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  • 301.
    Galstyan, V.
    et al.
    Department of Physics, Chemistry and Biology (IFM), Linköping University.
    Comini, E.
    Department of Physics, Chemistry and Biology (IFM), Linköping University.
    Vomiero, Alberto
    SENSOR Lab, Department of Chemistry and Physics, Brescia University and CNR-IDASC.
    Ponzoni, A.
    Department of Physics, Chemistry and Biology (IFM), Linköping University.
    Concina, Isabella
    Department of Physics, Chemistry and Biology (IFM), Linköping University.
    Brisotto, M.
    INSTM and Chemistry for Technologies Laboratory.
    Bontempi, E.
    INSTM and Chemistry for Technologies Laboratory.
    Faglia, G.
    Department of Physics, Chemistry and Biology (IFM), Linköping University.
    Sberveglieri, G.
    Department of Physics, Chemistry and Biology (IFM), Linköping University.
    Fabrication of pure and Nb-TiO 2 nanotubes and their functional properties2012Inngår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 536, nr SUPPL.1, s. S488-S490Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    TiO 2 and Nb-doped TiO 2 nanotubes were obtained on flexible polymeric substrates (Kapton HN) and alumina with high roughness (alumina substrate with granular surface). Nanotubes were prepared by electrochemical anodization of a Ti thick film. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to investigate the morphology of the structures and the roughness of the substrates. The functional properties of tubular arrays obtained on flexible and rough substrates were investigated towards two applications, namely, chemoresistive gas sensors and flexible dye sensitized solar cells. © 2011 Elsevier B.V. All rights reserved.

  • 302.
    Galstyan, V.
    et al.
    CNR-IDASC SENSOR Lab and Dipartimento di Chimica e Fisica per l'Ingegneria e per i Materiali.
    Vomiero, Alberto
    CNR-IDASC SENSOR Lab and Dipartimento di Chimica e Fisica per l'Ingegneria e per i Materiali.
    Comini, E.
    CNR-IDASC SENSOR Lab and Dipartimento di Chimica e Fisica per l'Ingegneria e per i Materiali.
    Faglia, G.
    CNR-IDASC SENSOR Lab and Dipartimento di Chimica e Fisica per l'Ingegneria e per i Materiali.
    Sberveglieri, G.
    CNR-IDASC SENSOR Lab and Dipartimento di Chimica e Fisica per l'Ingegneria e per i Materiali.
    TiO 2 nanotubular and nanoporous arrays by electrochemical anodization on different substrates2011Inngår i: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 1, nr 6, s. 1038-1044Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The preparation of nanotubular arrays on different substrates and nanoporous structures on titanium foil by means of electrochemical anodization of titanium layer has been investigated. Highly aligned nanotubes of TiO 2 on flexible, rough and flat substrates are reported. Modification of anodization conditions of titanium on specific substrates such as polyethylene terephthalate (PET), conducting glass and granular alumina was found to affect the morphology of TiO 2 nanotubes. Two different kinds of aqueous electrolytes have been applied, containing either glycerol or H 2SO 4, in order to investigate the effect of ion mobility on anodization process. Galvanostatic and potentiostatic anodization modes have been investigated: transition from nanotubes to nanoporous structures has been highlighted in galvanostatic mode, depending on the intensity of anodization current density. These results pave the way for massive production of TiO 2 nanotubes over, in principle, whatever substrate, enabling exploitation of new functional properties derived from the combination of tubes and substrates. This journal is © The Royal Society of Chemistry 2011.

  • 303.
    Galstyan, Vardan
    et al.
    CNR IDASC SENSOR Lab.
    Comini, Elisabetta
    CNR IDASC SENSOR Lab.
    Faglia, Guido
    CNR IDASC SENSOR Lab.
    Vomiero, Alberto
    CNR IDASC SENSOR Lab.
    Borgese, Laura
    INSTM and Chemistry for Technologies Laboratory.
    Bontempi, Elza
    INSTM and Chemistry for Technologies Laboratory.
    Sberveglieri, Giorgio
    CNR IDASC SENSOR Lab.
    Fabrication and investigation of gas sensing properties of Nb-doped TiO 2 nanotubular arrays2012Inngår i: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 23, nr 23, artikkel-id 235706Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Synthesis of Nb-containing titania nanotubular arrays at room temperature by electrochemical anodization is reported. Crystallization of pure and Nb-doped TiO 2 nanotubes was carried out by post-growth annealing at 400°C. The morphology of the tubes obtained was characterized by scanning electron microscopy (SEM). Crystal structure and composition of tubes were investigated by glancing incidence x-ray diffraction (GIXRD) and total reflection x-ray fluorescence (TXRF). For the first time gas sensing characteristics of Nb-doped TiO 2 nanotubes were investigated and compared to those of undoped nanotubes. The functional properties of nanotubular arrays towards CO, H 2, NO 2, ethanol and acetone were tested in a wide range of operating temperature. The introduction of Nb largely improves conductivity and enhances gas sensing performances of TiO 2 nanotubes. © 2012 IOP Publishing Ltd.

  • 304.
    Galstyan, Vardan
    et al.
    CNR IDASC SENSOR Lab.
    Vomiero, Alberto
    CNR-IDASC SENSOR Lab and Dipartimento di Chimica e Fisica per l'Ingegneria e per i Materiali.
    Concina, Isabella
    CNR IDASC SENSOR Lab.
    Braga, Antonio
    CNR IDASC SENSOR Lab.
    Brisotto, Mariangela
    INSTM and Chemistry for Technologies Laboratory.
    Bontempi, Elza
    INSTM and Chemistry for Technologies Laboratory.
    Faglia, Guido
    CNR IDASC SENSOR Lab.
    Sberveglieri, Giorgio
    CNR IDASC SENSOR Lab.
    Vertically aligned TiO 2 nanotubes on plastic substrates for flexible solar cells2011Inngår i: Small, ISSN 1613-6810, E-ISSN 1613-6829, Vol. 7, nr 17, s. 2437-2442Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electrochemical anodization of a titanium film on a Kapton HN substrate leads to the formation of closely packed aligned nanotubes, whose shape can be finely tuned by tailoring the anodization parameters. An amorphous-to-anatase phase transition is induced on nanotubes by annealing at 350 °C. The nanotubes are applied as photoanodes in flexible dye-sensitized solar cells (N719 dye; I 3 -/I - redox couple), resulting in a photoconversion efficiency of up to 3.5% under simulated sunlight irradiation air mass 1.5 global (AM 1.5G). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  • 305.
    Ganemi, B.
    et al.
    Kungliga tekniska högskolan, KTH.
    Björnbom, E.
    Kungliga tekniska högskolan, KTH.
    Demirel, B.
    Center for Applied Energy Research, Lexington, KY.
    Paul, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Zeolite Cu-ZSM-5: material characteristics and NO decomposition2000Inngår i: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 38, nr 2-3, s. 287-300Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Zeolite ZSM-5 (SiO2/Al2O3 ratio 53:1) ion exchanged with Cu2+ to 0%, 74% and 160% was characterized by X-ray diffraction (XRD), Thermogravimetric analysis (TGA), Infrared (IR) spectroscopy, Electron spectroscopy for chemical analysis (ESCA) and ammonia desorption. A more limited set of data was obtained for Cu-ZSM-5-33, ion exchanged with 0%, 104% and 210% Cu2+ ions. All catalysts lose water below 100°C. More strongly bound water, approximately two molecules per Cu2+ ion, emerge at a higher temperature. This corresponds either to an incomplete hydration shell for zeolite-bound Cu2+ ions or to the decomposition of Cu(OH)2 and simultaneous reactive adsorption of copper ions on the inner surface of the zeolite. The process occurs in the same temperature range, 150-350°C, where XRD reveals rearrangements in the H-form of the catalyst. Reactions between the exchangeable cations and the zeolite appear critical for lattice changes and possibly the formation and dispersion of catalytically active centers at these temperatures. Dehydroxylation and water desorption are observed between 350°C and 450°C for H-ZSM-5. This temperature range overlaps with the light-off temperature for direct NO decomposition over Cu-ZSM-5. This coincidence can be rationalized in terms of two effects of enhanced ionic mobility and dynamics of the zeolitic framework. ESCA shows that partial reduction, cupric to cuprous, occurs as a result of annealing in the same temperature range. It has been suggested that NO-derived surface intermediates act as site blockers for the direct decomposition below the light-off temperature until destabilized by lattice movements. The lower stability and thus higher mobility of low SiO2/Al2O3 ratio ZSM-5 zeolites would then rationalize an advantage of these materials as supports in catalysts for direct NO decomposition.

