| 1. |
- Achterberg, A., et al.
(författare)
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Detection of atmospheric muon neutrinos with the IceCube 9-string detector
- 2007
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Ingår i: Physical Review D - Particles, Fields, Gravitation and Cosmology. - 1550-7998. ; 76:2, s. 027101-
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Tidskriftsartikel (refereegranskat)abstract
- The IceCube neutrino detector is a cubic kilometer TeV to PeV neutrino detector under construction at the geographic South Pole. The dominant population of neutrinos detected in IceCube is due to meson decay in cosmic-ray air showers. These atmospheric neutrinos are relatively well understood and serve as a calibration and verification tool for the new detector. In 2006, the detector was approximately 10% completed, and we report on data acquired from the detector in this configuration. We observe an atmospheric neutrino signal consistent with expectations, demonstrating that the IceCube detector is capable of identifying neutrino events. In the first 137.4 days of live time, 234 neutrino candidates were selected with an expectation of 211 +/- 76.1(syst)+/- 14.5(stat) events from atmospheric neutrinos.
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| 2. |
- Achterberg, A., et al.
(författare)
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Five years of searches for point sources of astrophysical neutrinos with the AMANDA-II neutrino telescope
- 2007
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Ingår i: Physical Review D. Particles, fields, gravitation, and cosmology. - 1550-7998. ; 75:10, s. 102001-
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Tidskriftsartikel (refereegranskat)abstract
- We report the results of a five-year survey of the northern sky to search for point sources of high energy neutrinos. The search was performed on the data collected with the AMANDA-II neutrino telescope in the years 2000 to 2004, with a live time of 1001 days. The sample of selected events consists of 4282 upward going muon tracks with high reconstruction quality and an energy larger than about 100 GeV. We found no indication of point sources of neutrinos and set 90% confidence level flux upper limits for an all-sky search and also for a catalog of 32 selected sources. For the all-sky search, our average (over declination and right ascension) experimentally observed upper limit Phi0=((E/(1 TeV)))gamma·((d Phi)/dE) to a point source flux of muon and tau neutrino (detected as muons arising from taus) is Phinu[sub mu] + [overline nu ][sub mu]0+Phinu[sub tau] + [overline nu ][sub tau]0=11.1× 10-11 TeV-1 cm-2 s-1, in the energy range between 1.6 TeV and 2.5 PeV for a flavor ratio Phinu[sub mu] + [overline nu ][sub mu]0/Phinu[sub tau] + [overline nu ][sub tau]0=1 and assuming a spectral index gamma=2. It should be noticed that this is the first time we set upper limits to the flux of muon and tau neutrinos. In previous papers we provided muon neutrino upper limits only neglecting the sensitivity to a signal from tau neutrinos, which improves the limits by 10% to 16%. The value of the average upper limit presented in this work corresponds to twice the limit on the muon neutrino flux Phinu[sub mu] + [overline nu ][sub mu]0=5.5×10-11 TeV-1 cm-2 s-1. A stacking analysis for preselected active galactic nuclei and a search based on the angular separation of the events were also performed. We report the most stringent flux upper limits to date, including the results of a detailed assessment of systematic uncertainties.
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| 3. |
- Achterberg, A., et al.
(författare)
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Multiyear search for a diffuse flux of muon neutrinos with AMANDA-II
- 2007
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Ingår i: Physical Review D - Particles, Fields, Gravitation and Cosmology. - 1550-7998. ; 76:4, s. 042008-
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Tidskriftsartikel (refereegranskat)abstract
- A search for TeV-PeV muon neutrinos from unresolved sources was performed on AMANDA-II data collected between 2000 and 2003 with an equivalent live time of 807 days. This diffuse analysis sought to find an extraterrestrial neutrino flux from sources with nonthermal components. The signal is expected to have a harder spectrum than the atmospheric muon and neutrino backgrounds. Since no excess of events was seen in the data over the expected background, an upper limit of E-2 Phi(90%C.L.)< 7.4x10(-8) GeV cm(-2) s(-1) sr(-1) is placed on the diffuse flux of muon neutrinos with a Phi proportional to E-2 spectrum in the energy range 16 TeV to 2.5 PeV. This is currently the most sensitive Phi proportional to E-2 diffuse astrophysical neutrino limit. We also set upper limits for astrophysical and prompt neutrino models, all of which have spectra different from Phi proportional to E-2.
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| 4. |
- Achterberg, A., et al.
