6 research outputs found
3D Topological Semimetal Phases of Strained -Sn on Insulating Substrate
-Sn is an elemental topological material, whose topological phases
can be tuned by strain and magnetic field. Such tunability offers a substantial
potential for topological electronics. However, InSb substrates, commonly used
to stabilize -Sn allotrope, suffer from parallel conduction,
restricting transport investigations and potential applications. Here, the
successful MBE growth of high-quality -Sn layers on insulating, hybrid
CdTe/GaAs(001) substrates, with bulk electron mobility approaching 20000
cmVs is reported. The electronic properties of the samples
are systematically investigated by independent complementary techniques,
enabling thorough characterization of the 3D Dirac (DSM) and Weyl (WSM)
semimetal phases induced by the strains and magnetic field, respectively.
Magneto-optical experiments, corroborated with band structure modeling, provide
an exhaustive description of the bulk states in the DSM phase. The modeled
electronic structure is directly observed in angle-resolved photoemission
spectroscopy, which reveals linearly dispersing bands near the Fermi level. The
first detailed study of negative longitudinal magnetoresistance relates this
effect to the chiral anomaly and, consequently, to the presence of WSM.
Observation of the Berry phase in Shubnikov-de Haas oscillations agrees
with the topologically non-trivial nature of the investigated samples. Our
findings establish -Sn as an attractive topological material for
exploring relativistic physics and future applications.Comment: Main text: 35 pages, 7 figures; Supplementary Materials: 22 pages, 12
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Structural and optical properties of self-catalytic GaAs:Mn nanowires grown by molecular beam epitaxy on silicon substrates
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
Single-step synthesis of Er3+ and Yb3+ ions doped molybdate/Gd2O3 core–shell nanoparticles for biomedical imaging
Nanostructures as color-tunable luminescent markers have become major, promising tools for bioimaging and biosensing. In this paper separated molybdate/Gd2O3 doped rare earth ions (erbium, Er3+ and ytterbium, Yb3+) core–shell nanoparticles (NPs), were fabricated by a one-step homogeneous precipitation process. Emission properties were studied by cathodo- and photoluminescence. Scanning electron and transmission electron microscopes were used to visualize and determine the size and shape of the NPs. Spherical NPs were obtained. Their core–shell structures were confirmed by x-ray diffraction and energy-dispersive x-ray spectroscopy measurements. We postulated that the molybdate rich core is formed due to high segregation coefficient of the Mo ion during the precipitation. The calcination process resulted in crystallization of δ/ξ (core/shell) NP doped Er and Yb ions, where δ—gadolinium molybdates and ξ—molybdates or gadolinium oxide. We confirmed two different upconversion mechanisms. In the presence of molybdenum ions, in the core of the NPs, Yb3+– (mid2F7/2, 3T2〉) dimers were formed. As a result of a two 980 nm photon absorption by the dimer, we observed enhanced green luminescence in the upconversion process. However, for the shell formed by the Gd2O3:Er, Yb NPs (without the Mo ions), the typical energy transfer upconversion takes place, which results in red luminescence. We demonstrated that the NPs were transported into cytosol of the HeLa and astrocytes cells by endocytosis. The core–shell NPs are sensitive sensors for the environment prevailing inside (shorter luminescence decay) and outside (longer luminescence decay) of the tested cells. The toxicity of the NPs was examined using MTT assay.The research was partially supported by the European Union
within European Regional Development Fund, through grant
Innovative Economy (POIG.01.01.02-00-008/08) and was
partially supported by a grant from the Polish National Science Center 2013/11/B/N21/00089 and partially supported by the grant DEC-2012/07/B/ST5/02080 of the National
Science Center of Poland and Center of Excellence. This
work has been done in the NanoFun laboratories co-financed
by the European Regional Development Fund within the
Innovation Economy Operational Program, the Project no.
POIG.02.02.00-00-025/09/. This research has been co-finananced with the European Union funds by the European
Social Fund and was partially supported by the cluster of
Biomedical Engineering Center co-financed by European
Union funds under the Operational Programme Innovative
Economy (project number UDA-POIG.05.01.00-00). The
research was partially financed by the project Sonata from the
National Science Centre, UMO-2014/15/D/ST5/02604.
The research was partially supported by the Foundation for
Polish Science through the International Research Agenda
Programme co-financed by the European Union within Smart
Growth Operational Program. The research was supported by
the National Science Centre (Poland) through Grants No.
DEC-2014/14/M/ST3/00484.Peer reviewe
Spin Splitting Anisotropy in Single Diluted Magnetic Nanowire Heterostructures
We study the impact of the nanowire
shape anisotropy on the spin splitting of excitonic photoluminescence.
The experiments are performed on individual ZnMnTe/ZnMgTe core/shell
nanowires as well as on ZnTe/ZnMgTe core/shell nanowires containing
optically active magnetic CdMnTe insertions. When the magnetic field
is oriented parallel to the nanowire axis, the spin splitting is several
times larger than for the perpendicular field. We interpret this pronounced
anisotropy as an effect of mixing of valence band states arising from
the strain present in the core/shell geometry. This interpretation
is further supported by theoretical calculations which allow to reproduce
experimental results