Jing Zhang

An ambipolar amino acid, 5-aminovaleric acid (5AVA), is demonstrated to be able to coordinate lead and halides simultaneously with its carboxyl and amidogen groups. Those interactions not only reconstitute energy domains but also minimize the interfacial defects of perovskite films. Therefore, a maximum external quantum efficiency of 19.3% is achieved in quasi-2D green perovskite light-emitting diodes with current efficiency of 61.7 cd A⁻¹.

Abstract

Quasi-two-dimensional (quasi-2D) perovskite light-emitting diodes (PeLEDs) are considered as one of the most potential candidates in electroluminescence territory owing to their unique quantum confinement effect and excellent thermal stability of the light. Nevertheless, heterogeneous energy domain distribution leads to severe non-radiative recombination in the process of energy transfer, which enormously hinders the performance and application of PeLEDs. Herein, an ambipolar amino acid, 5-aminovaleric acid (5AVA), is demonstrated to be able to coordinate lead and halides simultaneously with its carboxyl and amidogen groups. The coordinated ambipolar molecule not only reconstitutes energy domains of perovskites but also minimizes the interfacial defects of PeLEDs. Accordingly, the presence of 5AVA in perovskite precursors leads to dramatic suppression of the n = 1 and n = 2 phases and accelerates energy transfer from wide bandgap domains to narrow bandgap ones. As a result, maximum external quantum efficiency (EQE) of 19.3% (18.20% ± 1.10%) is achieved in quasi-2D green PeLEDs with current efficiency of 61.7 cd A⁻¹.

In-plane polarization in MoS₂ is realized through contact with low-symmetric CrOCl. The emergence of asymmetric second harmonic generation pattern in MoS₂/CrOCl heterojunction indicates the variation of lattice symmetry in MoS₂, which stems from lattice-mismatch-induced uniaxial strain because of the strong interlayer interactions. More importantly, the strong linear polarization-sensitive photodetection is realized.

Abstract

2D materials with low-symmetry exhibit anisotropic physical properties, making them promising candidates for various applications. However, the lack of matured synthesis methods in anisotropic 2D materials is still the main obstacle to their future applications. Given the mature synthesis method of transition metal dichalcogenides (TMDCs), manipulating anisotropy in 2D TMDCs becomes a promising way to tune or trigger functional properties. Herein, for the first time, a van der Waals symmetry engineering is reported to introduce in-plane polarization in MoS₂ through contact with low-symmetric CrOCl. The emergence of asymmetric second harmonic generation pattern in MoS₂/CrOCl heterojunction indicates the variation of lattice symmetry in MoS₂. Furthermore, the theoretical simulation shows that such change stems from lattice-mismatch-induced uniaxial strain because of the strong interlayer interactions. The angle-dependent Raman and photoluminescence spectra further identify that the uniaxial strain gives rise to the in-plane polarization in MoS₂. In addition, the polarized MoS₂ exhibits excellent orientation-sensitive electrical characteristics with a conductance anisotropy ratio of ≈1.5. More importantly, the strong linear polarization-sensitive photodetection is realized, and the anisotropic ratio reached 1.25 with 532 nm. The results suggest that symmetric engineering potentially opens up a new field to endow high-symmetry 2D materials with anisotropic functionalities.

Performing multifield modulation of coupled localized laser writing and nonlocal moisture treatment on metal halide perovskites crystals enables the creation and manipulation of localized photoluminescence for optical encryption from 2D to 3D and 4D, such as reversible encryption–reading, repeatable erasing–refreshing, and even spatially and temporally resolved reading with high resolution.

