Charge Distribution in the Surface BEDT-TTF Layer of α-(BEDT-TTF)2I3 at Room Temperature with Scanning Tunneling Microscopy

The charge distribution in the surface BEDT-TTF layer of the alpha-(BEDT-TTF)(2)I-3 crystal with the charge disproportionation state at room temperature was studied in detail by a scanning tunneling microscope (STM), where BEDT-TTF (abbreviated as ET) is bis(ethylenedithio) tetrathiafulvalene. The obtained molecular charge distribution in the surface ET layer suggests that the electronic states of the surface ET layer at room temperature is the charge-ordered state, stable below 135K in bulk crystals, rather than the charge disproportionation state above 135 K. The most probable mechanism underlying this remarkable finding is the particular freedom to the surface ET layer. The missing of the I-3 layer partially removes the structural constraint of the steric interaction between the thermally vibrating ethylene groups and the neighboring two I-3 layers. This mechanism would have something in common with the layered ET complexes.