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et al. ; We report on the effect of cap layer material on the magnetic properties and aging of the Fe-NW (nanowire) arrays grown on oxidized vicinal Si (111) templates using atomic terrace low angle shadowing technique. We find that the Fe-NW arrays capped with metallic (Ag) layers do not show any sign of degradation with aging, whereas NW arrays capped with insulating dielectric (MgO) layers show degradation of the saturation magnetization and an out-of-plane unidirectional anisotropy. We find that this out-of-plane unidirectional anisotropy competes with the shape anisotropy which is still the dominant anisotropy. The origin of this additional anisotropy is explained on the basis of oxidation of Fe due to the presence of MgO that leads to the formation of an oxide interlayer. This oxide interlayer forms at the expense of NW materials, leading to reduction in the thickness of some of the Fe-NWs within the array, and orients their magnetic moments out-of-plane. The reduction in NW thickness and the presence of Fe-O interlayer facilitates stabilization of this anisotropy. Our model is supported by x-ray absorption spectroscopy studies performed as a function of aging, which suggests that the oxide interlayer thickness increases with aging. © 2013 AIP Publishing LLC. ; Work supported by the Science Foundation Ireland (SFI) under Contract No. 06/IN.1/I91, ERA-Net NANOWAVE program, the Irish Government's Program (ISPIRE) for Research in Third Level Institutions, Cycle 4, National Development Plan 2007-2013, the Spanish Ministerio de Ciencia y Innovación (EUI2008-03884 and PTA2008-1108-I), Agència de Gestió d'Ajuts Universitaris i de Recerca (2009 SGR 695), and Nanoaracat. ; Peer Reviewed

et al. ; Systematic investigations of magnetization behavior performed on planar arrays of 30 nm wide Fe-nanowires (NW) fabricated on oxidized step-bunched Si (111) templates reveal that the NW arrays exhibit an uniaxial anisotropy dominated by the shape of the wires, that facilitates in retaining the magnetization in-plane with easy axis parallel to the wires. The NWs possess polycrystalline character with bcc-crystal structure, and present an oxidized interface when capped with MgO. From the temperature dependent magnetization studies we find that for thick wires (>4.5 nm) the magnetization reversal is governed by the curling reversal mode. Whereas, for thin wires the reversal is dominated by thermal activation. © 2013 Bentham Science Publishers. ; Work supported by the Science Foundation Ireland (SFI) under Contract No. 06/IN.1/I91, ERA-Net NANOWAVE program, the Irish Government's Program (ISPIRE) for Research in Third Level Institutions, Cycle 4, National Development Plan 2007-2013, Naughton Fellowship Program, the Spanish Ministerio de Ciencia y Innovación (EUI2008-03884 and PTA2008-1108-I), Agència de Gestió d'Ajuts Universitaris i de Recerca (2009 SGR 695), and Nanoaracat. ; Peer Reviewed

12 páginas, 11 figuras.-- PACS number(s): 73.20.At, 73.20.Hb, 73.22.Dj, 68.37.Ef ; We report on a joint scanning tunneling microscopy (STM) and theoretical wave packet propagation study of field emission resonances (FER's) of nanosized alkali metal clusters deposited on a Cu(100) surface. In addition to FER's of the pristine Cu(100) surface, we observe the appearance of island-induced resonances that are particularly well resolved for STM bias voltage values corresponding to electron energies inside the projected band gap of the substrate. The corresponding dI/dV maps reveal island-induced resonances of different nature. Their electronic densities are localized either inside the alkali cluster or on its boundaries. Our model calculations allow us to explain the experimental results as due to the coexistence and mixing of two kinds of island-induced states. On the one side, since the alkali work function is lower than that of the substrate, the nanosized alkali metal clusters introduce intrinsic localized electronic states pinned to the vacuum level above the cluster. These states can be seen as the FER's of the complete alkali overlayer quantized by the cluster boundaries. On the other side, the attractive potential well due to the alkali metal cluster leads to two-dimensional (2D) localization of the FER's of the Cu(100) surface, the corresponding split component of the resonances appearing below the bottom of the parent continuum. Our main conclusions are based on the attractive nature of the alkali ad-island potential. They are of general validity and, therefore, significant to understand electron confinement in 2D. ; We acknowledge partial financial support from the European Research Council (StG 203239), the Spanish Ministerio de Ciencia e Innovación (MAT2010-15659 and FIS2010-19609-C02-01), the Basque Government-University of the Basque Country G.V.-UPV/EHU (IT-366-07), and the Catalan Agència de Gestió d'Ajuts Universitaris i de Recerca (2009 SGR 695). A.M. acknowledges the spanish Ministerio de Ciencia e Innovacion for financial support through the RyC program. ; Peer reviewed

