GROWTH AND CHARACTERIZATION OF C60 AND C70 CRYSTALS. Kenichi Kojima and Masaru Tachibana, Department of Physics, Faculty of Science, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama 236, Japan
The success in efficiently synthesizing fullerenes has generated much interest in the physical properties of this new class of molecular crystals. The growth of single crystals with high quality is required for studies on the intrinsic physical properties. In this work, C60 and C70 crystals of large size and high quality were grown from vapor by a continuous pulling technique, and their perfection were examined by X-ray topography and etching method.
C60 crystals of small size were used as the source material, which was deposited onto the closed end of a pyrex tube. The tube was evacuated to 1-3x10-6 Torr and then sealed off. The tube was placed in a horizontal furnace with two oppositely oriented temperature gradients, where the temperature of the middle portion of the furnace was kept at 530deg.C and its opposite sides were at 580deg.C. The tube was advanced towards the source at a pulling rate of 1 cm/day in the furnace. After 3-4 days, C60 crystals up to a size of about 8x4x3 mm3 were grown at the middle of the furnace. C70 crystals were also grown in the same way as C60. Here it was necessary to use higher temperatures of the furnace since the vapor pressure for C70 is lower than that for C60.
The perfection of the grown C60 crystals with fcc structures were examined by synchrotron topography. Some of dislocations were individually observed. Most of their Burgers vectors were identified to be 1/2<110>. Moreover, dislocation etch pits were observed by immersing the grown C60 crystals into toluene for 5 seconds. From the distribution of the etch pits, the dislocation density in most of the grown crystals was estimated to be less than 104 /cm2.
To make sure of the characteristics of defects, the mechanical properties, such as hardness and plasticity, of C60 and C70 crystals were investigated using the microindentation technique.