| 1. |
- Stehr, Jan Eric, 1981-, et al.
(författare)
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Evidence that fodipir (DPDP) binds neurotoxic Pt2+ with a high affinity : An electron paramagnetic resonance study
- 2019
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Oxaliplatin typically causes acute neuropathic problems, which may, in a dose-dependent manner, develop into a chronic form of chemotherapy-induced peripheral neuropathy (CIPN), which is associated with retention of Pt2+ in the dorsal root ganglion. A clinical study by Coriat and co-workers suggests that co-treatment with mangafodipir [Manganese(II) DiPyridoxyl DiPhosphate; MnDPDP] cures ongoing CIPN. These authors anticipated that it is the manganese superoxide dismutase mimetic activity of MnDPDP that explains its curative activity. However, this is questionable from a pharmacokinetic perspective. Another, but until recently undisclosed possibility is that Pt2+ outcompetes Mn2+/Ca2+/Zn2+ for binding to DPDP or its dephosphorylated metabolite PLED (diPyridoxyL EthylDiamine) and transforms toxic Pt2+ into a non-toxic complex, which can be readily excreted from the body. We have used electron paramagnetic resonance guided competition experiments between MnDPDP (10logKML ≈ 15) and K2PtCl4, and between MnDPDP and ZnCl2 (10logKML ≈ 19), respectively, in order to obtain an estimate the 10logKML of PtDPDP. Optical absorption spectroscopy revealed a unique absorption line at 255 nm for PtDPDP. The experimental data suggest that PtDPDP has a higher formation constant than that of ZnDPDP, i.e., higher than 19. The present results suggest that DPDP/PLED has a high enough affinity for Pt2+ acting as an efficacious drug in chronic Pt2+-associated CIPN.
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| 2. |
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Defects in Advanced Electronic Materials and Novel Low Dimensional Structures
- 2018. - 1
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Samlingsverk (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- Defects in Advanced Electronic Materials and Novel Low Dimensional Structures provides a comprehensive review on the recent progress in solving defect issues and deliberate defect engineering in novel material systems. It begins with an overview of point defects in ZnO and group-III nitrides, including irradiation-induced defects, and then look at defects in one and two-dimensional materials, including carbon nanotubes and graphene. Next, it examines the ways that defects can expand the potential applications of semiconductors, such as energy upconversion and quantum processing. The book concludes with a look at the latest advances in theory.While defect physics is extensively reviewed for conventional bulk semiconductors, the same is far from being true for novel material systems, such as low-dimensional 1D and 0D nanostructures and 2D monolayers. This book fills that necessary gap.
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| 3. |
- Gupta, G., et al.
(författare)
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Exploiting Mass Spectrometry to Unlock the Mechanism of Nanoparticle-Induced Inflammasome Activation
- 2023
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Ingår i: Acs Nano. - : AMER CHEMICAL SOC. - 1936-0851 .- 1936-086X. ; 17:17, s. 17451-17467
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Tidskriftsartikel (refereegranskat)abstract
- Nanoparticles (NPs) elicit sterile inflammation, but the underlying signaling pathways are poorly understood. Here, we report that human monocytes are particularly vulnerable to amorphous silica NPs, as evidenced by single-cell-based analysis of peripheral blood mononuclear cells using cytometry by time-of-flight (CyToF), while silane modification of the NPs mitigated their toxicity. Using human THP-1 cells as a model, we observed cellular internalization of silica NPs by nanoscale secondary ion mass spectrometry (nanoSIMS) and this was confirmed by transmission electron microscopy. Lipid droplet accumulation was also noted in the exposed cells. Furthermore, time-of-flight secondary ion mass spectrometry (ToF-SIMS) revealed specific changes in plasma membrane lipids, including phosphatidylcholine (PC) in silica NP-exposed cells, and subsequent studies suggested that lysophosphatidylcholine (LPC) acts as a cell autonomous signal for inflammasome activation in the absence of priming with a microbial ligand. Moreover, we found that silica NPs elicited NLRP3 inflammasome activation in monocytes, whereas cell death transpired through a non-apoptotic, lipid peroxidation-dependent mechanism. Together, these data further our understanding of the mechanism of sterile inflammation.
