| 1. |
- de Melo, Claudia, et al.
(författare)
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Semi-Transparent p‑Cu2O/n-ZnO Nanoscale-Film Heterojunctions for Photodetection and Photovoltaic Applications
- 2019
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Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 2:7, s. 4358-4366
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Tidskriftsartikel (refereegranskat)abstract
- Transparent nanoscale-film heterojunctions based on Cu2O and ZnO were fabricated by atomic layer deposition and reactive magnetron sputtering. The constitutive layers exhibit high crystalline quality and a local epitaxial relation between Cu2O and ZnO was achieved with [110] Cu2O || [001] ZnO and [001] Cu2O || [010] ZnO as evidenced by high resolution transmission electron microscopy and. Cu2O films show very low resistivity and high mobility values of 9–150 Ω cm and 19 cm2/V s, respectively. The Cu2O/ZnO heterojunctions exhibit a nonlinear rectifying behavior characteristic of a p–n junction, self-powered photoresponse under 1 Sun illumination and an average transmittance of 73% in the visible region of the electromagnetic spectrum. These results are promising for all-oxide transparent electronics, photodetection and photovoltaic applications.
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| 2. |
- de Melo, Claudia, et al.
(författare)
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Tunable Localized Surface Plasmon Resonance and Broadband Visible Photoresponse of Cu Nanoparticles/ZnO Surfaces
- 2018
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 10:47, s. 40958-40965
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Tidskriftsartikel (refereegranskat)abstract
- Plasmonic Cu nanoparticles (NP) were successfully deposited on ZnO substrates by atomic layer deposition (ALD) owing to the Volmer–Weber island growth mode. An evolution from Cu NP to continuous Cu films was observed with an increasing number of ALD cycles. Real and imaginary parts of the NP dielectric functions, determined by spectroscopic ellipsometry using an effective medium approach, evidence a localized surface plasmon resonance that can be tuned between the visible and near-infrared ranges by controlling the interparticle spacing and size of the NP. The resulting Cu NP/ZnO device shows an enhanced photoresponse under white light illumination with good responsivity values, fast response times, and stability under dark/light cycles. The significant photocurrent detected for this device is related to the hot-electron generation at the NP surface and injection into the conduction band of ZnO. The possibility of tuning the plasmon resonance together with the photoresponsivity of the device is promising in many applications related to photodetection, photonics, and photovoltaics.
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| 3. |
- El Albani, Abderrazak, et al.
(författare)
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Large colonial organisms with coordinated growth in oxygenated environments 2.1 Gyr ago
- 2010
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 466:7302, s. 100-104
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Tidskriftsartikel (refereegranskat)abstract
- The evidence for macroscopic life during the Palaeoproterozoic era (2.5-1.6 Gyr ago) is controversial(1-5). Except for the nearly 2-Gyr-old coil-shaped fossil Grypania spiralis(6,7), which may have been eukaryotic, evidence for morphological and taxonomic bio-diversification of macroorganisms only occurs towards the beginning of the Mesoproterozoic era (1.6-1.0 Gyr)(8). Here we report the discovery of centimetre-sized structures from the 2.1-Gyr-old black shales of the Palaeoproterozoic Francevillian B Formation in Gabon, which we interpret as highly organized and spatially discrete populations of colonial organisms. The structures are up to 12 cm in size and have characteristic shapes, with a simple but distinct ground pattern of flexible sheets and, usually, a permeating radial fabric. Geochemical analyses suggest that the sediments were deposited under an oxygenated water column. Carbon and sulphur isotopic data indicate that the structures were distinct biogenic objects, fossilized by pyritization early in the formation of the rock. The growth patterns deduced from the fossil morphologies suggest that the organisms showed cell-to-cell signalling and coordinated responses, as is commonly associated with multicellular organization(9). The Gabon fossils, occurring after the 2.45-2.32-Gyr increase in atmospheric oxygen concentration(10), may be seen as ancient representatives of multicellular life, which expanded so rapidly 1.5 Gyr later, in the Cambrian explosion.
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| 4. |
- Horwat, David, et al.
(författare)
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On the deactivation of the dopant and electronic structure in reactively sputtered transparent Al-doped ZnO thin films
- 2010
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 43:13, s. 132003-
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Tidskriftsartikel (refereegranskat)abstract
- We report on the possible origin of electrical heterogeneities in 4 at% Al-doped ZnO (AZO) reactively sputtered films. It is found through the Zn L-3 and Al K edge x-ray absorption near-edge structure that a fraction of the Al dopant is deactivated by its positioning in octahedral conformation with oxygen. This fraction as well as the conductivity, optical bandgap and c-axis parameter of ZnO wurtzite are all found to depend on the sample position during deposition. The present results suggest the formation of a metastable Al2O3 (ZnO) m homologous phase that degrades the electrical conductivity.
