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• 201. Demirel, B.
Analyses of products from autoclave reactions: derivations of reaction parameters1996In: Vol. 41, no 4, p. 1157-1160Article in journal (Refereed)

This work presents energetics for high pressure hydroprocessing reactions derived from post analyses of liquid and gaseous products. Specifically, GC and GC/MS were used to follow the product distribution fram the hydrocracking of methyldecalins over zeohte supported palladium and platinum catalysts as a function of temperature. Plain Arrhenius plots summarize key results and reveal possible connections in terms ofactivation energies between hydrogen consumption and the amounts of different products. The total cycloalkane production and the consumption ofhydrogen both show a simple temperature dependence with the same{open_quote}activation{close_quote} energies. Methane production varies more rapidly with temperature but can still be described by a single exponential term. The final example, conversion to aromatics, displays a more complicated dependence with an accelerated yield at high temperature. This form of data analyses connects to a new routine for mass balance evaluations and it is now applied to model catalyst performance and to understand optimum reaction conditions. Other branches of this project include surface spectroscopic measurements of fresh, sulfided and used catalysts, characterization of partially hydrogenated naphthalenes and modeling of hydrogen activity at metal sulfides.

• 202.
Institut Jean Lamour, Department P2M, UMR 7198 CNRS–Université de Lorraine, Ecole des Mines, 54042 Nancy.
Institut Jean Lamour, CNRS – Nancy Université, Laboratoire de Chimie du Solide Minéral, Nancy Université. Institut Jean Lamour, CNRS – Nancy Université, Laboratoire de Chimie du Solide Minéral, Nancy Université. Institut Jean Lamour, Nancy Universite. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Laboratoire de Synthèse Organométallique et Réactivité, Université Henri Poincaré - Nancy, Laboratoire de Structure et Réactivité des Systèmes Moléculaires Complexes, Nancy Université. Laboratoire de Structure et Réactivité des Systèmes Moléculaires Complexes, UMR 7565 CNRS–Université de Lorraine, 54506 Vandoeuvre-les-Nancy, Laboratoire de Synthèse Organométallique et Réactivité, Université Henri Poincaré - Nancy. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, Nancy Université, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, UMR 7564, CNRS–University of Lorraine. Institut Jean Lamour, Nancy Universite.
Covalent Functionalization of HiPco Single-Walled Carbon Nanotubes: Differences in the Oxidizing Action of H2SO4 and HNO3 during a Soft Oxidation Process2015In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 16, no 12, p. 2692-2701Article in journal (Refereed)

The results of a study on the evolution of HiPco single-walled carbon nanotubes during the oxidizing action of H2SO4 and HNO3 are presented. The process conditions used have been chosen so as to avoid any significant damage to the nanotube structure. The type and level of functionalization, the location of the grafted functions on the surface of the nanotube and the changes in morphological characteristics of the samples were examined by using a wide and complementary range of analytical techniques. We propose an explanation for the differences in the oxidizing action of sulfuric and nitric acids. The combined results allow us to suggest possible reaction mechanisms that occur on the surface of the nanotube.

• 203.
Istituto per la Sintesi Organica e Fotoreattivita' (ISOF), Consiglio Nazionale delle Ricerche.
Istituto per la Sintesi Organica e Fotoreattivita' (ISOF), Consiglio Nazionale delle Ricerche. Istituto per la Sintesi Organica e Fotoreattivita' (ISOF), Consiglio Nazionale delle Ricerche. Institute for Microelectronics and Microsystems (CNR-IMM). Istituto per lo studio dei Materiali, Nanostrutturati (ISMN), Consiglio Nazionale delle Ricerche. Istituto per la Sintesi Organica e Fotoreattivita' (ISOF), Consiglio Nazionale delle Ricerche. School of Chemistry, Cardiff University. Department of Chemistry Giacomo Ciamician, University of Bologna. School of Chemistry, Cardiff University. Center for Nano Science and Technology@PoliMi, Istituto Italiano di Tecnologia. Center for Nano Science and Technology@PoliMi, Istituto Italiano di Tecnologia. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Istituto per la Microelettronica e i Microsistemi (IMM), Consiglio Nazionale delle Ricerche. Istituto per la Microelettronica e i Microsistemi (IMM), Consiglio Nazionale delle Ricerche. Department of Mathematics and Physics, Ennio De Giorgi University of Salento, Lecce. Institute for Microelectronics and Microsystems (CNR-IMM). Istituto per la Sintesi Organica e Fotoreattivita' (ISOF), Consiglio Nazionale delle Ricerche.
Controlling the Functional Properties of Oligothiophene Crystalline Nano/Microfibers via Tailoring of the Self-Assembling Molecular Precursors2018In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 28, no 32, article id 1801946Article in journal (Refereed)

Oligothiophenes are π-conjugated semiconducting and fluorescent molecules whose self-assembly properties are widely investigated for application in organic electronics, optoelectronics, biophotonics, and sensing. Here an approach to the preparation of crystalline oligothiophene nano/microfibers is reported based on the use of a “sulfur overrich” quaterthiophene building block, T4S4 , containing in its covalent network all the information needed to promote the directional, π–π stacking-driven, self-assembly of Y-T4S4-Y oligomers into fibers with hierarchical supramolecular arrangement from nano- to microscale. It is shown that when Y varies from unsubstituted thiophene to thiophene substituted with electron-withdrawing groups, a wide redistribution of the molecular electronic charge takes place without substantially affecting the aggregation modalities of the oligomer. In this way, a structurally comparable series of fibers is obtained having progressively varying optical properties, redox potentials, photoconductivity, and type of prevailing charge carriers (from p- to n-type). With the aid of density functional theory (DFT) calculations, combined with powder X-ray diffraction data, a model accounting for the growth of the fibers from molecular to nano- and microscale is proposed

• 204.
Istituto per la Microelettronica e i Microsistemi, IMM-CNR, Via S. Sofia 64, 95123 Catania.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Istituto per la Microelettronica e i Microsistemi, IMM-CNR, Via Monteroni, 73100 Lecce. Istituto per la Microelettronica e i Microsistemi, IMM-CNR, Via S. Sofia 64, 95123 Catania, Italy. Istituto per la Microelettronica e i Microsistemi, IMM-CNR, Via Monteroni, 73100 Lecce, Italy.
Surface Modification by Vanadium Pentoxide Turns Oxide Nanocrystals into Powerful Adsorbents of Methylene Blue2019In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 533, p. 369-374Article in journal (Refereed)

Hypothesis: If nanocrystals of such semiconductor as SnO2 and TiO2, which are not known as powerful adsorbents, have their surface modified by layer of V2O5, how will the adsorption properties be affected? Answering this question would provide a new set of surface properties to be designed by surface engineering of oxide nanocrystals.

Experiments: SnO2 and TiO2 colloidal nanocrystals were prepared by coupling sol-gel and solvothermal synthesis. By co-processing with V chloroalkoxide and subsequent heat-treatment at 400-500 °C, surface deposition of V2O5 layers was obtained. The methylene blue adsorption onto the prepared materials was tested and compared with the pure oxide supports. Cycling of the materials and analysis of the adsorption process was also investigated.

Findings: The V-modified nanocrystals extracted ∼ 80% methylene blue from 1.5 x 10-5 M aqueous solution after 15 min only, contrarily to pure materials, which took up only 30% of the dye even after 120 min. Comparison with pure commercial V2O5 showed that the peculiar adsorption properties were imparted by the surface deposition of the V2O5-like layers. This report demonstrates that new classes of adsorbing materials can be conceived by suitably coupling different metal oxides.

