Sublattice identification in noncontact atomic force microscopy of the NaCl(001) surface

R. Hoffmann, D. Weiner, A. Schirmeisen, and A. S. Foster

Phys. Rev. B 80, 115426 – Published 21 September 2009

Abstract

We compare the three-dimensional force field obtained from frequency-distance measurements above the NaCl(001) surface to atomistic calculations using various tip models. In the experiments, long-range forces cause a total attractive force even on the similarly charged site. Taking force differences between two sites minimizes the influence of such long-range forces. The magnitude of the measured force differences are by a factor of 6.5–10 smaller than the calculated forces. This is an indication that for the particular tip used in this experiment several atoms of the tip interact with the surface atoms at close tip-sample distances. The interaction of these additional atoms with the surface is small at the imaging distance, because symmetric images are obtained. The force distance characteristics resemble those of a negative tip apex ion which could be explained, e.g., by a neutral Si tip.

Received 12 February 2009

DOI:https://doi.org/10.1103/PhysRevB.80.115426

Authors & Affiliations

R. Hoffmann¹, D. Weiner^2,3,*, A. Schirmeisen^2,3, and A. S. Foster^4,5

¹Physikalisches Institut and DFG Center for Functional Nanostructures (CFN), Universität Karlsruhe, D-76128 Karlsruhe, Germany
²Physikalisches Institut, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany
³Center for Nanotechnology (CeNTech), Heisenbergstraße 11, 48149 Münster, Germany
⁴Department of Applied Physics, Helsinki University of Technology, P.O. Box 1100, Helsinki 02015, Finland
⁵Department of Physics, Tampere University of Technology, P.O. Box 692, Tampere 33101, Finland

^*Present address: SPECS Zürich GmbH, Technoparkstrasse 1, 8005 Zürich, Switzerland.

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Issue

Vol. 80, Iss. 11 — 15 September 2009

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Images

Figure 1
(Color online) (a) Atomic resolution image obtained on the NaCl(001) surface at $Δ f = - 144.9 Hz$ . (b) Slice of the three-dimensional frequency-shift data across the position of the topographic maximum and minimum. (c) Slice of the three-dimensional frequency-shift data across the bridge positions.Reuse & Permissions
Figure 2
(Color online) (a) Experimental frequency shift and (b) short-range forces at specific atomic sites (maximum, minimum, and bridge site).Reuse & Permissions
Figure 3
(Color online) Atomic structures from simulations of (a) NaCl surface and O-terminated MgO tip (MgO-O), (b) OH-terminated MgO tip (MgO-OH), (c) short-edge NaCl cuboid tip (cub-sh), (d) long-edge NaCl cuboid tip (cub-lg), (e) OH-terminated NaCl cuboid tip (cub-OH), (f) Mg-terminated MgO tip (MgO-Mg), (g) Na-terminated NaCl tip (NaCl-Na), (h) Cl-terminated NaCl tip (NaCl-Cl), and (i) Na-terminated NaCl tip tilted by $30 °$ (NaCltilt-Na).Reuse & Permissions
Figure 4
(Color online) Calculated forces: maximum for tips with strongest attraction to (a) surface anions and (b) surface cations; minimum for tips with strongest attraction to (c) surface anions and (d) surface cations; bridge for tips with strongest attraction to (e) surface anions and (f) surface cations. All $x$ axes of the curves have been taken directly from the calculations.Reuse & Permissions
Figure 5
Measured force differences (black line): (a) $F_{B} - F_{A}$ , (b) $F_{B} - F_{C}$ , and (c) $F_{C} - F_{A}$ , where $A$ is the topographical maximum, $B$ the minimum and $C$ the bridge site. For comparison the results of the atomistic simulations for the NaCl tips have been included in this graph (square and cross symbols).Reuse & Permissions
Figure 6
(Color online) Calculated force difference curves: $F_{B} - F_{A}$ for tips with strongest attraction to (a) surface anions and (b) surface cations; $F_{B} - F_{C}$ for tips with strongest attraction to (c) surface anions and (d) surface cations; $F_{C} - F_{A}$ for tips with strongest attraction to (e) surface anions and (f) surface cations where $A$ is the topographical maximum, $B$ the minimum and $C$ the bridge site. All $x$ axes of the curves have been normalized so that zero is at the position of the first maximum in the minimum-maximum curves. The hatch shows the region where a nearly linear slope is observed. This slope is characteristic for the tip termination for all tips except the OH-terminated tips. The $z$ axes of all models are normalized such that the maxima in the min-max curve match and are set to 0.Reuse & Permissions

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