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1.
Infrared spectra in amorphous alumina
Luigi Giacomazzi, Nikita S Shcheblanov, Mikhail E Povarnitsyn, Yanbo Li, Andraž Mavrič, Barbara Zupančič, Jože Grdadolnik, Alfredo Pasquarello, zaključena znanstvena zbirka raziskovalnih podatkov

Opis: We present a combined study based on experimental measurements of infrared (IR) dielectric function and first-principles calculations of IR spectra and vibrational density of states (VDOS) of amorphous alumina (am-Al₂O₃). In particular, we show that the main features of the imaginary part of the dielectric function ε₂(ω) at ~380 and 630 cm-¹ are related to the motions of threefold coordinated oxygen atoms, which are the vast majority of oxygen atoms in am-Al₂O₃. Our analysis (involving three model structures) provides an alternative point of view with respect to an earlier suggested assignment of the vibrational modes, which relates them to the stretching and bending vibrational modes of AlOₙ (n = 4, 5, and 6) polyhedra. Our assignment is based on the additive decomposition of the VDOS and ε₂(ω) spectra, which shows that: (i) the band at ~380 cm-¹ features oxygen motions occurring in a direction normal to the plane defined by the three nearest-neighbor aluminum atoms, i.e. out-of-plane motions of oxygen atoms; (ii) Al-O stretching vibrations (i.e. in-plane motions of oxygen atoms) appear at frequencies above ~500 cm-¹, which characterize the vibrational modes underlying the band at ~630 cm-¹.
Ključne besede: amorphous alumina, infrared spectra, first-principles calculations
Objavljeno v RUNG: 15.09.2023; Ogledov: 686; Prenosov: 7
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2.
Infrared spectra in amorphous alumina : a combined ab initio and experimental study
Luigi Giacomazzi, Nikita S. Shcheblanov, Mikhail E. Povarnitsyn, Yanbo Li, Andraž Mavrič, Barbara Zupančič, Jože Grdadolnik, Alfredo Pasquarello, 2023, izvirni znanstveni članek

Opis: We present a combined study based on the experimental measurements of an infrared (IR) dielectric function and first-principles calculations of IR spectra and the vibrational density of states (VDOS) of amorphous alumina (am−Al2O3). In particular, we show that the main features of the imaginary part of the dielectric function ε2(ω) at ∼380 and 630 cm−1 are related to the motions of threefold-coordinated oxygen atoms, which are the vast majority of oxygen atoms in am-Al2O3. Our analysis provides an alternative point of view with respect to an earlier suggested assignment of the vibrational modes, which relates them to the stretching and bending vibrational modes of AlOn (n=4, 5, and 6) polyhedra. Our assignment is based on the additive decomposition of the VDOS and ε2(ω) spectra, which shows that (i) the band at ∼380cm−1 features oxygen motions occurring in a direction normal to the plane defined by the three nearest-neighbor aluminum atoms, i.e., out-of-plane motions of oxygen atoms; (ii) Al-O stretching vibrations (i.e., in-plane motions of oxygen atoms) appear at frequencies above ∼500cm−1, which characterize the vibrational modes underlying the band at ∼630cm−1. Aluminum and fourfold-coordinated oxygen atoms contribute uniformly to the VDOS and ε2(ω) spectra in the frequency region ∼350–650 cm−1 without causing specific features. Our numerical results are in good agreement with the previous and presently obtained experimental data on the IR dielectric function of am−Al2O3 films. Finally, we show that the IR spectrum can be modeled successfully by assuming isotropic Born charges for aluminum atoms and fourfold-coordinated oxygen atoms, while requiring the use of three parameters, defined in a local reference frame, for the anisotropic Born charges of threefold-coordinated oxygen atoms.
Ključne besede: dielectric properties, microstructure, amorphous materials, density functional calculations, infrared techniques, aluminium oxide
Objavljeno v RUNG: 10.05.2023; Ogledov: 1119; Prenosov: 6
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3.
Voltage-dependent FTIR and 2D infrared spectroscopies within the electric double layer using a plasmonic and conductive electrode
Nan Yang, Matthew J. Ryan, Minjung Son, Andraž Mavrič, Martin Zanni, 2023, izvirni znanstveni članek

