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We present an x-ray magnetic circular dichroism study performed at the U M4,5 edges on UFe2, a ferromagnet with almost itinerant 5f electrons. The analysis of the branching ratio of the U M4,5 edges confirms the fact that the occupation... more
We present an x-ray magnetic circular dichroism study performed at the U M4,5 edges on UFe2, a ferromagnet with almost itinerant 5f electrons. The analysis of the branching ratio of the U M4,5 edges confirms the fact that the occupation number of the 5f states in UFe2 is lower than in other compounds where the f electrons are more localized.
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By exploiting photo-induced reorientation in azo-polymer thin films, we demonstrate all-optical polarization-encoded information storage with a scanning near-field optical microscope. In the writing routine, 5-level bits are created by... more
By exploiting photo-induced reorientation in azo-polymer thin films, we demonstrate all-optical polarization-encoded information storage with a scanning near-field optical microscope. In the writing routine, 5-level bits are created by associating different bit values to different birefringence directions, induced in the polymer after illumination with linearly polarized light. The reading routine is then performed by implementing polarization-modulation techniques on the same near-field microscope, in order to measure the encoded birefringence direction.
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The optical phase in the feed gap of a plasmonic dipole antenna shows a transition from in-phase to counter-phase response, when its length is varied across the resonance length. We exploit this behavior in an asymmetric cross antenna... more
The optical phase in the feed gap of a plasmonic dipole antenna shows a transition from in-phase to counter-phase response, when its length is varied across the resonance length. We exploit this behavior in an asymmetric cross antenna structure, constituted of two perpendicular dipole antennas with different lengths, sharing the same feed gap, in order to shape the local polarization state. As an application of this concept, we propose a λ/4 nanowaveplate, able to shape and confine linearly polarized propagating waves into circularly polarized fields localized in the feed gap.
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The study of ferromagnetic(FM)/antiferromagnetic(AFM) interfaces has attracted great interest for fundamental reasons, related to the exchange bias effect, as well as for the possible technological applications. Here we report the study... more
The study of ferromagnetic(FM)/antiferromagnetic(AFM) interfaces has attracted great interest for fundamental reasons, related to the exchange bias effect, as well as for the possible technological applications. Here we report the study of the magnetic and structural properties by using Inverse PhotoEmission Spectroscopy and Spin Polarized Low Energy Electron Microscopy in very high quality epitaxial NiO and Fe/NiO films grown on Fe(001) [1]. The coupling between the two FM Fe layers is investigated for different combination of the NiO spacer and Fe overlayer thicknesses [2]. The nature of the coupling between the AFM NiO and the Fe substrate and the spin polarization along different quantization axes and its correlation with the Fe substrate magnetization M are also discussed. [1] L. Duò et al. Surf. Sci. 518 (2002) 234. [2] H. Ohldag et al. Phys. Rev. Lett. 86 (2001) 2878.
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The interaction of light with metal nanostructures gives rise to strong (up to several orders of magnitude) and spatially localized (on the nanometer scale) field amplitude enhancement, due to resonant excitation of Localized Surface... more
The interaction of light with metal nanostructures gives rise to strong (up to several orders of magnitude) and spatially localized (on the nanometer scale) field amplitude enhancement, due to resonant excitation of Localized Surface Plasmons (LSPs) and/or to lightning rod ...
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In this paper, a nonlinear aperture SNOM is used. It is based on a hollow pyramid tip, providing polarized high-peak-intensity femtosecond light pulses in the near field. Second harmonic (SH) images from single gold nanoellipsoids with... more
In this paper, a nonlinear aperture SNOM is used. It is based on a hollow pyramid tip, providing polarized high-peak-intensity femtosecond light pulses in the near field. Second harmonic (SH) images from single gold nanoellipsoids with various aspect ratio are obtained, with high contrast and sub-100-nm spatial resolution. The nonlinear response strongly depends on both LSP resonances and particle morphology.
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ABSTRACT Free-base H2TPP porphyrin layers have been grown on highly oriented pirolitic graphite by organic molecular beam epitaxy. The growth follows a Stranski-Krastanov (SK) mode, as observed by atomic force microscopy (AFM), showing 3D... more
ABSTRACT Free-base H2TPP porphyrin layers have been grown on highly oriented pirolitic graphite by organic molecular beam epitaxy. The growth follows a Stranski-Krastanov (SK) mode, as observed by atomic force microscopy (AFM), showing 3D porphyrin structures above a single flat porphyrin layer, which can be considered as an organic wetting layer. The 3D phase precludes a priori the possibility of studying and exploiting the physical-chemical properties of the pure 2D phase. Here we describe a promising post growth strategy to overcome the limitations imposed by the SK film evolution. We are able to reduce the number of 3D structures on the surface without perturbing the porphyrin wetting layer, as experimentally observed by AFM and optical spectroscopy. The strategy described in this work is fully generalizable and, in principle, could be extended to other free-base porphyrinic compounds.
