Regensburg 2010 – scientific programme

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O: Fachverband Oberflächenphysik

O 22: Methods: Scanning probe techniques III

O 22.5: Talk

Tuesday, March 23, 2010, 11:30–11:45, H32

Simulations of metastable states near the apex of a KBr tip — •Regina Hoffmann¹ and Alexis Baratoff² — ¹Physikalisches Institut, Karlsruhe Institute of Technology — ²Institut für Physik, Universität Basel

Telegraph-like noise in the low-temperature resistance of small conductors has been explained by a single defect hopping between two energy minima separated by a barrier. A similar phenomenon correlated with additional energy dissipation has been observed in dynamic AFM near contact to a KBr(001) sample [1]. The authors attributed this behaviour to a KBr molecule hopping near the apex of the tip, rather than between tip and sample. We report results of atomistic simulations for such a system using a code validated in studies of AFM on ionic crystals [2]. The simulated system consists of a 4*4*4 cube supplemented by one additional K ion bound to a nearby Br ion. Relaxation led to the first stable configuration A. Another stable configuration was found by flipping one of the Br coordinates (x) by about one lattice constant; subsequent relaxation led to the more stable position E. In order to map the potential energy landscape between positions A to E, we incremented the Br x-coordinate forward and backward while relaxing its other coordinates and those of the other ions. Simulations in the presence of a KBr(001) sample indicate that the molecule stays near the tip apex and that additional states with lower energy barriers occur. This may account for the observed jumps. [1] R. Hoffmann et al., Nanotechnology 18, 395503 (2007). [2] T. Trevethan and L. Kantorovich, Nanotechnology 15, S34 (2004)