Jing Zhang

Nature Communications, Published online: 06 May 2022; doi:10.1038/s41467-022-30161-6

The non-Hermitian skin effect has been discovered in a one dimensional open chain. Here, the authors establish the universality of this effect in two and higher dimensional non-Hermitian systems and propose two new types of skin effect.

Nature Materials, Published online: 05 May 2022; doi:10.1038/s41563-022-01245-x

A ferromagnetic transition in CrSBr is attributed to ordering of magnetic defects, and can be electrostatically manipulated.

A fluorination modulated supramolecular interactions strategy is used to modulate the intrinsic microstrain in two-dimensional perovskite (FPEA)₂PbI₄. (p-FPEA)₂PbI₄ can maximally release microstrain in the largest degree up to 60% during compressive bending. The corresponding photocurrent response of (p-FPEA)₂PbI₄ recovered about 300%. In contrast, the strong intralayer supramolecular interaction of (o-FPEA)₂PbI₄ prevents the microstrain from releasing in the bending process.

Abstract

The conductivity of 2D perovskite is mainly dominated by halide metal octahedron skeletons. However, in contrast to 3D perovskite structures, the layered inorganic skeletons are easily compressed or stretched by large organic cations, causing serious microstrain with impaired optoelectronic responses. Here, fluorination modulated supramolecular interactions in 2D fluorophenethylammonium lead iodide (FPEA₂PbI₄) perovskites are reported. In the double layered organic spacer, interlayer supramolecular interactions between electronegative F atoms and electron-rich benzene rings dominate the lattice microstrain of 2D (p-FPEA)₂PbI₄ perovskite, which can be released by interlayer interactions pulling during compressively bending the flexible devices. This strong electrostatic interaction can maximally release the compression to the inorganic octahedron skeleton during compressive bending, leading to a maximum degree of released microstrain with improved stability. The 60% microstrain can be released by compressive bending, and the corresponding photocurrent response is recovered by about three times in (p-FPEA)₂PbI₄ perovskite film. In contrast, intralayer supramolecular interactions dominate microstrain of 2D (o-FPEA)₂PbI₄ perovskites, which prevents the microstrain release during compressive bending. The strong electrostatic interaction design in the organic spacer of 2D perovskite takes an important role in releasing the microstrain and re-bursting the device performance of flexible perovskite devices.

Nature, Published online: 04 May 2022; doi:10.1038/s41586-022-04520-8

Two new plasmon modes are observed in macroscopic twisted bilayer graphene with a highly ordered moiré superlattice, the first being the signature of chiral plasmons and the second a slow plasmonic mode around 0.4 electronvolts.

Nature, Published online: 04 May 2022; doi:10.1038/s41586-022-04523-5

The epitaxial growth of bilayer molybdenum disulfide on sapphire enables the fabrication of field-effect transistor devices with improved performance in carrier mobility and on-state current over traditional monolayer films.

Nature, Published online: 04 May 2022; doi:10.1038/s41586-022-04514-6

A tuneable platform using twisted WTe2 stacks is described in which an electronic phase in the two-dimensional moiré lattice array is shown to resemble one-dimensional Luttinger liquids.

Nature Materials, Published online: 03 May 2022; doi:10.1038/s41563-022-01228-y

Spins become polarized along their momenta when travelling through chiral tellurium nanowires. The signs of chirality and current determine the orientations of polarized spins while the spin density can be tuned by electrical gating, current and external magnetic field.

FASnI₃ (FA, formamidinium) lead-free perovskite thin films are integrated in a PET substrate and cladded by a PMMA thin film. The resulting planar waveguide is designed to optimize the generation of optical gain. Amplified spontaneous emission is demonstrated with a threshold of 1 µJ cm⁻² together with the formation of random lasing lines (< 1 nm) caused by scattering in the polycrystalline grains.

Abstract

In this work, high-quality FASnI₃ (FA, formamidinium) lead-free perovskite thin films are successfully incorporated in a flexible polyethylene terephthalate (PET) substrate to demonstrate amplified spontaneous emission (ASE) and lasing. The waveguide (WG) consists of polymethylmethacrylate(PMMA)/FASnI₃ bilayer deposited on a PET substrate and is properly designed to allow single-mode propagation at the photoluminescence wavelength. This geometry optimizes the excitation of the emitting FASnI₃, enhances the light−matter interaction in the semiconductor thin film, provides a preferable direction for the emitted light and allows its direct outcoupling for on-chip or fiber-optic applications. As far as the authors know, ASE and random lasing are obtained for the first time in a flexible-based WG integrating a highly efficient lead-free perovskite. The high quality of the deposited films and the optimized design of the structure result in an extremely low ASE/lasing threshold in the range of 1 µJ cm⁻², which is only ten times higher than that measured in the same PMMA/FASnI₃ structure deposited on a rigid substrate (Si/SiO₂). More interestingly, these WGs exhibit a strong polarization anisotropy for the outcoupled ASE/lasing light with a preferable transverse electric polarization. This work is the base for the future development of ecofriendly, flexible, and efficient photonic devices.

