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Organic molecules are one of the most promising candidates to substitute inorganic materials in nanotechnology devices. Optoelectronic applications are the main field in which these materials began to be used and hence organic light emitting devices (OLED); organic transistors and so on are some of the new devices reported in the last years. Moreover, most of them take advantage of the confinement properties of nanostructuring organic molecules in either 1D nanowires or 2D thin film 1. On the other hand, 0D organic nano dots are envisioned as systems with potential applications. Our research is focused on the formation and study of 0D and 1D nanostructures of organic molecules.
We focused our study on 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) deposited on Au(111) surfaces, both clean and partially covered by iron atoms. We have seen, by STM images, that Fe deposited on small amounts on the Au(111) surface form islands at the corner of the hearing bone reconstruction 2. These islands can be used as nucleation points for promoting nano dots (0D) or molecular chains (1D) what connect these points. The structural arrangement of the molecules and the interaction between the Fe clusters and the organic molecules themselves are studied and discussed in relation to the amount of diffusing Fe adatoms. Scanning tunnelling spectroscopy images of the 0D structures show emergence of new electronic states, different to those of a complete layer of PTCDA, which are confined in the nano dot 2. Molecular nanowires are promoted for higher temperature suggesting that the crucial parameter for the formation of 1D chains is the amount of free iron adatoms diffusing on the substrate. We have seen that Fe atoms, which act as molecular linkers, stabilized these 1D structures. By means of density functional studies, we try to get insights into the bonding between PTCDA molecules and the Fe atoms.
References
[1] N. Nicoara, J. Mendez et al. Nanotechnology 13 (2002) 352.
[2] J. Mendez, R. Caillard et al Adv. Mater. 18 (2005) 2048-2052.
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