Luca Ravagnan is presently the CEO and founder of the Italian company WISE s.r.l., a start-up company having as primary objectives the research in the fields of nanotechnology, biotechnology and biomedicine, and the commercial exploitation of the obtained results.
In 1997 he achieved the International Baccalaureate at the United World College of the Adriatic (that he attended as the winner of a full scholarship under the high patronage of the President of the Italian Republic). In 2002 he graduated in Physics at the University of Milano (with full marks cum laude). During his graduating thesis he characterized, by in situ Raman spectroscopy, nanostructured carbon films synthesized by supersonic cluster beam deposition, demonstrating for the first time that chains made by sp-hybridized carbon atoms can be produced in stable form in a pure carbon solid. Based on this work he published the same year an article on the journal Physical Review Letters [L. Ravagnan et al., Phys. Rev. Lett. 89, 285506 (2002)], that up to date has been cited 100 times. He then continued his research activity at the same University during his doctorate, by characterising the electric transport, vibrational and electronic properties of sp-sp2 carbon. In 2005 he received the degree of Philosophy Doctor in Physics, Astrophysics and Applied Physics (marks: excellent) and from 2006 to present he continued his studies on sp-sp2 carbon as a Post-doc of the University of Milano. Since 2007 he developed an innovative approach for the production of biocompatible stretchable microcircuits on polymers based on neutral cluster implantation. Based on this research, he filed in 2010 an Italian patent and, in 2011, he founded together with 3 scientific partners and a seed capital company the company WISE s.r.l. that will industrially exploit this technology for biomedical applications.
He has published 23 articles on international journals peer reviewed (h-index 10) and he is the author of a chapter of the book "Polyynes: Synthesis, Properties, and Applications" edited by Franco Cataldo (published in 2005 by CRC Taylor&Francis). He presented the results of his research as oral contributions at more then 10 international conferences (among which 3 as invited speaker).
From 2003 he participated to six beamtimes at the ELETTRA and MAX-lab synchrotron facilities, characterizing both solid samples and free clusters in the gas phase. Regarding this latter, in 2006 he was awarded, as member of LGM laboratory, the "Prof. Luigi Tartufari" prize from the "Accademia dei Lincei" for his studies on free clusters.
From 2005 to 2011 he has been the activity coordinator for the Laboratory of Optical Spectroscopy of the centre of excellence CIMAINA of the University of Milano and from 2007 he is coordinating the Stretchable Electronics Group at the same centre. Since 2009 he is the scientific coordinator for a research project granted by the Cariplo Foundation.
In 2011 he has received the prize “TR35-Young Innovators” (awarded by the Research and Innovation Forum and by Italian edition of the Technology Review magazine), the 2nd prize “Medical Bisiness Idea 2011” (awarded by the “Charité Entrepreneurship Summit 2011” - Berlin), the “Isimbardi Prize 2011 – Young Talents” (awarded by the Province of Milan) and the prize “What’s Up Young Talents” for the research (awarded by the Journal “What’s Up”).
In 2011 the start-up WISE that he is administrating as CEO has received the 1st prize for the Life Sciences sector at the “Start Cup Milano Lombardia 2011” and the “Nanochallenge 2011” prize (300.000 euro prize awarded by Veneto Nanotech on November 11th 2011).
Abstract: Stretchable and compliant electrodes on polydimethylsiloxane (PDMS) are efficiently fabricated by the implantation of neutral metallic clusters aerodynamically accelerated by a supersonic expansion. The production of these nanocomposite electrodes avoids any charging or carbonization of PDMS and the electrodes can withstand many deformation cycles, decreasing their resistance upon cyclical stretching. Micrometric patterns can be simply fabricated by stencil mask patterning.
Abstract: The presence and stability of sp hybridized atoms in free carbon nanoparticles was investigated by NEXAFS spectroscopy. The experiments show that a predominant fraction of carbon atoms is found in linear sp-chains and that conversion into sp(2) structures proceeds already at low temperature and in the gas phase.
