[en] We report about very high-quality epitaxial NiO films grown on a Fe(0 0 1) passivated surface. X-ray magnetic linear dichroism at the Ni L₂ absorption edge has been applied to investigate the magnetic anisotropy in the NiO layer. We find that very thin NiO films (7-20 atomic layers) develop an in-plane uniaxial magnetic anisotropy, whose axis is found to be perpendicular to the Fe substrate magnetization M. This behaviour is in contrast with what observed in the specular Fe/NiO(0 0 1) interface, where the coupling is parallel

[en] We apply the principles of Optical Orientation to measure by Mott polarimetry the spin polarization of electrons photoemitted from different group-IV heterostructures. The maximum measured spin polarization, obtained from a Ge/Si_0.31Ge_0.69 strained film, undoubtedly exceeds the maximum value of 50% attainable in bulk structures. The explanation we give for this result lies in the enhanced band orbital mixing between light hole and split-off valence bands as a consequence of the compressive strain experienced by the thin Ge layer

[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] Full text: Since the discovery of superconductivity in alkali-doped solid C₆₀, the electronic structure of the host material (C₆₀) and the doped compounds (A_xC₆₀, where A is an alkali metal), has been the subject of a considerable amount of work, both theoretical and experimental. The spectroscopic investigations of the alkali-doped C₆₀ compounds has been mainly focussed on the valence states, while much less information is available on the unoccupied states. In particular, inverse photoemission data on the complete set of stable Rb_xC₆₀ compounds was, so far, still missing. We have performed Inverse Photoemission (IPE) spectroscopy on Rb_xC₆₀ compounds (x = 1, 3, 4, 6). IPE spectra were obtained using a band-pass photon detector (hv = 9.4 eV, FWHM = 0.7 eV) and scanning the kinetic energy of the electrons impinging on the sample. Rb was evaporated on C₆₀ films (thickness = 6-12 atomic layers) grown in situ on a Cu(100) substrate. The temperature of the substrate was kept equal to T = 100 deg C, which is lower than the C₆₀ sublimation temperature. The amount of Rb was checked by measuring the intensity of the C1s and Rb3d photoemission lines. After the required amount of Rb had been deposited, the samples were annealed to distillate the desired stable phase

[en] The spin features of surface resonance bands in single layer Bi on Ge(1 1 1) are studied by means of spin- and angle-resolved photoemission spectroscopy and inverse photoemission spectroscopy. We characterize the occupied and empty surface states of Ge(1 1 1) and show that the deposition of one monolayer of Bi on Ge(1 1 1) leads to the appearance of spin-polarized surface resonance bands. In particular, the C _3v symmetry, which Bi adatoms adopt on Ge(1 1 1), allows for the presence of Rashba-like occupied and unoccupied electronic states around the $\stackrel{¯<!--\; ??\; -->}{\text{M}}$ point of the Bi surface Brillouin zone with a giant spin–orbit constant $|{\mathrm{\alpha <!--\; ??\; -->}}_{\text{R}}|=(1.4\pm <!--\; ??\; -->0.1)$ eV · Å. (paper)

[en] We have incrementally grown bismuth thin films onto a n-doped Ge(111) substrate. Low energy electron diffraction reveals that the first Bi atomic layer is characterized by the $(\sqrt{3}\times <!--\; ??\; -->\sqrt{3})R{30}^{\circ <!--\; ???\; -->}$ reconstruction. By angle-resolved photoemission spectroscopy we observe Rashba-split bands that do not cross the Fermi level. At higher coverages, where a Rashba type of splitting should still be present, the density of occupied states close to the Fermi energy gradually increases, while extra diffraction spots, related to Bi(110) islands, appear. (paper)

[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] By means of X-ray photoemission spectroscopy and low energy electron diffraction, we show that it is possible to grow good quality thin epitaxial CoO films on Fe(001) substrates, through deposition in oxygen atmosphere. In particular, the composition and the structure of CoO(001)/Fe(001) bilayer systems and Fe(001)/CoO(001)/Fe(001) trilayer systems have been investigated by monitoring the evolution of the chemical interactions at the interfaces as a function of CoO thickness and growth temperature. We observe the presence of Fe oxides at the CoO/Fe interface and of a thin layer of metallic cobalt at the upper Fe/CoO interface of trilayer systems

[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.

[en] An optical analogue of a quantum particle bouncing on a hard surface under the influence of gravity (a quantum bouncer) is experimentally demonstrated using a circularly curved optical waveguide. Spatially resolved tunneling optical microscopy measurements of multiple beam reflections at the waveguide edge clearly show the appearance of wave packet collapses and revivals (either integer and fractional), corresponding to the full quantum regime of the quantum bouncer.