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| Home > Publications database > Ab initio investigations of π-conjugated-molecule-metal interfaces for molecular electronics and spintronics |
| Dissertation / PhD Thesis | FZJ-2015-00777 |
2014
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-89336-992-8
Please use a persistent id in citations: http://hdl.handle.net/2128/8469
Abstract: The demand for continuous miniaturization of electronic devices poses an enormous challenge to conventional electronics. Instead of further miniaturizing the already established silicon based technology beyond the nanoscale, designing electronic devices by the bottom-up strategy is a promising alternative. As the currently smallest imaginable parts for electronic devices, single atoms or molecules adsorbed on a substrate are the subject of research in the field of molecular electronics. In addition molecular spintronics is a quickly rising field, which promises advantages over electronics like a lower power consumption. In spintronics the charge current is replaced by a spin current. Both molecular electronics and molecular spintronics require a proper theoretical description to design new materials and to propose candidates for future devices. Density functional theory is the method of choice to efficiently describe the molecule surface interfaces under consideration. For a realistic description of the system a suitable approximation for the exchange correlation functional has to be made. In particular for weakly bound organic molecules adsorbed on surfaces common approximations to the exchange correlation functional fail to correctly account for van der Waals interactions, which are in this case the dominant contribution to the binding. To find a correction for this deficiency is still subject of current research. In this thesis we investigate molecule surface systems of small $\pi$ conjugated molecules adsorbed on metal surfaces. For thiophene on Cu(111) we find weak chemisorption as binding mechanism while cyclooctatetraene is physisorbed on Au(111) and chemisorbed on the metal (100) surfaces of Au, Ag and Cu. In all these regimes of binding strength we asses semi-empirical and $\textit{ab initio}$ approaches to correct for vdWinteractions in DFT. Based on the insights gained about the organic metal interfaces for different molecule surface interaction strengths, we propose two promising magnetic systems for molecular spintronics applications. Cyclooctatetraene adsorbed on magnetic transition metal adatoms on Au(111) shows sharp spin split molecular orbital like features, which are characteristic for a spin filter. Paracyclophane adsorbed on the ferromagnetic Fe/W(110) surface and the antiferromagnetic Fe/W(100) surface in addition to the spin filter characteristics is an example for the modification of the magnetic properties of a surface by the adsorption of organic molecules. In particular the exchange coupling strength between the Fe atoms directly interacting with the molecule is increased, which leads to higher coercivity fields and Curie temperatures of the sample.
Keyword(s): Dissertation
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