| AVS 56th International Symposium & Exhibition | |
| Surface Science | Thursday Sessions |
| Session SS2-ThM |
| Session: | Electron Activated Molecular Interfaces |
| Presenter: | C. Urban, Universidad Autonoma de Madrid, Spain |
| Authors: | C. Urban, Universidad Autonoma de Madrid, Spain D. Ecija, Universidad Autonoma de Madrid, Spain M. Trelka, Universidad Autonoma de Madrid, Spain R. Otero, UAM & IMDEA-Nano, Spain J.M. Gallego, ICMM-CSIC, Spain N. Martín, Universidad Complutense de Madrid, Spain R. Miranda, UAM & IMDEA-Nano, Spain |
| Correspondent: | Click to Email |
Molecular diffusion on solid surfaces is of fundamental importance for surface chemistry and also because of the important role it plays in the formation of self-assembled molecular mono and multilayers. Many studies have discussed the diffusion processes of a single, isolated molecule on the surface and the self-assembly process in terms of molecule-molecule and molecule-susbstrate interactions, but the relevant kinetic aspects have mostly not been dealt with. In addition, the growth of organic multilayers of two different types of functional molecules (e.g. donor and acceptor or magnetic and non-magnetic) with enough structural perfection requires a knowledge of intermixing processes at interfaces not yet available and intimately related to vacancy diffusion.
We directly visualized the surface diffusion of molecular vacancies in monolayers of exTTF (2-[9-(1,3-dithiol-
2-ylidene)anthracen-10(9H)-ylidene]-1,3-dithiole) self-assembled on Au(111) under UHV conditions. exTTF is a strong electron donor, and in combination with PCBM, it has been shown to produce a phase-segregated, mixed layer with optimal morphology for bulk heterojunction solar cells [1]. When deposited on Au(111), exTTF molecules modify the substrate surface reconstruction and self-assemble to form long rectangular islands, the space between them being occupied by a sea of diffusing, non-nucleated molecules, which are very mobile even down to 150 K. The continuous exchange of molecules between the islands and this sea creates many vacancies within the islands. By means of a variable temperature fast-STM, we have quantified the diffusion of these vacancies within the islands. The results indicate a non-isotropic, Brownian-type diffusion. The implication of these results and the relevance of this diffusion mechanism for the exchange processes observed in the growth of exTTF-PCBM mixed layers and multilayers will be discussed.
[1] R. Otero, D. Écija, G. Fernández, J.M. Gallego, L. Sánchez, N. Martín, R. Miranda, Nano Letters 7 (2007) 2602-2607.