KJN

Self‐propulsion of Leidenfrost droplets can be controlled by the asymmetric structures of the Janus‐textured substrates. At low temperatures, the droplets asymmetrically spread toward areas with high roughness. At high temperatures, the self‐propulsion occurs only on Janus‐textured substrates with sufficiently large difference in roughness. The self‐propulsion direction shifts toward the regions with low roughness.

Abstract

Controlled propulsion of liquid droplets on a solid surface offers viable applications in fog harvesting, heat transfer, microfluidics, and microdevice technologies. A prerequisite for the propulsion of liquid droplets is to break the wetting symmetry of a droplet and contact‐line pinning on the surface by harnessing surface energy gradient. Here, a series of Janus‐textured substrates is constructed to investigate the self‐propulsion of Leidenfrost droplets. It is found that the self‐propulsion of droplets occurs only on two special Janus‐textured substrates. Those are nanostructured silicon substrate bounded by smooth silicon substrate and the nanowire‐decorated microstructured silicon substrate bounded by micropillars with smooth surfaces. The difference in roughness between the two sides of the Janus‐textured substrates creates various numbers and sizes of vapor bubbles. The vapor bubbles cause the droplets to become turbulent, and a pressure gradient is generated. The sufficiently large pressure gradient propels the Leidenfrost droplet to move directionally. The propulsion direction is always toward areas with low roughness.

A “smart” composite microneedle patch is designed for delivering an insulin‐counterregulatory hormone, glucagon, in response to hypoglycemia (low blood sugar levels) in diabetic subjects. This system exploits the multifunctionality of embedded polymeric microgels that are optimized to stabilize and encapsulate native glucagon and for hypoglycemia‐triggered glucagon release.

Abstract

Insulin‐dependent patients with diabetes mellitus require multiple daily injections of exogenous insulin to combat hyperglycemia. However, administration of excess insulin can lead to hypoglycemia, a life‐threatening condition characterized by abnormally low blood glucose levels (BGLs). To prevent hypoglycemia associated with intensive insulin therapy, a “smart” composite microneedle (cMN) patch is developed, which releases native glucagon at low glucose levels. The cMN patch is composed of a photo‐crosslinked methacrylated hyaluronic acid (MeHA) microneedle array with embedded multifunctional microgels. The microgels incorporate zwitterionic moieties that stabilize loaded glucagon and phenylboronic acid moieties that provide glucose‐dependent volume change to facilitate glucagon release. Hypoglycemia‐triggered release of structurally unchanged glucagon from the cMN patch is demonstrated in vitro and in a rat model of type 1 diabetes (T1D). Transdermal application of the patch prevented insulin‐induced hypoglycemia in the diabetic rats. This work is the first demonstration of a glucose‐responsive glucagon‐delivery MN patch for the prevention of hypoglycemia, which has a tremendous potential to reduce the dangers of intensive insulin therapy and improve the quality of life of patients with diabetes and their caregivers.

A new crystal structure of WS₂ , 2M, is reported. It belongs to the 1T′‐phase family, members of which exhibit W–W zigzag chains along the b axis. Superconductivity with T _c of 8.8 K is reported in these 2M WS₂ crystals. Moreover, calculations show that a topological surface state exists on the their surface, making them potential candidates for topological superconductors.

Abstract

Recently the metastable 1T′‐type VIB‐group transition metal dichalcogenides (TMDs) have attracted extensive attention due to their rich and intriguing physical properties, including superconductivity, valleytronics physics, and topological physics. Here, a new layered WS₂ dubbed “2M” WS₂, is constructed from 1T′ WS₂ monolayers, is synthesized. Its phase is defined as 2M based on the number of layers in each unit cell and the subordinate crystallographic system. Intrinsic superconductivity is observed in 2M WS₂ with a transition temperature T _c of 8.8 K, which is the highest among TMDs not subject to any fine‐tuning process. Furthermore, the electronic structure of 2M WS₂ is found by Shubnikov–de Haas oscillations and first‐principles calculations to have a strong anisotropy. In addition, topological surface states with a single Dirac cone, protected by topological invariant Z₂, are predicted through first‐principles calculations. These findings reveal that the new 2M WS₂ might be an interesting topological superconductor candidate from the VIB‐group transition metal dichalcogenides.

