| 1. |
- Abe, K., et al.
(författare)
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J-PARC Neutrino Beamline Upgrade Technical Design Report
- 2019
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Rapport (refereegranskat)abstract
- In this document, technical details of the upgrade plan of the J-PARC neutrino beamline for the extension of the T2K experiment are described. T2K has proposed to accumulate data corresponding to 2×1022 protons-on-target in the next decade, aiming at an initial observation of CP violation with 3σ or higher significance in the case of maximal CP violation. Methods to increase the neutrino beam intensity, which are necessary to achieve the proposed data increase, are described.
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| 2. |
- Bruzzi, M, et al.
(författare)
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Radiation-hard semiconductor detectors for SuperLHC
- 2005
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 541:1-2, s. 189-201
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Tidskriftsartikel (refereegranskat)abstract
- An option of increasing the luminosity of the Large Hadron Collider (LHC) at CERN to 1035 cm-2 s-1 has been envisaged to extend the physics reach of the machine. An efficient tracking down to a few centimetres from the interaction point will be required to exploit the physics potential of the upgraded LHC. As a consequence, the semiconductor detectors close to the interaction region will receive severe doses of fast hadron irradiation and the inner tracker detectors will need to survive fast hadron fluences of up to above 1016cm-2. The CERN-RD50 project "Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders" has been established in 2002 to explore detector materials and technologies that will allow to operate devices up to, or beyond, this limit. The strategies followed by RD50 to enhance the radiation tolerance include the development of new or defect engineered detector materials (SiC, GaN, Czochralski and epitaxial silicon, oxygen enriched Float Zone silicon), the improvement of present detector designs and the understanding of the microscopic defects causing the degradation of the irradiated detectors. The latest advancements within the RD50 collaboration on radiation hard semiconductor detectors will be reviewed and discussed in this work.
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| 3. |
- Kowalik, I. A., et al.
(författare)
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Element-specific characterization of heterogeneous magnetism in (Ga,Fe)N films
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 85:18, s. 184411-
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Tidskriftsartikel (refereegranskat)abstract
- We employ x-ray spectroscopy to characterize the distribution and magnetism of particular alloy constituents in (Ga,Fe)N films grown by metal organic vapor phase epitaxy. Furthermore, photoelectron microscopy gives direct evidence for the aggregation of Fe ions, leading to the formation of Fe-rich nanoregions adjacent to the samples surface. A sizable x-ray magnetic circular dichroism (XMCD) signal at the Fe L edges in remanence and at moderate magnetic fields at 300 K links the high-temperature ferromagnetism with the Fe(3d) states. A sizable value of the orbital moment measured in remanence points to a large magnetic anisotropy and to a correspondingly high blocking temperature, which can stabilize the ferromagnetic-like response of the Fe-rich nanocrystals at 300 K. The XMCD response at the N K edge highlights that the N(2p) states, due to exchange coupling to Fe ions, carry considerable spin polarization. These results, supported by ab initio studies of XMCD spectra for various FeN delta nanocrystals, demonstrate that nanocrystals with delta > 0.25 account for the ferromagnetic behavior of (Ga,Fe)N films.
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| 4. |
- Sawicki, M., et al.
(författare)
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Homogeneous and heterogeneous magnetism in (Zn,Co)O : From a random antiferromagnet to a dipolar superferromagnet by changing the growth temperature
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 88:8
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Tidskriftsartikel (refereegranskat)abstract
- A series of (Zn,Co)O layers with Co contents x up to 40% grown by atomic layer deposition have been investigated. All structures deposited at 160 degrees C show magnetic properties specific to II-VI dilute magnetic semiconductors with localized spins S = 3/2 coupled by strong but short-range antiferromagnetic interactions resulting in low-temperature spin-glass freezing for x = 0.16 and 0.4. At higher growth temperature (200 degrees C) metallic Co nanocrystals precipitate in two locations giving rise to two different magnetic responses: (i) a superparamagnetic contribution coming from volume disperse nanocrystals; (ii) a ferromagneticlike behavior brought about by nanocrystals residing at the (Zn,Co)O/substrate interface. It is shown that the dipolar coupling within the interfacial two-dimensional dense dispersion of nanocrystals is responsible for the ferromagneticlike behavior.
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| 5. |
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| 6. |
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| 7. |
- Luque, Francisco J., et al.
(författare)
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Enantiosensitive Bonding of Chiral Molecules on a Magnetic Substrate Investigated by Means of Electron Spectroscopies
- 2018
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Ingår i: CHIMIA. - : Swiss Chemical Society. - 0009-4293 .- 2673-2424. ; 72:6, s. 418-423
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of purely organic chiral molecules on ferromagnetic Co thin films is studied under ultra high vacuum conditions by means of synchrotron radiation-based electron spectroscopies, namely X-ray absorption and ultraviolet photoemission. X-ray absorption reveals that enantiomers with opposite handedness (R,R) - and (S,S)- of two different molecules adsorb with different strength on the Co surfaces and their valence band photoemission spectra also display distinctive features. In view of the recent reports describing the chiral-induced spin selectivity (CISS) effect these results lead us to consider the possibility that some enantiosensitivity may appear when bonding chiral molecules to a substrate with an initial asymmetry in the population of the different spin orientations.
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| 8. |
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| 9. |
- Kowalik, I. A., et al.
(författare)
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MnAs dots grown on GaN( 000(1)over-bar)-(1x1) surface
- 2007
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969 .- 1098-0121. ; 75:23, s. 11-
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Tidskriftsartikel (refereegranskat)abstract
- MnAs has been grown by means of MBE on the GaN(000 (1) over bar)-(1x1) surface. Two options of initiating the crystal growth were applied: (a) a regular MBE procedure (manganese and arsenic were delivered simultaneously) and (b) subsequent deposition of manganese and arsenic layers. It was shown that spontaneous formation of MnAs dots with the surface density of 1x10(11) cm(-2) and 2.5x10(11) cm(-2), respectively (as observed by atomic force microscopy), occurred for the layer thickness higher than 5 ML. Electronic structure of the MnAs/GaN systems was studied by resonant photoemission spectroscopy. That led to determination of the Mn 3d-related contribution to the total density of states distribution of MnAs. It has been proven that the electronic structures of the MnAs dots grown by the two procedures differ markedly. One corresponds to metallic, ferromagnetic NiAs-type MnAs, the other is similar to that reported for half-metallic zinc-blende MnAs. Both systems behave superparamagnetically (as revealed by magnetization measurements), but with both the blocking temperatures and the intradot Curie temperatures substantially different. The intradot Curie temperature is about 260 K for the former system while markedly higher than room temperature for the latter one. Relations between growth process, electronic structure, and other properties of the studied systems are discussed. Possible mechanisms of half-metallic MnAs formation on GaN are considered.
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| 10. |
- Kowalik, I. A., et al.
(författare)
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Soft x-ray absorption spectroscopy on Co doped ZnO : structural distortions and electronic structure
- 2016
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Ingår i: 16th International Conference On X-Ray Absorption Fine Structure (XAFS16). - : IOP Publishing.
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Konferensbidrag (refereegranskat)abstract
- We present soft x-ray absorption spectra from a series of Co doped ZnO films. We discuss systematic variations of the Co L-edge white line intensity and multiplet features for this series of samples. We document sizeable differences in the electronic state of the Co ionic cores, as well as in the local environment of the host lattice atoms, characterised by means of x-ray absorption spectra at the O K-edge and Zn L-edges. Model calculations allow to correlate the observed effects to small structural distortions of the ZnO lattice.
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