Atom-resolved analysis of an ionic KBr(001) crystal surface covered with a thin water layer by frequency modulation...

Area of Science:

• Surface science
• Atomic force microscopy
• Physical chemistry

Background:

• Studying solid-liquid interfaces at the atomic level is crucial for understanding chemical and physical processes.
• Atomic force microscopy (AFM) is a powerful tool for nanoscale imaging, but its performance can be limited at liquid interfaces.
• Maintaining high Q-factor in AFM cantilevers is essential for sensitive force detection.

Purpose of the Study:

• To achieve atomic resolution imaging of an ionic crystal surface covered with a thin water layer using frequency modulation atomic force microscopy (FM-AFM).
• To investigate the influence of tip-sample interactions, specifically ion adsorption and hydration layers, on AFM measurements at the solid-liquid interface.
• To analyze the force-distance characteristics at the solid-water interface with high sensitivity.

Main Methods:

• Utilized frequency modulation atomic force microscopy (FM-AFM) with atomic resolution.
• Immersed only the tip apex of the AFM cantilever in the thin water layer to maintain a high Q-factor.
• Acquired spatial variation maps of the resonant frequency shift to analyze force-distance characteristics.
• Observed two types of atom-resolved contrast images.

Main Results:

• Achieved atomic resolution imaging of the KBr(001) surface covered with a thin water layer.
• Maintained a high Q-factor for the AFM cantilever, comparable to operation in air, enabling improved differential force detection.
• Observed distinct imaging contrasts, potentially due to different ions (K+ or Br-) on the tip apex and their interaction with hydration layers.
• Demonstrated atomic site-dependent oscillatory frequency shift-distance curves at the solid-water interface.

Conclusions:

• FM-AFM with a high Q-factor is effective for atomic resolution imaging of solid-water interfaces.
• Ion adsorption on the AFM tip and sample surface, along with hydration layers, significantly influences the observed contrast and force interactions.
• The study provides insights into the fundamental interactions governing solid-liquid interfaces at the atomic scale.