Berlin 2012 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 12: Surface dynamics

O 12.1: Vortrag

Montag, 26. März 2012, 16:00–16:15, H 2013

Density driven solidification of a 2D molecule gas on a bulk insulator: Co-Salen on NiO(001) — •Josef Grenz, Alexander Schwarz, and Roland Wiesendanger — Institute of Applied Physics, University of Hamburg, Jungiusstr. 11, 20355 Hamburg

Co-Salen is a planar metal-organic Schiff base complex and known for its oxygen affinity and tendency to pair in dimers. Previous atomic force microscopy studies in UHV have shown, that this molecule initially adsorbs on NaCl(001) as monomers and with increasing coverage exhibts a bimodal island growth with dimers as building blocks [1,2].
However, on NiO(001), which also crystallizes in the rocksalt structure, for low coverages (< 1 ML) no growth can be detected, only step edge decoration. After complete decoration, diffusing molecules can be observed on flat terraces using z(t)-spectroscopy on a fixed (x,y)-position: Whenever a molecule passes underneath the tip, its z-position is adjusted accordingly. Increasing the amount of deposited molecules leads to more frequent adjustments events. If the density of molecules becomes large enough, diffusion stops. High resolution AFM measurements at low temperatures reveal the formation of an amorphous monolayer consisting of monomers. After this density driven solidification of a molecule gas layer-by-layer step flow growth sets in.

[1] S. Fremy, et al., Nanotechnology 20, 405608 (2009).

[2] K. Lämmle, et al., Nano Lett. 10, 2965 (2010).