Jing Zhang

Nature Physics, Published online: 11 August 2022; doi:10.1038/s41567-022-01697-7

The anomalous Hall effect can signify that a material has a spontaneous magnetic order. Now, twisted bilayer graphene shows this effect at half filling, suggesting that the ground state is valley-polarized.

Star formation after the big bang appears much faster than models had forecast

Nature, Published online: 08 August 2022; doi:10.1038/d41586-022-02108-w

Electrons in a pure-carbon material display properties that are reminiscent of those in heavy-element compounds. A model inspired by this link hints at how a single-element material can exhibit complex electronic behaviour.

Nature, Published online: 10 August 2022; doi:10.1038/d41586-022-02147-3

Technology on the nanometre scale could provide solutions to move on from the solid-state era.

Nature Electronics, Published online: 08 August 2022; doi:10.1038/s41928-022-00803-0

An artificial neuron that detects dopamine using a carbon-based electrochemical sensor and then processes the sensory signals using a memristor with synaptic plasticity, before stimulating dopamine release via a heat-responsive hydrogel, can be used to trigger the controllable movement of a mouse leg and robotic hand.

Nature Electronics, Published online: 08 August 2022; doi:10.1038/s41928-022-00800-3

Vanadium diselenide van der Waals contacts made with a controlled crack formation process can be used to fabricate tungsten diselenide transistors with channel lengths of less than 100 nm, on-state current densities of up to 1.7 mA μm–1 and on-state resistances down to 0.50 kΩ μm.

Technical issues in integration of full-color micro-LED display, in the aspects of quantum efficiency, mass transfer technique, and color conversion technique, are reviewed. Various approaches for improving quantum efficiency of device along with methods of massively and accurately transferring them to a target substrate are discussed. Color conversion techniques and their deposition methods of quantum dots on micro-LEDs are introduced.

Abstract

The implementation of high-efficiency and high-resolution displays has been the focus of considerable research interest. Recently, micro light-emitting diodes (micro-LEDs), which are inorganic light-emitting diodes of size <100 µm², have emerged as a promising display technology owing to their superior features and advantages over other displays like liquid crystal displays and organic light-emitting diodes. Although many companies have introduced micro-LED displays since 2012, obstacles to mass production still exist. Three major challenges, i.e., low quantum efficiency, time-consuming transfer, and complex color conversion, have been overcome with technological breakthroughs to realize cost-effective micro-LED displays. In the review, methods for improving the degraded quantum efficiency of GaN-based micro-LEDs induced by the size effect are examined, including wet chemical treatment, passivation layer adoption, LED structure design, and growing LEDs in self-passivated structures. Novel transfer technologies, including pick-up transfer and self-assembly methods, for developing large-area micro-LED displays with high yield and reliability are discussed in depth. Quantum dots as color conversion materials for high color purity, and deposition methods such as electrohydrodynamic jet printing or contact printing on micro-LEDs are also addressed. This review presents current status and critical challenges of micro-LED technology and promising technical breakthroughs for commercialization of high-performance displays.

Nature Communications, Published online: 06 August 2022; doi:10.1038/s41467-022-32256-6

While light-driven water splitting offers a renewable means to produce fuel, the limited availability of high-performance materials inspires the search for new photocatalysts. Here, authors demonstrate two-dimensional NiPS3 to enhance semiconductor photocatalytic H2 evolution activities.

Nature Photonics, Published online: 08 August 2022; doi:10.1038/s41566-022-01051-6

A tilted plasmonic nanocavity enables shortening of the luminescence decay time of a rare-earth-doped nanoparticle to sub-50 ns. High quantum efficiency enhancement, chiral polarization and directional far-field emission are maintained.

Nature Photonics, Published online: 08 August 2022; doi:10.1038/s41566-022-01046-3

Near-infrared perovskite light-emitting diodes with extrapolated device lifespans on the scale of years are achieved by the use of a dipolar molecular stabilizer.

