ATOMIC SCALE SURFACE STUDIES OF CONDUCTIVE ORGANIC-COMPOUNDS .3. SCANNING TUNNELING MICROSCOPY STUDIES OF MONOCRYSTALS OF BIS(ETHYLENEDITHIO)TETRATHIOFULVALENE WITH TRIIODIDE, BETA-ET2I3

Scanning tunneling microscopy (STM) was applied to monocrystals of an organic superconductor, the charge transfer salt of bis(ethylenedithio)tetrathiofulvalene with triiodide, beta-ET2I3, under ambient conditions. The obtained results reveal details of the charge distribution on the surfaces of differently shaped monocrystals. The periodicity of STM patterns obtained from the largest face of an elongated plate-like monocrystal is compatible with that of the crystallographic (001) plane. The STM patterns are therefore compared to drawings of corresponding computer-simulated models based on known crystallographic data. The imaged surface layer seems to consist of I3- anions. This interpretation agrees with the assumption that the central iodine atom of the anion has a higher charge density than the adjacent atoms. STM images of a surface of another (block-like) monocrystal display a pattern which is compared with the atomic arrangement in the (001) plane of the crystallographic structure. Well-separated linear patterns may be interpreted as a visualization of two-dimensional conductive layers parallel to the (001) plane.