Chiral twisted van der Waals nanowires
Chiral twisted van der Waals nanowires, Published online: 22 April 2019; doi:10.1038/s41586-019-1147-x
A tunable interlayer twist that evolves naturally during synthesis of van der Waals nanowires made from layered crystals of germanium sulfide could produce new electronic structure and correlation phenomena.Two-dimensional copper nanosheets for electrochemical reduction of carbon monoxide to acetate
Two-dimensional copper nanosheets for electrochemical reduction of carbon monoxide to acetate, Published online: 08 April 2019; doi:10.1038/s41929-019-0269-8
Upgrading CO to high-value multicarbon products is a promising avenue for fuel and chemical feedstock production. Here triangular Cu nanosheets that selectively expose the (111) surface exhibit a high acetate partial current density (131 mA cm–2) and Faradaic efficiency (48%) in CO electroreduction.
A stepwise seeded growth method is developed for the synthesis of rod‐shaped plasmon nanostructures, which are vertically self‐aligned with respect to the surface of colloidal substrates. Dynamic tuning of the plasmon excitation, which allows the creation of an anticounterfeiting display, is realized by controlling the orientation of magnetic/plasmonic nanocomposites by applying a magnetic field.
Great opportunities emerge not only in the generation of anisotropic plasmonic nanostructures but also in controlling their orientation relative to incident light. Herein, a stepwise seeded growth method is reported for the synthesis of rod‐shaped plasmon nanostructures which are vertically self‐aligned with respect to the surface of colloidal substrates. Anisotropic growth of metal nanostructure is achieved by depositing metal seeds onto the surface of colloidal substrates and then selectively passivating the seed surface to induce symmetry breaking in the subsequent seed‐mediated growth process. The versatility of this method is demonstrated by producing nanoparticle dimers and linear trimers of Au, Au–Ag, Au–Pd, and Au–Cu2O. Further, this unique method enables the automatic vertical alignment of the resulting plasmonic nanostructures to the surface of the colloidal substrate, thereby making it possible to design magnetic/plasmonic nanocomposites that allow the dynamic tuning of the plasmon excitation by controlling their orientation using an external magnetic field. The controlled anisotropic growth of colloidal plasmonic nanostructures and their dynamic modulation of plasmon excitation further allow them to be conveniently fixed in a thin polymer film with a well‐controlled orientation to display polarization‐dependent patterns that may find important applications in information encryption.
Light entertainment: Chemical reactions induced by localized surface plasmons enable highly efficient conversion of solar energy into chemical energy. This Minireview summarizes the evolution of plasmon chemistry and discusses relevant chemical reactions in terms of excitation mechanisms. Guidance is provided for further study of plasmon chemistry in metal catalysis.
Chemical reactions induced by the localized surface plasmon (LSP) of metal nanostructures could be important for a sustainable society to achieve highly efficient conversion from solar energy to chemical energy. However, the reaction mechanism of plasmon chemistry in metal catalysis is still controversial. Mechanistic studies of plasmon chemistry involving direct interactions between the LSP and molecules are reviewed and discussed in terms of the excitation mechanisms of the molecules. We focus on the studies performed using plasmonic metal nanoparticles and highlight the recent progress in plasmon chemistry investigated using scanning probe microscopy with high spatial resolution to obtain mechanistic insights that cannot be obtained by macroscopic analytical methods. This Minireview delivers an overview of the mechanistic understanding of plasmon chemistry in metal catalysis at the current stage, and provides guidance for future studies with respect to clarifying reaction mechanisms.
A new hybrid lead halide material built of deformable post‐perovskite‐type chains exhibits an enhanced intrinsic white photoemission, setting a new record of 45% for photoluminescence quantum yield. The deformable lattice of this compound enables the self‐trapping of excitons responsible for broadband emission.
Hybrid metal halides containing perovskite layers have recently shown great potential for applications in solar cells and light‐emitting diodes. Such compounds exhibit quantum confinement effects leading to tunable optical and electronic properties. Thus, broadband white‐light emission has been observed from diverse metal halides and, owing to high color rendering index, high thermal stability, and low‐temperature solution processability, these materials have attracted interest for application in solid‐state lighting. However, the reported quantum yields for white photoluminescence (PLQY) remain low (i.e., in the range 0.5–9%) and no approach has shown to successfully increase the intensity of this emission. Here, it is demonstrated that the quantum efficiencies of hybrid metal halides can be greatly enhanced if they contain a polymorph of the [PbX4]2− perovskite‐type layers: the [PbX4]2− post‐perovskite‐type chains showing a PLQY of 45%. Different piperazines lead to a hybrid lead halide with either perovskite layers or post‐perovskite chains influencing strongly the presence of self‐trapped states for excitons. It is anticipated that this family of hybrid lead halide materials could enhance all the properties requiring the stabilization of trapped excitons.