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ABSTRACT We have investigated the behavior of the 2p3p3p and 2p3s3p Auger lines of CuO and Cu2O scanning the photon energy across the Cu L3 resonance. For both samples, when the excitation energy is below the L3 resonance, we observe the... more
ABSTRACT We have investigated the behavior of the 2p3p3p and 2p3s3p Auger lines of CuO and Cu2O scanning the photon energy across the Cu L3 resonance. For both samples, when the excitation energy is below the L3 resonance, we observe the 2p3p3p and 2p3s3p peaks at constant binding energy. This behavior is typical of nonradiative resonant Raman scattering. If the photon energy is raised above the L3 maximum, the two samples behave in different ways. In CuO, the Auger peaks are always observed at constant binding energy, while in Cu2O their kinetic energy first reaches a maximum at correspondence with the absorption threshold, and then stabilizes at a value slightly higher than the off-resonance Auger peaks. These differences are interpreted in terms of the different electronic structure of the Auger intermediate state at resonance. In CuO, the intermediate state corresponds to a single 2p3/2 core hole, with the Cu 3d band completely filled. On the contrary, in Cu2O the intermediate state is represented by the combination of a 2p3/2 hole with a 4sp electron in strong interaction with the O-2sp valence band. In CuO, for photon energies higher than 1.5 eV above the L3-edge maximum, the constant binding energy radiationless Raman peaks are accompanied by constant kinetic energy replicas. These are attributed to the relaxation of the Auger intermediate state through electron-hole pair generation across the band gap of the material. Satellites that could be associated to relaxation processes involving energies smaller than the band gap are not resolved. No variation of the lineshape of the Auger peaks is observed as a function of the sample temperature, indicating that different densities of thermally accessible excitations do not have a strong influence on the recombination process of the core hole.
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Page 1. 1 1 Low-Dimensional Antiferromagnetic Oxides : An Overview Marco Finazzi, Lamberto Du`o, and Franco Ciccacci 1.1 Introduction In the last two decades, the availability of experimental techniques endowed with high ...
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ABSTRACT In this work we show, by means of confocal photoluminescence measurements and fs pump-probe spectroscopy, that a large polarized stimulated emission band from polyfluorene keto defects is obtained in a mixture of polyfluorene... more
ABSTRACT In this work we show, by means of confocal photoluminescence measurements and fs pump-probe spectroscopy, that a large polarized stimulated emission band from polyfluorene keto defects is obtained in a mixture of polyfluorene with a nematic low molecular weight Liquid Crystal (LC). This mixture is placed in 9-micron thick cell constituted by two polyamide-coated plates rubbed to induce a macroscopic optical anisotropy of the LC molecules. In this blend a peculiar phase separation generates an ordered network of LC-rich micro-domains with the most of the polyfluorene chains placed on the microdomains boundaries. These well-defined phase boundaries have an anchoring effect so strong that the polymeric chains are forced to align parallel to them, despite the alignment of the nematic LC induced by the rubbing layers. The isolation and orientation of the polymeric chains reveal the possibility to obtain polarized optical gain from the keto defect, demonstrating that the fluorenone emission originates from a single-chain defect. The results are expected to have broad implications in the fields of photophysics and material design of polyfluorene materials, since the fomation of few fluorenone units can be seen not anymore as a form of degradation of the polyfluorene but as an improvement of the physical properties of this interesting polymer.
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Boosting nonlinear frequency conversion in extremely confined volumes remains a challenge in nano-optics research, but can enable applications in nanomedicine, photocatalysis and background-free biosensing. To obtain brighter nonlinear... more
Boosting nonlinear frequency conversion in extremely confined volumes remains a challenge in nano-optics research, but can enable applications in nanomedicine, photocatalysis and background-free biosensing. To obtain brighter nonlinear nanoscale sources, approaches that enhance the electromagnetic field intensity and counter the lack of phase matching in nanoplasmonic systems are often employed. However, the high degree of symmetry in the crystalline structure of plasmonic materials (metals in particular) and in nanoantenna designs strongly quenches second harmonic generation. Here, we describe doubly-resonant single-crystalline gold nanostructures with no axial symmetry displaying spatial mode overlap at both the excitation and second harmonic wavelengths. The combination of these features allows the attainment of a nonlinear coefficient for second harmonic generation of ∼5 × 10(-10) W(-1), enabling a second harmonic photon yield higher than 3 × 10(6) photons per second. Theoretica...
