ATOMIC-SCALE IMAGING OF ANISOTROPIC ORGANIC CONDUCTORS BY SCANNING PROBE TECHNIQUES (STM/AFM)

Monocrystals of the charge transfer complex of tetrathiofulvalene with tetracyanoquinodimethane (TTF/TCNQ) and the fluoranthenyl radical cation salt (FA)2PF6 were studied by scanning tunneling Microscopy (STM) and atomic force microscopy (AFM) at ambient conditions. Structures observed at the atomic scale in STM and AFM images agree well with the molecular arrangement of corresponding crystallographic planes. Patterns revealed in STM and AFM images were assigned to TTF and TCNQ stacks of the (001) surface. Comparison of results provides complementary electronic and atomic structure information. Features observed in STM images of different surfaces of (FA)2PF6 Correlate to charge density distribution assigned to fluoranthene molecules of the (011) plane forming stacks in the crystallographic a-direction. Dimerization of (FA) molecules observed in STM images has been found to be more pronounced than expected from X-ray data. Patterns corresponding to PF6- anions were observed only at certain tunneling conditions.