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| 2. |
- Arnalds, Unnar B., 1976-
(författare)
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Magnetic Order in Artificial Structures
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The topic of this thesis is the investigation of the magnetic properties of artificially created magnetic structures. Applying different characterization techniques, ranging from direct imaging methods to reciprocal space techniques, the properties of lithographically patterned arrays of magnetic thin film and multilayer elements are investigated by exploring their magnetic state, extending from the atomic scale up to collective ordering phenomena of nano-magnetic elements.Laterally patterned amorphous multilayer arrays of combined circular and ellipsoidal islands were investigated. The arrays contain a variety of length scales, ranging from their nanometer scale multilayer structure to their lateral periodicity in the micrometer range. The attributes of these arrays are explored using different techniques, applicable for addressing the magnetization at different length scales, including magneto-optical techniques, micromagnetic simulations and x-ray resonant magnetic scattering.Arrays of dipole interacting elongated magnetic elements composed of Pd(Fe) thin films were investigated. Pd(Fe) films have a low Curie temperature which can be tuned by the thickness of the Fe layer embedded in Pd. By this, the interaction and the shape anisotropy energies can be brought down to energy scales comparable to room temperature enabling the possibility of investigating the effect of thermal excitations on such arrays. The temperature dependent magnetization of an artificial square spin ice array was investigated by magneto-optical measurements demonstrating the possibility of observing an order-disorder transition in an artificial square spin ice system. The role of dipolar interactions and the possibility of achieving thermal ground state ordering was then further investigated by magnetically sensitive photoemission electron microscopy imaging of ring arrangements of elongated Pd(Fe) elements. The results reveal a high probability of achieving a thermal ground state ordering of the magnetization of the islands.
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| 3. |
- Arnalds, Unnar B., et al.
(författare)
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Thermal transitions in nano-patterned XY-magnets
- 2014
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 105:4, s. 042409-
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Tidskriftsartikel (refereegranskat)abstract
- We have fabricated ultra-thin disc shaped islands wherein shape anisotropy confines the moment to the island plane, creating XY-like superspins. At low temperatures, the superspins are blocked, and, as the temperature is increased, they undergo a transition into a superparamagnetic state. The onset of this dynamic superspin state scales with the diameter of the islands, and it persists up to a temperature governed by the intrinsic ordering temperature of the island material defining a range in temperature in which dynamic behavior of the magnetic islands can be obtained.
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| 4. |
- Eriksson, Anna Karin, et al.
(författare)
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Resistivity changes in Cr/V(0 0 1) superlattices during hydrogen absorption
- 2007
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 446, s. 526-529
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Tidskriftsartikel (refereegranskat)abstract
- The hydrogen induced resistivity changes in Cr/VHx(0 0 1) superlattices where investigated in the concentration range 0<x<0.7. Initially, the resistivity increases with H content, reaching a maximum at H/V≈0.5 atomic ratio. At concentration above 0.5, the resistivity decreases with increasing H concentration. These results are in stark contrast to the H induced resistivity changes in Fe/V(0 0 1) superlattices, in which the resistivity increases monotonically up to H/V≈1. The results unambiguously prove the importance of the interface scattering, which calls for better theoretical description of the H induces changes in the electronic structure in this type of materials.
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| 5. |
- Hanifpour, Fatemeh, et al.
(författare)
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Operando quantification of ammonia produced from computationally-derived transition metal nitride electro-catalysts
- 2022
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Ingår i: Journal of Catalysis. - : Elsevier. - 0021-9517 .- 1090-2694. ; 413, s. 956-967
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Tidskriftsartikel (refereegranskat)abstract
- Electrochemical reduction of dinitrogen to ammonia is investigated in a micro-reactor flow-cell using thin films of VN, CrN, NbN and ZrN. Chronoamperometry loops are used for ammonia production analysis. Operando ammonia quantification is accomplished in a flow injection analyzer. Results show the effect of presence/absence of N-2(g) within both the electrochemical characterization and ammonia production for ZrN. However, no ammonia is detected from studies on CrN. VN and NbN are inactivated upon reacting their N atoms of the surface top layer(s). Results obtained from ammonia measurements, electrochemical impedance spectroscopy analysis, surface stability checks, and surface characterization using X-ray reflectivity, reveal certain trends indicating catalytic behavior for ZrN. However, the concentration of produced ammonia is below the detection limit of the methods devised to analyze the samples from isotope labeling experiments. The onset of ammonia production on ZrN appears to be in close agreement with that predicted previously by computational studies.
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| 6. |
- Holmlid, Leif, 1942, et al.
(författare)
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Charged particle energy spectra from laser-induced processes: Nuclear fusion in ultra-dense deuterium D(0)
- 2016
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Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199. ; 41, s. 1080-1088
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Tidskriftsartikel (refereegranskat)abstract
- Clear high-energy particle signatures of laser-induced nuclear fusion are now observed by energy spectroscopy with standard scintillation detectors. The particles observed are ejected from ultra-dense deuterium D(0) on the laser target. A colored glass-filter is used to distinguish between particles that create multiple photons in the plastic scintillator (electrons and ions) and those that interact only in the glass filter or in the photomultiplier (mesons and muons). Ions are observed with energy in the MeV range as in previous timeof- flight experiments. They lose kinetic energy in a gas at a pressure up to 20 mbar as expected. Electron energy distributions with exponential shape corresponding to a temperature up to 600 MK indicate ignition of fusion. Intense emission of penetrating highenergy nuclear particles is detected at a high signal level as also reported previously (in this journal) for spontaneous processes. Both line-spectra and broad energy distributions are observed for these particles. The broad distributions give linear Kurie plots and are thus due to beta decay as concluded previously.