An inverse design algorithm based on deep-learning technology and evolution strategy is proposed to realize the rapid design of dielectric metasurfaces for multicolor meta-holography. The proposed algorithm can predict the entire reflection spectra of a dielectric nanostructure in the visible regime with an acceptable accuracy and realize the real-time inverse design of dielectric nanostructure with desired resonance wavelength, bandwidth, and phase delay.

Abstract

Multicolor holography, which can store and reconstruct wavefront information of optical waves at multiple wavelength channels, is demonstrated as a powerful platform for colorful image display. Recently, interleaved and segmented metasurfaces have emerged as appealing alternatives to realize the multicolor holography. However, the crosstalk among different wavelength channels can severely lower their performance. How to obtain the nanostructures with on-demand resonance wavelength, bandwidth, and phase delay is the key to overcome this challenge. Here, a hybrid framework composed of a neural network and an evolutionary strategy is proposed to implement the inverse design of nanostructures with desired resonance wavelength, bandwidth, and phase delay. With the proposed hybrid framework, the crosstalk between different wavelength channels can be eliminated by precisely controlling the resonance wavelength and the bandwidth of every nanostructure. As a proof of concept, a multicolor meta-holography for linear polarized light is experimentally and theoretically validated. The proposed hybrid framework provides a powerful platform for the design of metasurfaces for multi-frequency optical manipulation and multiplexing.

The second-order nonlinear optical susceptibility (χ⁽²⁾) determines a material's ability to modulate light in optoelectronic applications. Here, a digital alloy crystal growth technique is employed to produce high-quality, symmetric, multilayered InAs/AlSb quantum well (MQW) structures exhibiting a fourfold increase in χ⁽²⁾ compared to bulk AlSb. The results suggest a promising route toward engineering χ⁽²⁾ in asymmetric MQWs.

Abstract

A preliminary measurement of the second-order nonlinear optical susceptibility χMQW(2)\[\chi _{MQW}^{(2)}\] of symmetric, coupled, InAs/AlSb multiple quantum well (MQW) structures is acquired through optical second-harmonic generation (SHG) at fundamental wavelength 1.55 µm. High quality crystalline MQW structures of variable thickness and corresponding bulk AlSb control samples are achieved using a digital alloy epitaxial growth technique that avoids cluster formation and phase segregation. All samples are grown in between a GaSb cap and substrate layer. To isolate SHG from the MQW (or control) layers of interest from cap and substrate contributions, a multilayer optical response matrix model is built and independently tested by accurately reproducing linear reflectivity spectra. While a simplified response matrix analysis of SHG based solely on bulk χ⁽²⁾s does not reproduce the distinct SHG responses of the two sets of samples, the inclusion of an additional interface SHG contribution leads to a successful fit of the data and implies |χMQW(2)|≈4|χAlSb(2)|\[|\chi _{MQW}^{(2)}| \approx 4|\chi _{AlSb}^{(2)}|\]. The results demonstrate a proof-of-concept quantification of χ⁽²⁾ in symmetric MQWs and suggest the possibility of engineering χ⁽²⁾ in these structures, particularly with the introduction of well asymmetries.

A general scheme to achieve wide-angle deep-subwavelength structural colors at the single pixel level is developed with Al particle-on-film nanocavity. Both the angular dispersion and near-field coupling between adjacent pixels are suppressed with the excitation of gap-plasmon mode in the ultrathin gap. Full colors with the smallest reported pixels of 160 nm × 160 nm are experimentally demonstrated.

Abstract

Structural colorations with artificially engineered nanostructures provide a dye-free mechanism for subdiffraction color generation with enhanced stability and environment friendliness. However, it remains elusive to create universally deep subwavelength pixels for arbitrary coloration at the single pixel level. The main obstacles are the unavoidable near-field coupling between neighboring pixels and the angular dependent hues associated with the scattering process. Here, a generic principle is proposed and developed to create deep subwavelength bright-field structural colors at the single pixel level by using alumina disk-on-film nanocavities. As a result of the gap-plasmon-induced perfect absorption, wide-angle complementary colors are achieved across the full visible spectrum where both the near-field coupling and angular dispersion are strongly suppressed. Deep subwavelength pixels down to 160 nm × 160 nm and green colors produced by composite pixels are experimentally demonstrated. The strategy represents a significant step toward practical application of structural colors at the single pixel level for nanoscale optical and optoelectronic devices.

