Morphology, Structure, and Dynamics of Pentacene Thin Films and Their Nanocomposites with [C2 C1 im][NTf2 ] and [C2 C1 im][OTF] Ionic Liquids

Abstract

In this study, a homogeneous thin film growth of pentacene onto indium tin oxide (ITO) coated glass surfaces is explored using a high-resolution and reproducible vapor deposition methodology. Moreover, vacuum thermal evaporation of ionic liquids (ILs) ([C₂ C₁ im][NTf₂ ] and [C₂ C₁ im][OTF]) onto ITO, gold/palladium (AuPd) and pentacene surfaces were performed. A greater wettability behavior of ILs is observed for surfaces containing AuPd. Sequential and simultaneous depositions of ILs and pentacene were explored. Simultaneous depositions lead to the formation of nanocomposites films, consisting of IL micro- and nanodroplets covered by pentacene layers. Plasma surface treatment was used to induce the ILs droplets coalescence and explore the dynamics and phase separation of the nanocomposites. The [C₂ C₁ im][OTF] droplets were found to be completely covered with pentacene, which suggests a great affinity between cation-anion pairs and the aromatic moiety. Pentacene films and their nanocomposites with ILs exhibit a typical optical band gap of E_gap =1.77 eV, indicating that the nanocomposite phase domains are large enough to behavior as the bulk.

Keywords: nucleation and growth; plasma treatment; surface and interface; thermal evaporation; thin films.