Abstract: We fabricated highly adherent and electrically conductive micropatterns on SU-8 by supersonic cluster beam deposition (SCBD). This technique is based on the aerodynamical acceleration of neutral metallic nanoparticles produced in the gas phase. The kinetic energy acquired by the nanoparticles allows implantation in an SU-8 layer, thus producing a metal-polymer nanocomposite thin layer. The nanocomposite shows ohmic electrical conduction and it can also be used as an adhesion layer for further metallization with a metallic overlayer. We characterized the electrical conduction, adhesion and biocompatibility of microdevices obtained by SCBD on SU-8 demonstrating the compatibility of our approach with standard lift-off technology on 4 ââ wafer. A self-standing and flexible microelectrode array has been produced. Cytological tests with neuronal cell lines demonstrated improved cell growth on the nanocomposite layer.
Abstract: We studied the excitation dynamics and the photoluminescence spectra in polymeric matrix implanted with metallic nanoparticles. A supersonic beam of gold nanoparticles (sizes 2-7 nm) was generated by using a Pulsed Microplasma Cluster Source (PMCS). The nanoparticles were implanted in a thin polyfluorene film (thickness around 100 nm) spin coated on a PMMA (poly methyl methacrilate) substrate. We performed photoluminescence and pump-probe measurements using a Ti: Sapphire amplified laser system, the excitation pump pulse was centered at 400 nm with a 150 fs time duration. The experimental results show a suppression of the amplified spontaneous emission from the polyfluorene (PFO) film due to the presence of the implanted nanoparticles. The transient transmission spectra revealed the presence of a photoinduced absorption band due to the nanoparticles which overlaps with the stimulated emission band from the PFO, hindering the possibility of having amplified spontaneous emission. These results demonstrate the possibility of a local nanotailoring of the polymeric photophysics. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Abstract: We perform a systematic investigation of the resonance and vibrational properties of naphthylterminated sp carbon chains (dinaphthylpolyynes) by combined multi-wavelength resonant Raman (MWRR) spectroscopy, ultraviolet-visible spectroscopy, and Fourier-transform infrared (FT-IR) spectroscopy, plus ab initio density functional theory (DFT) calculations. We show that the MWWR and FT-IR spectroscopies are particularly suited to identify chains of different lengths and different terminations, respectively. By DFT calculations, we further extend those findings to sp carbon chains end-capped by other organic structures. The present analysis shows that combined MWRR and FT-IR provide a powerful tool to draw a complete picture of chemically stabilized sp carbon chains.
Abstract: Linear chains made by a single row of sp-hybridized carbon are predicted to display fascinating mechano-electronic properties connected with their termination and stabilization inside realistic carbon structures. The present work describes how the computed vibrational properties of cumulenic and polyynic carbon chains allow one to interpret the carbynic features observed in Raman spectra of cluster-assembled sp-sp(2) films. The overall picture is consistent with the measured decay of the components induced by air or oxygen exposure. [GRAPHICS] The electronic properties of carbon atomic chains attached to the edges of graphitic fragments can be controlled by a relative twist of the terminating planes. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Notes: 8th International Conference on Optics of Surfaces and Interfaces (OSI-VIII), Ischia, ITALY, SEP 07-11, 2009
Abstract: We report a combined study on the synthesis, spectroscopic characterization, and theoretical modeling of a series of alpha,omega-dinaphthylpolyynes. We synthesized this family of naphthyl-terminated sp carbon chains by reacting diiodoacetylene and 1-ethynylnaphthalene under the Cadiot-Chodkiewicz reaction conditions. By means of liquid chromatography (HPLC), we separated the products and recorded their electronic absorption spectra, which enabled us to identify the complete series of dinaphthylpolyynes Ar-C(2n)-Ar (with Ar = naphthyl group and n = number of acetilenic units) with n ranging from 2 to 6. The longest wavelength transition (LWT) in the electronic spectra of the dinaphthylpolyynes red shifts linearly with n away from the LWT of the bare termination. This result is also supported by DFT-LDA simulations. Finally, we probed the stability of the dinaphthylpolyynes in a solid-state precipitate by Fourier-transform infrared spectroscopy and by differential scanning calorimetry (DSC).
