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* old and bolonia study programme


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Molecular characterization of free tropospheric aerosol collected at the Pico Mountain Observatory
J. Hueber, Sumit Kumar, J. A. Perlinger, Katja Džepina, Claudio Mazzoleni, Paulo Fialho, Swarup China, Bo Zhang, R. Chris Owen, D. Helmig, 2015, original scientific article

Abstract: Free tropospheric aerosol was sampled at the Pico Mountain Observatory located at 2225 m above mean sea level on Pico Island of the Azores archipelago in the North Atlantic. The observatory is located ∼ 3900 km east and downwind of North America, which enables studies of free tropospheric air transported over long distances. Aerosol samples collected on filters from June to October 2012 were analyzed to characterize organic carbon, elemental carbon, and inorganic ions. The average ambient concentration of aerosol was 0.9 ± 0.7 µg m−3 . On average, organic aerosol components represent the largest mass fraction of the total measured aerosol (60 ± 51 %), followed by sulfate (23 ± 28 %), nitrate (13 ± 10 %), chloride (2 ± 3 %), and elemental carbon (2 ± 2 %). Water-soluble organic matter (WSOM) extracted from two aerosol samples (9/24 and 9/25) collected consecutively during a pollution event were analyzed using ultrahigh-resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Approximately 4000 molecular formulas were assigned to each of the mass spectra in the range of m/z 100–1000. The majority of the assigned molecular formulas had unsaturated structures with CHO and CHNO elemental compositions. FLEXPART retroplume analyses showed the sampled air masses were very aged (average plume age > 12 days). These aged aerosol WSOM compounds had an average O /C ratio of ∼ 0.45, which is relatively low compared to O /C ratios of other aged aerosol. The increase in aerosol loading during the measurement period of 9/24 was linked to biomass burning emissions from North America by FLEXPART retroplume analysis and Moderate Resolution Imaging Spectroradiometer (MODIS) fire counts. This was confirmed with biomass burning markers detected in the WSOM and with the morphology and mixing state of particles as determined by scanning electron microscopy. The presence of markers characteristic of aqueous-phase reactions of phenolic species suggests that the aerosol collected at the Pico Mountain Observatory had undergone cloud processing before reaching the site. Finally, the air masses of 9/25 were more aged and influenced by marine emissions, as indicated by the presence of organosulfates and other species characteristic of marine aerosol. The change in the air masses for the two samples was corroborated by the changes in ethane, propane, and ozone, morphology of particles, as well as by the FLEXPART retroplume simulations. This paper presents the first detailed molecular characterization of free tropospheric aged aerosol intercepted at a lower free troposphere remote location and provides evidence of low oxygenation after long-range transport. We hypothesize this is a result of the selective removal of highly aged and polar species during long-range transport, because the aerosol underwent a combination of atmospheric processes during transport facilitating aqueous-phase removal (e.g., clouds processing) and fragmentation (e.g., photolysis) of components.
Found in: ključnih besedah
Summary of found: ...state of particles as determined by scanning electron microscopy. The presence of markers characteristic of aqueous-phase reactions...
Keywords: organic aerosol, ultrahigh-resolution FT-ICR MS, electron microscopy, remote marine atmosphere, Pico Mountain Observatory
Published: 11.04.2021; Views: 944; Downloads: 0
.pdf Fulltext (4,36 MB)

Structural, morphological and chemical properties of metal/topological insulator interfaces
Katja Ferfolja, 2021, doctoral dissertation

Abstract: Topological insulators (TIs) represent a new state of matter that possess a different band structure than regular insulators or conductors. They are characterized with a band gap in the bulk and conductive topological states on the surface, which are spin polarized and robust toward contamination or deformation of the surface. Since the intriguing properties of the TIs are localized at the surface, it is important to obtain knowledge of the possible phenomena happening at the interface between TIs and other materials. This is especially true in the case of metals, due to the fact that such interfaces will be present in the majority of foreseen TI applications. The presented study combines microscopy and spectroscopy techniques for characterization of morphology, stability and chemical interaction at the interface between TI and metals deposited by means of physical vapor deposition. Our research is based on the interface of Bi2Se3 topological insulator with Ag, Ti and Pt – metals that can be encountered in devices or applications predicted to utilize the special properties of topological insulators. STM and SEM imaging of Ag/Bi2Se3 interface showed that Ag atoms arrange on the surface in the form of islands, whereas significantly bigger agglomerates are found at the surface steps. The interface was found to be unstable in time and resulted in the absorption of the metal into the crystal at room temperature. Evidences of a chemical reaction at the Ag/Bi2Se3 interface are presented, showing that new phases (Ag2Se, AgBiSe2 and metallic Bi) are formed. Deposition of Ti on Bi2Se3 resulted in different morphologies depending on the film thickness. At a very low coverage (<1 Å) islands are formed. However, the islands growth is hindered before the completion of a full layer due to the occurrence of a chemical reaction. No surface features could be detected by SEM for Ti coverage up to 20 nm. In contrary, when Ti thickness reached 40 nm, compressive stress triggered buckling of the deposited film. XPS analysis revealed that a redox solid-state reaction occurs at the Ti/Bi2Se3 interface at room temperature forming titanium selenides and metallic Bi. The reaction has significant kinetics even at cryogenic temperature of 130 K. Pt forms a homogenous film over the whole substrate surface, which is stable in time at room temperature. Although the interface of Pt with Bi2Se3 was found to be i less reactive compared to Ag and Ti, an interfacial phase formed upon annealing to ∼90 °C was detected by TEM cross section experiment. A model for prediction of interfacial reactions between a metal and Bi2Se3 based on the standard reduction potential of the metals and Gibbs free energy for a model reaction is presented. Based on these two values the reaction can be expected to result in the formation of binary and/or ternary selenides and Bi. Presented work shows on the importance of metal/topological insulator interfaces characterization taking into account the possibility of a chemical reaction with all of its consequences. Results should be considered for future theoretical and applicative studies involving such interfaces as well as for the possible engineering of 2D TI heterostructures.
Found in: ključnih besedah
Summary of found: ...of foreseen TI applications. The presented study combines microscopy and spectroscopy techniques for characterization of morphology,...
Keywords: topological insulators, topological surface states, Bi2Se3, thin films, Ag, Ti, Pt, morphology, interfaces, solid-state reaction, metal selenides, reactivity, stability, electron microscopy, dissertations
Published: 09.06.2021; Views: 1526; Downloads: 104
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Computer vision distortion correction of scanning probe microscopy images
Patrycja Paruch, Manisha Chhikara, Guillaume Rapin, Benedikt Ziegler, Philippe Tückmantel, Iaroslav Gaponenko, 2017, original scientific article