Abstract

The ability to generate and manipulate photoluminescence (PL) with high spatial resolution has been of primary importance for applications in micro-optoelectronics, while the emerging metal halide perovskites offer novel material platforms where diverse photonic functionalities and fine structuring are constantly explored. Herein, micro-PL patterns consisting of highly luminescent CsPbBr₃ nanocrystals (NCs) in nonluminescent perovskite crystals are directly fabricated by focused femtosecond laser irradiation. Further modulation with a moisture field leads to the selective dissolution of the laser-destabilized perovskite structures as revealed by density functional theory simulations, thus allowing for facile control of the reversible PL from the recrystallization of moisture-induced CsPbBr₃ NCs. By leveraging the coupled laser writing and moisture modulation, multimodal information encryption is realized by reversible encryption–reading and repeatable erasing–refreshing. This optical storage mechanism is also extended to 3D and 4D by realizing spatially and temporally resolved optical encryption. The coupled multifield modulation on perovskite crystals can enable potential applications in optical storage and encryption, and offer a novel solution for the creation and manipulation of localized PL structures with high temporal and spatial resolutions.

Nature Communications, Published online: 22 April 2022; doi:10.1038/s41467-022-29929-7

While material defect sites are active for chemical reactions, it is important to understand how different defect types impact reactivity. Here, authors prepare Frenkel-defected MoS2 monolayers and demonstrate improved performances for H2 evolution electrocatalysis than pristine or doped MoS2.

Nature Communications, Published online: 13 April 2022; doi:10.1038/s41467-022-29527-7

Graphene and related two-dimensional (2D) materials have been at the core of intense research and development for over fifteen years, however the market penetration of products based on this technology has lagged behind expectations. At Nature Communications we wish to support research providing insights into the path towards the industrialisation of 2D materials. We introduce a Collection that encapsulates the recent progress and outstanding challenges faced by research on atomically thin materials, and we focus, in particular, on the potential of 2D technologies for future impact at the commercial level.

Nature Materials, Published online: 21 April 2022; doi:10.1038/s41563-022-01232-2

The interface stacking order of twisted graphene can be actively flipped between locally stable states using a mechanical impulse, and this flipping propagates spontaneously through the network in a domino-like fashion.

Nature Physics, Published online: 21 April 2022; doi:10.1038/s41567-022-01574-3

Thermal transport measurements provide a complementary view of the electronic structure of a material to electronic transport. This technique is applied to twisted bilayer graphene, and highlights the particle–hole asymmetry of its band structure.

A 0D organic copper(I) iodide hybrid, (1,3-dppH₂ )₂Cu₄I₈∙H₂O, demonstrates a broadband orange-red emission peaking at 625 nm, with a full-width at half-maximum (FWHM) of 180 nm under 460 nm excitation, and it also exhibits an excellent anti-water stability. The blue-light-excitable characteristic and excellent moisture stability make these organic copper(I) iodide clusters highly suitable for solid-state lighting application.

Abstract

The discovery of rare-earth free luminescent materials with blue-light-excitable characteristic is of great importance for solid-sate lighting applications. Herein, a Cu(I)-based 0D luminescent hybrid (1,3-dppH₂ )₂Cu₄I₈∙H₂O is synthesized by a facile solution method, and it shows the orange-red emission peaking at 625 nm upon 460 nm excitation. The structure-related luminescence mechanism has been elaborated by experimental and theoretical investigations. Moreover, the emission intensity remains unchanged even after continuous water treatment for 60 days due to the improved structural stability originating from intermolecular π–π interaction between organic cations. A warm white light-emitting diode (LED) device with the color rendering index of 91.4% has been fabricated by combining the 440 nm LED chip, green-emitting Lu₃Al₅O₁₂:Ce³⁺, and (1,3-dppH₂ )₂Cu₄I₈∙H₂O. This work provides a new design route towards 0D cuprous halide materials and will initiate more exploration of their intrinsic luminescence mechanism.

Sustainable Wearable Energy Devices

In article number 2110535, Ming-Tsang Lee, Ha Beom Lee, Seung Hwan Ko, and co-workers discuss energy harvesting and storage devices to provide large amounts of energy needed to power wearable devices. Emphasis on nanomaterials, device fabrication techniques, and device architectures emerging from recent studies is provided.

Advanced Functional Materials, Volume 32, Issue 16, April 19, 2022.

