G. A. Baratta

National Institute of Astrophysics, Roma, Latium, Italy

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Publications (145)360.02 Total impact

  • Astronomy and Astrophysics 11/2015; DOI:10.1051/0004-6361/201527138 · 4.38 Impact Factor

  • Planetary and Space Science 08/2015; DOI:10.1016/j.pss.2015.08.011 · 1.88 Impact Factor
  • T. Sabri · G. A. Baratta · C. Jäger · M. E. Palumbo · T. Henning · G. Strazzulla · E. Wendler ·
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    ABSTRACT: Context. It has been confirmed that solid carbon dioxide (CO2) is abundantly present along the line of sight to quiescent clouds and star-forming regions via space IR observations with ISO-SWS and Spitzer Space Telescope. Since CO2 has low abundance in the gas-phase, the assumption is that it is synthesized on grains after energetic processing of icy mantles and surface reactions. Aims. The role of solid carbon is investigated as a reservoir for molecule formation and structural modifications of the material with and without an ice layer upon ion bombardment. Methods. A gas-phase condensation technique was used to prepare a layer of 13C amorphous grains. These grains were covered with H2O and O2 ice and finally bombarded with 200 keV protons. The formation of new molecular species was analyzed using IR spectroscopy. The formation cross sections of solid 13CO and 13CO2 were determined from the increase in the column density as a function of the fluence. In addition, bare carbon grains were bombarded with a comparable fluence of protons to study the processing of the grains without ice layer. Imaging techniques such as transmission electron microscopy were used to monitor the changes in the structure. Results. CO and CO2 were formed efficiently at the interface between ice and solid carbon grains at the expense of solid carbon, leading to strong grain erosion. Given the initial thickness of our C-samples (about 120nm), this resulted in an erosion of about 50% after 200 keV proton bombardment with 6.76 × 1016 ions/cm2. The column density of CO and CO2 follows an exponential trend as a function of the irradiation fluence. The asymptotic values obtained when O2 ice is deposited on top of the carbon grains are about one order of magnitude higher than the values obtained when H2O ice is deposited on the solid carbon layer. The carbon grains were strongly graphitized upon ion bombardment in a surface layer. Less graphitization accompanied by the formation of fullerene molecules and structures from cage fragments present in the original material were observed beneath the graphitic layer. Conclusions. The formation of CO and CO2 at the expense of solid carbon strongly restricts the lifetime of the solid carbon material and may influence the formation of more complex molecules in astrophysical environments. Graphitization of carbonaceous grains upon ion bombardment affect the spectral properties of the carbon grains in particular in the far-IR range.
    Astronomy and Astrophysics 03/2015; 575:A76. DOI:10.1051/0004-6361/201425154 · 4.38 Impact Factor
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    ABSTRACT: In this paper we present the formation of carbon nanowires (polyynes and polycumulenes) in the solid state by ion irradiation of frozen hydrocarbons (C6H6 and C2H2). Irradiations have been performed using H+ ions in the 100's keV energy regime using fluences up to 5 × 1014 ions/cm2. Beyond the intrinsic significance of these results in the field of material science, this work has been motivated by the fact that ion beam irradiation of hydrocarbon ices is one of the most important process thought to happen in several extraterrestrial environments where many spectroscopic features of polyyne molecules have been identified.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 04/2014; 326. DOI:10.1016/j.nimb.2013.10.065 · 1.12 Impact Factor
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    ABSTRACT: We present the analyses results of two bulk Terminal Particles, C2112,7,171,0,0 and C2112,9,171,0,0, derived from the Jupiter-family comet 81P/Wild 2 returned by the Stardust mission. Each particle embedded in a slab of silica aerogel was pressed in a diamond cell. This preparation, as expected, made it difficult to identify the minerals and organic materials present in these particles. This problem was overcome using a combination of three different analytical techniques, viz. FE-SEM/EDS, IR, and Raman microspectroscopy that allowed identifying the minerals and small amounts of amorphous carbon present in both particles. TP2 and TP3 were dominated by Ca-free and low-Ca, Mg-rich, Mg,Fe-olivine. The presence of melilite in both particles is supported by IR microspectroscopy, but is not confirmed by Raman microspectroscopy, possibly because the amounts are too small to be detected. TP2 and TP3 show similar silicate mineral compositions, but Ni-free and low-Ni, subsulfur (Fe,Ni)S grains are present in TP2 only. TP2 contains indigenous amorphous carbon hot spots; no indigenous carbon was identified in TP3. These nonchondritic particles probably originated in a differentiated body. This work found an unanticipated carbon contamination following the FE-SEM/EDS analyses. It is suggested that organic materials in the embedding silica aerogel are irradiated during FE-SEM/EDS analyses creating a carbon gas that develops a strong fluorescence continuum. The combination of the selected analytical techniques can be used to characterize bulk Wild 2 particles without the need of extraction and removal of the encapsulating aerogel. This approach offers a relatively fast sample preparation procedure, but compressing the samples can cause spurious artifacts, viz. silica contamination. Because of the combination of techniques, we account for these artifacts.
