有機硫化物及半導體高分子在Au(111)表面自組裝行為及其電性之探討

Abstract

The interfacial properties between the substrate and the deposited film are the major determinants of film construction. By forming a self-assembled monolayer (SAM) on a substrate surface, one can control the film characteristics and the metal-deposition process. This study reveals the self-assembly process and the effects on metal-deposition process of 3,3-Thiobis(1-propanesulfonic acid, sodium salt) (TBPS) via scanning tunneling microscopy (STM) and surface-enhanced infrared spectroscopy (SEIRAS). TBPS exhibits an adsorption behavior typically observed for dialkyl sulfides including intact adsorption and low coverage phases with molecules predominantly lying flat on the surface. On the other hand, an untypical chemical bond and well-ordered domains were determined which resemble the characteristics of alkenethiol SAMs. In situ STM studies in TBPS-containing electrolyte reveal a very complex, potential-dependent adsorption behavior. This behavior is attributed to the influence of the electrode potential on intermolecular and molecule-substrate interactions as well as on the TBPS coverage. The results also shows that Cu growth on Au(111) - which is known to be strongly kinetically hindered in additive-free, aqueous perchloric acid solutions - proceeds significantly faster in the presence of TBPS. The TBPS molecules either “float” on top of the growing film. Cu growth in the overpotential deposition (OPD) regime results in a smooth Cu film with low surface roughness, in contrast to defect-mediated 3D island growth in additive-free electrolytes. The performance of organic semiconductor devices depends to a great extent on the arrangement and conductivity of molecules adsorbed on metal substrate surfaces. A central challenge in the creation of well-ordered, supramolecular nanostructures are strong interactions between adsorbent and metal which often lead to poorly ordered adlayer phases. It, therefore, is very important to develop new techniques to produce organic semiconductor films with desired properties. We could succeed to fabricate well-ordered, supramolecular C60/poly(3-hexylthiophene) (P3HT) nanostructures on I-modified Au(111) surfaces. A bottom-up strategy to halide-pretreated single-crystal electrodes in the solution phase has been used because it is a simple and effective approach to fabricate defect-free, nanostructured, and bicontinuous composite-monolayers with exceptional conductivity. The p-type semiconductive polymer, P3HT, has widely been studied, but it has a problem to form randomly oriented and/or curvy-wire morphology on a bare Au(111) electrode. To overcome these problems, we have used iodine-modified Au(111) substrates to let the polymer chains stack and fold into well-organized arrays of two-dimensional, linear architectures with large, ordered domains. At sufficiently negative electrode potentials, electrons transfer from P3HT to iodine leading to iodine desorption and p-doping of the P3HT adlayer. As a consequence, the Fermi level shifts ~0.1 eV toward the HOMO position. This p-doped P3HT monolayer exhibits strong donor-acceptor interactions with n-type materials, like C60. Therefore, a stable C60/P3HT supramolecular nanostructure could be fabricated on Au(111) surfaces. It exhibits high conductivity which can resist a comparatively large potential change from 1 to 0 V. In contrast to previous studies, the nanostructures produced by the present method have a high degree of ordering. Furthermore, the preparation from the solution phase is cost-effective, easy to perform and fast compared to the UHV technique commonly employed in the literature.