Abstract: Ab 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 sp(3) or sp(2) 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.
Abstract: Nanocomposite 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.
Abstract: Synchrotron radiation-based experimental techniques are largely employed for the characterization of the reactivity of finite size systems; in particular, x-ray absorption spectroscopy (XAS) is a suitable tool to shed light on the local electronic structure and chemical status of atoms in nano-objects, as it is very sensitive to the local bonding environment of the probed site. In supported clusters intrinsic properties and reactivity are largely distorted and obscured by the changes imposed by the growth procedure and by the influence of the substrate, so the attainability of experiments on free clusters reacting with species in the gas phase is a primary goal in the development of cluster science. In this paper we report a proof of principle of the applicability of gas phase XAS technique to titanium and titanium oxide, hydride and hydrate systems. Experiments are performed by coupling a pulsed microplasma cluster source (PMCS) with a third generation synchrotron light source, and measuring the intensity of the electron yield coming from the interaction of VUV photons with the clusters seeded in a supersonic beam.
Notes: 15th International Conference on Vacuum Ultraviolet Radiation Physics, Berlin, GERMANY, JUL 29-AUG 03, 2007
Abstract: Amorphous carbon films with sp-sp(2) hybridization, produced by supersonic cluster beam deposition, shows the presence of both polyynic and cumulenic species [L. Ravagnan et al., Phys. Rev. Lett. 98, 216103 (2007)]. Here, we present an in situ. Raman characterization of the low-frequency vibrational region (400-800 cm(-1)) of sp-sp(2) films at different temperatures. We report the presence of two peaks at 450 and 720 cm(-1). The lower frequency peak shows an evolution with the variation of the sp content and it can be attributed, with the support of density functional theory simulations, to bending modes of sp linear structures. The peak at 720 cm(-1) does not vary with the sp content and it can be attributed to a feature in the vibrational density of states activated by the disorder of the sp(2) phase.
Abstract: We investigated the electrical transport properties of nanostructured carbon and carbon/titanium oxide nanocomposite films produced by supersonic cluster beam deposition and irradiated by highly focused vacuum UV photon beam. We have observed a relevant increase of the density of states at Fermi level, suggesting that the films acquire a âmetallicâ character. This is confirmed by the increment of the conductivity of four orders of magnitude for pure nanostructured carbon films and at least eight orders of magnitude for films containing 9 at. % of titanium. A partial reversibility of the process is observed by exposing the modified films to molecular oxygen or directly to air. We demonstrate the capability of writing micrometric conductive strips (2-3 mu m width and 60 mu m length) and controlling the variation of the conductivity as a function of the titanium concentration. (c) 2007 American Institute of Physics.
Abstract: We report the production and characterization of a form of amorphous carbon with sp-sp(2) hybridization (atomic fraction of sp hybridized species >= 20%) where the predominant sp bonding appears to be (=C=C=)(n) cumulene. Vibrational and electronic properties have been studied by in situ Raman spectroscopy and electrical conductivity measurements. Cumulenic chains are substantially stable in high vacuum conditions for temperatures lower than 250 K and they influence the electrical transport properties of the sp-sp(2) carbon through a self-doping mechanism by pinning the Fermi level closer to one of the mobility gap edges. Upon heating above 250 K the cumulenic species decay to form graphitic nanodomains embedded in the sp(2) amorphous matrix thus reducing the activation energy of the material. This is the first example of a pure carbon system where the sp hybridization influences bulk properties.
Abstract: The growth of sp and sp(2) 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-sp(2) carbon films [L. Ravagnan , 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.
Abstract: Synchrotron 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 Ti-n clusters in the mass range 15<n<1000. The x-ray absorption of Ti-n 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.