(författare)
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Search for neutrino-induced cascades from gamma-ray bursts with AMANDA
- 2007
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 664:1, s. 397-410
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Tidskriftsartikel (refereegranskat)abstract
- Using the neutrino telescope AMANDA-II, we have conducted two analyses searching for neutrino-induced cascades from gamma-ray bursts. No evidence of astrophysical neutrinos was found, and limits are presented for several models. We also present neutrino effective areas which allow the calculation of limits for any neutrino production model. The first analysis looked for a statistical excess of events within a sliding window of 1 or 100 s (for short and long burst classes, respectively) during the years 2001-2003. The resulting upper limit on the diffuse flux normalization times E2 for the Waxman-Bahcall model at 1 PeV is 1.6×10-6 GeV cm-2 s-1 sr-1 (a factor of 120 above the theoretical prediction). For this search 90% of the neutrinos would fall in the energy range 50 TeV to 7 PeV. The second analysis looked for neutrino-induced cascades in coincidence with 73 bursts detected by BATSE in the year 2000. The resulting upper limit on the diffuse flux normalization times E2, also at 1 PeV, is 1.5×10-6 GeV cm-2 s-1 sr-1 (a factor of 110 above the theoretical prediction) for the same energy range. The neutrino-induced cascade channel is complementary to the up-going muon channel. We comment on its advantages for searches of neutrinos from GRBs and its future use with IceCube.
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| 5. |
- Aevarsson, Arnthór, et al.
(författare)
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Going to extremes - a metagenomic journey into the dark matter of life
- 2021
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Ingår i: FEMS Microbiology Letters. - : Oxford University Press (OUP). - 1574-6968. ; 368:12
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Forskningsöversikt (refereegranskat)abstract
- The Virus-X-Viral Metagenomics for Innovation Value-project was a scientific expedition to explore and exploit uncharted territory of genetic diversity in extreme natural environments such as geothermal hot springs and deep-sea ocean ecosystems. Specifically, the project was set to analyse and exploit viral metagenomes with the ultimate goal of developing new gene products with high innovation value for applications in biotechnology, pharmaceutical, medical, and the life science sectors. Viral gene pool analysis is also essential to obtain fundamental insight into ecosystem dynamics and to investigate how viruses influence the evolution of microbes and multicellular organisms. The Virus-X Consortium, established in 2016, included experts from eight European countries. The unique approach based on high throughput bioinformatics technologies combined with structural and functional studies resulted in the development of a biodiscovery pipeline of significant capacity and scale. The activities within the Virus-X consortium cover the entire range from bioprospecting and methods development in bioinformatics to protein production and characterisation, with the final goal of translating our results into new products for the bioeconomy. The significant impact the consortium made in all of these areas was possible due to the successful cooperation between expert teams that worked together to solve a complex scientific problem using state-of-the-art technologies as well as developing novel tools to explore the virosphere, widely considered as the last great frontier of life.
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| 6. |
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| 7. |
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| 8. |
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| 9. |
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| 10. |
- Fors, Rickard, et al.
(författare)
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Comparison of Sol-Gel Derived and Pulsed Laser Deposited Epitaxial La0.67Ca0.33MnO3 Films for IR Bolometer
- 2004
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Ingår i: Mat. Res. Soc. Symp. Proc.. - : Springer Science and Business Media LLC. ; 811, s. E2.5.1-E2.5.6, s. 379-384
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial La0.67Ca0.33MnO3 films have been prepared on LaA1O3 crystals by pulsed laser deposition (PLD) and by a novel all-alkoxide sol-gel technique. Different out-of-plane lattice parameters are found for the as-prepared films, and scanning electron microscopy shows a more porous structure for sol-gel films as compared to PLD films. These differences are largely removed by post-annealing at 1000 °C. Transport measurements show maximum temperature coefficient of resistivity of 8.2 % K-1 at 258 K (PLD) and 6.1 % K-1 at 241 K (sol-gel) and :colossal magnetoresistance at 7 kOe of 35 % at 263 K (PLD) and 32 % at 246 K (sol-gel).
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| 11. |
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| 12. |
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| 13. |
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| 14. |
- Knut, Ronny, et al.
(författare)
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Photoinduced reduction of surface states in Fe:ZnO
- 2015
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 142:20
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Tidskriftsartikel (refereegranskat)abstract
- We report on the electronic structure of nano-crystalline Fe:ZnO, which has recently been found to be an efficient photocatalyst. Using resonant photoemission spectroscopy, we determine the binding energy of Fe 3d states corresponding to different valencies and coordination of the Fe atoms. The photo-activity of ZnO reduces Fe from 3+ to 2+ in the surface region of the nano-crystalline material due to the formation of oxygen vacancies. Electronic states corresponding to low-spin Fe2+ are observed and attributed to crystal field modification at the surface. These states are potentially important for the photocatalytic sensitivity to visible light due to their location deep in the ZnO bandgap. X-ray absorption and x-ray photoemission spectroscopy suggest that Fe is only homogeneously distributed for concentrations up to 3%. Increased concentrations does not result in a higher concentration of Fe ions in the surface region. This is limiting the photocatalytic functionality of ZnO, where the most efficient Fe doping concentration has been shown to be 1%-4%.
