1,720,970 research outputs found
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
Evaluation of hydrogen chemisorption in nanostructured carbon films by near edge X-ray absorption spectroscopy
No full textWe 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.%
High-rate production of functional nanostructured films and devices by coupling flame spray pyrolysis with supersonic expansion
No full textThe fabrication of functional thin films and devices by direct deposition of nanoparticles from
the gas phase is a promising approach enabling, for instance, the integration of complex
analytical and sensing capabilities on microfabricated platforms. Aerosol-based techniques
ensure large-scale nanoparticle production and they are potentially suited for this goal.
However, they are not adequate in terms of fine control over the lateral resolution of the
coatings, mild processing conditions (avoiding high temperature and aggressive chemicals),
low contamination and compatibility with microfabrication processes.
Here we report the high-rate and efficient production of functional nanostructured films
by nanoparticle assembling obtained by the combination of flame spray pyrolysis and
supersonic expansion. Our approach merges the advantages of flame spray pyrolysis for bulk
nanopowders such as process stability and wide material library availability with those of
supersonic cluster beam deposition in terms of lateral resolution and of direct integration of
nanomaterials on devices. We efficiently produced nanostructured films and devices (such as
gas sensors) using metal oxide, pure noble metal and oxide-supported noble metal
nanoparticles
Poly(methyl methacrylate)-palladium clusters nanocomposite formation by supersonic cluster beam deposition : a method for microstructured metallization of polymer surfaces
No full textNanocomposite films were fabricated by supersonic cluster beam deposition (SCBD) of
palladium clusters on poly(methyl methacrylate) (PMMA) surfaces. The evolution of the electrical conductance with cluster coverage and microscopy analysis show that Pd clusters are implanted in the polymer and form a continuous layer extending for several tens of nanometres beneath the polymer surface. This allows the deposition, using stencil masks, of cluster-assembled Pd microstructures on PMMA showing a remarkably high adhesion compared with metallic films obtained by thermal evaporation. These results suggest that SCBD is a promising tool for the fabrication of metallic microstructures on flexible polymeric
substrates
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
Electronic and vibrational properties of sp carbon atomic wires : effects of boundary constraints
No full textThe role of carbon-based devices in post-silicon nanoelectronics is gaining a rapidly increasing importance, due to the availability of carbon nanosystems, such as fullerenes, nanotubes, graphenes. These can be considered as potential building blocks of complex architectures with novel electronic and magnetic properties.
Carbon nanowires consisting of sp-hybridized linear carbon chains are potentially another strategic component to integrate these carbon nanosystems in complex architectures, as it is routinely done in silicon nanoelectronics. Linear sp-carbon chains, characterized by double bonds (cumulene) or alternating single and triple bonds (polyyne), have been object of theoretical studies as ideal molecular conductors, and as building blocks of low dimensional solids with unusual properties. Despite their potential properties, the role of sp nanowires in the carbon-based electronics arena is still generally perceived as somehow marginal: polyynes and cumulenes have been considered for several decades as exotic allotropic forms due to their high reactivity and their tendency to undergo cross-linking reaction to form sp2 carbon. Recently, we demonstrated that large carbon clusters where sp and sp2 hybridization coexist can be formed in the gas phase [1] and deposited on a substrate to form a nanostructured film where sp chains are stable at room temperature [2, 3].
Here we report on first-principles DFT calculations combined with experimental Raman spectra on cluster-assembled sp-sp2 carbon films [4]. Ab-initio total energy and phonon calculations were performed on a selected range of model structures sampling significantly the infinite variety of three-dimensional arrangements of sp-chains bridging graphitic fragments in different hybridization states (Figure 1). Theoretical results suggest that sp-carbon chains are stabilized by sp2 or sp3 terminations (in particular by bonding to the edges of graphitic nanofragments) and allow us to interpret the nontrivial features and decay of the experimental Raman spectra. Moreover, the data for sp2-terminated chains point towards a rich phenomenology driven by even/odd alternation effects and by the effects of torsional strain. This unexplored effect promises many exciting applications since it allows one to modify the conductive states near the Fermi level, suggesting the possibility to control the nanowire conductance, and to switch on and off the on-chain pi-electron magnetism, purely by twisting its sp2 termination.
