Adsorption of EP-PTCDI on Si(111) 7x7 surfaces

E.A. SÁNCHEZ, V.A. ESAULOV, J.E. GAYONE, O. GRIZZI, AND L.N. SERKOVIC

Donostia ? San Sebastián, España

Workshop; Elementary Reactive Processes at surfaces; 2007

The interest on the study of highly organized materials assembled from organic semiconductor molecules has increased in the last decades because of their applications to optoelectronic devices such as thin film transistors, photovoltaic, liquid crystal, light emitting diodes and very recently, to fabrication of single-molecule devices like fluorescence switches and sensors [1]. It has been shown that the electrical and optical properties of the selfassembled materials are strongly dependent on the intermolecular interactions and thus the dimensional structures. The particular interest of molecules derivative of perylene tetracarboxylic diimide (PTCDI) comes from their unique class of n-type semiconductor, in comparison to more common ptype counter part in organic semiconductors [1]. In this work the adsorption of EthylPropyl-PTCDI (EP-PTCDI) on Si(111) 7x7 and Ag(111) surfaces is studied by scanning tunneling microscopy (STM). The molecules were deposited from a carefully degased Knudsen cell under ultra high vacuum conditions onto the crystals held at different temperatures. At doses less than a monolayer (ML), no cluster formation but the adsorption of isolate single molecules on different adsorption sites have been observed on Si surfaces held at room temperature and at 150 ºC. The post annealing of the surface did not promote the formation of clusters but the desorption of molecules leaving a rougher surface. Furthermore, we have not observed preferential absorption on defects like vacancies nor on the Si step edges. This low molecule mobility can be due to the high reactivity of the clean Si surface with unsaturated dangling bonds, as it happens with similar perylene molecules (PTCDA) [2]. Contrary to the Si case, for the less reactive Ag(111) surface, the formation of self assembled monolayers has been observed at room temperature. For coverages less than a ML, the adsorption started on the step edges forming small ordered islands. At larger doses the completion of a single ML and the formation of ordered multilayers have been observed. We acknowledge partial financial support from ANPCyT (PICT 03-14452, PME 118), CONICET (PIP 5248), Fundación Antorchas and Universidad Nacional de Cuyo (06-C202). References 1. K.Balakrishnan, A. Datar, Tammene Naddo, J. Huang, R. Oitker, M. Yen, J. Zhao and L. Zang, J. Am. Chem. Soc. 128, 7390 (2006); and references therein. 2. T. Soubiron, F. Vaurette, J.P. Nys, B. Grandidier, X. Wallart and D. Stiévenard, Surf. Sci.128, 7390 (2006); and references therein. 2. T. Soubiron, F. Vaurette, J.P. Nys, B. Grandidier, X. Wallart and D. Stiévenard, Surf. Sci. 582, 178 (2005)., 178 (2005).