Graphene nanoribbons (GNRs) are used as a current carrying substrate in investigation of current-induced forces in a low-temperature STM (chapter 2). We demonstrate induced migration of Co adatoms... Show moreGraphene nanoribbons (GNRs) are used as a current carrying substrate in investigation of current-induced forces in a low-temperature STM (chapter 2). We demonstrate induced migration of Co adatoms on GNRs and on Au(111) using voltage pulses from the STM tip and we argue that motion is due to thermal excitations rather than the wind force. In chapter 3 we show that voltage signal is induced in a graphene strip when a droplet of ionic liquid is moved across its surface. Here we show that even deionized water can induce voltage over charged graphene surface due to the polarizability of water molecules. In chapter 4 we present a method for fabrication of graphene nanoelectrodes which we further test electrically in a modified STM. For the first time we demonstrate that the gap between two graphene nanoelectrodes can be tuned with subnanometric precision Show less
Atoms and molecules are the basic units of matter. If we keep dividing a bar of gold or a glass of water into smaller parts, at the end we are left with a single gold atom or a water molecule. We... Show moreAtoms and molecules are the basic units of matter. If we keep dividing a bar of gold or a glass of water into smaller parts, at the end we are left with a single gold atom or a water molecule. We could not divide them further without them losing their identity. Molecular electronics is the study of how electrons, which are fundamental particles in nature, flow through these basic units of the matter once connected between two electrical leads. At such small dimensions matter starts to lose its macroscopic properties and its behaviour is governed by the rules of quantum mechanics. A molecule can have various electronic and mechanical degrees of freedom (or eigenstates) with discrete energies. The electrons flowing through the molecule can interact with these degrees of freedom making single molecule devices. Better control and understanding of these interactions and study of how the atomic structure of the macroscopic electrical leads affect the electronic-transport forms the main focus of this thesis. Controlled manipulation of single atoms and molecules using a low-temperature scanning tunnelling microscope, probing charge transport using high-frequency shot-noise measurement and the use of graphene as possible electrodes are the three directions which are investigated here. Show less
Catalysis is one of the most important technical and scientific developments, on which present-day society is based. For example, it is crucial to the production of fertilizers or clean... Show more Catalysis is one of the most important technical and scientific developments, on which present-day society is based. For example, it is crucial to the production of fertilizers or clean fuels and needed for the abatement of exhaust gases. Frequently, the employed catalysts are being discovered in a very empirical way; by trial and error. However, designing catalysts based on detailed understanding is preferred. Obtaining understanding is very difficult, because catalysts are very complex materials. Furthermore, its properties often depend on the atmosphere surrounding the catalysts, i.e., the temperature and pressure of reactants and products, which they are exposed to, and these properties also change over time. The major part of this thesis focuses on structural changes of Pt model catalysts exposed to high oxygen pressures at elevated temperatures. The changes were measured with a ReactorSTM, a special version of a scanning tunneling microscope (STM) adapted to operate at high pressure and temperatures. These observations show that various surface oxide with a single-layer thickness form under reaction conditions. These oxides are structurally and chemically different from the Pt bulk oxides. The second part describes a set of experiments to understand the role of low-coordinated atoms and water in Au-catalyzed CO oxidation. Show less
Nuclear magnetic resonance force microscopy (MRFM) is a technique which combines magnetic resonance imaging (MRI) with scanning probe microscopy (SPM). The final goal is to develop this technique... Show moreNuclear magnetic resonance force microscopy (MRFM) is a technique which combines magnetic resonance imaging (MRI) with scanning probe microscopy (SPM). The final goal is to develop this technique to such a level that the atomic structure of a virus or protein can be revealed by this microscope. This thesis shows nuclear magnetic resonance force measurements on copper in which the interaction of the magnetic moments of the nuclei of copper with a magnetic cantilever has delivered a detectable signal at a temperature of 50 millikelvin. Furthermore, we show measurements, which support a new theory where at low magnetic field and low temperature, non contact friction between the magnetic cantilever and paramagnetic electron spins is described. These measurements were enabled by technical improvements such as vibration reduction in a cryogen free dilution refrigerator. As a benchmark for the low vibration, we show atomic resolution scanning tunneling microscopy at 15 millikelvin temperature on graphite. We also show a method to create small magnets for MRFM from a thin magnet film. With these small magnets the field gradient and therefore the sensitivity may be significantly enhanced. Show less
