Layer-by-Layer Growth of Incommensurate, Polycrystalline, Lying-Down Pentacene Thin Films on Au(111)

Abstract

Pentacene, as well as other polyacenes, is known to adsorb on metal surfaces in a lying-down geometry, that is, with the molecular plane parallel to the surface. Here we show using scanning tunneling microscopy that the lying-down pentacene monolayer seeds the growth of a multilayer polycrystalline film in a layerby-layer fashion, with the molecular planes parallel to the substrate surface. Growth in the submonolayer region is characterized by a large number of ordered molecular structures as coverage increases. The saturated monolayer structure remains approximately the same throughout multilayer coverages studied. Statistical analysis of molecular domain orientation reveals that the ordered pentacene structures are incommensurate with the Au(111) substrate and growth beyond the monolayer region is a mixture of epitaxy and nonepitaxy. We conclude that the relatively large footprint of a lying-down pentacene molecule smoothes out lateral corrugation in the adsorption energy landscape on the Au(111) surface, leading to the growth of an incommensurate, polycrystalline, and partially nonepitaxial thin film.

Scanning-induced structure transformation between self-assembled phases of pentacene on Ag/Si(111)

“…2b). The situation is similar to pentacene adsorption on Au(1 1 1) [11,12] and Au(1 0 0) [25]. Apart from the three predominant directions, there is a broad distribution of relative angles between the molecular chains.…”

“…The chain is 15.6 Å wide with the inter-chain separation of 28 Å . On Au (1 1 1), pentacene form a number of ordered structures in the striped form: Kang and Zhu observed five phases by STM, two of which having unit cells of 15.1 Å · 7.5 Å , 96°and 15.5 Å · 6.4 Å , 82°, respectively [12]. Parkinson et al reported a high density phase with a unit cell of 15 Å · 5.76 Å , 90° [11].…”

“…The condition for a given growth mode is determined by a delicate balance of the intralayer and overlayer-substrate interactions. For example, pentacene molecules stand up and form bulk crystalline phase or the thin film phase on insulating or inert surfaces such as SiO 2 , SiN, Al 2 O 3 and passivated Si [6][7][8], while they lie down and form varied 2D patterns (strip, brick-wall or herringbone) on noble metals [9][10][11][12][13] or some metallic interfaces [14][15][16] where the molecule-substrate interactions surpass the molecule-molecule interactions and lead to a planar adsorption geometry.…”

Balancing Intermolecular and Molecule–Substrate Interactions in Supramolecular Assemblies

“…The persistence of the surface-state in the case of DIP deposition reflects the weakness of the molecule-substrate interaction, as observed with most other organic molecules such as, e.g., PTCDA, CuPc, FePc, HBC, NTCDI, BDG, 6T, DH6T, pentacene, etc. [9,23,31,[34][35][36][37][38][39] A much stronger (and rarer) interaction becomes evident from the data for the F 16 CuPc layers. It is plausible that this interaction arises from a partial charge transfer from Au to F 16 CuPc.…”

Planar Growth of Pentacene on the Dielectric TiO2(110) Surface

“…12,13 Thin films of flat-oriented molecules on metals have been seldom reported, i.e., only when the substrate periodicity closely matches that of the pentacene bulk planes. [14][15][16] So far, no lying-down layers of pentacene have been reported on dielectric substrates.…”