs using the Cu K alpha (0 2 2) transmission setting evidence d that the seed-crystal interface is a very critical region giving rise to the formation of inclusions and grown-in dislocations. The absence of dislo cations revealed by X-ray topography in top seed grown crystals confirmed t he possibility of obtaining large volumes of crystal nearly dislocation fre e. The preparation of organic crystals for X-ray topographic characterization requires a careful preparation of surfaces. In monomethylurea single crysta ls this process is very critical leading to the formation of surface defect s which partly mask the topographic contrast from grown-in defects. (C) 200 0 Elsevier Science S.A. All rights reserved.