| 1. |
- Alm, Oscar, 1977-
(författare)
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Heterogeneous Photolytic Synthesis of Nanoparticles
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nanoparticles of iron, cobalt and tungsten oxide were synthesised by photolytic laser assisted chemical vapour deposition (LCVD). An excimer laser (operating at 193 nm) was used as an excitation source. The LCVD process, was monitored in situ by optical emission spectroscopy (OES). The synthesised particles were further analysed using transmission electron spectroscopy (TEM), X-ray diffraction (XRD), high resolution scanning electron microscopy (HRSEM), X-ray fluorescence spectroscopy (XRF), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy.Iron and cobalt single crystalline nanoparticles were synthesized using ferrocene and cobaltocene precursors. The diameter of the particles could be tailored by the experimental parameters (e.g., partial pressure and laser power) and were in the range 1 - 50 nm in diameter. In both cases, the particles were covered by a carbon shell, typically 7 nm thick. A thin graphitic layer was observed at the interface metal-carbon. Amorphous carbon was deposited on top of the graphitic carbon. Particle temperature, reaching the boiling point of the respective metal, was observed by OES of the thermal emission during the laser-induced particle formation process (and subsequent heating). Both bcc and fcc Fe phases were formed, both hcp and fcc for the Co phases. Size dependent magnetic properties were observed using superconducting quantum interference device (SQUID) measurements, where super-paramagnetic magnetic domains dominated for d < 10 nm. The iron particles were further processed, whereby the amorphous shell was removed by refluxing in nitric acid. In a subsequent step, the graphitic surface was functionalized by attaching an octyl ester, rendering the particles hydrophobic.Tungsten oxides were synthesized from combinations of WF6/H2/O2 as precursors. No particles could be deposited if H2 was removed from the gas-mixture. The as-deposited oxide nanoparticle film was amorphous. A monoclinic WO3 particle film could be achieved by annealing the amorphous oxide. Above 400°C, the oxide particles increased in size from ca. 20 nm to 60 nm through coalescence. The gas-sensing properties of the tungsten oxide were tested by conductance measurements using H2S as analyte. The sensitivity of the amorphous oxide nanoparticle film was found to be superior to that of a crystalline oxide nanoparticle film.
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| 2. |
- Alm, Oscar, et al.
(författare)
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Tungsten oxide nanoparticles synthesised by laser assisted homogeneous gas-phase nucleation
- 2005
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332. ; 247:1-4, s. 262-267
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Tidskriftsartikel (refereegranskat)abstract
- Tungsten oxide nanoparticles were generated by excimer (ArF) laser assisted chemical vapor deposition from WF6/H2/O2/Ar gas mixtures. The deposited particles were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. The deposition rate as a function of the partial pressures of the reactants and of the laser fluence was measured by X-ray fluorescence spectroscopy. The mean diameter of the deposited tungsten oxide particles varied with the experimental parameters and was typically 23 nm. Particles with a higher degree of crystallinity were observed at a laser fluence exceeding 130 mJ/cm2, and X-ray amorphous particles were obtained below 110 mJ/cm2. The amorphous tungsten oxide had a stoichiometry ranging from WO2.7 to WO3. Deposits were formed only when hydrogen was present in the gas mixture.
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| 3. |
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| 4. |
- Bryngelsson, Hanna, et al.
(författare)
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Electrodeposited Sb and Sb/Sb2O3 nanoparticle coatings as anode materials for Li-ion batteries
- 2007
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 19:5, s. 1170-1180
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Tidskriftsartikel (refereegranskat)abstract
- Galvanostatically electrodeposited coatings of pure Sb or co-deposited Sb and Sb2O3 nanoparticles, prepared from antimony tartrate solutions, were studied as anode materials in Li-ion batteries. It is demonstrated that the co-deposition of 20-25% (w/w) Sb2O3 results from a local pH increase at the cathode (due to protonation of liberated tartrate) in poorly buffered solutions. This causes precipitation of Sb2O3 nanoparticles and inclusion of some of the particles in the deposit where they become coated with a protecting layer of Sb. Chronopotentiometric cycling of the deposits, which also were characterized using, e.g., SEM, TEM, and XRD, clearly showed that the Sb2O3-containing deposits were superior as anode materials. While the Sb/Sb2O3 coatings exhibited a specific capacity close to the Sb theoretical value of 660 mA·h·g -1 during more than 50 cycles, the capacity for the Sb coatings gradually decreased to about 250 mA·h·g-1. This indicates that the influence of the significant volume changes present upon the formation and oxidation of Li3Sb was much smaller for the Sb/Sb2O3 nanoparticle coatings. The improved performance can be explained by significant formation of Sb2O3 during the reoxidation, the presence of smaller Sb particles in the Sb/Sb2O3 coatings, and the formation of buffering nanoparticles of Li2O in a matrix of Sb during the first reduction cycle for the Sb/Sb2O3 deposits.
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| 5. |
- Elihn, Karine, et al.