Opis: Strong electric fields exist between the electric double layer and charged surfaces. These fields impact molecular structures and chemistry at interfaces. We have developed a transparent electrode with infrared plasmonic enhancement sufficient to measure FTIR and two-dimensional infrared spectra at submonolayer coverages on the surface to which a voltage can be applied. Our device consists of an infrared transparent substrate, a 10–20 nm layer of conductive indium tin oxide (ITO), an electrically resistive layer of 3–5 nm Al2O3, and a 3 nm layer of nonconductive plasmonic gold. The materials and thicknesses are set to maximize the surface number density of the monolayer molecules, electrical conductivity, and plasmonic enhancement while minimizing background signals and avoiding Fano line shape distortions. The design was optimized by iteratively characterizing the material roughness and thickness with atomic force microscopy and electron microscopy and by monitoring the plasmon resonance enhancement with spectroscopy. The design is robust to repeated fabrication. This new electrode is tested on nitrile functional groups using a monolayer of 4-mercaptobenzonitrile as well as on CO and CC stretching modes using 4-mercaptobenzoic acid methyl ester. A voltage-dependent Stark shift is observed on both monolayers. We also observe that the transition dipole strength of the CN mode scales linearly with the applied voltage, providing a second way of measuring the surface electric field strength. We anticipate that this cell will enable many new voltage-dependent infrared experiments under applied voltages.
Ključne besede: two-dimensional infrared spectroscopy, infrared transparent substrate, voltage-dependent infrared experiments
Objavljeno v RUNG: 24.02.2023; Ogledov: 1099; Prenosov: 0
.pdf Celotno besedilo (6,07 MB)

4.
Tidal Disruption Events seen through the eyes of Vera C. Rubin Observatory
Katja Bučar Bricman, 2021, doktorska disertacija

Opis: Tidal Disruption Events (TDEs) are rare transients, which are considered to be promising tools in probing supermassive black holes (SMBHs) and their environments in quiescent galaxies, accretion physics, and jet formation mechanisms. The majority of $\approx$ 60 detected TDEs has been discovered with large field of view time-domain surveys in the last two decades. Currently, about 10 TDEs are discovered per year, and we expect this number will increase largely once the Legacy Survey of Space and Time (LSST) at Vera C. Rubin Observatory begins its observations. In this work we demonstrate and explore the capabilities of the LSST to study TDEs. To begin with, we simulate LSST observations of TDEs over $10$ years of survey duration by including realistic SED models from MOSFiT into the simulation framework of the LSST. SEDs are then converted into observed fluxes and light curves are simulated with the LSST observing strategy minion_1016. Simulated observations are used to estimate the number of TDEs the LSST is expected to observe and to assess the possibility of probing the SMBH mass distribution in the Universe with the observed TDE sample. We find that the LSST has a potential of observing ~1000 TDEs per year, the exact number depending on the SMBH mass distribution and the adopted observing strategy. In spite of this large number, we find that probing the SMBH mass distribution with LSST observed TDEs will not be straightforward, especially at the low-mass end. This is largely attributed to the fact that TDEs caused by low-mass black holes ($\le 10^6 M_\odot$) are less luminous and shorter than TDEs by heavier SMBHs ($> 10^6 M_\odot$), and the probability of observationally missing them with LSST is higher. Second, we built a MAF TDE metric for photometric identification of TDEs based on LSST data. We use the metric to evaluate the performance of different proposed survey strategies in identifying TDEs with pre-defined identification requirements. Since TDEs are blue in color for months after peak light, which separates them well from SNe and AGN, we include u-band observations as one of the criteria for a positive identification. We find that the number of identified TDEs strongly depends of the observing strategy and the number of u-band visits to a given field in the sky. Observing strategies with a larger number of u-band observations perform significantly better. For these strategies up to 10% of LSST observed TDEs satisfy the identification requirements.
Ključne besede: Ground-based ultraviolet, optical and infrared telescopes Astronomical catalogs, atlases, sky surveys, databases, retrieval systems, archives, Black holes, Galactic nuclei (including black holes), circumnuclear matter, and bulges, Infall, accretion, and accretion disks
Objavljeno v RUNG: 03.01.2022; Ogledov: 2566; Prenosov: 58
.pdf Celotno besedilo (124,61 MB)