This paper presents the first Förster resonance energy transfer (FRET)-based upconversion nanoparticle (UCNP) sensing scheme that accurately accounts for the effects of FRET and photon reabsorption. By choosing appropriate energy levels, one can achieve ratiometric sensing based solely on FRET or only on photon reabsorption. The strategy is readily applicable to any FRET-based UCNP sensing and can impact a wide range of biosensing applications.

Abstract

Förster resonance energy transfer (FRET)-based devices have been extensively researched as potential biosensors due to their highly localized responsivity. In particular, dye-conjugated upconverting nanoparticles (UCNPs) are among the most promising FRET-based sensor candidates. UCNPs have a multi-modal emission profile that allows for ratiometric sensing, and by conjugating a biosensitive dye to their surface, this profile can be used to measure localized variations in biological parameters. However, the complex nature of the UCNP energy profile as well as reabsorption of emitted photons must be taken into account in order to properly sense the target parameters. To the authors’ knowledge, no proposed UCNP-based sensor has accurately taken care of these intricacies. In this article, the authors account for these complexities by creating a FRET-based sensor that measures pH. This sensor utilizes Thulium (Tm³⁺)-doped UCNPs and the fluorescent dye fluorescein isothiocyanate (FITC). It is first demonstrated that photon reabsorption is a serious issue for the 475 nm Tm³⁺ emission, thereby limiting its use in FRET-based sensing. It is then shown that by taking the ratio of the 646 and 800 nm emissions rather than the more popular 475 nm one, it is possible to measure pH exclusively through FRET.

Solar-to-Ammonia Efficiency

In article 2108316, Damien Voiry and co-workers report a single atom catalyst based on iron single atoms supported on 2D MoS₂ nanosheets. The catalyst demonstrates near-unity selectivity for the electrosynthesis of ammonia with a solar-to-NH₃ efficiency of 3.4% when coupled to an external InGaP/GaAs/Ge triple-junction solar cell.

Dual-Mode Image Sensing Display

In article number 2111894, Cheolmin Park and co-workers develop a simple approach for doping metal ions into all-inorganic perovskite films by employing metal–organic framework (MOF) nanoparticles. With the self-decomposition of MOF nanoparticles at a certain humidity, metal ions are released into nearby perovskite crystals. The perovskite crystals with the defects passivated with the metal ions result in environmentally stable and enhanced photoluminescence of the perovskite for dual-mode image sensing display.

A high ZT of 0.73 at 773 K is achieved in graphite/Bi₂O₂Se hybrid bulk materials. Novel liquid-phase shear exfoliation enables strong texturing effect on the structure, and graphite layers act as unique “expressways” to accelerate the carrier mobility. The single parabolic band model confirms the optimized carrier density and ZT.

Abstract

As an eco-friendly oxide-based thermoelectric material, Bi₂O₂Se exhibits considerable potential for practical device application, but its low electrical conductivity needs to be further improved to achieve higher thermoelectric performance. Here, a record-high figure of merit, ZT of >0.7 at 773 K in the shear-exfoliated nanostructured Bi₂O₂Se with graphite nanosheets as multifunctional secondary nanoinclusions, is achieved. The introduced graphite nanosheets regularize the arrangement of Bi₂O₂Se nanograins, strengthen the anisotropy, and act as the “expressway” to improve the electrical conductivity by simultaneously enhancing the electron carrier concentration and mobility of the hybrid materials, leading to a high power factor of ≈6.0 µW cm^–1 K^–2 at 773 K. Also, the liquid-phase shear exfoliation refines both graphite and Bi₂O₂Se into nanosheets. Moreover, the as-sintered hybrid bulk materials composed of these nanosheets possess dense grain and phase boundaries, as well as various lattice imperfections, such as lattice distortions and stacking faults formed by physical shearing, which can significantly scatter the phonons with different wavelengths and in turn contribute to a low thermal conductivity of only 0.63 W m^–1 K^–1 at 773 K, both contributing to a competitive ZT of ≈0.73 at this temperature, indicating the great potential for practical applications.

Wirelessly-powered, biohybrid soft robots that are inspired by stretchable bioelectronic devices and accordion-like scaffold designs are demonstrated. The integration of wireless cell stimulators into human cardiac-tissue-based muscle actuators realizes electrically controlled movement of robots without requiring batteries and wires. The long penetration depth of the stimulation signal and inherent system extensibility may advance the development of biohybrid robotic systems that are controllable in both in vivo and in vitro environments.