This thesis uses the surface science approach to address questions regarding the interaction of oxygen with platinum and its subsequent reaction with carbon monoxide. A Pt(111) single crystal... Show moreThis thesis uses the surface science approach to address questions regarding the interaction of oxygen with platinum and its subsequent reaction with carbon monoxide. A Pt(111) single crystal surface is used as a model for the catalyst. Chapter 1 provides an overview of the literature on the subject. The description of employed experimental techniques and their backgrounds are presented in Chapter 2. Chapter 3 discusses the adsorption of oxygen on Pt(111) at various temperatures and its role in the oxidation of carbon monoxide. Chapter 4 gives an atomic scale insight into the reaction between adsorbed oxygen and carbon monoxide for different ratios of oxygen and carbon monoxide pressures. In Chapter 5, the reaction between CO and oxygen on Pt(111) was used to register noise in tunneling current due to diffusion and recombination of molecules on the catalytically active surface, to draw conclusions on the most likely rate-limiting step in the process Show less
Spin-crossover compounds showing thermal hysteresis exhibit magnetic and colourmetric bistablility, which is of interest for a number of applications such as information storage and optical... Show moreSpin-crossover compounds showing thermal hysteresis exhibit magnetic and colourmetric bistablility, which is of interest for a number of applications such as information storage and optical displays. Mononuclear iron(II) complexes hold considerable potential in this field, and their cooperative properties may suffer less from size reduction effects than polymeric SCO materials because the coordination environment remains well defined throughout the material. In this thesis, 13 new mononuclear spin-transition materials based on the bapbpy scaffold are described. One of these compounds, [Fe(bbpya)(NCS)2], shows one of the highest transition temperatures (418 K) recorded among known mononuclear SCO complexes. Most interestingly, it keeps a large hysteresis cycle of 21 K in spite of its high transition temperature. Meanwhile, metal dilution study on [Fe(bapbpy)(NCS)2] clearly shows that the two steps and the hysteresis cycles of the SCO are two consequences of the same phenomenon: intermolecular interactions between spin-switching molecules. Finally, a new bapphen-based ligand bearing a 12-carbon alkyl chain at the back of the tetrapyridyl ligand was prepared, which allowed self-assembling the corresponding iron(II) complex on a highly oriented pyrolytic graphite (HOPG) surface. The stable and highly ordered 2D patterns observed by STM are promising for the future study of cooperative spin crossover at surfaces. Show less
A study of the effect of chloride and sulfate anions, as well as of SPS molecules on Cu electrodeposition is presented in this thesis. The deposition process was analyzed by means of a home-built... Show moreA study of the effect of chloride and sulfate anions, as well as of SPS molecules on Cu electrodeposition is presented in this thesis. The deposition process was analyzed by means of a home-built fast electrochemical STM in situ after and during deposition. Show less
In this thesis I present my research on the physics of some important processes in the production of thin films. I studied physical vapour deposition (PVD) and thin film modification through ion... Show moreIn this thesis I present my research on the physics of some important processes in the production of thin films. I studied physical vapour deposition (PVD) and thin film modification through ion bombardment using a newly developed, high-speed scanning tunneling microscope (STM). The instrument has the special property that it can be tilted and azimuthally rotated to allow atom or ion beams a direct line-of-sight access to the region of the surface that is being imaged by the STM tip. With the microscope I have recorded STM movies (available as supplementary material) that offer a unique insight into the atomic surface processes that occur during thin film growth and ion beam sputtering. The __real-time STM__ was applied to the study of some key steps in the fabrication of Mo-Si multilayer optical coatings. I have investigated the non-idealities of these optics, i.e. the alloying of Mo and Si during deposition and the surface roughness formation of a deposited layer. Furthermore, I successfully used the STM to find a possibility to smooth a rough Mo layer after its deposition by means of ion bombardment. Show less
This thesis aimed at preparing and characterizing two different model catalysts after their exposure at different temperatures to oxygen, carbon monoxide and hydrogen. The experiments were... Show moreThis thesis aimed at preparing and characterizing two different model catalysts after their exposure at different temperatures to oxygen, carbon monoxide and hydrogen. The experiments were performed in an ultra-high vacuum (UHV) set-up using a range of techniques including scanning tunneling and atomic force microscopy. The first part of the thesis deals with platinum deposited onto highly oriented pyrolytic graphite (HOPG). It was found that a sub-monolayer of the deposited metal on this substrate forms randomly distributed two-/three-dimensional particles. Analysis of the morphology and height distribution of Pt particles on the HOPG(0001) surface after annealing in UHV and in the presence of low pressures of oxygen, carbon monoxide and hydrogen indicates that their growth proceeds via coalescence. The second part of the thesis is devoted to the preparation of model manganese oxide surfaces starting with the MnO(100) surface, which were used as a support for Pt deposits. The preparation of manganese oxide surfaces was based on annealing of MnO(100) single-crystals at different temperatures in UHV and in the presence of argon, oxygen and hydrogen. The first results of Pt deposition on the MnO(100) surface and on this surface altered by annealing in the presence of oxygen and hydrogen are described. Show less
