Congresso del Dipartimento di Fisica Highlights in Physics 2005

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Anode Interaction chamber: P = 10-8mbar Aerodinamical lenses 15 mm 1 kV/cm GAS Ambient air RH ~ 40% DEPOSITION CHAMBER 5 mm Cluster source Substrate 1 mm Vacuum Rotating cathode Differential vacuum chamber: P = 10-6mbar Cluster beam 20 mm cluster beam Molybdenum Beamline Ø 6.3 mm Prototype realized in collaboration with Maxwell Technologies.Inc SOURCE CHAMBER Carbon PMCS 100 nm 5 mm 5nm source pulsed HV 2mm e >> 1 Fragmentation e << 1 Memory effect Deposition Apparatus Pulsed valve Cathode 400m Gas stagnation point 40 mm 500 mm Substrate Stream Lines St~1 Skimmer Source performance for ns-C deposition PMCSwith an aerodynamic lenses system St<<1 St>>1 Area 75 mm2 Source Rate 5-10 Hz Deposition Rate 50-150 mm/h composite cathode Mass spectra of C clusters Standard cylindrical nozzle Focusing nozzle Aerodynamic lens assembly 2.5nm Winding technology Electrical contact Composite cathode electrode separtor COUPLED CATHODE: qualitative control on composition modifying the position of the interface between the two materials relative to the ablation point Electrode width 25 mm Electrode length 125 mm Thickness 5 mm collector Supercapacitors (ns-C) Gas-phase injection Capacitance C = 0.2 F Specific capacitance Cs = 12.7 F/g Resistance ESR = 24 Ohm Energy density E = 0.03 Wh/kg Power density P = 10 kW/kg Anode Aerodinamical lenses ns-C coated Al electrodes (double side) PMCS 5nm Inert gas input He Rotating catode Capacitive Humidity Sensor (ns-C) Metallorganic precursor bubbler SINTERED or COMPRESSED CATHODE: absolute control on composition E. Barborini et al., APL 81 , 3359 (2002) G. Bongiorno et al., Carbon 43, 1460 (2005) Sketch of the top view G. Bongiorno et al., J. Nanosci. Nanotech., 5, 1072, 2005< Sensor Concept: two serial capacitors with two Au rear electrodes, the ns-C film as the dielectric and a thin Au layer electrode on top. Fast and reversible changes in the capacitance have been observed as the relative humidity is cyclically varied. Air+H2O H+ Electrical contact Electrical contact Graphite charge collector Graphite charge collector Pt:ns-C film Cell performance: Surface exposed: 4.8 cm2 H2 pressure: 2 bar Air pressure: 2 bar Cell voltage 800mV (open circuit) Power: 30-50 mW (depending on sample) Specific power ~300W/gPt (best performance up to date) Pt:ns-C film PEM Fuel Cell (Pt:ns-C) Nafion Membrane Air H2 Pt:ns-C film deposited on both sides of Nafion membranes (area: 16 cm2; thickness: from few tens of nanometers to 500nm). e- e- Congresso del Dipartimento di Fisica Highlights in Physics 2005 11–14 October 2005, Dipartimento di Fisica, Università di Milano High intensity cluster beams: an enabling technology for nanostructured materials synthesis and free-cluster experiments G.Bongiorno, P.Piseri, E. Barborini, S. Vinati, T. Mazza and P.Milani CIMAINA and CNR-INFM, Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, I-20133 Milano, Italy. Supersonic Cluster Beam Deposition Abstract: Nanostructured cluster assembled materials are systems of great interest due to their high porosity and high specific surface. These properties make these systems interesting for applications in electrochemistry, catalysis and gas sensing. In order to deposit thin films of nanostructured cluster assembled materials for industrial applications the use of high intensity cluster beams is mandatory. The physical and chemical properties of cluster assembled materials are strictly related to the properties of the clusters free in the beam. Therefore it is very important to analyze the clusters prior to deposition, not only in terms of mass distribution, but also from the point of view of their structure, electronic properties, and thermodynamic state. As a result, high intensity cluster beams are needed not only to achieve high deposition rates but also to perform experiments on free clusters. In this poster we report on an evolved version of the Pulsed Microplasma Cluster Source (PMCS), developed at the Molecular Beams and Nanocrystalline Materials Laboratory in Milano, which is able to deliver highly collimated