The emerging two-dimensional
ferromagnetic materials present atomic
layer thickness and a perfect interface feature, which have become
an attractive research direction in the field of spintronics for low
power and deep nanoscale integration. However, it has been proven
to be extremely challenging to achieve a room-temperature ferromagnetic
candidate with well controlled dimensionality, large-scale production,
and convenient heterogeneous integration. Here, we report the growth
of wafer-scale two-dimensional Fe3GeTe2 integrated
with a topological insulator of Bi2Te3 by molecular
beam epitaxy, which shows a Curie temperature (T
c
) up to 400 K with perpendicular magnetic
anisotropy. Dimensionality-dependent magnetic and magnetotransport
measurements find that T
c
increases with decreasing Fe3GeTe2 thickness
in the heterostructures, indicating an interfacial engineering effect
from Bi2Te3. The theoretical calculation further
proves that the interfacial exchange coupling could significantly
enhance the intralayer spin interaction in Fe3GeTe2, hence giving rise to a higher T
c
. Our results provide great potential for the implementation
of high-performance spintronic devices based on two-dimensional ferromagnetic
materials.
Intrinsic valley polarization can be obtained in VSe monolayers with broken inversion symmetry and time reversal symmetry. First-principles investigations reveal that the magnitude of the valley splitting in magnetic VSe induced by spin-orbit coupling reaches as high as 78.2 meV and can be linearly tuned by biaxial strain. Besides conventional polarized light, hole doping or illumination with light of proper frequency can offer effective routes to realize valley polarization. Moreover, spin-orbit coupling in monolayer VSe breaks not only the valley degeneracy but also the three-fold rotational symmetry in band structure. The intrinsic and tunable valley splitting and the breaking of optical isotropy bring additional benefits to valleytronic and optoelectronic applications.
Cellular uptake, endosomal/lysosomal escape, and the effective dissociation from the carrier are a series of hurdles for specific genes to be delivered both in vitro and in vivo. To construct siRNA delivery systems, poly(allylamine hydrochloride) (PAH) and siRNA were alternately assembled on the surface of 11.8 ± 0.9 nm Au nanoparticles (GNP), stabilized by denatured bovine serum albumin, by the ionic layer-by-layer (LbL) self-assembly method. By manipulating the outmost PAH layer, GNP-PAH vectors with different surface electric potentials were prepared. Then, the surface potential-dependent cytotoxicity of the resultant GNP-PAH particles was evaluated via sulforhodamine B (SRB) assay, while the surface potential-dependent cellular uptake efficiency was quantitatively analyzed by using the flow cytometry method based on carboxyfluorescein (FAM)-labeled siRNA. It was revealed that the GNP-PAH particles with surface potential of +25 mV exhibited the optimal cellular uptake efficiency and cytotoxicity for human breast cancer MCF-7 cells. Following these results, two more positively charged polyelectrolytes with different protonating abilities in comparison with PAH, i.e., polyethylenimine (PEI), and poly(diallyl dimethyl ammonium chloride) (PDDA), were chosen to fabricate similarly structured vectors. Confocal fluorescence microscopy studies indicated that siRNA delivered by GNP-PAH and GNP-PEI systems was better released than that delivered by the GNP-PDDA system. Further flow cytometric assays based on immunofluorescence staining of the epidermal growth factor receptor (EGFR) revealed that EGFR siRNA delivered by GNP-PAH and GNP-PEI exhibited similar down-regulation effects on EGFR expression in MCF-7 cells. The following dual fluorescence flow cytometry assays by co-staining phosphatidylserine and DNA suggested the EGFR siRNA delivered by GNP-PAH exhibited an improved silencing effect in comparison with that delivered by the commercial transfection reagent Lipofectamine 2000.
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