arXiv:1502.00771v1 ; We combine experimental observations by scanning tunneling microscopy (STM) and density functional theory (DFT) to reveal the most stable edge structures of graphene on Ni(111) as well as the role of stacking-driven activation and suppression of edge reconstruction. Depending on the position of the outermost carbon atoms relative to hollow and on-top Ni sites, zigzag edges have very different energies. Triangular graphene nanoislands are exclusively bound by the more stable zigzag hollow edges. In hexagonal nanoislands, which are constrained by geometry to alternate zigzag hollow and zigzag top edges along their perimeter, only the hollow edge is stable, whereas the top edges spontaneously reconstruct into the (57) pentagon–heptagon structure. Atomically resolved STM images are consistent with either top-fcc or top-hcp epitaxial stacking of graphene and Ni sites, with the former being favored by DFT. Finally, we find that there is a one-to-one relationship between the edge type, graphene stacking, and orientation of the graphene islands. ; We acknowledge support from the Basque Departamento de Educacion, UPV/EHU (Grant No. IT-756-13), the Spanish Ministerio de Ciencia e Innovación (Grant Nos. MAT2013-46593-C6-2-P and MAT2013-46593-C6-5-P, MAT2007-62732), the ETORTEK program funded by the Basque Departamento de Industria, the European Union FP7-ICT Integrated Project PAMS under Contract No. 610446, the European Research Council (StG 203239 NOMAD), and Agència de Gestió d'Ajuts Universitaris i de Recerca (2014 SGR 715). ; Peer Reviewed

We investigate the scattering of electrons belonging to Shockley states of (111)-oriented noble metal surfaces using angle-resolved photoemission (ARPES) and scanning tunneling microscopy (STM). Both ARPES and STM indicate that monatomic steps on a noble metal surface may act either as strongly repulsive or highly transmissive barriers for surface electrons, depending on the coherence of the step lattice, and irrespectively of the average step spacing. By measuring curved crystal surfaces with terrace length ranging from 30 to 180 Å, we show that vicinal surfaces of Au and Ag with periodic step arrays exhibit a remarkable wave function coherence beyond 100 Å step spacings, well beyond the Fermi wavelength limit and independently of the projection of the bulk band gap on the vicinal plane. In contrast, the analysis of transmission resonances investigated by STM shows that a pair of isolated parallel steps defining a 58 Å wide terrace confines and decouples the surface state of the small terrace from that of the (111) surface. We conclude that the formation of laterally confined quantum well states in vicinal surfaces as opposed to propagating superlattice states depends on the loss of coherence driven by imperfection in the superlattice order. © 2013 American Physical Society. ; This work was supported in part by the Spanish MICINN (MAT2007-63083 and MAT2010-15659), the Basque Government (IT-257-07), and the Agència de Gestió d'Ajuts Universitaris i de Recerca (2009 SGR 695). The SRC is funded by the National Science Foundation (Award No. DMR-0084402). A.M. and J.L.-C. acknowledge funding from the Ramon y Cajal Fellowship program. ; Peer Reviewed