Abstract
In this paper we examine the stability of silicon tip apices by using density functional theory (DFT) calculations. We find that some tip structures - modelled as small, simple clusters - show variations in stability during manipulation dependent on their orientation with respect to the sample surface. Moreover, we observe that unstable structures can be revealed by a characteristic hysteretic behaviour present in the F(z) curves that were calculated with DFT, which corresponds to a tip-induced dissipation of hundreds of millielectronvolts resulting from reversible structural deformations. Additionally, in order to model the structural evolution of the tip apex within a low temperature NC-AFM experiment, we simulated a repeated tip–surface indentation until the tip structure converged to a stable termination and the characteristic hysteretic behaviour was no longer observed. Our calculations suggest that varying just a single rotational degree of freedom can have as measurable an impact on the tip–surface interaction as a completely different tip structure.
Highlights
The theoretical treatment of chemical interactions at the single atom level has driven considerable progress in NC-AFM over the past decade
In covalent systems in particular, density functional theory (DFT) calculations have been extremely successful in explaining the fundamental interactions that underpin NC-AFM experiments [2,3,13,14,15,16]
Atomistic simulations remain essential to many current studies in covalent [17,18,19] and ionic [20,21] systems because of the inherent difficulties in determining the tip apex structure from purely experimental evidence
Summary
The theoretical treatment of chemical interactions at the single atom level has driven considerable progress in NC-AFM over the past decade. Results are generally only presented for tip structures at a single orientation, even though modifying the tip–surface alignment can strongly affect calculated tip-force F(z) curves and the hysteresis pathways followed by the tip and surface structures [28].
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