Interaction of surface cations of cleaved mica with water in vapor and liquid forms

TL;DR

This study uses advanced microscopy and spectroscopy to directly observe how water interacts with mica surfaces at the atomic level in vapor and liquid states, revealing hydration processes and ion mobility.

Contribution

It provides the first direct experimental visualization of water-mica interactions at atomic resolution in UHV conditions, confirming theoretical predictions.

Findings

Water interacts with mica surface ions in vapor and liquid forms.

Ion mobility and partial proton exchange occur upon water exposure.

Experimental results align with previous theoretical models.

Abstract

Natural minerals contain ions that become hydrated when they come into contact with water in vapor and liquid forms. Muscovite mica -- a common phyllosilicate with perfect cleavage planes -- is an ideal system to investigate the details of ion hydration. The cleaved mica surface is decorated by an array of K$^+$ ions that can be easily exchanged with other ions or protons when immersed in an aqueous solution. Despite the vast interest in the atomic-scale hydration processes of these K$^+$ ions, experimental data under controlled conditions have remained elusive. Here, atomically resolved non-contact atomic force microscopy (nc-AFM) is combined with X-ray photoelectron spectroscopy (XPS) to investigate the cation hydration upon dosing water vapor at 100 K in ultra-high vacuum (UHV). The cleaved surface is further exposed to ultra-clean liquid water at room temperature, which promotes ion mobility and partial ion-to-proton substitution. The results offer the first direct experimental views of the interaction of water with muscovite mica in UHV. The findings are in line with previous theoretical predictions.