The thesis describes experimental steps towards reduction of friction on the macroscopic scale by scenarios of thermo- and superlubricity well-known on the nanoscale. The friction study involves... Show moreThe thesis describes experimental steps towards reduction of friction on the macroscopic scale by scenarios of thermo- and superlubricity well-known on the nanoscale. The friction study involves experiments on tailored Si nanopillar arrays, micropatterned Diamond-Like Carbon coating and high-quality graphene. Show less
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 work discusses the flow of granular materials (e.g. sand). Even though a single particle is a simple object, the collective behavior of billions of particles can be very complex. In a... Show moreThis work discusses the flow of granular materials (e.g. sand). Even though a single particle is a simple object, the collective behavior of billions of particles can be very complex. In a surprisingly large amount of cases, it is not exactly known how a granular material behaves, and this while these kinds of materials are omnipresent in everyday life, industry, and nature Similar to materials such as water, which can occur as ice, liquid water and vapor, sand can also exist in different phases of matter. If you for instance walk on the beach, sand behaves like a solid, but if you pour it out of your shoes afterwards, it flows like a liquid. This thesis is dedicated to experiments where we investigate what happens when you try to "liquefy" sand by weakly vibrating it. We use an experimental setup which enables us to study how much stress is required to make sand flow, depending on the desired flow rate and the amount of vibrations. These experiments reveal several physical principles that turn out to be important towards understanding the unique behavior of these kinds of materials Show less