The Weyl semimetal states naturally result in high mobility, large magnetoresistance, and extraordinary Nernst effect in Weyl semimetals. The benefits are inherited by polycrystalline Weyl semimetal of NbP_{1+ x} that contains planar stacking faults and Nb vacancies, leading to quasi-linear and large magnetoresistance (MR) of ≈2 × 10⁴% in 2 K and 55 T and outstanding Nernst power factor (PF_xy ) of 74.81 μW cm^–1 K^–2 in 9 T and 220 K.

Abstract

Unsaturated and extremely large magnetoresistance (MR), as well as the giant Nernst effect, are intriguing transport phenomena in Weyl semimetals, which are technically appealing for potential applications in magneto-electric sensors and transverse thermoelectric conversion. The prominent properties are originated from Weyl semimetal states, i.e., the coexistence of electron and hole pockets combined with linear band dispersion. However, previous studies have been focused on small-sized single crystals, rendering the practical applications of Weyl semimetals. Here, it is reported an unsaturated, quasi-linear MR as well as a very large Nernst power factor PF_xy in the prepared centimeter-sized and polycrystalline Weyl semimetal NbP. An extraordinary MR of ≈2 × 10⁴% is observed below 60 K with a magnetic field up to 55 T and persists to elevated temperatures. The unusual quasi-linear MR behavior is explained by the theory of classical linear MR arising from structural disorder. The polycrystalline NbP exhibits state-of-the-art PF_xy that reaches a maximum value of 74.81 μW cm^–1 K^–2 at 9 T and 220 K, which is 1.5 times larger than its longitudinal thermoelectric power factor PF_xx . Given that polycrystalline Weyl semimetal, NbP is suitable for large-scale production, the results pave the way for its practical applications in magneto-electric sensors and transverse thermoelectric conversion.

Here it is summarized comprehensively and systematically the recent progress made in developing SnSe and SnSe-based nanostructures beyond thermoelectricity. Specifically, the main preparation methods, properties, and applications are covered. On that basis, the challenges and potential perspectives in applying SnSe nanomaterials are highlighted.

Abstract

Layered SnSe is an emerging class of black phosphorus, which is non-toxic, eco-friendly, and chemically stable. Recently, SnSe nanostructures have triggered more research interest and enabled broad applications beyond demonstrating their great performances on thermoelectricity. However, there are also a great many significant studies of SnSe nanostructures beyond thermoelectricity. SnSe quantum dots, nanosheets, nanowires, and thin films with diverse morphologies have been synthesized using various chemical and physical preparation approaches. SnSe is a multi-phase semiconductor, and its nanostructures endow unique properties, including small electron effective mass, ultralow thermal conductivity, huge anisotropy, and the largest 2D piezoelectric coefficient ever predicted. The versatility of SnSe nanostructures can enable potential applications ranging from ultrafast photonics, logic devices, photodetectors, solar cells, photocatalysis, energy storage, and biology to more cutting-edge interdisciplinary subjects. In this review, the recent advances made in SnSe nanostructures are summarized, covering basics, synthesis, properties, and applications, just giving a passing comment on thermoelectricity. An in-depth perspective on the challenges and prospects of SnSe nanostructures toward broad and practical applications is also given.

Deterministic patterning of colloidal quantum dots into high-quality micro-/nanostructures is developed for the construction of multifunctional integrated photonic devices. Mode-tunable microlasers and waveguides are coupled to direct on-chip generation and propagation of coherent light, which permits a proof-of-concept demonstration of integrated photonic circuits for encoding photonic outputs into information bits.

Abstract

Colloidal quantum dots (CQDs) are promising for photonic applications toward lasers, waveguides, and photodetectors. However, integration of high-quality photonic elements into multifunctional devices is still restricted by optical losses stemming from the accumulation of defects and disorder in the solution process. Herein, a platform with a directional Laplace pressure is created for eliminating undesired pinning of liquid fronts in the solution process and boosting ordered assembly of CQDs into designable micro-/nanostructures. The versatility and robustness of this method are demonstrated by deterministic patterning of CQDs with different components and photoluminescence spectra onto various substrates. On the basis of this platform, microring lasers with tunable emission modes, low-loss waveguides, and their coupled structures have been reached for direct on-chip generation and propagation of coherent light. A proof-of-concept demonstration of integrated circuits is also conducted by combining microcavity lasers with waveguides for encoding photonic outputs into information bits.

