Figure 1

The gray scale height image shows the surface topography (raw data) at a constant frequency shift of $\Delta f=-138\mathrm{Hz}$ obtained in conventional scan mode of noncontact atomic force microscopy on NaCl(100) in ultrahigh vacuum. For 3D spectroscopy the frequency shift was acquired as a function of tip-sample distance $z$ for 34 points along the dashed line in $x$ direction and for 10 equidistant $y$ positions. The force map analysis was performed for a $y$ position along the corrugation maxima, equivalent to the indicated dashed line.Reuse & Permissions

Figure 2

(a) The image shows the measured frequency shift (unprocessed raw data) vs relative tip-sample separation $z$ as a function of the horizontal position along the $x$ axis. The image consists of 34 spectroscopy curves, each covering a distance range of $\Delta z=1.1\mathrm{nm}$. (b) Simultaneously acquired dissipation map showing the dissipated energy per oscillation cycle.Reuse & Permissions

Figure 3

(a) Image of the tip-sample potential energy (color coded) as a function of horizontal and vertical tip position. The black line indicates the $z$ positions of the potential energy minima. (b) The triangles denote the horizontal line profile along the energy minima [i.e., along the black line in (a)], which can be approximated by a sinusoidal curve (dashed line), yielding an effective potential energy barrier of $\Delta E_{\mathrm{barrier}}=48\mathrm{meV}$.Reuse & Permissions

Figure 4

(a) Forces as a function of relative tip-sample distance taken at the $x$ positions labeled $A$ and $B$. The dotted blue curve was constructed for the purpose of demonstration from the left part ($z<0.2\mathrm{nm}$) of the original blue curve, shifted by 0.9 nm to the right. The inset shows the experimental site $B$ force (blue) compared with the force curves expected from a double well potential energy model (dotted black), indicating the resulting hysteresis due to different forces during the forward and backward movement of the oscillating tip. (b) Left: tip atom approaching site $B$ of the surface. Right: beyond a certain distance the tip atom relaxes towards site $A$, which is represented by the sudden force drop from $B$ to $C$ in the inset of graph (a).Reuse & Permissions