THIN-FILMS OF BEDT-TTF AND BEDO-TTF RADICAL-CATION SALTS

In this communication we describe the fabrication and characterization of thin films of the radical cation salts alpha-, alpha(t)-(BEDT-TTF) (2)I-3 and (BEDO-TTF)(2.4)I-3. Thin films of these compounds were made by evaporation of the salts in high vacuum onto several substrates. T hey were characterized by X-ray diffraction, scanning electron microsc opy, infrared absorption, Raman scattering, de-conductivity measuremen ts and magnetically modulated microwave absorption. Depending on the t emperature of the substrate and the evaporation rate, the films of alp ha-(BEDT-TTF)(2)I-3 exhibit different degrees of microcrystallinity wh ich under the right conditions can be strongly reduced to obtain relat ively 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 alpha(t)-phase is possibl e and the high orientation is maintained. Due to grain boundaries, the dc-conductivity is thermally activated, but the single grains are sup erconducting. The best results in the fabrication of smooth, completel y covering films were obtained with (BEDO-TTF)(2.4)I-3 on NaCl single crystals. Here the orientation of the donor molecule with respect to t he substrate plane is different from the one found in the (BEDT-TTF)(2 )I-3 salts.