Drop-On-Demand Microdroplet Generation under Charge Injection by Corona Discharge.

In printing, microreactors, and bioassays, the precise control of micrometer-scale droplet generation is essential but challenging, often restricted by the equipment and nozzles used in traditional methods. We introduce a needle-plate electrode corona discharge technique that injects charges into an oil layer, enabling the precise manipulation of droplet polarization and splitting. This method allows for meticulous adjustment of microdroplet formation regarding location, size, and quantity by modulating the discharge voltage, discharge time, and electrode positioning. It enables the immediate initiation and cessation of droplet production, thereby facilitating on-demand droplet generation. Our study on the voltage-dependent droplet stretch coefficient shows that as the voltage increases, the droplets transition from controlled splitting to regular Taylor cone-like ejections, eventually reaching the Rayleigh limit and fully breaking apart. These advancements significantly improve microfluidic droplet manipulation, offering considerable benefits for applications in targeted drug delivery, rapid disease diagnostics, and precise environmental monitoring.

Dynamical Janus-Like Behavior Excited by Passive Cold-Heat Modulation in the Earth-Sun/Universe System: Opportunities and Challenges.

The utilization of solar-thermal energy and universal cold energy has led to many innovative designs that achieve effective temperature regulation in different application scenarios. Numerous studies on passive solar heating and radiation cooling often operate independently (or actively control the conversion) and lack a cohesive framework for deep connections. This work provides a concise overview of the recent breakthroughs in solar heating and radiation cooling by employing a mechanism material in the application model. Furthermore, the utilization of dynamic Janus-like behavior serves as a novel nexus to elucidate the relationship between solar heating and radiation cooling, allowing for the analysis of dynamic conversion strategies across various applications. Additionally, special discussions are provided to address specific requirements in diverse applications, such as optimizing light transmission for clothing or window glass. Finally, the challenges and opportunities associated with the development of solar heating and radiation cooling applications are underscored, which hold immense potential for substantial carbon emission reduction and environmental preservation. This work aims to ignite interest and lay a solid foundation for researchers to conduct in-depth studies on effective and self-adaptive regulation of cooling and heating.

Continuous Tunable Energy Band Tailoring Boosts Extending the Sensing of the Waveband Based on (InxGa1-x)2O3 Solar-Blind Photodetectors.

Rising wide bandgap semiconductor gallium oxide (Ga2O3) displays huge potential in performing solar-blind photodetection, with constraint in narrow detection wavebands in nature, whereas bandgap modulation through the introduction of exotic atoms into Ga2O3 has an essential effect on the tunable performance of photodetectors and the detection waveband. Here, a novel method for the preparation of (InxGa1-x)2O3 alloy films is proposed, and the continuous tuning of the bandgap in the range of 3.70-4.99 eV is achieved by varying the In-doping content. Alloy-based metal-semiconductor-metal photodetectors were fabricated, achieving a peak responsivity between 254 and 295 nm, superior performance compared to Ga2O3 photodetectors, with a photo-to-dark current ratio as high as 106, and a better optical image-sensing capability. This study offers new insight for high-performance detection of full solar-blind waveband ultraviolet light.

Enhanced Absolute Recovered Energy under Low Electric Field in All-Inorganic 0-3 Nanocomposition Thick Films.

Inorganic thick-film dielectric capacitors with ultrahigh absolute recovered energy at low electric fields are extremely desired for their wide application in pulsed power systems. However, a long-standing technological bottleneck exists between high absolute energy and large recovered energy density. A new strategy is offered to fabricate selected all-inorganic 0-3 composite thick films up to 10 µm by a modified sol-slurry method. Here, the ceramic powder is dispersed into the sol-gel matrix to form a uniform suspension, assisted by powder, therefore, the 2 µm-thickness after single layer spin coating. To enhance the energy-storage performances, the composites process is thoroughly optimized by ultrafine powder (<50 nm) technique based on a low-cost coprecipitation method instead of the solid-state and sol-gel methods. 0D coprecipitation powder has a similar dielectric constant to the corresponding 3D films, thus uneven electrical field distributions is overcome. Moreover, the increase of interfacial polarization is realized due to the larger specific surface area. A maximum recoverable energy density of 14.62 J cm-3 is obtained in coprecipitation thick films ≈2.2 times that of the solid-state powder and ≈1.3 times for sol-gel powder. This study provides a new paradigm for further guiding the design of composite materials.

