MELT GROWTH AND CHARACTERIZATION OF 2-METHYL-4-NITROANILINE CRYSTALS. Masaru Tachibanaa, Masaaki Satob, Kenichi Kojimaa, aFaculty of Science and bGraduate School of Integrated Science,Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama 236, Japan
Recently considerable interest has developed for organic materials with extremely high optical nonlinearities. In particular, 2-methyl-4-nitroaniline (MNA) is one of the most promising materials for nonlinear optical devices. The growth of single crystals with large size and high quality is important for accurate characterization and technical applications of the materials. In this work, MNA single crystals were grown from melt by Bridgman method, and their perfection was examined by X-ray topography.
MNA powder was well-purified not only by sublimation at 90deg.C but also by zone-refining, where its melting point is 132deg.C. The purified powder was deposited in a pyrex tube. The tube was placed in a vertical Bridgman furnace with two temperature zones, where the temperatures of upper zone and lower zone were kept at 139deg.C and at 110deg.C, respectively. The material in the tube was completely molten at the upper zone. The molten material was crystallized at the lower zone by slowly pulling down the tube at the rate of 0.8 mm/h. After the crystallization, the crystal was cooled down to room temperature at 0.5deg.C/h. Consequently single crystals with cylindrical shapes of 5 mm diameters were grown in the tubes. Large volumes of the crystals were optically clear and appeared pale yellow. The perfection of the grown crystals was examined not only by projection topography but also section topography. As a result, the crystal defects, especially dislocations, were characterized.
In addition, the nonlinear optical properties of the grown MNA crystals were investigated by the measurements of second harmonic generation (SHG).