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1.
  • Abbasiasl, Taher, et al. (författare)
  • Effect of intensified cavitation using poly (vinyl alcohol) microbubbles on spray atomization characteristics in microscale
  • 2020
  • Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 10:2
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, cavitating flows inside a transparent cylindrical nozzle with an inner diameter of 0.9 mm were visualized, and the effect of cavitation on atomization characteristics of emerging sprays was investigated. Different patterns of cavitating flows inside the nozzle were visualized using a high-speed camera. In-house codes were developed to process the captured images to study the droplet size distribution and droplet velocity in different flow regimes. The results show that cavitating flows at the microscale have significant effects on atomization characteristics of the spray. Two working fluids, namely, water and poly(vinyl alcohol) microbubble (PVA MB) suspension, were employed. Accordingly, the injection pressures were detected as 690 kPa, 1035 kPa, and 1725 kPa for cavitation inception, supercavitation, and hydraulic flip flow regimes in the case of water, respectively. The corresponding pressures for the aforementioned patterns for PVA MB suspension were 590 kPa, 760 kPa, and 1070 kPa, respectively. At the microscale, as a result of a higher volume fraction of cavitation bubbles inside the nozzle, there is no large difference between the cavitation numbers corresponding to cavitating and hydraulic flip flows. Although the percentage of droplets with diameters smaller than 200 μm was roughly the same for both cases of water and PVA MB suspension, the Sauter mean diameter was considerably lower in the case of PVA MBs. Moreover, higher droplet velocities were achieved in the case of PVA MBs at lower injection pressures.
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2.
  • Adebiyi, Abdulafeez, et al. (författare)
  • Effect of surface friction on ultrafast flame acceleration in obstructed cylindrical pipes
  • 2019
  • Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 9:3
  • Tidskriftsartikel (refereegranskat)abstract
    • The Bychkov model of ultrafast flame acceleration in obstructed tubes [Valiev et al., "Flame Acceleration in Channels with Obstacles in the Deflagration-to-Detonation Transition," Combust. Flame 157, 1012 (2010)] employed a number of simplifying assumptions, including those of free-slip and adiabatic surfaces of the obstacles and of the tube wall. In the present work, the influence of free-slip/non-slip surface conditions on the flame dynamics in a cylindrical tube of radius R, involving an array of parallel, tightly-spaced obstacles of size αR, is scrutinized by means of the computational simulations of the axisymmetric fully-compressible gasdynamics and combustion equations with an Arrhenius chemical kinetics. Specifically, non-slip and free-slip surfaces are compared for the blockage ratio, α, and the spacing between the obstacles, ΔZ, in the ranges 1/3 ≤ α ≤ 2/3 and 0.25 ≤ ΔZ/R ≤ 2.0, respectively. For these parameters, an impact of surface friction on flameacceleration is shown to be minor, only 1-4%, slightly facilitating acceleration in a tube with ΔZ/R = 0.5 and moderating acceleration in thecase of ΔZ/R = 0.25. Given the fact that the physical boundary conditions are non-slip as far as the continuum assumption is valid, the presentwork thereby justifies the Bychkov model, employing the free-slip conditions, and makes its wider applicable to the practical reality. Whilethis result can be anticipated and explained by a fact that flame propagation is mainly driven by its spreading in the unobstructed portion ofan obstructed tube (i.e. far from the tube wall), the situation is, however, qualitatively different from that in the unobstructed tubes, wheresurface friction modifies the flame dynamics conceptually.
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3.
  • Ahlberg Helgee, Edit, 1986, et al. (författare)
  • Adsorption of metal atoms at a buckled graphene grain boundary using model potentials
  • 2016
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226 .- 2158-3226. ; 6:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Two model potentials have been evaluated with regard to their ability to model adsorption of single metal atoms on a buckled graphene grain boundary. One of the potentials is a Lennard-Jones potential parametrized for gold and carbon, while the other is a bond-order potential parametrized for the interaction between carbon and platinum. Metals are expected to adsorb more strongly to grain boundaries than to pristine graphene due to their enhanced adsorption at point defects resembling those that constitute the grain boundary. Of the two potentials considered here, only the bond-order potential reproduces this behavior and predicts the energy of the adsorbate to be about 0.8 eV lower at the grain boundary than on pristine graphene. The Lennard-Jones potential predicts no significant difference in energy between adsorbates at the boundary and on pristine graphene. These results indicate that the Lennard-Jones potential is not suitable for studies of metal adsorption on defects in graphene, and that bond-order potentials are preferable.
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4.
  • Alnoor, Hatim, et al. (författare)
  • Effect of precursor solutions stirring on deep level defects concentration and spatial distribution in low temperature aqueous chemical synthesis of zinc oxide nanorods
  • 2015
  • Ingår i: AIP Advances. - : AMER INST PHYSICS. - 2158-3226. ; 5:8
  • Tidskriftsartikel (refereegranskat)abstract
    • Hexagonal c-axis oriented zinc oxide (ZnO) nanorods (NRs) with 120-300 nm diameters are synthesized via the low temperature aqueous chemical route at 80 degrees C on silver-coated glass substrates. The influence of varying the precursor solutions stirring durations on the concentration and spatial distributions of deep level defects in ZnO NRs is investigated. Room temperature micro-photoluminesnce (mu-PL) spectra were collected for all samples. Cathodoluminescence (CL) spectra of the as-synthesized NRs reveal a significant change in the intensity ratio of the near band edge emission (NBE) to the deep-level emission (DLE) peaks with increasing stirring durations. This is attributed to the variation in the concentration of the oxygen-deficiency with increasing stirring durations as suggested from the X-ray photoelectron spectroscopy analysis. Spatially resolved CL spectra taken along individual NRs revealed that stirring the precursor solutions for relatively short duration (1-3 h), which likely induced high super saturation under thermodynamic equilibrium during the synthesis process, is observed to favor the formation of point defects moving towards the tip of the NRs. In contrary, stirring for longer duration (5-15 h) will induce low super saturation favoring the formation of point defects located at the bottom of the NRs. These findings demonstrate that it is possible to control the concentration and spatial distribution of deep level defects in ZnO NRs by varying the stirring durations of the precursor solutions.
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5.
  • Amiri, A., et al. (författare)
  • A replacement model to simulate the nonlinear dynamics of electro-responsive liquid crystal coatings
  • 2023
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 13:3
  • Tidskriftsartikel (refereegranskat)abstract
    • An electric circuit replacement model is proposed to simulate the key nonlinear dynamics of electro-responsive liquid crystal polymer networks (LCNs). LCNs are known for having great potential to be integrated into smart functional surfaces due to their ability to generate various surface patterns. However, due to their complex molecular dynamics, low-order dynamic models that can accurately describe and predict their dynamic behavior are still lacking. In light of this research gap, we develop a lumped-parameter replacement model based on the observed dynamics in the experimental data and the physics of LCN dielectric properties. The unique assembly of lumped parameters in its simplest form describes the transformation of a high-frequency input voltage to a relatively slow increase in the local height of the LCN coating in between the electrodes, serving as an excitation mechanism to induce height change. The nonlinear dynamics of this height increase, as a function of both excitation frequency and voltage, is described by the proposed model. Furthermore, the comparison of the simulation results with the experimental data from LCN shows that key LCN response characteristics are captured well by the model. This model makes it possible to accurately predict and control the response of the electro-responsive LCN surfaces to obtain a predefined desired deformation pattern, which is a vital requirement for integrating them in haptic and smart surface devices.
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6.
