Temperature dependent growth morphologies of parahexaphenyl on SiO2 supported exfoliated graphene

Abstract

The growth of small conjugated molecules on graphene is of increasing interest, since the latter bears the potential to serve as a transparent electrode for organic solar cells and light emitting diodes. Here, parahexaphenyl thin films have been grown by hot wall epitaxy on SiO2 supported exfoliated graphene. The arising morphologies—studied by atomic force microscopy—exhibit a strong dependence on deposition temperature. At temperatures from 280 K–333 K, islands consisting of almost upright standing molecules and needles composed from lying molecules coexist on the graphene flake. Between 363 and 423 K solely needles—consisting of lying molecules—are present on the graphene. The needles form well-ordered networks with relative orientation angles of ∼30°, ∼60°, and ∼90° reflecting the symmetry of the graphene substrate.