Common metal salts are used to realize the controlled phase transformation of transition metal dichalcogenides (TMDs) from the conventional thermodynamically stable 2H phase to unconventional metastable 1T′ phase. This work not only paves the way to prepare high-quality and high-purity unconventional metastable 1T′-TMDs for fundamental and practical investigations, but also greatly simplifies the procedure for the large-scale production of 1T′-TMDs.

Abstract

Phase engineering of nanomaterials (PEN) has demonstrated great potential in the fields of catalysis, electronics, energy storage and conversion, and condensed matter physics. Recently, transition metal dichalcogenides (TMDs) with unconventional metastable phases (e.g., 1T and 1T′) have attracted increasing research interest due to their unique and appealing physicochemical properties. However, there is still a lack of a simple, universal, and controlled method for the preparation of large-scale and high-purity unconventional-phase TMD crystals, restricting their further fundamental study and practical applications. Here, a facile, one-step salt-assisted general strategy is reported for the controlled phase transformation of commercially available TMDs with conventional 2H phase, yielding a large amount of metastable 1T′-phase TMDs, including WS₂, WSe₂, MoS₂, and MoSe₂. It is found that the easily accessible metal salts, such as K₂C₂O₄·H₂O, K₂CO₃, Na₂CO₃, Rb₂CO₃, Cs₂CO₃, KHCO₃, NaHCO₃, and NaC₂O₄, can be used to assist the 2H-to-1T′ phase transformation, greatly simplifying the synthetic process for producing metastable 1T′-TMDs. Importantly, this method can also be used to prepare 1T′-TMD alloys, such as 1T′-WS_{2 x} Se_{2(1− x )}. This newly developed strategy is robust and highly effective, which can also be used for the phase engineering of other materials with various polymorphs.

A new high-resolution transmission electron microscopy (TEM) methodology, low-dose focal-series reconstruction (LD-FSR), enables near-atomic resolution of 1.6 Å. This method allows the distinction between co-existing organic polymorphs, and observation of crystal defects and atoms. Moreover, a new copper phthalocyanine polymorph (λ-CuPc) is identified using LD-FSR, resulting in real-space crystal structure elucidation.

Abstract

Structural analysis of beam-sensitive materials by transmission electron microscopy (TEM) represents a significant challenge, as high-resolution TEM (HRTEM) requires high electron doses that limit its applicability to stable inorganic materials. Beam-sensitive materials, e.g., organic crystals, must be imaged under low dose conditions, leading to problematic contrast interpretation and loss of fine structural details. Here, HRTEM imaging of organic crystalline materials with near-atomic resolution of up to 1.6 Å is described, which enables real-space studies of crystal structures, as well as observation of co-existing polymorphs, crystal defects, and atoms. This is made possible by a low-dose focal-series reconstruction methodology, which provides HRTEM images where contrast reflects true object structure and can be performed on contemporary cryo-EM instruments available to many research institutions. Copper phthalocyanine (CuPc), a perchlorinated analogue of CuPc, and indigo crystalline films are imaged. In the case of indigo crystals, co-existing polymorphs and individual atoms (carbonyl oxygen) can be observed. In the case of CuPc, several polymorphs are observed, including a new one, for which the crystal structure is found based on direct in-focus imaging, accomplishing real-space crystal structure elucidation. Such direct analysis can be transformative for structure studies of organic materials.

Sustainable Optics

Ores are everywhere on our earth and other planets, and many of them possess layered structures. In article 2110464, Baofu Ding, Bilu Liu, and co-workers develop a seawater-assisted green method to produce 2D minerals in large quantities from bulky ores. These 2D minerals are used as inorganic liquid crystals for color optics. This work creates novel opportunities of using abundant naturally minerals for advanced technological applications.

