Structural characterization of mixed-stack charge transfer films of 2-octadecyl-7,7,8,8-tetracyanoquinodimethane and 5,10-dimethyl-5,10-dihydrophenazine prepared by the Langmuir-Blodgett technique and donor doping .2. Morphology and annealing effects investigated by atomic force microscopy and ultraviolet-visible-near-infrared, and infrared spectroscopies

Morphology and annealing effects of mixed-stack charge transfer (CT) complex films of 2-octadecyl-7,7,8,8-tetracyanoquinodimethane (octadecyl-TCNQ) doped by 5,10-dimethyl-5,10-dihydrophenazine ((Me)(2)P) have been investigated by atomic force microscopy (AFM) and ultraviolet-visible-near-infrared (UV-vis-NIR) and infrared (IR) spectroscopies. The AFM measurements scanned at room temperature show that the 11-layer CT film consists of layered platelet microcrystal domains with a layer distance of 3.3 nm, which is in good agreement with the distance obtained by an X-ray diffraction experiment. It is likely that each layer in the CT film has a bimolecular layer structure as in the case of Langmuir-Blodgett (LB) films of neutral octadecyl-TCNQ. A two-dimensionally resolved molecular arrangement of octadecyl-TCNQ and (Me)(2)P is observed inside the domains by a high-resolution AFM image. The inter-and intrastack periods, which are across and along the CT stacks, are 0.96 and 0.83 nm, respectively, with an intersect angle of 59 degrees. A cyclic thermal treatment on the CT film up to 70 degrees C, which is below the dedope temperature, does not change its morphology, i.e., the molecular arrangement and layered structure in the microcrystal domains are nearly unchanged. However, when the CT film is heated above the dedope temperature, the layered structure vanishes completely and the molecular arrangement becomes similar to that in the LB film of neutral octadecyl-TCNQ. The UV-vis-NIR and IR spectra of the annealed CT films confirm the results obtained by AFM.