Abstract
Magnetic topological insulators (MTIs) offer a combination of topologically nontrivial characteristics and magnetic order and show promise in terms of potentially interesting physical ...phenomena such as the quantum anomalous Hall (QAH) effect and topological axion insulating states. However, the understanding of their properties and potential applications have been limited due to a lack of suitable candidates for MTIs. Here, we grow two-dimensional single crystals of Mn(Sb
x
Bi
(1-
x
)
)
2
Te
4
bulk and exfoliate them into thin flakes in order to search for intrinsic MTIs. We perform angle-resolved photoemission spectroscopy, low-temperature transport measurements, and first-principles calculations to investigate the band structure, transport properties, and magnetism of this family of materials, as well as the evolution of their topological properties. We find that there exists an optimized MTI zone in the Mn(Sb
x
Bi
(1-
x
)
)
2
Te
4
phase diagram, which could possibly host a high-temperature QAH phase, offering a promising avenue for new device applications.
The paper firstly reports one strategy for scalable synthesis of Ta1.1O1.05/biomass carbon composite by boron-doped graphene quantum dots. The strategy breaks through the limitations of low intrinsic ...conductivity and insufficient electroactive sites of tantalum oxide, realizes the remarkable improvement of supercapacitor performance, and shows a bright prospect of application in high-performance supercapacitors.
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•We report one promising strategy for scalable synthesis of Ta1.1O1.05/biomass carbon composite.•The composite offers small size of Ta1.1O1.05, Abundant oxygen vacancies and PN heterojunction.•Unique structure achieves to ultrahigh electron conductivity and electrochemical active sites.•The composite electrode provides excellent electrochemical performances for supercapacitors.•The study proves oxygen vacancy and PN heterojunction improve supercapacitor performance.
Low intrinsic conductivity and insufficient electroactive sites hinder wide applications of tantalum oxide in supercapacitors. The study reports scalable synthesis of Ta1.1O1.05/biomass carbon (C) composite with multiple structure engineering by boron-doped graphene quantum dot (B-GQD). B-GQD was orderly coordinated with Ta(V) ion to produce Ta-B-GQD complex, sucked into cotton and dried. Followed by annealing at 900 °C in N2 to obtain B-GQD-Ta1.1O1.05/C. Experimental result and theoretical calculation demonstrate that the introduction of B-GQD results in formation of Ta1.1O1.05 nanorods with low valence, small size, highly exposed high-index crystal faces, oxygen vacancies and PN junction. The structure dramatically improves the intrinsic conductivity, electroactive sites and voltage window range. The B-GQD-Ta1.1O1.05/C electrode exhibits high capacitance of 528.3 F g−1 at 0.5 A/g, which is more than that of Ta1.1O1.05 electrode (130.9 F g−1). The flexible symmetrical supercapacitor provides ultrahigh capacitance of 374.1 F g−1 at 1 A/g, high-rate capacity of 207.8 F g−1 at 50 A/g, capacity retention of 98.7 % after 10,000 cycles at 10 A/g and energy density of 113.9 W h Kg−1 at 521.2 W kg−1. The supercapacitor has been successfully applied in the self-powered attitude sensor driven via friction nanogenerator to monitor human walking posture.
The discovery of a new type‐II Dirac semimetal in Ir1−xPtxTe2 with optimized band structure is described. Pt dopants protect the crystal structure holding the Dirac cones and tune the Fermi level ...close to the Dirac point. The type‐II Dirac dispersion in Ir1−xPtxTe2 is confirmed by angle‐resolved photoemission spectroscopy and first‐principles calculations. Superconductivity is also observed and persists when the Fermi level aligns with the Dirac points. Ir1−xPtxTe2 is an ideal platform for further studies on the exotic properties and potential applications of type‐II DSMs, and opens up a new route for the investigation of the possible topological superconductivity and Majorana physics.
A type‐II Dirac semimetal in Ir1−xPtxTe2 with optimized Dirac dispersions is experimentally discovered by angle‐resolved photoemission spectroscopy. The Pt dopant protects the crystal structure holding the Dirac cones and tunes the Fermi level close to the Dirac point. Combining the type‐II Dirac cone, Fermi level tunability, and superconductivity together, Ir1−xPtxTe2 provides an ideal platform for more in‐depth research of type‐II DSMs.
Abstract The current strategies for building 2D organic-inorganic heterojunctions involve mostly wet-chemistry processes or exfoliation and transfer, leading to interface contaminations, poor ...crystallizing, or limited size. Here we show a bottom-up procedure to fabricate 2D large-scale heterostructure with clean interface and highly-crystalline sheets. As a prototypical example, a well-ordered hydrogen-bonded organic framework is self-assembled on the highly-oriented-pyrolytic-graphite substrate. The organic framework adopts a honeycomb lattice with faulted/unfaulted halves in a unit cell, resemble to molecular “graphene”. Interestingly, the topmost layer of substrate is self-lifted by organic framework via strong interlayer coupling, to form effectively a floating organic framework/graphene heterostructure. The individual layer of heterostructure inherits its intrinsic property, exhibiting distinct Dirac bands of graphene and narrow bands of organic framework. Our results demonstrate a promising approach to fabricate 2D organic-inorganic heterostructure with large-scale uniformity and highly-crystalline via the self-lifting effect, which is generally applicable to most of van der Waals materials.
