Layer-by-layer dissolution and recovery of KBr(001) surfaces covered with a nanometer-thick water film caused by a pressing tip controlled by frequency modulation atomic force microscopy

Abstract

We observed KBr(001) surfaces covered with a nanometer-thick water film (NWF) using frequency modulation atomic force microscopy (FM-AFM) with stiff force sensors. The NWF with a thickness of ∼3 nm was prepared in humid air at 50%-60% RH. The Δf-Z curves measured by FM-AFM exhibited a series of peaks over the surface, corresponding to the hydration layers, and unique multiple oscillation peaks under the surface. The AFM images showed that layer-by-layer dissolution of KBr(001) planes under the NWF was induced by tip pressing, and quick recovery of the KBr planes was achieved after tip retraction.