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Chemical and structural investigation of the cobalt phthalocyanine
Matija Stupar, 2015, magistrsko delo

Opis: In the last two decades, studies on organic molecules mimicking substances of fundamental importance in nature, like chlorophyll or hemoglobin, have attracted researchers’ attention. These molecules are building blocks for a family of materials also referred to as “organic semiconductors”. Such compounds can be implemented in numerous applications, ranging from data-storage to light harvesting. Some of their fundamental advantages include low cost, light weight, relatively easy engineering and mechanical flexibility, compatible with bending plastic substrates. In this thesis work we investigated the chemical, structural and electronic properties of cobalt phthalocyanines (CoPc). These molecules have promising applications in the field of magnetic data storage and spintronics in general, due to the ferromagnetic properties of the cobalt atom. Several techniques like photoemission core-level spectroscopy and valence band spectroscopy, together with X-ray absorption, have been used in order to determine the CoPc properties in gaseous phase, i.e. in the absence of interaction with the surrounding environment. Another set of experiments was devoted to the commissioning of the CITIUS time-resolved photoemission setup, that will be used in future studies of CoPc molecules on surfaces.
Najdeno v: ključnih besedah
Povzetek najdenega: ...spectroscopy (PES), X-ray absorption spectroscopy (XAS), synchrotron radiation, laser, high order harmonic generation (HHG), time...
Ključne besede: Cobalt phthalocyanine (CoPc), photoemission spectroscopy (PES), X-ray absorption spectroscopy (XAS), synchrotron radiation, laser, high order harmonic generation (HHG), time resolved spectroscopy
Objavljeno: 29.09.2015; Ogledov: 3972; Prenosov: 188
.pdf Polno besedilo (2,96 MB)

Gabrijela Zaharijas, B. L. Winer, 2016, izvirni znanstveni članek

Opis: The Fermi Large Area Telescope (LAT) has provided the most detailed view to date of the emission toward the Galactic center (GC) in high-energy γ-rays. This paper describes the analysis of data taken during the first 62 months of the mission in the energy range 1–100 GeV from a 15° × 15° region about the direction of the GC. Specialized interstellar emission models (IEMs) are constructed to enable the separation of the γ-ray emissions produced by cosmic ray particles interacting with the interstellar gas and radiation fields in the Milky Way into that from the inner ∼1 kpc surrounding the GC, and that from the rest of the Galaxy. A catalog of point sources for the 15° × 15° region is self-consistently constructed using these IEMs: the First Fermi-LAT Inner Galaxy Point Source Catalog (1FIG). The spatial locations, fluxes, and spectral properties of the 1FIG sources are presented, and compared with γ-ray point sources over the same region taken from existing catalogs. After subtracting the interstellar emission and point-source contributions a residual is found. If templates that peak toward the GC are used to model the positive residual the agreement with the data improves, but none of the additional templates tried account for all of its spatial structure. The spectrum of the positive residual modeled with these templates has a strong dependence on the choice of IEM.
Najdeno v: ključnih besedah
Povzetek najdenega: ...particles interacting with the interstellar gas and radiation fields in the Milky Way into that...
Ključne besede: cosmic rays – Galaxy: center – gamma-rays: general – gamma-rays: ISM – radiation mechanisms: non-thermal
Objavljeno: 02.03.2016; Ogledov: 2234; Prenosov: 172
.pdf Polno besedilo (6,36 MB)

Complementarity of Galactic radio and collider data in constraining WIMP dark matter models
Yann Mambrini, Michel H.G. Tytgat, Gabrijela Zaharijas, Brzan Zaldívar, 2012, izvirni znanstveni članek

Najdeno v: ključnih besedah
Povzetek najdenega: ...dark matter theory, dark matter experiments, absorption, radiation, ...
Ključne besede: dark matter theory, dark matter experiments, absorption, radiation
Objavljeno: 09.05.2017; Ogledov: 1341; Prenosov: 10
URL Polno besedilo (0,00 KB)

Atomic-level mechanisms of magnesium oxidation
Dmytro Orlov, Matjaž Valant, Sandra Gardonio, Mattia Fanetti, 2016, objavljeni znanstveni prispevek na konferenci

Opis: Magnesium has been recently becoming an increasingly popular material for various applications. However, excessive chemical reactivity, and oxidation rate in particular, is a major obstruction on the way of Mg to become widely adopted. A significant problem causing the lack of Mg reactivity control is insufficient understanding of mechanisms involved in the oxidation of magnesium surface. Herewith we present the investigation of atomic-level mechanisms of oxidation initiation and propagation in pure Mg. Namely, X-ray photoelectron spectroscopy at synchrotron Elettra was used as a surface sensitive direct method to determine the valence of Mg and O and the valence band states at the early stage of oxide formation over a principal, most densely packed, crystallographic plane (0001) in pure Mg. The mechanisms of oxygen adsorption on magnesium free surface followed by oxidation (i.e. initiation and kinetics of MgO formation) are clarified. Copyright © 2016 by The Minerals, Metals & Materials Society. All rights reserved.
Najdeno v: ključnih besedah
Povzetek najdenega: ...Magnesium, Oxidation, Synchrotron radiation, X-ray photoelectron spectroscopy...
Ključne besede: Magnesium, Oxidation, Synchrotron radiation, X-ray photoelectron spectroscopy
Objavljeno: 25.08.2017; Ogledov: 1716; Prenosov: 0
.pdf Polno besedilo (2,91 MB)

