Abstract
Surfaces exposed to air can change their structure due to external influences such as chemical reactions or material exchange and movement. The adsorbed water layer that is present under ambient conditions plays an important role especially for highly soluble materials. Surface atoms can easily diffuse into the thin water layer and, when surface conditions are favorable, they can re-attach to the surface. We collected atomic force microscopy images of KBr surfaces in a humidity-controlled glove box at various relative humidities below 40%. By scratching and poking the surface with the AFM tip, we constructed energetically unfavorable holes or scratch sites and material accumulations and recorded the evolution of these defects as a function of the time. We observed an exponential decay of the size of the defects and material accumulations, and from this data we determined energy barriers to dissolution and aggregation of approximately 0.9 eV.
Highlights
Defining surface properties under ambient conditions is challenging as they are heavily influenced by the environment
In this study we investigated the surface of KBr, a salt crystal, by using frequency-modulation atomic force microscopy (FMAFM) using a qPlus sensor [9,10,11]
Our studies of defect healing and erosion of accumulations in various ranges of relative humidity have shown that the speed of the material movement depends on several factors including the relative humidity, and size and shape of the accumulation or defect
Summary
Defining surface properties under ambient conditions is challenging as they are heavily influenced by the environment. Scratching holes are larger defects, created by poking the tip into the surface and scanning quadratic or rectangular areas with a freely determined edge length, of typically some tens of nanometers. The result is an almost rectangular hole with the removed material accumulated around the defect and to a small extent attached to the tip.
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