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We present results on the transition probabilities in isochromat inverse photoemission (hν=1025 eV) from La, Eu, and Lu together with selected photoemission results (10.840.8 eV). While the contribution of the empty 4f states to the... more
We present results on the transition probabilities in isochromat inverse photoemission (hν=1025 eV) from La, Eu, and Lu together with selected photoemission results (10.840.8 eV). While the contribution of the empty 4f states to the inverse photoemission spectra is ...
... VOLUME 47, NUMBER 23 Interaction of oxygen with polycrystalline cobalt studied by inverse-photoemission spectroscopy Lamberto Duo, Marco Finazzi, Franco Ciccacci, and Lucio Braicovich Dipartimento di Fisica, Politecnico di Milano,... more
... VOLUME 47, NUMBER 23 Interaction of oxygen with polycrystalline cobalt studied by inverse-photoemission spectroscopy Lamberto Duo, Marco Finazzi, Franco Ciccacci, and Lucio Braicovich Dipartimento di Fisica, Politecnico di Milano, piazza Leonardo da Vinci 32, 20133 ...
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... For a comparison of YMn 2 , YFe 2 , and YCo 2 , see S. Asano and S. Ishida, J. Phys. ... The rather broad angular definitions both in IPES and PES together with the polycrystalline nature of the sam-ples ensure that all the... more
... For a comparison of YMn 2 , YFe 2 , and YCo 2 , see S. Asano and S. Ishida, J. Phys. ... The rather broad angular definitions both in IPES and PES together with the polycrystalline nature of the sam-ples ensure that all the measurements are k integrated. ...
Magnetic circular x-ray dichroism experiments at the M4,5 absorption edges of cerium in the intermetallic compounds CeCuSi, CeRh3B2, and CeFe2 are reported. By applying general sum rules, it is shown that these experiments are able to... more
Magnetic circular x-ray dichroism experiments at the M4,5 absorption edges of cerium in the intermetallic compounds CeCuSi, CeRh3B2, and CeFe2 are reported. By applying general sum rules, it is shown that these experiments are able to yield both the magnitude and the direction of the 4f magnetic moment on Ce. An estimation of the orbital contribution to those 4f moments
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This paper describes four cases of canine rhinosporidiosis which occurred in Italy in 1994 and 1995. Four dogs with a history of exposure to the muddy environment of rice fields, developed respiratory signs. Rhinoscopy revealed nasal... more
This paper describes four cases of canine rhinosporidiosis which occurred in Italy in 1994 and 1995. Four dogs with a history of exposure to the muddy environment of rice fields, developed respiratory signs. Rhinoscopy revealed nasal polypoid lesions with a characteristic gross appearance due to the presence of multiple, tiny, white-yellowish spots representing sporangia filled with spores. In cytological samples obtained by brushing, many spores were present in an inflammatory background. Histologically, the polyps consisted of fibrovascular tissue embedding sporangia in different developmental stages, and free spores which elicited a severe pyogranulomatous inflammation. All the dogs were treated surgically and the condition did not recur in two cases during a year's follow-up and in the other two cases during two years.
Research Interests: Inflammation, Treatment Outcome, Dogs, Europe, Female, and 5 moreAnimals, Polyps, Male, Nasal cavity, and Veterinary Sciences
Since its introduction about 20 years ago, two-photon microscopy has become a widespread tool in high-spatial resolution imaging, especially of biological tissues, because of the quadratic dependence of absorption on the excitation... more
Since its introduction about 20 years ago, two-photon microscopy has become a widespread tool in high-spatial resolution imaging, especially of biological tissues, because of the quadratic dependence of absorption on the excitation intensity, which confines fluorescence and ...
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ABSTRACT Valleytronics targets the exploitation of the additional degrees of freedom in materials where the energy of the carriers may assume several equal minimum values (valleys) at non-equivalent points of the reciprocal space. In... more
ABSTRACT Valleytronics targets the exploitation of the additional degrees of freedom in materials where the energy of the carriers may assume several equal minimum values (valleys) at non-equivalent points of the reciprocal space. In single layers of transition metal dichalcogenides (TMDs) the lack of inversion symmetry, combined with a large spin-orbit interaction, leads to a conduction (valence) band with different spin-polarized minima (maxima) having equal energies. This offers the opportunity to manipulate information at the level of the charge (electrons or holes), spin (up or down) and crystal momentum (valley). Any implementation of these concepts, however, needs to consider the robustness of such degrees of freedom, which are deeply intertwined. Here we address the spin and valley relaxation dynamics of both electrons and holes with a combination of ultrafast optical spectroscopy techniques, and determine the individual characteristic relaxation times of charge, spin and valley in a MoS$_{2}$ monolayer. These results lay the foundations for understanding the mechanisms of spin and valley polarization loss in two-dimensional TMDs: spin/valley polarizations survive almost two-orders of magnitude longer for holes, where spin and valley dynamics are interlocked, than for electrons, where these degrees of freedom are decoupled. This may lead to novel approaches for the integration of materials with large spin-orbit in robust spintronic/valleytronic platforms.
