186,403 research outputs found
Free clusters in a supersonic beam probed by multicoincidence technique after core-level photoionization
No full textParameterization of a two-stage mass spectrometer performing second-order space focusing
No full textHigh mass resolution can be achieved with a time-of-flight mass spectrometer performing first-order space focusing in combination with supersonic molecular beams. The introduction of a second-order correction of the space focus allows an enhancement of the resolution. We present a general parameterization for designing a two-stage mass spectrometer performing second-order space focusing. This formalism is well suited for the design of instruments devoted to the study of clusters in molecular beams. Numerical simulations of the performance are presented
Fractal analysis of sampled profiles: Systematic study
No full textA quantitative evaluation of the influence of sampling on the numerical fractal analysis of experimental profiles is of critical importance. Although this aspect has been widely recognized, a systematic analysis of the sampling influence is still lacking. Here we present the results of a systematic analysis of synthetic self-affine profiles in order to clarify the consequences of the application of a poor sampling (up to 1000 points) typical of scanning probe microscopy for the characterization of real interfaces and surfaces. We interpret our results in terms of a deviation and a dispersion of the measured exponent with respect to the "true" one. Both the deviation and the dispersion have always been disregarded in the experimental literature, and this can be very misleading if results obtained from poorly sampled images are presented. We provide reasonable arguments to assess the universality of these effects and propose an empirical method to take them into account. We show that it is possible to correct the deviation of the measured Hurst exponent from the "true" one and give a reasonable estimate of the dispersion error. The last estimate is particularly important in the experimental results since it is an intrinsic error that depends only on the number of sampling points and can easily overwhelm the statistical error. Finally, we test our empirical method calculating the Hurst exponent for the well-known 1 + 1 dimensional directed percolation profiles, with a 512-point sampling
Growth of sp-sp2 nanostructures in a carbon plasma
No full textThe growth of sp and sp2 nanostructures in a carbon plasma is simulated by tight-binding molecular dynamics. The simulations are arranged so as to mimic the cluster formation conditions typical of a pulsed microplasma cluster source which is used to grow nanostructured sp-sp2 carbon films [ L. Ravagnan et al. Phys. Rev. Lett. 98 216103 (2007)]. The formation of linear, ring, and fullerenelike objects in the carbon plasma is found to proceed through a very long multistep process. Therefore, tight-binding simulations of unprecedented duration have been performed by exploiting the disconnected topology of the simulated carbon plasma which made it possible to implement a computationally efficient divide-and-diagonalize procedure. Present simulations prove that topologically different structures can be formed in experiments, depending on the plasma temperature and density. A thorough characterization of the observed structures as well as their evolution (caused both by thermal annealing and by cluster ripening) is provided
«Avanzandomi tempo [...] ho imparato un poco de scrivere». Studio sulla progressiva caratterizzazione di genere delle lettere dei figli degli Sforza negli anni della loro formazione
No full textManipulation of nanoparticles in supersonic beams for the production of nanostructured materials
No full textProduction and manipulation of nanoparticles in the gas phase is of primary importance for the synthesis of nanostructured materials and for the development of industrial processes based on nanotechnology. In this review we will present and discuss the approach based on the use of aerodynamic focusing methods coupled to supersonic expansions to obtain high intensity cluster beams with a control on nanoparticle mass and spatial distribution. The implication of this techniques for the synthesis of nanostructured materials will be also presented
Cluster beam deposition : a tool for nanoscale science and technology
No full textGas phase nanoparticle production, manipulation and deposition is of primary importance for the synthesis of nanostructured and nanocomposite materials and for the development of industrial processes based on nanotechnology. In this presentation we will present and discuss this approach, introducing cluster sources, nanoparticle particle formation and growth mechanisms and the use of aerodynamic focusing methods that are coupled with supersonic expansions to obtain high intensity cluster beams with a control on nanoparticle mass and spatial distribution [1]. The implication of this technique for the synthesis of nanostructured and nanocomposite materials will be presented and applications will be highlighted [1, 2]. The recent results on the production of polymer supported Micro-Electrode Array device will be also discussed in dept.
[1] K. Wegner et al., J. Phys. D: Appl. Phys. 39, R439 (2006);
[2] L. Ravagnan et al., arXiv:0902.022
Time-of-flight analysis of neutral cluster beams through detection of charged particles produced by cluster impact on a channeltron
No full textElectrical conduction in nanostructured carbon films produced by supersonic cluster beam deposition
No full textWe present a study on electrical conduction in nanostructured carbon films produced by deposition of a supersonic beam of neutral carbon clusters. The electrical transport properties have been investigated by measuring the electrical conductance both in-situ, during the film deposition, and ex-situ, after the film exposure to ambient air. The I-V characteristic indicates a strict ohmic behavior all over the measured electric field range up to (2 kV/cm). Changes in the electrical conductance have been observed due to gas adsorption-desorption mechanisms. The exposure to air leads to a passivation of the film with an increase of resistivity up to ∼ 0.1 GΩ.cm. Current-temperature characteristics measured in vacuum in the temperature range 150-400 K, both in-situ and ex-situ, indicate a thermally activated conductivity with energy of ∼ 0.3 eV
Electrochemical impedance spectroscopy on nanostructured carbon electrodes grown by supersonic cluster beam deposition
No full textNanostructured porous films of carbon with density of about 0.5 g/cm3 and 200 nm thickness were deposited at room temperature by supersonic cluster beam deposition (SCBD) from carbon clusters formed in the gas phase. Carbon film surface topography, determined by atomic force microscopy, reveals a surface roughness of 16 nm and a granular morphology arising from the low kinetic energy ballistic deposition regime. The material is characterized by a highly disordered carbon structure with predominant sp2 hybridization as evidenced by Raman spectroscopy. The interface properties of nanostructured carbon electrodes were investigated by cyclic voltammetry and electrochemical impedance spectroscopy employing KOH 1 M solution as aqueous electrolyte. An increase of the double layer capacitance is observed when the electrodes are heat treated in air or when a nanostructured nickel layer deposited by SCBD on top of a sputter deposited film of the same metal is employed as a current collector instead of a plain metallic film. This enhancement is consistent with an improved charge injection in the active material and is ascribed to the modification of the electrical contact at the interface between the carbon and the metal current collector. Specific capacitance values up to 120 F/g have been measured for the electrodes with nanostructured metal/carbon interface
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