Charakterisierung der katalytischen Aktivität metallischer Nanopartikel über die Austrittsarbeit
Zusammenfassung der Projektergebnisse
We introduced a procedure to determine accurate and precise force-distance curves in dynamic force measurements utilizing a sharp tip. While single force curves are prone to systematic, often unnoticed errors, we demonstrated their self-consistent retrieval by an alignment procedure using repetitive measurements with the force probe oscillating at varied amplitude. By processing model data, we showed that the procedure provides the valid force curve, the actual oscillation amplitude, and fully compensates thermal drift. The benefit of the method was demonstrated by application to experimental data. We extended the mathematical description of dynamic AFM to include the case of an inclined sampling path. We found that the inclination of the tip movement can have critical consequences for data interpretation, especially for measurements on nanostructured surfaces exhibiting significant lateral force components. Inclination effects have been illustrated by simulation results that resemble the representative experimental conditions of measuring a heterogeneous atomic surface. We propose to measure the AFM observables along a path parallel to the oscillation direction in order to reliably recover the force along this direction. We further introduced the fundamental framework for charge force microscopy (CFM) and investigated charges located in, on, or above the surface of a dielectric substrate supported by a metal electrode. A comprehensive analysis of CFM signal generation now allows us to unravel the dependency of the CFM signal on all relevant system parameters. Most importantly, we untangled the influence from nearby charges when quantifying the magnitude of a central charge of interest in presence of many surrounding charges. We found that charge quantification from regular imaging bears many ambiguities, while mapping the CFM signal perpendicular to the sample surface allows to untangle many signal contributions. Thus, by accounting for measurement parameters and nonlocal influences, quantitative measurements are possible with CFM. The static charge within a gold nanoparticles–on–reduced CeO2(111) system has been determined using CFM. Single gold nanoparticles are found to contain negative charge, with a measurement of (−7.5 ± 0.5) e for one representative particle. In contrast, the CeO 2 surface nearby the particles is found to accumulate positive charge, giving direct evidence for a charge transfer mechanism from the reduced CeO2 substrate to the metal nano-particles. To accomplish such measurements, a two-step procedure for charge quantification has been developed. First, distance-dependent data of the tip-surface capacitance signal are acquired from analysing the signal at the second harmonic of the bias modulation frequency. These data yield parameters for the electrostatic model. Second, the weight function for charges is calculated from the electrostatic model and the charge of the nanoparticle of interest is retrieved from a fit of the weight function to the CFM signal measured at the bias modulation frequency.
Projektbezogene Publikationen (Auswahl)
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Alignment method for the accurate and precise quantification of tip-surface forces. Physical Review B, 103(7).
Heile, Daniel; Olbrich, Reinhard; Reichling, Michael & Rahe, Philipp
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Quantitative dynamic force microscopy with inclined tip oscillation. Beilstein Journal of Nanotechnology, 13, 610-619.
Rahe, Philipp; Heile, Daniel; Olbrich, Reinhard & Reichling, Michael
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Modeling nanoscale charge measurements. Physical Review B, 108(8).
Heile, Daniel; Olbrich, Reinhard; Reichling, Michael & Rahe, Philipp
