Photoemission Tomography of a One-Dimensional Row Structure of a Flat-Lying Picene Multilayer on Ag(110).

We applied photoemission tomography (PT) to a unique one-dimensional row structure of a picene multilayer realized on an anisotropic Ag(110) surface. Taking advantage of the simplified structure of the multilayer film, we successfully deconvoluted the photoelectron momentum maps of three frontier orbitals of picene. Thereafter, the clearly deconvoluted experimental momentum maps were compared to the Fourier transform simulation of the molecular orbitals of picene in detail, enabling not only the evaluation of the electronic structure of the picene in the multilayer but also the determination of the molecular orientation in the multilayer within a few degrees. In addition, the PT results indicated the orientation of the molecules in all layers to be flat-lying. The successful demonstration of PT of the multilayer molecular film marks an important step toward the wide-range utilization of the PT technique.

Fabrication of Highly Oriented Multilayer Films of Picene and DNTT on Their Bulklike Monolayer.

Highly oriented, multilayer molecular films of picene and dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) molecules with the long axis parallel to the substrate (parallel configuration, hereafter) were fabricated on their characteristic bulklike monolayer. These molecules form a dense monolayer with a bulklike molecular arrangement on metal surfaces such as Au(111), which allows further stacking of parallel molecules. Indeed, upon adsorption of picene and DNTT on these dense monolayers, growth of straight islands of multilayer without the dendritic layer was observed. Particularly, in the case of picene, one-dimensional islands with lengths over 100 µm were formed and aligned in 3-fold symmetric directions of the substrate, which was not observed in the case of DNTT. X-ray diffraction measurements revealed the presence of [201̅] and [211̅] planes and the absence of the [001] diffractions, indicating that the one-dimensional islands of picene indeed consist of parallel molecules. The formation of huge crystalline islands in the case of picene, in contrast to the case of DNTT, is likely induced by the stronger intermolecular force, as suggested from the calculation of the vibrational energy.