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
We study the dynamics of single molecules and individual gold nanorods in glycerol at variable temperatures. We demonstrate temperature-cycle microscopy on FRET-labeled polyproline and double... Show moreWe study the dynamics of single molecules and individual gold nanorods in glycerol at variable temperatures. We demonstrate temperature-cycle microscopy on FRET-labeled polyproline and double-stranded DNA molecules to access micro-second dynamics of single molecules, and reveal the influences of dye-dye interaction at short interdye distances on the observed FRET values. We use neutron-scattering techniques to examine the origin of solid-like structures suggested in previous reports and the influence of the thermal history. We find that crystal nucleation takes place in glycerol at temperatures very close to the glass transition temperature. This observation suggests that the thermal history of the glycerol sample needs to be controlled for studying dynamical heterogeneity in supercooled liquids. For the first time, we demonstrate gold nanorods as local viscosity reporter to study heterogeneity in supercooled liquids. Following rotational dynamics of individual gold nanorods in glycerol upon cooling below 226K, we start to observe deviations of local viscosity from the bulk viscosity of glycerol. Our observation suggests heterogeneity on relatively large length scale exists at surprisingly high temperatures. In the end, we demonstrate gold nanorods for enhancing fluorescence from single molecules and for fluorescence correlation spectroscopy at micromolar concentrations with single-molecule sensitivity. Show less