• 205.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
Scanning probe microscopy studies of interaction forces between particles: emphasis on magnetite, bentonite and silica.2014Doctoral thesis, comprehensive summary (Other academic)

Scanning probe microscopy (SPM), such as the atomic force microscope (AFM), using colloidal probes is a highly suitable technique to probe single particle-particle interactions in aqueous solution. The interaction force between a colloidal probe on the AFM cantilever and sample surface is measured. Ultrasmall intermolecular and surface forces, down to the piconewton level, can reliably be measured under controlled experimental conditions with AFM. The interaction between magnetite, bentonite and silica particles plays an important role in many different applications. One important application is in the steel production process where high-quality iron ore pellets are used. Moreover, the interaction between magnetite nanoparticles with Ca2+ ions and with silica particles has high importance in several medical applications and for nanoelectronics. It is known and widely studied that particle surface properties significantly affect the particle dispersion and aggregation. Also, the particles are often treated in aqueous suspensions or in moist conditions prior to the final aggregation, for instance in a pelletizing processes. Thus, different dissolved chemical species may modify the magnetite, bentonite and silica surfaces, which causes the surface properties to change. However, the exact mechanism how the dissolved chemical species influence the direct particle-particle interaction and particle adhesion is not well known.The main focus of this thesis was the study of magnetite particle force interaction with natural and synthetic magnetite, silica and bentonite particles in aqueous solution with SPM. In addition, complimentary methods, such as scanning electron microscopy (SEM), vertical scanning interferometry (VSI), energy dispersive spectroscopy (SEM-EDS), x-ray diffraction (XRD) and electrophoresis techniques were used for surface morphology investigation, chemical characterization, determination of atomic structure and measurements of zeta-potential. The particle interaction forces were examined in solutions with various Ca2+ ion concentrations and in NaCl solution to determine the effect of Ca2+ ions on the surface properties. Also, the effect of pH at various concentrations was studied. The colloidal probes in the studies were natural magnetite and bentonite particles, micrometer-sized spherical silica particles. Sample surfaces were natural magnetite particles, smooth layers of synthetic magnetite nanoparticles and bentonite flakes.Qualitative changes in adhesion forces, i.e. interaction trends, and forces on approach for magnetite-magnetite, magnetite-silica, magnetite-bentonite and bentonite-silica interaction systems with an increase of Ca2+ ion concentration and pH were measured and evaluated. The interaction trends were consistent in most cases with zeta-potential measurements. Possible surface modification and formation of calcium silicates and calcium carbonates at pH 10 on the magnetite surfaces was discussed. The long-range repulsive interaction, similar to a steric-like interaction, was observed in the interactions for bentonite-silica and magnetite-silica systems, likely due to the swelling of bentonite layers and rising of bentonite flakes from the surface. The rising of bentonite flakes in water was verified with cryo-scanning electron microcopy investigation. Furthermore, the measured adhesion forces were compared with calculated adhesion forces, which were evaluated with the use of a few contact mechanics models. The comparison revealed discrepancies, which could be explained by the particle surface roughness. Additionally, a comparison of VSI and AFM techniques for surface characterization was performed on samples possessing sharp periodic surface structures and three stage plateaux honed cast iron surface. This comparison is of high relevance to the accurate calculation of tribological surface roughness parameters. Moreover, force measurements on biological samples and between magnetic particles are also briefly discussed in the thesis.The work within this thesis shows that SPM methods can be successfully applied to measure and predict forces between natural particles, such as magnetite and bentonite, in solution. The obtained and presented results are new and of high interest in applications where the knowledge of the dispersion and aggregation of studied particle interaction is important.

• 206.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
Surface characterization and force measurements applied to industrial materials with atomic force microscopy2012Licentiate thesis, comprehensive summary (Other academic)

The thesis focuses on the application of force measurements with atomic force microscopy (AFM) on materials with a few surface contacts/asperities and chemically modified surfaces. The technique allows measurements of ultra-small intermolecular and surface forces, down to the piconewton level. The force measurements between surfaces of well-defined geometry are often used to measure and model the interaction between different systems of charged and neutral surfaces in various environments. However, detailed knowledge of the contacting surface profile geometry and surface properties is required to model the fundamental forces involved in the interaction. The preparation of such well-defined and idealized surfaces is often time consuming and the surfaces may not possess the behavior and properties of a source material in real processes, such as in industry. Moreover, external factors such as magnetic fields, ionic strengths and pH-values in a solution, may further complicate the evaluation. Hence, it is desirable to explore and develop techniques for trustable measurements of forces between “real” surfaces. These are often a complex composition of various force interactions and multiple surface contacts.The AFM probe technique was explored to measure force interactions between “real” particle surfaces. The work shows the applicability of the AFM technique to study the interaction forces despite the forecasted difficulties with the roughness of the particles.A technique to measure the adhesion and work of adhesion from AFM force curves was implemented and used. The thermal tune method was implemented in our commercial NT-MDT microscope to determine cantilever spring constants. The force interactions between natural microsize (m-s) magnetite particles and synthetic nanosize (n-s) magnetite particles were studied in calcium solution with concentrations of 1, 10, 100 mM and at pH values 4, 6 and 10. The changes in force interactions, due to variations in calcium concentration and pH were investigated. The adhesion force change with the concentration and pH was similar for m-s/m-s and m-s/n-s systems, and the adhesion force increased with the concentration at pH 6, except for the highest calcium concentration of 100 mM at pH 10. It was found that the magnetite surface modification could appear at the highest calcium concentration at pH 10. Moreover, the thesis contains preliminary results of the force interaction study between natural and synthetic bentonite-magnetite particles in calcium solution with concentrations of 1, 10 and 100 mM at pH 6.The influence of roughness on the calculation of contact mechanics parameters were studied with AFM and Vertical Scanning Interferometry (VSI). This is important for future development of a model to describe and characterize the force interaction between samples with multiple surface contacts. It was found that the optical artifacts, induced by VSI, have a large influence on all the roughness parameters calculated on the calibration grids, which represent extreme surface topographies.

• 207.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
Scanning probe microscopy study of magnetite particle force interactions in a solution2011Conference paper (Other academic)
• 208.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
Application of AFM to probe micro- and nano-sized magnetite particle interaction in Ca2+ solution2014In: Proceedings of the International Summer School on Application of Scanning Probe Microscopy in Life Sciences, Soft Matter and Nanofabrication", Aalborg: River Publishers, 2014Conference paper (Other academic)

Natural magnetite is used for producing iron ore pellets, one of the raw materials in steel production. The quality of produced pellets depends on many factors, including the properties of the magnetite concentrate fed to pelletization. To be able to minimize the effect of the variations in feed properties on pellets quality, investigation of magnetite particle interaction with a focus on the surface properties is required. Atomic force microscopy (AFM), using the colloidal probe technique, is a suitable tool for measuring such particle-particle interaction in-situ. Natural particles are usually of micro-sizes (m-s) and have different sizes and shapes, which complicates an accurate investigation of particle interaction with AFM. To overcome such difficulties, synthetic nanoparticles are used instead. Process water chemistry is one of the factors affecting magnetite surface properties. Partial dissolution of calcite and apatite minerals, present in iron ore, results in high Ca2+ concentrations in the process water, which has been shown to have a major effect on the charge of the magnetite particles [1, 2]. The aim of this study was therefore to investigate forces and aggregation between magnetite particles, of micro- and nano-size (n-s), in Ca2+ solutions at various pH values. The spherical monodispersed magnetite nano-sized particles, with a diameter of approx. 10 nm, were synthesized by the precipitation technique [3]. Measurements were performed for m-s probe/m-s layer and m-s probe/n-s layer systems. Natural magnetite particles of 10-30 µm size were glued to NP-S cantilevers (Digital Instruments/Bruker, Santa Barbara, CA) with a measured spring constant of 0.12 N/m. Nano-sized particles were deposited on the glass slides by dip-coating. Roughness (Ra) of the n-s layers was measured with AFM and was about 10 nm for areas 1×1µm2, a representative high-resolution image is shown in Figure 1. Particle interaction was similar for m-s and n-s magnetite particles at pH 4 and 6. At pH 10, the interaction behavior was different due to probable surface modification of natural magnetite particles by ions from process water. The adhesion force for both interacting systems was measured, see ref. [4] for a detailed description of the results. To verify that ϛ-potential measurements could be used to predict the interaction between charged particles (in this case silica and magnetite) in solutions containing inorganic ions, force measurements between n-s magnetite layer and a SiO2 spherical probe (3.5 µm in diameter) were performed and correlated with the ϛ-potential results for these particles in the same solutions. Also, a DLVO simulation was performed to theoretically confirm the experimental interaction based on surface charge trends. An example of the simulated force curves is shown in Figure 2. The interaction between the probe and the magnetite surface was attractive at pH 4 and 6 but became repulsive at pH 8 and 10, which is in agreement with what could be expected from the ϛ-potential results for these particles.