Free-Standing Electrode and Fixed Surface Tiny Electrode Implemented Triboelectric Nanogenerator with High Instantaneous Current.

Conventional triboelectric nanogenerators (TENGs) face challenges pertaining to low output current density at low working frequencies and high internal impedance. While strategies, such as surface modification to enhance surface charge density, permittivity regulation of materials, and circuit management, have partially mitigated these issues. However, they have also resulted in increased complexity in the fabrication process. Therefore, there is an urgent demand for a universal and simplified approach to address these challenges. To fulfill this need, this work presents a free-standing electrode and fixed surface tiny electrode implemented triboelectric nanogenerator (FFI-TENG). It is fabricated by a straightforward yet effective method: introducing a tiny electrode onto the surface of the tribo-negative material. This approach yields substantial enhancements in performance, notably a more than tenfold increase in output current density, a reduction in effective working frequencies, and a decrease in matching resistance as compared to vertical contact-separation TENGs (CS-TENGs) or single-electrode TENGs (SE-TENGs). Simultaneously, a comprehensive examination and proposition regarding the operational mechanism of FFI-TENG, highlighting its extensive applicability are also offered. Significantly, FFI-TENG excels in mechanical energy harvesting even under ultra-low working frequencies (0.1 Hz), outperforming similar contact-separation models. This innovation positions it as a practical and efficient solution for the development of low-entropy energy harvesters.

Self-powered solar-blind detector array based on ε-Ga2O3 Schottky photodiodes for dual-mode binary UV communication.

In this work, a solar-blind UV metal-semiconductor Schottky photodiode array is constructed by using metalorganic chemical vapor deposition grown ε-Ga2O3 thin film, possessing high-performance and self-powered characteristics, toward dual-mode (self-powered and biased modes) binary light communication. For the array unit, the responsivity, specific detectivity, and external quantum efficiency are 30.8 A/W/6.3 × 10-2 A/W, 1.51 × 104%/30.9%, 1.28 × 1014/5.4 × 1012 Jones for biased (-10 V)/self-powered operation. The rise and decay time are 0.19 and 7.96 ms at biased modes, respectively, suggesting an ability to trace fast light signal. As an array, the deviation of photocurrent is only 4.3%, highlighting the importance of accurate information communication. Through certain definition of "1/0" binary digital information, the "NY" and "IC" characters are communicated to illustrate the self-powered and biased modes by right of ASCII codes, based on the prepared ε-Ga2O3 solar-blind UV Schottky photodiode array. This work made dual-mode binary deep-UV light communication come true and may well guide the development of UV optoelectronics.

A Flexible Piezocapacitive Pressure Sensor with Microsphere-Array Electrodes.

Flexible pressure sensors that emulate the sensation and characteristics of natural skins are of great importance in wearable medical devices, intelligent robots, and human-machine interfaces. The microstructure of the pressure-sensitive layer plays a significant role in the sensor's overall performance. However, microstructures usually require complex and costly processes such as photolithography or chemical etching for fabrication. This paper proposes a novel approach that combines self-assembled technology to prepare a high-performance flexible capacitive pressure sensor with a microsphere-array gold electrode and a nanofiber nonwoven dielectric material. When subjected to pressure, the microsphere structures of the gold electrode deform via compressing the medium layer, leading to a significant increase in the relative area between the electrodes and a corresponding change in the thickness of the medium layer, as simulated in COMSOL simulations and experiments, which presents high sensitivity (1.807 kPa-1). The developed sensor demonstrates excellent performance in detecting signals such as slight object deformations and human finger bending.

Triboelectric Nanogenerators Based on 2D Materials: From Materials and Devices to Applications.

Recently, there has been an increasing consumption of fossil fuels such as oil and natural gas in both industrial production and daily life. This high demand for non-renewable energy sources has prompted researchers to investigate sustainable and renewable energy alternatives. The development and production of nanogenerators provide a promising solution to address the energy crisis. Triboelectric nanogenerators, in particular, have attracted significant attention due to their portability, stability, high energy conversion efficiency, and compatibility with a wide range of materials. Triboelectric nanogenerators (TENGs) have many potential applications in various fields, such as artificial intelligence (AI) and the Internet of Things (IoT). Additionally, by virtue of their remarkable physical and chemical properties, two-dimensional (2D) materials, such as graphene, transition metal dichalcogenides (TMDs), hexagonal boron nitride (h-BN), MXenes, and layered double hydroxides (LDHs), have played a crucial role in the advancement of TENGs. This review summarizes recent research progress on TENGs based on 2D materials, from materials to their practical applications, and provides suggestions and prospects for future research.