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| 5. |
- Norrby, Niklas, 1984-
(författare)
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Microstructural evolution of TiAlN hard coatings at elevated pressures and temperatures
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A typical hard coating on metal cutting inserts used in for example turning, milling or drilling operations is TiAlN. At elevated temperatures, TiAlN exhibits a well characterized spinodal decomposition into coherent cubic TiN and AlN rich domains, which is followed by a transformation from cubic to hexagonal AlN. Using in-situ synchrotron x-ray radiation, the kinetics of the second transformation was investigated in this thesis and the strong temperature dependence on the transformation rate indicated a diffusion based nucleation and growth mechanism. The results gave additional information regarding activation energy of the transformation and the critical wavelength of the cubic domains at the onset of hexagonal AlN. After nucleation and growth, the hexagonal domains showed a striking resemblance with the preexisting cubic AlN microstructure.During metal cutting, the tool protecting coating is subjected to temperatures of ~900 ºC and pressure levels in the GPa range. The results in this thesis have shown a twofold effect of the pressure on the decomposition steps. Firstly, the spinodal decomposition was promoted by the applied pressure during metal cutting which was shown by comparisons with annealed samples at similar temperatures. Secondly, the detrimental transformation from cubic to hexagonal AlN was shown to be suppressed at elevated hydrostatic pressures. A theoretical pressure/temperature phase diagram, validated with experimental results, also showed suppression of hexagonal AlN by an increased temperature at elevated pressures.The spinodal decomposition during annealing and metal cutting was in this work also shown to be strongly affected by the elastic anisotropy of TiAlN, where the phase separation was aligned along the elastically softer <100> directions in the crystal. The presence of the anisotropic microstructure enhanced the mechanical properties compared to the isotropic case, mainly due to a shorter distance between the c-AlN and c-TiN domains in the anisotropic case. Further improvement of the metal cutting behavior was realized by depositing individual layers with an alternating bias. The individual bias layers exhibited microstructural differences with different residual stress states. The results of the metal cutting tests showed an enhanced wear resistance in terms of both crater and flank wear compared to coatings deposited with a fixed bias.
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| 6. |
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| 7. |
- Raza, Mohsin, et al.
(författare)
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Thermal stability of oxygen vacancy stabilized zirconia (OVSZ) thin films
- 2021
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Ingår i: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 409
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Tidskriftsartikel (refereegranskat)abstract
- Thermal stability of reactive magnetron sputter deposited oxygen vacancy stabilized cubic zirconia (OVSZ) thin films containing 16 and 3 at.% oxygen vacancies is reported. Temperature-resolved grazing incidence X-ray diffraction (TR-GIXRD) measurements (200-900 degrees C) in air and nitrogen atmosphere were performed. TR-GIXRD data show that the deposited films are stable up to 750 degrees C irrespective of the annealing atmosphere or the oxygen vacancy concentration. However, above 750 degrees C a fraction of zirconia transforms from cubic to monoclinic structure. This structural transition is explained by the compressive stresses, generated as a result of discrepancy in film-substrate thermal expansion coefficients. Thermal cycling of the deposited OVSZ thin films is also performed at 700 degrees C and show that films retain their initial cubic structure.
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| 8. |
- Soranno, Patricia A., et al.
(författare)
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LAGOS-NE : A multi-scaled geospatial and temporal database of lake ecological context and water quality for thousands of U.S. lakes
- 2017
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Ingår i: GigaScience. - : Oxford University Press (OUP). - 2047-217X. ; 6:12, s. 1-22
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the factors that affect water quality and the ecological services provided by freshwater ecosystems is an urgent global environmental issue. Predicting how water quality will respond to global changes not only requires water quality data, but also information about the ecological context of individual water bodies across broad spatial extents. Because lake water quality is usually sampled in limited geographic regions, often for limited time periods, assessing the environmental controls of water quality requires compilation of many data sets across broad regions and across time into an integrated database. LAGOS-NE accomplishes this goal for lakes in the northeastern-most 17 US states. LAGOS-NE contains data for 51101 lakes and reservoirs larger than 4 ha in 17 lake-rich US states. The database includes 3 datamodules for: lake location and physical characteristics for all lakes; ecological context (i.e., the land use, geologic, climatic, and hydrologic setting of lakes) for all lakes; and in situmeasurements of lake water quality for a subset of the lakes fromthe past 3 decades for approximately 2600–12 000 lakes depending on the variable. The database contains approximately 150000 measures of total phosphorus, 200 000 measures of chlorophyll, and 900 000 measures of Secchi depth. The water quality data were compiled from87 lake water quality data sets fromfederal, state, tribal, and non-profit agencies, university researchers, and citizen scientists. This database is one of the largest andmost comprehensive databases of its type because it includes both in situmeasurements and ecological context data. Because ecological context can be used to study a variety of other questions about lakes, streams, and wetlands, this database can also be used as the foundation for other studies of freshwaters at broad spatial and ecological scales
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| 9. |
- von Fieandt, Kristina, et al.