While strong coupling is common in inorganic systems, the ultrastrong regime, where quantum coherent phenomena become efficient, is the domain of organic systems. Here, the large oscillator strength of the C exciton in MoS₂ is exploited to demonstrate ultrastrong coupling in a CMOS-compatible inorganic semiconductor in the visible spectrum at room temperature.

Abstract

The 2D transition-metal dichalcogenides (2D TMDCs) are an intriguing platform for studying strong light–matter interactions because they combine the electronic properties of conventional semiconductors with the optical resonances found in organic systems. However, the coupling strengths demonstrated in strong exciton–polariton coupling in the 2D TMDCs remain much lower than those found in organic systems. In this paper, a new approach is taken by utilizing the large oscillator strength of the above-band gap C exciton in few-layer molybdenum disulphide (FL-MoS₂). A k-space Rabi splitting of 293 meV is shown when coupling FL-MoS₂ C excitons to surface plasmon polaritons at room temperature. This value is 11% of the uncoupled exciton energy (2.67 eV or 464 nm), ≈2× what is typically seen in the TMDCs, placing the system in the ultrastrong coupling regime. The results take a step toward finally achieving the efficient quantum coherent processes of ultrastrong coupling in a CMOS-compatible system—the 2D TMDCs—in the visible spectrum.

Nature Nanotechnology, Published online: 10 August 2022; doi:10.1038/s41565-022-01194-1

Pufin ID is a Danish start-up commercializing anti-counterfeiting technology based on nanoscale photophyics.

Nature Nanotechnology, Published online: 11 August 2022; doi:10.1038/s41565-022-01186-1

A 2D material based liquid-crystal shows an extremely large optical anisotropy factor in the deep ultraviolet region, showing magnetically tunable birefringence.

Nature Nanotechnology, Published online: 11 August 2022; doi:10.1038/s41565-022-01183-4

Double ionic gated transistors enable excellent control of the band structure of atomically thin semiconductors. Perpendicular electric fields as large as 3 V nm−1 can fully quench the gap of bi- and few-layer WSe2.

Nature Nanotechnology, Published online: 11 August 2022; doi:10.1038/s41565-022-01187-0

A ‘dual-ligand passivation system’ is designed and synthesized to functionalize colloidal quantum dots to realize ultra-high resolution patterns by direct photolithography.

Nature Communications, Published online: 04 August 2022; doi:10.1038/s41467-022-31134-5

Here, the authors demonstrate a chip-scale device that realizes a comprehensive set of resonant second order nonlinear processes including optical parametric oscillation with a threshold power of 70 microwatts.

Nature, Published online: 03 August 2022; doi:10.1038/d41586-022-02014-1

Microscopic light-emitting diodes (LEDs) have applications ranging from augmented-reality displays to large-screen products, but their brightness typically decreases as their size is reduced. A solution to this problem has now been found and used to manufacture bright blue nanoscale LEDs.

Sellotape is used to exfoliate layered Ruddlesden–Popper quasi-2D perovskite film, and the surface defect layer is mechanically peeled off by the sellotape without damaging the crystalline region below, resulting in high photoluminescence quantum yield up to 83.2%. An efficient perovskite light-emitting diode based on the exfoliated quasi-2D perovskite thin film is achieved with high current efficiency of 46.0 cd m⁻² and excellent external quantum efficiency up to 14.8%.

Abstract

In 2004, K. S. Novoselov and A. K. Geim et al. have used sellotape to peel off the layered 2D graphite, and successfully obtained few-layer thin graphene. Inspired by this, herein, the sellotape is initially used to exfoliate the layered Ruddlesden–Popper (RP) quasi-2D perovskite film for efficient light-emitting diodes application. The top surface layer of quasi-2D perovskite film is mechanically peeled off by the sellotape without damaging the crystalline region below, which minimizes the poor conductivity issue of quasi-2D perovskite film owing to the decreased defect density. Moreover, the exfoliated quasi-2D film exhibits low charge traps density and enhanced energy transfer from low-dimensional to high-dimensional domains due to the elimination of surface defective layer and the recrystallization of quasi-2D perovskite crystal, leading to high photoluminescence quantum yield (PLQY) up to 83.2%. Subsequently, an efficient perovskite light-emitting diode based on the exfoliated quasi-2D perovskite thin film is achieved with high current efficiency of 46.0 cd m⁻² and excellent external quantum efficiency (EQE) up to 14.8%.