  • 306.
    Ganemi, B.
    et al.
    Kungliga tekniska högskolan, KTH.
    Björnbom, E.
    Kungliga tekniska högskolan, KTH.
    Paul, Jan
    Conversion and in situ FTIR studies of direct NO decomposition over Cu-ZSM51998Inngår i: Applied Catalysis B: Environmental, ISSN 0926-3373, E-ISSN 1873-3883, Vol. 17, nr 4, s. 293-311Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Copper ion-exchanged zeolites ZSMS with SiO2:Al2O3 molar ratios 33 and 53 have been subjected to activity tests for direct decomposition of NO (2000 ppm, GHSV 560-5400 h(-1)). In situ infrared measurements were used to follow the reaction and surface and gas phase compositions. IR studies were also done in excess oxygen with rapid NO2 formation in the gas phase. A high level of overexchange of copper in the zeolite in combination with a low concentration of acid sites, concurrent with a high SiO2:Al2O3 ratio, enhances the conversion of NO. A vibrational band at 1631 cm(-1) is observed below the light-off temperature and interpreted as a bridged nitrate group bound to Cu2+-O-Cu2+ dimers. This band disappears above the light-off temperature but the intensity below this temperature correlates with the catalytic activity. We interpret that these bridge bound nitrate groups act as siteblockers on the active sites for NO conversion and that a tentative reaction intermediate, N2O3, also binds in a bridge configuration to the same Cu2+-O-Cu2+ dimers.A second nitrate group with unidentate coordination and vibrational bands at 1598/1575 cm(-1) probes isolated copper ions.A third infrared band at 2130 cm(-1) confirms previous observations of NO2+-ions bound to the zeolite. We conclude that these species are coordinated to deprotonated and negatively charged sites on the zeolite and that these sites for NO2+ adsorption are blocked by Cu2+ ion-exchange. The 2130 cm(-1) species appear to have no role in direct NO decomposition but the adsorption sites are crucial for the stability of the zeolite and intimately related to ion mobility in the lattice.Prolonged immersion of the zeolite in dilute solutions of copper ions improves the catalyst performance by copper hydroxylation leading to enhanced formation of the above dimers.A high SiO2:Al2O3 ratio leads to more stable catalysts, particularly in combination with a modest overexchange of copper ions. Excessive amounts of copper escalates the deactivation of the Cu-ZSM5 catalyst through the migration and sintering of cupric oxide crystallites.

  • 307.
    Gergely, Andras
    et al.
    Department of Physical Chemistry, Institute of Chemistry, University of Pannonia, Egyetem, Hungary .
    Szabó, Péter
    Department of General and Inorganic Chemistry, Institute of Chemistry, University of Pannonia, Egyetem, Hungary .
    Krojer, Antal
    Department of Inspection and Maintenance, Mol Nyrt., Olajmunkás, Hungary .
    Nagy, Bence
    Refining Research and Innovation, Mol Nyrt., Hungary .
    Kristof, Tamas
    Department of Physical Chemistry, Institute of Chemistry, University of Pannonia, Egyetem, Hungary .
    Hydrogen Sulfide Corrosion of Carbon and Stainless Steel Alloys in Mixtures of Renewable Fuel Sources under Co-Processing Conditions2018Inngår i: Modern Applied Science, ISSN 1913-1844, E-ISSN 1913-1852, Vol. 12, nr 4, s. 227-255Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Corrosion rates of steel alloys were investigated in gas oil and its mixture with waste cooking oil and animal waste lard over 1, 3, 7 and 21 days under desulfurizing condition. Co-processing conditions were attempted to simulate by batch-reactor experiment at temperatures between 200 and 300oC and pressures between 20 and 90 bar in the presence of 2 volume% hydrogen sulfide. Integral and differential corrosion rates were defined by weight losses. Intense sulfide corrosion of carbon steels was less impacted by the biomass sources. Thinner scales in gas oil was probably due to frequent cohesive failure, whereas thicker layers in biomass mixtures were allowed to form to afford limited physical protection. The high corrosion rate of low alloy steel with temperature over time is related to inefficient protection by the metal sulfide scales. Greater activation energy and enthalpy balance in the formation of activated complex is expected to reflect in thick cohesive scales. Loose layers and the less unfavorable entropy balance in the transition state did not lead to valuable barrier protection. High sulfide corrosion resistance of stainless steels is in chemical in nature markedly impacted by the biomass fuel sources and contributed especially by the acidic species. Corrosion rates increased with temperature by magnitude similar to those of carbon steels, which probably owes to the less unfavorable entropy and free energy balance between the initial and transition states of the reactants.

  • 308.
    Gergely, András
    et al.
    Department of Physical Chemistry, Institute of Chemistry, University of Pannonia.
    Locskai, Roland
    Department of Physical Chemistry, Institute of Chemistry, University of Pannonia.
    Szabo, Peter
    Krójer, Antal
    Department of Inspection and Maintenance.
    Kristóf, Tamás
    Department of Physical Chemistry, Institute of Chemistry, University of Pannonia.
    Hydrogen Sulphide Corrosion of Carbon and Stainless Steel Alloys Immersed in Mixtures of Renewable Fuel Sources and Tested Under Co-processing Conditions2016Inngår i: Hungarian Journal of Industry and Chemistry, ISSN 2450-5102, Vol. 44, nr 1, s. 55-70Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In accordance with modern regulations and directives, the use of renewable biomass materials as precursors for the production of fuels for transportation purposes is to be strictly followed. Even though, there are problems related to processing, storage and handling in wide range of subsequent uses, since there must be a limit to the ratio of biofuels mixed with mineral raw materials. As a key factor with regards to these biomass sources pose a great risk of causing multiple forms of corrosion both to metallic and non-metallic structural materials. To assess the degree of corrosion risk to a variety of engineering alloys like low-carbon and stainless steels widely used as structural metals, this work is dedicated to investigating corrosion rates of economically reasonable engineering steel alloys in mixtures of raw gas oil and renewable biomass fuel sources under typical co-processing conditions. To model a desulphurising refining process, corrosion tests were carried out with raw mineral gasoline and its mixture with used cooking oil and animal waste lard in relative quantities of 10% (g/g). Co-processing was simulated by batch-reactor laboratory experiments. Experiments were performed at temperatures between 200 and 300ºC and a pressure in the gas phase of 90 bar containing 2% (m3/m3) hydrogen sulphide. The time span of individual tests were varied between 1 and 21 days so that we can conclude about changes in the reaction rates against time exposure of and extrapolate for longer periods of exposure. Initial and integral corrosion rates were defined by a weight loss method on standard size of coupons of all sorts of steel alloys. Corrosion rates of carbon steels indicated a linear increase with temperature and little variation with composition of the biomass fuel sources. Apparent activation energies over the first 24-hour period remained moderate, varying between 35.5 and 50.3 kJ mol−1. Scales developed on carbon steels at higher temperatures were less susceptible to spall and detach. Nonetheless, moderate deceleration of corrosion rates as a function of time are due to the less coherent, frequently spalling and low compactness, higher porosity of the scales evolved at lower and higher temperatures, respectively. On the surface of high alloy steels, sulphide scales of an enhanced barrier nature formed during the induction periods and the layer formation mechanism was found to be assisted by the increasing temperature as initial reaction rates considerably decreased over time. Nevertheless, corrosion-related sulphide conversion of metals and mass loss of the high alloys are strongly affected by the composition of the biomass fuel sources especially animal waste lard. Thermal activation in the first 24 hours decreased from 68.9 to 35.2 kJ mol−1. A greater degree of failure to develop protective sulphide scales was experienced by changing to composition of the biomass fuel sources than the impact of thermal activation between a narrow temperature range at around 100ºC. In accordance with the literature, high free fatty acid contents lead to high corrosion rates accounted for direct corrosion of high alloy steels and assisted solubilisation of corrosion products. In addition, the pronounced acceleration of sulphide corrosion is connected to the diminishing inhibition effect of the sulphide scales

  • 309.
    Ghamgosar, Pedram
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Advanced Metal Oxide Semiconductors for Solar Energy Harvesting and Solar Fuel Production2017Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Increasing energy consumption and its environmental impacts make it necessary to look for alternative energy sources. Solar energy as huge energy source which is able to cover the terms sustainability is considered as a favorable alternative. Solar cells and solar fuels are two kinds of technologies, which make us able to harness solar energy and convert it to electricity and/or store it chemically.

    Metal oxide semiconductors (MOSs) have a major role in these devices and optimization of their properties (composition, morphology, dimensions, crystal structure) makes it possible to increase the performance of the devices. The light absorption, charge carriers mobility, the time scale between charge injection, regeneration and recombination processes are some of the properties critical to exploitation of MOSs in solar cells and solar fuel technology.

    In this thesis, we explore two different systems. The first one is a NiO mesoporous semiconductor photocathode sensitized with a biomimetic Fe-Fe catalyst and a coumarin C343 dye, which was tested in a solar fuel device to produce hydrogen. This system is the first solar fuel device based on a biomimetic Fe-Fe catalyst and it shows a Faradic efficiency of 50% in hydrogen production. Cobalt catalysts have higher Faradic efficiency but their performance due to hydrolysis in low pH condition is limited. The second one is a photoanode based on the nanostructured hematite/magnetite film, which was tested in a photoelectrochemical cell. This hybrid electrode improved the photoactivity of the photoelectrochemical cell for water splitting. The main mechanism for the improvement of the functional properties relies with the role of the magnetite phase, which improves the charge carrier mobility of the composite system, compared to pure hematite, which acts as good light absorber semiconductor.

    By optimizing the charge separation and mobility of charge carriers of MOSs, they can be a promising active material in solar cells and solar fuel devices due to their abundance, stability, non-toxicity, and low-cost. The future work will be focused on the use of nanostructured MOSs in all-oxide solar cell devices. We have already obtained some preliminary results on 1-dimensional heterojunctions, which we report in Chapter 3.3. While they are not conclusive, they give an idea about the future direction of the present research. 