    03/2014; 49(4). DOI:10.1111/maps.12274
  • F. Islam · G. A. Baratta · M. E. Palumbo ·
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    ABSTRACT: Context. Interstellar ices are known to be simultaneously processed by both cosmic-ray bombardment and UV photolysis. Our knowledge of the effects of energetic processing on relevant icy samples is mainly based on laboratory investigations. In the past 35 years many experiments have been performed to study these effects separately but, to the best of our knowledge, never simultaneously. Aims: The aim of this work is to study the effects of simultaneous processing of ices by both cosmic rays and UV photons to investigate to what extent the combined effect of ion bombardment and UV photolysis influences the chemical pathways. Methods: We carried out the simultaneous processing of CH3OH:N2 ice held at 16 K by 200 keV H+ ions and Lyman-alpha 10.2 eV UV photons. The samples were analyzed by in situ transmission infrared spectroscopy. The un-combined processes of UV irradiation and bombardment by H+ ions of CH3OH:N2 ice were also studied. This mixture was chosen because the effects of ion bombardment and UV photolysis on methanol and nitrogen have been extensively studied in previous investigations. This mixture enables one to investigate whether simultaneous processing (a) influences the destruction of original species; (b) influences the formation of new species; or (c) causes synergistic effects since Lyman-alpha photons have a very low efficiency in breaking the dinitrogen bond because N2 is almost transparent at Lyman-alpha wavelengths. Results: After processing a CH3OH:N2 sample, the intensity of the methanol bands was observed to decrease at the same rate in all cases. After ion bombardment, species such as CO2, CO, H2CO, CH4, N2O, HNCO, and OCN- are formed in the ice mixture. After UV photolysis, species such as CO2, CO, H2CO, and CH4 are formed, but no N-bearing species are detected. Spectra of ices processed by both UV photons and ions were compared with spectra of ices bombarded only by ions. We find that there are no differences in the band area and profile of N-bearing species for the two types of experiment at the same ion fluence; therefore, the addition of UV irradiation to ion bombardment does not affect the abundance of N-bearing species. The initial formation rate of CH4, within the experimental uncertainties, is the same in all cases studied, while the saturation value of CH4 is higher for UV photolysis than for ion bombardment when they act separately. In the case of simultaneous processing, when the dose (eV/16u) given by UV photons is similar to the dose given during ion bombardment, the saturation value of CH4 reaches a value intermediate between the value obtained after UV photolysis and ion bombardment separately. Conclusions: Our results confirm that when UV photolysis and ion bombardment act separately, their effects are very similar from a qualitative point of view, while significant quantitative difference may exist. In the case of simultaneous processing we did not detect any synergistic effect, but in some instances the behavior of newly formed species (such as CH4) can significantly depend on the UV/ions dose ratio.