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| 4. |
- Jansson, Mattias, 1989-
(författare)
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Magnetooptical properties of dilute nitride nanowires
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nanostructured III-V semiconductors have emerged as one of the most promising materials systems for future optoelectronic applications. While planar III-V compounds are already at the center of the ongoing lighting revolution, where older light sources are replaced by modern white light LEDs, fabricating such materials in novel architectures, such as nanowires and quantum dots, creates new possibilities for optoelectronic applications. Not only do nanoscale structures allow the optically active III-V materials to be integrated with silicon microelectronics, but they also give rise to new fascinating properties inherent to the nanoscale.One of the key parameters considered when selecting materials for applications in light-emitting and photovoltaic devices is the band gap energy. While alloying of conventional III-V materials provides a certain degree of band gap tunability, a significantly enhanced possibility of band gap engineering is offered by so-called dilute nitrides, where incorporation of a small percentage of nitrogen into III-V compounds causes a dramatic down-shift of the conduction band edge. In addition, nitrogen-induced splitting of the conduction band in dilute nitrides can be utilized in intermediate band solar cells, belonging to the next generation of photovoltaic devices.For any material to be viable for optoelectronic applications, detailed knowledge of the electronic structure of the material, as well as a good understanding of carrier recombination processes is vital. For example, alloying may not only cause changes in the electronic structure but can also induce disorder. Disorder-induced potential fluctuations may alter charge carrier and exciton dynamics, and may even induce quantum confinement. Moreover, various defects in the material may introduce detrimental non-radiative (NR) states in the band gap deteriorating radiative efficiency. It is evident that, due to their different growth mechanisms, such properties could be markedly different in nanowires as compared to their planar counterparts. In this thesis, I aim to describe the electronic structure of dilute nitride nanowires, and its effects on the optical properties. Firstly, we investigate the electronic structure, and the structural and optical properties of novel GaNAsP nanowires, with a particular focus on the dominant recombination channels in the material. Secondly, we show how short-range fluctuations in the nitrogen content lead to the formation of quantum dots in dilute nitride nanowires, and investigate their electronic structure. Finally, we investigate the combined charge carrier and exciton dynamics of the quantum dots and effects of defects in their surroundings.Before considering individual sources of NR recombination, it is instructive to investigate the overall effects of nitrogen incorporation on the structural properties of the nanowires. In Paper I, we show that nitrogen incorporation up to 0.16\% in Ga(N)AsP nanowires does not affect the overall structural quality of the material, nor does nitrogen degrade the good compositional uniformity of the nanowires. It is evident from our studies, however, that nitrogen incorporation has a strong and complex effect on recombination processes. We first show that nitrogen incorporation in GaNAsP nanowires reduces the NR recombination at room temperature as compared to the nitrogen-free nanowires (Paper I). This is in stark contrast to dilute nitride epilayers, where nitrogen incorporation enhances NR recombination. The reason for this difference is that in nanowires the surface recombination, rather than recombination via point defects, is the dominant NR recombination mechanism. We suggest that the nitrogen-induced suppression of the NR surface recombination in the nanowires is due to nitridation of the nanowire surface.Another NR recombination channel common in III-V nanowires is caused by the presence of structural defects, such as rotational twin planes and stacking faults. Interestingly, while nitrogen incorporation does not appear to affect the density of such structural defects, increasing nitrogen incorporation reduces the NR recombination via the structural defects (Paper II). This is explained by competing trapping of excited carriers/excitons to the localized states characteristic to dilute nitrides, and at nitrogen-induced NR defects. This effect is, however, only present at cryogenic temperatures, while at room temperature the NR recombination via the structural defects is not the dominant recombination channel.Importance of point defects in carrier recombination is highlighted in Paper III. Using the optically detected magnetic resonance technique, we show that gallium vacancies (VGa) that are formed within the nanowire volume act as efficient NR recombination centers, degrading optical efficiency of the Ga(N)AsP-based nanowires. Interestingly, while the defect formation is promoted by nitrogen incorporation, it is also readily present in ternary GaAsP nanowires. This contrasts with previous studies on planar