  • 310.
    Ghamgosar, Pedram
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Rigoni, Federica
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Gilzad Kohan, Mojtaba
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    You, Shujie
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Morales, Edgar Abarca
    Luleå tekniska universitet.
    Mazzaro, Raffaello
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Morandi, Vittorio
    Institute for Microelectronics and Microsystems Section of Bologna , National Research Council , Bologna , Italy..
    Almqvist, Nils
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Concina, Isabella
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Vomiero, Alberto
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Self-Powered Photodetectors Based on Core-Shell ZnO-Co3O4 Nanowire Heterojunctions2019Inngår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 11, nr 26, s. 23454-23462Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Self-powered photodetectors operating in the UV–visible–NIR window made of environmentally friendly, earth abundant, and cheap materials are appealing systems to exploit natural solar radiation without external power sources. In this study, we propose a new p–n junction nanostructure, based on a ZnO–Co3O4 core–shell nanowire (NW) system, with a suitable electronic band structure and improved light absorption, charge transport, and charge collection, to build an efficient UV–visible–NIR p–n heterojunction photodetector. Ultrathin Co3O4 films (in the range 1–15 nm) were sputter-deposited on hydrothermally grown ZnO NW arrays. The effect of a thin layer of the Al2O3 buffer layer between ZnO and Co3O4 was investigated, which may inhibit charge recombination, boosting device performance. The photoresponse of the ZnO–Al2O3–Co3O4 system at zero bias is 6 times higher compared to that of ZnO–Co3O4. The responsivity (R) and specific detectivity (D*) of the best device were 21.80 mA W–1and 4.12 × 1012 Jones, respectively. These results suggest a novel p–n junction structure to develop all-oxide UV–vis photodetectors based on stable, nontoxic, low-cost materials.

  • 311.
    Ghamgosar, Pedram
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Rigoni, Federica
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    You, Shujie
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Dobryden, Iliya
    Division of Surface and Corrosion Science, KTH Royal Institute of Technolog.
    Gilzad Kohan, Mojtaba
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Pellegrino, Anna Lucia
    Dipartimento Scienze Chimiche, Università degli Studi di Catania, INSTM UdR-Catania.
    Concina, Isabella
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Almqvist, Nils
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Malandrino, Graziella
    Dipartimento Scienze Chimiche, Università degli Studi di Catania, INSTM UdR-Catania.
    Vomiero, Alberto
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    ZnO-Cu2O core-shell nanowires as stable and fast response photodetectors2018Inngår i: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 51, s. 308-316Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work, we present all-oxide p-n junction core-shell nanowires (NWs) as fast and stable self-powered photodetectors. Hydrothermally grown n-type ZnO NWs were conformal covered by different thicknesses (up to 420 nm) of p-type copper oxide layers through metalorganic chemical vapor deposition (MOCVD). The ZnO NWs exhibit a single crystalline Wurtzite structure, preferentially grown along the [002] direction, and energy gap Eg=3.24 eV. Depending on the deposition temperature, the copper oxide shell exhibits either a crystalline cubic structure of pure Cu2O phase (MOCVD at 250 °C) or a cubic structure of Cu2O with the presence of CuO phase impurities (MOCVD at 300 °C), with energy gap of 2.48 eV. The electrical measurements indicate the formation of a p-n junction after the deposition of the copper oxide layer. The core-shell photodetectors present a photoresponsivity at 0 V bias voltage up to 7.7 µA/W and time response ≤0.09 s, the fastest ever reported for oxide photodetectors in the visible range, and among the fastest including photodetectors with response limited to the UV region. The bare ZnO NWs have slow photoresponsivity, without recovery after the end of photo-stimulation. The fast time response for the core-shell structures is due to the presence of the p-n junctions, which enables fast exciton separation and charge extraction. Additionally, the suitable electronic structure of the ZnO-Cu2O heterojunction enables self-powering of the device at 0 V bias voltage. These results represent a significant advancement in the development of low-cost, high efficiency and self-powered photodetectors, highlighting the need of fine tuning the morphology, composition and electronic properties of p-n junctions to maximize device performances.

  • 312.
    Gilzad Kohan, Mojtaba
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mazzaro, Raffaello
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. CNR-IMM, Area della Ricerca di Bologna, Bologna, Italy.
    Morandi, Vittorio
    CNR-IMM, Area della Ricerca di Bologna, Bologna, Italy.
    You, Shujie
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Concina, Isabella
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Vomiero, Alberto
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Plasma assisted vapor solid deposition of Co3O4 tapered nanorods for energy applications2019Inngår i: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 7, nr 46, s. 26302-26310Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Self-standing, 1-dimensional (1D) structures of p-type metal oxide (MOx) have been the focus of considerable attention, due to their unique properties in energy storage and solar light conversion. However, the practical performance of p-type MOx is intrinsically limited by their interfacial defects and strong charge recombination losses. Single crystalline assembly can significantly reduce recombination at interface and grain boundaries. Here, we present a one-step route based on plasma assisted physical vapor deposition (PVD), for the rational and scalable synthesis of single crystalline 1D vertically aligned Co3O4 tapered nanorods (NRs). The effect of PVD parameters (deposition pressure, temperature and duration) in tuning the morphology, composition and crystalline structure of resultant NRs is investigated. Crystallographic data obtained from X-ray diffraction and high-resolution transmission electron microscopy (TEM) indicated the single crystalline nature of NRs with [111] facet preferred orientation. The NRs present two optical band gaps at about 1.48 eV and 2.1 eV. Current–voltage (I–V) characteristic of the Co3O4 NRs electrodes, 400 nm long, present two times higher current density at −1 V forward bias, compared to the benchmarking thin film counterpart. These array structures exhibit good electrochemical performance in lithium-ion adsorption–desorption processes. Among all, the longest Co3O4 NRs electrodes delivers a 1438.4 F g−1 at current density of 0.5 mA cm−2 and presents 98% capacitance retention after 200 charge–discharge cycles. The very low values of charge transfer resistance (Rct = 5.2 Ω for 400 nm long NRs) of the NRs testifies their high conductivity. Plasma assisted PVD is demonstrated as a facile technique for synthesizing high quality 1D structures of Co3O4, which can be of interest for further development of different desirable 1D systems based on transition MOx.

  • 313.
    Gisenti, A
    et al.
    Dipartimento di Scienze Chimiche, Università di Padova.
    Frasson, A
    Dipartimento di Scienze Chimiche, Università di Padova.
    Galenda, A
    Dipartimento di Scienze Chimiche, Università di Padova.
    Ferroni, Matteo
    CNR IDASC SENSOR Lab.
    Concina, Isabella
    CNR IDASC SENSOR Lab.
    Natilea, M.M.
    Dipartimento di Scienze Chimiche, Università di Padova.
    Synthesis and characterization of Ag/CeO2 nanocomposites2010Inngår i: Materials Research Society Symposium Proceedings, Materials Research Society, 2010, Vol. 1257, s. 323-328Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Two Ag/CeO2 nanocomposite samples were prepared by deposition-precipitation (Ag/Ce nominal atomic ratio = 0.03 and 0.12). XPS data suggest the possible presence of traces of Ce(III). Beside Ag (0), oxidized silver species are also revealed in the Ag/CeO2 sample with lower metal content. The deposition of metal increases surface hydroxylation and carbonation. Methanol interacts molecularly and dissociatively with the samples; oxidation products are observed from low temperature and depend on Ag content. Both the samples reveal a high activity in methanol complete oxidation; traces of partial oxidation products are observed in the sample with lower Ag content

  • 314.
    Glaz, Waldemar
    et al.
    Nonlinear Optics Division, Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań.
    Bancewicz, Tadeusz
    Nonlinear Optics Division, Faculty of Physics, Adam Mickiewicz University.
    Godet, Jean Luc
    Laboratoire de Photonique D'Angers, Université D'Angers.
    Gustafsson, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Haskopoulos, Anastasios
    Department of Chemistry, University of Patras.
    Maroulis, George
    Department of Chemistry, University of Patras.
    Effects of anisotropic interaction-induced properties of hydrogen-rare gas compounds on rototranslational Raman scattering spectra: Comprehensive theoretical and numerical analysis2016Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 145, nr 3, artikkel-id 34303Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A comprehensive study is presented of many aspects of the depolarized anisotropic collision induced (CI) component of light scattered by weakly bound compounds composed of a dihydrogen molecule and a rare gas (Rg) atom, H2-Rg. The work continues a series of earlier projects marking the revival of interest in linear light scattering following the development of new highly advanced tools of quantum chemistry and other theoretical, computational, and experimental means of spectral analyses. Sophisticated ab initio computing procedures are applied in order to obtain the anisotropic polarizability component's dependence on the H2-Rg geometry. These data are then used to evaluate the CI spectral lines for all types of Rg atoms ranging from He to Xe (Rn excluded). Evolution of the properties of CI spectra with growing polarizability/masses of the complexes studied is observed. Special attention is given to the heaviest, Kr and Xe based, scatterers. The influence of specific factors shaping the spectral lines (e.g., bound and metastable contribution, potential anisotropy) is discussed. Also the share of pressure broadened allowed rotational transitions in the overall spectral profile is taken into account and the extent to which it is separable from the pure CI contribution is discussed. We finish with a brief comparison between the obtained results and available experimental data