  • Azina, Clio, et al. (författare)
  • Effect of titanium and zirconium carbide interphases on the thermal conductivity and interfacial heat transfers in copper/diamond composite materials
  • 2019
  • Ingår i: AIP Advances. - : AMER INST PHYSICS. - 2158-3226. ; 9:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Thermal properties of metal matrix composite materials are becoming ever more relevant with the increasing demand for thermally efficient materials. In this work, the thermal conductivity and heat transfers at the interfaces of copper matrix composite materials reinforced with diamond particles (Cu/D) are discussed. The composite materials contain either ZrC or TiC interphases and exhibit, respectively, higher and lower thermal conductivities with respect to their pure Cu/D counterparts. These thermal conductivities are accounted to the presence of strong covalent bonds and increased relative densities. The role of these interphases is also discussed regarding the phonon transmission at the interfaces. (c) 2019 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
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7.
  • Azzouz, Hatim, et al. (författare)
  • Efficient single particle detection with a superconducting nanowire
  • 2012
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 2:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Detection of alpha- and beta-particles is of paramount importance in a wide range of applications. Current particle detectors are all macroscopic and have limited time resolution. We demonstrate a nanoscale particle detector with a small detection volume, high detection efficiency, short dead times and low dark count levels. We measure alpha- and beta-particle detection efficiencies close to unity using different sources and also demonstrate blindness towards gamma-rays. Our nanoscale detector offers particle detection measurements with unprecendented spatial resolution.
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8.
  • Bejhed Stjernberg, Rebecca, et al. (författare)
  • Magnetic nanobeads present during enzymatic amplification and labeling for a simplified DNA detection protocol based on AC susceptometry
  • 2015
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 5:12
  • Tidskriftsartikel (refereegranskat)abstract
    • Magnetic biosensors are promising candidates for low-cost point-of-care biodiagnostic devices. For optimal efficiency it is crucial to minimize the time and complexity of the assay protocol including target recognition, amplification, labeling and read-out. In this work, possibilities for protocol simplifications for a DNA biodetection principle relying on hybridization of magnetic nanobeads to rolling circle amplification (RCA) products are investigated. The target DNA is recognized through a padlock ligation assay resulting in DNA circles serving as templates for the RCA process. It is found that beads can be present during amplification without noticeably interfering with the enzyme used for RCA (phi29 polymerase). As a result, the bead-coil hybridization can be performed immediately after amplification in a one-step manner at elevated temperature within a few minutes prior to read-out in an AC susceptometer setup, i.e. a combined protocol approach. Moreover, by recording the phase angle xi = arctan(chi ''/chi'), where chi and chi '' are the in-phase and out-of-phase components of the AC susceptibility, respectively, at one single frequency the total assay time for the optimized combined protocol would be no more than 1.5 hours, often a relevant time frame for diagnosis of cancer and infectious disease. Also, applying the phase angle method normalization of AC susceptibility data is not needed. These findings are useful for the development of point-of-care biodiagnostic devices relying on bead-coil binding and magnetic AC susceptometry.
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9.
  • Bergström, Magnus (författare)
  • A theoretical investigation of the influence of the second critical micelle concentration on the solubilization capacity of surfactant micelles
  • 2018
  • Ingår i: AIP Advances. - : AMER INST PHYSICS. - 2158-3226. ; 8:5
  • Tidskriftsartikel (refereegranskat)abstract
    • The solubilization of hydrophobic components by surfactants that form microemulsion droplets has been investigated from a theoretical point of view. By means of combining thermodynamics of self-assembly to form small systems with bending elasticity theory, we have been able to demonstrate a strong correlation between the second critical micelle concentration (CMC2) of surfactant micelles and their solubilization capacity (sigma). The correlation may be rationalized as a consequence of all three bending elasticity constants spontaneous curvature (H-0), bending rigidity (k(c)) and saddle-splay constant ((k) over bar (c)) showing similar trends with respect to the two quantities, i.e. sigma increases and CMC2 decreases with decreasing values of k(c)H(0) and increasing values of k(c) and (k) over bar (c), respectively. As a result, we demonstrate that the solubilization capacity is predicted to always be higher for a gemini surfactant with CMC2 = 11 mM as compared with a gemini surfactant with CMC2 = 18 mM. The predicted correlation between solubilization capacity and CMC2 agrees with experimental observations showing that surfactants forming larger micelles in general have better solubilization capacity than surfactants forming smaller micelles. The theory also demonstrates, in agreement with experiments, that sigma is raised in the entire range of surfactant concentrations, below as well as aboveCMC(2), regardless of micelle size. Consequently, our theory predicts that small micelles formed below CMC2 increase in size, whereas large rodlike or wormlike micelles formed above CMC2 decrease in size, as a hydrophobic solubilizate is added to a micellar solution.
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10.
  • Bondarenko, Artem, 1992-, et al. (författare)
  • Stochastic dynamics of strongly-bound magnetic vortex pairs
  • 2017
  • Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 7:5
  • Tidskriftsartikel (refereegranskat)abstract
    • We demonstrate that strongly-bound spin-vortex pairs exhibit pronounced stochastic behaviour. Such dynamics is due to collective magnetization states originating from purely dipolar interactions between the vortices. The resulting thermal noise exhibits telegraph-like behaviour, with random switching between different oscillation regimes observable at room temperature. The noise in the system is further studied by varying the external field and observing the related changes in the frequency of switching and the probability for different magnetic states and regimes. Monte Carlo simulations are used to replicate and explain the experimental observations.
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11.
  • Buermans, J., et al. (författare)
  • Triple Langmuir probe calibration in TOMAS ECRH plasma
  • 2023
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 13:5
  • Tidskriftsartikel (refereegranskat)abstract
    • In the TOMAS device, a triple Langmuir probe is used to measure the electron temperature and density. The accuracy of this measurement depends on correct determination of the effective collecting area of the probe, which depends on complex plasma transport processes. The probe can be calibrated by electron cyclotron resonance heating experiments using the cut-off density of the ordinary wave (O-wave). This threshold only depends on the frequency of the injected wave, and the occurrence of this phenomenon is clearly visible in the temperature evolution. The value of density is consequently known at this point and can be used to calibrate the density measurements of the triple Langmuir probe.
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12.
  • Capriata, Corrado Carlo Maria, et al. (författare)
  • Grain structure influence on synchronized two-dimensional spin-Hall nano-oscillators
  • 2023
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 13:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Nanoconstriction spin-Hall nano-oscillators (NC-SHNOs) are excellent devices for a wide variety of applications, from RF communication to bio-inspired computing. NC-SHNOs are easy to fabricate in large arrays, are CMOS compatible, and feature a narrow linewidth and high output power. However, in order to take full advantage of the device capabilities, a systematic analysis of the array behavior with respect to the number and dimensions of oscillators, the temperature of operation, and the influence of layer quality is needed. Here, we focus on micromagnetic simulations of 2 x 2 and 4 x 4 NC-SHNO arrays with single oscillators separated by up to 300 nm. We observe a synchronization scheme that allows for column-wise selection of the oscillation frequency for a larger pitch. However, for smaller pitches, a coherent oscillation volume was observed, and this volume included both the constrictions and extended beyond that region. A local variation in the exchange coupling in the active oscillator region was investigated by placing physical grains in the free magnetic layer, and it was shown to influence both the stable current range and the resulting frequency and output power. De-coupling the oscillators along rows or columns could provide higher power due to more favorable phase shifts between oscillators. Our investigation helps in achieving a deeper understanding of the intrinsic working principles of NC-SHNO arrays and how they reach fully synchronized states, and this will help to expand non-conventional computing capabilities.
