Ordering of organic molecules on passivated reactive substrates: PTCDA on O-p(2x2)-Ni(1 1 1)

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.