F. Fuso

Università di Pisa, Pisa, Tuscany, Italy

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Publications (128)211.27 Total impact

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    ABSTRACT: Polarization modulated scanning near-field optical microscopy (PM-SNOM) is effective in detecting circular and linear dichroism with sub-wavelength resolution. PM-SNOM investigation of the chiroptical properties of single ribbon-like nanosized J-aggregates formed by acid induced aggregation of tris-(4-sulfonatophenyl)phenylporphyrin are reported. Linear dichroism maps give evidence of well-organized chromophores packed in linear arrays within the structure of the nanoribbons. Circular dichroism maps indicate that the molecules forming the nanoribbon own an inherently chiral structure at the local scale.
    Nanoscale 07/2014; · 6.23 Impact Factor
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    ABSTRACT: Polymer fibers are currently exploited in tremendously important technologies. Their innovative properties are mainly determined by the behavior of the polymer macromolecules under the elongation induced by external mechanical or electrostatic forces, characterizing the fiber drawing process. Although enhanced physical properties were observed in polymer fibers produced under strong stretching conditions, studies of the process-induced nanoscale organization of the polymer molecules are not available, and most of fiber properties are still obtained on an empirical basis. Here we reveal the orientational properties of semiflexible polymers in electrospun nanofibers, which allow the polarization properties of active fibers to be finely controlled. Modeling and simulations of the conformational evolution of the polymer chains during electrostatic elongation of semidilute solutions demonstrate that the molecules stretch almost fully within less than 1 mm from jet start, increasing polymer axial orientation at the jet center. The nanoscale mapping of the local dichroism of individual fibers by polarized near-field optical microscopy unveils for the first time the presence of an internal spatial variation of the molecular order, namely the presence of a core with axially aligned molecules and a sheath with almost radially oriented molecules. These results allow important and specific fiber properties to be manipulated and tailored, as here demonstrated for the polarization of emitted light.
    Macromolecules. 07/2014; 47(14).
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    ABSTRACT: Since its discovery, surface-enhanced Raman spectroscopy (SERS) has pushed researchers’ interest to develop different kinds of active substrates for high sensitivity molecular detection. Defocused ion beam sputtering (IBS) represents a viable route for the production of large scale, highly reproducible SERS-active substrates consisting of near-field coupled nanowires featuring localized surface plasmon resonances in the visible and the near-infrared. Here we investigate the field enhancement and spatial confinement in the visible and the near-infrared of arrays of optically resonant gold nanowires, using two complementary techniques: SERS and scanning near-field optical microscopy (SNOM). While SERS allows us to quantify the field enhancement factor, SNOM is used to image the localization of the enhanced electromagnetic fields. We show that in the visible (633 nm) the nanowires are SERS active only for excitation polarized parallel to the wire-to-wire nanocavities, yielding enhancement factors of 7 × 103. In the near-infrared (785 nm) we observe a 2-fold larger SERS enhancement (1.3 × 104) for excitation parallel to the nanocavities and detect the onset of SERS amplification for excitation polarization parallel to the nanowires long axis. Polarization-sensitive SNOM in the near-infrared (830 nm) enables the correlation of the scattered intensity with the sample morphology at the local scale. We demonstrate that the field enhancement stems from the wire-to-wire nanocavity regions when the excitation field is polarized parallel to the wire-to-wire nanocavity, while we observe more complex field confinement patterns related to the partially inhomogeneous morphology of the substrate when the polarization is parallel to the nanowires long axis. Our experiments strongly suggest IBS-fabricated nanowires as novel substrates for plasmon-enhanced spectroscopies.
    The Journal of Physical Chemistry C. 04/2014; 118(16):8571–8580.