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13.
  • Cuadra, Jorge, 1982, et al. (författare)
  • Hybrid dielectric waveguide spectroscopy of individual plasmonic nanoparticles
  • 2017
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226 .- 2158-3226. ; 7:7, s. Article no: 075207 -
  • Tidskriftsartikel (refereegranskat)abstract
    • Plasmonics is a mature scientific discipline which is now entering the realm of practical applications. Recently, significant attention has been devoted to on-chip hybrid devices where plasmonic nanoantennas are integrated in standard Si 3 N 4 photonic waveguides. Light in these systems is usually coupled at the waveguide apexes by using multiple objectives and/or tapered optical fibers, rendering the analysis of spectroscopic signals a complicated task. Here, we show how by using a grating coupler and a low NA objective, quantitative spectroscopic information similar to standard dark-field spectroscopy can be obtained at the single-nanoparticle level. This technology may be useful for enabling single-nanoparticle studies in non-linear excitation regimes and/or in complex experimental environments, thus enriching the toolbox of nanophotonic methods.
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14.
  • Derek, Vedran, et al. (författare)
  • Micropatterning of organic electronic materials using a facile aqueous photolithographic process
  • 2018
  • Ingår i: AIP Advances. - : AMER INST PHYSICS. - 2158-3226. ; 8:10
  • Tidskriftsartikel (refereegranskat)abstract
    • Patterning organic semiconductors via traditional solution-based microfabrication techniques is precluded by undesired interactions between processing solvents and the organic material. Herein we show how to avoid these problems easily and introduce a simple lift-off method to pattern organic semiconductors. Positive tone resist is deposited on the substrate, followed by conventional exposure and development. After deposition of the organic semiconductor layer, the remaining photoresist is subjected to a flood exposure, rendering it developable. Lift-off is then performed using the same aqueous developer as before. We find that the aqueous developers do not compromise the integrity of the organic layer or alter its electronic performance. We utilize this technique to pattern four different organic electronic materials: epindo-lidione (EPI), a luminescent semiconductor, p-n photovoltaic bilayers of metal-free phthalocyanine and N, N-dimethyltetracarboxylic diimide, and finally the archetypical conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT). The result of our efforts is a facile method making use of well-established techniques that can be added to the toolbox of research and industrial scientists developing organic electronics technology. (c) 2018 Author(s).
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15.
  • Dhaka, Veer, et al. (författare)
  • Protective capping and surface passivation of III-V nanowires by atomic layer deposition
  • 2016
  • Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 6:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Low temperature (similar to 200 degrees C) grown atomic layer deposition (ALD) films of AlN, TiN, Al2O3, GaN, and TiO2 were tested for protective capping and surface passivation of bottom-up grown III-V (GaAs and InP) nanowires (NWs), and top-down fabricated InP nanopillars. For as-grown GaAs NWs, only the AlN material passivated the GaAs surface as measured by photoluminescence (PL) at low temperatures (15K), and the best passivation was achieved with a few monolayer thick (2 angstrom) film. For InP NWs, the best passivation (similar to 2x enhancement in room-temperature PL) was achieved with a capping of 2nm thick Al2O3. All other ALD capping layers resulted in a de-passivation effect and possible damage to the InP surface. Top-down fabricated InP nanopillars show similar passivation effects as InP NWs. In particular, capping with a 2 nm thick Al2O3 layer increased the carrier decay time from 251 ps (as-etched nanopillars) to about 525 ps. Tests after six months ageing reveal that the capped nanostructures retain their optical properties. Overall, capping of GaAs and InP NWs with high-k dielectrics AlN and Al2O3 provides moderate surface passivation as well as long term protection from oxidation and environmental attack.
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16.
  • Diesen, Elias, et al. (författare)
  • Accuracy of XAS theory for unraveling structural changes of adsorbates : CO on Ni(100)
  • 2020
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 10:11
  • Tidskriftsartikel (refereegranskat)abstract
    • Studying surface reactions using ultrafast optical pump and x-ray probe experiments relies on accurate calculations of x-ray spectra of adsorbates for the correct identification of the spectral signatures and their dynamical evolution. We show that experimental x-ray absorption can be well reproduced for different binding sites in a static prototype system CO/Ni(100) at a standard density functional theory generalized-gradient-approximation level of theory using a plane-wave basis and pseudopotentials. This validates its utility in analyzing ultrafast x-ray probe experiments. The accuracy of computed relative core level binding energies is about 0.2 eV, representing a lower limit for which spectral features can be resolved with this method. We also show that the commonly used Z + 1 approximation gives very good core binding energy shifts overall. However, we find a discrepancy for CO adsorbed in the hollow site, which we assign to the significantly stronger hybridization in hollow bonding than in on-top.
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17.
  • Dmitriev, Yurij A., et al. (författare)
  • H/D isotope effect observed in the isotropic Fermi contact interaction of formyl radical : Experimental and theoretical analysis of the inter- and intra-molecular dynamics
  • 2020
  • Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 10:12
  • Tidskriftsartikel (refereegranskat)abstract
    • An unexpected deficit of the computed hyper fine coupling constant in normal formyl HCO radicals, compared to that expected based on the proton to deuteron gyromagnetic ratio of the DCO species, was observed in experimental electron paramagnetic resonance studies of HCO and DCO radicals in a CO solid matrix at cryogenic conditions. Still, the matrix was found to have only a small effect on the anisotropic parts of the magnetic parameter tensors. The underlying isotope effect between the lighter proton and the heavier deuteron on the motional dynamics was verified and elucidated by quantum chemical calculations. The experimental results obtained within a temperature range of 1.4 K–4.2 K require special attention due to the tunneling motions of the molecule and its constituent particles. The effect from vibrational, rotational, and librational motion observed in the molecular states of formyl as a probe, averaged over the dynamics of the low temperature CO matrix isolation, reveals a clear proton isotope effect under both classical and quantum conditions.
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18.
  • Eklund, Per, et al. (författare)
  • Epitaxial growth of by reactive high-power impulse magnetron sputtering
  • 2014
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 4:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Al2O3 was deposited by reactive high-power impulse magnetron sputtering at 600 C onto pre-deposited Ti2AlC(0001) thin films on Al2O3(0001) substrates. The Al2O 3 was deposited to a thickness of 65 nm and formed an adherent layer of epitaxial γ-Al2O3(111) as shown by transmission electron microscopy. The demonstration of epitaxial growth of γ-Al 2O3 on Ti2AlC(0001) open prospects for growth of crystalline alumina as protective coatings on Ti2AlC and related nanolaminated materials. The crystallographic orientation relationships are γ-Al2O3(111)//Ti2AlC(0001) (out-of-plane) and Al2O3//Ti2AlC(112̄0)γ-Al 2O3(22̄0)// Ti 2 AlC (112̄0) (in-plane) as determined by electron diffraction. Annealing in vacuum at 900 C resulted in partial decomposition of the Ti2AlC by depletion of Al and diffusion into and through the γ-Al2O3 layer.
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19.
