Dynamische Rasterkraftmikroskopie mit kleinen Amplituden an Luft und in Flüssigkeiten

Elisabeth Wutscher
2012
In this thesis measurements in air and liquid with small amplitudes were done by dynamic scanning force microscopy. In the last years it was discovered, that the best resolution of surfaces can be achieved by using small oscillation amplitudes of the force sensors [2, 5]. T he most common force sensor are cantilevers with integrated tips made of silicon, which have a stiffness of around 40 N/m and a resonance frequency around 150 kHz. But for measurements in air and liquid it is quite hard to
more » ... is quite hard to image with small amplitudes due to the low sensor stiffness. This imaging mechanism can be simplified by using the qPlus sensor as a force sensor, which has a higher stiffness of around 4300 N/m and resonance frequencies of 50 kHz. Noise considerations show that the high stiffness and the low resonance frequency of the qPlus sensor are a disadvantage for the minimal detectable force gradient. This can be compensated by using qPlus sensors with high Q-values. The shown topography pictures have a high resolution which could only be achieved by using self broken diamond tips. These tips show, compared to metal tips, less wear and also reduce the acting capillary forces because of their hydrophobic nature. In air, high resolution pictures of epitaxial graphene are recorded by frequency modulation atomic force microscopy (FM-AFM). By implementing a new current-to-voltage converter the existing deflection noise density could be reduced by 60%. Thereby it was possible to resolve beside the known steps and ridges also a new structure on the surface. These wrinkles on the graphene surface have a distance of around 5,6 nm and were imaged in two directions with an angle of 60° in between, which leads to the assumption that the underlaying graphene lattice is a starting point for the wrinkles. The cause of the wrinkles could not be clarified yet. One possibility could be the implementation of oxygen atom into the graphene lattice. With the qPlus Sensor on calcite in polyethylenglycol it was possible to resolve atomic steps. Additionally [...]
doi:10.5283/epub.25132 fatcat:z7pc25ihfrdobbfi7kheyigfg4