Temperature dependent growth morphologies of parahexaphenyl on SiO2 supported exfoliated graphene

Abstract

Growth condition dependence of morphology and electric properties of ZnO films on sapphire substrates prepared by molecular beam epitaxyThe 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 SiO 2 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.

Layer Dependent Wetting in Parahexaphenyl Thin Film Growth on Graphene

“…Based on simple surface energy considerations, one should expect 6P growing on Gr in the same mode as on the SiO 2 substrate. This is indeed partially observed for low deposition temperatures [37] but in contradiction to the observations at higher deposition temperatures. Usually, the adsorption energy of a single lying 6P molecule is considerably higher than that of an upright standing one.…”

“…6P molecules deposited on graphene surfaces formdependent on the substrate temperature -two different kinds of morphologies: islands consisting of molecules with their long molecular axes oriented roughly perpendicular to the surface, and needles composed of molecules with their long axis parallel to the substrate surface [37]. In the following and throughout the manuscript we will term structures consisting of molecules with their long axis parallel to the surface as needles, and those composed of upright standing molecules as islands.…”

“…There, wrinkles [34] -always present on Gr grown by chemical vapor deposition -play an important role in the nucleation of 6P crystallites [35,36]. In a previous work, we investigated the temperature dependence of 6P growth morphologies on SiO 2 supported exfoliated Gr [37]. Exfoliated Gr is wrinkle free and offers the possibility to study homogeneous nucleation.…”

Effects of polymethylmethacrylate-transfer residues on the growth of organic semiconductor molecules on chemical vapor deposited graphene

“…[9][10][11][12][13][14][46][47][48][49][50][51][52][53][54][55][56][57][58] We find that 6P grows in a flat-lying needle-type morphology on CVD MLG transferred to oxidized Si wafers, irrespective of observed PMMA residue levels and MLG defects. This indicates that MLG dominates interface properties even in the case of severe contamination or damage.…”

Wear properties of graphene edges probed by atomic force microscopy based lateral manipulation

“…Therefore, graphene can be applied as an extremely compact protective coating for friction and wear reduction [2,4,5,6,7,8], as an anti-corrosion layer [9], for van der Waals screening [10], as a lubricant for rotating and sliding electrical contacts [11], for the mechanical encapsulation and protection of molecules and 10 cells [12,13,14,15], and for flexible optoelectronics [16,17,18,19].…”