Colloidal crystals have brought the promise of revolution to modern engineering. The authors report a surface tension gradient-driven self-assembly strategy for the ultrafast fabrication of large-area colloidal crystals. The colloidal crystal monolayers exceeding 1000 cm² can be fabricated within minutes. The nanoparticle transfer printing method is further proposed to convert the close-packed nanoparticle monolayers into high-resolution conformal micropatterns.

Abstract

Colloidal crystals have brought the promise of revolution to modern engineering, yet commonly used fabrication technologies are still limited by the small preparation area, time-consuming process, and dependence on sophisticated equipment. Here, a surface tension gradient-driven self-assembly strategy is proposed for the ultrafast fabrication of large-area colloidal crystals. The hydrogel loaded with sodium dodecyl sulfate is devised to construct a stable and continuous liquid-air interfacial tension gradient, and the resulting Marangoni effect can drive the micro-nano particles to instantaneously form (within several seconds) highly ordered colloidal crystals. Benefiting from the long range of surface tension gradients, the fabrication area of colloidal crystal films is demonstrated to exceed an astonishing 1000 cm² without compromising their quality, showing great potential in scale-up manufacture. Moreover, particles of a wide variety of sizes, materials, and functionalities can form close-packed self-assembly monolayers and be transferred to various substrates without damage, exhibiting great versatility. Inspired by ink microprinting, an ultrafast nanoparticle transfer printing method is further proposed to convert the close-packed nanoparticle monolayers into large-area conformal micropatterns with single-nanoparticle resolution. The great potential of nanoparticle micropatterns is demonstrated in flexible micro-electronics/skin electronics. This user-friendly, efficient self-assembly, and micropatterning strategy provide promising opportunities for academic and real industrial applications.

Z. Huo, Y. Wei, Y. Wang, Z. L. Wang, Q. Sun

In this review, integrated self-powered sensors based on 2D materials are introduced in detail. The applications of TENG/PENG self-powered sensors based on 2D materials in different research fields are discussed.

With the development of the Internet of Things, there is an increasing need for clean energy and large-scale sensory systems. Triboelectric/piezoelectric nanogenerators (TENGs/PENGs), have attracted considerable attention as a new type of power generation terminal, which can harvest surrounding energy and convert it into electrical energy. To improve the output performance of nanogenerators (NGs) and diversify related applications, 2D materials with high carrier mobility and excellent piezoelectric properties can be directly used or integrated as different types of self-powered sensors. In this review, the authors first introduce the excellent piezoelectric and optoelectronic properties of 2D materials, followed by the triboelectric series of 2D materials used in TENGs. The categories of integrated self-powered sensors based on 2D materials are then summarized according to their different structures and compositions. We also discuss in detail the recent applications of integrated self-powered sensors based on 2D materials from five aspects. Finally, the challenges and outlooks in the research field of self-powered sensors are featured. Given the continuous development of self-powered sensors based on 2D materials, they are considered to have significant potential for applications in biomedicine, environmental detection, human motion monitoring, energy harvesting, and smart wearable devices.

The first silver/antimony-based double perovskite photoferroelectric, (4,4-difluoropiperidinium)₄AgSbI₈, is discovered, which exhibits ferroelectric photovoltaic effect and photostrictive effect under light radiation. Moreover, (4,4-difluoropiperidinium)₄AgSbI₈ exhibits an exciting X-ray responsivity including a sensitivity as high as 704.8 μC Gy_air ⁻¹ cm⁻² at 100 V bias and a detection limit as low as 0.36 μGy_air s^–1, both of which are the best among all HHDP photoferroelectrics.