Oscillatory Motion of Water Droplets Both in Oil and on Superhydrophobic Surface under Corona Discharge.

Charged droplets driven by Coulomb force are an important part of a droplet-based micro reactor. In this study, we realized the rapid oscillatory motion of droplets both in oil and on superhydrophobic surface by injecting charges through corona discharge. Distinct from the oscillatory motion of water droplets under a DC electric field, charge injection can make the motion of water droplets more flexible. A droplet in the oil layer can move up and down regularly under the action of corona discharge, and the discharge voltage can control the movement period and height of the droplet. In addition, the left-right translation of droplets on a superhydrophobic surface can be achieved by injecting charges into the hydrophobic film surface through corona discharge. Two kinds of droplet motion behaviors are systematically analyzed, and the mechanism of droplet motion is explained. The present results could help establish new approaches to designing efficient machines in microfluidics and micromechanical equipment.

Versatile self-assembled electrospun micropyramid arrays for high-performance on-skin devices with minimal sensory interference.

On-skin devices that show both high performance and imperceptibility are desired for physiological information detection, individual protection, and bioenergy conversion with minimal sensory interference. Herein, versatile electrospun micropyramid arrays (EMPAs) combined with ultrathin, ultralight, gas-permeable structures are developed through a self-assembly technology based on wet heterostructured electrified jets to endow various on-skin devices with both superior performance and imperceptibility. The designable self-assembly allows structural and material optimization of EMPAs for on-skin devices applied in daytime radiative cooling, pressure sensing, and bioenergy harvesting. A temperature drop of ~4 °C is obtained via an EMPA-based radiative cooling fabric under a solar intensity of 1 kW m-2. Moreover, detection of an ultraweak fingertip pulse for health diagnosis during monitoring of natural finger manipulation over a wide frequency range is realized by an EMPA piezocapacitive-triboelectric hybrid sensor, which has high sensitivity (19 kPa-1), ultralow detection limit (0.05 Pa), and ultrafast response (≤0.8 ms). Additionally, EMPA nanogenerators with high triboelectric and piezoelectric outputs achieve reliable biomechanical energy harvesting. The flexible self-assembly of EMPAs exhibits immense potential in superb individual healthcare and excellent human-machine interaction in an interference-free and comfortable manner.

A high-performance triboelectric nanogenerator with improved output stability by construction of biomimetic superhydrophobic nanoporous fibers.

The utilization of nanoporous materials is an extremely effective approach to enhance the electrical performance of triboelectric nanogenerators (TENGs). However, existing methods for preparing nanoporous tribo-materials are not only complicated, costly and time-consuming, but also waste a lot of material. Meanwhile, fabricated nanoporous tribo-materials that have low roughness by nature possess poor surface hydrophobicity, causing low output stability in humid environments. Here, a bio-inspired petiole-like micron fiber-based tribo-material with inner nanopores, rough surface nanostructures and superhydrophobicity is first designed that uses an extraordinarily simple, ultralow-waste and efficient single-component electrospinning process. The petiole-like structures and superhydrophobicity endow the assembled triboelectric nanogenerator (PMF-TENG) with outstanding electrical performance and superior output stability under humid conditions. With a giant power density of 56.9 W m-2 and a high peak-to-peak output voltage of 2209 V, the optimized PMF-TENG can not only be used as a biomechanical energy harvester to directly drive 833 light-emitting-diodes and small electronics, but also serve as a self-powered sensor to detect body motions. Moreover, under a high relative humidity of 80%, the output retention rate of the optimized PMF-TENG is 1.7 and 2.2 times higher than the TENG assembled with the traditional smoother solid nanofiber-based tribo-material and the monolithic nanoporous tribo-material-based TENG, respectively. This work provides an easy-to-fabricate high-performance nanoporous material-based TENG with ultralow material waste and extends its potential for application in humid conditions.