Investigation of Water Nucleation on Designed Single Crystalline Oxide Surfaces - a Step Towards Understanding the Complex Behavior of Atmospheric Aerosols

The interaction between water molecules and solid surfaces during water/ice nucleation is of extreme importance in physical, biological, geological, and environmental research. Aerosols in the atmosphere, including inorganic mineral dust particles and organic compounds from biogenic and anthropogenic sources, are recognized to be effective ice nuclei (IN) that lead to the formation of ice crystals. These ice crystals play important roles in climate through their interactions with solar and terrestrial radiation. However, a detailed understanding is hampered by the fact that the aerosols vary in size, chemical composition, morphology, crystal orientation, and local defects. In EMSL, some of those challenges can be addressed by utilizing state-of-the-art synthesis and characterization capabilities. By using molecular beam epitaxy (MBE), we are able to synthesis materials, such as TiO2 and Fe2O3, that are commonly found in mineral dusts in their single crystalline thin film form with controlled surface termination. Fundamental studies on these designed surfaces allow us to vary some of the variables independently so that a concrete cause and effect relationship can be established. In this study, we grow epitaxial rutile TiO2(110) and anatase TiO2(001) films and investigate water adsorption and water nucleation processes on these surfaces by ultra-high vacuum scanning tunneling microscopy (STM) and environmental scanning electron microscopy (E-SEM). The surface reaction dynamics revealed can be of critical importance in understanding the water/ice nucleation process on complex aerosols.