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| 15. |
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| 16. |
- Lagerqvist, Ulrika, et al.
(författare)
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Morphology effects on exchange anisotropy in Co-CoO nanocomposite films
- 2015
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 576, s. 11-18
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Tidskriftsartikel (refereegranskat)abstract
- Co-CoO composite films were prepared by solution chemical technique using amine-modified nitrates and acetates in methanol. We study how particle size and porosity can be tuned through the synthesis parameters and how this influences the magnetic properties. Phase content and microstructure were characterised with grazing incidence X-ray diffraction and electron microscopy, and the magnetic properties were studied by magnetometry and magnetic force microscopy. Composite films were obtained by heating spin-coated films in Ar followed by oxidation in air at room temperature, and the porosity and particle size of the films were controlled by gas flow and heating rate. The synthesis yielded dense films with a random distribution of metal and oxide nanoparticles, and layered films with porosity and sintered primary particles. Exchange anisotropy, revealed as a shift towards negative fields of the magnetic hysteresis curve, was found in all films. The films with a random distribution of metal and oxide nanoparticles displayed a significantly larger coercivity and exchange anisotropy field compared to the films with a layered structure, whereas the layered films displayed a larger nominal saturation magnetisation. The magnitude of the coercivity decreased with increasing Co grain size, whereas increased porosity caused an increased tilt of the magnetic hysteresis curve. (C) 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license
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| 17. |
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| 18. |
- Lagerqvist, Ulrika, 1980-
(författare)
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Solution-Chemical Synthesis of Cobalt and Iron:Zinc Oxide Nanocomposite Films
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The potentially most important challenges today are related to energy and the environment. New materials and methods are needed in order to, in a sustainable way, convert and store energy, reduce pollution, and clean the air and water from contaminations. In this, nanomaterials and nanocomposites play a key role, and hence knowledge about the relation between synthesis, structure, and properties of nanosystems is paramount.This thesis demonstrates that solution-chemical synthesis, using amine-modified acetates and nitrates, can be used to prepare widely different nanostructured films. By adjusting the synthesis parameters, metals, oxides, and metal–oxide or oxide–oxide nanocomposites were prepared for two systems based on Co and Zn:Fe, respectively, and the films were characterised using diffraction, spectroscopy, and microscopy techniques, and SQUID magnetometry.A variety of crystalline cobalt films—Co metal, CoO, Co3O4, and composites with different metal:oxide ratios—were synthesised. Heat-treatment parameters and control of the film thickness enabled tuning of the phase ratios. Random and layered Co–CoO composites were prepared by utilising different heating rates and gas flow rates together with a morphology effect associated with the furnace tube. The Co–CoO films exhibited exchange bias due to the ferromagnetic–antiferromagnetic interaction between the Co and CoO, whereas variations in e.g. coercivity and exchange bias field were attributed to differences in the structure and phase distribution.Ordered structures of wurtzite ZnO surrounded by amorphous ZnxFeyO were prepared through controlled phase segregation during the heating, which after multiple coating and heating cycles yielded ZnO–ZnxFeyO superlattices. The amorphous ZnxFeyO was a prerequisite for superlattice formation, and it profoundly affected the ZnO phase, inhibiting grain growth and texture, already from 1% Fe. In addition, ZnO–ZnxFeyO exhibited a photocatalytic activity for the oxidation of water that was higher than results reported for pure ZnO, and comparable to recent results reported for graphene-modified ZnO.
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| 19. |
- Lagerqvist, Ulrika, et al.
(författare)
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Synthesis and characterization of cobalt oxide and composite thin films
- 2014
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Ingår i: Advances in Materials. - : Science Publishing Group. - 2327-2503. ; 3:5, s. 52-57
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Tidskriftsartikel (refereegranskat)abstract
- Cobalt oxide and composite thin films were synthesized by spin-coating technique, followed by heating to 500°C in oxidizing, inert, or reducing atmospheres. Methanolic solutions of triethanolamine complexes of cobalt acetates and nitrates were spin-coated at 1000, 2000, and 3000 rpm. The influence of heating parameters and film thickness on the phase content of the films were investigated, using grazing incidence X-ray diffraction, X-ray reflectivity, and scanning electron microscopy. By tuning the synthesis parameters, Co3O4, CoO and Co films were obtained, as well as CoO-Co and Co3O4-CoO composite films of varying phase ratios.