Found in: ključnih besedah
Keywords: scanning probe microscopy, distortion correction
Published: 12.07.2021; Views: 781; Downloads: 3
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Unraveling the Role of Major Facilitator Superfamily (MFS) Transporters in Plant Abiotic Stress Tolerance
Christina Paparokidou, 2014, final research report

Abstract: The yields of worldwide crop production are negatively affected by adverse environmental conditions, such as drought, salinity, heavy metal contamination and nutrient depletion in cultivated soils (Yan et al., 2013; Golldack et al., 2011; Yadav, 2010; Kobayashi and Nishizawa, 2012). This reduced crop production constitutes a major problem for food sustainability world-wide (Spiertz, 2013). Indeed, one of the major challenges for plant biotechnology will be to satisfy the increased demand for food on one hand, and to compensate for the loss of crop production on the other. Thus, the discovery of new plant genes that are able to cope with these conditions is critical and expected not only to elucidate the molecular mechanisms underlying crop abiotic stress, but also to pioneer genetic engineering strategies for improved crop productivity. The goal of this project was to identify novel genes belonging to the Major Facilitator Superfamily (MFS) of plant membrane transporters with potential major roles in conferring abiotic stress tolerance, namely to heavy metal, osmotic and iron deficiency stress. We selected three Arabidopsis thaliana MFS transporter genes, provisionally called MFS10, MFS11 and MFS12, which based on publicly available microarray data display specific expression patterns suggesting roles in plant tolerance to different abiotic stresses. RT-PCR analyses showed that in fact the MFS10 gene is highly induced by cadmium (Cd), selenium (Se), salt and mannitol, while the MFS11 gene is upregulated by abscisic acid (ABA) and glucose, and the MFS12 gene by iron (Fe) deficiency, ABA and glucose. Furthermore, subcellular localization of fluorescent reporter fusions indicated that the MFS10 and MFS11 gene products are both plasma membrane localized transporters, while the encoded product of the MFS12 gene appears to be an endoplasmic reticulum localized transporter. Finally, reverse genetics using a null mutant allele for the MFS10 gene demonstrated that it functions as a regulator of plant responses to hyperosmotic (drought and salt) stress.
Found in: ključnih besedah
Keywords: Major Facilitator Superfamily (MFS), abiotic stress tolerance, heavy metals, osmotic stress, ABA stress, iron deficiency, T-DNA insertion lines, RT-PCR, confocal microscopy.
Published: 03.05.2022; Views: 284; Downloads: 0
.pdf Fulltext (1,54 MB)

Optical response of plasmonic Bi2Se3 topological insulator nanoplatelets investigated by cathodoluminescence microscopy
Blaž Belec, Mattia Fanetti, 2022, published scientific conference contribution abstract

Found in: ključnih besedah
Keywords: microscopy, cathodoluminescence, topological insulator
Published: 02.06.2022; Views: 203; Downloads: 0
.pdf Fulltext (24,42 MB)

Evolution of fractal dimension in pulsed laser deposited MoO3 film with ablation time and annealing temperature
SWAPNA MOHANACHANDRAN NAIR SINDHU, 2021, original scientific article

Abstract: The multifractal analysis is a potential method for assessing thin flm surface morphology and its changes due to diferent deposition conditions and post-deposition treatments. In this work, the multifractal analysis is carried out to understand the surface morphology—root mean square (RMS) surface roughness—of nanostructured MoO3 flms prepared by pulsed laser deposition technique by varying the ablation time and post-deposition annealing. The XRD analysis shows the evolution of crystalline nature with annealing temperature. The XRD pattern of all the annealed flms shows the characteristic peak of the orthorhombic MoO3 phase. The FESEM and AFM analysis reveals the morphological modifcation with ablation time and annealing temperature. The multifractal analysis of the AFM images shows that the box—counting, information and correlation dimension varies with the annealing temperature. The study also reveals the inverse relation between the fractal dimension and the RMS surface roughness due to the annealing induced particle size variation and reorientation. The fractal dimension’s evolution in the pulsed laser deposited MoO3 flm with ablation time and annealing temperature is also investigated. Thus, the study reveals the potential of multifractal analysis in the thin flm surface characterizatio
Found in: ključnih besedah
Summary of found: ...deposition · Molybdenum oxide · Atomic force microscopy · Fractal dimension...
Keywords: Multifractal analysis · Pulsed laser deposition · Molybdenum oxide · Atomic force microscopy · Fractal dimension
Published: 04.07.2022; Views: 88; Downloads: 0
.pdf Fulltext (2,53 MB)

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