Figure 2
(a–e, k–o) Experimental constant-height \(\Delta f\) images as a function of tip-sample distance (raw data) measured with a CO tip on \(\hbox {CaF}_{2}\)(111) at the same spot on the sample. \(z_{\text{exp}} = 0\,\hbox {pm}\) is defined as the closest tip-sample approach in the experiment. (f–j, p–t) Constant-height images calculated with the probe particle model for a CO tip on \(\hbox {CaF}_{2}\)(111) over a similar tip-sample distance range as the experimental images. The calculation reproduces all measured contrast in good agreement. z is defined as the vertical distance between the F\(^-_{\text{top}}\) and the tip apex oxygen nuclei. The unit cell defined in Fig. 1f is drawn in all images.