(författare)
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Optical and electrical properties of hard (Hf,Nb,Ti,V,Zr)N-x thin films
- 2021
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Ingår i: Vacuum. - : Elsevier. - 0042-207X .- 1879-2715. ; 193
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Tidskriftsartikel (refereegranskat)abstract
- (Hf,Nb,Ti,V,Zr)N-x coatings with nitrogen content between 0 and 49 at.% were deposited by sputter deposition, and thoroughly characterised. Nitrogen-free coatings were found to have a bcc structure, low hardness (8 GPa), and an electrical resistivity of 144 mu Omega cm. The nitride coatings (43-49 at.% N) had NaCl-type structure, consistent with a multi-component solid solution phase. Photoelectron core level binding energies indicate that the electronic structure of the multi-component nitride differs from that of the binary nitrides, probably a result of charge transfer between the metal atoms. The nitride coatings exhibited a dense microstructure and a hardness between 29 and 33 GPa, and electrical resistivities of 141-254 mu Omega cm. They also exhibited a minimum in the optical reflectance, similar to that of TiN, indicating plasmonic properties. The position of this minimum was found to be shifted to smaller wavelengths (272-339 nm) compared to a TiN reference (428 nm) and varied with nitrogen content. The tuneability of the optical properties, in combination with the potential to influence the electronic structure through charge transfer between metal atoms point to new interesting routes to design optical materials, and a new class of optical materials based on the concept of multi-component nitrides.
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| 10. |
- von Fieant, Kristina
(författare)
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Reactive Sputtering of Complex Multi-component Nitride Thin Films
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The ever-increasing demand on improvement of protective nitride thin films has led to an expansion of the research field into multi-element based materials. The work in this thesis has focused on exploring new complex, multi-component nitride thin films based on three different material systems: Al-Ge-N, Hf-Nb-Ti-V-Zr-N and Al-Cr-Nb-Y-Zr-N. All films were synthesised by reactive dc magnetron sputtering and characterised with regard to structure and material properties, in particular the mechanical, optical and corrosion properties.The Al-Ge-O-N coatings exhibited amorphisation of the structure upon oxygen addition, via the formation of a crystalline (Al1-xGex)(N1-yOy) solid solution phase for low O contents. The mechanical properties were improved, and hardness values up to 29 GPa were achieved for low O and Ge concentrations, most likely due to nanocomposite hardening. The optical absorption edge was tuneable towards shorter and longer wavelengths with increasing the O and Ge content respectively. Annealing to 850°C showed indications of increased thermal stability for the quaternary Al-Ge-O-N films compared to the ternary Al-Ge-N films.Coatings in the Hf-Nb-Ti-V-Zr-N system were found to be highly crystalline featuring a single solid solution phase with NaCl-type structure for low Hf content, whereas an additional, tetragonally distorted, phase appeared for higher Hf contents. The mechanical properties, such as hardness and Young’s modulus increased with increasing Hf content, although the values were relatively low compared to those for transition metal nitrides in general.The Al-Cr-Nb-Y-Zr-N films also crystallised in the NaCl-type structure for the films with high nitrogen contents, i.e. between 46 and 51 at.%. However, partial elemental segregation was present, mainly for yttrium, both within the grains and in the column boundaries. XPS results suggested that yttrium was in a metallic state, while the remaining elements were present in a nitrided environment. The partial segregation could possibly explain the observed ductile behaviour of the nitride films. Electrochemical tests showed that the corrosion resistance increased with increased nitrogen content and the films performed in some cases better than a hyper-duplex stainless steel.This thesis demonstrates that solid solutions are formed for three relatively different nitride material systems when varying the composition. The solubilities of the solid solution phases were found to be limited as shown by amorphisation, partial elemental segregation or formation of a two-phase material. The limited solubility and the phase changes can be used to design the material properties.
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