Search

Here, we use KPFM to directly distinguish AB-BLG (BLG), ABA-TLG (TLG), and twisted bilayer graphene (tBLG). Furthermore, we have explored the relationship between the surface potential and the different twist angles of tBLG.

Landau quantization associated with the quantized cyclotron motion of electrons under magnetic field provides the effective way to investigate topologically protected quantum states with entangled degrees of freedom and multiple quantum numbers. Here we report the cascade of Landau quantization in a strained type-II Dirac semimetal NiTe2 with spectroscopic-imaging scanning tunneling microscopy. The uniform-height surfaces exhibit single-sequence Landau levels (LLs) at a magnetic field originating from the quantization of topological surface state (TSS) across the Fermi level. Strikingly, we reveal the multiple sequence of LLs in the strained surface regions where the rotation symmetry is broken. Firstprinciples calculations demonstrate that the multiple LLs attest to the remarkable lifting of the valley degeneracy of TSS by the in-plane uniaxial or shear strains. Our findings pave a pathway to tune multiple degrees of freedom and quantum numbers of TMDs via strain engineering for practical applications such as high-frequency rectifiers, Josephson diode and valleytronics., Nano Letters 23, 3274 (2023)

As a ferromagnetic topological semimetal with a strong anomalous Hall effect (AHE), Co3Sn2S2 has been extensively explored for manipulating the topological state via the changed magnetic order as well as device applications connecting dissipationless spin and charge transport1-3. However, the main challenge is the improvement of the crystal quality, which is crucial for enhancing physical properties including AHE, carrier mobility, and magnetoresistance4,5. Here, we report the synthesis of ultra pure Co3Sn2S2 single crystals with an ultra low impurity density by an innovative crystal-sourced chemical vapor transport (CS-CVT) approach, achieving ultrahigh anomalous Hall angle (AHA) of 40%, carrier mobility and magnetoresistance (MR) of 10490 cm2V-1s-1 and 2500%, respectively. These values represent a huge improvement on previously reported highest values of either pristine or doped Co3Sn2S2 (of 33%, 2600 cm2V-1s-1, and 180% respectively)4,6. Equally importantly, the anomalous Hall conductivity (AHC) of our crystals reached 1600 Ω-1cm-1, which is larger than the theoretically predicted value of 1310 Ω-1cm-1 from the integral of Berry curvature7. Observation of an ultranarrow flat band and topological surface states near the Fermi level provides good microscopic understanding of this gigantic anomalous Hall effect. Our high-quality magnetic topological materials are expected to facilitate a full understanding of the strong electronic correlation and may perhaps lead to the discovery of a quantum AHE in the 2D limit.

Water electrolysis is a promising technique for carbon neutral hydrogen production. A great challenge remains at developing robust and low-cost anode catalysts. Many pre-catalysts are found to undergo surface reconstruction to give high intrinsic activity in the oxygen evolution reaction (OER). The reconstructed oxyhydroxides on the surface are active species and most of them outperform directly synthesized oxyhydroxides. The reason for the high intrinsic activity remains to be explored. Here, a study is reported to showcase the unique reconstruction behaviors of a pre-catalyst, thiospinel CoFe2 S4 , and its reconstruction chemistry for a high OER activity. The reconstruction of CoFe2 S4 gives a mixture with both Fe-S component and active oxyhydroxide (Co(Fe)Ox Hy ) because Co is more inclined to reconstruct as oxyhydroxide, while the Fe is more stable in Fe-S component in a major form of Fe3 S4 . The interface spin channel is demonstrated in the reconstructed CoFe2 S4 , which optimizes the energetics of OER steps on Co(Fe)Ox Hy species and facilitates the spin sensitive electron transfer to reduce the kinetic barrier of O-O coupling. The advantage is also demonstrated in a membrane electrode assembly (MEA) electrolyzer. This work introduces the feasibility of engineering the reconstruction chemistry of the precatalyst for high performance and durable MEA electrolyzers. Ministry of Education (MOE) National Research Foundation (NRF) Submitted/Accepted version The authors thank the support from the Singapore Ministry of Education Tier 2 Grant (MOE-T2EP10220-0001) and the Singapore National Research Foundation under its Campus for Research Excellence and Technological Enterprise (CREATE) programme, through the Cambridge Center for Carbon Reduction in Chemical Technology (C4T) and eCO2EP programmes.

Producing hydrogen by water electrolysis suffers from the kinetic barriers in the oxygen evolution reaction (OER) that limits the overall efficiency. With spin-dependent kinetics in OER, to manipulate the spin ordering of ferromagnetic OER catalysts (e.g., by magnetization) can reduce the kinetic barrier. However, most active OER catalysts are not ferromagnetic, which makes the spin manipulation challenging. In this work, we report a strategy with spin pinning effect to make the spins in paramagnetic oxyhydroxides more aligned for higher intrinsic OER activity. The spin pinning effect is established in oxideFM/oxyhydroxide interface which is realized by a controlled surface reconstruction of ferromagnetic oxides. Under spin pinning, simple magnetization further increases the spin alignment and thus the OER activity, which validates the spin effect in rate-limiting OER step. The spin polarization in OER highly relies on oxyl radicals (O∙) created by 1st dehydrogenation to reduce the barrier for subsequent O-O coupling., Water oxidation to triplet oxygen requires a spin polarization process for faster kinetics. Here, the authors show an interface spin pinning effect between ferromagnetic oxides and reconstructed oxyhydroxide surface layer, where the spin ordering in paramagnetic oxyhydroxide catalyst layer can be tuned to improve the intrinsic activity.