    Astronomy and Astrophysics 01/2014; 561:73-. DOI:10.1051/0004-6361/201322010 · 4.38 Impact Factor
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    ABSTRACT: Inter- and circumstellar ices comprise different molecules accreted on cold dust particles. These icy dust grains provide a molecule reservoir where particles can interact and react. As the grain acts as a third body, capable of absorbing energy, icy surfaces in space have a catalytic effect. Chemical reactions are triggered by a number of possible processes; (i) irradiation by light, typically UV photons from the interstellar radiation field and Ly-alpha radiation emitted by excited hydrogen, but also X-rays, (ii) bombardment by particles, free atoms (most noticeably hydrogen, but also N, C, O and D-atoms), electrons, low energy ions and cosmic rays, and (iii) thermal processing. All these effects cause ices to (photo)desorb, induce fragmentation or ionization in the ice, and eventual recombination will make molecules to react and to form more and more complex species. The effects of this solid state astrochemistry are observed by astronomers; nearly 180 different molecules (not including isotopologues) have been unambiguously identified in the inter- and circumstellar medium, and the abundances of a substantial part of these species cannot be explained by gas phase reaction schemes only and must involve solid state chemistry. Icy dust grains in space experience different chemical stages. In the diffuse medium grains are barely covered by molecules, but upon gravitational collapse and darkening of the cloud, temperatures drop and dust grains start acting as micrometer sized cryopumps. More and more species accrete, until even the most volatile species are frozen. In parallel (non)energetic processing can take place, particularly during planet and star formation when radiation and particle fluxes are intense. The physical and chemical properties of ice clearly provide a snapshotroot to characterize the cosmological chemical evolution. In order to fully interpret the astronomical observations, therefore, dedicated laboratory experiments are needed that simulate dust grain formation and processing as well as ice mantle chemistry under astronomical conditions and in full control of the relevant parameters; ice morphology (i.e., structure), composition, temperature, UV and particle fluxes, etc., yielding parameters that can be used for astrochemical modeling and for comparison with the observations. This is the topic of the present manuscript. Laboratory experiments simulating the conditions in space are conducted for decades all over the world, but particularly in recent years new techniques have made it possible to study reactions involving inter- and circumstellar dust and ice analogues at an unprecedented level of detail. Whereas in the past "top-down scenarios" allowed to conclude on the importance of the solid state for the chemical enrichment of space, presently "bottom-up approaches" make it possible to fully quantify the involved reactions, and to provide information on processes at the molecular level. The recent progress in the field of "solid state laboratory astrophysics" is a consequence of the use of ultra high vacuum systems, of new radiation sources, such as synchrotrons and laser systems that allow extensions to wavelength domains that long have not been accessible, including the THz domain, and the use of highly sensitive gas phase detection techniques, explicitly applied to characterize the solid state such as fluorescence, luminescence, cavity ring-down spectroscopy and sophisticated mass spectrometric techniques. This paper presents an overview of the techniques being used in astrochemical laboratories worldwide, but it is incomplete in the sense that it summarizes the outcome of a 3-day workshop of the authors in November 2012 (at the Observatoire de Meudon in France), with several laboratories represented, but not all. The paper references earlier work, but it is incomplete with regard to latest developments of techniques used in laboratories not represented at the workshop.
    Space Science Reviews 12/2013; 180(1-4-1-4):101-175. DOI:10.1007/S11214-013-0020-8 · 6.28 Impact Factor
  • S. Scollo · G. A. Baratta · M. E. Palumbo · S. Corradini · G. Leto · G. Strazzulla ·
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    ABSTRACT: In this work, we applied infrared spectroscopy to investigate the spectral signature of the volcanic ash particles emitted during the 21–24 July 2001 eruption at Mount Etna, in Italy. We used a Bruker Equinox‐55 Fourier transform infrared spectrometer in the range 7000–600 cm−1 (1.43–16.67 µm) and, for every collected spectrum, an image of the volcanic ash particles was recorded in the visible spectral range through the same microscope. These images were then analyzed by standard image analysis software in order to evaluate the main features of the particle: the length of the major and minor axes (Max and Min L), Feret diameter (FD), equivalent diameter (ED), and aspect ratio (AR). We measured transmission spectra in different conditions; spectra of one single particle (Single‐Particle Measurement, SPM), spectra of a number of particles from two to ten (Multi‐Particle Measurements type 1, MPM1) and of more than a hundred particles (Multi‐Particle Measurements type 2, MPM2). For SPM, Max and Min L range between 5 and 24 µm and 3.5 and 15 µm, FD ranges between 5.5 and 25 µm, ED varies between 5 and 19 µm, and AR between 0.45 and 0.95. For MPM1 and MPM2, the mean values of Max and Min L are between 4–17 µm and 3–10 µm, FD and ED between 5 and 19 µm and 3.5 and 23 µm, and AR between 0.3 and 1. The optical depth spectra as a function of the wave number clearly show the presence of the Christiansen effect that produces high transmission at a given frequency in the infrared region (Christiansen frequency). We find that the effect depends on the particle size through a linear relation. Both the Christiansen effect and their relationship with the ash particle effective radius were compared with radiative transfer model simulations using different ash refractive indexes. The combined use of the linear relationship and the spectral position of the Christiansen frequency also indicated the possibility to characterize ash type. All these information can be used to improve the IR remote sensing volcanic ash quantitative estimations.