Abstract

The integration of flexible and stretchable electronics into biohybrid soft robotics can spur the development of new approaches for fabricating biohybrid soft machines, thus enabling a wide variety of innovative applications. Inspired by flexible and stretchable wireless-based bioelectronic devices, untethered biohybrid soft robots are developed that can execute swimming motions, which are remotely controllable by the wireless transmission of electrical power into a cell simulator. To this end, wirelessly-powered, stretchable, and lightweight cell stimulators are designed to be integrated into muscle bodies without impeding the robots’ underwater swimming abilities. The cell stimulators function by generating controlled monophasic pulses of up to ≈9 V in biological environments. By differentiating induced pluripotent stem cell-derived cardiomyocytes directly on the cell stimulators using an accordion-inspired, three-dimensional (3D) printing construct, the native myofiber architecture are replicated with comparable robustness and enhanced contractibility. Wirelessly modulated electrical frequencies enables the control of speed and direction of the biohybrid soft robots. A maximum locomotion speed of ≈580 µm s⁻¹ is achieved in robots possessing a large body size by adjusting the pacing frequency. This innovative approach will provide a platform for building untethered and biohybrid systems for various biomedical applications.

A simple strategy has been reported to make high power factors of ≈1800 and ≈1000 µW m⁻¹-K⁻² of p- and n-type multi-walled carbon nanotube films, respectively. A Lego-like thermoelectric generator is fabricated, which generates a voltage of ≈1.4 V and output power of ≈120 µW from a hot pipe of ≈80 °C for hydrogen generation by electrolysis of water.

Abstract

Lightweight and low-cost flexible thermoelectric (TE) materials improve the heat-to-electricity conversion efficiency compared to rigid materials by minimizing the heat loss between TE devices and heat sources in waste heat recovery. Multi-walled carbon nanotube (MWCNT) has excellent mechanical and electrical properties. However, the TE power factor (PF) of MWCNTs is much lower than single/double-walled carbon nanotube (S/DWCNT), which is often lower than 40 µW m⁻¹-K⁻². Herein an effective way to achieve high PFs of ≈1800 µW m⁻¹-K⁻² for p-type and ≈1000 µW m⁻¹-K⁻² for n-type in flexible MWCNT films is reported. The high power factor is achieved by taking advantage of the anisotropic electrical conductivity and isotropic Seebeck coefficient feature of 1D CNTs as well as the following doping and cold-pressing to improve the electrical conductivity of MWCNT films. The PF values are comparable to that of state-of-the-art S/DWCNT films and most inorganic TE materials. A Lego-like TE generator (TEG) with an assembling structure is fabricated to show the heat-to-electricity ability of the materials, which exhibits the highest areal output power of ≈27 W m⁻² among CNT-based flexible TEGs. This method may be extended to other 1D-material based composites to boost the development of high PF flexible TE materials.

A hybrid nanocomposite of PbSe colloidal quantum dots blended with CsPbBr_1.5I_1.5 nanocrystals is integrated for photodetectors ITO/ZnO/PbSe:CsPbBr_1.5I_1.5/P3HT/Au. As a result, a photoresponsivity of 6.16 A W⁻¹ with a specific detectivity of 5.96 × 10¹³ Jones and an ON/OFF current ratio of 10⁵ is obtained in self-powered mode. Also, the device performance is simulated with Technology Computer-Aided Design software, and the physical mechanisms are discussed in detail.

Abstract

Self-powered broadband photodetectors exhibit excellent self-powered and wide-band photoresponse from visible to infrared region and attract enormous attention due to their promising applications in imaging, sensing, and optical communication. PbSe colloidal quantum dots (CQDs) and halide perovskites nanocrystals (NCs) are commonly used for photodetectors due to their strong absorption capability, tunable bandgap, and high aspect ratio. However, due to suffering from low charge carrier mobility and high trap density, the performance of individual PbSe CQDs and perovskites-based photodetectors is not satisfactory. Integration of PbSe CQDs with inorganic mixed-halide perovskite nanomaterials can provide an opportunity to overcome these drawbacks. In this work, a hybrid nanocomposite of PbSe CQDs blended with all-inorganic mixed halide perovskite NCs is integrated to fabricate bulk-heterojunction-based high-performance photodetectors. The transportation of photogenerated carriers is enhanced by employing electrons- and holes-extracting layers. As a result, the photoresponsivity of 6.16 A W⁻¹ and a specific detectivity of 5.96 × 10¹³ Jones with an ON/OFF current ratio of 10⁵ is obtained for bulk-heterojunction photodetector ITO/ZnO/PbSe:CsPbBr_1.5I_1.5/P3HT/Au in the self-powered mode. Meanwhile, the device performance of the fabricated photodetector is numerically simulated by using Technology Computer-Aided Design software, and the physical mechanisms for photogenerated carriers’ transportation are discussed in detail.