5.
First principles vibrational spectra of tetrahedrally-bonded glasses: sio2, geo2 and gese2
Luigi Giacomazzi, 2007, doktorska disertacija

Ključne besede: Silica, Germania, Chalcogenide Glasses, Vibrational Spectra, Raman Spectroscopy, Infrared, First-principles
Objavljeno v RUNG: 31.01.2019; Ogledov: 4164; Prenosov: 0
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6.
Medium-range structure of vitreous SiO2 obtained through first-principles investigation of vibrational spectra
Luigi Giacomazzi, Paolo Umari, Alfredo Pasquarello, 2009, izvirni znanstveni članek

Ključne besede: silica, Raman, infrared, v-DOS, first-principles, glass
Objavljeno v RUNG: 15.10.2018; Ogledov: 3114; Prenosov: 0
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7.
Amorphous nanocomposite of polycarbosilanes and aluminum oxide
Andraž Mavrič, 2018, doktorska disertacija

Opis: This work presents a paradigm for high temperature stabilization of bulk amorphous aluminium oxide. The thermodynamic stabilization is achieved by preparing a nanocomposite, where polymethylsilane dendritic molecules are dispersed in an aluminium hydroxide gel. Upon heat-treatment the gel transforms to the amorphous aluminium oxide that is stable up to 900°C. The dispersion of the macromolecules and their covalent bonding to the alumina matrix induce homogeneously distributed strain fields that keep the alumina amorphous. The first part of the thesis focuses on the synthesis, characterization and solubility properties of the dendritic polymethylsilane. The polymethylsilane is synthetized by electrochemical polymerization from trichloromethylsilane monomer. The polymerization mechanism, involving a single polymerization pathway, is identified. The polymer growth proceeds through reduction of the monomers to the silyl anions and their addition to the growing polymer. The solubility of three chemically related but topologically different polysilanes (linear, dendritic and network) were studied by dynamic light scattering. At room temperature the agglomerates in a range from 500 to 1300 nm are present. They undergo de-agglomeration at slightly elevated temperatures of around 40°C. The de-agglomeration results in formation of stable solutions, where a hydrodynamic diameter of the individual polymer molecules was measured to be in a range from 20 to 40 nm. The obtained diameters of two dendritic polymethylsilane macromolecules, synthesized under different electrolysis conditions, are much larger than the theoretical size estimated for an ideal dendrimer. We determined by 29Si NMR that the reason for this is in a large number of branching irregularities (defects) contained in the molecular structure. Combining the experimental values obtained by DLS and density measurements with a structural model that considers the branching irregularities, it is shown that the inclusion of the defects allows the dendritic polymer to exceed the sterical limitations and form the hyperbranched dendritic structure. The final size depends on a relative amount of the branching defects. In the second part, the synthetized polymethylsilane molecules were successfully used for the nanocomposite formation. The aluminium hydroxide gel with the dispersed polymethylsilane molecules was prepared as a precursor. Upon heat-treatment it gives the amorphous aluminium oxide stable up to 900°C. The dispersed macromolecules induce homogeneously distributed strain fields that keep the aluminium oxide amorphous during the thermal treatment the dispersed macromolecules covalently bind to the matrix, inducing the interface strain. The amorphous state was confirmed by the presence of penta-coordinated aluminium detected by 27Al NMR and a low bandgap measured by UV-vis absorption spectroscopy.
Ključne besede: amorphous aluminium oxide, polymethylsilane, nanocomposite, electropolymerization, solubility, agglomeration, de-agglomeration, dendrimer, hyperbranched dendritic structure, dynamic light scattering, thermal analysis, transmission electron microscopy, scanning electron microscopy, X-ray diffraction, infrared spectroscopy, UV-Vis spectroscopy
Objavljeno v RUNG: 19.07.2018; Ogledov: 6009; Prenosov: 210
.pdf Celotno besedilo (5,07 MB)

