In this study we use ab initio calculations and a pure silicon tip to study the tip-surface interaction with four characteristic insulating surfaces: ͑i͒ the narrow gap TiO 2 ͑110͒ surface, ͑ii͒ the classic oxide MgO ͑001͒ surface, ͑iii͒ the ionic solid CaCO 3 (101 4) surface with molecular anion, and ͑iv͒ the wide gap CaF 2 ͑111͒ surface. Generally we find that the tip-surface interaction strongly depends on the surface electronic structure due to the dominance of covalent bond formation with the silicon tip. However, we also find that in every case the strongest interaction is with the highest anion of the surface. This result suggests that, if the original silicon tip can be carefully controlled, it should be possible to immediately identify the species seen as bright in images of insulating surfaces. In order to provide a more complete picture we also compare these results to those for contaminated tips and suggest how applied voltage could also be used to probe chemical identity.

We use first principles density functional theory calculations to study the interaction of a model dangling bond silicon tip with the surfaces of CaF 2 , Al 2 O 3 , TiO 2 , and MgO. In each case the strongest interaction is with the highest anions in the surface. We show that this is due to the onset of chemical bonding with the surface anions, which can be controlled by an electric field across the system. Combining our results and previous studies on semiconductor surfaces suggests that using dangling bond Si tips can provide immediate identification of surface species in atomically resolved noncontact atomic force microscopy and facilitate selective measurements of short-range interactions with surface sites.

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We have modelled NC-AFM imaging of organic molecules adsorbed on the MgO(100) and TiO2(110) surfaces, to study whether molecules adsorbed at well determined surface sites could serve as markers for chemical resolution of surface species and possible mechanisms of adsorption and manipulation of such molecules with NC-AFM tips. We calculated images of perfect MgO and TiO2 surfaces and considered the adsorption of the formate ion and 3-{4-[Tris-(3,5-di-tert-butyl-phenyl)-methyl]-phenoxy}-propionic acid (C52H72O3) at the MgO(100) and TiO2(110) surfaces, respectively, using several types of oxide tip models. The results demonstrate that using adsorption of even small molecules, such as formate, for identifying surface chemical species in NC-AFM images may not be practical. The interaction of hydrocarbon molecules with perfect oxide surfaces is weak and their adsorption should be aided by attaching special anchoring groups. Flat molecules can be identified by their shape, but simultaneous atomic resolution inside the molecule and on the substrate under the same imaging conditions is not feasible.

We investigate the mechanisms of contrast formation in NC‐AFM imaging of self‐assembled monolayers of alkanethiols on the Au (111) surface. Comparing the potential models with implicit and explicit electrostatics, we demonstrate that, similar to the imaging of polar solid surfaces, the electrostatic interaction plays the central role in contrast formation. Careful comparison of several tip models showed that the model of a clean SiO2 tip gives the closest agreement with the experimental data.