Responsive optical nanomaterials have attracted long‐standing research interests owing to their promise in both fundamental studies and practical applications. The current research activities on responsive optical nanomaterials are reviewed, with special focus on optical diffraction, absorption, refraction, and emission. Perspectives are also provided to point out the possible directions for future research.
Responsive optical nanomaterials that can sense and translate various external stimuli into optical signals, in the forms of observable changes in appearance and variations in spectral line shapes, are among the most active research topics in nanooptics. They are intensively exploited within the regimes of the four classic optical phenomena—diffraction in photonic crystals, absorption of plasmonic nanostructures, as well as color‐switching systems, refraction of assembled birefringent nanostructures, and emission of photoluminescent nanomaterials and molecules. Herein, a comprehensive review of these research activities regarding the fundamental principles and practical strategies is provided. Starting with an overview of their substantial developments during the latest three decades, each subtopic discussion is led with fundamental theories that delineate the correlation between nanostructures and optical properties and the delicate research strategies are elaborated with specific attention focused on working principles and optical performances. The unique advantages and inherent limitations of each responsive optical nanoscale platform are summarized, accompanied by empirical criteria that should be met and perspectives on research opportunities where the developments of next‐generation responsive optical nanomaterials might be directed.
Inspired by butterfly wings, synthetic scale surfaces using flexible, curved carbon nanotube structures are designed and fabricated, demonstrating anisotropic drop adhesion properties. The anisotropic adhesion is tailored by the precisely controlled scale geometry, stiffness, and surface wettability, replicating the mechanism of drop‐surface interaction observed on natural butterfly scales.
Many natural surfaces such as butterfly wings, beetles' backs, and rice leaves exhibit anisotropic liquid adhesion; this is of fundamental interest and is important to applications including self‐cleaning surfaces, microfluidics, and phase change energy conversion. Researchers have sought to mimic the anisotropic adhesion of butterfly wings using rigid surface textures, though natural butterfly scales are sufficiently compliant to be deflected by capillary forces exerted by drops. Here, inspired by the flexible scales of the Morpho aega butterfly wing, synthetic surfaces coated with flexible carbon nanotube (CNT) microscales with anisotropic drop adhesion properties are fabricated. The curved CNT scales are fabricated by a strain‐engineered chemical vapor deposition technique, giving ≈5000 scales of ≈10 µm thickness in a 1 cm2 area. Using various designed CNT scale arrays, it is demonstrated that the anisotropy of drop roll‐off angle is influenced by the geometry, compliance, and hydrophobicity of the scales; and a maximum roll‐off anisotropy of 6.2° is achieved. These findings are supported by a model that relates the adhesion anisotropy to the scale geometry, compliance, and wettability. The electrical conductivity and mechanical robustness of the CNTs, and the ability to fabricate complex multidirectional patterns, suggest further opportunities to create engineered synthetic scale surfaces.
The confinement of anthracene molecules in a metal–organic framework enables reversible yellow‐to‐purple photoswitching of the fluorescence emission. The photoresponse of the host–guest system strongly relies on the unique properties of the MOF host, that is, the pore geometry, connectivity, and volume as well as the structural flexibility. The solid‐state photoswitching enabled the development of photopatternable, erasable, and rewritable paper.
Metal–organic frameworks (MOFs) enable the design of host–guest systems with specific properties. In this work, we show how the confinement of anthracene in a well‐chosen MOF host leads to reversible yellow‐to‐purple photoswitching of the fluorescence emission. This behavior has not been observed before for anthracene, either in pure form or adsorbed in other porous hosts. The photoresponse of the host–guest system is caused by the photodimerization of anthracene, which is greatly facilitated by the pore geometry, connectivity, and volume as well as the structural flexibility of the MOF host. The photoswitching behavior was used to fabricate photopatternable and erasable surfaces that, in combination with data encryption and decryption, hold promise in product authentication and secure communication applications.
Water repellent and light: Hydrophobic 2D Pb and Sn halide perovskites were synthesized under ambient conditions by solution‐based methods and showed contact angles over 90° as well as dispersibility and photoluminescence in water, thus highlighting their hydrophobic behavior. The perovskites were also effective photocatalysts for visible‐light‐driven redox‐neutral decarboxylation and oxidative dehydrogenation reactions.
Two‐dimensional lead and tin halide perovskites were prepared by intercalating the long alkyl group 1‐hexadecylammonium (HDA) between the inorganic layers. We observed visible‐light absorption, narrow‐band photoluminescence, and nanosecond photoexcited lifetimes in these perovskites. Owing to their hydrophobicity and stability even in humid air, we applied these perovskites in the decarboxylation and dehydrogenation of indoline‐2‐carboxylic acids. (HDA)2PbI4 or (HDA)2SnI4 were investigated as photoredox catalysts for these reactions, and quantitative conversion and high yields were observed with the former.