• 209.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
Force interactions between magnetite, silica, and bentonite studied with atomic force microscopy2015In: Physics and chemistry of minerals, ISSN 0342-1791, E-ISSN 1432-2021, Vol. 42, no 4, p. 319-326Article in journal (Refereed)

Iron ore pellets consist of variety of mineral particles and are an important refined product used in steel manufacturing. Production of high-quality pellets requires good understanding of interactions between different constituents, such as magnetite, gangue residues, bentonite, and additives. Much research has been reported on magnetite, silica, and bentonite surface properties and their effect on pellet strength but more scant with a focus on a fundamental particle–particle interaction. To probe such particle interaction, atomic force microscopy (AFM) using colloidal probe technique has proven to be a suitable tool. In this work, the measurements were performed between magnetite–magnetite, bentonite–magnetite, silica–bentonite, and silica–magnetite particles in 1 mM CaCl2 solution at various pH values. The interaction character, i.e., repulsion or attraction, was determined by measuring and analyzing AFM force curves. The observed quantitative changes in interaction forces were in good agreement with the measured zeta-potentials for the particles at the same experimental conditions. Particle aggregation was studied by measuring the adhesion force. Absolute values of adhesion forces for different systems could not be compared due to the difference in particle size and contact geometry. Therefore, the relative change of adhesion force between pH 6 and 10 was used for comparison. The adhesion force decreased for the magnetite–magnetite and bentonite–silica systems and slightly increased for the magnetite–bentonite system at pH 10 as compared to pH 6, whereas a pronounced decrease in adhesion force was observed in the magnetite–silica system. Thus, the presence of silica particles on the magnetite surface could have a negative impact on the interaction between magnetite and bentonite in balling due to the reduction of the adhesion force.

• 210.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Chemistry, Division of Surface and Corrosion Science, KTH Royal Institute of Technology, Stockholm, SE-100 44, Sweden.
Physics Condensed Matter Laboratory, Faculty of Science of Tunis, University of Tunis El-Manar. Physics Condensed Matter Laboratory, Faculty of Science of Tunis, University of Tunis El-Manar. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Physics Condensed Matter Laboratory, Faculty of Science of Tunis, University of Tunis El-Manar. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
Morphological and electrical characterization of Cu-doped PbS thin films with AFM2017In: Advanced Materials Letters, ISSN 0976-3961, E-ISSN 0976-397X, Vol. 8, no 11, p. 1029-1037Article in journal (Refereed)

Lead sulphide (PbS) is a direct band gap IV–VI intrinsic p-type semiconductor with good potential for application in solar cells, sensors, etc. Doping the films with Cu2+ ions may improve the electrical properties. Here, Cu-doped PbS films were deposited on conducting glass substrates. The morphology, topography and thickness of the doped PbS films were examined using atomic force microscopy (AFM) and high-resolution SEM. AFM analysis showed decreasing surface roughness and grain size with the increase of Cu2+ concentration from 0.5 to 2.0 at%. Local surface electrical measurements using conducting AFM and Kelvin probe force microscopy showed the possibility to probe semi-quantitatively the changes in surface potential, work function, and Fermi level upon doping of the films. The estimated apparent work function for the un-doped PbS grains in the film was slightly above 4.5 eV, while it decreased to a minimum value of 4.43-4.45 eV at 1–1.5 at% Cu-doping. Conducting AFM measurements showed that local resistance of the doped samples is lower than on pure PbS films. These results indicate Cu doping as an effective strategy to tune the electrical properties of PbS thin films toward the development of suitable optically active materials for application in photovoltaics.

• 211.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
An atomic force microscopy study of the interaction between magnetite particles: the effect of Ca2 + ions and pH2013In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 233, p. 116-122Article in journal (Refereed)

Force interactions between a microsize (m-s) magnetite probe and thin layers of synthesized magnetite particles as well as microsize (m-s) magnetite particles from magnetite concentrate were investigated using atomic force microscopy (AFM). Of special interest was the influence of Ca2 + ions and pH on the interaction between the probe and the two different magnetite particle surfaces. The probe and the magnetite surfaces were immersed in aqueous Ca2 + solutions (100, 10, and 1 mM) at various pH values (4, 6, and 10). The colloidal probe technique and a self-made computer program for automatic evaluation of adhesion forces were used. The analysis revealed an increase in adhesion force with increased calcium concentration at pH 6 for both the systems investigated. However, the adhesion behavior between the probe and the m-s and n-s magnetite particle surfaces is different at pH 10. The possible appearance of calcium carbonate precipitated onto the magnetite surfaces as well as the possible influence of already adsorbed silicate on magnetite particles from the concentrate is discussed. In addition to Ca, Cl and Na atoms, added to the working solutions, and the Fe and O detected signals, the SEM-EDS analysis also detected Si atoms on the surface of the m-s particles.

• 212.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
Interaction forces between surface modified magnetite particles in aqueous solution2011Conference paper (Other academic)
• 213.
SENSOR Lab., Department of Information Engineering, University of Brescia.
SENSOR Lab., Department of Information Engineering, University of Brescia. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. SENSOR Lab., Department of Information Engineering, University of Brescia. Department of Mathematics and Physics, Catholic University of Sacred Heart. Department of Mathematics and Physics, Catholic University of Sacred Heart. National Institute of Optics, National Research Council (CNR-INO), Unit of Brescia. SENSOR Lab., Department of Information Engineering, University of Brescia. SENSOR Lab., Department of Information Engineering, University of Brescia. SENSOR Lab., Department of Information Engineering, University of Brescia.
Anomalous gas sensing behaviors to reducing agents of hydrothermally grown α-Fe2O3 nanorods2018In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 273, p. 1237-1245Article in journal (Refereed)

α-Fe2O3 nanorods have been grown by hydrothermal method, dispersed in ethanol and drop casted on a pre-patterned alumina substrate with Pt electrodes. Their morphology, crystalline and electronic properties have been investigated by Scanning Electron Microscopy, Raman and X-ray Photoelectron Spectroscopies and X-ray Diffraction. The so-fabricated devices have been used for hydrogen gas sensing, showing their ability to detect H2 at operating temperatures > 200 °C, at relative humidity values comprised from 0% to 50%. The sensing behavior of α-Fe2O3 nanorods is compatible with an n to p conductivity transition when the operating temperature is increased up to 300 °C. Outstanding p-type hydrogen sensing performances of α-Fe2O3 have been observed and reported. Besides H2 detection, the α-Fe2O3 nanorods-based device is a good humidity sensor, at room temperature (n-type) and at 400 °C (p-type). CO and ethanol sensing performances have been investigated at different operating temperatures and relative humidity values. CO and ethanol anomalous acceptor-like behaviors at 200 °C in humid air has been explained by the interactions of these target gases with the water molecules adsorbed on the metal oxide surfaces. An explanation of the n–p behavior transition at T > 200 °C in terms of band bending is reported.

• 214.
Laboratory of Physics, Faculty of Electrical Engineering, University of Ljubljana, Ljubljana, Slovenia.Laboratory of Clinical Biophysics, Chair of Orthopaedic Surgery, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia.
Laboratory of Physics, Faculty of Electrical Engineering, University of Ljubljana, Ljubljana, Slovenia. Luleå University of Technology, Department of Engineering Sciences and Mathematics. Laboratory of Physics, Faculty of Electrical Engineering, University of Ljubljana, Ljubljana, Slovenia. Laboratory of Clinical Biophysics, Faculty of Health Sciences, University of Ljubljana, Ljubljana, Slovenia. Department of Surface Engineering and Optoelectronics, “Jožef Stefan” Institute, Ljubljana, Slovenia. Laboratory of Clinical Biophysics, Faculty of Health Sciences, University of Ljubljana, Ljubljana, Slovenia. Institute of Biosciences and BioResources, National Research Council of Italy, Italy. Condensed Matter Physics Department, “Jožef Stefan” Institute, Ljubljana, Slovenia. Faculty of Natural Sciences and Mathematics, University of Maribor, Maribor, Slovenia. Laboratory of Physics, Faculty of Electrical Engineering, University of Ljubljana, Ljubljana, Slovenia. Laboratory of Clinical Biophysics, Chair of Orthopaedic Surgery, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia. Institute of Biosciences and BioResources, National Research Council of Italy, Italy.
Chapter Six - The role of membrane vesiculation and encapsulation in cancer diagnosis and therapy2019In: Advances in Biomembranes and Lipid Self-Assembly, ISSN 2451-9634, Vol. 29, p. 159-199Article in journal (Refereed)

We summarize recent findings and advances in cancer diagnostics in relation to extracellular vesicles (EVs) and emerging therapeutic options of nanomaterials. We revise the common mechanism for EV inception, vesiculation, through a physical model of the liquid mosaic membrane with laterally mobile membrane rafts that determine local spontaneous curvature. If such in-plane orientational ordering is present, we show that spatial non-homogeneities may trigger energetically favourable membrane vesiculation. In addition, we revise a novel technique of cancer therapy using multifunctional titanium nanobeads (NBs) that form a fully biocompatible system used for optical imaging, magnetic resonance imaging and selective reactive oxygen species photo-generation. We study the encapsulation of these functional NBs theoretically with Monte Carlo (MC) simulations and find that the wrapping transition depends on the strength of mobile charges, giving insight into future functional optimization for maximum therapeutic benefit.