    11/2013; 118(21). DOI:10.1002/2013JD020433
  • S Ioppolo · I Sangiorgio · GA Baratta · ME Palumbo ·
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    ABSTRACT: Context. Solid interstellar CO2 is an abundant component of ice dust mantles. Its ubiquity towards quiescent molecular clouds, as well as protostellar envelopes, has recently been confirmed by the IRS (InfraRed Spectrograph) aboard the Spitzer Space Telescope. Although it has been shown that CO2 cannot be efficiently formed in the gas phase, the CO2 surface formation pathway is still unclear. To date several CO2 surface formation mechanisms induced by energetic (e.g., UV photolysis and cosmic ray irradiation) and non-energetic (e.g., cold atom addition) input have been proposed. Aims: Our aim is to investigate the contribution of cosmic ray irradiation to the formation of CO2 in different regions of the interstellar medium (ISM). To achieve this goal we compared quantitatively laboratory data with the CO2 bending mode band profile observed towards several young stellar objects (YSOs) and a field star by the Spitzer Space Telescope. Methods: All the experiments presented here were performed at the Laboratory for Experimental Astrophysics in Catania (Italy). The interstellar relevant samples were all irradiated with fast ions (30-200 keV) and subsequently annealed in a stainless steel high vacuum chamber (P < 10-7 mbar). Chemical and structural modifications of the ice samples were monitored by means of infrared spectroscopy. Laboratory spectra were then used to fit some thirty observational spectra. Results: A qualitative analysis shows that a good fit can be obtained with a minimum of two components. The choice of the laboratory components is based on the chemical-physical condition of each source. A quantitative analysis of the sources with known visual extinction (AV) and methanol abundances highlights that the solid carbon dioxide can be efficiently and abundantly formed after ion irradiation of interstellar ices in all the selected YSOs in a time compatible with cloud lifetimes (3 × 107 years). Only in the case of field stars can the expected CO2 column density formed upon energetic input not explain the observed abundances. This result, to be confirmed along the line of sight to different quiescent clouds, gives an indirect indication that CO2 can also be formed in an early cloud stage through surface reactions induced by non-energetic mechanisms. In a later stage, when ices are exposed to higher UV and cosmic ray doses, the CO2 total abundance is strongly affected by energetic formation mechanisms. Conclusions: Our results indicate that energetic processing of icy grain mantles significantly contribute to the formation of solid phase interstellar CO2.
    Astronomy and Astrophysics 04/2013; 554. DOI:10.1051/0004-6361/201321176 · 4.38 Impact Factor
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    ABSTRACT: Life Marker Chip (LMC) is a bioanalytical instrument on board of the ESA Exomars mission to detect specific organic molecules that may be associated with life on Mars. Observation of possible biomarkers is critical for the understanding of prebiotic evolution and to detect signature of past and/or present life on other extraterrestrial body. Biomarkers usually are associated with mineral matrix, so it is necessary to investigate the nature of the interaction of organic molecules with minerals. Our approach is to combine physical-chemical analisys (adsorption isotherm, adsorption kinetics, surface area measurement, etc.) with FTIR and Raman spectroscopy in order to clarify the kind of interaction at molecular level between biomarkers and minerals. In particular we focus our attention on nucleobases that are the precursor of genetic material (DNA, RNA) with several minerals (MgO, forsterite, TiO2, hydroxylapatite, olivine) that mimic extraterrestrial materials. A second objective was to investigate the desorption processes in order to optimize the experimental procedure for the detection of biomarkers in the contest of LMC. In this study we have evaluated the effect of several parameters such as sonication and temperature on the extraction efficiency. Moreover because the desorption process strongly depends on the chemical nature of organics and minerals and on their own interaction, we have also evaluated the capability of different solvent mixtures (water, methanol, etc.) with different polarity and the use of surfactant (Tween 80) to extract previously adsorbed biomolecules. The results obtained could contribute to improve the biomarker extraction procedure in the LMC experiment.
