Role of tip apices in scanning force spectroscopy on alkali halides at room temperature-chemical nature of the tip apex and atomic-scale deformations

We have revealed processes of the tip apex distortion in the measurements of non-contact scanning force microscopy. High-spatial-resolution two-dimensional force mapping on KCl(100) surfaces for a large number of tips, seven tips, enabled us to see the complex behavior of the tip apex distortion. The tips are from Si without additional coating, but are altered by the tip-sample interaction and show the behavior of different atomic species. On the KCl(001) surfaces, the tip apex, consisting of K and Cl atoms or of Si, distorted several times while changing the distance even in a weak attractive region. There are variations in rigidity of the tip apex, but all tips distorted in the small attractive region. This complex behavior was categorized in patterns by our analyses. We compare the experimental force-distance data to atomistic simulations using rigid KCl-terminated tips and KCl-terminated tips with an additional KCl-pair designed to perform atomic jumps. We also compare the experimental force-distance data to first principles simulations using Si tips. We mainly find K-terminated tips and Si-terminated tips. We find that Si tips show only one force minimum whereas KCl-terminated tips show two force minima in line with the stronger rigidity of Si compared to KCl. At room temperature, the tip apex atoms can perform atomic jumps that change the atomic configuration of the tip apex.

Automated summary

The study revealed complex behaviors of tip apex distortion during non-contact scanning force microscopy measurements, showing variations in rigidity and atomic composition of the tips on different surfaces. Atomistic simulations and first principles simulations were used for comparison, indicating differences in force minima between different types of terminated tips. Additionally, it was found that tip apex atoms can undergo atomic jumps at room temperature, changing the atomic configuration of the tip apex.