An interpretation for the STM imaging of an organic molecule, tetrathiafulvalene - tetracyanoquinodimethane (TTF - TCNQ)

The surface morphology of a tetrathiafulvalene - tetracyanoquinodimethane (TTF - TCNQ) thin film deposited on a mica substrate in high vacuum was studied with molecular resolution by scanning tunneling microscopy (STM). On the basis of highly reproducible STM images of the TTF - TCNQ surface, it has been confirmed that there exist two types of molecular image, an acute-angle chevron type and an obtuse-angle chevron type, changing from time to time in each molecular row during scanning. Here we present an interpretation for such STM images from the viewpoint of the relative phase difference of the molecular orbital of each organic molecule for the first time.