Tetrathiofulvalene and tetracyanoquinodimethane crystals: Conducting surface versus interface

When a tetrathiofulvalene (TTF) crystal is placed onto a 7,7,8,8-tetracyanoquinodimethane (TCNQ) crystal at room temperature, a highly conducting layer is formed. In this study, we explore to what degree this is due to physical contact or transfer by sublimation of one species onto the other crystal. We have performed a variety of time-dependent surface conductivity measurements, including TTF lamination on TCNQ at room temperature and low temperatures, as well as deposition of TTF molecules from the gas phase. Crystal-to-crystal contact insignificantly modifies material conductivity while TTF sublimation onto TCNQ is shown to dominate electronic modification. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4731244]