The production of hydrogen by water electrolysis suffers from the kinetic barriers in the oxygen evolution reaction (OER) that limits the overall efficiency. As spin-dependent kinetics exist in OER, the spin alignment in active OER catalysts is critical for reducing the kinetic barriers in OER. It is effective to facilitate the spin polarization in ferromagnetic catalysts by applying external magnetic field, which increases the OER efficiency. However, more active OER catalysts tend to have dynamic open-shell orbital configurations with disordered magnetic moments, without showing an apparent long-range interatomic ferromagnetism; thus controlling the spin alignment of these active catalysts is challenging. In this work, we report a strategy with spin pinning effect to make the spins in active oxyhydroxides more aligned for higher intrinsic OER activity. Such strategy bases on a controllable reconstruction: ferromagnetic oxides with controlled sulfurization can evolve into stable oxideFM/oxyhydroxide configurations with a thin oxyhydroxide layer under operando condition. The spin pinning effect is found at the interface of oxideFM/oxyhydroxide. The spin pinning effect can promote spin selective electron transfer on OER intermediates to generate oxygens with parallel spin alignment, which facilitates the production of triplet oxygen and increases the intrinsic activity of oxyhydroxide by ~ 1 order of magnitude. Under spin pinning, the spins in oxyhydroxide can become more aligned after magnetization as long-range ferromagnetic ordering is established on the magnetic domains in oxideFM. The OER kinetics are facilitated accordingly after magnetization, implying that the spin pinning effect is involved in the rate-determining step and this step is spin dependent. The spin polarization process in OER under spin pinning is also believed to be sensitive to the existence of active oxygen ligand (O(-)) in oxyhydroxide. When the O(-) is created in 1st deprotonation step under high pH, the spin polarization of ligand oxygens will be facilitated, which reduces the barrier for subsequent O-O coupling and promotes the O2 turnover.

Colloid-synthesized matchstick-shaped Au–ZnO heterogeneous nanorods are found to have the Zn ion terminated plane in the ZnO–Au interface without the formation of Au–O bonds based on the atomic-resolution observation of their interfacial structure and electronic states, which is greatly different from the other reported results. The Au–ZnO heterogeneous nanorods with a good expitaxial interface have shown a stronger surface-enhanced Raman scattering (SERS) signal of the dopamine molecules than Au nanoscale seeds alone, which is attributed to the enhanced charge transfer (CT) effect of ZnO which is greatly improved by the plasmon-induced hot electron from Au nanostructures. The enhanced CT effect has also been proved by a higher photocatalysis efficiency. Furthermore, the plasmon-induced hot electron transfer mechanism in Au–ZnO heterogeneous nanorods has been confirmed by a slow rise time of electrons in the transient absorption measurements. These findings suggest the dependency of the plasmon-induced hot electron transfer mechanism on the different mixing of the metal and semiconductor band levels.

Few-layer two-dimensional (2D) semiconductor nanosheets with a layer-dependent band gap are attractive building blocks for large-area thin-film electronics. A general approach is developed to fast prepare uniform and phase-pure 2H-WSe2 semiconducting nanosheets at a large scale, which involves the supercritical carbon dioxide (SC-CO2) treatment and a mild sonication-assisted exfoliation process in aqueous solution. The as-prepared 2H-WSe2 nanosheets preserve the intrinsic physical properties and intact crystal structures, as confirmed by Raman, x-ray photoelectron spectroscopy (XPS), and scanning transmission electron microscope (STEM). The uniform 2H-WSe2 nanosheets can disperse well in water for over six months. Such good dispersivity and uniformity enable these nanosheets to self-assembly into thickness-controlled thin films for scalable fabrication of large-area arrays of thin-film electronics. The electronic transport and photoelectronic properties of the field-effect transistor based on the self-assembly 2H-WSe2 thin film have also been explored.

Metal–semiconductor Janus nanostructures with asymmetry and directionality have recently aroused significant interest, both in fundamental light–matter interactions mechanism and in technological applications. Here we report the synthesis of different Au–ZnO Janus nanostructures via a facile one-pot colloid method. The growth mechanism is revealed by a series of designed synthesis experiments. The light absorption properties are determined by both the decrease of dipole oscillations of the free electrons and the plasmon-induced hot-electron transfer. Moreover, the finite-difference time-domain (FDTD) simulation method is used to elucidate the electric field distributions of these Janus nanostructures.