Interpretation of scanning tunneling and atomic force microscopy images of TCNQ salts

The surfaces of the TCNQ salts TTF-TCNQ, Qn(TCNQ)2, 4EP(TCNQ)2 and TEA(TCNQ)2 (TCNQ=tetracyanoquinodimethane, TTF=tetrathiafulvalene, Qn=quinolinium, 4EP=4-ethyl-N-methylpyridinium, TEA=triethylammonium) were examined by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The STM and AFM images of these salts were interpreted on the basis of the ρ(r0, ef), and ρ(r0) plots of their molecular layers calculated with the extended Hueckel tight-binding electronic structure method. The present work shows that a close interplay between experiment and theory is necessary for the rational surface analysis with STM and AFM. (orig.)