Analysis and characterization of thermal systematic effects on the PLANCK LFI data
Tanja Petrushevska, 2010, magistrsko delo

Opis: The cosmic microwave background radiation discovered by Penzias and Wilson in 1965, is considered one of the most important experimental evidences in favour of the Hot Big Bang standard cosmological model. This radiation provides an image of the Universe when it was about 380,000 years old and has a blackbody spectral distribution at temperature T=2.725±0.002 K, index of thermodynamic equilibrium with the mater in epoch when it was released. The cosmic background radiation presents anisotropies at level of 10 5 which provide valuable information about the origin and the evolution of the Universe. After the discovery of background radiation, tens of experiments have been performed to measure this radiation and its anisotropies. In 1992 the COBE satellite revolutionized cosmology by detecting temperature anisotropies for the first time. Launched on May 14, 2009, Planck is a European Space Agency mission designed to measure the CMB anisotropies with an accuracy set by fundamental astrophysical limits. To do this, Planck is imaging the whole sky with an unprecedented combination of sensitivity ( ΔT/T~2*10^-6), angular resolution (to 5’), and 9 frequency coverage (30 857 GHz). To reach these ambitious requirements, Planck uses an active cryogenic thermal system which cools the instruments to 0.1 K. The high sensitivity of the instrument and the cryogenic system makes the thermal systematic effects study of crucial importance to the scientific success. The thesis is divided into six chapters: 1. Chapter 1 explains the properties of the cosmic background radiation and its anisotropies; 2. Chapter 2 presents a short overview of the various experiments dedicated to the study of cosmic background radiation; 3. Chapter 3 describes the Planck mission, its instruments and its goals, in particular the Low Frequency Instrument (LFI) and its thermal structure; Chapter 4 discusses the analysis of the LFI thermal stability. This work was carried out in the Physics department at the University of Trieste, at the LFI Data Processing Centre located at INAF (Instituto Nazionale di AstroFisica) - OATS (Astronomical Observatory of Trieste); Chapter 5 presents the results of this analysis; in Chapter 6 conclusions are drawn and proposals for future work are discussed.
Najdeno v: ključnih besedah
Povzetek najdenega: ...The cosmic microwave background radiation discovered by Penzias and Wilson in 1965,...
Ključne besede: Cosmic background radiation, CMB, Planck, satellite mission
Objavljeno: 24.01.2018; Ogledov: 890; Prenosov: 37
.pdf Polno besedilo (23,33 MB)

Radiation Effects on Optical Fibers and Fiber-Based Sensors
Nicolas Richard, Philippe Paillet, Youcef Ouerdane, A. Boukenter, Sylvain Girard, Layla Martin-Samos, Luigi Giacomazzi, Claude Marcandella, 2015, samostojni znanstveni sestavek ali poglavje v monografski publikaciji

Najdeno v: ključnih besedah
Ključne besede: Optical Fibers, radiation-induced point defects, dosimetry, ab-initio
Objavljeno: 24.10.2018; Ogledov: 987; Prenosov: 0
.pdf Polno besedilo (632,99 KB)

Blaž Winkler, doktorska disertacija

Opis: This work is primarily focused on application of standard first-principle computational approaches to model oxygen excess related point defects in amorphous silica. Atomic models with their respective electronic and optical properties are explored together with some conversion mechanisms between defect models. The first chapter overviews extensive literature about the already known properties of oxygen related defects. Second chapter briefly introduces main methods that have been used in this research, in particular Density Functional Theory (DFT) as energy and force engine with short description of minimal energy path (MEP) algorithm used for modeling chemical/migration reactions, GW approximation for charged electronic excitations (band structure) and Bethe-Salpeter Equation (BSE) for neutral excitations (optical absorption and excitonic structure including electron hole interaction). The third chapter is devoted to the presentation of results. Thanks to the calculation of optical properties of peroxy bridge (POL), a correlation has been found between structural disorder, specifically dihedral angle dispersion, and low coupling with light, which has been identified as main reason why no clear absorption bands have been assigned to the POL. Structure and stability of some other defects, like interstitial ozone molecule (ozonyl) and dioxasilirane (silicon analogy of dioxirane), have been studied. These defects are usually not considered as most important species, however their calculated formation energies are lower compared to some known defects, which indicates they might be present in silica. From a detailed study on possible reaction mechanisms, it has been found that ozonyl might be one of the most important intermediate steps for oxygen exchange reactions. Results also show that dioxasilirane can be spontaneously created during the interaction of oxygen with lone pair defects. By exploring different reactions between oxygen and pre-existing oxygen deficiency centers (ODCs), calculations predict two kinds of passivation behaviors: single-barrier reversible mechanisms with the formation of dioxasilirane-like groups, for which the network keeps the memory of the precursory lone pair defects, and single or multiple-barrier mechanisms, for which the network loses its memory, either because of the high reverse barrier or because of a reconstruction. Final part of this research has been devoted to experimental characterization of the response and tolerance of optical fibers loaded with oxygen under irradiation. These include experiments on commercial fiber along with canonical samples (Optical fibers developed with the intention of studying correlations between different fabrication parameters, dopant/impurity concentration and doping concentrations). Studied fibers also include rare-earth doped fibers.
Najdeno v: ključnih besedah
Povzetek najdenega: ...oxygen deficiency centers, optical absorption, optical fibers, radiation induced attenuation....
Ključne besede: Silica, DFT, GW-approximation, Bethe-Salpeter equation, NEB, defect, oxygen, oxygen excess centers, oxygen deficiency centers, optical absorption, optical fibers, radiation induced attenuation.
Objavljeno: 07.05.2019; Ogledov: 1082; Prenosov: 67
.pdf Polno besedilo (13,18 MB)

