Metallic and molecular nanostructures on well-defined surfaces

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KROTZKY, Sören Gabriel, 2014. Metallic and molecular nanostructures on well-defined surfaces [Dissertation]. Konstanz: University of Konstanz

@phdthesis{Krotzky2014Metal-31637, title={Metallic and molecular nanostructures on well-defined surfaces}, year={2014}, author={Krotzky, Sören Gabriel}, address={Konstanz}, school={Universität Konstanz} }

2015-08-27T13:40:30Z The present thesis is concerned with the growth of nanostructures on well-defined metal substrates. Four experimental chapters address various effects, which occur upon deposition of molecules and/or single metal atoms on atomically clean surfaces. Two main objectives are pursued. (i) The investigation of the building mechanism of low dimensional structures and (ii) the magnetic characterization of the interaction of single atoms and small clusters. The main experimental tool to analyse the realized structures is the scanning tunnelling microscope (STM). To reveal the magnetic properties of the samples standard x-ray based techniques like x-ray magnetic circular dichroism (XMCD) are used.<br /><br />The first part of the thesis deals with the architecture of one-dimensional organometallic polymers. A precursor molecule 2,7-dibromobenzothieno[3,2-b]benzothiophene (BrBTBT) is sublimed on an Ag(111) surface. Combining STM and density functional theory (DFT) the intermediate step of the Ullmann coupling reaction is revealed. The results show, that the organometallic polymers can be ordered in a side by side manner by annealing the molecules in distinct steps, while the polymers can be grown with length of several tens of nanometers.<br /><br />In the second part of the thesis, molecular and metal-ligand interactions were used to build two-dimensional (2D) supramolecular structures on an Ag(111) surface. The structural properties of a precursor molecule [1]Benzothieno[3,2-b][1]benzothiophene- 2,7-dicarbonitrile (CyanoBTBT) are examined by means of STM, Auger electron spectroscopy (AES) and DFT. The study of the pure molecular phase revealed the appearance of two different phases of CyanoBTBT on the surface, which is attributed to the prochiral structure of the molecule. The formation of metalorganic networks is shown for the deposition of Iron atoms and precursor molecules at room temperature. A temperature dependent study reveals different steps of an irreversible phase separation and addresses the distinct structures of molecules and Iron atoms and clusters.<br /><br />The third part of the thesis addresses the unique properties of a single layer of hexagonal Boron Nitride (h-BN) and graphene. Chemical-vapour-deposition (CVD) is used to grow atomically thin layers of each h-BN and graphene on Rh(111) and Ni(111). All substrates are studied by means of STM, AFM, AES and for the case of Ni(111) by means of magnetic force microscopy (MFM) and XMCD. The h-BN layer served as substrate for two different approaches to obtain free-standing graphene. (i) Commercially available graphene was transferred using standard wetetching techniques. (ii) CVD was used to grow graphene in-situ under ultra clean conditions. The results show that depending on the growth parameters graphene can be grown on top of an insulating material. Furthermore the structural properties of the graphene for both approaches are intensively studied, in particular multilayer, folding, Moire pattern and wrinkles are addressed. In a final step the magnetic interaction between Cobalt adatoms and clusters and the underlying Ni(111) substrate via the graphene/h-BN heterojunction are examined using XMCD. The results show, that both metals are magnetically decoupled, which opens the door for interesting spin valve experiments.<br /><br />The last part of the thesis combines STM and XMCD experiments to reveal the magnetic interaction between Iron atoms on two different metal substrates. Iron atoms were deposited both at room temperature and at low temperature of T = 8 K on Ru(0001) and Rh(111). The evolution of the magnetic signal is studied with increasing Iron coverage ranging from impurities up to a coverage of 0.35 % of a monolayer by means of XMCD. The results show, that the nearest-neighbour exchange interaction is very small for both substrates and show an opposite sign for Ru(0001) and Rh(111). A complex magnetic order is revealed for higher coverages, which is due to the competition between nearest-neighbour exchange interaction and indirect exchange interaction. The development of a Monte Carlo simulation for these particular systems and the combination with DFT calculations, reveal the preferred magnetic ground state of Iron monomers and clusters of sizes up to tetramers for different adsorption sites and both substrates. It is shown that the evolution of the magnetic ground state is mainly driven by the Rudermann-Kittel-Kasuya-Yosida interaction for the case of Rh(111), while for the case of Ru(0001) the long-range order interaction is rather small. 2014 eng terms-of-use 2015-08-27T13:40:30Z Krotzky, Sören Gabriel Krotzky, Sören Gabriel Metallic and molecular nanostructures on well-defined surfaces

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