| 1. |
- Šiušys, Aloyzas, et al.
(författare)
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All wurtzite (In,Ga)As-(Ga,Mn)As core-shell nanowires
- 2014
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 14:8, s. 4263-4272
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Tidskriftsartikel (refereegranskat)abstract
- Structural and magnetic properties of (In,Ga)As-(Ga,Mn)As core−shell nanowires grown by molecular beam epitaxy on GaAs(111)B substrate with gold catalyst have been investigated. (In,Ga)As core nanowires were grown at high temperature (500 °C) whereas (Ga,Mn)As shells were deposited on the {11̅00} side facets of the cores at much lower temperature (220 °C). High-resolution transmission electron microscopy images and high spectral resolution Raman scattering data show that both the cores and the shells of the nanowires have wurtzite crystalline structure. Scanning and transmission electron microscopy observations show smooth (Ga,Mn)As shells containing 5% of Mn epitaxially deposited on (In,Ga)As cores containing about 10% of In without any misfit dislocations at the core−shell interface. With the In content in the (In,Ga)As cores larger than 5% the (In,Ga)As lattice parameter is higher than that of (Ga,Mn)As and the shell is in the tensile strain state. Elaborated magnetic studies indicate the presence of ferromagnetic coupling in (Ga,Mn)As shells at the temperatures in excess of 33 K. This coupling is maintained only in separated mesoscopic volumes resulting in an overall superparamagnetic behavior which gets blocked below ∼17 K.
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| 2. |
- Fröhlich-Gildhoff, Klaus, et al.
(författare)
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Violence Prevention and Resilience Promotion in Schools : Report about the international research project STRONG - Supportive Tools for Resilient Open-minded and Non-violent Grassroots work in schools
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Violent prevention research findings suggest different key aspects for the application of a powerful prevention strategy. The project tries to tackle the complexity of supporting a healthy mental development in children while also meeting the requirments for succesful prevention. Resilience promotion proved to be a suitable concept for implementing a violence prevention strategy in secondary schools. This two-year practice-oriented research project, with international partners from five contries had the aim of supporting schools in developing a resilience-promoting and violence-preventing strategy in a multi-level and multi-setting approach. As a result, a toolbox for resource-oriented training in schools for teachers and pupils was created. The measures undertaken during the project have been evaluated empirically and the iflunce of resilience-promoting acivities in school has been assessed. Different national implementations in easch country are presented as well as international comparisons, reflections and perspectives.
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| 3. |
- Gas, Katarzyna, et al.
(författare)
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Structural and optical properties of self-catalytic GaAs:Mn nanowires grown by molecular beam epitaxy on silicon substrates
- 2013
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 5:16, s. 7410-7418
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Tidskriftsartikel (refereegranskat)abstract
- Mn-doped GaAs nanowires were grown in the self-catalytic growth mode on the oxidized Si(100) surface by molecular beam epitaxy and characterized by scanning and transmission electron microscopy, Raman scattering, photoluminescence, cathodoluminescence, and electron transport measurements. The transmission electron microscopy studies evidenced the substantial accumulation of Mn inside the catalyzing Ga droplets on the top of the nanowires. Optical and transport measurements revealed that the limit of the Mn content for self-catalysed growth of GaAs nanowires corresponds to the doping level, i.e., it is much lower than the Mn/Ga flux ratio (about 3%) used during the MBE growth. The resistivity measurements of individual nanowires confirmed that they are conductive, in accordance with the photoluminescence measurements which showed the presence of Mn2+ acceptors located at Ga sites of the GaAs host lattice of the nanowires. An anomalous temperature dependence of the photoluminescence related to excitons was demonstrated for Mn-doped GaAs nanowires.
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| 4. |
- Sadowski, Janusz, et al.
(författare)
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Bi incorporation and segregation in the MBE-grown GaAs-(Ga,Al) As-Ga(As,Bi) core shell nanowires
- 2022
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Incorporation of Bi into GaAs-(Ga,Al)As-Ga(As,Bi) core-shell nanowires grown by molecular beam epitaxy is studied with transmission electron microscopy. Nanowires are grown on GaAs(111)B substrates with Au-droplet assisted mode. Bi-doped shells are grown at low temperature (300 degrees C) with a close to stoichiometric Ga/As flux ratio. At low Bi fluxes, the Ga(As,Bi) shells are smooth, with Bi completely incorporated into the shells. Higher Bi fluxes (Bi/As flux ratio similar to 4%) led to partial segregation of Bi as droplets on the nanowires sidewalls, preferentially located at the nanowire segments with wurtzite structure. We demonstrate that such Bi droplets on the sidewalls act as catalysts for the growth of branches perpendicular to the GaAs trunks. Due to the tunability between zinc-blende and wurtzite polytypes by changing the nanowire growth conditions, this effect enables fabrication of branched nanowire architectures with branches generated from selected (wurtzite) nanowire segments.
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| 5. |
- Sadowski, Janusz, et al.
(författare)
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GaAs-MnAs nanowires
- 2011
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Ingår i: Physica Status Solidi. B: Basic Research. - : Wiley. - 0370-1972. ; 248:7, s. 1576-1580
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Tidskriftsartikel (refereegranskat)abstract
- Different strategies for obtaining nanowires (NWs) with ferromagnetic properties using the molecular beam epitaxy (MBE) grown nanostructures combining GaAs and Mn were investigated. Four types of structures have been studied: (i) self-catalyzed GaAs: Mn NWs grown at low temperatures on GaAs(100) substrates; (ii) GaAs: Mn NWs grown at high temperatures on Si(100) substrates; (iii) GaAs-GaMnAs core-shell NW structures; (iv) GaAs-MnAs core-shell NW structures grown on Si(100). Structures of types (i), (iii), and (iv) exhibit ferromagnetic properties. Right: Scanning electron microscopy image of Mn doped GaAs NWs with Ga droplets at the tops, grown by MBE on oxidized Si(100) substrate in the autocatalytic growth mode. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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| 6. |
- Wadge, Ashutosh S., et al.
(författare)
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Electronic properties of TaAs2 topological semimetal investigated by transport and ARPES
- 2022
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 34:12
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Tidskriftsartikel (refereegranskat)abstract
- We have performed electron transport and angle-resolved photo-emission spectroscopy ( ARPES) measurements on single crystals of transition metal dipnictide TaAs2 cleaved along the ((2) over bar 01) surface which has the lowest cleavage energy. A Fourier transform of the Shubnikov-de Haas oscillations shows four different peaks whose angular dependence was studied with respect to the angle between magnetic field and the [(2) over bar 01] direction. The results indicate elliptical shape of the Fermi surface cross- sections. Additionally, a mobility spectrum analysis was carried out, which also reveals at least four types of carriers contributing to the conductance (two kinds of electrons and two kinds of holes). ARPES spectra were taken on freshly cleaved ((2) over bar 01) surface and it was found that bulk states pockets at constant energy surface are elliptical, which confirms the magnetotransport angle dependent studies. First-principles calculations support the interpretation of the experimental results. The theoretical calculations better reproduce the ARPES data if the theoretical Fermi level (FL) is increased, which is due to a small n-doping of the samples. This shifts the FL closer to the Dirac point, allowing investigating the physics of the Dirac andWeyl points, making this compound a platform for the investigation of the Dirac andWeyl points in three-dimensional materials.
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