Magnetic phase control is the source of fascinating correlated phenomena and the frontier research direction in materials science and spintronic devices. Magnetic anisotropy control and a dramatically enhanced T _c up to 400 K are realized in van der Waals ferromagnet Fe₅GeTe₂ during a high-pressure loading–deloading process, shedding light on exploring the exchange interaction mechanism and realizing practical spintronic applications.

Abstract

The technological appeal of van der Waals ferromagnetic materials is the ability to control magnetism under external fields with desired thickness toward novel spintronic applications. For practically useful devices, ferromagnetism above room temperature or tunable magnetic anisotropy is highly demanded but remains challenging. To date, only a few layered materials exhibit unambiguous ferromagnetic ordering at room temperature via gating techniques or interface engineering. Here, it is demonstrated that the magnetic anisotropy control and dramatic modulation of Curie temperature (T _c) up to 400 K are realized in layered Fe₅GeTe₂ via the high-pressure diamond-anvil-cell technique. Magnetic phases manifesting with in-plane anisotropic, out-of-plane anisotropic and nearly isotropic magnetic states can be tuned in a controllable way, depicted by the phase diagram with a maximum T _c up to 360 K. Remarkably, the T _c can be gradually enhanced to above 400 K owing to the Fermi surface evolution during a pressure loading–deloading process. Such an observation sheds light on the understanding and control of emergent magnetic states in practical spintronic applications.

Periodic substrate modulation perturbs the electronic states of graphene, duplicates Dirac cones, and effectively couples the two valleys of the Dirac states in epitaxial monolayer graphene. The intervalley interaction is controlled by the substrate lattice constant. Moiré flat bands emerge at certain magic values of the substrate lattice constant.

Abstract

Tuning interactions between Dirac states in graphene has attracted enormous interest because it can modify the electronic spectrum of the 2D material, enhance electron correlations, and give rise to novel condensed-matter phases such as superconductors, Mott insulators, Wigner crystals, and quantum anomalous Hall insulators. Previous works predominantly focus on the flat band dispersion of coupled Dirac states from different twisted graphene layers. In this work, a new route to realizing flat band physics in monolayer graphene under a periodic modulation from substrates is proposed. Graphene/SiC heterostructure is taken as a prototypical example and it is demonstrated experimentally that the substrate modulation leads to Dirac fermion cloning and, consequently, the proximity of the two Dirac cones of monolayer graphene in momentum space. Theoretical modeling captures the cloning mechanism of the Dirac states and indicates that moiré flat bands can emerge at certain magic lattice constants of the substrate, specifically when the period of modulation becomes nearly commensurate with the (3 × 3)R30o\[(\sqrt 3 \; \times \;\sqrt 3 )R{30^o}\] supercell of graphene. The results show that epitaxial single monolayer graphene on suitable substrates is a promising platform for exploring exotic many-body quantum phases arising from interactions between Dirac electrons. 

Nature Nanotechnology, Published online: 18 April 2022; doi:10.1038/s41565-022-01111-6

Motion is a key characteristic of every form of life. In this work, the authors use graphene drums to probe the nanomotion of a single bacterium and develop a new way for performing antibiotic susceptibility testing with single-cell resolution.

Nature Nanotechnology, Published online: 18 April 2022; doi:10.1038/s41565-022-01106-3

An endoepitaxy approach enables the realization of two-dimensional mosaic heterostructures with atomically sharp heterojunction interfaces.

Nature Nanotechnology, Published online: 18 April 2022; doi:10.1038/s41565-022-01104-5

Naturally occurring 2H-stacked bilayer WSe2 enables the observation of exciton condensates in the strong coupling limit.

Nature Nanotechnology, Published online: 20 April 2022; doi:10.1038/s41565-022-01084-6

A combination of periodic laser patterning, anisotropic thermal etching and endoepitaxial growth enables the realization of monolayer mosaic heterostructures with atomically sharp interfaces.

Nature Nanotechnology, Published online: 21 April 2022; doi:10.1038/s41565-022-01099-z

A microscopic robotic device is remotely controlled in two dimensions in all three degrees of freedom independently by the interaction between unfocused light and four plasmonic nanoantennas.