Au and Ag on the Bi2Se3(0001) Surface: Experimental Electronic and Physical Properties
Sandra Gardonio, Mattia Fanetti, Katja Ferfolja, Matjaž Valant, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: Binary bismuth chalcogenides, Bi2Se3 and Bi2Te3, have been extensively studied as reference topological insulators (TIs). These materials are bulk insulators with topological surface states (TSS) crossing the Fermi level. In contrast to conventional surface states of metals, the TSS are extremely robust against local modifications at the surface, such as adsorbed adatoms, localized defects or changes in the surface termination. This aspect makes the TIs attractive for applications in spintronics, plasmonics, quantum computing and catalysis. A theoretical model of charge transport by the TI surface states predicts that the TSS survive, provided that bonding at the metal/TI interface is weak. Ab-initio calculations have been done to understand the electronic properties of Au, Ni, Pt, Pd and graphene layers in a contact with Bi2Se3. These calculations showed that for Au and graphene the spin-momentum locking of TSS is maintained at the interface. In another theoretical study, Ag and Au thin layers on Bi2Se3 have been predicted to show a large Rashba splitting and a high spin polarization of the Ag quantum wells, providing a great potential for development of the spintronic devices. Finally, the calculations have foreseen that the presence of the robust TSS affects the adsorption properties of metals (Au bi-layer and clusters of Au, Ag, Cu, Pt, and Pd) supported on TI, in some cases resulting in the enhancement of the catalytic processes. Despite the fundamental importance of the metal/TI interfaces and a number of theoretical studies predicting exotic interfacial phenomena, the experimental knowledge about the metals on the TI surfaces is surprisingly limited, especially concerning combined study of morphology, growth mode, electronic and chemical properties. In order to exploit the predicted physical properties of such systems, it is especially important to extend the study above the diluted coverage regime and to understand what is the growth morphology of the metal on the TI surface, to what extent the metal overlayer interacts with the TI substrate, how the TSS change with the presence of the metal overlayer and what is the reactivity of the system at the different stages of the overlayer growth. Within this frame, we present a comprehensive surface sensitive study, of Au and Ag on Bi2Se3 by means of ARPES, XPS, SEM, LEED and XRD. The obtained results allow us to discuss the relation between electronic and physical properties at two of the most important model metal/TI interfaces
Najdeno v: ključnih besedah
Ključne besede: topological insulator, electronic properties, synchrotron radiation
Objavljeno: 27.06.2019; Ogledov: 771; Prenosov: 0
.pdf Polno besedilo (5,72 MB)

Coherent THz Emission Enhanced by Coherent Synchrotron Radiation Wakefield
Primož Rebernik Ribič, Giovanni De Ninno, 2018, izvirni znanstveni članek

Opis: We demonstrate that emission of coherent transition radiation by a ∼1 GeV energy-electron beam passing through an Al foil is enhanced in intensity and extended in frequency spectral range, by the energy correlation established along the beam by coherent synchrotron radiation wakefield, in the presence of a proper electron optics in the beam delivery system. Analytical and numerical models, based on experimental electron beam parameters collected at the FERMI free electron laser (FEL), predict transition radiation with two intensity peaks at ∼0.3 THz and ∼1.5 THz, and extending up to 8.5 THz with intensity above 20 dB w.r.t. the main peak. Up to 80-µJ pulse energy integrated over the full bandwidth is expected at the source, and in agreement with experimental pulse energy measurements. By virtue of its implementation in an FEL beam dump line, this work promises dissemination of user-oriented multi-THz beamlines parasitic and self-synchronized to EUV and x-ray FELs.
Najdeno v: ključnih besedah
Ključne besede: terahertz radiation, free-electron lasers, coherent transition radiation
Objavljeno: 12.01.2020; Ogledov: 460; Prenosov: 0
.pdf Polno besedilo (1,62 MB)

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