Jiuxiang Dai

Nature Nanotechnology, Published online: 12 August 2021; doi:10.1038/s41565-021-00953-w

Optical spectroscopy can identify chiral indices of individual carbon nanotubes, but has so far been unable to determine their handedness because of the weak chiroptical signal. Rayleigh scattering circular dichroism now enables the identification of both chiral indices and handedness of individual nanotubes.

The temperature dependence of bandgap in inorganic lead-halide perovskites is found to be variable with material dimensionality. In sharp contrast to the monotonous redshift usually observed in quasi-3D bulk-like CsPbBr₃ nanocrystals (NCs), the bandgap of 2D 2-monolayer-thick (2-ML-thick) CsPbBr₃ nanoplatelets (NPLs) exhibits an initial blueshift then redshift trend with decreasing temperature (290–10 K).

Abstract

Understanding the origin of temperature-dependent bandgap in inorganic lead-halide perovskites is essential and important for their applications in photovoltaics and optoelectronics. Herein, it is found that the temperature dependence of bandgap in CsPbBr₃ perovskites is variable with material dimensionality. In contrast to the monotonous redshift ordinarily observed in bulk-like CsPbBr₃ nanocrystals (NCs), the bandgap of 2D CsPbBr₃ nanoplatelets (NPLs) exhibits an initial blueshift then redshift trend with decreasing temperature (290–10 K). The Bose–Einstein two-oscillator modeling manifests that the blueshift-redshift crossover of bandgap in the NPLs is attributed to the significantly larger weight of contribution from electron-optical phonon interaction to the bandgap renormalization in the NPLs than in the NCs. These new findings may gain deep insights into the origin of bandgap shift with temperature for both fundamentals and applications of perovskite semiconductor materials.

The ferromagnetic order in NdNiO₃ (NNO) film is induced by the stray field from the La_0.67Sr_0.33MnO₃ (LSMO) layer in proximity. Consequently, the magnetic coupling between the NNO film and the LSMO layer melts the metal–insulator transition in the NNO layer. Thus, this study illuminates the intimate connection between magnetic order and electronic properties in RENO.

Abstract

Employing X-ray magnetic circular dichroism (XMCD), angle-resolved photoemission spectroscopy (ARPES), and momentum-resolved density fluctuation (MRDF) theory, the magnetic and electronic properties of ultrathin NdNiO₃ (NNO) film in proximity to ferromagnetic (FM) La_0.67Sr_0.33MnO₃ (LSMO) layer are investigated. The experimental data shows the direct magnetic coupling between the nickelate film and the manganite layer which causes an unusual ferromagnetic (FM) phase in NNO. Moreover, it is shown the metal–insulator transition in the NNO layer, identified by an abrupt suppression of ARPES spectral weight near the Fermi level (E _F), is absent. This observation suggests that the insulating AFM ground state is quenched in proximity to the FM layer. Combining the experimental data (XMCD and AREPS) with the momentum-resolved density fluctuation calculation (MRDF) reveals a direct link between the MIT and the magnetic orders in NNO systems. This work demonstrates that the proximity layer order can be broadly used to modify physical properties and enrich the phase diagram of RENiO₃ (RE = rare-earth element).

The authors describe herein, the first synthesis of highly stable hexagonal ZnO nanoplatelets with the atomically precise thickness, and by means of dynamic nuclear polarization-enhanced solid-state ¹⁵N NMR, the original bimodal stabilization of the ZnO surface is revealed by the benzamidine ligands, which can bind to both the polar and non-polar facets, acting either as X- or L-type ligands, respectively.

Abstract

Colloidal nanoplatelets (NPLs) and nanosheets with controlled thickness have recently emerged as an exciting new class of quantum-sized nanomaterials with substantially distinct optical properties compared to 0D quantum dots. Zn-based NPLs are an attractive heavy-metal-free alternative to the so far most widespread cadmium chalcogenide colloidal 2D semiconductor nanostructures, but their synthesis remains challenging to achieve. The authors describe herein, to the best of their knowledge, the first synthesis of highly stable ZnO NPLs with the atomically precise thickness, which for the smallest NPLs is 3.2 nm (corresponding to 12 ZnO layers). Furthermore, by means of dynamic nuclear polarization-enhanced solid-state ¹⁵N NMR, the original role of the benzamidine ligands in stabilizing the surface of these nanomaterials is revealed, which can bind to both the polar and non-polar ZnO facets, acting either as X- or L-type ligands, respectively. This bimodal stabilization allows obtaining hexagonal NPLs for which the surface energy of the facets is modulated by the presence of the ligands. Thus, in-depth study of the interactions at the organic–inorganic interfaces provides a deeper understanding of the ligand–surface interface and should facilitate the future chemistry of stable-by-design nano-objects.

