Seminars Archive

Copper surface functionalisation by aromatic thiols adsorption

Abstract
In recent years, several experimental and theoretical efforts have been concentrated on the study of self-assembled monolayers (SAMs) onto metal surface, as a consequence of their wide range of technological applications [1-3]. In fact, SAMs offer a convenient and flexible system with which to tailor the metal surface properties in desired manner by a simple bottom-up approach from either the liquid or the vapour phase. The ability to engineer surface properties by a suitable choice of the molecular backbone and endgroup is certainly one reason for the attractiveness of SAMs. In this work, a benzenethiolate SAM onto a copper surface is studied and then used as a buffer layer for the growth of pentacene molecules, which act as semiconductive phase in organic thin film transistors (OTFTs) devices [4-6]. It is shown that the nature of the substrate is fundamental for the semiconductor crystallinity and the corresponding device performances. The adsorption of benzenethiol (BT) and diphenyldisulfide (DPDS) from vapour phase in UHV environment on a Cu(100) single crystal is investigated by means of AES, LEED, TDS, XPS and NEXAFS [7-10]. The controlled conditions and the model surface allow us to clarify the role of the aromatic ring on the resulting structure and on the electronic properties of the interface, as well as on phenomena like growing and ordering. In particular, they permit to understand the role of the phenyl ring and its competitive interaction toward the metal surface with respect to the -SH headgroup. The BT (or DPDS) adsorption happens through the formation, at saturation, of a benzenethiolate monolayer with a c(2x6) two-domain reconstruction of the substrate and a standing-up configuration of the adsorbed species. Since it was claimed that order and low defect density determine very high mobility in prototype devices based on aromatic layers, our idea is to use the aromatic monolayer as a very ordered basis for further growth, exploiting the SAM as a soft template where pentacene can land and build up a regular layer. Then, the effect of the benzenethiolate SAM with respect to the bare surface during the pentacene deposition is studied combining NEXAFS, XPS and TDS measurements [8,10]. Hence, the role of the interaction with the substrate on the orientation of pentacene molecules with respect to the surface plane is determined. The pentacene molecules are flat-lying on the bare copper surface, while they adopt a standing-up configuration on the SAM-covered substrate, as a consequence of the different interaction. [1] Schreiber F., Prog. Surf. Sci. 65 (2000) 151 [2] Love J.C., Estroff L.A., Kriebel J.K., Nuzzo R.G., Whitesides G.M., Chem. Rev. 105 (2005) 1103 [3] Chen D., Li J., Surf. Sci. Rep. 61 (2006) 445 [4] Koch N., Chem. Phys. Chem. 8 (2007) 1438 [5] Ihm K., Kim B., Kang T.-H., Kim K.-J., Joo M.H., Kim T.H., Yoon S.S., Chung S., Appl. Phys. Lett. 89 (20006) 033504 [6] Ruiz R., Choudhary D., Nickel B., Toccoli T., Chang K.-C., Mayer A.C., Clancy P., Blakely J.M., Headrick R.L., Iannotta S., Malliaras G.G., Chem. Mater. 16 (2004) 4497 [7] Kanjilal A., Bussolotti F., Crispoldi F., Beccari M., Di Castro V., Betti M.G., Mariani C., J. Phys. IV France 132 (2006) 301 [8] Kanjilal A., Ottaviano L., Di Castro V., Beccari M., Betti M.G., Mariani C., J. Phys. Chem. C. 111 (2007) 286 [9] Allegretti F., Bussolotti F., Woodruff D.P., Dhanak V.R., Beccari M., Di Castro V., Betti M.G., Mariani C., Surf. Sci. 602 (2008) 2453 [10] Chiodi M., Gavioli L., Beccari M., Di Castro V., Cossaro A., Floreano L., Morgante A., Kanjilal A., Mariani C., Betti M.G., Phys. Rev. B 77 (2008) 115321