  • Eklund, Per, et al. (författare)
  • Epitaxial growth of gamma-Al2O3 on Ti2AlC(0001) by reactive high-power impulse magnetron sputtering
  • 2014
  • Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 4:1, s. 017138-
  • Tidskriftsartikel (refereegranskat)abstract
    • Al2O3 was deposited by reactive high-power impulse magnetron sputtering at 600 degrees C onto pre-deposited Ti2AlC(0001) thin films on alpha-Al2O3(0001) substrates. The Al2O3 was deposited to a thickness of 65 nm and formed an adherent layer of epitaxial gamma-Al2O3(111) as shown by transmission electron microscopy. The demonstration of epitaxial growth of gamma-Al2O3 on Ti2AlC (0001) open prospects for growth of crystalline alumina as protective coatings on Ti2AlC and related nanolaminated materials. The crystallographic orientation relationships are gamma-Al2O3(111)//Ti2AlC(0001) (out-of-plane) and gamma-Al2O3(2 (2) over bar0)//Ti2AlC(11 (2) over bar0) (in-plane) as determined by electron diffraction. Annealing in vacuum at 900 degrees C resulted in partial decomposition of the Ti2AlC by depletion of Al and diffusion into and through the gamma-Al2O3 layer.
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20.
  • Elamain, Omaima Abubakr, et al. (författare)
  • Periodic pattern formation in an achiral bent core nematic
  • 2018
  • Ingår i: Aip Advances. - : AIP Publishing. - 2158-3226. ; 8:9
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigated a periodic flexoelectric domain pattern, which appeared as regular parallel stripes in an achiral bent core nematic liquid crystal when dc electric field was applied. We found that such a pattern was first formed at the substrate surface and took place in sandwich cells with a gap larger than 2 mu m. The field-induced periodic pattern was preserved in the field-off state by a polymer network formed in the cell and was found to exhibit a polar as well as a linear electro-optic response due to in-plane switching of the sample optic axis. A comparison between this response and the one obtained in short cholesteric liquid crystals, aligned in ULH (uniform lying helix) texture, and short pitch ferroelectric liquid crystals, respectively, suggested that a heliconical molecular order is most probably formed in the field-induced periodic stripe pattern, with the helix axis orthogonal to the stripes. To our knowledge, this is the first experimental evidence of field-induced chiral-symmetry breaking in the flexoelectric periodic stripe pattern in achiral bent core nematic, resulting in heliconical molecular order, resembling the one of twist-bend (TB) nematic phase in this kind of nematics. (C) 2018 Author(s).
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21.
  • Eriksson, Martin O., et al. (författare)
  • Recombination processes in Mg doped wurtzite InN films with p- and n-type conductivity
  • 2019
  • Ingår i: AIP Advances. - : AMER INST PHYSICS. - 2158-3226. ; 9:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Obtaining high quality, wurtzite InN films with p-type conductivity is a challenge, and there is limited information about the photoluminescence (PL) characteristics of such films. In this study, we present a comprehensive PL study and discuss in detail the recombination processes in Mg-doped InN films with varying Mg concentrations. We find that at low Mg-doping of 1x10(18) cm(-3), which yields p-type conductivity, the PL in InN is spatially inhomogeneous. The latter is suggested to be associated with the presence of n-type pockets, displaying photoluminescence at 0.73 eV involving electrons at the Fermi edge above the conduction band edge. Increasing the Mg concentration to 2.9x10(19) cm(-3) in p-type InN yields strong and spatially uniform photoluminescence at 0.62 eV and 0.68 eV visible all the way to room temperature, indicating homogeneous p-type conductivity. An acceptor binding energy of 64 meV is determined for the Mg acceptor. Further increase of the Mg concentration to 1.8x10(20) cm(-3) leads to switching conductivity back to n-type. The PL spectra in this highly doped sample reveal only the emission related to the Mg acceptor (at 0.61 eV). In the low-energy tail of the emission, the multiple peaks observed at 0.54 - 0.58 eV are suggested to originate from recombination of carriers localized at stacking faults. (C) 2019 Author(s).
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22.
  • Fan, W., et al. (författare)
  • Investigation of magnetization dynamics damping in Ni80Fe20/Nd-Cu bilayer at room temperature
  • 2018
  • Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 8:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Focusing on the Ni80Fe20 (Py)/Nd-Cu bilayers, the magnetization dynamic damping from spin pumping effect is investigated systematically by doping itinerant Cu in rear earth metal Nd. Various Ta/Py/Nd1-xCux/Ta/Si films with x = 0%, 16%, 38%, 46% and 58% are prepared by magnetron sputtering. For every content of Cu, the thickness of Nd-Cu layer is changed from 1 nm to 32 nm. The damping coefficient increases with increasing the thickness of Nd-Cu layer, which shows the trend of the spin pumping behavior. Also, with increasing Cu concentration in the Nd-Cu layer, the damping coefficient decreases, implying that the spin-orbit coupling in Nd-Cu layer is indeed cut down by high itinerant of Cu dopants. It is interesting that the spin diffusion length (λSD) in the Nd-Cu layer for different Cu dopants is not found to increase monotonously.
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23.
  • Fu, Chaochao, et al. (författare)
  • Understanding the microwave annealing of silicon
  • 2017
  • Ingår i: AIP Advances. - : AMER INST PHYSICS. - 2158-3226. ; 7:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Though microwave annealing appears to be very appealing due to its unique features, lacking an in-depth understanding and accurate model hinder its application in semiconductor processing. In this paper, the physics-based model and accurate calculation for the microwave annealing of silicon are presented. Both thermal effects, including ohmic conduction loss and dielectric polarization loss, and non-thermal effects are thoroughly analyzed. We designed unique experiments to verify the mechanism and extract relevant parameters. We also explicitly illustrate the dynamic interaction processes of the microwave annealing of silicon. This work provides an in-depth understanding that can expedite the application of microwave annealing in semiconductor processing and open the door to implementing microwave annealing for future research and applications.
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24.
  • Fu, Jie, et al. (författare)
  • Ab initio molecular dynamics study of fluid H2O-CO2 mixture in broad pressure-temperature range
  • 2017
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 7:11
  • Tidskriftsartikel (refereegranskat)abstract
    • Properties of H2O and CO2 fluid and their mixtures under extreme pressures and temperatures are poorly known yet critically important in a number of applications. Several hundreds of first-principles molecular dynamics (FPMD) runs have been performed to obtain the pressure-volume-temperature (P-V-T) data on supercritical H2O, CO2, and H2O-CO2 mixtures. The pressure-temperature (P-T) range are from 0.5 GPa to 104 GPa (48.5 GPa for CO2) and from 600 K to 4000 K. Based on these data, we evaluate several existing equations of state (EOS) for the fluid H2O, CO2, and H2O-CO2 mixture. The results show that the EOS for H2O from Belonoshko et al. [Geochim. Cosmochim. Acta 55, 381-387; Geochim. Cosmochim. Acta 55, 3191-3208; Geochim. Cosmochim. Acta 56, 3611-3626; Comput. Geosci. 18, 1267-1269] not only can be used in the studied P-T range but also is accurate enough to be used for prediction of P-V-T data. In addition, IAPWS-95 EOS for H2O shows excellent extrapolation behavior beyond 1.0 GPa and 1273 K. However, for the case of CO2, none of the existing EOS produces data in agreement with the FPMD results. We created new EOS for CO2. The precision of the new EOS is tested by comparison to the calculated P-V-T data, fugacity coefficient of the CO2 fluid derived from high P-T experimental data as well as to the (very scarce) experimental volumetric data in the high P-T range. On the basis of our FPMD data we created a new EOS for H2O-CO2 mixture. The new EOS for the mixture is in reasonable agreement with experimental data.
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25.