• 215.
Laboratoire de Physique Corpusculaire, Université Blaise Pascal Clermont-Ferrand.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
Preon trinity: a schematic model of leptons, quarks and heavy vector bosons2002In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 60, no 2, p. 188-194Article in journal (Refereed)

Quarks, leptons and heavy vector bosons are suggested to be composed of stable spin- (1/2) preons, existing in three flavours, combined according to simple rules. Straightforward consequences of an SU(3) preon-flavour symmetry are the conservation of three lepton numbers, oscillations and decays between some neutrinos, and the mixing of the d and s quarks, as well as of the vector fields W0 and B0. We find a relation between the Cabibbo and Weinberg mixing angles, and predict new (heavy) leptons, quarks and vector bosons, some of which might be observable at the Fermilab Tevatron and the future CERN LHC. A heavy neutrino might even be visible in existing data from the CERN LEP facility.

• 216. Dugne, Jean-Jacques
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
Higgs pain? Take a preon!1997In: Proceedings of the Meeting on 'The Fundamental Structure of Matter' and 'Tests of the Electroweak Symmetry Breaking', Ouranoupolis, Greece, May 1997, 1997Conference paper (Refereed)

The Higgs mechanism is the favourite cure for the main problem with electroweak unification, namely how to reconcile a gauge theory with the need for massive gauge bosons. This problem does not exist in preon models for quark and lepton substructure with composite $Z^0$ and $W$s, which, consequently, also avoid all other theoretical complications and paradoxes with the Higgs mechanism. We present a new, minimal preon model, which explains the family structure, and predicts several new, heavy quarks, leptons and vector bosons. Our preons obey a phenomenological supersymmetry, but without so-called squarks and sleptons, since this SUSY is effective only on the composite scale.

• 217. Dugne, Jean-Jacques
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
Preon Trinity: a new model of leptons and quarks1999In: Beyond the desert 1999: accelerator, non-accelerator, and space approaches into the next millennium ; proceedings of the Second International Conference on Particle Physics Beyond the Standard Model, Castle Ringberg, Germany, 6 - 12 June 1999 / [ed] Hans Volker Klapdor-Kleingrothaus, Berlin: Encyclopedia of Global Archaeology/Springer Verlag, 1999Conference paper (Refereed)

A new model for the substructure of quarks, leptons and weak gauge bosons, is discussed. It is based on three fundamental and absolutely stable spin-1/2 preons. Its preon flavour SU(3) symmetry leads to a prediction of nine quarks, nine leptons and nine heavy vector bosons. One of the quarks has charge $-4e/3$, and is speculated to be the top quark (whose charge has not been measured). The flavour symmetry leads to three conserved lepton numbers in all known weak processes, except for some neutrinos, which might either oscillate or decay. There is also a (Cabibbo) mixing of the $d$ and $s$ quarks due to an internal preon-antipreon annihilation channel. An identical channel exists inside the composite $Z^0$, leading to a relation between the Cabibbo and Weinberg mixing angles.

• 218. Dugne, Jena-Jacques
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.

We present a new minimal model for the substructure of all known quarks, leptons and weak gauge bosons, based on only three fundamental and stable spin-1/2 preons. As a consequence, we predict three new quarks, three new leptons, and six new vector bosons. One of the new quarks has charge $-4e/3$. The model explains the apparent conservation of three lepton numbers, as well as the so-called Cabibbo-mixing of the $d$ and $s$ quarks, and predicts electromagnetic decays or oscillations between the neutrinos $\bar{\nu}_{\mu}$ ($\nu_{\mu}$) and $\nu_e$ ($\bar{\nu}_e$). Other neutrino oscillations, as well as rarer quark mixings and CP violation can come about due to a small quantum-mechanical mixing of two of the preons in the quark and lepton wave functions.

• 219.
Luleå tekniska universitet.
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
Full potential calculations on the electron band structures of Sphalerite, Pyrite and Chalcopyrite2003In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 206, no 1-4, p. 300-313Article in journal (Refereed)

The metal contents of ore can be as low as 0.4%m This means sophisticated methods of enrichment have to be applied. Better understanding of the processes of flotation and leaching may lead to higher yields and less damage to the environment. The bulk electronic structures of Sphalerite, Pyrite and Chalcopyrite have been calculated within an ab initio, full potential, density functional approach. The exchange term was approximated with the Dirac exchange functional, the Vosko-Wilk-Nusair parameterization of the Cepler-Alder free electron gas was used for correlation and linear combinations of Gaussian type orbitals were used as basis functions. The Sphalerite (zinc blend) band gap was calculated to be direct with a width of 2.23 eV. The Sphalerite valence band was 5.2 eV wide and composed of a mixture of sulfur and zinc orbitals. The band below the valence band located around -6.2 eV was mainly composed of Zn 3d orbitals. The S 3s orbitals gave rise to a band located around -12.3 eV. Pyrite was calculated to be a semiconductor with an indirect band gap of 0.51 eV, and a direct gap of 0.55 eV. The valence band was 1.25 eV wide and mainly composed of non-bonding Fe 3d orbitals. The band below the valence band was 4.9 eV wide and composed of a mixture of sulfur and iron orbitals. Due to the short inter-atomic distance between the sulfur dumbbells, the S 3s orbitals in Pyrite were split into a bonding and an anti-bonding range. Chalcopyrite was predicted to be a conductor, with no band-crossings at the Fermi level. The bands at -13.2 eV originate from the sulfur 3s orbitals and were quite similar to the sulfur 3s bands in Sphalerite, though somewhat shifted to lower energy. The top of the valence band consisted of a mixture of orbitals from all the atoms. The lower part of the same band showed metal character. Computational modeling as a tool for illuminating the flotation and leaching processes of Pyrite and Chalcopyrite, in connection with surface science experiments, is discussed.

• 220.
Kungliga tekniska högskolan, KTH.
Rice University, Houston. University of Hongkong. Umeå universitet. Chuparosa Research, Mesa, Arizona. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
The effect of water on the Fe3+/Fe2+ reduction potential of heme2000In: Biochemical and Biophysical Research Communications - BBRC, ISSN 0006-291X, E-ISSN 1090-2104, Vol. 268, no 3, p. 683-687Article in journal (Refereed)

Hemeproteins can act as catalysts, oxygen carriers or electron conductors. The ferric/ferrous reduction potential Em7 of iron in the center of the prosthetic group ranges from negative values for peroxidases to an extreme positive value for cytochrome a3 with Hb and Mb in the middle [1]. Proteins exercise their influence on Em7 in several ways: via substituents at the periphery of the chelate structure, via the proximal ligand, and via interaction with the surrounding medium, amino acid side chains, or polar solvents. Work on recombined proteins and 2,4-substituted free hemes documented that the first two effects are additive [2]. For the third effect, models of the dielectric media on a molecular level have been successfully applied [3-5]. Em7 has also been empirically correlated to the degree of heme exposure to water [6-8]. The apoprotein/porphyrin and water/porphyrin interfaces are complementary since water molecules fill any empty space in the crevice and surround any pertinent part of heme outside the protein boundary. The present work links to this idea by a combination of statistical mechanics simulations and quantum mechanical calculations comparing heme in water with heme in an apolar environment. Our results show that polarization of the porphyrin π-electron cloud by the field from water dipoles influences Em7. The dominant effect of this and other determinates of iron electron availability is perturbations of delocalized electron density in the porphyrin chelate, reproduced by a model where the prosthetic group is treated as a disc of uniform electron density. The present work is also of interest since the interfacial energy constitutes the main barrier for heme-protein separation [9-11].

• 221. Edholm, O.
The barrier for heme-protein separation estimated by non-equilibrium molecular dynamics simulations1998In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 291, no 5-6, p. 501-508Article in journal (Refereed)

In heme-containing proteins the heme group is usually non-covalently bound in a pocket. Molecular dynamics (MD) simulations have been performed to estimate the barrier height for heme-protein separation. In simulations of myoglobin dissolved in water, a force has been applied to pull the heme out of the binding pocket. With forces above 0.5 nN, the heme group is easily pulled out of the pocket in times of the order of tens of picoseconds. With weaker forces, heme release becomes too slow to be monitored in an MD simulation covering a couple of hundred picoseconds. These results are consistent with a free energy barrier to heme release of about 100 kJ/mol. The results show that the main energetic change that occurs during the release is a conversion of heme/protein Lennard-Jones energy into heme/water Lennard-Jones energy. The release is essentially barrierless in energy indicating that the main part of the barrier is entropic.