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| 20. |
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| 21. |
- Lenz, Annika, et al.
(författare)
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Computational study of the catalytic effect of platinum on the decomposition of DNT
- 2012
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Ingår i: International Journal of Quantum Chemistry. - : Wiley-Blackwell. - 0020-7608 .- 1097-461X. ; 112:7, s. 1852-1858
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Tidskriftsartikel (refereegranskat)abstract
- The catalytic decomposition of dinitrotoluene (DNT; 3-4-DNT), a by-product of the explosive trinitrotoluene (trotyl), on a platinum surface is investigated computationally. Reaction paths have been computed for a DNT molecule interacting with a Pt-cluster under varying temperatures using quantum-chemical density functional theory. Two possible initiation steps where DNT split either into nitro-tolyl and NO2, or in nitro-tolyl-oxidanyl and NO, are considered. The energy barrier for the catalytic process is found to decrease significantly for the Pt catalyzed reaction compared with the uncatalyzed reaction.
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| 22. |
- Lenz, Annika, et al.
(författare)
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The electronic structure and reflectivity of PEDOT:PSS from density functional theory
- 2011
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Ingår i: Chemical Physics. - : Elsevier Science B.V., Amsterdam.. - 0301-0104 .- 1873-4421. ; 384:03-jan, s. 44-51
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Tidskriftsartikel (refereegranskat)abstract
- The geometric and electronic structure of condensed phase organic conducting polymer PEDOT:PSS blends has been investigated by periodic density functional theory (DFT) calculations with a generalized-gradient approximation (GGA) functional, and a plane wave basis set. The influence of the degree of doping of the PEDOT polymer on structural and optical parameters such as the reflectivity, absorbance, conductivity, dielectric function, refractive index and the energy-loss function is studied. A flip from the benzoid to the quinoid structure is observed in the calculations when the neutral PEDOT is doped by negatively charged PSS. Also the optical properties are affected by the doping. In particular, the reflectivity was found to be very sensitive to the degree of doping, where higher doping implies higher reflectivity. The reflectivity is highly anisotropic, with the dominant contribution stemming from the direction parallel to the PEDOT polymer chain.
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| 23. |
- Pohl, Annika, et al.
(författare)
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Alkoxide Based Sol-Gel Processing of CMR Manganites
- 2005
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Ingår i: Materials Research Society Vol. 848.
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Konferensbidrag (refereegranskat)abstract
- We have prepared a soluble manganese alkoxide, and used in the first all-alkoxide synthesis of Ca, Sr, and Ba substituted lanthanum manganites. The phase development from gel to target oxide was monitored by TGA, DSC, powder-XRD, FT¨CIR spectroscopy, and TEM-EDS. Here we present the effect of dopant on the phase development. It was found that the dopants influence the temperature of complete oxide formation (¡Ý650¡ãC). The main difference in phase evolution was seen in the 300-600¡ãC range, where the formation of crystalline phases in trace quantities seemed to temporarily reduce the elemental homogeneity.
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| 24. |
- Pohl, Annika, et al.
(författare)
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Alkoxide Route to La0.5Sr0.5CoO3 Films and Powders
- 2005
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Ingår i: Journal of the American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 88:8, s. 2099-2105
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Tidskriftsartikel (refereegranskat)abstract
- An all-alkoxide route to films and nano-phase powders of the La0.5Sr0.5CoO3 perovskite is described. To our knowledge, this is the first purely alkoxide-based route to (La1xSrx)CoO3, and it yields phase-pure and elementally homogeneous perovskite at 700°C by heating at 2°C/min. At 700°C, a cubic unit cell was obtained with ac=3.853Å, and after further heating to 1000°C, a rhombohedral cell could be indexed: ar=5.417 Å, r=59.94°. Ninety to 130 nm thick films of La0.5Sr0.5CoO3 were obtained by spin coating. The gel-to-oxide conversion was studied in some detail, using thermo-gravimetric analysis, differential scanning calorimetry, powder X-ray diffraction, IR spectroscopy, and transmission electron microscope equipped with an energy-dispersive X-ray spectrometer.
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| 25. |
- Pohl, Annika, et al.