  • 315.
    Gobbi, Emanuela
    et al.
    Univ Udine.
    Falasconi, Matteo
    CNR IDASC SENSOR Lab, University of Brescia.
    Concina, Isabella
    CNR IDASC SENSOR Lab.
    Mantero, G
    Biodivers SPA, Brescia,.
    Bianchi, F
    Univ Studi Parma, Dipartimento Chim Gen & Inorgan,.
    Mattarozzi, M
    Univ Studi Parma, Dipartimento Chim Gen & Inorgan,.
    Musci, M
    Univ Studi Parma, Dipartimento Chim Gen & Inorgan,.
    Sberveglieri, Giorgio
    SENSOR Lab, Department of Information Engineering, University of Brescia.
    Electronic nose and Alicyclobacillus spp. spoilage of fruit juices: An emerging diagnostic tool2010Inngår i: Food Control, ISSN 0956-7135, E-ISSN 1873-7129, Vol. 21, nr 10, s. 1374-1382Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The application of an electronic nose equipped with a Metal Oxide Semiconductor sensor array for the detection of Alicyclobacillus acidoterrestris and A. acidocaldarius artificially inoculated in peach, orange and apple fruit juices is described in this study. Overall the system was able to detect the presence of Alicyclobacillus spp. in all the tested fruit juices at 24 h from inoculation. The electronic nose could detect bacterial concentration as low as <10(2) colony forming unit/ml and it was also able to classify bacterial contamination independently of the Alicyclobacillus species. The gas chromatography-mass spectrometry characterization of the volatile profile of orange juices confirmed the existence of quantitatively different patterns between contaminated and uncontaminated samples.

  • 316.
    Goliath, Martin
    et al.
    Stockholms Universitet.
    Nilsson, Ulf S.
    Stockholms Universitet.
    Uggla, Claes
    Luleå tekniska universitet.
    Spatially self-similar spherically symmetric perfect-fluid models1998Inngår i: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 15, nr 1, s. 167-186Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Einstein's field equations for spatially self-similar spherically symmetric perfect-fluid models are investigated. The field equations are rewritten as a first-order system of autonomous differential equations. Dimensionless variables are chosen in such a way that the number of equations in the coupled system is reduced as far as possible and so that the reduced phase space becomes compact and regular. The system is subsequently analysed qualitatively with the theory of dynamical systems

  • 317.
    Goliath, Martin
    et al.
    Department of Physics, Stockholm University.
    Nilsson, Ulf S.
    Department of Physics, Stockholm University.
    Uggla, Claes
    Luleå tekniska universitet.
    Timelike self-similar spherically symmetric perfect-fluid models1998Inngår i: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 15, nr 9, s. 2841-2863Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Einstein's field equations for timelike self-similar spherically symmetric perfect-fluid models are investigated. The field equations are rewritten as a first-order system of autonomous differential equations. Dimensionless variables are chosen in such a way that the number of equations in the coupled system is reduced as far as possible and so that the reduced phase space becomes compact and regular. The system is subsequently analysed qualitatively using the theory of dynamical systems

  • 318.
    Golubev, Nikolay V.
    et al.
    Department of Chemistry, M. V. Lomonosov Moscow State University.
    Bezrukov, Dmitry S.
    Department of Chemistry, M. V. Lomonosov Moscow State University.
    Gustafsson, Magnus
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Nyman, Gunnar
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Antipov, Sergey V.
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Formation of the SiP radical through radiative association2013Inngår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 117, nr 34, s. 8184-8188Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Formation of the SiP radical through radiative association of Si( 3P) and P(4S) atoms is studied using classical and quantum dynamics. Rate coefficients for formation in the two lowest doublet states and the two lowest quartet states are calculated for T = 10-20 000 K. Breit-Wigner theory is used to properly account for contribution from quantum mechanical resonances.

  • 319.
    Gonella, F.
    et al.
    CNR-IDASC SENSOR Lab and Dipartimento di Chimica e Fisica per l'Ingegneria e per i Materiali.
    Canton, P.
    CNR-IDASC SENSOR Lab and Dipartimento di Chimica e Fisica per l'Ingegneria e per i Materiali.
    Cattaruzza, E.
    CNR-IDASC SENSOR Lab and Dipartimento di Chimica e Fisica per l'Ingegneria e per i Materiali.
    Quaranta, A.
    Dipartimento di Ingegneria dei Materiali e delle Tecnologie Industriali, Università di Trento.
    Sada, C.
    Dipartimento di Fisica Sperimentale, Università di Torino.
    Vomiero, Alberto
    CNR-INFM SENSOR Laboratory.
    Field-assisted ion diffusion of transition metals for the synthesis of nanocomposite silicate glasses2006Inngår i: Materials science & engineering. C, biomimetic materials, sensors and systems, ISSN 0928-4931, E-ISSN 1873-0191, Vol. 26, nr 5-7, s. 1087-1091Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Field-assisted ion diffusion of metals was realized for the controlled doping of silicate glasses. Metallic films deposited onto the substrates by the rf-sputtering technique were used as the metal ions source. In particular, cobalt was, for the first time, introduced into a soda-lime glass by field-assisted ion exchange, giving rise to diffusion profiles that were observed to depend on the preparation parameters, namely, temperature and electric field intensity across the samples. This technique, which allowed to dope the glass matrix with high metal concentration values, can be used as the first step in combined methodologies for the preparation of nanostructured glass composites. The shape of the measured Co diffusion profiles indicates that the migration process depends not only on the experimental parameters but also on the behavior of alkali ions within the glass. Chemical phenomena occurring at the metal/glass interface also play a significant role in the penetration of the Co ions. The possibility of doping the glass with two different metal species was also investigated, with the aim to create the condition for the formation of core-shell or alloy nanoclusters. In particular, preliminary results on Co + Au field-assisted co-diffusion are presented. © 2005 Elsevier B.V. All rights reserved.

  • 320.
    Gorbatov, Oleg
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Department of Materials Science and Engineering, KTH Royal Institute of Technology, Stockholm, Sweden. Laboratory for Mechanics of Gradient Nanomaterials, Nosov Magnitogorsk State Technical University, Magnitogorsk, Russia.
    Stroev, A. Yu.
    National Research Centre, Kurchatov Institute, Moscow, Russia. Moscow Institute of Physics and Technology (State University), Dolgoprudny, Moscow Region, Russia.
    Gornostyrev, Yu. N.
    Institute of Metal Physics, Ural Division RAS, Ekaterinburg, Russia. Institute of Quantum Materials Science, Ekaterinburg, Russia.
    Korzhavyi, P. A.
    Department of Materials Science and Engineering, KTH Royal Institute of Technology, Stockholm, Sweden. Institute of Metal Physics, Ural Division RAS, Ekaterinburg, Russia.
    Effective cluster interactions and pre–precipitate morphology in binary Al-based alloys2019Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 179, s. 70-84Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The strengthening by coherent, nano-sized particles of metastable phases (pre-precipitates) continues to be the main design principle for new high-performance aluminium alloys. To describe the formation of such pre-precipitates in Al–Cu, Al–Mg, Al–Zn, and Al–Si alloys, we carry out cluster expansions of ab initio calculated energies for supercell models of the dilute binary Al-rich solid solutions. Effective cluster interactions, including many-body terms and strain-induced contributions due to the lattice relaxations around solute atoms, are thus systematically derived. Monte Carlo and statistical kinetic theory simulations, parameterized with the obtained effective cluster interactions, are then performed to study the early stages of decomposition in the binary Al-based solid solutions. We show that this systematic approach to multi-scale modelling is capable of incorporating the essential physical contributions (usually referred to as atomic size and electronic structure factors) to the free energy, and is therefore able to correctly describe the ordering temperatures, atomic structures, and morphologies of pre-precipitates in the four studied alloy systems.

  • 321.
    Gowda, Vasantha
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Sarma, Bipul
    Department of Chemical Sciences, Division of Chemical Engineering, Tezpur University, Tezpur, Assam.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Telkki, Ville-Veikko
    University of Oulu, NMR Research Group, Division of Chemical Engineering, Faculty of Science, University of Oulu.
    Larsson, Anna-Carin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Lantto, Perttu
    University of Oulu, NMR Research Group, Division of Chemical Engineering, Faculty of Science, University of Oulu.
    Antzutkin, Oleg
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Structure Elucidation of an Yttrium Diethyldithiocarbamato-Phenanthroline Complex by X-ray Crystallography, Solid-State NMR, and ab-initio Quantum Chemical Calculations2016Inngår i: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-1948, Vol. 20, s. 3278-3291Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a structural analysis method for molecular and electronic structure of yttrium diethyldithiocarbamato-phenanthroline complex {[Y(S2CNR2)3PHEN] with R = C2H5 and PHEN = 1,10-phenanthroline} combining solid-state NMR spectroscopy, XRD, and first principles DFT calculations. Replacing the Nd3+ ion with Y3+ in the reported crystal structure of [Nd(S2CNR2)3PHEN] complex generated an approximate 3D structure of the title complex. The structure was then subjected to first principles quantum chemical geometry optimisation using periodic DFT method. The quality of the method is discussed by comparing predicted and experimental powder XRD patterns. Full assignment of 13C and 15N solid-state CP-MAS NMR spectra as well as analyses of the principal values of the chemical shift tensors were carried out using periodic scalar relativistic DFT modelling. Spin-orbit relativistic effects, estimated by SO-ZORA formalism for one molecular unit, were evaluated. Finally, the X-ray structure of the title complex was determined, which proved that the former procedure is appropriate. The most important orbital interactions were investigated by Natural Bond Orbital analysis. The isotropic shielding values for S2CN-carbons were analysed by Natural Localised Molecular Orbital analysis. The present approach can be further extended to study other rare earth metal complexes, particularly those having similar but not yet solved crystal structures

  • 322.
    Grenman, Tiia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Dusty Globules and Globulettes2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Interstellar gas and dust can condense into clouds of very different size, ranging from giant molecular cloud complexes to massive, isolated, dark cloudlets, called globules with a few solar masses.