Abstract: Nanostructured carbon thin films can be grown by deposition of cluster beams produced in supersonic expansions. By using a pulsed microplasma cluster source and by exploiting aerodynamic focusing effects typical of supersonic expansions, the structure and the properties of the films can be controlled by varying the cluster mass distribution prior to deposition. Nanocomposite films can be produced by co-depositing carbon clusters and metallic nanoparticles. The films have been characterized by various spectroscopic techniques and tested in view of applications for field emission, supercapacitors, gas sensing. The possibility of patterning cluster-assembled carbon films by shadow masking or by ultraviolet photon irradiation suggests interesting perspective for the integration of nanostructured carbon films on microfabricated devices and for the production of components for an all-carbon electronics.
Abstract: We present a near edge X-ray absorption fine structure spectroscopy characterization of nanostructured carbon films containing carbynoid species. By a careful data analysis and normalization of the spectra at the carbon K-edge we have quantitatively evaluated the extent of valence sp hybridization of the films. A sp/sp(2) ratio between 10% and 25% has been obtained. This result allowed the evaluation of the ratio between the sp and sp(2) Raman cross section at different excitation laser wavelengths. (C) 2005 Elsevier Ltd. All rights reserved.
Abstract: A multi-scale investigation of nanostructured carbon films has been performed by means of inelastic light scattering (Raman and Brillouin scattering). Carbon films with different nano- and mesostructure have been deposited from supersonic cluster beams in a low energy deposition regime by exploiting aerodynamic focusing effects. Acoustic phonon propagation in the porous amorphous structure, where disorder acts as a damping factor, is investigated by Brillouin scattering. Depending on the nano- and meso-structure, acoustic phonons can either propagate along the medium, which acts as an elastic continuum at the meso-scale (i.e., hundreds of nm), or turn to overdamped oscillations localized by the structural disorder. Nevertheless, we show that it is always possible to measure the elastic constants of thin and porous films, when other techniques (e.g., nano-indentation) become critical. At the nano-scale, Raman scattering measurements show the typical structure of an amorphous carbon, where the structural disorder is affected by the primeval cluster mass distribution. The synthesis of cluster-assembled carbon films and the in situ Raman characterization in a UHV system allowed to observe the presence of a relevant fraction of sp(1)-hybridized carbon chains (also known as carbynoid structures) embedded in the sp(2) amorphous network.
Notes: Symposium on Advanced Multifunctional Nanocarbon Materials and Nanosystems held at the E-MRS Spring Meeting, Strasbourg, FRANCE, MAY 24-28, 2004
Abstract: We report an experimental and theoretical investigation of the growth and structure of large carbon clusters produced in a supersonic expansion by a pulsed microplasma source. The absence of a significant thermal annealing during the cluster growth causes the formation of disordered structures, where sp(2) and sp hybridizations coexist for particles larger than similar to 90 atoms. Among the various structures, we recognize sp2 closed networks encaging sp chains. This ânutshellâ configuration can prevent the fragmentation of sp species upon deposition of the clusters, thus allowing the formation of nanostructured films containing carbynoid species, as shown by Raman spectroscopy. Atomistic simulations confirm that the observed Raman spectra are the signature of the sp/sp(2) hybridization typical of isolated clusters and surviving in the film and they provide information about the structure of the sp chains. Endohedral sp chains in sp(2) cages represent a novel way in which carbon nanostructures may be organized with potentially interesting functional properties.
Abstract: In situ Raman spectroscopy from nanostructured carbon films, produced by supersonic cluster beam deposition, has revealed a high fraction of sp(1) linear carbon chains (also known as carbynoid structures) embedded in a Sp(2) amorphous matrix. The presence of sp(1) linear carbon chains is revealed by a large structured band with a main peak at nearly 2100 cm(-1) and a shoulder at 1980 cm(-1), assigned to polyyne (alternating single-triple bonds) and polycumulene (double bonds) moietes respectively. The stability of these species has been analysed following the temporal evolution of the characteristic sp(1) Raman band intensity under exposure to several gases (He, N(2), H(2) and dry air). The carbynoid species appear to be very reactive to oxygen-rich environment, whereas the effects of other gases are less destructive. Actually, exposure to oxygen reveals different decay mechanisms with respect to other gases. The thermal stability in ultra high vacuum has been also studied up to 200 degreesC. We observe different decay kinetics as a function of annealing temperature, showing thresholds in the chain stability. (C) 2003 Elsevier Ltd. All rights reserved.