structures, where VGa was not formed in the absence of nitrogen, unless subjected to irradiation by high-energy particles or heavy n-type doping. This, again, highlights how the defect formation is strikingly different in nanowires as compared to planar structures, likely due to the different growth processes.Potential fluctuations in the conduction band, caused by non-uniformity of the nitrogen incorporation, is characteristic to dilute nitrides and is known to cause exciton/carrier localization. We find that in dilute nitride nanowires, such fluctuations at the short range cause three-dimensional quantum confinement of excitons, resulting in optically active quantum dots with spectrally ultranarrow and highly polarized emission lines (Paper IV). A careful investigation of such quantum dots reveals that their properties are strongly dependent on the host material (Papers V, VI). While the principal quantization axis of the quantum dots formed in the ternary GaNAs nanowires is preferably oriented along the nanowire axis (Paper V), it switches to the direction perpendicular to the nanowire axis in the quaternary GaNAsP nanowires (Paper VI). Another aspect illustrating the influence of the host material on the quantum-dot properties is the electronic character of the captured hole. In both alloys, we show coexistence of quantum dots where the captured holes are of either a pure heavy-hole character or a mixed light-hole and heavy-hole character. In the GaNAs quantum dots, the main cause of the light- and heavy-hole splitting is uniaxial tensile strain induced by a combination of lattice mismatch with the nanowire core and local alloy fluctuations (Paper V). In the GaNAsP quantum dots, however, we suggest that the main mechanism for the light- and heavy-hole splitting is local fluctuations in the P/As ratio (Paper VI).Using time correlation single-photon counting, we show that the quantum dots in these dilute nitride nanowires behave as single photon emitters (Paper VI), confirming the three-dimensional quantum confinement of the emitters. Finally, since the quantum dots are formed by fluctuations mainly in the conduction band, only electrons are preferentially captured in the 0D confinement potential, whereas holes are expected to be mainly localized through the Coulomb interaction once an electron is captured by the quantum dot. In Paper VII, we investigate this rather peculiar capture mechanism, which we show to lead to unipolar, negative charging of the quantum dot. Moreover, we demonstrate that carrier capture by some quantum dots is strongly affected by the presence of defects in their local surroundings, which further alters the charge state of the quantum dot, where formation of the negatively charged exciton is promoted at the expense of its neutral counterpart. This underlines that the local surroundings of the quantum dots may greatly affect their properties and illustrates a possible way to exploit the defects for charge engineering of the quantum dots.In summary, in this thesis work, we identify several important non-radiative recombination processes in dilute nitride nanowires that can undermine the potential of these novel nanostructures for future optoelectronic applications. The gained knowledge could be found useful for designing strategies to mitigate these harmful processes, thereby improving the efficiency of future light-emitting and photovoltaic devices based on these nanowires. Furthermore, we uncover a set of optically bright quantum dot single-photon emitters embedded in the dilute nitride nanowires, and reveal their unusual electronic structure with strikingly different confinement potentials between electrons and holes. Our findings open a new pathway for charge engineering of the quantum dots in nanowires, attractive for applications in e.g. quantum computation and optical switching.
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| 5. |
- Rudko, G.Yu, et al.
(författare)
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Optically detected magnetic resonance study of relaxation/emission processes in the nanoparticle-polymer composite
- 2019
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Ingår i: SPQEO. - Kiev, Ukraine : Natsional'na Akademiya Nauk Ukrainy * Instytut Fizyky Napivprovidnykiv. - 1605-6582. ; 22:3, s. 310-318
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Tidskriftsartikel (refereegranskat)abstract
- Two nanocomposites containing CdS nanoparticles in polymeric matrices were studied using the photoluminescence (PL) and optically detected magnetic resonance (ODMR) methods. Due to equal sizes of NPs in the composites (~5 nm) but different matrices – the oxygen-containing polymer PVA (polyvinyl alcohol) and oxygen-free polymer PEI (polyethyleneimine) – differences of nanocomposites properties are predominantly caused by different interfacial conditions. ODMR spectra have revealed five types of centers related to the PL emission – four centers involved in radiative recombination and one center related to non-radiative recombination processes. The oxygen-related interfacial center in CdS/PVA (LK1-center) and sulfur vacancy center in CdS/PEI (Vs-center) were identified.
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| 6. |
- Shakeri Yekta, Sepehr, 1982-, et al.
