ATOMIC SCALE SURFACE STUDIES OF CONDUCTIVE ORGANIC-COMPOUNDS .1. SCANNING TUNNELING MICROSCOPY OF TETRATHIOFULVALENE-7,7',8,8'-TETRACYANOQUINODIMETHANE (TTF-TCNQ) AND TRIETHYLAMMONIUM-TCNQ2 (TEA-TCNQ2)

The results of STM studies under ambient conditions of two conductive organic charge transfer complexes - tetracyanoquinodimethane (TCNQ) with tetrathiofulvalene (TTF) and triethylammonium (TEA) - are presented. The nature of STM images and their variations are discussed. Large scale images reveal the topographic features of monocrystals. At the atomic level the STM images consist of well-ordered patterns which permit detailed studies of electronic and molecular surface structures. For a monocrystal of TTF-TCNQ, the correspondence of STM patterns (observed on one of the monocrystal surfaces) with the atomic surface structure simulated from the crystallographic data is shown. For a TEA-TCNQ2 monocrystal, the correlation between real surface and crystallographic axes was verified by X-ray diffraction. Subsequently, this surface was imaged by STM, and the correspondence between charge density patterns and surface atomic distribution was confirmed. The peculiarities of STM imaging of charge transfer systems and an interpretation of STM images are discussed.