(författare)
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Body mass index influences plasma concentration of neuropeptide Y in healthy female volunteers : A pilot study
- 2003
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Ingår i: Gynecological Endocrinology. - : Informa UK Limited. - 0951-3590 .- 1473-0766. ; 17:5, s. 409-412
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Tidskriftsartikel (refereegranskat)abstract
- Neuropeptide Y (NPY) was measured in plasma obtained from healthy female volunteers twice in the natural menstrual cycle or the hormonal cycle caused by oral contraceptives about 2 weeks apart. The ratio between the NPY plasma concentration in the second sample and the first sample was influenced negatively by body mass index (BMI). There were no differences in NPY plasma concentrations on comparing the first and second samples. Age and the use or non-use of oral contraceptives did not exert any influence. BMI might be a confounding factor when determining NPY in the plasma of healthy women.
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| 26. |
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| 27. |
- Pohl, Annika, et al.
(författare)
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Porous and dense perovskite films
- 2007
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Ingår i: Nanostructured Materials and Nanotechnology, Vol 28. ; , s. 153-163
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Konferensbidrag (refereegranskat)abstract
- Lao.5Sro.5Co03 (LSCO) and La0.67Ca0.33MnO3 (LCMO) films were prepared by sol-gel techniques and their structural and transport properties investigated. Films were spin-coated onto (001) LaAlO3 (LAO), (001) SrTiO3 (STO), Pt/TiO2/SiO2/Si, and Al2O3 substrates, and ictural properties were investigated using X-ray diffraction, scanning and transmission electron microscopy (SEM and TEM). SEM studies showed that the films were crack-free and adhered well to the substrates. No preferential orientation of the pervoskite films was observed on Si- or Pt/TiCVSiCVSi-substrates, but films deposited on LAO and STO showed good alignment with the substrate. Transport measurements of epitaxial LCMO films show maximum temperature coefficient of resisth (TCR) of 6.1 % K1 aät 241 K and colossal magnetoresistance (CMR) of 32 % a at 246 K. The conductivity of around l .9 mQcm.
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| 28. |
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| 29. |
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| 30. |
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| 31. |
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| 32. |
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| 33. |
- Pohl, Annika, et al.
(författare)
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Sol-gel derived Nd1/3La1/3Ca1/3MnO3 : Phase evolution and preparation of films and nanopowders
- 2007
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Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 22:6, s. 1737-1743
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Tidskriftsartikel (refereegranskat)abstract
- An all-alkoxide sol-gel route to the formation of Nd1/3La1/3Ca1/3MnO3 thin films and powders has been developed. The microstructural evolution on heat treatment of the gel to yield the perovskite oxide was monitored by means of thermogravimetric analysis-differential scanning calorimetry, powder x-ray diffraction (XRD), Fourier transform infrared spectroscopy, and transmission electron microscopy (TEM)-energy dispersive spectroscopy (EDS). It was found that the amorphous gel consists of hydrated oxo-carbonate without organic residues, and on heating it decomposes in several steps, finally forming single-phase perovskite at 680 degrees C. Further heating results in only slight changes in the cell parameters and crystal growth. Films were prepared by spin coating, followed by heat treatment in air to a temperature of 800 degrees C, and studied by scanning electron microscopy, TEM-EDS, and XRD. Films on Al2O3 were more porous, while films on Pt-TiO2-SiO2-Si were rather dense and consisted of areas with different crystal orientations.
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| 34. |
- Pohl, Annika, 1972-
(författare)
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Sol−Gel Synthesis of CMR Manganites
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The development of more advanced materials forms the basis of technological progress. One group of fascinating compounds with many potential applications in spintronic devices are the mixed-valence perovskite manganites. These have attracted considerable interest during the last decade through their very large magnetoresistance near the Curie Temperature. Although the properties of a material determinie any application, the development of reliable and flexible synthesis methods is crucial, as is the understanding of these methods. Knowledge of how different materials are formed is also of general importance in tailoring new materials. The aim of this project has therefore been not only to develop a new synthesis route, but also to understand the mechanisms involved.This thesis describes the synthesis and characterization of a novel manganese alkoxide and its use in sol–gel processing of magnetoresistive perovskite manganites. In searching for a soluble manganese alkoxide for sol–gel processing, we found that the methoxy-ethoxide, [Mn19O12(moe)14(moeH)10]·moeH, has a high solubility in appropriate organic solvents. Being 1.65 nm across, it is one of the largest alkoxides reported; it is also of interest because of its (for oxo-alkoxides) rare planar structure. After mixing with La, Nd, Ca, Sr, and Ba methoxy-ethoxides, [Mn19O12(moe)14(moeH)10]·moeH was used in the first purely alkoxide based sol–gel processing of perovskites manganites. The phase evolution on heating xerogel powders to 1000°C was studied, and thin films were prepared by spin-coating.It was found that the easily oxidised Mn-alkoxide facilitates the formation of high oxygen-excess modifications of the perovskites. The reactive precursor system yields fully hydrolysed gels almost without organic residues, but the gel absorbs CO2 from the air, leading to carbonate formation. The carbonate decomposition is the limiting step in oxide formation. Transport measurements of La0.67Ca0.33MnO3 films on LaAlO3 substrate show that all-alkoxide sol–gel derived films can compete with PLD films in terms of quality of epitaxy and transport. The somewhat different behaviour of the sol–gel derived films compared to PLD films is attributed to differences in morphology and oxygen stoichiometry.