(författare)
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Size and structure of nanoparticles formed via ultraviolet photolysis of ferrocene
- 2007
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 101:3, s. 034311-
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Tidskriftsartikel (refereegranskat)abstract
- Iron nanoparticles enclosed in carbon shells were formed by laser-assisted chemical vapor decomposition of ferrocene (Fe(C5H5)2) vapor in Ar gas atmosphere. The particle size dependence on the total ambient gas pressure and on laser fluence of the pulsed ArF excimer laser was examined and, e.g., an effective size decrease of the iron core was observed at elevated laser fluences. Characterizations of the iron and carbon microstructures were performed by x-ray diffraction and transmission electron microscopy, while relative iron deposition rates were measured by x-ray fluorescence spectroscopy. Both -Fe and -Fe phases were found for the single crystalline iron cores, surrounded by graphitic (inner) and amorphous (outer) carbon layers. The temperature rise of the laser-excited particles was also determined by optical spectroscopy of the emitted thermal radiation, which allowed an estimation of the iron loss of the nanoparticles due to evaporation. The estimated and measured iron losses are in good agreement.
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| 6. |
- Grennberg, Helena, et al.
(författare)
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Functionalization and Area-Selective Deposition of Magnetic Carbon-Coated Iron Nanoparticles from Solution
- 2011
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Ingår i: Journal of Nanotechnology. - : Hindawi publishing. - 1687-9503 .- 1687-9511. ; , s. 342368-
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Tidskriftsartikel (refereegranskat)abstract
- A route to area-selective deposition of carbon-coated iron nanoparticles, involving chemical modification of the surface of the particles, is described. Partial oxidative etching of the coating introduces carboxylic groups, which then are esterified. The functionalized particles can be selectively deposited on the Si areas of Si/SiO2 substrates by a simple dipping procedure. Nanoparticles and nanoassemblies have been analyzed using SEM, TEM, and XPS.
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| 7. |
- Marking, Ulrika, et al.
(författare)
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Correlates of protection and viral load trajectories in omicron breakthrough infections in triple vaccinated healthcare workers
- 2023
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- Vaccination offers protection against severe COVID-19 caused by SARS-CoV-2 omicron but is less effective against infection. Characteristics such as serum antibody titer correlation to protection, viral abundance and clearance of omicron infection in vaccinated individuals are scarce. We present a 4-week twice-weekly SARS-CoV-2 qPCR screening in 368 triple vaccinated healthcare workers. Spike-specific IgG levels, neutralization titers and mucosal spike-specific IgA-levels were determined at study start and qPCR-positive participants were sampled repeatedly for two weeks. 81 (cumulative incidence 22%) BA.1, BA.1.1 and BA.2 infections were detected. High serum antibody titers are shown to be protective against infection (p < 0.01), linked to reduced viral load (p < 0.01) and time to viral clearance (p < 0.05). Pre-omicron SARS-CoV-2 infection is independently associated to increased protection against omicron, largely mediated by mucosal spike specific IgA responses (nested models lr test p = 0.02 and 0.008). Only 10% of infected participants remain asymptomatic through the course of their infection. We demonstrate that high levels of vaccine-induced spike-specific WT antibodies are linked to increased protection against infection and to reduced viral load if infected, and suggest that the additional protection offered by pre-omicron SARS-CoV-2 infection largely is mediated by mucosal spike-specific IgA.
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| 8. |
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| 9. |
- Mecea, Vasile Mihai, et al.
(författare)
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Out-of-plane vibrations of quartz resonators used in quartz crystal microbalance measurements in gas phase
- 2006
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Ingår i: Sensors and Actuators A. - : Elsevier BV. - 0924-4247. ; 125:2, s. 143-147
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Tidskriftsartikel (refereegranskat)abstract
- The article reveals that shear-mode quartz crystal resonators, currently used in quartz crystal microbalance (QCM) measurements, exhibit an out-of-plane vibration without being in contact with a liquid. Laser assisted CVD was used to deposit carbon-nanoparticles on the surface of a quartz resonator. The in-plane, shear vibration of the quartz resonator, produces a mega-gravity acceleration which induces a sedimentation of the carbon-nanoparticles, while the out-of-plane vibration produces a mega-gravity acceleration, normal to the crystal surface, which induces an expelling of the deposited carbon-nanoparticles. The two opposite effects reveal a complex situation on the quartz resonator surface in QCM measurements.
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| 10. |
- Mesaros-Hristea, Amalia, et al.
(författare)
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Luminescent thin films of nanocrystalline YTaO4 : Nb by pulsed laser deposition
- 2008
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 516:23, s. 8431-8435
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Tidskriftsartikel (refereegranskat)abstract
- Low dimensional nanostructures of YTaO4:Nb thin films were deposited on Si (100) substrate using pulsed laser deposition (lambda= 193 nm) at room temperature. X-ray Diffraction, Scanning Electron Microscopy and Transmission Electron Microscopy analysis revealed the nanocrystalline nature of YTaO4:Nb film consisting of grains of 20-40 nm in size. The photoluminescence spectra measured on the films confirmed the luminescence characteristics of YTaO4:Nb powders, the emission peak appeared shifted as compared to the luminescence spectrum of the bulk target. The spectral shift is about 15 nm and is correlated to the nanocrystalline nature of the film.
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