Thin Films of BEDT-TTF and BEDO-TTF Radical Cation Salts

Abstract

In this communication we describe the fabrication and characterization of thin films of the radical cation salts α-, α_t-(BEDT-TTF)₂I₃ and (BEDO-TTF)_2.4I₃. Thin films of these compounds were made by evaporation of the salts in high vacuum onto several substrates. They were characterized by X-ray diffraction, scanning electron microscopy, infrared absorption, Raman scattering, de-conductivity measurements and magnetically modulated microwave absorption. Depending on the temperature of the substrate and the evaporation rate, the films of α-(BEDT-TTF)₂I₃ exhibit different degrees of microcrystallinity which under the right conditions can be strongly reduced to obtain relatively smooth, completely covering films. Additionally such films have a high degree of orientation with respect to the substrate plane. The conversion into films of the superconducting α_t-phase is possible and the high orientation is maintained. Due to grain boundaries, the dcconductivity is thermally activated, but the single grains are superconducting. The best results in the fabrication of smooth, completely covering films were obtained with (BEDO-TTF)_2.4I₃ on NaCl single crystals. Here the orientation of the donor molecule with respect to the substrate plane is different from the one found in the (BEDT-TTF)₂I₃ salts.