Abstract

2D hybrid halide double perovskites (HHDPs) have been demonstrated to be a promising alternative to conventional lead-based halide perovskites as a new system of photoferroelectrics, due to their unique characteristics of environmental friendliness, favorable stability, and fascinating optoelectronic properties. Herein, for the first time, a 2D iodide double perovskite photoferroelectric is reported based on Ag/Sb ions, (4,4-DFPD)₄AgSbI₈ (4,4-DFPD = 4,4-difluoropiperidinium), which possesses a high Curie temperature of 414 K (above BaTiO₃), a large spontaneous polarization of 9.6 μC cm⁻², ferroelectric photovoltaic effect, and photostrictive effect. Notably, to the best of the authors’ knowledge, the discovery of photostriction in HHDP photoferroelectrics is unprecedented. Moreover, (4,4-DFPD)₄AgSbI₈ exhibits an impressive X-ray responsivity, with a sensitivity as high as 704.8 μC Gy_air ⁻¹ cm⁻² at 100 V bias and a detection limit as low as 0.36 μGy_air s⁻¹ at 10 V bias, both of which outperform the current all HHDP photoferroelectrics. This work enriches the photoferroelectric family, and proves that Ag/Sb-based HHDP photoferroelectrics are a promising candidate for the next-generation optoelectronic devices.

Hybrid metal–semiconductor structures fabricated by direct femtosecond laser writing are proposed as a novel design of physically unclonable anti-counterfeiting labels. Each structure has a unique white-light photoluminescence signal, which is encoded by discrete cosine transform for the signal decorrelation and multilevel polar codes for unique key generation. Presented easy-to-fabricate structures and encoding protocol offer a high-level anti-counterfeiting protection.

Abstract

Luminescent security labels are effective platforms for protection of consumer goods from counterfeiting. However, the lifetimes of such security approaches are limited due to narrow-band photoluminescent features of the label elements, which can be used for the protection technology disclosure. In this paper, a novel concept for the application of non-linear white-light luminescence from hybrid metal–semiconductor structures fabricated by direct femtosecond laser writing for the creation of physically unclonable security labels is proposed. A close connection is demonstrated between the internal composition of hybrid structures, which is controlled at the fabrication stage, and their non-linear optical signals. It is shown that the application of decorrelation procedure based on discrete cosine transform and polar codes for label coding can overcome the problem of the white-light photoluminescent spectra correlation. The proposed fabrication approach and coding strategy allows reaching a high degree of device uniqueness (up to 99%), bit uniformity (close to 0.5), and encoding capacity up to 1.25 × 10⁴³⁷ in a single label element. The results demonstrate that the barriers for the application of white-light luminescent nano-objects for the creation of physically unclonable labels are removed.

Layered 2D crystals are exemplar energy conversion materials, able to convert light, heat, or motion to electricity. These energy conversion processes can also occur synchronously, leading to complex energy interplay networks during energy harvesting/transducing. This synchronous multisource energy conversion needs to be studied and understood to enable the fabrication of next-generation energy harvesting and conversion systems.

Abstract

Layered 2D crystals have unique properties and rich chemical and electronic diversity, with over 6000 2D crystals known and, in principle, millions of different stacked hybrid 2D crystals accessible. This diversity provides unique combinations of properties that can profoundly affect the future of energy conversion and harvesting devices. Notably, this includes catalysts, photovoltaics, superconductors, solar-fuel generators, and piezoelectric devices that will receive broad commercial uptake in the near future. However, the unique properties of layered 2D crystals are not limited to individual applications and they can achieve exceptional performance in multiple energy conversion applications synchronously. This synchronous multisource energy conversion (SMEC) has yet to be fully realized but offers a real game-changer in how devices will be produced and utilized in the future. This perspective highlights the energy interplay in materials and its impact on energy conversion, how SMEC devices can be realized, particularly through layered 2D crystals, and provides a vision of the future of effective environmental energy harvesting devices with layered 2D crystals.

Nature Nanotechnology, Published online: 01 August 2022; doi:10.1038/s41565-022-01180-7

Twisted WSe2 AB-homobilayers enable the realization of bilayer Hubbard models in the weak interlayer hopping limit.