305 research outputs found
Observation of a hole-size-dependent energy shift of the surface-plasmon resonance in Ni antidot thin films
© 2015 AIP Publishing LLC. A combined experimental and theoretical study of the magneto-optic properties of a series of nickel antidot thin films is presented. The hole diameter varies from 869 down to 636 nm, while the lattice periodicity is fixed at 920 nm. This results in an overall increase of the polar Kerr rotation with decreasing hole diameter due to the increasing surface coverage with nickel. In addition, at photon energies of 2.7 and 3.3 eV, where surface-plasmon excitations are expected, we observe distinct features in the polar Kerr rotation not present in continuous nickel films. The spectral position of the peaks exhibits a red shift with decreasing hole size. This is explained within the context of an effective medium theory by a change in the effective dielectric function of the Ni thin films.H.F. gratefully acknowledges China Scholarship Council (CSC) for financial support and AndrĂ© Schirmeisen for the data of Ni film. A.G.-M. and B.C. acknowledge funding from Spanish Ministry of Economy and Competitiveness through grants âFUNCOATâ CONSOLIDER CSD2008-00023 and âMAPSâ MAT2011-29194-C02-01. J.C.C. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (Contract No. FIS2011-28851-C02-01) and from the Comunidad de Madrid (Contract No. S2013/MIT-2740). E.M.A. and M.G. acknowledge financial support by the European Union under the project CosmoPHOS with the number â3100337â.Peer Reviewe
Observation of a hole-size-dependent energy shift of the surface-plasmon resonance in Ni antidot thin films
A combined experimental and theoretical study of the magneto-optic properties of a series of nickel antidot thin films is presented. The hole diameter varies from 869 down to 636 nm, while the lattice periodicity is fixed at 920 nm. This results in an overall increase of the polar Kerr rotation with decreasing hole diameter due to the increasing surface coverage with nickel. In addition, at photon energies of 2.7 and 3.3 eV, where surface-plasmon excitations are expected, we observe distinct features in the polar Kerr rotation not present in continuous nickel films. The spectral position of the peaks exhibits a red shift with decreasing hole size. This is explained within the context of an effective medium theory by a change in the effective dielectric function of the Ni thin filmsH.F. gratefully acknowledges China Scholarship Council (CSC) for financial support and AndrĂ© Schirmeisen for the data of Ni film. A.G.-M. and B.C. acknowledge funding from Spanish Ministry of Economy and Competitiveness through grants âFUNCOATâ CONSOLIDER CSD2008-00023 and âMAPSâ MAT2011-29194-C02-01. J.C.C. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (Contract No. FIS2011-28851-C02-01) and from the Comunidad de Madrid (Contract No. S2013/MIT- 2740). E.M.A. and M.G. acknowledge financial support by the European Union under the project CosmoPHOS with the number â310337
Rayleigh surface waves propagating in (111) Si substrate decorated with Ni phononic nanostructure
The paper reports results of the Surface Brillouin Light Scattering at the
silicon (111) surface loaded with a periodic 2D nickel nanostructure.
Measurements were made for samples loaded with nanostructures of different
period (different size) but of the same height. The relation between the
nanostructure size and the velocity of surface Rayleigh waves was proved to be
nonlinear. Anisotropy of the surface Rayleigh wave velocity was compared with
the results of theoretical modelling based on the Finite Element Method
Elementary transitions and magnetic correlations in two-dimensional disordered nanoparticle ensembles
The magnetic relaxation processes in disordered two-dimensional ensembles of
dipole-coupled magnetic nanoparticles are theoretically investigated by
performing numerical simulations. The energy landscape of the system is
explored by determining saddle points, adjacent local minima, energy barriers,
and the associated minimum energy paths (MEPs) as functions of the structural
disorder and particle density. The changes in the magnetic order of the
nanostructure along the MEPs connecting adjacent minima are analyzed from a
local perspective. In particular, we determine the extension of the correlated
region where the directions of the particle magnetic moments vary
significantly. It is shown that with increasing degree of disorder the magnetic
correlation range decreases, i.e., the elementary relaxation processes become
more localized. The distribution of the energy barriers, and their relation to
the changes in the magnetic configurations are quantified. Finally, some
implications for the long-time magnetic relaxation dynamics of nanostructures
are discussed.Comment: 19 pages, 6 figure
Transparent metal electrodes from ordered nanosphere arrays
We show that perforated metal electrode arrays, fabricated using nanosphere
lithography, provide a viable alternative to conductive metal oxides as
transparent electrode materials. The inter-aperture spacing is tuned by
varying etching times in an oxygen plasma, and the effect of inter-aperture