BACH, the new soft x-ray beamline for polarization dependent experiments at the Italian synchrotron radiation facility ELETTRA, has been commissioned, characterized and opened to external users. Based on two APPLE II undulators, it covers... more
BACH, the new soft x-ray beamline for polarization dependent experiments at the Italian synchrotron radiation facility ELETTRA, has been commissioned, characterized and opened to external users. Based on two APPLE II undulators, it covers an energy range between 35 eV and 1600 eV with the control of the light polarization. The monochromator works either in high resolution or high flux
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ABSTRACT Epitaxial γ-Ce thin films, stabilised at low temperatures when sandwiched by W(110) buffer and capping layers, have been studied by X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) in a temperature... more
ABSTRACT Epitaxial γ-Ce thin films, stabilised at low temperatures when sandwiched by W(110) buffer and capping layers, have been studied by X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) in a temperature range of 5–300K and with an applied magnetic field μ0H=0–7T, at the M4,5 edges on the beamline ID12B at ESRF. The mean 4f occupancy, nf, was found to be intermediate to that of α and γ-phases, which is proposed to arise from an increase of the valence at the W/Ce interface. In addition, a reversible decrease of nf is observed when the temperature is decreased from which we estimate a bulk Ce Kondo temperature TK=150K. The XMCD shows that Ce is Curie–Weiss paramagnetic down to the lowest examined temperature with small |θp|
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We present the results obtained on FexNi1-x alloy films epitaxially grown on Cu(100). They are characterized by a fcc structure pseudomorphic to the substrate over a wide range of concentration and thickness. In particular, the... more
We present the results obtained on FexNi1-x alloy films epitaxially grown on Cu(100). They are characterized by a fcc structure pseudomorphic to the substrate over a wide range of concentration and thickness. In particular, the martensitic transition which in bulk alloys occurs around the ``Invar'' concentration (x≈0.65) is suppressed. We report the concentration dependence at low temperature of the total
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The effect of gold capping on magnetic and transport properties of optimally doped manganite thin films is studied. An extraordinary suppression of conductivity and magnetic properties occurs in epitaxial (001) La_0.67Sr_0.33MnO_3 (LSMO)... more
The effect of gold capping on magnetic and transport properties of optimally doped manganite thin films is studied. An extraordinary suppression of conductivity and magnetic properties occurs in epitaxial (001) La_0.67Sr_0.33MnO_3 (LSMO) films grown on SrTiO_3 upon deposition of 2 nm of Au: in the case of ultrathin films of LSMO (4 nm thick) the resistivity increases by four orders
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We have investigated the behavior of the 2p3s3p, 2p3p3p, and 2p3s3s Auger lines of NiO, a model compound in the class of strongly correlated 3d systems, while varying the photon energy across the Ni L3 and L2 absorption edges. The... more
We have investigated the behavior of the 2p3s3p, 2p3p3p, and 2p3s3s Auger lines of NiO, a model compound in the class of strongly correlated 3d systems, while varying the photon energy across the Ni L3 and L2 absorption edges. The experimental data are discussed in comparison with a theoretical model based on a charge-transfer multiplet approach. When the excitation energy is below the L3 resonance, we observe the 2p3p3p and 2p3s3p peaks at a constant binding energy. This behavior is typical of nonradiative resonant Raman scattering. If the photon energy is increased further, the 2p3p3p and 2p3s3p lines rapidly transform into constant kinetic energy features, showing a normal Auger behavior. The transition from Raman- to Auger-like behavior takes place for photon energies lower than the ones corresponding to excitations of the photoelectron into ligand-hole states. This might indicate the participation of inelastic processes in the recombination of the core hole involving energies much smaller than the NiO gap, or the possible presence of nonlocal effects. On the high photon energy side of the L3 edge, the constant kinetic energy of the 2p3p3p and 2p3s3p peaks is systematically larger than the one observed for an excitation well above the L2,3 edges. We attribute this behavior to the intervention of an intermediate state of 2p53d10 character, which has very little weight but is strongly enhanced at resonance.
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A photon- and electron-spin-resolved core level photoemission experiment on ferromagnetic Fe is reported. The Fe 3p spectrum shows a circular magnetic dichroism of 40%. We demonstrate that besides the exchange-induced spin polarization... more
A photon- and electron-spin-resolved core level photoemission experiment on ferromagnetic Fe is reported. The Fe 3p spectrum shows a circular magnetic dichroism of 40%. We demonstrate that besides the exchange-induced spin polarization the dichroism is accompanied by spin-orbit-induced spin polarization, which depends on the photon helicity but not on sample magnetization. In the spin-integrated as well as spin-resolved data, we