  We have performed charge transfer phase formation studies on the
donor/acceptor system
bis(ethylendithio)tetrathiafulvalene,(BEDT-TTF)/tetracyanoquinodimethane,(TCNQ)
by means of physical vapor deposition. We prepared donor/acceptor bilayer
structures on glass and Si(100)/SiO_2 substrates held at room temperature and
analyzed the layer structures by optical microscopy, X-ray diffraction and
focused ion beam cross sectioning before and after annealing. We found clear
evidence for the formation of a charge transfer phase during the annealing
procedure. For the as-grown samples we could not detect the occurrence of a
charge transfer phase. X-ray diffraction indicated that the monoclinic variant
of the (BEDT-TTF)-TCNQ was formed. This was further corroborated by
single-source evaporation experiments from pre-reacted (BEDT-TTF)-TCNQ obtained
from solution growth, and in particular from co-evaporation experiments of
(BEDT-TTF)-TCNQ and TCNQ. In the course of these experiments we found that
(0,l,l)-oriented BEDT-TTF layers can be prepared on alpha-Al_2O_3 (1,1,-2,0)
substrates at about 100 C using (BEDT-TTF)-TCNQ as source material. We
speculate that due to its high vapor pressure the TCNQ component serves as a
carrier gas for BEDT-TTF vapor phase transport.

Materials Science;Soft Condensed Matter