A 3D‐printed millimeter‐scale motor (3DP‐motor) can act as an “aircraft carrier” of TiO₂/Pt Janus micromotors and be used for degradation of nitroaromatic explosive over a large solution area under light illumination. Moreover, a wall‐following motion of the 3DP‐motor in the absence of external guidance is demonstrated that is able to autonomously navigate within a complex pathway reaching the desired final destination.

Abstract

Self‐propelled micro‐/nanomotors are in the forefront of materials research, for applications ranging from environmental remediation to biomedicine. However, due to their limited sizes, they can only navigate within small distances, typically in the order of millimeters, which inevitably hinder their use for large‐volume real applications. Here it is shown that a 3D‐printed millimeter‐scale motor (3DP‐motor) can act as “aircraft carrier” of TiO₂/Pt Janus micromotors and be used for enhanced large‐volume environmental remediation applications. The 3DP‐motor can move fast for tens of meters through the Marangoni effect by asymmetrically releasing ethanol. During its navigation, this 3DP‐motor can carry and slowly release in solution TiO₂/Pt Janus micromotors which can be propelled by light illumination while acting as photodegradation agents. Highly efficient degradation of nitroaromatic explosives over a large solution area is achieved. A wall‐following motion of the 3DP‐motor without external guidance is also demonstrated which is generated by the chemiosmotic flow at the wall vicinity. This can be easily tuned by changing the wettability of the wall surface and also modifying the shape of 3DP‐motor, leading to different motion behaviors. This work introduces a new concept of micromotors carried by large millimeter sized motors to traverse long distances and it should find a broad range of applications.

Solution‐processed lateral photodetectors have many advantages in preparation, operation, and application. From active materials to device architectures, the developed strategies toward high performance for devices based on different kinds of active materials are reviewed. The strategies are discussed in detail, and the common physical rules behind all these strategies are generalized.

Abstract

Due to their low cost and ease of integration, solution‐processed lateral photodetectors (PDs) are becoming an important device type among the PD family. In recent years, enormous effort has been devoted to improving their performances, and great achievements have been made. A summary of the core progress, especially from the perspective of design principles and device physics, is necessary to further the development of the field, but is currently lacking. Here, to address this need, first, the working mechanism of PDs and the device figures‐of‐merit are introduced. Second, by classifying the active materials into four categories, including inorganic, organic, hybrid, and perovskite, the developed strategies toward high performance are discussed respectively. To close, the common physical rules behind all these strategies are generalized, and suggestions for future development are given accordingly.

High‐efficiency electro‐optical switches based on single CdS nanobelts that show low drive voltage, ultrahigh on/off ratio, and broad operational‐wavelength range are demonstrated. Their properties are due to unique electric‐field‐dependent phonon‐assisted optical transitions. Furthermore, functional NOT, NOR, and NAND optical logic gates are realized by designing simple but effective configuration of individual nanobelts on patterned electrodes.

Abstract

High‐performance nanostructured electro‐optical switches and logic gates are highly desirable as essential building blocks in integrated photonics. In contrast to silicon‐based optoelectronic devices, with their inherent indirect optical bandgap, weak light‐modulation mechanism, and sophisticated device configuration, direct‐bandgap‐semiconductor nanostructures with attractive electro‐optical properties are promising candidates for the construction of nanoscale optical switches for on‐chip photonic integrations. However, previously reported semiconductor‐nanostructure optical switches suffer from serious drawbacks such as high drive voltage, limited operation spectral range, and low modulation depth. High‐efficiency electro‐optical switches based on single CdS nanobelts with low drive voltage, ultra‐high on/off ratio, and broad operation wavelength range, properties resulting from unique electric‐field‐dependent phonon‐assisted optical transitions, are demonstrated. Furthermore, functional NOT, NOR, and NAND optical logic gates are demonstrated based on these switches. These switches and optical logic gates represent an important step toward integrated photonic circuits.

