| 1. |
- Hussain, Ghulam, et al.
(författare)
-
Pentagonal nanowires from topological crystalline insulators : a platform for intrinsic core-shell nanowires and higher-order topology
- 2024
-
Ingår i: Nanoscale Horizons. - : Royal Society of Chemistry. - 2055-6764 .- 2055-6756. ; 9, s. 1290-1300
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the experimental realization of Pb1-xSnx Te pentagonal nanowires (NWs) with [110] orientation using molecular beam epitaxy techniques. Using first-principles calculations, we investigate the structural stability of NWs of SnTe and PbTe in three different structural phases: cubic, pentagonal with [001] orientation and pentagonal with [110] orientation. Within a semiclassical approach, we show that the interplay between ionic and covalent bonds favors the formation of pentagonal NWs. Additionally, we find that this pentagonal structure is more likely to occur in tellurides than in selenides. The disclination and twin boundary cause the electronic states originating from the NW core region to generate a conducting band connecting the valence and conduction bands, creating a symmetry-enforced metallic phase. The metallic core band has opposite slopes in the cases of Sn and Te twin boundaries, while the bands from the shell are insulating. We finally study the electronic and topological properties of pentagonal NWs unveiling their potential as a new platform for higher-order topology and fractional charge. These pentagonal NWs represent a unique case of intrinsic core-shell one-dimensional nanostructures with distinct structural, electronic and topological properties between the core and the shell region. (a) Scanning transmission electron microscopy image of a pentagonal nanowire; the inset shows the disclination and core chain (CC). The red bands from the core connect the valence and conduction bands for (b) cation and (c) anion twin-boundaries.
|
|
| 2. |
- Kaleta, Anna, et al.
(författare)
-
Enhanced Ferromagnetism in Cylindrically Confined MnAs Nanocrystals Embedded in Wurtzite GaAs Nanowire Shells
- 2019
-
Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 19:10, s. 7324-7333
-
Tidskriftsartikel (refereegranskat)abstract
- Nearly a 30% increase in the ferromagnetic phase transition temperature has been achieved in strained MnAs nanocrystals embedded in a wurtzite GaAs matrix. Wurtzite GaAs exerts tensile stress on hexagonal MnAs nanocrystals, preventing a hexagonal to orthorhombic structural phase transition, which in bulk MnAs is combined with the magnetic one. This effect results in a remarkable shift of the magneto-structural phase transition temperature from 313 K in the bulk MnAs to above 400 K in the tensely strained MnAs nanocrystals. This finding is corroborated by the state of the art transmission electron microscopy, sensitive magnetometry, and the first-principles calculations. The effect relies on defining a nanotube geometry of molecular beam epitaxy grown core-multishell wurtzite (Ga,In)As/(Ga,Al)As/(Ga,Mn)As/GaAs nanowires, where the MnAs nanocrystals are formed during the thermal-treatment-induced phase separation of wurtzite (Ga,Mn)As into the GaAs-MnAs granular system. Such a unique combination of two types of hexagonal lattices provides a possibility of attaining quasi-hydrostatic tensile strain in MnAs (impossible otherwise), leading to the substantial ferromagnetic phase transition temperature increase in this compound.
|
|
| 3. |
- Lawniczak-Jablonska, Krystyna, et al.
(författare)
-
Magnetic properties of MnSb inclusions formed in GaSb matrix directly during molecular beam epitaxial growth
- 2011
-
Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 109:7
-
Tidskriftsartikel (refereegranskat)abstract
- Despite of intensive search for the proper semiconductor base materials for spintronic devices working at room temperature no appropriate material based on ferromagnetic semiconductors has been found so far. We demonstrate that the phase segregated system with MnSb hexagonal inclusions inside the GaSb matrix, formed directly during the molecular beam epitaxial growth reveals the ferromagnetic properties at room temperature and is a good candidate for exploitation in spintronics. Furthermore, the MnSb inclusions with only one crystalline structure were identified in this GaMn:MnSb granular material. The SQUID magnetometry confirmed that this material exhibits ferromagnetic like behavior starting from helium up to room temperature. Moreover, the magnetic anisotropy was found which was present also at room temperature, and it was proved that by choosing a proper substrate it is possible to control the direction of easy axis of inclusions' magnetization moment between in-plane and out-of-plane; the latter is important in view of potential applications in spintronic devices. (C) 2011 American Institute of Physics. [doi:10.1063/1.3562171]
|
|
| 4. |
- Sadowski, Janusz, et al.
(författare)
-
Bi incorporation and segregation in the MBE-grown GaAs-(Ga,Al) As-Ga(As,Bi) core shell nanowires
- 2022
-
Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 12:1
-
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.
|
|
| 5. |
- Sadowski, Janusz, et al.
(författare)
-
Defect-free SnTe topological crystalline insulator nanowires grown by molecular beam epitaxy on graphene
- 2018
-
Ingår i: Nanoscale. - : Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 10:44, s. 20772-20778
-
Tidskriftsartikel (refereegranskat)abstract
- SnTe topological crystalline insulator nanowires have been grown by molecular beam epitaxy on graphene/SiC substrates. The nanowires have a cubic rock-salt structure, they grow along the [001] crystallographic direction and have four sidewalls consisting of {100} crystal planes known to host metallic surface states with a Dirac dispersion. Thorough high resolution transmission electron microscopy investigations show that the nanowires grow on graphene in the van der Waals epitaxy mode induced when the catalyzing Au nanoparticles mix with Sn delivered from a SnTe flux, providing a liquid Au-Sn alloy. The nanowires are totally free from structural defects, but their {001} sidewalls are prone to oxidation, which points out the necessity of depositing a protective capping layer in view of exploiting the magneto-electric transport phenomena involving charge carriers occupying topologically protected states.
|
|
