Thermal Behavior of Mixed-Stack Charge Transfer Films of 2-Octadecyl-7,7,8,8-tetracyanoquinodimethane and 3,3‘,5,5‘-Tetramethylbenzidine Prepared by the Langmuir−Blodgett Technique and Donor Doping. 2. Morphology and Annealing Effects of the Films Investigated by Atomic Force Microscopy and Ultraviolet−Visible−Near Infrared and Infrared Spectroscopies

Morphology and annealing effects of Langmuir−Blodgett (LB) films of a mixed-stack charge transfer (CT) complex of 2-octadecyl-7,7,8,8-tetracyanoquinodimethane (octadecyl-TCNQ) doped by 3,3‘,5,5‘-tetramethylbenzidine (TMB) have been investigated by atomic force microscopy (AFM) and ultraviolet−visible−near infrared (UV−vis−NIR) and infrared (IR) spectroscopies. AFM images of the LB films of the CT complex scanned at room temperature show that the films consist of numerous one-dimensional needle-like microcrystals and that a periodic structure exists inside these needle-like microcrystals. A cyclic thermal treatment on one-, three-, and 11-layer films of the CT complex up to 110 °C, which is below their dedope temperatures, makes the needle-like microcrystals thinner and flatter while the molecular arrangement and structure in the crystals are nearly unchanged. However, when the temperature of the CT complex films is elevated above their respective dedope temperatures, the needle-like microcrystals become much thinner, resulting in the formation of plate-like microcrystal domains which are characteristics of LB films of octadecyl-TCNQ. The molecular arrangement and structure in the CT complex films after the annealing above the dedope temperature differ from those before the annealing and seem to exist in two different forms. One is just like that of LB films of octadecyl-TCNQ, while the other is neither like that of the CT complex films before the annealing nor like that of the LB films of octadecyl-TCNQ.