Periodic Reporting for period 2 - WatFun (Water at Oxide Surfaces: A Fundamental Approach)
Période du rapport: 2022-07-01 au 2023-12-31
In this project, we take a radically new approach to investigate the water/oxide interface at the most fundamental, the atomic, scale: we have found a way to integrate bulk liquid water into ultrahigh vacuum (UHV) setups, where an arsenal of highly-developed techniques is available to investigate surfaces. Most notably, the latest developments in non-contact Atomic Force Microscopy (ncAFM) provide atomically-resolved images of insulating materials. This offers the opportunity to accurately determine fundamental quantities that were hitherto inaccessible and to obtain clear-cut experimental results for interpreting and predicting molecular-scale processes.
Our objective is to develop novel measurement concepts and apply them to minerals. Following a broad work plan, we are:
- measuring the surface tension of neat water and the surface free energies of solids with unprecedented purity;
- devising a method to determine, site-by-site, the intrinsic proton affinity, the fundamental property that determines the point of zero charge of oxides in solutions, and their Brønsted acidity in gas-phase reactions;
- investigating, at the atomic scale, how liquid water affects surface structure and how oxides become hydroxylated, dissolve, and ‘age’;
- discover how ice nucleates on the mineral aerosol surfaces that are crucial in cloud formation;
- study how dissolved CO2 reacts with natural minerals, which affects the global carbon cycle;
- address the hydrated oxides that form the basis of cements in concrete.
While this project focuses on providing a fresh view of environmentally relevant surface chemistry, our approach can impact a much wider range of areas.
As the representative images in the figure show, we have successfully mastered this for alpha-alumina, mica, and feldspars.
Specifically, we have (a) found that the surface of alumina is reconstructed because of strain effects, (b) evaluated the short-range ordering of K+ cations on muscovite mica in its most pristine, as-cleaved condition, and (c) provided the very first images of alkali feldspars (orthoclase and microcline, a superior ice nucleator), where we found that their surfaces readily hydroxylate even when cleaved under UHV conditions.
We have also started to build a dedicated apparatus to measure the surface tension of liquid water with the highest accuracy.