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    D. Sicilia · S. Ioppolo · T. Vindigni · G. A. Baratta · M. E. Palumbo ·
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    ABSTRACT: Context. High CO depletion as well as depletion of N-bearing species is observed in dense pre-stellar cores. It is generally accepted that depleted species freeze out onto dust grains to form icy mantles and that these ices suffer energetic processing due to cosmic ion irradiation and ion-induced UV photons. Aims: The aim of this work is to study the chemical and structural effects induced by ion irradiation on different CO:N2 mixtures at low temperature (16 K) to simulate the effects of cosmic ion irradiation of icy mantles. Methods: Different CO:N2 mixtures and pure CO and pure N2 were irradiated with 200 keV H+ at 16 K. Infrared transmittance spectra of the samples were obtained in situ before and after irradiation. The samples were warmed up and spectra were taken at different temperatures. The residues left over on the substrate at room temperature were analysed ex situ by micro Raman spectroscopy. Results: Several new absorption features are present in the infrared spectra after irradiation, indicating that new species are formed. The most abundant are nitrogen oxides (such as NO, NO2 and N2O), carbon chain oxides (such as C2O, C3O and C3O2), carbon chains (such as C3 and C6), O3 and N3. A refractory residue is also formed after ion irradiation and is clearly detected by Raman spectroscopy. Conclusions: We suggest that carbon chains and nitrogen oxides observed in the gas phase towards star-forming regions are formed in the solid phase after cosmic ion irradiation of icy grain mantles and are released into the gas phase after desorption of grain mantles. We expect that the Atacama Large Millimeter/submillimeter Array (ALMA), thanks to its high sensitivity and resolution, will increase the number of nitrogen oxides and carbon chain oxides detected towards star-forming regions.
    Astronomy and Astrophysics 07/2012; 543(A155). DOI:10.1051/0004-6361/201219390 · 4.38 Impact Factor
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    ABSTRACT: The surfaces of the Jupiter's Galilean moons are dominated by frozen sulfur dioxide (Io) or water ice (Europa, Ganimede and Callisto) and exhibit traces of other carbon and/or sulfur bearing molecular species. Being dipped in the Jovian magnetosphere those surfaces are continuously modified by irradiation of magnetospheric ions. The study of the induced effects is based on laboratory simulations. Here we review some of the results of experiments performed by our group, namely implantation of reactive ions in ices. In particular we present results relative to carbon implantation in water ice and of proton in frozen sulfur dioxide. We find that a relevant quantity of CO_2 can be formed by carbon ions implantation on Europa, Ganimede and Callisto, but this is not the dominant formation mechanism. Implantation of protons into sulfur dioxide produces mainly SO_3 and polymers, and O_3 but not H-S bonds. These results do not support the hypothesis that H implantation could result in the formation of H_2SO_3 on Io.
    01/2012; 20:94-.
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    ABSTRACT: Raman analyses have been performed on Interplanetary Dust Particles (IDPs) collected in the lower stratosphere by NASA high-flying aircrafts, dust from comet 81P/Wild2 collected by Stardust mission, and three particles collected in the upper stratosphere by the balloon-borne DUSTER instrument. All samples contain amorphous carbon (aC) with different degrees of structural order. Fe oxides were detected in the IDPs, aliphatic chains were found in comet grains, and three particles collected in the upper stratosphere are calcium carbonate (calcite or aragonite). Raman spectroscopy is a valuable tool for the nondestructive analyses of micrometer-scale constituents of complex natural materials.
    Spectroscopy Letters 10/2011; 44(7-7-8):549-553. DOI:10.1080/00387010.2011.610424 · 0.85 Impact Factor
  • Z. Kaňuchová · G. A. Baratta · R. Brunetto · D. Fulvio · G. Strazzulla ·
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    ABSTRACT: The most of the observed Phobos area is characterized by redder spectral unit (PRU), while bluer spectral unit (PBU) is being generally associated with the interior and the ejecta of Stickney crater. We present a model that is based on laboratory experiments and using which we try to explain the difference in spectral slopes of the two parts of Phobos surface.
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    ABSTRACT: We present some results of an ongoing experimental research aimed at simulating the effects of ion bombardment (space weathering) in solid objects of the Solar System. In particular we have investigated the color changes induced by the ion bombardment in the UV-Vis-IR In this contribution we focus on materials (silicates) and spectral range (200-300 nanometers) particularly relevant to the study of the Mercury's surface.
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    ABSTRACT: Context. Infrared observations show the presence of icy mantles along the line of sight toward young stellar objects (YSOs), where a temperature gradient is expected and indirectly observed. In this environment, icy mantles are affected by ion and UV irradiation. Laboratory experiments show that molecules are formed after irradiation of icy mixtures. However, most of the experiments done so far have been performed in the temperatures range of 10-20 K. Aims: To extend previous work we irradiated some icy mixtures, namely H2O:CO=10:1, H2O:CH4=4:1, and H2O:CO2=3:1 at two different temperatures (12 K and 40 or 60 K) to study the effects of temperature on the synthesis of molecules and the decrease in their parent species after ion irradiation. Methods: The experiments were performed in a high-vacuum chamber (P < 10-7 mbar), where icy samples were irradiated with 30 keV He+ ions and analyzed by a FTIR spectrophotometer. Infrared spectra of the samples were recorded after various steps of irradiation. Results: We found that the temperature affects the behavior of the volatile species (i.e., CO and CH4) during irradiation. As a consequence, the production of molecular species is generally more prevalent at 12 K than at either 40 or 60 K, while the decrease in their parent volatile species is faster at high temperature. Conclusions: We conclude that the behavior of each species depends on the value of its sublimation temperature with respect to the temperature of the sample. If this latter is higher than the sublimation temperature of a given species, then the effects of thermal desorption compete with those due to irradiation.
