Fabrication of Conducting Thin Films on the Surfaces of 7,7,8,8-Tetracyanoquinodimethane Single-Component and Charge-Transfer Complex Single Crystals: Nucleation, Crystal Growth, Morphology, and Charge Transport

Abstract

Electrically conducting TTF–TCNQ thin films are fabricated on various molecular crystals containing 7,7,8,8-tetracyanoquinodimethane (TCNQ) by exposing a tetrathiafulvalene (TTF) vapor under ambient conditions. To systematically investigate the properties of the films, mixed-stack TCNQ charge-transfer (CT) complex crystals with nine kinds of donors have been prepared as the substrates, and the morphology change of the films on the surfaces at the initial stage of the TTF vapor contact has been observed. When the substrate is a TCNQ single-component crystal, randomly oriented TTF–TCNQ nanometer-size needle crystals are grown by the reaction with a TTF vapor. However, when the substrate is a TCNQ CT complex crystal, TTF–TCNQ crystals are grown with alignment of their needle axis along the mixed-stack direction of the substrate. The surface roughness, the size of the needle crystals, and the degree of the dense packing of the needles have been found to systematically depend on the strength of the CT interact...