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1.
Adv Mater ; 34(30): e2202072, 2022 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-35580350

RESUMO

Surface oxygen vacancies have been widely discussed to be crucial for tailoring the activity of various chemical reactions from CO, NO, to water oxidation by using oxide-supported catalysts. However, the real role and potential function of surface oxygen vacancies in the reaction remains unclear because of their very short lifetime. Here, it is reported that surface oxygen vacancies can be well confined electrostatically for a polarization screening near the perimeter interface between Pt {111} nanocrystals and the negative polar surface (001) of ferroelectric PbTiO3. Strikingly, such a catalyst demonstrates a tunable catalytic CO oxidation kinetics from 200 °C to near room temperature by increasing the O2 gas pressure, accompanied by the conversion curve from a hysteresis-free loop to one with hysteresis. The combination of reaction kinetics, electronic energy loss spectroscopy (EELS) analysis, and density functional theory (DFT) calculations, indicates that the oxygen vacancies stabilized by the negative polar surface are the active sites for O2 adsorption as a rate-determining step, and then dissociated O moves to the surface of the Pt nanocrystals for oxidizing adsorbed CO. The results open a new pathway for tunable catalytic activity of CO oxidation.

2.
Science ; 372(6543): 721-724, 2021 05 14.
Artigo em Inglês | MEDLINE | ID: mdl-33986177

RESUMO

The oxide interface between LaAlO3 and KTaO3(111) can harbor a superconducting state. We report that by applying a gate voltage (V G) across KTaO3, the interface can be continuously tuned from superconducting into insulating states, yielding a dome-shaped T c-V G dependence, where T c is the transition temperature. The electric gating has only a minor effect on carrier density but a strong one on mobility. We interpret the tuning of mobility in terms of change in the spatial profile of the carriers in the interface and hence, effective disorder. As the temperature is decreased, the resistance saturates at the lowest temperature on both superconducting and insulating sides, suggesting the emergence of a quantum metallic state associated with a failed superconductor and/or fragile insulator.

3.
Sci Adv ; 7(13)2021 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-33762343

RESUMO

Although the phenomenon of tunneling has been known since the advent of quantum mechanics, it continues to enrich our understanding of many fields of science. Commonly, this effect is described in terms of electrons traversing the potential barrier that exceeds their kinetic energy due to the wave nature of electrons. This picture of electron tunneling fails, however, for tunnel junctions, where the Fermi energy lies sufficiently close to the insulator valence band, in which case, hole tunneling dominates. We demonstrate the deterministic control of electron and hole tunneling in interface-engineered Pt/BaTiO3/La0.7Sr0.3MnO3 ferroelectric tunnel junctions by reversal of tunneling electroresistance. Our electrical measurements, electron microscopy and spectroscopy characterization, and theoretical modeling unambiguously point out to electron or hole tunneling regimes depending on interface termination. The interface control of the tunneling regime offers designed functionalities of electronic devices.

4.
Phys Rev Lett ; 126(2): 026802, 2021 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-33512194

RESUMO

We report on the observation of a T_{c}∼0.9 K superconductivity at the interface between LaAlO_{3} film and the 5d transition metal oxide KTaO_{3}(110) single crystal. The interface shows a large anisotropy of the upper critical field, and its superconducting transition is consistent with a Berezinskii-Kosterlitz-Thouless transition. Both facts suggest that the superconductivity is two-dimensional (2D) in nature. The carrier density measured at 5 K is ∼7×10^{13} cm^{-2}. The superconducting layer thickness and coherence length are estimated to be ∼8 and ∼30 nm, respectively. Our result provides a new platform for the study of 2D superconductivity at oxide interfaces.

5.
Adv Mater ; 32(14): e1904415, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-32090416

RESUMO

Topologically protected magnetic states have a variety of potential applications in future spintronics owing to their nanoscale size (<100 nm) and unique dynamics. These fascinating states, however, usually are located at the interfaces or surfaces of ultrathin systems due to the short interaction range of the Dzyaloshinskii-Moriya interaction (DMI). Here, magnetic topological states in a 40-unit cells (16 nm) SrRuO3 layer are successfully created via an interlayer exchange coupling mechanism and the interfacial DMI. By controlling the thickness of an antiferromagnetic and ferromagnetic layer, interfacial ionic polarization, as well as the transformation between ferromagnetic and magnetic topological states, can be modulated. Using micromagnetic simulations, the formation and stability of robust magnetic skyrmions in SrRuO3 /BiFeO3 heterostructures are elucidated. Magnetic skyrmions in thick multiferroic heterostructures are promising for the development of topological electronics as well as rendering a practical approach to extend the interfacial topological phenomena to bulk via antiferromagnetic order.

6.
J Hazard Mater ; 381: 120972, 2020 01 05.
Artigo em Inglês | MEDLINE | ID: mdl-31563671

RESUMO

With recently increasing environmental issues and foreseeable energy crisis, it is desirable to design cheap, efficient, and visible-light responsive nano-photocatalyst for CO2 conversion and pollutant degradation. Herein, we report a flower-like of MoS2-based hybrid photocatalyst with high efficiency through nanostructure and electronic structure engineering. Nanostructure control is used to fabricate MoS2 in to flower-like nanosheets (NSs) with large surface active area. Then MoS2 is coupled with conduction-band edge matched tin dioxide (SnO2) and decorated with Ag nanoparticles for suitable work function to create a unique cascade band alignment electronic structure to facilitate photoexcited charge transfer. It is shown that the amount-optimized nanocomposite of SnO2/Ag/MoS2 exhibits exceptional visible-light photocatalytic activities for conversion of carbon dioxide (CO2) to methane (CH4), approximately one order of magnitude enhancement than original MoS2 with the apparent quantum efficiency 2.38% at 420 nm. Similarly, the optimized sample also shows high activities for 2,4-diclorophenol, Methylene-Blue, Rhodamine-B and Methyl-Orange degradation as compared to pure MoS2. It is clearly demonstrated through combination of hydroxyl radical evaluation, photoelectrochemical and electrochemical impedance, that the enhanced photoactivities are attributed to the increased specific surface area, optimized band alignment for charge transfer and suppressed recombination. Our current work provides feasible routes for further research.

7.
Nano Lett ; 19(5): 3057-3065, 2019 05 08.
Artigo em Inglês | MEDLINE | ID: mdl-30964306

RESUMO

Complex oxide thin-film heterostructures often exhibit magnetic properties different from those known for bulk constituents. This is due to the altered local structural and electronic environment at the interfaces, which affects the exchange coupling and magnetic ordering. The emergent magnetism at oxide interfaces can be controlled by ferroelectric polarization and has a strong effect on spin-dependent transport properties of oxide heterostructures, including magnetic and ferroelectric tunnel junctions. Here, using prototype La2/3Sr1/3MnO3/BaTiO3 heterostructures, we demonstrate that ferroelectric polarization of BaTiO3 controls the orbital hybridization and magnetism at heterointerfaces. We observe changes in the enhanced orbital occupancy and significant charge redistribution across the heterointerfaces, affecting the spin and orbital magnetic moments of the interfacial Mn and Ti atoms. Importantly, we find that the exchange coupling between Mn and Ti atoms across the interface is tuned by ferroelectric polarization from ferromagnetic to antiferromagnetic. Our findings provide a viable route to electrically control complex magnetic configurations at artificial multiferroic interfaces, taking a step toward low-power spintronics.

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