    This thesis focuses on a new category of small globules, named globulettes.These have been found in the bright surroundings of H II regions of young, massive stellar clusters. The globulettes are much smaller and less massive than normal globules. The analysis is based on H-alpha images ofe.g., the Rosette Nebula and the Carina Nebula collected with the Nordic Optical Tele-scope and the Hubble Space Telescope.

    Most globulettes found in different H II regions have distinct contours and are well isolated from the surrounding molecular shell structures. Masses and densities were derived from the extinction of light through the globulettes and the measured shape of the objects. A majority of the globulettes have planetary masses,<13MJ (Jupiter masses). Very few objects have masses above 100MJ≈0.1M(Solar masses). Hence, there is no smooth overlap between globulettes and globules, which makes us conclude that globulettes represent a distinct, new class of objects.

    Globulettes might have been formed either by the fragmentation of larger filaments, or by the disintegration of large molecular clouds originally hosting compact and small cores. At a later stage, globulettes expand, disrupt or evaporate. However, preliminary calculations of their lifetimes show that some might survive for a relatively long time, in several cases even longer than their estimated contraction time.

    The tiny high density globulettes in the Carina Nebula indicate that they are in a more evolved state than those in the Rosette Nebula, and hence they may have survived for a longer time. It is possible that the globulettes could host low mass brown dwarfs or planets.

    Using the virial theorem on the Rosette Nebula globulettes and including only the thermal and gravitational potential energy indicated that the 133 found globulettes are all either expanding or disrupting. When the ram and the radiation pressure were included, we found that about half of our objectsare gravitationally bound or unstable to contraction and could collapse to form brown dwarfs or free floating planets.

    We also estimated the amount of globulettes and the number of free floating planetary mass objects, originating from globulettes, during the history of the Milky Way. We found that a conservative value of the number of globulettes formed is 5.7×1010. A less conservative estimate gave 2×1011globulettes andif 10% of these forms free floating planets then the globulettes have contributed about 0.2 free floating planets per star.

    In the Crab Nebula, which is a supernova remnant from the explosion of a massive old star, one can find dusty globules appearing as dark spots against the background nebulosity. These globules are very similar to the globulettes we have found in H II regions. The total mass of dust in globules was estimated to be 4.5×10−4M, which corresponds to.2% of the total dust content of the nebula. These globules move outward from the center with transversal velocities of 60–1600 km s−1. Using the extinction law for globules, we found that the dust grains are similar to the interstellar dust grains. This means that they contribute to the ISM dust population. We concluded that the majority of the globules are not located in bright filaments and we proposed that these globules may be products of cell-like blobs or granules in the atmosphere of the progenitor star. Theses blobs collapse and form globules during the passage of the blast wave during the explosion.

  • 323.
    Grenman, Tiia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Globulettes: a new class of very small and dense interstellar clouds2006Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The space between stars is not empty, but filled with a thin gas and microscopic dust grains, together forming the so-called interstellar medium. Matter is concentrated into clouds of very different sizes, ranging from giant molecular cloud complexes to massive isolated dark small isolated cloudlets, called globules. In bright emission regions, surrounding young massive stars, one can find many tiny, isolated and cold objects appearing as dark spots against the background nebulosity. These objects are much smaller and less massive than normal globules. Such small clouds are the topic of the present Licentiate thesis, where they have been baptised globulettes. The analysis is based on H-alpha images of the Rosette Nebula and IC 1805 Nebula, collected with the Nordic Optical Telescope in the years 1999 and 2000. In total 151 globulettes in these two regions were catalogued, measured and analysed. Positions, orientations, sizes, masses, densities and pressures were derived, as well as their present condition with regard to gravitational stability. From these data, their origins and possible evolutionary history were discussed. Most globulettes are sharp-edged and well isolated from the surrounding. The size distributions are quite similar in the two studied nebulae. The masses and densities were derived from the extinction of light and the measured shape of the objects. In a few cases the masses have been estimated earlier by another team, from radio emission of CO gas, and our values are in line with their estimates for these particular globulettes. A majority of the objects have masses < 20 Jupiter masses, and the mass distribution drops rapidly towards higher values. Very few objects have masses above 100 Jupiter masses, which we define as the lower mass limit for normal globules. However, there is no smooth overlap between the two types of clouds, which makes us conclude that globulettes represent a distinct, new class of objects. The column density profile of a typical globulette was found to be rather uniform in the central parts, but flattens at the periphery, as compared to what is expected from a sphere of constant volume density. The virial theorem, including only the kinetic and gravitational energy, indicates that all 133 globulettes are expanding or disrupting. However, other forces, such as outer gas and radiation pressures, can help to confine the globulettes. Our results show that about half of these objects are gravitationally bound and even unstable against contraction, which opens some evolutionary scenarios not expected in the first place. Some massive globulettes could therefore collapse to form stars with very low masses, for instance, so-called brown dwarfs, while the low-mass globulettes could contract to free-floating planets. Globulettes might have been formed either by the fragmentation of larger filaments, or by the disintegration of large molecular clouds originally hosting compact and small cores. At a later stage even the confine globulettes might disrupt because of evaporation form the action of external radiation and gas flows. or evaporate. However, preliminary calculations of their lifetimes show that some might survive for a relatively long time and even longer than their estimated contraction time. No evidence of embedded infrared-emitting sources was found in independent IR studies, but one cannot exclude that globulettes already host low-mass brown dwarfs or planets.

  • 324.
    Grenman, Tiia
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Elfgren, Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Weber, Hans
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    History of Globulettes in the Milky Way2018Inngår i: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 363, nr 2, artikkel-id 28Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Globulettes are small (radii $< 10$ kAU) dark dust clouds, seen against the background of bright nebulae.

    A majority of the objects have planetary mass.

    These objects may be a source of brown dwarfs and free floating planetary mass objects in the galaxy.

    In this paper we investigate how many globulettes could have formed in the Milky Way and how they could contribute to the total population of free floating planets.

    In order to do that we examine H-alpha images of 27 H~II regions. In these images, we find 778 globulettes.

    We find that a conservative value of the number of globulettes formed is $5.7\times 10^{10}$.

    If 10 \% of the globulettes form free floating planets then they have contributed with $5.7\times 10^{9}$ free floating planets in the Milky Way. A less conservative number of globulettes would mean that the globulettes could contribute $2.0\times 10^{10}$ free floating planets.

    Thus the globulettes could represent a non-negligible source of free floating planets in the Milky Way.

  • 325.
    Grenman, Tiia
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Gahm, Gösta F.
    Stockholm Observatory, AlbaNova University Centre, Stockholm University.
    The tiny globulettes in the Carina nebula2014Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 565, artikkel-id A107Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context. Small molecular cloudlets are abundant in many H ii regions surrounding newborn stellar clusters. In optical images these so-called globulettes appear as dark silhouettes against the bright nebular background. Aims. We aim to make an inventory of the population of globulettes in the Carina nebula complex, and to derive sizes and masses for comparisons with similar objects found in other H ii regions. Methods. The globulettes were identified from Hα images collected at the Hubble Space Telescope. Results. We have located close to 300 globulettes in the Carina complex, more than in any other region surveyed so far. The objects appear as well-confined dense clumps and, as a rule, lack thinner envelopes and tails. Objects with bright rims are in the minority, but more abundant than in other regions surveyed. Some globulettes are slightly elongated with their major axes oriented in the direction of young clusters in the complex. Many objects are quite isolated and reside at projected distances >1.5 pc from other molecular structures in the neighbourhood. No globulette coincides in position with recognized pre-main-sequence objects in the area. The objects are systematically much smaller, less massive, and much denser than those surveyed in other H ii regions. Practically all globulettes are of planetary mass, and most have masses less than one Jupiter mass. The average number densities exceed 105 cm-3 in several objects. We have found a statistical relation between density and radius (mass) in the sense that the smallest objects are also the densest. Conclusions. The population of small globulettes in Carina appears to represent a more advanced evolutionary state than those investigated in other H ii regions. The objects are subject to erosion in the intense radiation field, which would lead to a removal of any thinner envelope and an unveiling of the core, which becomes more compact with time. We discuss the possibility that the core may become gravitationally unstable, in which case free-floating planetary mass objects can form.

