Thin film properties of tetracyanoquinodimethane (TCNQ) with novel templating effects

Abstract

The morphological and structural properties of films based on the strong electron acceptor molecule, 7,7,8,8,-tetracyanoquinodimethane (TCNQ) are presented and the influence of growth rate and the nature of the substrate are investigated. On weakly-interacting substrates, TCNQ films grown by Organic Molecular Beam Deposition (OMBD) exhibit randomly oriented micron-sized islands with significant curvature and three preferential orientations suggested by diffraction from (022), (021) and (020) planes. Pre-coating with 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) is shown to result in morphological and structural modifications to the TCNQ films, characterized by uniform rectangular-shaped micron-sized islands, with the preferential molecular orientation reduced to only (020), compared to the films on bare substrates. We rationalise the interactions between TCNQ and PTCDA based on the match between the displacement of the perylene-H atoms/anhydride groups in PTCDA and that of the CN groups in TCNQ. These results suggest an alternative approach for using templating to control the molecular orientation in organic heterostructures.