1,721,031 research outputs found
Air‐Resistant Titanium Oxide Capping for Graphene/Ferromagnet Heterostructures (Adv. Phys. Res. 10/2025)
No full textGraphene/ferromagnet interfaces have widely demonstrated the capability to host peculiar magnetic and electronic properties relevant for spintronic devices. In principle, besides strengthening perpendicular magnetic anisotropy (PMA) and sizable Dzyaloshinskii–Moriya interaction (DMI), graphene provides an additional advantage by acting as a protective layer against oxidation of the underlying metal film. However, the structural imperfections of graphene, often resulting from its growth conditions, can facilitate intercalation, which can compromise the underlying ferromagnetic layer. To address this issue, here, the use of a titania capping layer as a protective barrier for a heterostructure consisting of monolayer graphene grown on a thin cobalt film is proposed. The results demonstrate that the titanium oxide layer does not alter the properties of the interface, as confirmed by X-ray photoemission spectroscopy (XPS) and X-ray magnetic circular dichroism (XMCD) imaging. Furthermore, magneto-optic Kerr effect (MOKE) measurements reveal that the interface's magnetic properties remain stable after prolonged exposure to ambient conditions. Absorption profile simulations show that the capping layer is transparent to visible wavelengths, demonstrating its capability to enable optical studies of atomic interfacial effects without the need for an ultra-high vacuum (UHV) environment. These findings position titanium oxide as a robust, non-invasive capping material for graphene-based spintronic heterostructures
Reversible redox reactions in metal-supported porphyrin: the role of spin and oxidation state
Get PDFOn-surface molecular functionalization paved the way for the stabilization of chelated ions in different oxidation and spin states, allowing for the fine control of catalytic and magnetic properties of metalorganic networks. Considering two model systems, a reduced Co(I) and an open-shell Co(II) metal-supported 2D molecular array, we investigate the interplay between the low valence oxidation and unpaired spin state in the molecular reactivity. We show that the redox reaction taking place at the cobalt tetraphenylporphyrin/Cu(100) interface, stabilizing the low-spin Co(I) state with no unpaired electrons in its valence shell, plays a pivotal role in changing the reactivity. This goes beyond the sole presence of unpaired electrons in the valence state of the Co(II) metal–organic species, often designated as being responsible for the reactivity towards small molecules like NO and NO2. The reversible Co–NO2 interaction, established with the Co(I) leads to the stabilization of the Co(III) oxidation state
Doping of epitaxial graphene by direct incorporation of nickel adatoms
Get PDFDirect incorporation of Ni adatoms during graphene growth on Ni(111) is evidenced by scanning tunneling microscopy. The structure and energetics of the observed defects is thoroughly characterized at the atomic level on the basis of density functional theory calculations. Our results show the feasibility of a simple scalable method, which could be potentially used for the realization of macroscopic practical devices, to dope graphene with a transition metal. The method exploits the kinetics of the growth process for the incorporation of Ni adatoms in the graphene network
Stripe‐Like hBN Monolayer Template for Self‐Assembly and Alignment of Pentacene Molecules
Get PDFMetallic surfaces with unidirectional anisotropy are often used to guide the self-assembly of organic molecules along a particular direction. Such supports thus offer an avenue for the fabrication of hybrid organic–metal interfaces with tailored morphology and precise elemental composition. Nonetheless, such control often comes at the expense of detrimental interfacial interactions that might quench the pristine properties of molecules. Here, hexagonal boron nitride grown on Ir(100) is introduced as a robust platform with several coexisting 1D stripe-like moiré superstructures that effectively guide unidirectional self-assemblies of pentacene molecules, concomitantly preserving their pristine electronic properties. In particular, highly-aligned longitudinal arrays of equally-oriented molecules are formed along two perpendicular directions, as demonstrated by comprehensive scanning tunneling microscopy and photoemission characterization performed at the local and non-local scale, respectively. The functionality of the template is demonstrated by photoemission tomography, a surface-averaging technique requiring a high degree of orientational order of the probed molecules. The successful identification of pentacene's pristine frontier orbitals underlines that the template induces excellent long-range molecular ordering via weak interactions, preventing charge transfer
Thermally Induced Chemical and Structural Transformations in Thin Cobalt Films
No full textThe effect of annealing and cooling on the structural properties of thin cobalt films possessing either hcp(0001) or fcc(100) crystalline arrangement is studied on clean and carbon-reconstructed W(110), respectively. The films grown on a clean W(110) crystal present a surface with hexagonal symmetry and undergo the well-known hcp–fcc structural transition upon annealing to temperatures higher than 700 K, while after cooling down to room temperature, the film is characterized by a laterally heterogeneous morphology featuring different stacking configurations. On carbide-covered W(110), Co grows, instead, in an fcc(100) arrangement with a high level of disorder, for which annealing leads to an improved crystalline order. Further annealing to above 900 K induces an irreversible transition from fcc(100) to hcp(0001) stacking via domain nucleation and growth on a micrometer scale. This recrystallization process is accompanied by a change in the film’s chemical composition and magnetic structure. The excess carbon resulting from recrystallization leads to the growth of micrometer-sized graphene islands on top of the hcp regions
Operando atomic-scale study of graphene CVD growth at steps of polycrystalline nickel
Get PDFAn operando investigation of graphene growth on (100) grains of polycrystalline nickel (Ni) surfaces was performed by means of variable-temperature scanning tunneling microscopy complemented by density functional theory simulations. A clear description of the atomistic mechanisms ruling the graphene expansion process at the stepped regions of the substrate is provided, showing that different routes can be followed, depending on the height of the steps to be crossed. When a growing graphene flake reaches a monoatomic step, it extends jointly with the underlying Ni layer; for higher Ni edges, a different process, involving step retraction and graphene landing, becomes active. At step bunches, the latter mechanism leads to a peculiar ‘staircase formation’ behavior, where terraces of equal width form under the overgrowing graphene, driven by a balance in the energy cost between C–Ni bond formation and stress accumulation in the carbon layer. Our results represent a step towards bridging the material gap in searching new strategies and methods for the optimization of chemical vapor deposition graphene production on polycrystalline metal surfaces
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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