2D Metal Chalcogenide Heterostructures

2D metal chalcogenide heterostructures (2DMCHs) are a current research hotspot due to their unique electronic and optoelectronic properties. In article number 2100515, Xing Zhou, Tianyou Zhai, and co-workers provide an overview of the recent advances in controllable chemical vapor deposition growth and the emerging novel applications of 2DMCHs, and discuss the challenges and future prospects in this field.

Nature Communications, Published online: 10 August 2021; doi:10.1038/s41467-021-25164-8

Previous work has shown the existence of spin-orbit-entangled excitons and their coupling to antiferromagnetism in the correlated insulator NiPS3. Here the authors show that non-equilibrium driving of these excitons produces a transient metallic antiferromagnetic state that cannot be achieved by tuning the temperature in equilibrium.

Lithium Metal Batteries

In article number 2101261, Seon Joon Kim, Young Soo Yun, and co-workers study lithiophilic surface-guided lithium metal nucleation and growth behaviors using a large-area Ti₃C₂T _x MXene electrode containing a large number of oxygen and fluorine dual heteroatoms. The lithiophilic MXene substrate significantly affects the surface tension of the lithium metal nuclei as well as the nucleation overpotential, forming highly reversible metal clusters composed of spherical lithium nanoparticles.

Two-dimensional (2D) metal nanomaterials have gained ever-growing research interests owing to their fascinating physicochemical properties and promising applications, especially in the field of electrocatalysis. In this review, we briefly introduce the recent advances in the wet-chemical synthesis of 2D metal nanomaterials. Subsequently, the catalytic performances of 2D metal nanomaterials towards a variety of electrochemical reactions are illustrated. Finally, we summarize the current challenge and highlight our perspectives on preparing high-performance 2D metal electrocatalysts.

Nature, Published online: 11 August 2021; doi:10.1038/s41586-021-03701-1

High-performance optoelectronic devices that operate in the infrared regime at room temperature exhibit wide-range, active and reversible tunability of the operating wavelengths with black phosphorus.

Scalable fabrication of magnetic 2D materials and heterostructures constitutes a crucial step for scaling down current spintronic devices and the development of novel spintronic applications. Here, we report on van der Waals (vdW) epitaxy of the layered magnetic metal Fe 3 GeTe 2 (FGT)—a 2D crystal with highly tunable properties and a high prospect for room temperature ferromagnetism (FM)—directly on graphene by employing molecular beam epitaxy. Morphological and structural characterization confirmed the realization of large-area, continuous FGT/graphene heterostructure films with stable interfaces and good crystalline quality. Furthermore, magneto-transport and x-ray magnetic circular dichroism investigations confirmed a robust out-of-plane FM in the layers, comparable to state-of-the-art exfoliated flakes from bulk crystals. These results are highly relevant for further research on wafer-scale growth of vdW heterostructures combining FGT with other layered c...

A low-cost post-processing method to etch the defects in phase-transition-assisted CVD-grown 2H-MoTe₂ by using the triiodide ion solution is reported. The etching mechanism is discussed based on the high Te-vacancy densities in defects and 1T′ phase. The etching results are confirmed by electrical measurements and chemical analysis.

Abstract

2D molybdenum ditelluride (MoTe₂) with polymorphism is a promising candidate to developing phase-change memory, high-performance transistors and spintronic devices. The phase-transition-assisted chemical vapor deposition (CVD) process has been used to prepare large-scale 2H-MoTe₂ with large grain size and low density of grain boundary. However, because of the lack of precise control of the growth condition, some defects including the amorphous regions and grain boundaries in 2H-MoTe₂ are hardly avoidable. Here, a facile method of selectively etching defects in large-scale CVD-grown 2H-MoTe₂ by triiodide ion (I₃ ⁻) solution is reported. The defect etching is attributed to the reduced lattice symmetry, high chemisorption activity and high conductivity of the defects due to the high density of Te vacancies. The treated 2H-MoTe₂ shows the suppressed hysteresis in the electrical transfer curve, enhances hole mobility and the higher effective barrier height on the metal contact, suggesting the decreased density of defects. Further chemical analysis indicates that the 2H-MoTe₂ is not damaged or doped by I₃ ⁻ solution during the etching process. This simple and low-cost post-processing method is effective for etching the defects in large-area 2H-MoTe₂ for high-performance device applications.