The ordering of an organic molecular layer on a ferromagnetic substrate is studied using scanning tunnelling microscopy. Highly ordered layers of perylene-tetracarboxylic-dianhydride (PTCDA) were prepared by vacuum sublimation on an oxygen precovered Ni(1 1 1) surface. The structure of thin layers of PTCDA deposited at room temperature was investigated as a function of growth rates and thickness. It is demonstrated that oxygen passivation reduces the reactivity sufficiently to lead to well-ordered overlayers of PTCDA. For thin films grown at low deposition rates, a herringbone-like structure has been observed. This structure is consistently observed in the islands with typically 100 nm in diameter and 1-2 ML thickness. Depositing thicker films at higher deposition rates results in polycrystalline islands. Within the polycrystalline islands two distinct stripe-like phases are observed in domains with a lateral size of typically 10 nm. The potential impact of these results for organo-metallic spintronic devices is addressed. © 2001 Elsevier Science B.V. All rights reserved.
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