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    ABSTRACT: In the present work, the preparation of different styrene-based polymer films containing small amounts of TPE and the evaluation of their photoluminescent behaviour is reported. When TPE is dispersed in a poor solvent or in a glassy PS matrix, the arrested intramolecular rotations of its aryls favour the strong emission of light centred at about 455–460 nm. Conversely, TPE fluorescence significantly weakens to a faint signal when good solvents or viscous but not glassy polymer matrices are used. Near-field optical microscopy correlates the fluorescence behaviour with the different matrix morphologies. These results should be able to be used for developing a new tool for polymer traceability.
    Macromolecular Chemistry and Physics 01/2014; · 2.39 Impact Factor
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    ABSTRACT: Microholes for the production of gasoline direct injection nozzles were obtained by ultrashort pulsed laser machining in martensitic stainless steels. The inner surface analysis was carried out by a specifically conceived Scanning Probe Microscopy instrument and revealed the presence of periodic surface microstructures whose formation was studied as a function of process parameters (pulse energy, repetition rate, rotational speed, drilling strategy). Experiments demonstrated that geometrical features of the microstructures can be varied by a proper parameter selection and open the perspective for an optimized process enabling a reduction of coking accumulation during service life and a more effective atomization of the fuel jet.
    CIRP Annals - Manufacturing Technology 01/2014; · 2.25 Impact Factor
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    ABSTRACT: The properties of polymeric nanofibers can be tailored and enhanced by properly managing the structure of the polymer molecules at the nanoscale. Although electrospun polymer fibers are increasingly exploited in many technological applications, their internal nanostructure, determining their improved physical properties, is still poorly investigated and understood. Here, we unravel the internal structure of electrospun functional nanofibers made by prototype conjugated polymers. The unique features of near-field optical measurements are exploited to investigate the nanoscale spatial variation of the polymer density, evidencing the presence of a dense internal core embedded in a less dense polymeric shell. Interestingly, nanoscale mapping the fiber Young's modulus demonstrates that the dense core is stiffer than the polymeric, less dense shell. These findings are rationalized by developing a theoretical model and simulations of the polymer molecular structural evolution during the electrospinning process. This model predicts that the stretching of the polymer network induces a contraction of the network toward the jet center with a local increase of the polymer density, as observed in the solid structure. The found complex internal structure opens an interesting perspective for improving and tailoring the molecular morphology and multifunctional electronic and optical properties of polymer fibers.
    Nano Letters 10/2013; · 13.03 Impact Factor
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    ABSTRACT: We propose a source for high-brightness ion and electron beams based on the ionization of an effusive atomic beam which is transversely laser cooled and compressed. The very low transverse temperature (mK range) and the relative low density of the starting atomic sample ensure excellent initial conditions for obtaining bright and monochromatic charge sources. In contrast to the standard photoionization techniques used by similar sources, we utilize field ionization of Rydberg atoms. This approach allows a substantial reduction of the required laser power and copes differently with the problems of the energy spread created during the ionization process and of the stochastic space-charge effect. Theoretical modeling and prospective ideas of this emerging technology are given.
    Physical Review A 09/2013; 88(3):033424. · 3.04 Impact Factor
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    ABSTRACT: The high tensional stresses during electrospinning of semidilute polymer solutions affect the dynamic conformation of the polymer network within the liquid jet, leaving a distinctive trace in the molecular structure after solidification. We investigated such effects in electrospun nanofibers made of conjugated polymers. Modeling the polymer network evolution during electrospinning showed that as the network stretches axially, it contracts towards the jet core. The model represents the semi-flexible conjugated polymer chains as flexible freely-jointed chains, whose joints are bonding defects. Using the conjugated polymer MEH-PPV dissolved in a mixture of THF and DMF solvents, and taking advantage of its unique photophysical characteristics, we investigated optically the variations in the density and orientation of the polymer macromolecules in electrospun nanofibers. In agreement with our model, we found higher density and axial orientation at the fiber core, while lower density and radial orientation closer to the fiber surface. The non-uniformity of the resulting molecular structure can be tuned and exploited in diverse optical and structural applications.