Nanopatterning bridges the microstructure of 2D materials and integrated chip devices, essentially enabling and prompting their successful application in industry. A critical summary on the recent development of key nanopatterning technologies of 2D materials, with the aim of realizing large-scale device integration, is provided. This contribution offers a pioneering reference and guidelines to promote 2D materials from laboratory research to practical use.

Abstract

With the reduction of feature size and increase of integration density, traditional 3D semiconductors are unable to meet the future requirements of chip integration. The current semiconductor fabrication technologies are approaching their physical limits based on Moore's law. 2D materials such as graphene, transitional metal dichalcogenides, etc., are of great promise for future memory, logic, and photonic devices due to their unique and excellent properties. To prompt 2D materials and devices from the laboratory research stage to the industrial integrated circuit-level, it is necessary to develop advanced nanopatterning methods to obtain high-quality, wafer-scale, and patterned 2D products. Herein, the recent development of nanopatterning technologies, particularly toward realizing large-scale practical application of 2D materials is reviewed. Based on the technological progress, the unique requirement and advances of the 2D integration process for logic, memory, and optoelectronic devices are further summarized. Finally, the opportunities and challenges of nanopatterning technologies of 2D materials for future integrated chip devices are prospected.

CrSBr is a layered material possessing intralayer ferromagnetic and interlayer antiferromagnetic (AFM) ordering at low temperatures (T < 132 K). At higher temperatures or in the presence of modest magnetic fields, AFM correlations are suppressed, yielding a magnetic phase with a comparatively high sheet susceptibility (χ^2D). Magnetic force microscopy is sensitive to χ^2D and identifies local nanoscale magnetic ordering.

Abstract

2D materials can host long-range magnetic order in the presence of underlying magnetic anisotropy. The ability to realize the full potential of 2D magnets necessitates systematic investigation of the role of individual atomic layers and nanoscale inhomogeneity (i.e., strain) on the emergence of stable magnetic phases. Here, spatially dependent magnetism in few-layer CrSBr is revealed using magnetic force microscopy (MFM) and Monte Carlo-based simulations. Nanoscale visualization of the magnetic sheet susceptibility is extracted from MFM data and force–distance curves, revealing a characteristic onset of both intra- and interlayer magnetic correlations as a function of temperature and layer-thickness. These results demonstrate that the presence of a single uncompensated layer in odd-layer terraces significantly reduces the stability of the low-temperature antiferromagnetic (AFM) phase and gives rise to multiple coexisting magnetic ground states at temperatures close to the bulk Néel temperature (T _N). Furthermore, the AFM phase can be reliably suppressed using modest fields (≈16 mT) from the MFM probe, behaving as a nanoscale magnetic switch. This prototypical study of few-layer CrSBr demonstrates the critical role of layer parity on field-tunable 2D magnetism and validates MFM for use in nanomagnetometry of 2D materials (despite the ubiquitous absence of bulk zero-field magnetism in magnetized sheets).

2D MBenes, early transition metal borides, have recently gained tremendous attention due to their unique properties. This Perspective sheds light on the material–structure–property relationship of MBenes and elucidates the most prospective applications in various fields, thus opening a promising paradigm for designing new functional systems and high-performance devices with multipurpose functionalities.

Abstract

2D MBenes, early transition metal borides, are a very recent derivative of ternary or quaternary transition metal boride (MAB) phases and represent a new member in the flatland. Although holding great potential toward various applications, mainly theoretical knowledge about their potential properties is available. Theoretical calculations and preliminary experimental attempts demonstrate their rich chemistry, excellent reactivity, mechanical strength/stability, electrical conductivity, transition properties, and energy harvesting possibility. Compared to MXenes, MBenes’ structure appears to be more complex due to multiple crystallographic arrangements, polymorphism, and structural transformations. This makes their synthesis and subsequent delamination into single flakes challenging. Overcoming this bottleneck will enable a rational control over MBenes’ material–structure–property relationship. Innovations in MBenes’ postprocessing approaches will allow for the design of new functional systems and devices with multipurpose functionalities thus opening a promising paradigm for the conscious design of high-performance 2D materials.