Damage of superhydrophobic coatings is inevitable despite improvements in mechanical durability and/or self‐healing. In article number https://doi.org/10.1002/adfm.2019006881900688, Mizuki Tenjimbayashi, Masanobu Naito, and Sadaki Samitsu demonstrate a system of simultaneous detection and repair of damaged surface areas using the wetting transition phenomenon of liquid marbles. In this system, the liquid marble recovers the surface wettability in response to wetting defects, which enables sustainable material interfaces.

A strong and tough glass can be fabricated through a direct‐solidification process using a nanoparticle self‐dispersion mechanism, delivering a 6.1% strain limit and strength close to the theoretical limit. The fracture toughness of this glass is significantly higher than any other inorganic glasses. This new method opens up remarkable opportunities for glass and ceramic research, manufacturing, and applications.

Abstract

Glassy materials can be broadly defined as any amorphous solid, which are important in nature and have significant societal value for their applications in daily life and industry. Although many methods have been applied, the fracture toughness of traditional glasses is still very low due to intrinsic brittleness, significantly limiting their use for structural applications. While nanoelements may be added into glasses and ceramics to form nanocomposites with enhanced properties, it is extremely difficult to distribute and disperse them inside the liquid glass/ceramic matrix with traditional processing methods. It is shown that a strong and tough glass can be fabricated through a direct‐solidification process using a nanoparticle self‐dispersion mechanism in a glass melt (2MgO·2Al₂O₃·5SiO₂) with the assistance of B₂O₃, delivering a 6.1% strain limit and strength up to E/14 (E is elastic modulus), which is close to the theoretical limit of E/10 and one of the highest among all materials reported so far. The fracture toughness of the glass with 30 vol% SiC nanoparticles is significantly higher than any other inorganic glass tested under similar conditions. This new method opens up remarkable opportunities for glass and ceramic research, manufacturing, and applications.

Recent progress in the development of wood and its derivative materials for advanced energy storage devices, including supercapacitors and rechargeable batteries, is reviewed, in particular for their micro/nanostructure, structure engineering strategies, and electrochemical performance.

Abstract

Over the past decade, wood‐derived materials have attracted enormous interest for both fundamental research and practical applications in various functional devices. In addition to being renewable, environmentally benign, naturally abundant, and biodegradable, wood‐derived materials have several unique advantages, including hierarchically porous structures, excellent mechanical flexibility and integrity, and tunable multifunctionality, making them ideally suited for efficient energy storage and conversion. In this article, the latest advances in the development of wood‐derived materials are discussed for electrochemical energy storage systems and devices (e.g., supercapacitors and rechargeable batteries), highlighting their micro/nanostructures, strategies for tailoring the structures and morphologies, as well as their impact on electrochemical performance (energy and power density and long‐term durability). Furthermore, the scientific and technical challenges, together with new directions of future research in this exciting field, are also outlined for electrochemical energy storage applications.

Using in situ microscopy, thermolysis of an amorphous precursor to form 2D MoS₂ crystals is observed at atomic resolution. Critical steps such as nucleation of nanograins and grain growth through aggregation of nanograins are analyzed using atomic resolution STEM images. The research sheds light on the controlled synthesis of 2D MoS₂ thin films through a thermolysis approach.

Abstract

Understanding and controlling the transformations of transition metal dichalcogenides (TMDs) from amorphous precursors into two‐dimensional (2D) materials is important for guiding synthesis, directing fabrication, and tailoring functional properties. Here, the combined effects of thermal energy and electron beam irradiation are explored on the structural evolution of 2D MoS₂ flakes through the thermal decomposition of a (NH₄)₂MoS₄ precursor inside an ultrahigh vacuum (10⁻⁹ Torr) scanning transmission electron microscope (STEM). The influence of reaction temperature, growth substrate, and the initial precursor morphology on the resulting 2D MoS₂ flake morphology, edge structures, and point defects are explored. Although thermal decomposition occurs extremely fast at elevated temperatures and is difficult to capture using current STEM techniques, electron beam irradiation can induce local transformations at lower temperatures, enabling direct observation and interpretation of critical growth steps including oriented attachment and transition from single‐ to multilayer structures at atomic resolution. An increase in the number of layers of the MoS₂ flakes from island growth is investigated using electron beam irradiation. These findings provide insight into the growth mechanisms and factors that control the synthesis of few‐layer MoS₂ flakes through thermolysis and toward the prospect of atomically precise control and growth of 2D TMDs.

