Perylene monolayer on the Ru(0001) surface

Abstract

The growth of epitaxial monolayer of perylene on Ru(0001) was investigated by means of scanning tunneling microscopy (STM). The STM images showed a coexistence of the ordered phase with a 12×12 superstructure and the disordered phase in a monolayer of perylene on Ru(0001). In the disordered region, the perylene molecules are randomly distributed, and orientated uniformly with their long axis in the [1000] direction. For the ordered phase, a model of the Ru(0001)-(12×12)-8 perylene superstructure was proposed. The results indicate that the growth behavior of perylene on Ru(0001) is mainly controlled by laterally repulsive molecule-molecule interaction.

Studies of growth behavior of tetracene on Ru(101¯0)

“…The ordering of organic molecules on metal surfaces was governed by the subtle balance between the intermolecular and adsorbate-substrate interactions [1,2,13,14]. In the submonolayer regime, stronger interaction between molecule and substrate will lead to an amorphous (disordered) growth.…”

“…In the case of relatively weaker interaction between molecule and substrate, laterally attractive molecule-molecule interaction will result in an island growth in submonolayer coverage, while laterally repulsive (weak) interaction will normally give rise to a 2D liquid-like growth mode in submonolayer coverage, and form ordered phase in a monolayer coverage. Actually, tetracene forms islands with an ordered structure on Ag(1 1 0) at the submonolayer coverages under the laterally attractive molecule-molecule interaction [13], and the organic semiconductor of perylene form an ordered (12 · 12) superstructure for a monolayer of perylene on Ru(0 0 0 1) under the driving force of the laterally repulsive molecule-molecule interaction [2]. However, in the present case of tetracene growth on Ruð1 0 1 0Þ, similar to the PVBA growth on Pd(1 1 0) surface [22,23], the results of the formation of disordered (neither island nor ordered structure) structure indicate that the growth of tetracene on Ruð1 0 1 0Þ is mainly controlled by the relatively stronger molecule-substrate interaction, and the laterally molecule-molecule interaction, which is mostly a van de Waals one, should has little influence on the tetracene growth in the monolayer regime.…”

“…4(a) demonstrates the details of the internal structures of tetracene molecules with three different orientations, i.e., with the long molecular axis parallel to ½1 2 1 0, perpendicular to ½1 2 1 0, and tilted 57.7°with respect to ½1 2 1 0, labeled by A, B and C respectively, and the substrate structures, especially the Ru atomic rows are clearly resolved. The image was recorded with a tunneling condition very near to the Fermi level (V s = À2 mV, I t = 0.71 nA), which is typical of that required for aromatic molecules with their p-orbitals parallel to the surface [2]. The internal structures of tetracene molecules in the STM Fig.…”

“…The flatlying adsorption geometry of tetracene on Ag(1 1 0) and Cu(1 1 0) was also observed [13,14]. The molecular plane of tetracene lying flat on the surface suggests that the adsorbate-substrate interaction is dominated by the p-orbitals bonding to the d-orbitals of the Ru substrate [2,14,21].…”

“…The electronic and optical properties of organic crystalline films depend crucially on their orientations and long-range ordering. Recently, great attentions have been focused on the growth of ordered organic thin layers on different single-crystalline substrates [1][2][3][4]. However, understanding of the growth and two-dimensional (2D) ordering of organic semiconductors is still limited.…”