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Vahedi Tafreshi H. Piseri P. Barborini E. Benedek G. Milani P. 《Journal of nanoparticle research》2002,4(6):511-524
We describe a simulation of the nanoparticle trajectories in a pulsed cluster beam source. Clusters, formed by condensation of atomic vapor in a helium bath, and considered here as rigid spheres having a diameter of 1.5nm, were tracked during their travel inside the source cavity, an aerodynamic lens, and a cylindrical nozzle. Steady state supersonic laminar flow of helium is considered in an axi-symmetric geometry aiming to simulate, within some limitations, the conditions under which cluster formation takes place in a pulsed microplasma cluster source. In spite of the unsteady nature of the pulsed source, the time scale characterizing particle motion in the flow field is significantly smaller than the characteristic time constant for the evolution of gas pressure in the source. For this reason, a steady simulation can shed some light on the understanding of processes governing nanoparticle motion in a pulsed vaporization source. The extent to which the Brownian diffusion can affect the particle extraction from the source is investigated. Simulations have shown that the Brownian motion perturbs the clusters from the trajectories dictated by the carrier gas and increases the rate of cluster deposition on the source internal walls. However, it does not hinder the aerodynamic focalization produced by the lens even in nano-size cluster regime. This result is qualitatively confirmed by experiment. 相似文献
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C.?LenardiEmail author M.?Marino E.?Barborini P.?Piseri P.?Milani 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,46(3):441-447
We have developed a method for the quantitative evaluation of
the chemisorbed fraction of hydrogen in nanostructured carbon films using Near Edge X-ray Absorption
Spectroscopy (NEXAFS). In the carbon K-edge spectrum the peak related to carbon bonded to hydrogen is
assumed to be correlated with the amount of hydrogen bonded to carbon. This
assumption is supported by a comparative analysis of gas-phase
hydrocarbons obtained via Electron Energy Loss Spectroscopy
(EELS). We applied the method to nanostructured carbon (ns-C)
films synthesized by supersonic cluster beam deposition. The
evaluated quantity of chemisorbed hydrogen in different samples
exposed to molecular hydrogen (pressure of 0.12 MPa, for 3 hours
at room temperature) is ∼1.5 wt.%. 相似文献
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E. Barborini I. N. Kholmanov A. M. Conti P. Piseri S. Vinati P. Milani C. Ducati 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):277-282
Nanostructured titanium dioxide films have been deposited
by supersonic cluster beam deposition (CBD). Nanoparticles are
produced by a pulsed microplasma cluster source (PMCS) and
selected by aerodynamic separation effects. The as-deposited
film is a complex mixture where amorphous material coexists, at
the nanoscale, with anatase and rutile crystal phases. The
nanocrystalline fraction of the film is characterized by crystal
size ranging from 100 nm to less than 5 nm. We have
characterized the film structure by transmission electron
microscopy, Raman spectromicroscopy, X-ray diffraction, and
UV-visible spectroscopy showing that correlations exist between
cluster size and film properties. In particular if very small
clusters are deposited, the film shows a predominant rutile
phase whereas larger clusters form films with mainly anatase
structure. Our observations suggest that phonon confinement
effects are responsible for a significant shift and broadening
observed for the Raman peaks. In addition, optical gap tuning is
provided by mass selection: large clusters assembling generates
a film with 3.22 eV optical gap, while smallest clusters 3.52
eV. 相似文献
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Bisio F Prato M Barborini E Canepa M 《Langmuir : the ACS journal of surfaces and colloids》2011,27(13):8371-8376
This article presents a study of the interaction of octadecanethiol molecules (C(18)) with nanoporous cluster-assembled gold films under a liquid environment based on a combined spectroscopic ellipsometry and X-ray photoelectron spectroscopy investigation. By comparing the optical response, following the deposition of C(18), of cluster-assembled films with varying degrees of porosity with that of flat surfaces and by resolving the corresponding features of the molecule-Au bond, we have been able to define the conditions that either favor molecular in-depth diffusion into the pores or promote the formation of a molecular self-assembled monolayer (SAM) restricted to the film surface. In the presence of abundant open pores, C(18) molecules strongly diffuse within the film interior and bind to the pore walls, whereas in the presence of porous films with less abundant open pores we have observed that the molecules tend to remain confined to the surface region, adopting a SAM-like configuration. 相似文献