(författare)
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Pretreatment of anaerobic digester samples by hydrochloric acid for solution-state H-1 and C-13 NMR spectroscopic characterization of organic matter
- 2018
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Ingår i: Chemosphere. - : Elsevier. - 0045-6535 .- 1879-1298. ; 199, s. 201-209
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Tidskriftsartikel (refereegranskat)abstract
- Pretreatment of anaerobic digester samples by hydrochloric acid (HCl) resulted in removal of Fe-based mineral and coordination compounds, attenuating their interferences with solution-state nuclear magnetic resonance (NMR) spectroscopic characterization of the solid phase organic matter. Substrate (influent) and digestate (effluent) samples from two full-scale anaerobic digesters, designated CD (co-digester) and SSD (sewage sludge digester), were investigated. Pretreatment of CD samples with 0.2-2.0 mol l(-1) HCl and pretreatment of SSD samples with 1.0-3.0 mol l(-1) HCl removed 96-100% and 76-80% of total Fe, respectively. Pretreatment declined overall paramagnetic characteristics of digestate samples, manifested by 50% (CD) and 70% (SSD) decrease in electron paramagnetic resonance signal intensities. As a result, meaningful solution-state H-1,C-13 heteronuclear single quantum coherence and H-1 NMR spectra of DMSO-d(6) soluble organic matter could be acquired. Sample pretreatment with the lowest concentration of HCl resulted in alteration of C:N ratios in solid phase, likely due to removal of labile organic and inorganic C- and N-containing compounds, while elevating the HCl concentration did not further change the C:N ratios. Furthermore, sample pretreatment increased the solubility of carbohydrates and proteins in DMSO-d(6), enabling the detection of NMR resonances from certain structural units of carbohydrates (e.g. anomeric O2CH) and proteins (e.g. CH alpha in amino acids). Both attenuation of the paramagnetic matrix as well as art enhanced solubility of carbohydrate and protein fractions of the samples in DMSO-d(6) solvent contributed to an improved molecular characterization of anaerobic digester samples by solution-state NMR analysis.
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| 7. |
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| 8. |
- Stehr, Jan Eric, 1981-, et al.
(författare)
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Effects of growth temperature and thermal annealing on optical quality of GaNAs nanowires emitting in the near-infrared spectral range
- 2020
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Ingår i: Nanotechnology. - : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 31:6
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Tidskriftsartikel (refereegranskat)abstract
- We report on optimization of growth conditions of GaAs/GaNAs/GaAs core/shell/shell nanowire (NW) structures emitting at ~1 μm, aiming to increase their light emitting efficiency. A slight change in growth temperature is found to critically affect optical quality of the active GaNAs shell and is shown to result from suppressed formation of non-radiative recombination (NRR) centers under the optimum growth temperature. By employing the optically detected magnetic resonance spectroscopy, we identify gallium vacancies and gallium interstitials as being among the dominant NRR defects. The radiative efficiency of the NWs can be further improved by post-growth annealing at 680 °C, which removes the gallium interstitials.
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| 9. |
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| 10. |
- Stehr, Jan Eric, 1981-, et al.
(författare)
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Effects of N implantation on defect formation in ZnO nanowires
- 2019
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Ingår i: Thin Solid Films. - : ELSEVIER SCIENCE SA. - 0040-6090 .- 1879-2731. ; 687
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Tidskriftsartikel (refereegranskat)abstract
- One-dimensional ZnO nanowires are a promising material system for a wide range of optoelectronic and photonic applications. Utilization of ZnO, however, requires high-quality ZnO with reliable n-type and p-type conductivity, with the latter remaining elusive, so far. In this work we report on effects of N doping via ion implantation on defect formation in ZnO nanowires studied by optically detected paramagnetic resonance (ODMR) spectroscopy complemented by photoluminescence spectroscopy. After N implantation, zinc interstitial shallow donors, which are formed as a result of ion implantation, are observed in addition to effective mass type shallow donors. Additionally, ODMR signals related to oxygen vacancies can be observed. Implantation also causes formation of a new nitrogen related defect center, which acts as an acceptor. The present findings are of importance for understanding impacts of different defects and impurities on electronic properties of nanostructured ZnO and achieving p-type conductivity via nitrogen doping.
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