and intense pulsed cluster beams of refractory materials (in the case of carbon cluster beams the deposition rate is about 100µm/h at 500mm source-substrate distance and with a 1cm2 of covered area). The mass distribution of the produced beams is lognormal in the range 0-few thousands of atoms/cluster, with an average size of few hundreds of atoms/cluster depending on the source operation conditions. By means of aero-dynamical effects is possible to operate mass selection on the produced clusters (aero-dynamical nozzles can be used as band-pass filters) and to greatly collimate the beams. Nanostructured thin films prepared with this approach have been used as active components in gas and humidity sensors and fuel cells. The high intensity of this source (up to 1013 cluster/cm3) has been employed in order to perform mass resolved X-ray absorption experiments on free titanium clusters (mass distribution range 0-1000 atoms/cluster with a maximum at 320 atoms/cluster) in PEPICO mode at the Ti L-edge. Pulsed Microplasma Cluster Source: Principle Of Operation Deposition Regime Cathode 2 1 3 4 Pulsed valve Nozzle Anodes Injection of anhighly collimatedgas pulse Thermalization of the ablated material and cluster aggregation Supersonic expansion of the mixture gas-clusters Microplasma formation due to an intense electric discharge and ion sputtering of cathode surface P. Milani, S. Iannotta, Cluster Beam Synthesis of Nanostructured Materials, Springer Verlag, Berlin 1999 Aerodynamic confined target erosion • Erosion performances with graphite target: • Localized erosion: FWHM < 0.7 mm • C: ~ 2·10-4 mm3/pulse • C: ~ 2·1016 atoms C / pulse • No contamination from the source body H. Vahedi-Tafreshi et al., Aerosol Sci. Technol. 36, 593 (2002) H. Vahedi-Tafreshi et al., J. Nanoparticle Res. 4, 511 (2002) E. Barborini, P. Piseri, P.Milani, J. Phys. D, Appl. Phys. 32, L105 (1999) Pulsed Microplasma Cluster Source Source-nozzle: mass selection and inertial focusing “…the essential action of a gas centrifuge could be reproduced without any moving parts by allowing gas to expand at high velocity into a jet having curved lines of flow.” P.A.M. Dirac, Rep. Of U.K.A.E.A. declassified in 1953 • Control on clusters: • Dimensions • Position • Chemical reactivity • Coalescence Mass selection mechanism Focusing nozzle Developed at Laboratorio Getti Molecolari e Materiali Nanocristallini,Department of Physics, University of Milano (Italy) P. Piseri, et al., Rev. Sci. Instrum.72, 2261 (2001) H. Vahedi Tafreshi et al., Aerosol Sci. Technol.36, 593 (2002) Stokes number is defined as the ratio between particle stopping distance and a characteristic length of the system. It depends of upstream pressure, nozzle diameter, particle size and density. Exists a critical Stokes number St*, at which particles cross the jet axis at infinity, corresponding to zero divergence angle downstream of the nozzle. Particles with a Stokes number smaller than St* do not have enough inertia to cross the jet axis, while particles with a Stokes number larger than St* cross the axis at finite distances and the divergence angle increases asymptotically as St increases. Performance: low divergence and high deposition rate High resolution patterning by means of stencil masks Nanoparticle focusing in aerodynamic lens systems P0 = 2.6 Torr dp = 15nm Ns-C patterned film P0 = 2.6 Torr dp = 1000nm Substrate Mask E. Barborini et al. Appl. Phys. Lett.77, 1059 (2000) F.J. de la Mora, P. Riesco-Chueca, J. Fluid. Mech. 195, 1 (1988) Microfabrication of nanostructured 3D-objects CESyRa project @ Gasphase Total Ion Yield NEXAFS spectrum of free Titanium clusters Cluster assembled ns-C Photodiode • Source working @ 5 Hz; • Ti Cluster density (peak): 1013 cl/(cm3s) • Pulse length: ~ 50 ms; • Beam velocity: ~ 1000 m/s; Light clusters Heavy clusters Piezo Ti L-edge Electron counting: ~ 1 kHz Ns-C tower created by depositing an highly collimated beam produced by means of a 5 lenses aerodynamic system Ions are in the mass range 80 – 1960 Ti atoms Channeltrons Electrochemical applications Chemistry in the PMCS Mo:ns-C Pt:ns-C ns-CNx NH3 as carrier gas metallorganic precursor composite cathode