  • 326.
    Grenman, Tiia
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Gahm, Gösta F.
    Stockholm Observatory, AlbaNova University Centre, Stockholm University.
    Elfgren, Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Dusty globules in the Crab Nebula2017Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 599, artikkel-id A110Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context. Dust grains are widespread in the Crab Nebula. A number of small, dusty globules, are visible as dark spots against the background of continuous synchrotron emission in optical images. Aims. Our aim is to catalogue such dusty globules and investigate their properties. Methods. From existing broad-band images obtained with the Hubble Space Telescope, we located 92 globules, for which we derived positions, dimensions, orientations, extinctions, masses, proper motions, and their distributions. Results. The globules have mean radii ranging from 400 to 2000 AU and are not resolved in current infrared images of the nebula. The extinction law for dust grains in these globules matches a normal interstellar extinction law. Derived masses of dust range from 1 to 60 × 10-6M, and the total mass contained in globules constitute a fraction of approximately 2% or less of the total dust content of the nebula. The globules are spread over the outer part of the nebula, and a fraction of them coincide in position with emission filaments, where we find elongated globules that are aligned with these filaments. Only 10% of the globules are coincident in position with the numerous H2-emitting knots found in previous studies. All globules move outwards from the centre with transversal velocities of 60 to 1600 km s-1, along with the general expansion of the remnant. We discuss various hypotheses for the formation of globules in the Crab Nebula

  • 327.
    Grip, Carl-Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Elfgren, Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Söderström, Mats
    Linköping University, Energy Systems.
    Thollander, Patrik
    Linköping University, Energy Systems.
    Berntsson, Thore
    Chalmers University of Technology, Department of Energy and Environment, Division of Heat and Power Technology.
    Åsblad, Anders
    CIT Industriell Energi.
    Wang, Chuan
    Swerea MEFOS AB.
    Possibilities and problems in using exergy expressions in process integration2011Inngår i: Proceedings of the World Renewable Energy Congress 2011 (WREC 2011): 9-13 May, Linköping, Linköping: Linköping University Electronic Press, 2011Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Industrial energy systems are complicated networks, where changes in one process influence its neighboring processes. Saving energy in one unit does not necessarily lead to energy savings for the total system. A study has been carried out on the possibility to use the exergy concept in the analysis of industrial energy systems. The exergy concept defines the quality of an amount of energy in relation to its surrounding, expressing the part that could be converted into work. The study consists of literature studies and general evaluations, an extensive case study and an interview study. In the latter it was found that non technical factors are major obstacles to the introduction of exergy.

  • 328.
    Grishin, A.
    et al.
    Kungliga tekniska högskolan, KTH.
    Niska, John
    Luleå tekniska universitet.
    Loberg, Bengt
    Weber, Hans
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Straightened voltage effect in high-Tc superconductors1994Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 76, nr 10, s. 6947-6949Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new effect called ``ac-current straightening'' has been observed in ceramic (Bi,Pb)-2223 slabs carrying ac current Idc+Iac cos(ωt). The current-voltage (I-V) characteristics of the ceramic were measured at 77 K at frequencies ranging from 50 to 20 000 Hz. A spectrum analyzer showed a series of high harmonics in the voltage signal as well as a constant voltage drop. The full set of experimental data has been explained theoretically using the Bean-Kim critical state model with a magnetic field dependent critical current jc(H)=jc(0)/(1+H/H0). A low transport ac current gives a voltage linearly proportional to the frequency and quadratically proportional to the ac-current amplitude Iac. It consists of odd harmonics only. If a bias dc current is switched on, then even harmonics and a dc-voltage drop appear. Their amplitudes are proportional to the small parameter Iac/cH0 and depend on the Idc/Iac ratio.

  • 329.
    Groth, Margareta Ring
    et al.
    Luleå tekniska universitet.
    Mannelquist, Anders
    Luleå tekniska universitet.
    Comparison of fractal analyses methods and fractal dimension for pre-treated stainless steel surfaces and the correlation to adhesive joint strength2001Inngår i: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 73, nr 3, s. 347-355Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The fractal dimensions of six differently mechanically pre-treated stainless steel samples were investigated using five fractal algorithms. The surfaces were analyzed using a profiler, atomic force microscopy (AFM), scanning electron microscopy (SEM) and light microscopy (LM), and thereafter adhesively bonded and tested in single-overlap joints to test their tensile strength. All samples showed different fractal behavior, depending on the microscopic methods and fractal algorithms. However, the overall relation between fractal dimension and tensile strength is qualitatively the same, except for the SEM images. This verifies that tensile strength is correlated to fractal dimension, although only within the length-scale of the profiler and the light microscope (,0.5-100 7m). The AFM method was excluded in this comparison, since the limitation in the z-direction for the AFM scanner made it difficult to scan the rougher parts of the blasted samples. The magnitude of the surfaces is a parameter not often considered in fractal analysis. It is shown that the magnitude, for the Fourier method, is correlated to the arithmetic average difference, Ra, but only weakly to the fractal dimension. Hence, traditional parameters, such as Ra, tell us very little about the spatial distribution of the elevation data

  • 330.
    Grånäs, Oscar
    et al.
    Uppsala universitet, Department of Physics and Astronomy, Uppsala University.
    Marco, Igor di
    Uppsala universitet, Department of Physics and Astronomy, Uppsala University.
    Eriksson, Olle
    Uppsala universitet, Department of Physics and Astronomy, Uppsala University.
    Nordström, Lars
    Uppsala universitet, Department of Physics and Astronomy, Uppsala University.
    Etz, Corina
    Department of Physics and Astronomy, Uppsala University.
    Electronic structure, cohesive properties, and magnetism of SrRuO32014Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 90, artikkel-id 165130Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have performed an extensive test of the ability of density functional theory within several approximations for the exchange-correlation functional, local density approximation + Hubbard U, and local density approximation + dynamic mean field theory to describe magnetic and electronic properties of SrRuO3. We focus on the ferromagnetic phase, illustrating differences between the orthorhombic low-temperature structure versus the cubic high-temperature structure. We assess how magnetism, spectral function, and cohesive properties are affected by methodology, onsite Hubbard U, and double-counting corrections. Further, we compare the impact of the impurity solver on the quasiparticle weight Z, which is in turn compared to experimental results. The spectral functions resulting from the different treatments are also compared to experimental data. Finally, the impact of spin-orbit coupling is studied, allowing us to determine the orbital moments. In the orthorhombic phase, the orbital moments are found to be tilted with respect to the spin moments, emphasizing the importance of taking into account the distortion of the oxygen octahedra

  • 331.
    Guidi, V.
    et al.
    University of Ferrara.
    Antonini, A.
    University of Ferrara.
    Baricordi, S.
    University of Ferrara.
    Logallo, F.
    University of Ferrara.
    Malagù, C.
    University of Ferrara.
    Milan, E.
    University of Ferrara.
    Ronzoni, A.
    University of Ferrara.
    Stefancich, M.
    University of Ferrara.
    Martinelli, G.
    University of Ferrara.
    Vomiero, Alberto
    INFN Laboratori Nazionali di Legnaro.
    Tailoring of silicon crystals for relativistic-particle channeling2005Inngår i: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 234, nr 1-2, s. 40-46Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the last years, the research on channeling of relativistic particles has progressed considerably. A significant contribution has been provided by the development of techniques for quality improvement of the crystals. In particular, a planar etching of the surfaces of the silicon crystals proved useful to remove the superficial layer, which is a region very rich in imperfections, in turn leading to greater channeling efficiency. Micro-fabrication techniques, borrowed from silicon technology, may also be useful: micro-indentation and deposition of tensile or compressive layers onto silicon samples allow one to impart an even curvature to the samples. In this way, different topologies may be envisaged, such as a bent crystal for deflection of protons and ions or an undulator to force coherent oscillations of positrons and electrons. © 2005 Elsevier B.V. All rights reserved.

  • 332.
    Guidi, V.
    et al.
    University of Ferrara, INFN.
    Baricordi, S.
    University of Ferrara, INFN.
    Fiorini, M.
    University of Ferrara, INFN.
    Martinelli, G.
    University of Ferrara, INFN.
    Mazzolari, A.
    University of Ferrara, INFN.
    Milan, E.
    University of Ferrara, INFN.
    Scandale, W.
    CERN.
    Chesnokov, Y.
    IHEP Protvino.
    Marchi, E. Boscolo
    INFN-LNL.
    Mea, G. Della
    INFN-LNL.
    Milan, R.
    INFN-LNL.
    Todros, S.
    INFN-LNL.
    Vomiero, Alberto
    INFN Laboratori Nazionali di Legnaro.
    Ivanov, Y. M.
    PNPI.
    Carnera, A.
    University of Padova.
    Salvador, D. De
    University of Padova.
    Sambo, A.
    University of Padova.
    Characterization of crystals for steering of protons through channelling in hadronic accelerators2006Inngår i: EPAC 2006: 10th European Particle Accelerator Conference EPAC 2006 ; a Europhysics conference ; Edinburgh, Scotland, International Conference Centre (EICC), 26 - 30 June 2006, Edinburgh: European Physical Society Accelerator Group (EPS-AG) , 2006, s. 1523-1525Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Channeling of relativistic particles through a crystal may be useful for many applications in accelerators, and particularly for collimation in hadronic colliders. Efficiency proved to be dependent on the state of the crystal surface and hence on the method used for preparation. We investigated the morphology and structure of the surface of the samples that have been used in accelerators with high efficiency. We found that crystal fabrication by only mechanical methods (dicing, lapping, and others) leads to a superficial damaged layer, which is correlated to performance limitation in accelerators. A planar chemical etching was studied and applied in order to remove the superficial damaged layer. RBS channeling analysis with low-energy protons and 4He + highlighted better crystal perfection at surface, as a result of the etching. A protocol for preparation and characterization of crystal for channelling has been developed, which may be of interest for reliable operation with crystals in accelerators.