• 222.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
NASA Ames Research Center.
Correlation of subsurface ice content and gully locations on Mars; testing the shallow aquifer theory of gully formation2006In: Lunar and planetary science, XXXVII: papers presented to the Thirty-seventh lunar and planetary science conference / [ed] Stephen J. Mackwell, Houston, Tex: Lunar and planetary institute , 2006Conference paper (Other academic)
• 223. Eilam, G.
Small angle production from nuclear and nucleon targets1980In: Lettere al Nuovo Cimento della Società Italiana di Fisica, ISSN 0375-930X, Vol. 27, p. 299-Article in journal (Refereed)
• 224. Ekelin, Svante
Hadron pT correlations in quark jets1986In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 56, no 22, p. 2428-2428Article in journal (Refereed)
• 225. Ekelin, Svante
Large-pT protons from constituent diquark scattering1984In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 149, no 6, p. 509-513Article in journal (Refereed)

Recent data from the CERN ISR on the fractional proton yield in pp collisions are explained within the Stockholm diquark model. Describing the proton as a u(ud)0 system, the observed high magnitude and fall-off pT, θ and √s of the proton yield are natural consequences of constituent diquark elastic scattering. The pT and θ dependence favour a value of around 10 GeV2/c2 for the size parameter in the diquark form factor, corresponding to a diquark rms radius of around 0.2 fm. This is consistent with earlier results of the model applied to deep inelastic lepton-nucleon scattering and e+e- annihilation

• 226. Ekelin, Svante
Baryons from diquarks in e+e- annihilation1983In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 28, no 1, p. 257-259Article in journal (Other academic)

We find experimental support for the view that diquarks appear only as spin-0 objects. When their production rate in the color field of a quark from e+e- annihilation is described by the appropriate Schwinger formula for scalars, it turns out that they must be substantially lighter than earlier believed in order to explain the baryon yield.

• 227. Ekelin, Svante
Indications of hard diquarks in e+e- annihilation1984In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 30, no 11, p. 2310-2315Article in journal (Refereed)

It is suggested that very small spin-0 diquarks are directly produced in e+e- annihilation and then fragment into leading baryons and other hadrons. The most influential diquark is the charmed diquark (uc), due to its high charge. It gives a sizable contribution to the hadronic R factor and to the two-jet angular distribution in the energy region W=4-8 GeV. At these energies, a careful study of Λ production would provide the best additional test of the model.

• 228.
Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
Calibration and evaluation of the secondary sensors for the Mini-EUSO space instrument2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis

The Mini-EUSO (Mini - Extreme Universe Space Observatory) is an instrument for observation of ultra-high energy cosmic rays (UHECR) from space. It is designed to observe Earth from the international space station (ISS) in the ultra-violet (UV), visible (VIS) and near-infrared (NIR) light ranges. The UV sensor is the main sensor, designed and built by the EUSO collaboration. The visible and near-infrared sensors are secondary sensors. These are two cameras, FMVU-13S2C-CS and CMLN-13S2M-CV, from Point Grey Research Inc. The near-infrared light camera has a phosphor coating on the sensor to convert from near-infrared light to visible light, which is detectable by the camera's CCD.

This thesis deals with the calibration and evaluation of the secondary sensors. This is done by first evaluating the bias and dark current for both cameras. After which a calibration is done using the light measurement sphere, located at the National Instituteof Polar Research (NIPR) in Midori-cho, Tachikawa-shi, Japan. Due to the low sensitivity of the near-infrared light camera, an evaluation of its ability to see celestialobjects are also performed.

It is found that the visible light camera has a high bias with values around 5 ADU (Analog-to-Digital unit), but almost non-existing dark current, with mean values below 1 ADU. The visible light camera has good sensitivity for all the colors: red, green and blue. However, it is most sensitive to green. Due to this, it is easy to saturate the pixels with too much light. Therefore, saturation intensity was also examined for the shutter times of the visible light camera. This is found to be between 900μWm-2sr-1 and 1·107μWm-2sr-1, depending on color and shutter time.

The near-infrared light camera is the opposite; it has a low bias with values below 1 ADU and a high dark current. The values of the dark current for the near-infrared light camera are highly dependent on the temperature of the camera. Mean values are below 1 ADU for temperatures around 310K, but mean values of almost 2 ADU at temperatures around 338K. The sensitivity of the near-infrared light camera is very low, therefore, the only way to detect a difference between the light levels of the light measurement sphere was to use a high ADC amplication gain. With this it was found that there is a power-law behavior, values between 1.33 and 1.50, of the relationship between pixel values and light intensity. This is likely due to the phosphor coating used to convert to visible light. When trying to detect celestial objects, the faintest object detected was Venus with a magnitude of less than -4.

• 229.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
Cosmic dust and heavy neutrinos2007Doctoral thesis, comprehensive summary (Other academic)

This Doctoral thesis treats two subjects. The first subject is the impact of early dust on the cosmic microwave background (CMB). The dust that is studied comes from the first generation of stars, which were hot and short-lived, ending their lives as giant supernovae. In the supernova explosions, heavy elements, produced through the fusion in the stars, were ejected into the interstellar medium. These heavy elements condensed to form dust, which can absorb and thus perturb the CMB radiation. The dust contribution to this radiation is calculated and found negligible. However, since the dust is produced within structures (like galaxy clusters), it will have a spatial correlation that could be used to detect it. This correlation is calculated with relevant assumptions. The planned Planck satellite could eventually detect and thus confirm this correlation. The second subject is heavy neutrinos and their impact on the diffuse gamma ray background. Neutrinos heavier than M_Z /2 ~ 45 GeV are not excluded by particle physics data. Stable neutrinos heavier than this might contribute to the cosmic gamma ray background through annihilation in distant galaxies as well as to the dark matter content of the universe. The evolution of the heavy neutrino density in the universe is calculated as a function of its mass, M_N, and then the subsequent gamma ray spectrum from annihilation of distant N-Nbar (from 0 < z < 5). The evolution of the heavy neutrino density in the universe is calculated numerically. In order to obtain the enhancement due to structure formation in the universe, the distribution of N is approximated to be proportional to that of dark matter in the GalICS model. The calculated gamma ray spectrum is compared to the measured EGRET data. A conservative exclusion region for the heavy neutrino mass is 100 to 200 GeV, both from EGRET data and our re-evalutation of the Kamiokande data. The heavy neutrino contribution to dark matter is found to be at most 15%. Finally, heavy neutrinos are considered within the context of a preon model for composite leptons and quarks, where such particles are natural. The consequences of these are discussed, with emphasis on existing data from the particle accelerator LEP at CERN. A numerical method for optimizing variable cuts in particle physics is also included in the thesis.

• 230.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
Dust in the early universe2005Licentiate thesis, comprehensive summary (Other academic)

This Licentiate thesis treats the impact of early dust on the Cosmic Microwave Background (CMB). The dust that is studied comes from the first generation of stars, which were hot and short-lived, ending their lives as giant supernovæ. In the supernova explosions, heavy elements, produced through the fusion in the stars, were ejected into the interstellar medium. These heavy elements condensed to form dust, which can absorb and thus perturb the Cosmic Microwave Background radiation. The dust contribution to this radiation is calculated and found negligible. However, as the dust will be produced within structures (like galaxy clusters), it will have a spatial correlation that could be used to detect it. This correlation is calculated using relevant assumptions. The planned Planck satellite is likely to be able to measure and thus confirm this correlation.

• 231.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
Laboratoire d’Astrophysique, Observatoire de Grenoble.
Dust from reionization2004In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 425, p. 9-14Article in journal (Refereed)

The possibility that population III stars have reionized the Universe at redshifts greater than 6 has recently gained momentum with WMAP polarization results. Here we analyse the role of early dust produced by these stars and ejected into the intergalactic medium. We show that this dust, heated by the radiation from the same population III stars, produces a submillimetre excess. The electromagnetic spectrum of this excess could account for a significant fraction of the FIRAS (Far Infrared Absolute Spectrophotometer) cosmic far infrared background above 700 micron. This spectrum, a primary anisotropy (Delta T) spectrum times the nu2 dust emissivity law, peaking in the submillimetre domain around 750 micron, is generic and does not depend on other detailed dust properties. Arcminute-scale anisotropies, coming from inhomogeneities in this early dust, could be detected by future submillimetre experiments such as Planck HFI.

• 232.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
Laboratoire d’Astrophysique, Observatoire de Grenoble. Université Lyon 1, Centre de Recherche Astrophysique de Lyon, Observatoire de Lyon.
Dust distribution during reionization2007In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 476, p. 1145-1150Article in journal (Refereed)

Context. The dust produced by the first generation of stars will be a foreground to cosmic microwave background.Aims. In order to evaluate the effect of this early dust, we calculate the power spectrum of the dust emission anisotropies and compare it with the sensitivity limit of the Planck satellite.Methods. The spatial distribution of the dust is estimated through the distribution of dark matter.Results. At small angular scales l ≥ 1000 the dust signal is found to be noticeable with the Planck detector for certain values of dust lifetime and production rates. The dust signal is also compared to sensitivities of other instruments. The early dust emission anisotropies are finally compared to those of local dustand they are found to be similar in magnitude at mm wavelengths.