    Astronomy and Astrophysics 04/2011; 528(A118). DOI:10.1051/0004-6361/201015341 · 4.38 Impact Factor
  • M.G. Grimaldi · P. Baeri · G. Baratta ·

    MRS Online Proceeding Library 01/2011; 157. DOI:10.1557/PROC-157-419
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    ABSTRACT: Molecules in the solid phase have been detected in the line of sight of quiescent molecular clouds and star forming regions as icy mantles on dust grains. Water (H_2O), carbon monoxide (CO), carbon dioxide (CO_2), methanol (CH_3OH), carbonyl sulfide (OCS), methane (CH_4), ammonia (NH_3) and sulfur dioxide (SO_2) are the most abundant observed species (e.g. Gibb et al. 2004). It is generally accepted that some of these species (such as CO) freeze out from the gas phase while others (such as water and methanol) are formed on grains after surface reactions (Ioppolo et al. 2008). CO_2 and OCS are not expected to freeze out from the gas phase and grain surface models do not account for their observed abundance (Ruffle & Herbst 2001; Garrod et al. 2007). It has been suggested that these molecules are formed after energetic processing (i.e. cosmic ion and UV irradiation) of icy grain mantles (d'Hendecourt et al. 1986; Moore et al. 1991; Palumbo & Strazzulla 1993; Ioppolo et al. 2009; Garozzo et al. 2010 ). Here we will present the results of laboratory experiments which show the formation of CO_2 and OCS after ion irradiation of relevant ice mixture at low temperature (10-20 K). We will also present the comparison between the profile of bands in laboratory spectra with those observed in space. We will show that laboratory spectra well reproduce the interstellar features and that the amount of carbon dioxide and carbonyl sulfide formed after ion irradiation can account for the observed amount towards molecular clouds.
    Proceedings of the International Astronomical Union 01/2011; 280.
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    ABSTRACT: The crystallization kinetics of as-deposited amorphous Ge2Sb2Te5 thin films has been measured by in situ time resolved reflectivity. X-ray diffraction and Raman scattering analyses of partially transformed samples allowed to correlate the evolution of the transition to the structural modification in the long and short range configuration. The experimental results evidenced that during the early stages of crystallization there is a reduction of Ge-Te tetrahedral bonds, characteristics of the Ge coordination in amorphous Ge2Sb2Te5 films.
    MRS Online Proceeding Library 01/2011; 1072. DOI:10.1557/PROC-1072-G02-05
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    ABSTRACT: The defects produced in 4H–SiC epitaxial layers by irradiation with 800keV C+ were characterized by Low Temperature Photoluminescence. Ion beam irradiation induces the formation of some sharp lines in the wavelength range 428–441nm of the photoluminescence spectra, that are typically known as “alphabet lines”. These photoluminescence features are due to the recombination of excitons at structural defects. The photoluminescence results allow to single out two groups of peaks: the P1 lines (e–f–g) and the P2 lines (a–b–c–d), that exhibit a different trend with the ion fluence. The P1 group intensity increases with fluence and tends to reach a saturation value at high fluence. The P2 group yield, instead, exhibits a threshold at low fluence and then increases toward a saturation. Subsequent UV-laser irradiation decreases the intensity of the P2 lines related to a change in the structural configuration of the associated defects.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 10/2010; 268(19):2947-2950. DOI:10.1016/j.nimb.2010.05.015 · 1.12 Impact Factor

Publication Stats

2k Citations
360.02 Total Impact Points


  • 2003-2014
    • National Institute of Astrophysics
      Roma, Latium, Italy
  • 1989-2011
    • University of Catania
      • Department of Physics and Astronomy (DFA)
      Catania, Sicily, Italy
  • 2008
    • Polytechnical University of Valencia
      • Department of Applied Physics
      Valenza, Valencia, Spain
  • 1998
    • University of Virginia
      • Laboratory for Atomic and Surface Physics (LASP)
      Charlottesville, Virginia, United States