  • 333. Guidi, V.
    et al.
    Martinelli, G.
    Schiffrer, G.
    Vomiero, Alberto
    INFN - Legnaro National Laboratories.
    Mea, G. Della
    Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology, Bombay.
    Comini, E.
    Department of Physics and Chemistry, INFM — University of Brescia.
    Ferroni, M.
    Department of Physics and Chemistry, INFM — University of Brescia.
    Sberveglieri, G.
    Department of Physics and Chemistry, INFM — University of Brescia.
    Diffusion-equation approach to describe ionic mobility in nanostructured titania2005Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, nr 15, artikkel-id 155401Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The linear diffusion equation is proposed to provide a macroscopic description of ionic mobility in nanostructures. This approach has been demonstrated to account for diffusion processes in nanostructured titania-based films. The formulation of a classical diffusion inverse problem and the experimental determination of concentration profiles by Rutherford backscattering spectrometry were used for the purpose. The model has allowed the measurement of the diffusion coefficient of W and Mo impurities in titania. © 2005 The American Physical Society.

  • 334. Guidi, Vincenzo
    et al.
    Martinelli, Giuliano
    Schiffrer, Giuliano
    Vomiero, Alberto
    INFN - Legnaro National Laboratories.
    Scian, Carlo
    INFN - Legnaro National Laboratories.
    Mea, Gianantonio Della
    INFN - Legnaro National Laboratories.
    Comini, Elisabetta
    Department of Physics and Chemistry, INFM — University of Brescia.
    Ferroni, Matteo
    Department of Physics and Chemistry, INFM — University of Brescia.
    Sberveglieri, Giorgio
    Department of Physics and Chemistry, INFM — University of Brescia.
    Selective sublimation processing of thin films for gas sensing2005Inngår i: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 108, nr 1-2 SPEC. ISS., s. 15-20Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The selective sublimation processing (SSP) is a useful and easy method for production of semiconducting thin films via reactive sputtering for gas sensing. We have investigated the mechanism of film growth and processing for an insight into the main parameters that control the preparation methodology. A model based on diffusion equation, in the framework of a linear theory, has been proposed and compared to experimental evidences. Rutherford backscattering spectrometry has been extensively used as a tool for determination of concentration profiles in the layers. The model allowed a deeper understanding of film preparation with a physical description of the processes involved, which would open up the design of innovative nanostructured materials that rely on SSP. Titania thin films produced by this methodology and proved capable of sensing target gases of interest for many applications. © 2004 Elsevier B.V. All rights reserved.

  • 335.
    Gulzar, Ali
    et al.
    Dr M.A. Kazi Institute of Chemistry, University of Sindh, Jamshoro, Pakistan .
    Tahira, Aneela
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Mallah, Arfana Begum
    Dr M.A. Kazi Institute of Chemistry, University of Sindh, Jamshoro, Pakistan .
    Ahmed Mallah, Sarfraz
    Dr M.A. Kazi Institute of Chemistry, University of Sindh, Jamshoro, Pakistan .
    Ibupoto, Akila
    Institute of Chemistry, Shah Abdul Latif University, Khairpur, Pakistan .
    Ahmed Khand, Aftab
    School of Life Sciences, Tsinghua University, Beijing, China .
    Baradi, Waryani
    Department of Fresh Water Biology and Fisheries, University of Sindh, Jamshoro, Pakistan .
    Willander, Magnus
    Department of Science and Technology, Campus Norrkoping, Linkoping University, Norrkoping, Sweden .
    Yu, Cong
    State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, People’s Republic of China .
    Hussain Ibupoto, Zafar
    Dr M.A. Kazi Institute of Chemistry, University of Sindh, Jamshoro, Pakistan; State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, People’s Republic of China .
    Functional CuO Microstructures for Glucose Sensing2018Inngår i: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 47, nr 2, s. 1519-1525Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    CuO microstructures are produced in the presence of water-soluble amino acids by hydrothermal method. The used amino acids include isoleucine, alpha alanine, and arginine as a soft template and are used for tuning the morphology of CuO nanostructures. The crystalline and morphological investigations were carried out by x-ray diffraction (XRD) and scanning electron microscopy techniques. The XRD study has shown that CuO material obtained in the presence of different amino acids is of high purity and all have the same crystal phase. The CuO microstructures prepared in the presence of arginine were used for the development of sensitive and selective glucose biosensor. The linear range for the glucose detection are from 0.001 mM to 30 mM and limit of detection was found to be 0.0005 mM. The sensitivity was estimated around 77 mV/decade. The developed biosensor is highly selective, sensitive, stable and reproducible. The glucose biosensor was used for the determination of real human blood samples and the obtained results are satisfactory. The CuO material is functional therefore can be capitalized in wide range of applications such as lithium ion batteries, all oxide solar cells and supercapacitors.

  • 336.
    Gunell, H.
    et al.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Nilsson, H.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Amerstorfer, U.V.
    Space Research Institute, Austrian Academy of Sciences.
    Carlsson, Ella
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Indications of plasma instabilities near Mars2006Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    It has been suggested in the literature that the Kelvin-Helmholtz instability can be responsible for significant ion loss at Mars through the detachment of ionospheric plasma clouds. Clouds of detached ionospheric plasma were observed at Venus by the Pioneer Venus orbiter. The conditions at Mars differ somewhat from those at Venus. The ratio between the ion gyro radius and the radius of the planet is larger at Mars than at Venus, since Mars is a smaller planet and the solar wind magnetic field is weaker at Mars than at Venus. It is therefore interesting to study instabilities at Mars and to compare the results from Mars with those from Venus. We search the ASPERA-3 data for signatures of instabilities at Mars, in particular looking at the magnetosheath and the induced magnetosphere boundary.

  • 337.
    Gunell, Herbert
    et al.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Nilsson, H.
    Amerstorfer, U.
    Carlsson, Ella
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Grima, C.
    Plasma instabilities near Mars2006Inngår i: Ikke angivet, Committee on Space Research , 2006, s. 2338-Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    It has been suggested in the literature that the Kelvin-Helmholtz instability can be responsible for significant ion loss at Mars through the detachment of ionospheric plasma clouds Clouds of detached ionospheric plasma were observed at Venus by the Pioneer Venus orbiter The conditions at Mars differ somewhat from those at Venus The ratio between the ion gyro radius and the radius of the planet is larger at Mars than at Venus since Mars is a smaller planet and the solar wind magnetic field is weaker at Mars than at Venus It is therefore interesting to study instabilities at Mars and to compare the results from Mars with those from Venus We search the ion and electron data from the ASPERA-3 instrument on the Mars Express spacecraft for signatures of instabilities at Mars We present data indicative of instabilities in the magnetosheath and the induced magnetosphere boundary downstream of the planet

  • 338.
    Gustafsson, Magnus
    Department of Chemistry, University of Gothenburg.
    Career achivements of Professor Lothar Frommhold2010Inngår i: 20th International Conference on Spectral Line Shapes: St. John's, Newfoundland, Canada, 6 - 11 June 2010 ; [20th ICSLS] / [ed] John K.C. Lewis; Adriana Predoi-Cross, Melville, NY: American Institute of Physics (AIP), 2010, s. 294-300Konferansepaper (Annet vitenskapelig)
  • 339.
    Gustafsson, Magnus
    University of Texas, Physics Department.
    Collision-induced Absorption and Anisotropy of the Intermolecular Potential2002Doktoravhandling, med artikler (Annet vitenskapelig)
  • 340.
    Gustafsson, Magnus
    Department of Chemistry, University of Gothenburg.
    Diatom-diatom interactions with light: Applications and line shape theoretical aspects2008Inngår i: Spectral line shapes, volume 15: 19th International Conference on Spectral Line Shapes, Valladolid, Spain, 15 - 20 June 2008 ; ICSLS / [ed] Marco A. Gigosos; Manuel A. González, Melville, NY: American Institute of Physics (AIP), 2008, s. 297-301Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Recent advances in calculations of collision-induced absorption- and Raman-spectra in pure diatomic gases are presented. An extensive calculation of H2-H2 absorption from 40 K to 400 K has provided improved understanding of the atmosphere of Uranus. A highly advanced close-coupling calculation of H2-H2 light scattering has verified that the line shapes are affected by interference between the permanent H2 and the H2-H2 interaction-induced polarizabilities. A few directions that the research in astrophysical applications of collision-induced absorption is taking are also described. For instance, H2-H 2 dipole and potential surfaces for vibrations higher than v = 1 are currently being developed to enable simulations of collision-induced absorption at temperatures relevant for white dwarf atmospheres. For low temperature N 2-N2 absorption there is unresolved discrepancy between measurement and simulation. A possible solution to this puzzle is suggested

  • 341.
    Gustafsson, Magnus
    Department of Chemistry, University of Gothenburg.
    Far Wing Asymmetry of Rotational Raman Lines in Hydrogen2010Inngår i: International Journal of Spectroscopy, ISSN 1687-9449, E-ISSN 1687-9457, Vol. 2010, artikkel-id 705896Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Depolarized Raman spectra of compressed hydrogen gas have been computed rigorously previously for 36 K and 50 K (Gustafsson et al. (2009)). The far wings of the rotational lines show asymmetry that goes beyond that expected from the theory for intracollisional interference and Fano line shapes. Here we analyze the (0) line for pure hydrogen at 36 K in detail. The added asymmetry stems partly from a shape resonance which adds significant intensity to the higher frequency side of the line profile. The influence of the threshold energy for the rotational transition accounts for the remainder.