    03/2013;
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    ABSTRACT: The micro-electrical discharge drilling process was studied by means of experiments with the twofold objective of increasing the surface quality while minimizing the drilling time. To characterize the inner surface of micro-drilled holes obtained by EDM a specifically conceived scanning probe microscopy technique was used. Discharge current and pulse duration were used as input parameters with the aim of quantifying the effects of applied spark energies on surface characteristics. 150 μm diameter holes were drilled using combinations of process parameters defining spark energies within the range of 3.25 μJ and 15 μJ. Results showed that the surface texture can be characterized by (i) maximum peak-to-valley distance and (ii) periodicity whose dimensions were related to the adopted spark energy. Standard Rq derived from the measured cylindrical surfaces was found to vary between 240 nm and 380 nm. Experiments testified that removal rates higher respect to those commonly used in industry can be adopted when followed by a lateral erosion phase at low energy which reduces Rq of 32% without changing the drilling time.
    CIRP Journal of Manufacturing Science and Technology 01/2013;
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    ABSTRACT: To characterize the inner surface of the fuel injector nozzle holes drilled by EDM and water jet guided laser drilling (Laser Micro-Jet) a specifically conceived scanning probe microscopy technique with true non-contact operating mode was used. A difference in morphology of the drilled surfaces is evident from the acquired surface topography along the hole axis for the two compared drilling techniques. Results showed that the surface texture can be characterized by (i) maximum peak-to-valley distance and (ii) periodicity. Acquired maps confirm that electro-eroded surfaces are an envelope of craters randomly distributed with total excursion up to 1.7 μm with a crater size of 15 μm. While, the efficient melt expulsion and immediate cooling of water jet guided laser generates a peak to valley distance of 800 nm with a periodicity of 18 μm. Average Rq derived from the measured cylindrical surfaces was 450 nm and 150 nm for EDM and Laser Micro-Jet, respectively. Water jet guided laser drilling has proved to be a reliable alternative to EDM from the point of view of repeatability of the results and surface quality to facilitate the atomization of the fuel jet.
    Journal of Manufacturing Processes 01/2013; 15(4):524–532.
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    ABSTRACT: Photoionization of a slow and cold Cesium atomic beam has been produced out of a Magneto-Optical Trap (MOT) and investigated towards applications in the Focused Ion Beam (FIB) technology.
    Laser Science; 10/2012
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    ABSTRACT: Block copolymers P(MA4-block-MMA)10 and P(MA4-block-MMA)20 and a random copolymer P(MA4-ran-MMA)10 were prepared from azobenzene methacrylate (MA4) and methyl methacrylate (MMA). The former monomer was introduced as both a photoresponsive and a mesogenic component, and the latter as a transparent non-mesogenic component. Thin films of the copolymers were used to investigate all-optical writing by linear-polarized illumination in the pulsed regime to modify the local birefringence at the microscopic scale. The optical properties of P(MA4-block-MMA)10 were compared with those of P(MA4-ran-MMA)10 having the same chemical composition (10 mol% MA4) but different distributions of the two components. It was found that in the block copolymers relatively intense pulses as short as 100 μs produced a remarkable local increase in the birefringence, stable in the time-scale (up to several days) explored in the experiment. In contrast, efficient and stable optical modifications could not be achieved in the random copolymer.
    Journal of Materials Chemistry 07/2012; 22(29):14510-14517. · 5.97 Impact Factor
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    ABSTRACT: We report on pure optical nanowriting in the near-field of spin-coated films of a specifically synthesized azobenzene-containing block copolymer. Writing is accomplished by linear polarized blue laser radiation, which is efficiently absorbed by the material, and readout is based on polarization-modulation of red laser radiation, which is practically unabsorbed. Purely optical, stable, and reversible modifications are observed at the ∼100 nm scale. Remarkably, they are not accompanied by any observable topographical change. We attribute the result to the use of a small azobenzene content (3% mol) and to the block architecture of the material.