  • Gandhi, Hemi H., et al. (författare)
  • Chalcogen-hyperdoped germanium for short-wavelength infrared photodetection
  • 2020
  • Ingår i: AIP Advances. - : AMER INST PHYSICS. - 2158-3226. ; 10:7
  • Tidskriftsartikel (refereegranskat)abstract
    • Obtaining short-wavelength-infrared (SWIR; 1.4 mu m-3.0 mu m) room-temperature photodetection in a low-cost, group IV semiconductor is desirable for numerous applications. We demonstrate a non-equilibrium method for hyperdoping germanium with selenium or tellurium for dopant-mediated SWIR photodetection. By ion-implanting Se or Te into Ge wafers and restoring crystallinity with pulsed laser melting induced rapid solidification, we obtain single crystalline materials with peak Se and Te concentrations of 10(20) cm(-3) (10(4) times the solubility limits). These hyperdoped materials exhibit sub-bandgap absorption of light up to wavelengths of at least 3.0 mu m, with their sub-bandgap optical absorption coefficients comparable to those of commercial SWIR photodetection materials. Although previous studies of Ge-based photodetectors have reported a sub-bandgap optoelectronic response only at low temperature, we report room-temperature sub-bandgap SWIR photodetection at wavelengths as long as 3.0 mu m from rudimentary hyperdoped Ge:Se and Ge:Te photodetectors.
  •  
26.
  • Gevari, Moein Talebian, et al. (författare)
  • Deagglomeration of nanoparticle clusters in a "cavitation on chip" device
  • 2020
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 10:11
  • Tidskriftsartikel (refereegranskat)abstract
    • Due to the potential of significant energy release in cavitating flows, early cavitation inception and intensification of cavitating flows are of great importance. To use this potential, we investigated the deagglomeration of nanoparticle clusters with the implementation of hydrodynamic cavitation in a microfluidic device. For this purpose, a microfluidic device with a micro-orifice geometry was designed and fabricated using standard microfabrication processes. The system was tested with distilled water in the assembled experimental setup. The flow patterns were characterized using the cavitation number and inlet pressure. Titania nanoparticles were utilized to prepare nanoparticle suspensions. The suspensions were heated to allow agglomeration of nanoparticles. The system was operated with the new working fluid (nanoparticle clusters) at different inlet pressures. After characterizing flow patterns, the flow patterns were compared with those of pure water. The deagglomeration effects of hydrodynamic cavitation on nanoparticle clusters showed the possibility to apply this method for the stabilization of nanoparticles, which paves way to the implementation of nanoparticle suspensions to thermal fluid systems for increased energy efficiency as well as to drug delivery. Our results also indicate that the presence of nanoparticles in the working fluid enhanced cavitation intensity due to the increase in the number of heterogeneous nucleation sites.
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27.
  • Giani, L., et al. (författare)
  • Isotope effect on the formation of CN by radiative association reactions
  • 2024
  • Ingår i: AIP ADVANCES. - 2158-3226. ; 14:3
  • Tidskriftsartikel (refereegranskat)abstract
    • The formation of CN and its isotopologue (CN)-N-15 through radiative association has been investigated. We considered two processes for the collisions of ground state C(P-3) and N(S-4) atoms (A(2)Pi -> X-2 Sigma(+) and b(4)Pi -> a(4)Sigma(+)), as well as, for the first time, we investigated the radiative association of ground state C(P-3) and excited N(D-2) atoms (B-2 Sigma(+) -> X-2 Sigma(+)). The cross-sections for the three processes have been calculated using semi-classical, quantum mechanical, and Breit-Wigner theories. The rate constants, derived from the combination of semi-classical and Breit-Wigner results, have been fitted to the Kooij formula to be used in astrochemical modeling. The rate constant for the B-2 Sigma(+) -> X-2 Sigma(+) process dominates in the investigated temperature range (10-10 000 K), when its own asymptotic energy is used as a reference level. Moreover, the B-2 Sigma(+) -> X-2 Sigma(+ )process presents the most pronounced isotope effect on the rate constant. We suggest considering these newly investigated radiative association processes for the formation of CN and (CN)-N-15 in the interstellar medium.
  •  
28.
  • Gogova, Daniela, et al. (författare)
  • Epitaxial growth of β -Ga 2 O 3 by hot-wall MOCVD
  • 2022
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 12:5, s. 055022-055022
  • Tidskriftsartikel (refereegranskat)abstract
    • The hot-wall metalorganic chemical vapor deposition (MOCVD) concept, previously shown to enable superior material quality and highperformance devices based on wide bandgap semiconductors, such as Ga(Al)N and SiC, has been applied to the epitaxial growth ofβ-Ga2O3. Epitaxial β-Ga2O3 layers at high growth rates (above 1 μm/h), at low reagent flows, and at reduced growth temperatures(740 ○C) are demonstrated. A high crystalline quality epitaxial material on a c-plane sapphire substrate is attained as corroborated by a combination of x-ray diffraction, high-resolution scanning transmission electron microscopy, and spectroscopic ellipsometry measurements. Thehot-wall MOCVD process is transferred to homoepitaxy, and single-crystalline homoepitaxial β-Ga2O3 layers are demonstrated with a 201 ¯rocking curve width of 118 arc sec, which is comparable to those of the edge-defined film-fed grown (201) ¯ β-Ga2O3 substrates, indicative ofsimilar dislocation densities for epilayers and substrates. Hence, hot-wall MOCVD is proposed as a prospective growth method to be furtherexplored for the fabrication of β-Ga2O3
  •  
29.
  • Gogova, Daniela, 1967-, et al. (författare)
  • Epitaxial growth of β-Ga2O3 by hot-wall MOCVD
  • 2022
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 12:5
  • Tidskriftsartikel (refereegranskat)abstract
    • The hot-wall metalorganic chemical vapor deposition (MOCVD) concept, previously shown to enable superior material quality and high performance devices based on wide bandgap semiconductors, such as Ga(Al)N and SiC, has been applied to the epitaxial growth of beta-Ga2O3. Epitaxial beta-Ga2O3 layers at high growth rates (above 1 mu m/h), at low reagent flows, and at reduced growth temperatures (740 degrees C) are demonstrated. A high crystalline quality epitaxial material on a c-plane sapphire substrate is attained as corroborated by a combination of x-ray diffraction, high-resolution scanning transmission electron microscopy, and spectroscopic ellipsometry measurements. The hot-wall MOCVD process is transferred to homoepitaxy, and single-crystalline homoepitaxial beta-Ga2O3 layers are demonstrated with a 201 rocking curve width of 118 arc sec, which is comparable to those of the edge-defined film-fed grown (201) beta-Ga2O3 substrates, indicative of similar dislocation densities for epilayers and substrates. Hence, hot-wall MOCVD is proposed as a prospective growth method to be further explored for the fabrication of beta-Ga2O3.
  •  
30.
  • Grishin, Alexander M., et al. (författare)
  • Gadolinia nanofibers as a multimodal bioimaging and potential radiation therapy agent
  • 2015
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 5:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Continuous bead-free C-type cubic gadolinium oxide (Gd2O3) nanofibers 20-30 mu m long and 40-100 nm in diameter were sintered by sol-gel calcination assisted electrospinning technique. Dipole-dipole interaction of neighboring Gd3+ ions in nanofibers with large length-to-diameter aspect ratio results in some kind of superparamagnetic behavior: fibers are magnetized twice stronger than Gd2O3 powder. Being compared with commercial Gd-DTPA/Magnevist (R), Gd2O3 diethyleneglycol-coated (Gd2O3-DEG) fibers show high 1/T-1 and 1/T-2 proton relaxivities. Intense room temperature photoluminescence, high NMR relaxivity and high neutron scattering cross-section of Gd-157 nucleus promise to integrate Gd2O3 fibers for multimodal bioimaging and neutron capture therapy.
  •  
31.
