[en] Highlights: • CoO grown on the Co(001)-p(1 × 1)O surface of a 5 ML thick Co layer on Fe(001). • The growth process does not induce Fe cation migration and/or oxidation. • A misfit dislocation network develops in the very early stages of CoO growth. • Such a network acts as a template for a three-dimensional CoO nanostructuration. • The dimensions of CoO wedding-cake square mounds scale linearly with thickness. - Abstract: The realization of nanometer-scale structures through bottom-up strategies can be accomplished by exploiting a buried network of dislocations. We show that, by following appropriate growth steps in ultra-high vacuum molecular beam epitaxy, it is possible to grow nano-structured films of CoO coupled to Fe(001) substrates, with tunable sizes (both the lateral size and the maximum height scale linearly with coverage). The growth mode is discussed in terms of the evolution of surface morphology and chemical interactions as a function of the CoO thickness. Scanning tunneling microscopy measurements reveal that square mounds of CoO with lateral dimensions of less than 25 nm and heights below 10 atomic layers are obtained by growing few-nanometers-thick CoO films on a pre-oxidized Fe(001) surface covered by an ultra-thin Co buffer layer. In the early stages of growth, a network of misfit dislocations develops, which works as a template for the CoO nano-structuring. From a chemical point of view, at variance with typical CoO/Fe interfaces, neither Fe segregation at the surface nor Fe oxidation at the buried interface are observed, as seen by Auger electron spectroscopy and X-ray Photoemission Spectroscopy, respectively.

[en] Ultrathin CoO films can be grown onto Fe(001) by exploiting Co buffer layers with nanometer thickness, with the result of avoiding the formation of Fe oxides at the interface. Such a system is characterized by a magnetic anisotropy that influences the magnetization reversal behavior, making the Fe easy magnetization axes inequivalent. Here, we exploit Magnetic Second Harmonic Generation to show that such an anisotropy is related to the buried interface and that it is not related to the magnetic properties of the antiferromagnetic CoO layer. In fact, CoO is magnetically ordered already at room temperature, even for low thicknesses and independently on the presence of Fe oxides. The magnetic domains configuration of CoO mimics those of both Fe and Co in all cases, as testified by magnetic PhotoElectron Emission Microscopy measurements.

[en] We report evidence that the body-centered cubic (bcc)-face-centered cubic (fcc) transition that occurs during Ni film growth on a Fe(001) substrate is preceded by a pre-martensitic phase, as demonstrated by low-energy electron diffraction. The corresponding film superstructure is characterized by a displacement of Ni atoms along the main 〈100〉 crystallographic axes of iron, without any rotation of the unit cell with respect to the (001) plane, in contrast with the martensitic transition that shows four fcc Ni domains with the Ni〈211〉 crystallographic directions aligned with the Fe〈110〉 axes. In addition, the martensitic transition is detected not at 6 ML, as previously believed, but above 20 ML if the Ni sample is rigorously kept at room temperature. The surface morphology of the bcc-fcc transition is characterized by the development of Ni mounds oriented along the 〈110〉 directions, as shown by scanning tunneling microscopy. (paper)

[en] We report on an X-ray photoemission spectroscopy investigation of the early stages of growth of ultra-thin Cr films on the oxygen-passivated Fe(0 0 1)–p(1 × 1)O surface. The Cr coverages ranged from sub-monolayer up to a few atomic layers. Cr has been grown either at 380 K or at 570 K. Our investigation reveals that during the Cr film growth oxygen floats toward the free surface. The presence of a metallic Cr signal from the very beginning of film growth is discussed in relation to Cr–Fe intermixing and alloy formation at the interface. Our findings are independent from the growth temperature, indicating that it has a very little influence on the chemical interactions at the interface, at variance with the oxygen-free Cr/Fe interface.