Surface solitonic charge distribution on 2D materials investigated using Kelvin probe force microscopy technique based on qplus atomic force microscopy

Recently, charged solitons have been found in a two-dimensional CoCl₂/HOPG system, whose microscopic nature remains to be elusive. In this work, we investigate the charged solitons in monolayer CoCl₂ using scanning tunneling microscopy (STM) and atomic force microscopy (AFM). Moreover, we study the electrical properties of the charged solitons at zero electric field by measuring local contact potential difference (LCPD) via Kelvin probe force microscopy (KPFM) using the Δf(V) method. The compensation voltage corresponding to the vertex of the parabola is obtained by fitting the quadratic relationship between Δf and sample bias. The results show that, without an external electric field, the solitons behave as negatively charged entities. Meanwhile, the LCPD mapping characterizes the spatial distribution of the potential at the charged solitons, which agrees well with those obtained from STM band bending measurements.