    Applied Physics Letters 02/2012; 100(8). · 3.79 Impact Factor
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    ABSTRACT: In this paper, we experimentally show the effect of waveguide discontinuity on the propagation of the surface plasmon in metal stripes and tapered terminations. Dual-plane leakage microscopy and near-field microscopy were performed on Au stripes with varied widths to image the surface plasmon intensity distribution in real and reciprocal spaces. We unambiguously demonstrate that edge diffraction is the limiting process determining the cutoff conditions of the surface plasmon mode. Finally, we determine the optimal tapered geometry leading to the highest transmission.
    Journal of the Optical Society of America B 01/2012; 29(2):226-231. · 2.21 Impact Factor
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    ABSTRACT: Correctly c-axis oriented HgBa2CaCu2O6+δ thin films have been produced on (100) MgO single crystal substrates and characterized. Pulsed laser deposition has been exploited to deposit Hg-free Re-doped precursor which then underwent synthesis in evacuated and sealed quartz tubes. X-ray diffraction pattern of the precursor target shows the expected composition of oxides. Scanning electron microscopy analysis have been performed on the surface of the precursor film. Hg-1212 films have been analyzed by θ-2θ Bragg-Brentano X-ray diffractometry. The patterns show little contributions in composition of Hg-1223 phase. The films exhibit a transition temperature >120 K with zero-resistance at around 115 K.
    International Journal of Modern Physics B 01/2012; 14(25n27). · 0.46 Impact Factor
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    ABSTRACT: We have applied pulsed laser deposition (PLD) to fabricate YBCO/YSZ films (short length) onto biaxially textured NiFe substrates. Macroscopic characterization of the samples has been carried out by electrical measurements, XRD patterns and pole figures. Our best films are characterized by Tcs around 89 K and transition widths around 5–6 K. Bragg–Brentano spectra and pole figures acquired on the {111} peak for YSZ and {013} for YBCO show the achievement of the correct crystalline structure and stoichiometry both in YSZ and in YBCO layers. They are largely in-plane textured (respectively (001) <110> for YSZ and (001) <100> for YBCO), and the superconducting YBCO layer exhibits a relatively low mosaicity. Atomic-force microscopy (AFM) analysis confirmed the presence of large grains (1–2 μm typical dimensions), and the occurrence of a complex morphology in the YBCO layer.
    International Journal of Modern Physics B 01/2012; 17(04n06). · 0.46 Impact Factor
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    ABSTRACT: Two relevant examples are described here concerning polymer composite films contg. dyes of different structure characterized by luminescent responsiveness to external stimuli. These systems provides evicence on how the optical smart response can be exploited for the development of smart and intelligent polymer devices for sensing and safety applications. (c) 2012 American Institute of Physics. [on SciFinder(R)]
    AIP Conf. Proc. 01/2012; 1459:89-91.
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    ABSTRACT: Surface plasmon propagation along striped Gold structures has been investigated by collection-mode near-field microscopy, leading to map the field intensity at the structure surface and to assess the system behavior at the nanoscale.
    Frontiers in Optics 2011/Laser Science XXVII; 01/2011
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    ABSTRACT: Interplay of optical effects with the surface morphology at the nanometer scale in samples of Au nanowires is exploited in optical near-field microscopy with polarization control in the mode collection.
    Frontiers in Optics; 10/2010
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    ABSTRACT: Photoluminescent nanostructured semiconductor/metal systems consisting of silicon nanocrystals and gold nanoparticles are obtained by gold-catalyzed chemical etching. The interplay between silicon and gold nanostructures is investigated by photoluminescence spectroscopy upon continuous and pulsed excitation, both at room and low temperature. Comparison with reference samples, obtained removing gold particles by selective etching, highlights an enhanced emission in samples containing silicon and gold nanoparticles, explained in terms of both surface modifications and optical coupling between emitting nanocrystals and nanoparticles featuring localized plasmon resonances.
    Applied Physics Letters 10/2010; 97(14):143113-143113-3. · 3.79 Impact Factor