2D photonic nanostructures, inspired by the attractive optical properties found on the inner surfaces of seashells, are fabricated in a facile and scalable way. 2D–2D graphene–TiO₂ heterostructures and 2D–2D TiO₂–TiO₂ exhibit strong light interactions and fascinating metallic structural color and ultrafast interfacial carrier generation and transfer, and thus are promising for high‐performance electronic and optoelectronic applications.

Abstract

The discovery of novel materials that possess extraordinary optical properties are of special interest, as they inspire systems for next‐generation solar energy harvesting and conversion devices. Learning from nature has inspired the development of many photonic nanomaterials with fascinating structural colors. 2D photonic nanostructures, inspired by the attractive optical properties found on the inner surfaces of seashells, are fabricated in a facile and scalable way. The shells generate shining clusters for preying on phototactic creatures through interaction with incident solar light in water. By alternately depositing graphene and 2D ultrathin TiO₂ nanosheets to form 2D–2D heterostructures and homostructures, seashell‐inspired nanomaterials with well‐controlled parameters are successfully achieved. They exhibit exceptional interlayer charge transfer properties and ultrafast in‐plane electron mobility and present fascinating nacre‐mimicking optical properties and significantly enhanced light‐response behavior when acting as photoelectrodes. A window into the fabrication of novel 2D photonic structures and devices is opened, paving the way for the design of high‐performance solar‐energy harvesting and conversion devices.

Rapid thermal annealing of irradiated diamond particulates up to 2100 °C provides controlled and highly reproducible formation of specific color centers in type Ib synthetic diamond particles with vibrant luminescence in the red, green, and blue spectral ranges.

Abstract

The current study reports a breakthrough method for production of multicolor diamond particulates using a rapid thermal annealing (RTA) approach with precise temperature and time control, enabling annealing of diamond particulates up to 2100 °C without extensive graphitization. The RTA method generates conditions which allow formation of one‐, two‐, and three‐atom nitrogen complexes with vacancies in electron irradiated type Ib synthetic diamond, providing vibrant luminescence in the red, green, and blue spectral ranges, correspondingly. Controlled and highly reproducible formation of specific color centers previously not possible in type Ib synthetic diamond particles opens new opportunities for particulate diamond in a plethora of fluorescence imaging applications in biological and industrial fields.

An open air plasma system is used to deposit a robust, superhydrophilic titania film in a single step without additional heating or postprocessing. The film is an effective antifog coating, related to nanoscale roughness, nonmetal dopants and oxygen vacancies, and surface activation by the plasma to enable strong interaction with water.

Abstract

A method for the deposition and functionalization of a nanostructured organotitanate thin film, which imparts superhydrophilicity to a surface with a one‐step, open‐air process, is described. Extreme wetting (Θ < 5°) is achieved through synergistic contributions from both nanoscale roughness, visible light absorption caused by nonmetal dopants, and oxygen vacancies and surface activation by reactive plasma species. To test the efficacy of this material as an antifog coating, glass is coated and subjected to aggressive changes in humidity. Under both fogging and defrosting conditions, the superhydrophilic coating achieves a high degree of transparency, showing nearly two orders of magnitude improvement over the bare glass. The measured adhesion of the superhydrophilic coating is 5.9 J m⁻², nearly double that of the solution‐processed control. The reliability of the coating is further validated by demonstrating scratch‐resistance. Additionally, the incorporation of organic matter into the molecular structure of the coating disrupts long‐range crystallinity from developing. This structural and subsequent chemical analysis of the coating reveals that inorganic and organic species are intimately connected at the nanoscale via alkyl and alkoxy bridges. The amorphous organotitanate material is distinct from conventional TiO₂, which requires high temperature crystallization and extensive UV irradiation to display similar superhydrophilic qualities.