  • Gu, Enyao, et al. (författare)
  • A real-time Raman spectroscopy study of the dynamics of laser-thinning of MoS2 flakes to monolayers
  • 2017
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 7:12
  • Tidskriftsartikel (refereegranskat)abstract
    • Transition metal dichalcogenides (TMDCs) in monolayer form have attracted a great deal of attention for electronic and optical applications. Compared to mechanical exfoliation and chemical synthesis, laser thinning is a novel and unique “on-demand” approach to fabricate monolayers or pattern desired shapes with high controllability and reproducibility. Its successful demonstration motivates a further exploration of the dynamic behaviour of this local thinning process. Here, we present an in-situ study of void formation by laser irradiation with the assistance of temporal Raman evolution. In the analysis of time-dependent Raman intensity, an empirical formula relating void size to laser power and exposure time is established. Void in thinner MoS2 flakes grows faster than in thicker ones as a result of reduced sublimation temperature in the two-dimensional (2D) materials. Our study provides useful insights into the laser-thinning dynamics of 2D TMDCs and guidelines for an effective control over the void formation.
  •  
32.
  • Guo, Tingbiao, et al. (författare)
  • Thermal management with a highly emissive and thermally conductive graphite absorber
  • 2019
  • Ingår i: AIP Advances. - : AMER INST PHYSICS. - 2158-3226. ; 9:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Thermal management on a variety of length scales is essential for many industrial, solar and computational systems. Here we explore the thermal properties of a nearly perfect graphite absorber with both high emissivity and thermal conductivity which is fabricated by simple one-step etching. The hemispherical reflectance of the absorber is around 1% in the visible range and the normal specular reflectance is less than 1% from 1.5 mu m to 10 mu m. The thermal conductivity of the absorber is measured above 630 Wm(-1) K-1, which is 2.5 times larger than the aluminum used in commercial heat sinks. Heat dissipation testing indicates that a device is 3.7 +/- 2 degrees cooler with the graphite absorber as the heat spreader than a pristine graphite sheet and 9.1 +/- 2 degrees cooler than an Au-coated graphite sheet, primarily due to improved radiation cooling. A theoretical analysis accounts for the results. Further analysis suggests that the radiative heat dissipation is more prominent in the low-convection environment, especially for a convection coefficient below 10 Wm(-2) K-1. 
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33.
  • Harrysson Rodrigues, Isabel, 1993, et al. (författare)
  • On the angular dependence of InP high electron mobility transistors for cryogenic low noise amplifiers in a magnetic field
  • 2019
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226 .- 2158-3226. ; 9:8
  • Tidskriftsartikel (refereegranskat)abstract
    • The InGaAs-InAlAs-InP high electron mobility transistor (InP HEMT) is the preferred active device used in a cryogenic low noise amplifier (LNA) for sensitive detection of microwave signals. We have investigated the angular dependence of the InP HEMT when oriented in a magnetic field at 2 K ambient temperature up to 14 T. A sharp angular dependence as a function of the magnetic field was measured for the output current of the InP HEMT. This was accurately described by a geometrical magnetoresistance expression for all angles and magnetic field strengths. Key device parameters such as transconductance and on-resistance were significantly affected at small angles and magnetic fields. The strong angular dependence of the InP HEMT output current in a magnetic field has important implications for the alignment of cryogenic LNAs in microwave detection experiments involving magnetic fields. This work was performed in GigaHertz Centre in a joint research project between Chalmers University of Technology, Low Noise Factory AB, Wasa Millimeter Wave AB, Omnisys Instruments AB and RISE Research Institutes of Sweden. We are grateful to Serguei Cherednichenko for valuable assistance in the noise measurements and Niklas Wadefalk for the LNA design.
  •  
34.
  • Holmlid, Leif, 1942 (författare)
  • Heat generation above break-even from laser-induced fusion in ultra-dense deuterium
  • 2015
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 5:8
  • Tidskriftsartikel (refereegranskat)abstract
    • Previous results from laser-induced processes in ultra-dense deuterium D(0) give conclusive evidence for ejection of neutral massive particles with energy > 10 MeV u−1. Such particles can only be formed from nuclear processes like nuclear fusion at the low laser intensity used. Heat generation is of interest for future fusion energy applications and has now been measured by a small copper (Cu) cylinder surrounding the laser target. The temperature rise of the Cu cylinder is measured with an NTC resistor during around 5000 laser shots per measured point. No heating in the apparatus or the gas feed is normally used. The fusion process is suboptimal relative to previously published studies by a factor of around 10. The small neutral particles HN(0) of ultra-dense hydrogen (size of a few pm) escape with a substantial fraction of the energ. Heat loss to the D2 gas (at < 1 mbar pressure) is measured and compensated for under various conditions. Heat release of a fewWis observed, at up to 50% higher energy than the total laser input thus a gain of 1.5. This is uniquely high for the use of deuterium as fusion fuel. With a slightly different setup, a thermal gain of 2 is reached, thus clearly above break-even for all neutronicity values possible. Also including the large kinetic energy which is directly measured for MeV particles leaving through a small opening gives a gain of 2.3. Taking into account the lower efficiency now due to the suboptimal fusion process, previous studies indicate a gain of at least 20 during long periods.
  •  
35.
  • Holmlid, Leif, 1942, et al. (författare)
  • Phase transition temperatures of 405-725 K in superfluid ultra-dense hydrogen clusters on metal surfaces
  • 2016
  • Ingår i: Aip Advances. - : AIP Publishing. - 2158-3226. ; 6:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Ultra-dense hydrogen H(0) with its typical H-H bond distance of 2.3 pm is superfluid at room temperature as expected for quantum fluids. It also shows a Meissner effect at room temperature, which indicates that a transition point to a non-superfluid state should exist above room temperature. This transition point is given by a disappearance of the superfluid long-chain clusters H-2N(0). This transition point is now measured for several metal carrier surfaces at 405 - 725 K, using both ultra-dense protium p(0) and deuterium D(0). Clusters of ordinary Rydberg matter H(l) as well as small symmetric clusters H-4(0) and H-3(0) (which do not give a superfluid or superconductive phase) all still exist on the surface at high temperature. This shows directly that desorption or diffusion processes do not remove the long superfluid H-2N(0) clusters. The two ultra-dense forms p(0) and D(0) have different transition temperatures under otherwise identical conditions. The transition point for p(0) is higher in temperature, which is unexpected. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
  •  
36.
  • Huang, Z., et al. (författare)
  • Ab initio understanding of magnetic properties in Zn2+ substitution of Fe3O4 ultra-thin film with dilute Zn substitution
  • 2018
  • Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 8:5
  • Tidskriftsartikel (refereegranskat)abstract
    • The mechanism of the magnetic properties on the Zn2+ substituted Fe3O4 film have been investigated based on first principle calculations. It is found that the surface effect plays an important role in the occupation of Zn ion, and in turn changes the magnetic moment. It may also destroy the half metallic behavior of Fe3O4 film even if the Zn2+ concentration only is one Zn2+ per unit cell (4%), which is different from that in bulk material.
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37.
  • Hussain, Tanveer, et al. (författare)
  • Improvement in the hydrogen desorption from MgH2 upon transition metals doping : A hybrid density functional calculations
  • 2013
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 3:10, s. 102117-
  • Tidskriftsartikel (refereegranskat)abstract
    • This study deals with the investigations of structural, electronic and thermodynamic properties of MgH2 doped with selected transition metals (TMs) by means of hybrid density functional theory (PBE0). On the structural side, the calculated lattice parameters and equilibrium volumes increase in case of Sc, Zr and Y opposite to all the other dopants indicating volumetrically increased hydrogen density. Except Fe, all the dopants improve the kinetics of MgH2 by reducing the heat of adsorption with Cu, Nb, Ni and V proving more efficient than others studied TM's. The electronic properties have been studied by density of states and correlated with hydrogen adsorption energies.