Perovskites are versatile ABX3 crystals, hosting many intriguing physical properties. While most are inorganic compounds with cationic A‐ and B‐, and anionic X‐sites, recently, the introduction of organic ions (hybrid perovskites) and structures with inverted ionic charges (inverse (hybrid) perovskites) have been explored. Thus, the combinatorial space for design with optimized properties has new dimensions.
Materials science evolves to a state where the composition and structure of a crystal can be controlled almost at will. Given that a composition meets basic requirements of stoichiometry, steric demands, and charge neutrality, researchers are now able to investigate a wide range of compounds theoretically and, under various experimental conditions, select the constituting fragments of a crystal. One intriguing playground for such materials design is the perovskite structure. While a game of mixing and matching ions has been played successfully for about 150 years within the limits of inorganic compounds, the recent advances in organic–inorganic hybrid perovskite photovoltaics have triggered the inclusion of organic ions. Organic ions can be incorporated on all sites of the perovskite structure, leading to hybrid (double, triple, etc.) perovskites and inverse (hybrid) perovskites. Examples for each of these cases are known, even with all three sites occupied by organic molecules. While this change from monatomic ions to molecular species is accompanied with increased complexity, it shows that concepts from traditional inorganic perovskites are transferable to the novel hybrid materials. The increased compositional space holds promising new possibilities and applications for the universe of perovskite materials.
Up to five‐photon excited luminescence is exhibited in a host–guest metal–organic framework (MOF) and perovskite quantum dot (QD) hybrid single‐crystal ZJU‐28⊃MAPbBr3 via an in situ growth approach. The framework confinement and protection of the MOF for perovskite‐QDs result in significantly enhanced multiphoton excited luminescence, demonstrating high multiphoton action cross‐sections and high photostability.
The development of the photostable higher‐order multiphoton‐excited (MPE) upconversion single microcrystalline material is fundamentally and technologically important, but very challenging. Here, up to five‐photon excited luminescence in a host–guest metal–organic framework (MOF) and perovskite quantum dot (QD) hybrid single crystal ZJU‐28⊃MAPbBr3 is shown via an in situ growth approach. Such a MOF strategy not only results in a high QD loading concentration, but also significantly diminishes the aggregation‐caused quenching (ACQ) effect, provides effective surface passivation, and greatly reduces the contact of the QDs with the external bad atmosphere due to the confinement effect and protection of the framework. These advantages make the resulting ZJU‐28⊃MAPbBr3 single crystals possess high PLQY of ≈51.1%, a high multiphoton action cross‐sections that can rival the current highest record (measured in toluene solution), and excellent photostability. These findings liberate the excellent luminescence and nonlinear optical properties of perovskite QDs from the solution system to the solid single‐crystal system, which provide a new avenue for the exploitation of high‐performance multiphoton excited hybrid single microcrystal for future optoelectronic and micro–nano photonic integration applications.
Large‐scale flexible photodetector arrays are fabricated based on patterned CH3NH3PbI3− x Cl x film. In addition, the device, with outstanding optoelectronic performance and excellent electrical stability, is applied to capture a real‐time light trajectory and detect a multipoint light distribution, indicating that it has widespread potential in photosensing and imaging for optical communication, imaging, and artificial electronic skin applications.
The quest for novel deformable image sensors with outstanding optoelectronic properties and large‐scale integration becomes a great impetus to exploit more advanced flexible photodetector (PD) arrays. Here, 10 × 10 flexible PD arrays with a resolution of 63.5 dpi are demonstrated based on as‐prepared perovskite arrays for photosensing and imaging. Large‐scale growth controllable CH3NH3PbI3− x Cl x arrays are synthesized on a poly(ethylene terephthalate) substrate by using a two‐step sequential deposition method with the developed Al2O3‐assisted hydrophilic–hydrophobic surface treatment process. The flexible PD arrays with high detectivity (9.4 × 1011 Jones), large on/off current ratio (up to 1.2 × 103), and broad spectral response exhibit excellent electrical stability under large bending angle (θ = 150°) and superior folding endurance after hundreds of bending cycles. In addition, the device can execute the functions of capturing a real‐time light trajectory and detecting a multipoint light distribution, indicating that it has widespread potential in photosensing and imaging for optical communication, digital display, and artificial electronic skin applications.
Quantifying the role of surface plasmon excitation and hot carrier transport in plasmonic devices
Quantifying the role of surface plasmon excitation and hot carrier transport in plasmonic devices, Published online: 23 August 2018; doi:10.1038/s41467-018-05968-x
Understanding the role of plasmon excitation is crucial for the realization of hot carrier devices. Here, the authors report internal quantum efficiency measurements in photoexcited gold gallium nitride Schottky diodes and elucidate the roles of surface plasmon excitation, hot carrier transport, and carrier injection in device performance.