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E. Barborini C. Lenardi P. Piseri P. Milani R. G. Agostino T. Caruso E. Colavita S. La Rosa M. Bertolo C. Ducati 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):273-276
Inclusions of metals in the growth process of carbon
cluster assembled materials (ns-C) induce modifications in the
structural and electronic properties of the material. A novel
pulsed microplasma cluster source (PMCS) is able to deliver
highly intense, collimated and stable beams suitable for
producing bulk quantities of cluster-assembled nanocomposite
films. Loading of metal nanoparticles into carbon cluster based
films is obtained either by mixing a gas phase metallorganic
compound with the carrier gas (He) before entering into the
source (for example molybdenum (V) isopropoxide), or by using a
double component sputtering target (metal (Ti, Ni)/graphite). The study of film
morphology on nanometer scale, carried out by transmission
electron microscopy (TEM), reveals the dispersion in a ns-C
matrix of metallic particles and, in the case of molybdenum
containing films, also of carbide particles. Spatially resolved
ultraviolet photoemission spectroscopy confirms the segregation
of metal particles and exhibits evident anisotropy in the
Mo:ns-C films, mainly ascribable to the formation of carbide
nanoparticles. 相似文献
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M.?Bruzzi P.?Piseri S.?Miglio G.?Bongiorno E.?Barborini C.?Ducati J.?Robertson P.?MilaniEmail author 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(1):3-13
We have studied the electrical conduction in nanostructured carbon (ns-C) films produced by deposition of a supersonic beam of neutral carbon clusters. The d.c. conduction properties of these films have been measured in situ during the deposition process and ex situ as a function of the temperature in vacuum and in ambient of different gases (H2, N2, CH4, He). The ns-C films exhibit an ohmic behavior with a room temperature resistivity in the range of 107-109
W{\rm\Omega}
cm depending on the growth and storage conditions. Conductivity vs. temperature measured in vacuum in the range 290-400 K is characterized by activation energies in the range of 0.3-1.7 eV, the current response does not differ significantly in gas atmosphere. Nanocomposite carbon-metal films have been obtained by adding small amounts of metallorganic precursors containing molybdenum and cobalt during the formation of carbon clusters prior to deposition. The films are characterized by porous carbon networks containing small metal and metal carbide clusters. Electrical transport properties of these films have been studied as a function of temperature, gas pressure and relative humidity. In particular, the electrical conductivity of the sample produced with molybdenum showed to be much sensitive to changes in gas pressure and relative humidity, being characterised by fast and reversible responses. 相似文献
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Batani D Strati F Stabile H Tomasini M Lucchini G Ravasio A Koenig M Benuzzi-Mounaix A Nishimura H Ochi Y Ullschmied J Skala J Kralikova B Pfeifer M Kadlec Ch Mocek T Präg A Hall T Milani P Barborini E Piseri P 《Physical review letters》2004,92(6):065503
We present an experimental point for the carbon equation of state (EOS) at megabar pressures, obtained by laser-driven shock waves. The rear side emissivity of "two-materials two-steps" targets (Al-C) was recorded with space and time resolution and, by applying the impedance mismatch method, allowed a direct determination of relative EOS points. Experiments were performed at the PALS and LULI laboratories using carbon samples with two different values of initial density, in order to explore a wider region of the phase diagram. Previously unreached pressures were obtained. The results are compared with previous experiments and with available theoretical models and seem to show a high compressibility of carbon at megabar pressures. 相似文献
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