Structural Analysis of Langmuir-Blodgett Films of Alkylated Tetracyanoquinodimethanes

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Abstract
Structural characterization of alkylated tetracyanoquinodimethane (TCNQ) Langmuir and Langmuir-Blodgett (LB) films has been carried out. Scanning electron microscope (SEM) and atomic force microscope (AFM) observations reveal numerous platelet microcrystal domains in the alkylated TCNQ Langmuir films transferred onto a quartz substrate. The analysis of height distribution in the AFM data proves that these domains have periodic layered structure. The thickness of these layered structures agrees well with the d-values obtained by X-ray diffraction analysis of the alkylated TCNQ LB films. Moreover, the high-resolution AFM image and the d-value of the 2-dodecyl-TCNQ Langmuir film suggest that the structure of the second and the upper layers in the domains is identical to that of the single crystal. SEM and AFM measurements prove that the LB films consist of numerous platelet microcrystal domains which are superposed upon each other, resembling a mosaic structure. Therefore, the periodic structures observed in X-ray diffraction measurements of the alkylated TCNQ LB films are ascribed to the layered structure in these domains, although they are usually explained as well-defined multilayered structure.