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| 35. |
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| 36. |
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| 37. |
- Westin, Gunnar, et al.
(författare)
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Alkoxide route to La0.5Sr0.5CoO3 epitaxial thin films on SrTiO3
- 2008
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 516:15, s. 4673-4678
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Tidskriftsartikel (refereegranskat)abstract
- An all alkoxide based sol–gel route was investigated for preparation of epitaxial La0.5Sr0.5CoO3 (LSCO) films on 100 SrTiO3 (STO) substrates. Films with 20–30 to 80–100 nm thickness were prepared by spin-coating 0.2–0.6 M (metal) solutions on the STO substrates and heat treatment to 800 °C at 2 °C min− 1, 30 min, in air. The films were epitaxial with a cube-on-cube alignment and the LSCO cell was strained to match the STO substrate of 3.905 Å closely; a and b = 3.894 Å and 3.897 Å for the 20–30 and 80–100 nm films, respectively. The c-axis was compressed to 3.789 Å and 3.782 Å for the 20–30 and 80–100 nm films, respectively, which resulted in an almost unchanged cell volume as compared to polycrystalline film and nano-phase powders prepared in the same way. The SEM study showed mainly very smooth, featureless surfaces, but also some defects. A film prepared in the same way on an -Al2O3 substrate was dense and polycrystalline with crystallite sizes in the range 10–50 nm and gave cubic cell dimensions of ac = 3.825 Å. The conductivity of the ca 30–40 nm thick polycrystalline film was 1.7 mΩcm, while the epitaxial 80–100 nm film had a conductivity of around 1.9 mΩcm.
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| 38. |
- Westin, Gunnar, et al.
(författare)
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All alkoxide route to manganate and coboltate perovskite films and powders : effects of processing parameters
- 2008
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Ingår i: Journal of Sol-Gel Science and Technology. - : Springer. - 0928-0707 .- 1573-4846. ; 48:1-2, s. 194-202
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Tidskriftsartikel (refereegranskat)abstract
- Manganate and cobaltate perovskites having the general formula ABO3 have many technologically important applications. Here we present all alkoxide based routes to manganate and coboltate perovskite films and nano-phase powders of the compositions; LCMO (La0.67Ca0.33MnO3), LSMO (La0.75Sr0.25MnO3), LNCMO (La0.33Nd0.33Ca0.33MnO3), LBSMO (La0.75Ba0.125Sr0.125MnO3) and LSCO (La0.50Sr0.50CoO3). The Mn and Co (oxo) methoxy-ethoxide precursors were prepared by reaction of MnCl2 or CoCl2 with 2 Kmoe in methoxy-ethanol-toluene. After hydrolysis of the alkoxide solutions by atmospheric air all systems produced X-ray and electron diffraction amorphous gels of high elemental homogeneity, and the IR spectra showed that they consisted of hydrated oxo-carbonates. Heating in air resulted in similar weight-loss curves for all studied gels passing; loss of H2O in the range 20–300 °C, decomposition of carbonate groups into oxide and CO2 in the temperature range 300–700 °C, and in some cases loss of a small amount of oxygen in the temperature range 700–1,000 °C. The pure perovskites were obtained at 690–770 °C with heat rates of typically 5–20 °C min−1 without annealing. Perovskites could also be obtained at 550 °C by annealing, but these perovskites are prone to be A-site ion inhomogeneous according to the TEM EDS studies, which was not the case for the perovskites heat-treated to at least the carbonate decomposition temperature. This A-site inhomogeneity is ascribed to sequential decomposition of carbonates due to their different thermal stabilities, which is probably a general feature also with other sol–gel precursors and low temperature annealing. High quality polycrystalline films were prepared on Si/SiO2/TiO2/Pt substrates with all compositions and high quality epitaxial films were prepared of LCMO (on 100 LaAlO3) and LSCO (on 100 SrTiO3). The colossal magneto resistance (CMR) of the epitaxial LCMO films of 32% (246 K) is in parity with PLD derived films. The conductivities of the epitaxial and polycrystalline LSCO films were 1.9 mΩcm (on STO) and 1.7 mΩcm (on α-Al2O3, respectively).