Notes: Symposium on Advanced Multifunctional Nanocarbon Materials and Nanosystems held at the 2003 EMRS Spring Meeting, Strasbourg, FRANCE, JUN 10-13, 2002-2003
Abstract: Nanostructured carbon films consisting of sp chains (polyynes and polycumulenes) embedded in an sp(2) matrix are grown using supersonic carbon cluster beam deposition in ultrahigh vacuum at room temperature. All the specimens have been analyzed by in situ Raman spectroscopy. The use of different excitation wavelengths (532 and 632.8 nm) confirms the presence of distinct carbynoid species. Chemical stability of the sp species has been studied by exposing the as-deposited films to 500 mbar of H-2, He, N-2, and dry air. Gas exposure produces an exponential decay of the carbynoid fraction slightly affecting the sp(2) component. Helium, hydrogen, and nitrogen do not chemically interact with the sp chains whereas oxygen reacts with the carbynoids species causing their fast and almost complete destruction. The films have been also thermally annealed at 20degrees, 100degrees, 150degrees, and 200 degreesC. The amount of carbynoid species is rapidly and strongly reduced at temperature larger than room temperature. The relevance for material science and interstellar chemistry of the production of a bulk form of carbon where sp and sp(2) hybridizations coexist is addressed.
Abstract: Nanostructured carbon films produced by supersonic cluster beam deposition have been studied by in situ Raman spectroscopy. Raman spectra show the formation of a sp(2) solid with a very large fraction of sp-coordinated carbyne species with a long-term stability under ultrahigh vacuum. Distinct Raman contributions from polyyne and cumulene species have been observed, as well as different stabilities under gas exposure. Our experiments confirm theoretical predictions and demonstrate the possibility of producing a carbyne-rich pure carbon solid. The stability of the sp(2)-sp network has important implications for astrophysics and for the production of novel carbon-based systems.
Abstract: UV absorption from carbon nanoparticles is a very interesting astrophysical topic. The prominent hump centred at 217.5 nm is the most dominant feature in the interstellar extinction curve and also the most controversial and a long-standing problem in astrophysics. At the University of Milano an experimental set-up based on a Pulsed Microplasma Cluster Source has been developed for the investigation of free clusters at the Elettra Gas Phase beamline. The cluster source produces very intense cluster beams with tunable size distribution. The design of the apparatus is extended with a chamber for gas phase reaction (water vapour, CO, H2...) providing a unique opportunity to study the gas phase properties of carbonaceous particles in different environments.
We plan to investigate Resonant Raman scattering of free carbon particles tuning the high brilliance UV/VIS storage ring FEL of ELETTRA across the region of 217.5 nm where the UV absorption hump in astrophysical data is observed and where a number of electronic transitions exist for variable size linear carbon chains.
Abstract: Linear nanostructures made by sp1 hybridized carbon atoms have recently been observed in nanostructured carbon films deposited by supersonic cluster beams. In situ Raman measurements have revealed the presence of a large amount of these carbynoid structures embedded in the film sp2 amorphous network. These structures show a long-term stability in UHV without any stabilizing chemical species (e.g. metallic or metal-organic complex molecules). In situ measurements presented in this work have been performed to follow the evolution of these metastable structures under different environmental conditions. The reactivity of the carbon chains has been thus investigated for samples, after different gas exposures and for different annealing temperatures. We observe distinct decay mechanisms after H2, He, N2 exposures with respect to oxygen exposure and energy thresholds in the thermal stability.