  •  
38.
  • Indykiewicz, Kornelia, 1986, et al. (författare)
  • Current-induced enhancement of photo-response in graphene THz radiation detectors
  • 2022
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226 .- 2158-3226. ; 12:11
  • Tidskriftsartikel (refereegranskat)abstract
    • Thermoelectric readout in a graphene terahertz (THz) radiation detector requires a p-n junction across the graphene channel. Even without an intentional p-n junction, two latent junctions can exist in the vicinity of the electrodes/antennas through the proximity to the metal. In a symmetrical structure, these junctions are connected back-to-back and therefore counterbalance each other with regard to rectification of the ac signal. Because of the Peltier effect, a small dc current results in additional heating in one and cooling in another p-n junction, thereby breaking the symmetry. The p-n junctions then no longer cancel, resulting in a greatly enhanced rectified signal. This allows simplifying the design and controlling the sensitivity of THz radiation detectors.
  •  
39.
  • Jansson, Helen, 1964, et al. (författare)
  • Silicate species of water glass and insights for alkali-activated green cement
  • 2015
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 5:6
  • Tidskriftsartikel (refereegranskat)abstract
    • Despite that sodium silicate solutions of high pH are commonly used in industrial applications, most investigations are focused on low to medium values of pH. Therefore we have investigated such solutions in a broad modulus range and up to high pH values (similar to 14) by use of infrared (IR) spectroscopy and silicon nuclear magnetic resonance (Si-29-NMR). The results show that the modulus dependent pH value leads to more or less charged species, which affects the configurations of the silicate units. This in turn, influences the alkali-activation process of low CO2 footprint cements, i.e. materials based on industrial waste or by-products
  •  
40.
  • Jiang, Sheng, et al. (författare)
  • Tuning the magnetodynamic properties of all-perpendicular spin valves using He+ irradiation
  • 2018
  • Ingår i: Aip Advances. - : AIP Publishing. - 2158-3226. ; 8:6
  • Tidskriftsartikel (refereegranskat)abstract
    • Using He+ ion irradiation, we demonstrate how the magnetodynamic properties of both ferromagnetic layers in all-perpendicular [Co/Pd]/Cu/[Co/Ni] spin valves can be tuned by varying the He+ ion fluence. As the perpendicular magnetic anisotropy of both layers is gradually reduced by the irradiation, different magnetic configurations can be achieved from all-perpendicular (up arrow up arrow), through orthogonal (->up arrow), to all in-plane (paired right arrows). In addition, both the magnetic damping (alpha) and the inhomogeneous broadening (Delta H-0) of the Co/Ni layer improve substantially with increasing fluence. While the GMR of the spin valve is negatively affected, decreasing linearly from an original value of 1.14% to 0.4% at the maximum fluence of 50x10(14) He+/cm(2), most of the Co/Ni layer improvement is achieved already at a fluence of 10x10(14) He+/cm(2), for which GMR only reduces to 0.9%. (C) 2018 Author(s).
  •  
41.
  • Kateb, Movaffaq, et al. (författare)
  • Effect of atomic ordering on the magnetic anisotropy of single crystal Ni80Fe20
  • 2019
  • Ingår i: AIP Advances. - : AMER INST PHYSICS. - 2158-3226. ; 9:3
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate the effect of atomic ordering on the magnetic anisotropy of Ni80Fe20 at.% (Py). To this end, Py films were grown epitaxially on MgO(001) using dc magnetron sputtering (dcMS) and high power impulse magnetron sputtering (HiPIMS). Aside from twin boundaries observed in the latter case, both methods present high quality single crystals with cube-on-cube epitaxial relationship as verified by the polar mapping of important crystal planes. However, X-ray diffraction results indicate higher order for the dcMS deposited film towards L1(2) Ni3Fe superlattice. This difference can be understood by the very high deposition rate of HiPIMS during each pulse which suppresses adatom mobility and ordering. We show that the dcMS deposited film presents biaxial anisotropy while HiPIMS deposition gives well defined uniaxial anisotropy. Thus, higher order achieved in the dcMS deposition behaves as predicted by magnetocrystalline anisotropy i.e. easy axis along the [111] direction that forced in the plane along the [110] direction due to shape anisotropy. The uniaxial behaviour in HiPIMS deposited film then can be explained by pair ordering or more recent localized composition non-uniformity theories. Further, we studied magnetoresistance of the films along the [100] directions using an extended van der Pauw method. We find that the electrical resistivities of the dcMS deposited film are lower than in their HiPIMS counterparts verifying the higher order in the dcMS case.
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42.
  • Kenawy, Ahmed, 1991, et al. (författare)
  • Tunnel magnetoresistance of magnetic molecules with spin-vibron coupling
  • 2017
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226 .- 2158-3226. ; 7:5, s. 055708-
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of molecular vibrations on the tunnel magnetoresistance (TMR) of a mag- netic tunnel junction with a single spin-anisotropic molecule interconnecting its elec- trodes is investigated theoretically. We demonstrate that if these vibrations couple at the same time to the charge of tunneling electrons and to the spin of the molecule, the spin anisotropy of such a molecule becomes enhanced. This has, in turn, a profound impact on the TMR of such a device showing that molecular vibrations lead to a significant change of spin-polarized transport, differing for the parallel and antiparallel magnetic configuration of the junction.
  •  
43.
  • Khosa, Rabia Y., et al. (författare)
  • Electrical characterization of amorphous Al2O3 dielectric films on n-type 4H-SiC
  • 2018
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226 .- 2158-3226. ; 8:2
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on the electrical properties of Al 2 O 3 films grown on 4H-SiC by successive thermal oxidation of thin Al layers at low temperatures (200°C - 300°C). MOS capacitors made using these films contain lower density of interface traps, are more immune to electron injection and exhibit higher breakdown field (5MV/cm) than Al 2 O 3 films grown by atomic layer deposition (ALD) or rapid thermal processing (RTP). Furthermore, the interface state density is significantly lower than in MOS capacitors with nitrided thermal silicon dioxide, grown in N 2 O, serving as the gate dielectric. Deposition of an additional SiO 2 film on the top of the Al 2 O 3 layer increases the breakdown voltage of the MOS capacitors while maintaining low density of interface traps. We examine the origin of negative charges frequently encountered in Al 2 O 3 films grown on SiC and find that these charges consist of trapped electrons which can be released from the Al 2 O 3 layer by depletion bias stress and ultraviolet light exposure. This electron trapping needs to be reduced if Al 2 O 3 is to be used as a gate dielectric in SiC MOS technology.
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44.
  • Konkoli, Zoran, 1966, et al. (författare)
  • Forces on an attractive surface generated from a thermoresponsive polymer gel
  • 2014
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226 .- 2158-3226. ; 4:8, s. 087137 -
  • Tidskriftsartikel (refereegranskat)abstract
    • Interaction between polymers and soft-matter surfaces in the biological cell is a common yet incompletely understood phenomenon. This work investigates a generic situation where a thermoresponsive polymer gel is placed in the vicinity of an adsorbing surface, and starts contracting. The force is mediated by polymer chains that partially attach to the surface and partially to the contracting gel. The main goal was to understand how the force generated by the transforming polymer gel depends on key parameters that describe the system, most importantly, the concentration of the polymer, the length of the force-mediating polymer, and the the distance between the surface and the outer border of the contracting polymer gel. The key result of the paper is the Laplace transform (with regard to the polymer length) of the pulling force expression. Analytical approximations for the force have been obtained, and the exact expression for the pulling force is presented for the situation when the gel starts contracting. In depth analysis of the force behavior revealed several phases adopted by the polymer during the gel contraction.
