1,721,132 research outputs found
Plasmon dispersion and damping in two-dimensional electron gases on metal substrates
No full textHerein we report on high-resolution electron energy loss spectroscopy (HREELS) measurements on surface plasmon dispersion in systems exhibiting quantum well states, i.e. Na/Cu(111), Ag/Cu(111), and Ag/Ni(111). Our results demonstrate that the dominant coefficient of surface plasmon dispersion for thin and layer-by-layer Ag films presenting quantum well states is quadratic even at small q, in contrast with previous measurements on Ag semi-infinite media and Ag thin films deposited on Si(111). We suggest that this behavior is due to screening effects enhanced by the presence of quantum well states shifting the position of the centroid of the induced charge less inside the geometrical surface compared to Ag surfaces and Ag/Si(111). For ultrathin Ag films, i.e. two layers, the dispersion was found to be not positive, as theoretically predicted. Annealing of the Ag film caused an enhancement of the free-electron character of the quantum well states, thus inducing a negative linear term of the dispersion curve of the surface plasmon. Moreover, we report the first experimental evidence of chemical interface damping in thin films for K/Ag/Ni(111). As regards Na/Cu(111), we found a different dispersion curve compared to thick Na films, thus confirming the enhanced screening by Na quantum well states. Results reported here should shed light on the influence of quantum well states on dynamical screening phenomena in thin films. © 2011 by Nova Science Publishers, Inc. All rights reserved
Unveiling the origin of room-temperature ferromagnetism in monolayer VSe2: The role of extrinsic effects
No full textRoom-temperature ferromagnetism in monolayer vanadium diselenide (VSe2) on graphiteis the object of a controversial debate. Herein, we unveil the contribution from extrinsic factors to the magnetic properties of monolayer VSe2 by means of density functional theory. Specifically, we demonstrate that either intrinsic defects or the adsorption of molecules enhances ferromagnetic interactions. The expansion of the VSe2 lattice increases the magnetic moment on vanadium ions, whereas both compression and out-of-plane distortion withdraw magnetic moments. The exchange interactions between vanadium ions and magnetic defects (vacancies and impurities) in the surface and subsurface layers of the substrate are able to turn the unstable two-dimensional (2D) ferromagnetism into stable three-dimensional (3D) ferromagnetism. Definitely, the combination of effects related to chemisorption, substrate-induced distortion and magnetic defects of the substrate could enhance or suppress ferromagnetism in monolayer VSe2
Influence of electron quantum confinement on the electronic response of metal/metal interfaces
No full textNovel Undamped Gapless Plasmon Mode in a Tilted Type-II Dirac Semimetal
No full textWe predict the existence of a novel long-lived gapless plasmon mode in a type-II Dirac semimetal (DSM). This gapless mode arises from the out-of-phase oscillations of the density fluctuations in the electron and the hole pockets of a type-II DSM. It originates beyond a critical wave vector along the direction of the tilt axis, owing to the momentum separation of the electron and hole pockets. A similar out-of-phase plasmon mode arises in other multicomponent charged fluids as well, but generally, it is Landau damped and lies within the particle-hole continuum. In the case of a type-II DSM, the open Fermi surface prohibits low-energy finite momentum single-particle excitations, creating a "gap" in the particle-hole continuum. The gapless plasmon mode lies within this particle-hole continuum gap and, thus, it is protected from Landau damping
Insight on Thermally Activated Hydrocarbon Dehydrogenation on the Pt3Ni(111) Surface: From Adsorbed Hydrocarbons up to Graphene Formation
No full textEvaluation of the free-vibration frequency and the variation of the bending rigidity of graphene nanoplates: The role of the shape geometry and boundary conditions
No full textIn this work, the dependence of the bending rigidity and the free vibrations in graphene nanostructures on the shape geometry and the boundary conditions has been investigated. For graphene-based square, rectangular, parallelogram and circular nanostructures, finite elements analysis allows the estimation of the frequency of the first vibration mode. Therefore, it was possible to evaluate the change of the bending rigidity upon varying boundary conditions. In addition, we calculate by finite element methods the first mode of vibration of state-of-the-art nanoelectromechanical devices, whose outer contour cannot be reduced to elementary geometrical shapes
Photothermal response of plasmonic nanofillers for membrane distillation
No full textLight-to-heat conversion in plasmonic nanoparticles (NPs) inside polymeric membranes is beneficial for improving the efficiency of membrane distillation for seawater desalination. However, the physical mechanisms ruling photothermal membrane distillation are unclear yet. Here, we model the plasmonic photothermal light-to-heat conversion from Ag, Au, and Cu nanofillers in polymeric membranes for membrane distillation. Photothermal effects in the cases of isolated metallic NPs and their assembly are investigated considering size effects and excitation sources. The increasing content of metallic NPs improves the efficiency of the light-to-heat conversion. For a polymeric membrane, filled with 25% Ag NPs, our model well reproduces the experimental temperature increase of 10 K. Specifically, we find that Ag NPs with a radius of around 30-40 nm are favorite candidates for membrane heating with excitation energy in the visible/near-UV range. The incorporation of a term associated with heat losses into the heat transfer equation well reproduces the cooling effect associated with vaporization at the membrane surface. Compared to Ag NPs, Au and Cu NPs show a broadened absorption cross section and their resonance has a nonlinear behavior with varying the excitation energy, better matching with sunlight radiation spectrum
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
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