• 233.
Luleå University of Technology, Department of Engineering Sciences and Mathematics.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
Mass limits for heavy neutrinos2008In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 479, no 2, p. 347-353Article in journal (Refereed)

Context. Neutrinos heavier than MZ/2 ∼ 45 GeV are not excluded by particle physics data. Stable neutrinos heavier than this might contribute to the cosmic gamma ray background through annihilation in distant galaxies, as well as to the dark matter content of the universe.Aims. We calculate the evolution of the heavy neutrino density in the universe as a function of its mass, MN, and then the subsequent gamma ray spectrum from annihilation of distant N ¯N (from 0 < z < 5).Methods. The evolution of the heavy neutrino density in the universe is calculated numerically. To obtain the enhancement due to structure formation in the universe, we approximate the distribution of N to be proportional to that of dark matter in the GalICS model. The calculated gamma ray spectrum is compared to the measured EGRET data.Results. A conservative exclusion region for the heavy neutrino mass is 100 to 200 GeV, both fromEGRET data and our re-evalutation of the Kamiokande data. The heavy neutrino contribution to dark matter is found to be at most 15%.

• 234.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. Swerea MEFOS AB. SSAB.
Possibility to combine exergy with other process integration methods for a steelmaking case2010In: PRES 2010, 13th Conference on Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction / [ed] Jirí J. Klemeš; Hon Loong Lam; Petar S. Varbanov, AIDIC Servizi S.r.l. , 2010, p. 1375-1380Conference paper (Refereed)

The energy system of Luleå consists of the steel plant, a local CHP using process gases from the plant and the district heating system. Process integration work to improve the efficiency of the system is presently carried out by mathematical programming using a MILP tool (reMIND). Further improvements would need an improved possibility of the tool to consider the thermodynamic quality of the energy flows. This project aims to include exergy parameters in the node equations and object functions. This has been carried out for a test case, including a part of the system. Programming principles and some results are described.

• 235.
Department of Engineering Mathematics and Physics, Faculty of Engineering, Cairo University.
Laboratoire de photonique d'Angers, Université d'Angers. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Chemistry, University of Patras.
Multi-property isotropic intermolecular potentials and predicted spectral lineshapes of collision-induced absorption (CIA), collision-induced light scattering (CILS) and collision-induced hyper-Rayleigh scattering (CIHR) for H2Ne, −Kr and −Xe2018In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 209, p. 232-242Article in journal (Refereed)

Quantum mechanical lineshapes of collision-induced absorption (CIA), collision-induced light scattering (CILS) and collision-induced hyper-Rayleigh scattering (CIHR) at room temperature (295 K) are computed for gaseous mixtures of molecular hydrogen with neon, krypton and xenon. The induced spectra are detected using theoretical values for induced dipole moment, pair-polarizability trace and anisotropy, hyper-polarizability and updated intermolecular potentials. Good agreement is observed for all spectra when the literature and the present potentials which are constructed from the transport and thermo-physical properties are used.

• 236.
Astronomy Unit, Queen Mary and Westfield College, University of London.
Luleå tekniska universitet.
General relativistic 1 + 3 orthonormal frame approach1997In: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 14, no 9, p. 2673-2695Article in journal (Refereed)

The dynamical equations of an extended 1 + 3 orthonormal frame approach to the relativistic description of spacetime geometries are explicitly presented and discussed in detail. In particular, the Bianchi identities for the Weyl curvature tensor occur in a fully expanded form, as they are given a central role in the extended formalism. It is shown how one can naturally introduce local coordinates, both in the 1 + 3 threading and the ADM 3 + 1 slicing context. By specializing the general 1 + 3 dynamical equations it is demonstrated how a number of problems of interest can be obtained. In particular, the simplest choices of spatial frames for spatially homogeneous cosmological models, locally rotationally symmetric spacetime geometries, cosmological models with an Abelian isometry group G2 and 'silent' dust cosmological models are discussed.

• 237.
Astronomy Unit, Queen Mary and Westfield College, University of London.
Luleå tekniska universitet. Department of Applied Mathematics, University of Fort Hare. Department of Applied Mathematics, University of Cape Town. School of Mathematical Studies, Portsmouth University.
Integrability of irrotational silent cosmological models1997In: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 14, no 5, p. 1151-1162Article in journal (Refereed)

We revisit the issue of integrability conditions for the irrolational silent cosmological models. We formulate the problem both in 1 + 3 covariant and 1 + 3 orthonormal frame notation and show that there exists a series of constraint equations that need to be satisfied. These conditions hold identically for FLRW-linearized silent models, but not in the general exact nonlinear case. Thus there is a linearization instability and it is highly unlikely that there is a large class of silent models We conjecture that there are no spatially inhomogeneous solutions with Weyl curvature of Petrov type I and indicate further issues that await clarification.

• 238.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
CNR-IFN, Istituto di Fotonica e Nanotecnologie, CSMFO Lab. & FBK-CMM. Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca’ Foscari Venezia. Meridionale Impianti SpA. Laboratoire des Technologies Innovantes, LTI, Département de Génie industriel ENSA – Tanger. Laboratoire des Technologies Innovantes, LTI, Département de Génie industriel ENSA – Tanger. Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca’ Foscari Venezia. M. Ferrari . Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi, Piazza del Viminale . Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca’ Foscari Venezia. Institute of Low Temperature and Structure Research, PAS.
Silver doping of silica-hafnia waveguides containing Tb3+/Yb3+ rare earths for downconversion in PV solar cells2016In: Optical materials (Amsterdam), ISSN 0925-3467, E-ISSN 1873-1252, Vol. 60, p. 264-269Article in journal (Refereed)

The aim of this paper is to study the possibility to obtain an efficient downconverting waveguide which combines the quantum cutting properties of Tb3+/Yb3+ codoped materials with the optical sensitizing effects provided by silver doping. The preparation of 70SiO(2)-30HfO(2) glass and glass-ceramic waveguides by sol-gel route, followed by Ag doping by immersion in molten salt bath is reported. The films were subsequently annealed in air to induce the migration and/or aggregation of the metal ions. Results of compositional and optical characterization are given, providing evidence for the successful introduction of Ag in the films, while the photoluminescence emission is strongly dependent on the annealing conditions. These films could find potential applications as downshifting layers to increase the efficiency of PV solar cells

• 239.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
CSMFO Lab., Istituto di Fotonica e Nanotecnologie CNR. Laboratoire des Technologies Innovantes, LTI, Université Abdelmalek Essâadi, Tanger. Laboratoire des Technologies Innovantes, LTI, Université Abdelmalek Essâadi, Tanger. CSMFO Lab., Istituto di Fotonica e Nanotecnologie CNR. Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi, Piazza del Viminale . Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi. Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi.
Visible to NIR downconversion process in Tb3+-Yb3+ codoped silica-hafnia glass and glass-ceramic sol-gel waveguides for solar cells2018In: Journal of Luminescence, ISSN 0022-2313, E-ISSN 1872-7883, Vol. 193, p. 44-50Article in journal (Refereed)

The efficiency of photovoltaic solar cells is strongly related to the spectral absorption and photo-conversion properties of the cell's active material, which does not exploit the whole broadband solar spectrum. This mismatch between the spectrum of the solar light and the wavelength dependent cell's response can be partially overcome by using luminescent conversion layers in front or in the back of the solar cell. In this paper, the investigation of Tb3+-Yb3+ co-doped SiO2-HfO2 glass and glass-ceramic waveguides is presented. Due to a down-conversion process based on cooperative energy transfer between one Tb3+ ion and two Yb3+ ions, a blue photon at 488 nm can be divided in two NIR photons at 980 nm. Films with different molar concentrations of rare earths, up to a total amount of [Tb+Yb] = 15%, were prepared by a sol-gel route, using dip-coating deposition on SiO2 substrates. For all the films, the molar ratio [Yb]/[Tb] was taken equal to 4. The comparison of the energy-transfer efficiency between Tb3+ and Yb3+ ions in the glass and in the glass-ceramic materials demonstrated the higher performance of the glass-ceramic, with a maximum quantum transfer efficiency of 179% for the highest rare earth doping concentration. Moreover, experimental results and comparison with proper rate equations modelling showed a linear dependence of the photoluminescence emission intensity for the Yb3+ ions 2F5/22F7/2 transition at 980 nm on the excitation power, indicating a direct transfer process from Tb3+ to Yb3+ ions. The reported waveguides could find applications not only as downconverting filters in transmission but also as efficient solar concentrators in the near-IR spectral region