  • 342.
    Gustafsson, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Hydrogen dimer features in low temperature collision-induced spectra2017Inngår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 810, nr 1, artikkel-id 012017Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The absorption of radiation in pure hydrogen (H2) gas around the S(0) and S(1) rotational transitions is computed at 20 K and compared with laboratory data. All transitions involving free state are included in the calculations of the absolute absorption. These calculations are done with an isotropic approximation for the H2–H2 pair potential. Agreement with the experiment is observed around the S(0) transition, while the computational approach appears to be slightly worse around the S(1) transition. The positions for bound-to-bound transitions are computed including the full anisotropic pair potential. The anisotropy seems to be crucial to achieve agreement with the measured bound-to-bound transition frequencies. However, those transitions contribute little to the total absorption. The present computed absolute absorptions will provide improved input for radiative transfer models of planetary atmospheres.

  • 343.
    Gustafsson, Magnus
    et al.
    Department of Chemistry, University of Gothenburg.
    Antipov, Sergey V.
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Calculation of interaction-induced spectra using complex absorbing potentials2010Inngår i: 20th International Conference on Spectral Line Shapes: St. John's, Newfoundland, Canada, 6 - 11 June 2010 ; [20th ICSLS] / [ed] John K.C. Lewis; Adriana Predoi-Cross, Melville, NY: American Institute of Physics (AIP), 2010, s. 240-244Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A complex absorbing potential method is implemented for calculation of collision-induced spectra. The scheme provides a way to avoid the integration of the Schrödinger equation to very large separations of the collisional pair. The method is tested by reproducing a previously computed absorption spectrum for H-He at two different temperatures.

  • 344.
    Gustafsson, Magnus
    et al.
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Antipov, Sergey V.
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Franz, Jan
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Nyman, Gunnar
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Refined theoretical study of radiative association: cross sections and rate constants for the formation of SiN2012Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 137, nr 10, artikkel-id 104301Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Radiative association of silicon mononitride (SiN) in its two lowest molecular electronic states is studied through quantum and classical dynamics. Special attention is paid to the behavior of the cross section at high collision energies. A modified expression for the semiclassical cross section is presented which excludes transitions to continuum states. This gives improved agreement with quantum mechanical perturbation theory at high energies. The high energy cross section is overestimated if conventional semiclassical theory is used. The modified semiclassical theory should be valid in general for radiative association transitions from an upper to a lower electronic state. We also implement a quantum dynamical optical potential method with the same type of modification. The rate coefficient is calculated using Breit–Wigner theory and the modified semiclassical formula for the resonance and direct contributions, respectively, for temperatures from 10 K to 20 000 K. A rapid decrease in the rate constant for formation of ground state SiN is observed above 2000 K which was not seen previously.

  • 345.
    Gustafsson, Magnus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Forrey, Robert C.
    Pennsylvania State University, Reading, USA.
    Semiclassical methods for calculating radiative association rate constants for different thermodynamic conditions: Application to formation of CO, CN, and SiN2019Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, ISSN 0021-9606, Vol. 150, nr 22, artikkel-id 224301Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It is well-known that resonances can serve as a catalyst for molecule formation. Rate constants for resonance-induced molecule formation are phenomenological as they depend upon the mechanism used to populate the resonances. Standard treatments assume tunneling from the continuum is the only available population mechanism, which means long-lived quasibound states are essentially unpopulated. However, if a fast resonance population mechanism exists, the long-lived quasibound states may be populated and give rise to a substantial increase in the molecule formation rate constant. In the present work, we show that the semiclassical formula of Kramers and ter Haar [Bull. Astron. Inst. Neth. 10, 137 (1946)] may be used to compute rate constants for radiative association in the limit of local thermodynamic equilibrium. Comparisons are made with quantum mechanical and standard semiclassical treatments, and results are shown for two limits which provide upper and lower bounds for the six most important radiative association reactions leading to the formation of CO, CN, and SiN. These results may have implications for interstellar chemistry in molecular clouds, where the environmental and thermodynamic conditions often are uncertain.

  • 346.
    Gustafsson, Magnus
    et al.
    Department of Chemistry, University of Gothenburg.
    Frommhold, Lothar
    University of Texas, Physics Department.
    Effects of the anisotrophy of the intermulucular potential2002Inngår i: Spectral line shapes: volume 12 ; 16th International Conference on Spectral Line Shapes, ICSLS, Berkeley, California, 3-7 June 2002 / [ed] Christina A. Back, Melville, NY: American Institute of Physics (AIP), 2002, s. 216-227Konferansepaper (Fagfellevurdert)
  • 347.
    Gustafsson, Magnus
    et al.
    Department of Chemistry and Biochemistry, University of Colorado, Boulder.
    Frommhold, Lothar
    University of Texas, Physics Department.
    Infrared absorption by H2-Ar collisional complexes and the anisotropy of the intermolecular interaction potential2006Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 74, artikkel-id 54703Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    H2-Ar scattering processes in the presence of a weak photon field are considered. Calculations are based on an accurate ab initio interaction-induced electric dipole surface and an anisotropic intermolecular potential energy surface. The close-coupled scheme of integrating the Schrödinger equation is employed to calculate the rototranslational absorption spectrum of H2-Ar pairs in the far-infrared region of the electromagnetic spectrum. The results are compared with previous work where the weak anisotropy of the intermolecular interaction potential was suppressed. Under the conditions considered, accounting for the anisotropy modifies the rototranslational absorption spectrum discernibly, but only at some frequency bands where the corrections are negative, typically below 10%.

  • 348.
    Gustafsson, Magnus
    et al.
    University of Texas, Physics Department.
    Frommhold, Lothar
    University of Texas, Physics Department.
    Infrared Absorption Spectra of Collisionally Interacting He and H Atoms2001Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 546, nr 2, s. 1168-1170Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    On the basis of recent state-of-the-art ab initio calculations of the interatomic potential and dipole surface of interacting helium (He) and hydrogen (H) atoms, we calculate the collision-induced absorption spectra in the infrared of the He-H pair, using a rigorous quantum mechanical formalism. Furthermore, we present a simple analytical model which is capable of reproducing these calculated spectra with precision, for frequencies from 50 to roughly 10,000 cm-1 and temperatures from 1500 to 10,000 K. For a given temperature and frequency, the ratio of the absorption coefficient and the product of the H and He densities may be evaluated in seconds, even on small computers (e.g., PCs), provided this ratio exceeds a certain (very small) lower numerical limit.

  • 349.
    Gustafsson, Magnus
    et al.
    University of Texas, Physics Department.
    Frommhold, Lothar
    University of Texas, Physics Department.
    Intracollisional interference of R lines of HD in mixtures of deuterium hydride and helium gas2001Inngår i: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 63, nr 5, artikkel-id 52514Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Line shapes of the R0(0) and R0(1) lines in the pure rotational band, and of the R1(0) and R1(1) lines in the fundamental band of HD are computed from first principles for HD molecules that interact collisionally with He atoms. Interference of the permanent dipole of the HD molecule and the interaction-induced dipole of HD–He supermolecular complex shapes these profiles. We use the close-coupling scheme for the scattering calculations which take into account the anisotropy of the HD–He interaction potential. Thus rotational level mixing is accounted for in a non-perturbative manner. The treatment is fully quantum mechanical and takes into account single binary collisions between HD and He. Spectral absorption profiles and line shape parameters of the R-lines are computed for comparison with existing measurements at 77 K. Agreement between theory and measurements is observed in the low-helium-density limit of the measured absorption as expected.

  • 350.
    Gustafsson, Magnus
    et al.
    Department of Chemistry, University of Gothenburg.
    Frommhold, Lothar
    University of Texas, Physics Department.
    Spectra of 2- and 3-body van der Waals complexes2003Inngår i: Weakly interacting molecular pairs: unconventional absorbers of radiation in the atmosphere: [proceedings of the NATO Advanced Research Workshop on Weakly Interacting Molecular Pairs: Unconventional Absorbers of Radiation in the Atmosphere, Fontevraud, France, 29 April - 3 May, 2002] / [ed] Claude Camy-Peyret, Dordrecht: Kluwer Academic Publishers, 2003, s. 3-22Konferansepaper (Fagfellevurdert)
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