âwireâ thickness on the optical and electronic properties of perforated silver
films is shown. Optical transmission is limited by reflection and surface
plasmons, and for these results do not exceed 73%. Electrical sheet resistance
is shown to be as low as 3âΩââ»â1 for thermally evaporated silver films. The
performance of organic photovoltaic devices comprised of a P3HT:PCBM bulk
heterojunction deposited onto perforated metal arrays is shown to be limited
by optical transmission, and a simple model is presented to overcome these
limitations
Interactions between magnetic nanoparticles and model lipid bilayersâFourier transformed infrared spectroscopy (FTIR) studies of the molecular basis of nanotoxicity
The toxicity of nanoparticles (nanotoxicity) is often associated with their
interruption of biological membranes. The effect of polymer-coated magnetic
nanoparticles (with different Fe3O4 core sizes and different polymeric
coatings) on a model biological membrane system of vesicles formed by
dimyristoylphosphatidylcholine (DMPC) was studied. Selected magnetic
nanoparticles with core sizes ranging from 3 to 13ânm (in diameter) were
characterised by transmission electron microscopy. Samples with 10% DMPC and
different nanoparticle concentrations were studied by attenuated total
reflectanceâFourier transform infrared spectroscopy to establish the influence
of nanoparticles on the phase behaviour of model phospholipid systems
CuAu-type ordering in epitaxial CuInS<sub>2</sub> films
Ordering of Cu and In atoms in near-stoichiometric CuInS2 epitaxial films grown on Si (111) by molecular beam epitaxy was studied by transmission electron microscopy. Nonchalcopyrite ordering of the metal atoms in CuInS2 is observed, which is identified as CuAu-type ordering. Sharp spots in electron diffraction patterns reveal the ordered Cu and In atom planes alternating along the [001] direction over a long range. High-resolution electron microscopy confirms this ordering. The CuAu-ordered structure coexists with the chalcopyrite ordered structure, in agreement with theoretical prediction
Towards spectrally selective catastrophic response
We study the large-amplitude response of classical molecules to electromagnetic radiation, showing the universality of the transition from linear to nonlinear response and breakup at sufficiently large amplitudes. We demonstrate that a range of models, from the simple harmonic oscillator to the successful Peyrard-Bishop-Dauxois type models of DNA, which include realistic effects of the environment (including damping and dephasing due to thermal fluctuations), lead to characteristic universal behavior: formation of domains of dissociation in driving force amplitude-frequency space, characterized by the presence of local boundary minima. We demonstrate that by simply following the progression of the resonance maxima in this space, while gradually increasing intensity of the radiation, one must necessarily arrive at one of these minima, i.e., a point where the ultrahigh spectral selectivity is retained. We show that this universal property, applicable to other oscillatory systems, is a consequence of the fact that these models belong to the fold catastrophe universality class of Thom's catastrophe theory. This in turn implies that for most biostructures, including DNA, high spectral sensitivity near the onset of the denaturation processes can be expected. Such spectrally selective molecular denaturation could find important applications in biology and medicine
Scaling behavior of the dipole coupling energy in two-dimensional disordered magnetic nanostructures
Numerical calculations of the average dipole-coupling energy in two-dimensional disordered magnetic nanostructures are
performed as function of the particle coverage . We observe that scales as with an
unusually small exponent --1.0 for coverages
. This behavior is shown to be primarly given by the
contributions of particle pairs at short distances, which is intrinsically
related to the presence of an appreciable degree of disorder. The value of
is found to be sensitive to the magnetic arrangement within the
nanostructure and to the degree of disorder. For large coverages
we obtain with , in agreement
with the straighforward scaling of the dipole coupling as in a periodic
particle setup. Taking into account the effect of single-particle anisotropies,
we show that the scaling exponent can be used as a criterion to distinguish
between weakly interacting () and strongly interacting
() particle ensembles as function of coverage.Comment: accepted for publication in Phys.Rev.
Effect of surfactant for magnetic properties of iron oxide nanoparticles
For different medical applications nanoparticles (NPs) with well-defined
magnetic properties have to be used. Coating ligand can change the magnetic
moment on the surface of nanostructures and therefore the magnetic behavior of
the system. Here we investigated magnetic NPs in a size of 13 nm conjugated
with four different kinds of surfactants. The surface anisotropy and the
magnetic moment of the system were changed due to the presence of the
surfactant on the surface of iron oxide NPs
- âŠ