Characterization of bis(1,2,5-thiadiazolo)-p-quinobis(1,3-dithiole) thin films grown by organic molecular beam deposition

Crystalline thin films of the organic compound, bis(1,2,5-thiadiazolo)-p-quinobis(1,3-dithiole) (BTQBT) were grown by the ultrahigh vacuum process of organic molecular beam deposition on various substrates including highly ordered pyrolytic graphite, Si(0 0 1), glass and thermal silicon dioxide films on Si. In situ reflection high-energy electron diffraction, scanning electron microscopy, atomic force microscopy, X-ray diffraction, temperature-dependent photoluminescence spectroscopy, and electrical conductivity measurements were employed to characterize the various properties of the films. We find that ordered, polycrystalline films of the planar BTQBT molecules can be grown on a variety of substrates. The BTQBT molecules stack on substrates with their stacking axis perpendicular to the substrate plane. The degree and extent of film ordering strongly depends on the growth conditions: higher growth rates favor more ordered and uniform films. The room-temperature electrical conductivity of the films is (1.2 +/- 0.1) x 10(-3) and (7.5 +/- 0.4) x 10(-4) S cm(-1) perpendicular and parallel to the substrate surface, respectively. Both the remarkably high value of conductivity and its small anisotropy are explained in terms of the unusual crystal structure of BTQBT. (C) 2001 Elsevier Science B.V. All rights reserved.