This title appears in the Scientific Report : 2016 
Scanning tunneling microscopy of single-molecule magnets and hybrid-molecular magnets: Two approaches to molecular spintronics
Heß, Volkmar (Corresponding author)
Elektronische Eigenschaften; PGI-6
Jülich Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag 2016
X, 127 S.
Universität Köln, Diss., 2016
978-3-95806-128-6
Book
Dissertation / PhD Thesis
Addenda
Schriften des Forschungszentrums Jülich. Reihe Schlüsseltechnologien / Key Technologies 121
Diss.
OpenAccess
Please use the identifier: http://hdl.handle.net/2128/10391 in citations.


Molecular spintronics attempts both to improve the properties of current electronic devices and develop completely new devices by combining the advantages of molecular electronics and spintronics into one research field. Investigating and evaluating the properties of molecular magnets and to eventually employ them in devices is a major goal of molecular spintronics. Two different kinds of molecular magnets are promising candidates for device development: Single-molecule magnets (SMMs) and hybrid-molecular magnets. Both are ideal building blocks for spintronic devices, such as spin-transistors and spin-valves. However the fabrication of devices requires the deposition on surfaces. Due to the interaction between molecules and surfaces being highly complex, only a fundamental understanding of these phenomena will eventually lead to the succesful application of molecular magnets in devices. To improve the understanding of the molecule-surface interaction both approaches have been investigated experimentally in this dissertation. Since surfaces are prone to contamination, these experiments were conducted in ultra-high vacuum. To gain more insight in such systems and to understand the adsorption phenomena, their structural, electronic and magnetic properties were studied on a microscopic scale with scanning tunneling microscopy (STM) and spectroscopy (STS). The interaction between SMMs and surfaces was exemplarily studied by depositing {Ni$_{4}$} on Au(111). {Ni$_{4}$} is a recently synthesized SMM where a cubane {Ni$^{II}_{4}$($\mu_{3}$ - Cl)$_{4}$} core is responsible for the magnetic properties [1]. The magnetic core is protected by organic ligands exhibiting a thioether surface functionalization. Since thioether functionalized ligands had been widely neglected in earlier experiments, the deposition of {Ni$_{4}$} on Au(111) from solution and the resulting adsorption phenomena were studied by XPS and STM. Both methods revealed strong evidence for a ligand detachment during adsorption. The magnetic core however might be still structurally intact as indicated by XPS. Attempts to desorb the detached ligands and to subsequently image the magnetic core with STM by $\textit{in-situ}$ post-annealing were unsuccessful. Instead the post-annealing lead to the decomposition of the magnetic core and to a most likely sulfur induced reconstruction of the Au(111) surface. As a results of this study new strategies have been proposed to avoid the ligand detachment in future experiments. In a complementary approach the interaction between molecules and surfaces is exploited for the formation of hybrid-molecular magnets. Here, comparatively stable non-magnetic molecules are deposited on magnetic surfaces. The interaction leads to a magnetic molecule-surface hybrid, or "hybrid-molecular magnet". This approach requires a magnetic substrate. For this task the well known Fe/W(110)system was chosen and charaterized by spin-polarized STM (SP-STM). The fabrication of suitable magnetic tips for SP-STM is a well known challenge due to its poor predictability and reproducibilty. The characterization of tips was performed by SP-STM measurements on the Fe/W(110) system and reveals that Cr-coated tips exhibit the required out-of-plane magnetization direction for the following experiments on hybrid-molecular magnet systems. Furthermore an effective spin polarization of up to 12.4% for the whole tip-sample tunnel junction was found. [...]