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| 39. |
- Westin, Gunnar, et al.
(författare)
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All Alkoxide Sol-Gel Route to CoO-TiO2 Nano-Powders
- 2004
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Ingår i: Journal of Sol-Gel Science and Technology. ; :31, s. 25-29
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Tidskriftsartikel (refereegranskat)abstract
- CoO-TiO2 anatase materials have become highly interesting after the discovery of ferromagnetism above room-temperature, which makes them promising candidates for spintronic devices. There is however still uncertainty, and even contradictory ideas on the origin of the ferromagnetism and detailed microstructures ofthese materials. Here the synthesis and studies of CoO-doped TiO2 nano-phase powders with 0-12 mol% CoO using Co-methoxy-ethoxide and Ti(OPri)4 as precursors is presented. The amorphous precipitates or gels obtained by: (1) air hydrolysis and (2) quench hydrolysis with excess of water were amorphous and completely homogeneous in their Co:Ti ratio. Infrared (IR) spectroscopic and thermo-gravimetric (TG) studies showed that the air-hydrolysed samples Containrd a small amount of methoxy-ethoxide groups, besides coordinated water, while the quench-hydrolysed samples contained large amounts of coordinated water and lacked organic groups. According to the X-ray diffraction (XRD) patterns, the air-hydrolysed samples heated to 600°C contained both anatase and rutile. The rutile formationis ascribed to influence from the residual organic groups. The quench-hydrolysed precipitates yielded phase pure anatase at 480 and 600°C for the 0-6.7 mol% CoO range. At CoO contents of 8-12 mol%, the XRD i studies showed that anatase was obtained at 600°C, but in the 12% case, CoTiO3 was also detected. In addition, the 8-12 mol% samples showed two peaks in the Raman spectrum that might be due to CoO dissolved in anatase at high concentration. The studies were performed with TGA, IR and Raman-spectroscopy, XRD, scanning and transmission electron-microscopes (SEM and TEM, respectively) equipped with energy-dispersive X-ray spectrometers (EDS).
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| 44. |
- Westin, Gunnar, et al.
(författare)
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Direct processing of porous nano-structured ZnO-CoOx films
- 2007
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 515:20-21, s. 7751-7757
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Tidskriftsartikel (refereegranskat)abstract
- Highly porous nano-structured films and powders of ZnO:Co (0–5 metal% Co) or ZnO:Co and (Zn,Co)3O4 (10–35% Co) particles were obtained by deposition of mixed Zn- and Co-methoxy-ethoxide precursors on spinning or non-spinning substrates, and heating to 600 °C. The Co- and Zn-methoxy-ethoxide solutions were prepared by metathesis of CoCl2 and potassium methoxy-ethoxide, and reaction of diethylzinc and methoxy-ethanol, respectively. Compositions in the range 0–35% Co were investigated by IR spectroscopy, scanning electron microscopy, transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and X-ray diffraction. The gels obtained consisted of hydrated amorphous oxo-carbonates and were of good elemental homogeneity in the TEM. Thermogravimetric analysis showed that all residual groups had been removed at 550–600 °C, 5 °C min− 1. The materials heated to 600 °C contained ZnO of the hexagonal modification with cell-edges in close agreement with un-doped ZnO regardless of composition and temperature. TEM-EDS studies showed that the ZnO:Co and (Zn,Co)3O4 spinel particles were well mixed, of similar shape and size, ca 10–25 nm. Heating of the 10% Co sample to 800 °C decomposed the spinel phase and left Co-doped ZnO.
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| 45. |
- Westin, Gunnar, et al.
(författare)
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Preparation and Studies of ZnO:Al Films and Powders
- 2004
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Ingår i: Journal of Sol-Gel Science and Technology. ; 31, s. 283-286
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Tidskriftsartikel (refereegranskat)abstract
- ZnO:Al (0–10 at% Al) films and powders were produced using acac-modified methoxy-ethoxide precursors, obtained from Zn(C2H5)2 and Al4(OPri)12. The conversion to oxide powders was monitored with TGA and DSC, and the phase development was investigated with XRD, FT-IR spectroscopy, and TEM-EDS. The gels obtained by air-hydrolysis contained ca 0.5 acac/(Zn + Al) and a small amount of water and hydroxyls. All residual groups were removed to yield ZnO:Al by heating to ca 400°C. The powders obtained at 400 and 500°C were elementally homogeneous, and consisted of hex-ZnO:Al as ca 3–5 (10 at% Al) or 20–30 (3 at% Al) nm sized crystalline particles. Spin-coating on quartz, Si/SiO2, and window glass, followed by heating to 500°C resulted in 150–200 nm thick films of hex-ZnO:Al. 500 nm thick films were obtained by repeating the deposition and heat-treatment twice. The films were visually very clear and the measured transmittance high over the 400–800 nm range (91–93% at 800 nm) for ca 300 nm thick films.