• 240.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi, Roma.
Laboratoire des Technologies Innovantes, LTI, Université Abdelmalek Essâadi, Tanger. Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca’ Foscari Venezia, Mestre, Venezia. Laboratoire des Technologies Innovantes, LTI, Université Abdelmalek Essâadi, Tanger. Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca’ Foscari Venezia. Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi, Roma. Dipartimento di Ingegneria Industriale (DII), Università degli Studi di Padova. Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi, Roma. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi, Roma. Department of Chemistry and Chemical Engineering, Chalmers University of Technology. Dipartimento di Ingegneria Industriale (DII), Università degli Studi di Padova. Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca’ Foscari Venezia, Mestre, Venezia. Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca’ Foscari Venezia, Mestre, Venezia. Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi, Roma. Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca’ Foscari Venezia, Mestre, Venezia. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi, Roma.
Ag nanoaggregates as efficient broadband sensitizers for Tb3+ ions in silica-zirconia ion-exchanged sol-gel glasses and glass-ceramics2018In: Optical materials (Amsterdam), ISSN 0925-3467, E-ISSN 1873-1252, Vol. 84, p. 668-674Article in journal (Refereed)

In this paper we report the study of down-shifting silica-zirconia glass and glass-ceramic films doped by Tb3+ ions and Ag nanoaggregates, which combine the typical spectral properties of the rare-earth-ions with the broadband sensitizing effect of the metal nanostructures. Na-Tb co-doped silica-zirconia samples were obtained by a modified sol-gel route. Dip-coating deposition followed by annealing for solvent evaporation and matrix densification were repeated several times, obtaining a homogeneous crack-free film. A final treatment at 700 °C or 1000 °C was performed to control the nanoscale structural properties of the samples, resulting respectively in a glass (G) or a glass-ceramic (GC), where tetragonal zirconia nanocrystals are surrounded by an amorphous silica matrix. Ag introduction was then achieved by ion-exchange in a molten salt bath, followed by annealing in air to control the migration and aggregation of the metal ions. The comparison of the structural, compositional and optical properties are presented for G and GC samples, providing evidence of highly efficient photoluminescence enhancement in both systems, slightly better in G than in GC samples, with a remarkable increase of the green Tb3+ PL emission at 330 nm excitation: 12 times for G and 8 times for GC samples. Furthermore, after Ag-exchange, the shape of Tb3+ excitation resembles the one of Ag ions/nanoaggregates, with a broad significant absorption in the whole UV-blue spectral region. This broadband enhanced downshifting could find potential applications in lighting devices and in PV solar cells.

• 241.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Museo Storico della Fisica e Centro Studi e Ricerche “Enrico Fermi”, Roma, Italy. Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca’ Foscari Venezia, Venezia, Italy.
Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca’ Foscari Venezia, Venezia, Italy. Museo Storico della Fisica e Centro Studi e Ricerche “Enrico Fermi”, Roma, Italy. Istituto di Fotonica e Nanotecnologie del Consiglio Nazionale delle Ricerche (IFN-CNR), Laboratorio CSMFO and Fondazione Bruno Kessler (FBK) Photonics Unit, Trento, Italy. Museo Storico della Fisica e Centro Studi e Ricerche “Enrico Fermi”, Roma, Italy. Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca’ Foscari Venezia, Venezia, Italy. Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca’ Foscari Venezia, Venezia, Italy. Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca’ Foscari Venezia, Venezia, Italy. Museo Storico della Fisica e Centro Studi e Ricerche “Enrico Fermi”, Roma, Italy. Istituto di Fisica Applicata Nello Carrara del Consiglio Nazionale delle Ricerche (IFAC-CNR), Firenze, Italy. Dipartimento di Scienze Molecolari e Nanosistemi, Università Ca’ Foscari Venezia, Venezia, Italy. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Museo Storico della Fisica e Centro Studi e Ricerche “Enrico Fermi”, Roma, Italy. Istituto di Fotonica e Nanotecnologie del Consiglio Nazionale delle Ricerche (IFN-CNR), Laboratorio CSMFO and Fondazione Bruno Kessler (FBK) Photonics Unit, Trento, Italy.
Ag-Sensitized Yb3+ Emission in Glass-Ceramics2018In: Micromachines, ISSN 2072-666X, E-ISSN 2072-666X, Vol. 9, no 8, article id 380Article in journal (Refereed)

Rare earth doped materials play a very important role in the development of many photonic devices, such as optical amplifiers and lasers, frequency converters, solar concentrators, up to quantum information storage devices. Among the rare earth ions, ytterbium is certainly one of the most frequently investigated and employed. The absorption and emission properties of Yb3+ ions are related to transitions between the two energy levels 2F7/2 (ground state) and 2F5/2 (excited state), involving photon energies around 1.26 eV (980 nm). Therefore, Yb3+ cannot directly absorb UV or visible light, and it is often used in combination with other rare earth ions like Pr3+, Tm3+, and Tb3+, which act as energy transfer centres. Nevertheless, even in those co-doped materials, the absorption bandwidth can be limited, and the cross section is small. In this paper, we report a broadband and efficient energy transfer process between Ag dimers/multimers and Yb3+ ions, which results in a strong PL emission around 980 nm under UV light excitation. Silica-zirconia (70% SiO2-30% ZrO2) glass-ceramic films doped by 4 mol.% Yb3+ ions and an additional 5 mol.% of Na2O were prepared by sol-gel synthesis followed by a thermal annealing at 1000 °C. Ag introduction was then obtained by ion-exchange in a molten salt bath and the samples were subsequently annealed in air at 430 °C to induce the migration and aggregation of the metal. The structural, compositional, and optical properties were investigated, providing evidence for efficient broadband sensitization of the rare earth ions by energy transfer from Ag dimers/multimers, which could have important applications in different fields, such as PV solar cells and light-emitting near-infrared (NIR) devices.

• 242.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
School of Physics and Materials for Energy Research Group, University of the Witwatersrand, Johannesburg. Historical Museum of Physics and Study & Research Centre “Enrico Fermi”.
Plasmonic enhanced solar cells: Summary of possible strategies and recent results2018In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 82, no 3, p. 2433-2439Article in journal (Refereed)

Plasmonic structures for light manipulation at sub-wavelength scale have received great interest in the field of photovoltaic (PV) solar cells for their potential to significantly enhance the cell's efficiency.

The performance of any solar cell is determined by the capability to absorb incoming light and produce electric charges, which, in turn, has a number of limiting factors. One is related to the ever-reducing size and acceptance angle of the active region. Another is the limited spectral sensitivity of the active material, which cannot make use of significant parts of the solar spectrum.

Correspondingly, the energy harvesting may be improved in two ways, namely by adopting light trapping schemes and by exploiting spectral modification processes to shift frequencies of the solar spectrum, which are initially not absorbed, into the region of maximum absorption of the cell.

Plasmonic nanoparticles (NPs) can give a significant boost to both these aspects, by scattering and concentrating the electromagnetic field into the active region of the device, and by doing that within specific spectral regions, which can be properly tuned by optimizing the size, shape, distribution of the plasmonic NPs, and by choosing the right surrounding medium.

During the last ten years, many papers have been published on very specific issues, but also on general properties of plasmonics applied to solar cells, with a strong increase between 2006 and 2012, followed by a period of significant, but stable, literature productivity. Given these premises, an organized and schematic summary of the main strategies and of the recent results on the field is given in this review, where different plasmonic approaches are compared and discussed, also by recalling specific examples from the literature and providing a few key conclusions to understand the main aspects and the future perspectives of the field.

• 243.
Luleå tekniska universitet.
Aspects of quarks in exotic matter1999Licentiate thesis, comprehensive summary (Other academic)

In this licentiate thesis, two different aspects of particle physics have been studied. The results are presented in four papers. In papers I and II, a model for a joint origin of gamma-ray bursts and dark matter is presented. The common denominator is the deconfined state of quarks, the Quark-Gluon Plasma (QGP). We propose that such quark objects surviving the quark-hadron transition in the early universe, constitute the dark matter and that mergers of these objects are the inner engine of gamma-ray bursts. We have computed stability criteria for macroscopic quark objects, as well as the merger frequency assuming a lognormal distribution in size. In paper III, the helicity amplitudes for rare-meson production invirtual gamma-gamma collisions are computed. We show that it is possible to apply a generalised version of the Brodsky-Lepage scheme for exclusive processes in QCD, when computing these amplitudes. In paper IV, we analyse consequences of the new supernova data, suggesting a non-zero vacuum energy density in the universe. We calculate the intrinsic luminosity correction for high-redshift objects such as gamma-ray bursts and quasars. Two different extensions of the Friedmann-Robertson-Walker universe are used; a non-zero cosmological constant and a time-dependent spatially inhomogeneous energy density component (so-called quintessence). The results show a correction of up to 30% for the conventionally computed luminosities.

