This thesis presents insights from our study of various correlated electron systems with a scanning tunneling microscope (STM). In ordinary metals, electron-electron interactions exist, but get... Show moreThis thesis presents insights from our study of various correlated electron systems with a scanning tunneling microscope (STM). In ordinary metals, electron-electron interactions exist, but get substantially screened due to the sheer number of electrons. We therefore describe electrons in ordinary metals as a gaseous state of free, or weakly interacting charged particles. This adequately explains their properties, however, this picture does not work for correlated electron materials. The prominent electron-electron interactions present in these materials enable a wide range of exotic electronic phenomena, some of which are presented in this work. In chapter 2, we present STM results measured on an overdoped copper oxide compound and show that the superconducting state that occurs in these materials cannot be described by conventional BCS theory, contrary to what is commonly believed. In chapter 3, we study twisted bilayer graphene devices, and quantify their local twist angle and strain on the nanoscale. In chapter 4, we describe how to build and characterize the hardware needed to do noise spectroscopy measurements in a conventional, low temperature STM setup. Finally, in chapter 5, we present our noise spectroscopy measurements on Sr2IrO4, and explain how random telegraph noise could lead to the observed noise enhancements. Show less
The work in this thesis demonstrates how to obtain an atomic-scale picture of a diverse set of complex surface structures observed using STM, under disparate conditions. Chapters 4−6 each represent... Show moreThe work in this thesis demonstrates how to obtain an atomic-scale picture of a diverse set of complex surface structures observed using STM, under disparate conditions. Chapters 4−6 each represent a different approach to answer the same question: How can we find out what a surface looks like at the atomic scale? By employing appropriate theoretical tools that complement the experimental conditions and measurement techniques, it is possible to compare the results from theory and experiment in an intuitive manner to obtain additional insights. Additionally, Chapter 4 shows that theoretical studies, which do not take experimental conditions into account appropriately, can lead to wrong conclusions. Show less
In surface science there is great effort to move from studying simple, flat model surfaces in vacuum to investigating more complex model catalysts in gas environments (in situ). This thesis gives... Show moreIn surface science there is great effort to move from studying simple, flat model surfaces in vacuum to investigating more complex model catalysts in gas environments (in situ). This thesis gives three examples of such studies using microscopy and spectroscopy.Exposure of ZnO(10-10) to moderate pressures of water in an in situ scanning tunneling microscope reveals that the surface roughens. The flat ZnO(10-10) is thus only conditionally suited as a model catalyst for reactions involving water.In the same microscope, surface gold oxide formation is observed on TiO2/Au(111) during CO oxidation at 1 bar pressure. Comparisons to the Au(111) surface suggest that the titania does not supply atomic oxygen to the Au(111) substrate as part of the reaction mechanism of the CO oxidation.Co(0001) is investigated as a model catalyst for Fischer-Tropsch synthesis, the reaction of CO and H2 to form hydrocarbons. In this thesis the oxidation behavior of the cobalt and the adsorption of carbon species during the reaction are investigated using near-ambient pressure X-ray photoelectron spectroscopy.Generally, this thesis exemplifies the significant influence that small concentrations of contaminants in gases and materials can have on the structure and behavior of surfaces in in situ studies. Show less
This thesis described the development of novel scanning tunneling microscopy techniques to investigate strongly correlated electronic states in quantum matter.
This work covers two closely related topics: a theoretical study on the origins of friction and an experimental study on the growth of graphene. Both fundamental studies are focusing on the atomic... Show moreThis work covers two closely related topics: a theoretical study on the origins of friction and an experimental study on the growth of graphene. Both fundamental studies are focusing on the atomic processes involved. The study on friction treats the dissipation that takes places at one single friction contact. We show that the current explanations result in a discrepancy that we solve by evalutation of the mass involved: this mass is orders of magnitude smallar than assumed. The very small and dynamic mass at a friction contact forms an efficient channel of dissipation. This explanation allows us to understand and predict the friction behavior of surfaces at both the small and large scale. The study of graphene growth investigates the growth process of graphene at the atomic scale with a Scannning Tunneling Microscope in situ. We use our high- and, variable-temperature STM to determine the lowest nucleation temperature of graphene on Ir(111). Additionaly, individual steps that follow up each other during growth are clarified and presented. The graphene film closure is studied as well, which showed that graphene introduces internal strain in order to prevent local lattice defects. Our results are important for the improvement of the quality of graphene. Show less
This thesis describes the construction of a second generation high-pressure, high-temperature scanning tunneling microscope, the ReactorSTM, with which the surfaces of catalysts can be studied... Show moreThis thesis describes the construction of a second generation high-pressure, high-temperature scanning tunneling microscope, the ReactorSTM, with which the surfaces of catalysts can be studied under relevant reaction conditions. Furthermore, the thesis describes three separate catalytic systems at ~ 1 bar, and elevated temperatures. Firstly, NO reduction on Pt(100), in which a mathematical model for the reaction mechanism, following Langmuir-Hinshelwood kinetics, is proposed. Secondly, CO oxidation, in which the Pt(110) surface is atomically resolved at high p, T. Thirdly, the thesis describes a successful pilot experiment about the hydrodesulphurization of thiophene, which is catalytically activated by molybdenum disulphide nano-crystallites on an Au(111) support. Show less