Carbon atomic chains bridging graphene nanogaps, recently proposed as an explanation of the conductance switching in two-terminals graphene devices [5, 6], could hence originate an unexpected variety of geometrically-driven physical effects with many potential applications. Recently such systems have also been experimentally realized and observed by HR-TEM [7], thus opening the way to a completely new class of all-carbon devices.
[1] M. Bogana et al., New J. Phys. 2005, 7, 81.
[2] L. Ravagnan et al., Phys. Rev. Lett. 2002, 89, 285506.
[3] L. Ravagnan et al., Phys. Rev. Lett. 2007, 98, 216103.
[4] L. Ravagnan et al., Phys. Rev. Lett. in print, arXiv:0902.2573v4.
[5] B. Standley et al., Nano Lett. 2008, 8, 3345.
[6] Y. Li, A. Sinitskii, et al., Nat. Mater. 2008, 7, 966.
[7] C. Jin et al., Phys. Rev. Lett. 2009, 102, 205501
Effect of Axial Torsion on sp Carbon Atomic Wires
No full textAb initio calculations within density-functional theory combined with experimental Raman spectra on cluster-beam deposited pure-carbon films provide a consistent picture of sp-carbon chains stabilized by sp3 or sp2 terminations, the latter being sensitive to torsional strain. This unexplored effect promises many exciting applications since it allows one to modify the conductive states near the Fermi level and to switch on and off the on-chain pi-electron magnetism
Accessing the fractal dimension of free clusters in supersonic beams
No full textIn this paper a method for the quantitative determination of a morphology descriptor of free clusters with complex nanostructure is presented and applied to transition metal nanoparticles produced by a pulsed vaporization source. The method, which is based on the low-pressure aerodynamic mobility of neutral particles, can be applied as a characterization tool to a broad class of gas-phase nanoparticle sources for on-line investigation of particle growth and for quantifying coalescence versus agglomerate aggregation. We report on the application of this method for the characterization of free titanium clusters produced by a pulsed microplasma cluster source in the size range of approximately 300-6000 atoms. The clusters have an open fractal-like structure, with the fractal dimension depending on their thermal history during growth and evolving towards softer aggregates for longer residence times where lowertemperature conditions characterize the growth environment
Hydrogen uptake in cluster-assembled carbon thin films: experiment and computer simulation
No full textX-ray absorption measurements and large-scale molecular dynamics simulations are used to investigate the storage capacity of hydrogen in cluster-assembled carbon films. Experimental results show that nanostructured carbon exposed to H2 at 0.12 MPa for 3 h at room temperature can store up to 1.5 wt % of hydrogen. These experimental results are in good quantitative agreement with the computational data. Both experiments and simulations confirm that hydrogen is chemisorbed on the carbon. The simulations provide information about the spatial distribution of the sorption sites of atomic and molecular hydrogen
Core level spectroscopy of free titanium clusters in supersonic beams
No full textSynchrotron radiation x-ray absorption spectroscopy (XAS) is one of the most powerful techniques to interrogate the local electronic structure and chemical status of bulk and nanostructured systems. The application of this technique to the study of size effects in free clusters of transition metal atoms would advance substantially fundamental knowledge of nano-objects and the
tailoring of their magnetic and catalytic properties. To date core level spectroscopy
of free transition metal clusters has been out of reach due to the lack of a cluster
source able to produce clusters in the gas phase with a density suitable for
synchrotron radiation sources. Here we demonstrate the XAS characterization
of free titanium clusters in a supersonic molecular beam. We use a high-intensity cluster beam source coupled to a synchrotron beamline to investigate the size dependence of core level excitation of Tin clusters in the mass range 15 < n < 1000. The x-ray absorption of Tin evolves from a multi-peaked complex structure similar to that of Ti atoms towards spectra characterized by two main
absorption features as in bulk titanium. The intensities and the fine structure of the
spectra are size dependent showing regularities compatible with geometric shell
closings and the presence of a structural transition at about 540 atoms/cluster
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