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| 7. |
- Holmlid, Leif, 1942, et al.
(författare)
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Decay of muons generated by laser-induced processes in ultra-dense hydrogen H(0)
- 2019
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Ingår i: Heliyon. - : Elsevier BV. - 2405-8440. ; 5:6
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Tidskriftsartikel (refereegranskat)abstract
- © 2019 The Authors This work reports identification of muons by their characteristic life-time of 2.20 μs after laser-induction of their precursor mesons, both kaons K± and KL0 and pions π± in ultra-dense hydrogen H(0). The pair-production signal from scattered muons at a metal converter in front of a photo-multiplier detector is observed with its decay. The observed signal intensity is decreased by a metal beam-flag which intercepts the meson and muon flux to the detector. Using D(0), the observed decay time is (2.23 ± 0.05) μs in agreement with the free muon lifetime of 2.20 μs. This signal is apparently due to the preferential generation of positive muons. Using p(0), the observed decay time is in the range 1–2 μs, thus shorter than the free muon lifetime, as expected when the signal is mainly caused by negative muons which interact with matter by muon capture.
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| 8. |
- Holmlid, Leif, 1942, et al.
(författare)
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Laser-induced annihilation: Relativistic particles from ultra-dense hydrogen H(0)
- 2021
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Ingår i: High Energy Density Physics. - : Elsevier BV. - 1574-1818. ; 40
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Tidskriftsartikel (refereegranskat)abstract
- Particle annihilation means that nuclear particles annihilate each other (for example nucleons like a neutron and an anti-neutron) and generate showers of mesons (mainly kaons and pions) at high energy. The kaons decay via pions and muons to electrons, positrons, neutrinos and photons. The energy which can be extracted from the very fast particles is of the order of 50% of the total energy of the nucleon masses involved or 500 MeV per mass unit. Several reports have been published recently on the meson showers ejected by pulsed-laser impact on ultra-dense hydrogen H(0). Since the particle velocities often are relativistic at >100 MeVu 1 it is clear that a much more efficient nuclear process is responsible than in a normal hydrogen isotope fusion process (which can give only 3 and 15 MeV per mass unit out). The first experiment showing heat production above break-even in a laser-induced nuclear process in H(0) was published in AIP Avances as early as 2015. Here, we use a standard method for relativistic particle detection to show that the particles ejected by the laser pulse from D(0) are charged (thus not photons), and in fact positive, and that the signals decay with the characteristic decay times of kaons and pions with uncertainty < 1%. Using the measured kinetic energies of the mesons gives exact energy conservation. We conclude that annihilation of nucleons in H(0) is observed. This may have profound effects on future energy production, since the efficiency of the fuel in annihilation is roughly a factor of 100 higher than in a nuclear fusion process. Ordinary hydrogen (protium and deuterium) can be used as fuel instead of radioactive tritium. This means that energy is generated at low cost and with very little harmful radiation both for terrestrial and space applications (Acta Astronautica 2020).
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| 9. |
- Holmlid, Leif, 1942, et al.
(författare)
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Muon detection studied by pulse-height energy analysis: Novel converter arrangements
- 2015
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 86:8
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Tidskriftsartikel (refereegranskat)abstract
- Muons are conventionally measured by a plastic scintillator–photomultiplier detector. Muons from processes in ultra-dense hydrogen H(0) are detected here by a novel type of converter in front of a photomultiplier. The muon detection yield can be increased relative to that observed with a plastic scintillator by at least a factor of 100, using a converter of metal, semiconductor (Ge), or glass for interaction with the muons penetrating through the metal housing of the detector. This detection process is due to transient formation of excited nuclei by the well-known process of muon capture, giving beta decay. The main experimental results shown here are in the form of beta electron energy spectra detected directly by the photomultiplier. Events which give a high-energy tail in the energy spectra are probably due to gamma photons from the muons. Sharp and intense x-ray peaks from a muonic aluminium converter or housing material are observed. The detection conversion in glass and Ge converters has a time constant of the order of many minutes to reach the final conversion level, while the process in metal converters is stabilized faster. The time constants are not due to lifetimes of the excited nuclei or neutrons but are due to internal charging in the insulating converter material. Interaction of this charging with the high voltage in the photomultiplier is observed.
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| 10. |
- Holmlid, Leif, 1942, et al.
(författare)
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Spontaneous ejection of high-energy particles from ultra-dense deuterium D(0)
- 2015
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Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199. ; 40:33, s. 10559-10567
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Tidskriftsartikel (refereegranskat)abstract
- High-energy particles are detected from spontaneous processes in an ultra-dense deuterium D(0) layer. Intense distributions of such penetrating particles are observed using energy spectroscopy and glass converters. Laser-induced emission of neutral particles with time-of-flight energies of 1-30 MeV u(-1) was previously reported in the same system. Both spontaneous line-spectra and a spontaneous broad energy distribution similar to a beta-decay distribution are observed. The broad distribution is concluded to be due to nuclear particles, giving straight-line Kurie-like plots. It is observed even at a distance of 3 m in air and has a total rate of 10(7)-10(10) s(-1). If spontaneous nuclear fusion or other nuclear processes take place in D(0), it may give rise to the high-energy particle signal. Low energy nuclear reactions (LENR) and so called cold fusion may also give rise to such particles.
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