The intercalation of metal is a promising method for the modulating electronic properties in transition metal dichalcogenides (TMDs). However, there still lacks enough knowledge about how the ...intercalated atoms directly impact the two-dimensional structural layers and modulate the band structures therein. Taking advantage of X-ray absorption fine structure and angle-resolved photoemission spectroscopy, we studied how Cu intercalation influences the host TaSe
2
layers in Cu
0.03
TaSe
2
crystals. The intercalated Cu atoms form bonds with Se of the host layers, and there is charge transfer from Cu to Se. By examining the changes of band dispersions, we show that the variation of electronic structures is beyond a simple rigid band model with merely charge doping effect. This work reveals that the unusual change of band dispersions is associated with the formation of bonds between the intercalated metal elements and anion ions in the host layers, and provides a reference for the comprehensive understanding of the electronic structures in intercalated materials.
The phenomenon of oxygen incorporation-induced superconductivity in iron telluride (Fe1+yTe, with antiferromagnetic (AFM) orders) is intriguing and quite different from the case of FeSe. Until now, ...the microscopic origin of the induced superconductivity and the role of oxygen are far from clear. Here, by combining in situ scanning tunneling microscopy/spectroscopy (STM/STS) and X-ray photoemission spectroscopy (XPS) on oxygenated FeTe, we found physically adsorbed O2 molecules crystallized into c (2/3 × 2) structure as an oxygen overlayer at low temperature, which was vital for superconductivity. The O2 overlayer were not epitaxial on the FeTe lattice, which implied weak O2 –FeTe interaction but strong molecular interactions. The energy shift observed in the STS and XPS measurements indicated a hole doping effect from the O2 overlayer to the FeTe layer, leading to a superconducting gap of 4.5 meV opened across the Fermi level. Our direct microscopic probe clarified the role of oxygen on FeTe and emphasized the importance of charge transfer effect to induce superconductivity in iron-chalcogenide thin films.
Intercalating magnetic atoms in 2D transition‐metal dichalcogenides (TMDCs) is a feasible route for fabricating 2D magnetic materials. As a 2D‐TMDC, the ground state of monolayer (ML) 1T‐VSe2 should ...be the charge‐density‐wave state rather than the ferromagnetic state. In this study, magnetism is induced in 1T‐VSe2 via the realization of selectable molecular beam epitaxial growth of both ML 1T‐VSe2 and ML V5Se8 films on a bilayer graphene substrate. The morphologies of the grown 1T‐VSe2 and V5Se8 films are characterized using scanning tunneling microscope, which showed differences in the heights of the domains. Subsequently, combining in situ X‐Ray photoemission spectroscopy measurements, it is determined that the grown V5Se8 film contained 26.7% more V atoms than the 1T‐VSe2 film, thereby confirming the chemical stoichiometry of the created samples. In addition, using in situ angle‐resolved photoemission spectroscopy measurements, the different electronic structures of the ML 1T‐VSe2 and ML V5Se8 films are studied. The results obtained indicate that the method applied is an effective way for realizing selective growth of 1T‐VSe2 or V5Se8 films, while providing significant information on their electronic structure differences, which can aid in investigating the magnetic properties of V5Se8.
Using the molecular beam epitaxial method, the selectable growth of monolayer 1T‐VSe2 and V5Se8 films on graphene substrate is realized by applying different substrate temperatures. Their distinct phase structures and electronic structures are investigated by reflection high‐energy electron diffraction, scanning tunneling microscopy, X‐Ray photoemission spectroscopy, and angle‐resolved photoemission spectroscopy.
By restricting the dilated deformation, surface modification can stimulate multiple shear banding and improve the plasticity of bulk metallic glasses (BMGs). Aimed at modifying the surface of BMGs by ...thin layers, a crystalline Ni coating with ultrafine grains was coated on the surface of a Ti-based BMG by electroless plating. With a thickness of about 10 μm, the prepared thin coating could effectively limit the fast propagation of primary shear bands and stimulate the nucleation of multiple shear bands. As a result, the compression plasticity of the coated Ti-based BMG was improved to about 3.7% from near 0% of the non-coated BMG. Except for a small amount of Ni coating was adhered to the BMG substrate after fracture, most of the coatings were peeled off from the surface. It can be attributed to the abnormal growth of some coarse grains/particles in local region of the coating, which induces a large tensile stress at the interface between the coating and the BMG substrate. It is suggested that, for electroless nickel plating, improving the adhesive bonding strength between the coating and the substrate has a better geometric restriction effect than simply increasing the thickness of the coating.
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