Scanning force microscope for investigating solid-liquid interfaces

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A scanning force microscope is applied for, which shall be used for high-resolution imaging of solid-liquid interfaces. An important aspect of the applied instrument is the possibility to precisely control the measurement conditions such as atmosphere, humidity and temperature in a wide range of possible values. The instruments will be used for research projects that require well-defined measurement conditions. This particularly applies for research projects in which pH-dependent processes are studied at the calcite-water interface, as the pH value of the solution depends on the carbon dioxide partial pressure in the surrounding atmosphere. The composition of the solution is then defined by the carbonate equilibrium at the given pH value.In this context, we aim at studying the incorporation of boron into calcite. The boron concentration and isotope composition in maritime calcite samples is used as a climate proxy to reconstruct the atmospheric carbon dioxide partial pressure in the past. As compared to ice core records, the boron incorporation in principle provides the possibility to obtain insights into the ancient atmosphere more than 800,000 years ago. However, the details of the incorporation mechanism are still under debate. In this project, we want to directly image boron defects in calcite under well-controlled conditions to shed light on the way boron is incorporated. Here we will benefit from the fact that defects can be imaged with atomic resolution and changes in the three-dimensional hydration structure above a defect site are ion specific.A further research area in which the applied scanning force microscope will be used is ice nucleation on mineral surfaces. It is known that mineral dust in the atmosphere can be highly efficient as ice nucleating particles. For understanding ice formation in clouds and developing reliable climate models, ice nucleating particles are extensively studied. The molecular-level mechanisms during ice nucleation at aerosol particles are, however, still poorly understood. In particular, it remains largely unclear why some minerals are highly active while others are not. In this context, we want to study the hydration structure at the mineral-water interface of active and less active ice nucleating minerals. As for the above project, we will make use of the fact that the scanning force microscope not only provides two-dimensional images but also allows for investigating a three-dimensional volume at the interface. This will enable to directly map and compare the hydration structure of different ice nucleating minerals and to identify characteristic properties of active ice nucleating particles.