Epitaxial growth of thermally stable cobalt films on Au(111)

Abstract

Ferromagnetic thin films play a fundamental role in spintronic applications as a source for spin polarized carriers and in fundamental studies as ferromagnetic substrates. However, it is challenging to produce such metallic films with high structural quality and chemical purity on single crystalline substrates since the diffusion barrier across the metal-metal interface is usually smaller than the thermal activation energy necessary for smooth surface morphologies. Here, we introduce epitaxial thin Co films grown on an Au(111) single crystal surface as a thermally stable ferromagnetic thin film. Our structural investigations reveal an identical growth of thin Co/Au(111) films compared to Co bulk single crystals with large monoatomic Co terraces with an average width of 500 Å, formed after thermal annealing at 575 K. Combining our results from photoemission and Auger electron spectroscopy, we provide evidence that no significant diffusion of Au into the near surface region of the Co film takes place for this temperature and that no Au capping layer is formed on top of Co films. Furthermore, we show that the electronic valence band is dominated by a strong spectral contribution from a Co 3d band and a Co derived surface resonance in the minority band. Both states lead to an overall negative spin polarization at the Fermi energy.

Observation of Exchange Interaction in Iron(II) Spin Crossover Molecules in Contact with Passivated Ferromagnetic Surface of Co/Au(111)

“…Figure 1c,d shows representative STM topographic images of Co films on Au(111) surface before (1c) and after (1d) annealing. The morphology is similar to previous results [ 40,43 ] and shows that the Co film is dominated by random islands without thermal annealing but forms large flat terraces after annealing. The Au passivated surface shows a moiré pattern on the surface that is absent before annealing.…”

“…The moiré structure is characteristic for the lattice misfit between Co and Au and has also been observed on thinner Co films on Au(111). [ 43,47,48 ] After annealing, the orientation of magnetization in the Co film was verified to be in‐plane by in situ magneto‐optical Kerr effect (MOKE) measurements, showing a low coercivity of ≈ 5 mT (see Figure , Supporting Information). After these processes, the [Fe II (Pyrz) 2 ] molecules were deposited onto the substrate held at room temperature from a Knudsen cell at 175°.…”

“…Recent studies showed that [Fe II (Pyrz) 2 ] deposited on inert metallic surface preserves the spin state switching. [21][22][23]26,27,34] The Au/Co/Au(111) system, which has been studied in all detail due to its spin reorientation transition and spintronic applications, [39][40][41][42][43][44][45] was used as a ferromagnetic substrate with inert surface for molecular deposition. Due to the lower free surface energy of Au in comparison with Co, Au shows the tendency for up diffusion when Co/Au(111) system was annealed such that the Co film tends to be covered by a monolayer of Au, as deduced from an analysis of STM images.…”

C60 Adsorbed on Ni(111) and Co(0001) Surfaces

“…This represents a strain of between 10–15%, which may be observed in a pseudomorphic monolayer, but is vanishingly unlikely to persist in a film more than 7 ML thick. The same group has reported that the lattice parameter reverts to the Co bulk value at 7 ML, in a LEED study of the Co film without C 60 molecules present . 2.…”

“…The same group has reported that the lattice parameter reverts to the Co bulk value at 7 ML, in a LEED study of the Co film without C 60 molecules present. 33 2. In some cases, the domains coexist on the same layer.…”