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| 47. |
- Westin, Gunnar, et al.
(författare)
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Solution processing of conducting dense and porous films; doped ZnO and TiO2, and perovskites
- 2009
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Ingår i: International Journal of Nanotechnology. ; 6:9, s. 828-849
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Tidskriftsartikel (refereegranskat)abstract
- Soln. based processing of porous and dense films by all-alkoxide based precursor systems have been investigated and compared, with a focus on the connection between the precursors and heat-treatment, and the product oxide quality and structure. Three systems were investigated typically with TGA, DSC, XPS, IR spectroscopy, X-ray diffraction, TEM-EDS and SEM-EDS, but also with other advanced characterization techniques: (i) manganate and cobaltate perovskites of the LCMO (La0.67Ca0.33MnO3), LSMO (La0.75Sr0.25MnO3), LNCMO (La0.33Nd0.33Ca0.33MnO3), LBSM (La0.75Ba0.125Sr0.125MnO3) and LSCO (La0.50Sr0.50CoO3) compns. were investigated. Highly epitaxial films of LCMO and LSCO were prepd., and the CMR properties of the LCMO were comparable to those of PVD derived films. Polycryst. films were prepd. for all perovskites. (ii) Three routes to ZnO : Co/Al were investigated and compared; an acetate based route and two alkoxide based routes with different heat-treatments. With the acetate based and the alkoxide based route using hydrolysis in air, a max. Co doping of 6% was obtained, while in absence of CO2 and O2, the doping range could be extended to 20%Co. Both dense films and porous nano-structured films were prepd. The magnetic properties of the Co-doped films did not show any room-temp. ferro-magnetism. (iii) ZrO2 and NbO2.5 doped anatase TiO2 were prepd. by heat-treatment or hydrothermal routes. Alio-valent doping of up to more than 35% of NbO2.5 could be achieved in the anatase. It is believed that the pentavalent metal doping is compensated by metal vacancies, and as expected from this assumption, the materials have a low d. ZrO2 doping in titania led to an increase in the dye-sensitized solar cell efficiency and highly active and stable photo-catalysts.
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| 48. |
- Westin, Gunnar, et al.
(författare)
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Solution processing of conducting dense and porous films; doped ZnO and TiO2, and perovskites
- 2009
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Ingår i: International Journal of Nanotechnology. - 1475-7435. ; 6:9, s. 828-849
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Tidskriftsartikel (refereegranskat)abstract
- Solution based processing of porous and dense films by all-alkoxide based precursor systems have been investigated and compared, with a focus on the connection between the precursors and heat-treatment, and the product oxide quality and structure. Three systems were investigated typically with TGA, DSC, XPS, IR spectroscopy, X-ray diffraction, TEM-EDS and SEM-EDS, but also with other advanced characterisation techniques: (i) manganate and cobaltate perovskites of the LCMO (La0.67Ca0.33MnO3), LSMO (La0.75Sr0.25MnO3), LNCMO (La0.33Nd0.33Ca0.33MnO3), LBSM (La0.75Ba0.125Sr0.125MnO3) and LSCO (La0.50Sr0.50CoO3) compositions were investigated. Highly epitaxial films of LCMO and LSCO were prepared, and the CMR properties of the LCMO were comparable to those of PVD derived films. Polycrystalline films were prepared for all perovskites. (ii) Three routes to ZnO : Co/Al were investigated and compared; an acetate based route and two alkoxide based routes with different heat-treatments. With the acetate based and the alkoxide based route using hydrolysis in air, a maximum Co doping of 6% was obtained, while in absence of CO2 and O2, the doping range could be extended to 20%Co. Both dense films and porous nano-structured films were prepared. The magnetic properties of the Co-doped films did not show any room-temperature ferro-magnetism. (iii) ZrO2 and NbO2.5 doped anatase TiO2 were prepared by heat-treatment or hydrothermal routes. Alio-valent doping of up to more than 35% of NbO2.5 could be achieved in the anatase. It is believed that the pentavalent metal doping is compensated by metal vacancies, and as expected from this assumption, the materials have a low density. ZrO2 doping in titania led to an increase in the dye-sensitised solar cell efficiency and highly active and stable photo-catalysts.
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