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Insights into the single-particle composition, size, mixing state, and aspect ratio of freshly emitted mineral dust from field measurements in the Moroccan Sahara using electron microscopy
Agnesh Panta, Konrad Kandler, Andrés Alastuey, Cristina González-Flórez, Adolfo Gonzalez-Romero, Martina Klose, Xavier Querol, Cristina Reche, Jesús Yus-Díez, Carlos Pérez García-Pando, 2023, original scientific article

Abstract: Abstract. The chemical and morphological properties of mineral dust aerosols emitted by wind erosion from arid and semi-arid regions influence climate, ocean, and land ecosystems; air quality; and multiple socio-economic sectors. However, there is an incomplete understanding of the emitted dust particle size distribution (PSD) in terms of its constituent minerals that typically result from the fragmentation of soil aggregates during wind erosion. The emitted dust PSD affects the duration of particle transport and thus each mineral's global distribution, along with its specific effect upon climate. This lack of understanding is largely due to the scarcity of relevant in situ measurements in dust sources. To advance our understanding of the physicochemical properties of the emitted dust PSD, we present insights into the elemental composition and morphology of individual dust particles collected during the FRontiers in dust minerAloGical coMposition and its Effects upoN climaTe (FRAGMENT) field campaign in the Moroccan Sahara in September 2019. We analyzed more than 300 000 freshly emitted individual particles by performing offline analysis in the laboratory using scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectrometry (EDX). Eight major particle-type classes were identified with clay minerals making up the majority of the analyzed particles both by number and mass, followed by quartz, whereas carbonates and feldspar contributed to a lesser extent. We provide an exhaustive analysis of the PSD and potential mixing state of different particle types, focusing largely on iron-rich (Fe oxide-hydroxides) and feldspar particles, which are key to the effects of dust upon radiation and clouds, respectively. Nearly pure or externally mixed Fe oxide-hydroxides are present mostly in diameters smaller than 2 µm, with the highest fraction below 1 µm at about 3.75 % abundance by mass. Fe oxide-hydroxides tend to be increasingly internally mixed with other minerals, especially clays, as particle size increases; i.e., the volume fraction of Fe oxide-hydroxides in aggregates decreases with particle size. Pure (externally mixed) feldspar represented 3.2 % of all the particles by mass, of which we estimated about a 10th to be K-feldspar. The externally mixed total feldspar and K-feldspar abundances are relatively invariant with particle size, in contrast to the increasing abundance of feldspar-like (internally mixed) aggregates with particle size with mass fractions ranging from 5 % to 18 %. We also found that overall the median aspect ratio is rather constant across particle size and mineral groups, although we obtain slightly higher aspect ratios for internally mixed particles. The detailed information on the composition of freshly emitted individual dust particles and quantitative analysis of their mixing state presented here can be used to constrain climate models including mineral species in their representation of the dust cycle.
Keywords: mineral dust, Moroccan Sahara, electron microscopy
Published in RUNG: 13.05.2024; Views: 292; Downloads: 3
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Recent progress and applications of thermal lens spectrometry and photothermal beam deflection techniques in environmental sensing
Mladen Franko, Leja Goljat, Mingqiang Liu, Hanna Budasheva, Mojca Žorž, Dorota Korte, 2023, original scientific article

Abstract: This paper presents recent development and applications of thermal lens microscopy (TLM) and beam deflection spectrometry (BDS) for the analysis of water samples and sea ice. Coupling of TLM detection to a microfluidic system for flow injection analysis (µFIA) enables the detection of microcystin-LR in waters with a four samples/min throughput (in triplicate injections) and provides an LOD of 0.08 µg/L which is 12-times lower than the MCL for microcystin-LR in water. µFIA-TLM was also applied for the determination of total Fe and Fe(II) in 3 µL samples of synthetic cloudwater. The LODs were found to be 100 nM for Fe(II) and 70 nM for total Fe. The application of µFIA-TLM for the determination of ammonium in water resulted in an LOD of 2.3 µM for injection of a 5 µL sample and TLM detection in a 100 µm deep microfluidic channel. For the determination of iron species in sea ice, the BDS was coupled to a diffusive gradient in the thin film technique (DGT). The 2D distribution of Fe(II) and total Fe on DGT gels provided by the BDS (LOD of 50 nM) reflected the distribution of Fe species in sea ice put in contact with DGT gels.
Keywords: thermal lens microscopy, beam deflection spectrometry, microfluidic system, microcystin-LR detection, iron species determination, ammonium detection
Published in RUNG: 03.01.2023; Views: 1531; Downloads: 24
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Evolution of fractal dimension in pulsed laser deposited MoO3 film with ablation time and annealing temperature
Mohanachandran Nair Sindhu Swapna, 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
Keywords: Multifractal analysis · Pulsed laser deposition · Molybdenum oxide · Atomic force microscopy · Fractal dimension
Published in RUNG: 04.07.2022; Views: 1393; Downloads: 0
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Optical response of plasmonic Bi2Se3 topological insulator nanoplatelets investigated by cathodoluminescence microscopy
Blaž Belec, Mattia Fanetti, 2022, published scientific conference contribution abstract

Keywords: microscopy, cathodoluminescence, topological insulator
Published in RUNG: 02.06.2022; Views: 1524; Downloads: 0
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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.
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 in RUNG: 03.05.2022; Views: 1551; Downloads: 0
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Structural, morphological and chemical properties of metal/topological insulator interfaces : dissertation
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.
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 in RUNG: 09.06.2021; Views: 4074; Downloads: 176
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