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

Abstract

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 m...