• 244. Enström, Daniel
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
Luminosities of high-redshift objects in an accelerating universe1999Report (Other academic)

The results from the Supernova Cosmology Project indicate a relation between cosmic distance and redshift that corresponds to an accelerating Universe, and, as a consequence, the presence of an energy component with negative pressure. This necessitates a re-evaluation of such astrophysical luminosities that have been derived through conventional redshift analyses of, e.g., gamma-ray bursts and quasars. We have calculated corrected luminosity distances within two scenarios; the standard one with a non-zero cosmological constant, and the more recently proposed `quintessence'', with a slowly evolving energy-density component. We find luminosity corrections from +30 to -40 per cent for redshifts with $z=0 - 10$. This finding implicates that the SCP data do not, by themselves, require a revision of the current, rather qualitative modeling of gamma-ray bursts and quasar properties.

• 245. Enström, Daniel
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Kungliga tekniska högskolan, KTH.
A Quark matter dominated universe1998Report (Other academic)

We present a new scenario for the development of the Universe after the Big Bang, built on the conjecture that a vast majority of the primordial quark matter did not undergo a phase transition to normal nuclear matter, but rather split up into massive quark objects that remained stable. Hence, such primordial quark matter would make up the so-called dark matter. We discuss, mostly in qualitative terms, the consequences for galaxy formation, the origin of normal matter, the occurrence of massive black-holes in galactic centres and the cosmic gamma-ray bursts.

• 246. Enström, Daniel
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Kungliga tekniska högskolan, KTH.
Gamma-Ray Bursts and Dark Matter: a joint origin?1998Conference paper (Refereed)
• 247.
Istituto per la Microelettronica e i Microsistemi, IMM-CNR.
Istituto per lo Studio dei Materiali Nanostrutturati, ISMN-CNR. Istituto per lo Studio dei Materiali Nanostrutturati, ISMN-CNR. Istituto di Cristallografia, IC-CNR. Istituto di Cristallografia, IC-CNR. Electrochemical Processes Unit, IMDEA Energy Institute, Avda. NMR Unit, Centro de Apoyo Tecnológico, Universidad Rey Juan Carlos. Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and The Barcelona Institute of Science and Technology, Campus UAB, Bellaterra. Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and The Barcelona Institute of Science and Technology, Campus UAB, Bellaterra. Istituto per la Microelettronica e i Microsistemi, IMM-CNR. Department of Information Engineering, Brescia University. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
Inorganic Photocatalytic Enhancement: Activated RhB Photodegradation by Surface Modification of SnO2 Nanocrystals with V2O5-like species2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 44763Article in journal (Refereed)

SnO2 nanocrystals were prepared by precipitation in dodecylamine at 100 °C, then they were reacted with vanadium chloromethoxide in oleic acid at 250 °C. The resulting materials were heat-treated at various temperatures up to 650 °C for thermal stabilization, chemical purification and for studying the overall structural transformations. From the crossed use of various characterization techniques, it emerged that the as-prepared materials were constituted by cassiterite SnO2 nanocrystals with a surface modified by isolated V(IV) oxide species. After heat-treatment at 400 °C, the SnO2 nanocrystals were wrapped by layers composed of vanadium oxide (IV-V mixed oxidation state) and carbon residuals. After heating at 500 °C, only SnO2 cassiterite nanocrystals were obtained, with a mean size of 2.8 nm and wrapped by only V2O5-like species. The samples heat-treated at 500 °C were tested as RhB photodegradation catalysts. At 10-7 M concentration, all RhB was degraded within 1 h of reaction, at a much faster rate than all pure SnO2 materials reported until now.

• 248.
Istituto per la Microelettronica e i Microsistemi, IMM-CNR, Lecce, Italy.
Istituto per lo Studio dei Materiali Nanostrutturati, ISMN-CNR, Roma, Italy. Istituto per lo Studio dei Materiali Nanostrutturati, ISMN-CNR, Roma, Italy. Istituto di Cristallografia, IC-CNR, Bari, Italy. Istituto di Cristallografia, IC-CNR, Bari, Italy. Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and The Barcelona Institute of Science and Technology (BIST), Barcelona, Catalonia, Spain; Catalonia Institute for Energy Research (IREC), Barcelona, Catalonia, Spain. Catalonia Institute for Energy Research (IREC), Barcelona, Catalonia, Spain. Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and The Barcelona Institute of Science and Technology (BIST), Barcelona, Catalonia, Spain; ICREA, Barcelona, Catalonia, Spain. Istituto per la Microelettronica e i Microsistemi, IMM-CNR, Lecce, Italy. Department of Information Engineering, Brescia University, Brescia, Italy; SENSOR, Brescia University & CNR INO, Brescia, Italy. Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
Solvothermal Synthesis, Gas-Sensing Properties, and Solar Cell-Aided Investigation of TiO2-MoOx Nanocrystals2017In: ChemNanoMat, ISSN 2199-692X, Vol. 3, no 11, p. 798-807Article in journal (Refereed)

Titania anatase nanocrystals were prepared by sol-gel/solvothermal synthesis in oleic acid at 250 °C, and modified by co-reaction with Mo chloroalkoxide, aimed at investigating the effects on gas-sensing properties induced by tailored nanocrystals surface modification with ultra-thin layers of MoOx species. For the lowest Mo concentration, only anatase nanocrystals were obtained, surface modified by a disordered ultra-thin layer of mainly octahedral MoVI oxide species. For larger Mo concentrations, early MoO2 phase segregation occurred. Upon heat treatment up to 500 °C, the sample with the lowest Mo concentration did not feature any Mo oxide phase segregation, and the surface Mo layer was converted to dense octahedral MoVI oxide. At larger Mo concentrations all segregated MoO2 was converted to MoO3. The two different materials typologies, depending on the Mo concentration, were used for processing gas-sensing devices and tested toward acetone and carbon monoxide, which gave a greatly enhanced response, for all Mo concentrations, to acetone (two orders of magnitude) and carbon monoxide with respect to pure TiO2. For the lowest Mo concentration, dye-sensitized solar cells were also prepared to investigate the influence of anatase surface modification on the electrical transport properties, which showed that the charge transport mainly occurred in the ultra-thin MoOx surface layer.

• 249.
Luleå University of Technology, Department of Engineering Sciences and Mathematics.
Nanoscale electrical properties of heterojunction interfaces for solar cells: modeling and experiments2018Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis

A numerical model have been developed in order to describe and achieve deeper understanding of experimentally obtained I-V curves from Cu2O/ZnO p-n heterojunctions for potential use as future solar cell material. The model was created using the simulation software COMSOL Multiphysics® and their semiconductor module. To experimentally study the samples two approaches were taken: (1) macro-electrical measurements and (2) local I-V measurements using conductive AFM. The final model is one-dimensional, time dependent and with the ability to study photovoltaic effects of samples with different layer thickness at different voltage ramping speeds and different light irradiance. The model is also able to study the effects of using different contact materials by treating the contacts as ideal Schottky contacts. The dynamic behavior of a Cu_2O/ZnO heterojunction was studied by considering the systems response to a voltage step and the effect of changing the voltage ramping speed. The output from the step response, the current as a function of time, is varying a short time after a step has occurred before settling on to a steady value. The response also shows an overshoot of the current in the direction of the voltage step and the final steady value depends on whether the junction is conducting or not. The effects of this behavior on the shape of the I-V curves are witnessed when studying the different voltage ramping speeds. The voltage is ramped from 2 V to -2 V and back again for different speeds (V/s). The I-V curves have different shapes when sweeping the voltage in different directions and the magnitude increases with increasing speed. The photovoltaic effects were studied by applying different light irradiances. The behavior of the model agrees well with the theory for an ideal diode solar cell. An investigation was done of how the work function of the metal in contact with the Cu_2O affects the shape of the I-V curve under dark and illuminated conditions. The metal work function was changed from 4.5 eV to 6.5 eV in steps of 0.4 eV and does not affect the shape of the I-V curves much in dark after increasing it above 4.5 eV. The effects are more visible under illuminated conditions where a "step"-behavior appears for the lower values of the work function. Only one of the physical samples show a noticeable light effect. The macro-electrical measurement on this sample is compared with simulated results and are in qualitative agreement with each other. The agreement between the local electrical measurements and the simulated results is not as good with the current model.

• 250.
Luleå University of Technology, Department of Engineering Sciences and Mathematics.
Evaluation of properties of a digital micromirror device applied for light shaping2019Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
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