8.
VizieR Online Data Catalog: Measured photometry of SN 2014J from HST (Amanullah+, 2014)
R. Amanullah, Tanja Petrushevska, zaključena znanstvena zbirka raziskovalnih podatkov

Opis: We obtained observations (Program DD-13621; PI: Goobar) of SN 2014J with HST in the four UV broadband filters F218W, F225W, F275W, and F336W for seven epochs using a total of seven HST orbits during Cycle 21. In addition to this we also obtained optical broad-, medium-, and narrowband photometry in filters F467M, F631N, and F845M for visits (1, 3) and optical broadband photometry using F438W, F555W, and F814W for the remaining five visits. All observations were obtained with the Wide-Field Camera-3 (WFC3) using the UVIS aperture UVIS2-C512C-SUB.
Ključne besede: Supernovae, Photometry: HST, Photometry: UBVRI, Photometry: infrared, Extinction
Objavljeno v RUNG: 23.01.2018; Ogledov: 3209; Prenosov: 0
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9.
VizieR Online Data Catalog: A 1689 HAWK-I J-band image (Petrushevska+, 2016)
Tanja Petrushevska, zaključena znanstvena zbirka raziskovalnih podatkov

Opis: The NIR data were obtained with the High Acuity Wide field K-band imager mounted on the VLT (Programmes ID 082.A-0431, 0.83.A-0398, 090.A-0492, 091.A-0108, P.I. Goobar). The HAWK-I has an array of four 2048x2048 HgCdTe detectors covering a total area of 7.5'x7.5' with a sampling of 0.106"/pix per pixel. The chips are separated by a 15" gap.
Ključne besede: Clusters: galaxy, Infrared sources
Objavljeno v RUNG: 23.01.2018; Ogledov: 3571; Prenosov: 0
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10.
Extraction of Organochlorine Pesticides from Plastic Pellets and Plastic Type Analysis
Maryline Pflieger, Petra Makorič, Manca Kovač Viršek, Špela Koren, 2017, pregledni znanstveni članek

Opis: Plastic resin pellets, categorized as microplastics (≤5 mm in diameter), are small granules that can be unintentionally released to the environment during manufacturing and transport. Because of their environmental persistence, they are widely distributed in the oceans and on beaches all over the world. They can act as a vector of potentially toxic organic compounds (e.g., polychlorinated biphenyls) and might consequently negatively affect marine organisms. Their possible impacts along the food chain are not yet well understood. In order to assess the hazards associated with the occurrence of plastic pellets in the marine environment, it is necessary to develop methodologies that allow for rapid determination of associated organic contaminant levels. The present protocol describes the different steps required for sampling resin pellets, analyzing adsorbed organochlorine pesticides (OCPs) and identifying the plastic type. The focus is on the extraction of OCPs from plastic pellets by means of a pressurized fluid extractor (PFE) and on the polymer chemical analysis applying Fourier Transform-InfraRed (FT-IR) spectroscopy. The developed methodology focuses on 11 OCPs and related compounds, including dichlorodiphenyltrichloroethane (DDT) and its two main metabolites, lindane and two production isomers, as well as the two biologically active isomers of technical endosulfan. This protocol constitutes a simple and rapid alternative to existing methodology for evaluating the concentration of organic contaminants adsorbed on plastic pieces.
Ključne besede: Environmental Sciences, Issue 125, Microplastics, resin pellets, pesticides, persistent organic pollutants, organochlorine pesticides, dichlorodiphenyltrichloroethane, endosulfan, hexachlorocyclohexane, lindane, Fourier transform infrared spectroscopy, pressurized fluid extractor
Objavljeno v RUNG: 10.07.2017; Ogledov: 4381; Prenosov: 0

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