Tetrathiafulvalene-tetracyanoquinodimethane thin films grown by physical vapor deposition: Influence of substrate structures and substrate materials

We present results on the formation of thin films of the charge transfer salts tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ) prepared by physical vapor deposition on several substrates in a high vacuum. We mainly investigate the influence of the substrate materials and surface structures on the surface morphology of the thin films. The obtained results show that the surface structure of the substrate has a stronger influence on the film morphology than that of the material. In particular, we report the influence of surface nano-structure on the growth mode of TTF-TCNQ. The flat TTF-TCNQ thin films were continuously grown on both 2° off-SiO2/Si(111) and NaCl(100) substrates. The maximum conductivities of the films grown on 2° off-SiO2/Si(111) and NaCl(100) were 0.4 and 4 Ω− 1 cm− 1, respectively. With a CaF2 substrate, a large number of TTF-TCNQ nano-scale ribbon-like crystals grew on the as-deposited CaF2/CaF2(110) substrate. This indicates that we could realize a TTF-TCNQ adsorption site by depositing CaF2.