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45.
  • Koop, Björn C., et al. (författare)
  • Static and dynamic properties of vortex pairs in asymmetric nanomagnets
  • 2016
  • Ingår i: AIP Advances. - : American Institute of Physics Inc.. - 2158-3226. ; 6:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Stacked spin-vortex pairs in magnetic multilayered nanopillars, with vertical separation between the vortices small compared to the vortex core size and pure magnetostatic coupling, exhibit spin dynamics absent in individual vortices. This dynamics is nonlinear and is due to the strong direct core-core coupling in the system, dominating energetically for small-signal excitation. We observe and explain the appearance of spin resonance modes, forbidden within linear dynamics, and discuss how they depend on the magnetic and morphological asymmetries in the samples.
  •  
46.
  • Kotipalli, R., et al. (författare)
  • Investigating the electronic properties of Al2O3/Cu(In, Ga)Se-2 interface
  • 2015
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 5:10
  • Tidskriftsartikel (refereegranskat)abstract
    • Atomic layer deposited (ALD) Al2O3 films on Cu(In, Ga)Se-2 (CIGS) surfaces have been demonstrated to exhibit excellent surface passivation properties, which is advantageous in reducing recombination losses at the rear metal contact of CIGS thin-film solar cells. Here, we report, for the first time, experimentally extracted electronic parameters, i.e. fixed charge density (Q(f)) and interface-trap charge density (D-it), for as-deposited (AD) and post-deposition annealed (PDA) ALD Al2O3 films on CIGS surfaces using capacitance-voltage (C-V) and conductance-frequency (G-f) measurements. These results indicate that the AD films exhibit positive fixed charges Q(f) (approximately 10(12) cm(-2)), whereas the PDA films exhibit a very high density of negative fixed charges Q(f) (approximately 10(13) cm(-2)). The extracted D-it values, which reflect the extent of chemical passivation, were found to be in a similar range of order (approximately 10(12) cm(-2) eV(-1)) for both AD and PDA samples. The high density of negative Q(f) in the bulk of the PDA Al2O3 film exerts a strong Coulomb repulsive force on the underlying CIGS minority carriers (n(s)), preventing them to recombine at the CIGS/Al2O3 interface. Using experimentally extracted Q(f) and D-it values, SCAPS simulation results showed that the surface concentration of minority carriers (n(s)) in the PDA films was approximately eight-orders of magnitude lower than in the AD films. The electrical characterization and estimations presented in this letter construct a comprehensive picture of the interfacial physics involved at the Al2O3/CIGS interface. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
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47.
  • Kou, R. H., et al. (författare)
  • Charge transfer-tuned magnetism in Nd-substituted Gd5Si4
  • 2018
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 8:12
  • Tidskriftsartikel (refereegranskat)abstract
    • We report a charge-transfer mechanism in tuning of magnetism of Nd-substituted Gd5-xNdxSi4 (x=1 and 2.5) compounds. The X-ray absorption near edge structure measurements demonstrated that Nd substitutions for Gd induce charge transfer of 5d electrons from Gd to Nd. The charge transfer weakens spin-orbital coupling of Gd but strengthens that of Nd. Consequently, the magnetization responses of the substituted compounds to low magnetic fields are increased while their saturation magnetization is reduced. Electronic structure calculations showed that the charge transfer stabilizes a ferromagnetic and a ferrimagnetic structure in the compounds with x = 1 and 2.5, respectively, but that it does not change the 5d-3p hybridization significantly. It is suggested that the charge transfer of 5d electrons may occur in other rare earth-substituted Gd5Si4 compounds allowing for tuning of their magnetism.
  •  
48.
  • Kravets, Anatolii, et al. (författare)
  • Effect of nanostructure layout on spin pumping phenomena in antiferromagnet/nonmagnetic metal/ferromagnet multilayered stacks
  • 2017
  • Ingår i: AIP Advances. - : American Institute of Physics Inc.. - 2158-3226. ; 7:5
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work we focus on magnetic relaxation in Mn80Ir20(12 nm)/Cu(6 nm)/Py(dF) antiferromagnet/Cu/ferromagnet (AFM/Cu/FM) multilayers with different thickness of the ferromagnetic permalloy layer. An effective FM-AFM interaction mediated via the conduction electrons in the nonmagnetic Cu spacer - the spin-pumping effect - is detected as an increase in the linewidth of the ferromagnetic resonance (FMR) spectra and a shift of the resonant magnetic field. We further find experimentally that the spin-pumping-induced contribution to the linewidth is inversely proportional to the thickness of the Py layer. We show that this thickness dependence likely originates from the dissipative dynamics of the free and localized spins in the AFM layer. The results obtained could be used for tailoring the dissipative properties of spintronic devices incorporating antiferromagnetic layers.
  •  
49.
  • Kudryavtsev, Daniil, et al. (författare)
  • Raman high-pressure study of butane isomers up to 40 GPa
  • 2018
  • Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 8:11
  • Tidskriftsartikel (refereegranskat)abstract
    • Raman spectroscopy studies on n and i-butane were performed at pressures of up to 40 GPa at ambient temperatures using the DAC technique. Normal butane undergoes two phase transitions at 1.9(5) GPa and 2.9(5) GPa and isobutane at 2.7(5) GPa and 3.5(5) GPa. These phase transitions were identified based on observations of the splitting Raman modes and the appearance or disappearance of particular Raman peaks. Our results demonstrate the complex, high-pressure behavior of butane isomers.
  •  
50.
  • Kumar, Rohan, et al. (författare)
  • Transforming the transportation sector : Mitigating greenhouse gas emissions through electric vehicles (EVs) and exploring sustainable pathways
  • 2024
  • Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 14:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Transportation-related emissions in Pakistan have been rapidly increasing in recent years. This study aims to determine how important it is to electrify road transportation in Pakistan to reduce greenhouse gas (GHG) emissions from the transportation sector. Motivated by the need to tackle the growing environmental issues related to conventional fuel-powered automobiles, this research explores the application of electrification techniques in the context of Pakistan’s transportation system. During the 2019 fiscal year, the transportation industry in Pakistan consumed 23 × 106 tonnes of energy from the burning of fossil fuels and produced 52.9 × 106 metric tons of CO2, which made up 31% of the country’s total carbon emissions. In this research, different scenarios, such as business as usual, low carbon, strengthen low carbon, and Pakistan National Electric Vehicle Policy 2040, are evaluated for the transportation sector of the country. Using the LEAP model, this study projects the effects of electrification on Pakistan road transportation over 30 years. When estimating how electrification will affect road transportation in Pakistan over the next 30 years, several factors were taken into account, including policy frameworks, changing consumer behavior, technology advancements, and infrastructure improvements. The analysis covered the emission levels, adoption hurdles, and possible advantages of transitioning to electric vehicles (EVs). The outcomes illustrate that adopting EVs can produce substantial drops in fuel consumption and environmental emissions, providing a sustainable solution to mitigate global warming. This work is directly associated with various Sustainable Development Goals, including SDG3 (good health and well-being), SDG7 (affordable and clean energy), and SDG13 (climate action). The results of this study highlight the considerable potential for GHG reduction associated with the widespread adoption of EVs, offering crucial insights to stakeholders and policymakers.
  •  
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