Vacuum deposited film growth, morphology and interfacial electronic structures of 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene (C8-BTBT)

Abstract

Interfaces play critical roles in electronic devices and provide great diversity of film morphology and device performance. We retrospect the substrate mediated vacuum film growth of benchmark high mobility material 2, 7-dioctyl[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) and the interface electronic structures. The film growth of C8-BTBT molecules is diversified depending on the substrate-molecule and molecule-molecule interactions. On atomic smooth substrates C8-BTBT film grows in layer-by-layer mode while on coarse substrate it grows in islands mode. The initial molecular layer at dielectric, semiconductor and conductive substrates displays slight different lattice structure. The initial molecule orientation depends on the substrate and will gradually change to standing up configuration as in bulk phase. C8-BTBT behaves as electron donor when contacting with dielectric and stable conductive materials. This usually induces a dipole layer pointing to C8-BTBT and an upward bend bending in C8-BTBT side toward the interface. Although it is air stable, C8-BTBT is chemically reactive with some transition metals and compounds. The orientation change from lying down to standing up in the film usually leads to decrease of ionization potential. The article provides insights to the interface physical and chemical processes and suggestions for optimal design and fabrication of C8-BTBT based devices.

Keywords

interface / film morphology / packing configuration / growth mode / electronic structure / chemical reaction / interface dipole

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