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The piezo-phototronic effect (a coupling effect of piezoelectric, photoexcitation and semiconducting properties, coined in 2010) has been demonstrated to be an ingenious and robust strategy to manipulate optoelectronic processes by tuning the energy band structure and photoinduced carrier behavior. The piezo-phototronic effect exhibits great potential in improving the quantum yield efficiencies of optoelectronic materials and devices and thus could help increase the energy conversion efficiency, thus alleviating the energy shortage crisis. In this review, the fundamental principles and challenges of representative optoelectronic materials and devices are presented, including photocatalysts (converting solar energy into chemical energy), solar cells (generating electricity directly under light illumination), photodetectors (converting light into electrical signals) and light-emitting diodes (LEDs, converting electric current into emitted light signals). Importantly, the mechanisms of how the piezo-phototronic effect controls the optoelectronic processes and the recent progress and applications in the above-mentioned materials and devices are highlighted and summarized. Only photocatalysts, solar cells, photodetectors, and LEDs that display piezo-phototronic behavior are reviewed. Material and structural design, property characterization, theoretical simulation calculations, and mechanism analysis are then examined as strategies to further enhance the quantum yield efficiency of optoelectronic devices via the piezo-phototronic effect. This comprehensive overview will guide future fundamental and applied studies that capitalize on the piezo-phototronic effect for energy conversion and storage.

Contact-electrification is a universal effect for all existing materials, but it still lacks a quantitative materials database to systematically understand its scientific mechanisms. Using an established measurement method, this study quantifies the triboelectric charge densities of nearly 30 inorganic nonmetallic materials. From the matrix of their triboelectric charge densities and band structures, it is found that the triboelectric output is strongly related to the work functions of the materials. Our study verifies that contact-electrification is an electronic quantum transition effect under ambient conditions. The basic driving force for contact-electrification is that electrons seek to fill the lowest available states once two materials are forced to reach atomically close distance so that electron transitions are possible through strongly overlapping electron wave functions. We hope that the quantified series could serve as a textbook standard and a fundamental database for scientific research, practical manufacturing, and engineering., The mechanism of contact electrification remains a topic of debate. Here, the authors present a quantitative database of the triboelectric charge density and band structure of many inorganic materials, verifying that contact electrification between solids is an electron quantum transition effect.

In the semi-arid regions of the world, irrigation and fertilization are essential for cereals growth and production because of water shortages and unfertile soils. However, inappropriate water and fertilizer management always causes unstable grain weight and yield. This study aims to explore the responses of grain filling characteristics, grain weight and productivity of winter wheat to varying water and fertilizer supplies. A three-year (2014–2017) experiment was conducted on winter wheat (Triticum aestivum L. ‘Xinong 979’) under drip fertigation, with three irrigation rates and three fertilization rates. The temporal dynamics of grain weight was simulated using determinate-growth equation. The appearance time of maximum filling rate (tm) and growth termination time (te) increased as fertilization rate increased, whereas the maximum and average filling rate increased and then had a slight decrease. The tm and te decreased with the increase of water deficit, the mild water deficit obtained higher grain filling rate. The grain weight percentage of spike weight (GPS) and spike moisture content (SMC) had extremely significant correlations with grain weight. GPS tended to decrease one week before maturity, and declined with the increase in water stress. SMC decreased in a parabolic form, and exhibited a dramatic decline about one week before maturity. With the increase of water or fertilizer supply, the grain weight firstly increased and then decreased, where the mild water deficit and appropriate fertilization improve grain filling and productivity of winter wheat.

Triboelectrification is a well-known phenomenon that commonly occurs in nature and in our lives at any time and any place. Although each and every material exhibits triboelectrification, its quantification has not been standardized. A triboelectric series has been qualitatively ranked with regards to triboelectric polarization. Here, we introduce a universal standard method to quantify the triboelectric series for a wide range of polymers, establishing quantitative triboelectrification as a fundamental materials property. By measuring the tested materials with a liquid metal in an environment under well-defined conditions, the proposed method standardizes the experimental set up for uniformly quantifying the surface triboelectrification of general materials. The normalized triboelectric charge density is derived to reveal the intrinsic character of polymers for gaining or losing electrons. This quantitative triboelectric series may serve as a textbook standard for implementing the application of triboelectrification for energy harvesting and self-powered sensing., Triboelectric charging is a well-known phenomenon, but triboelectric polarization has only been ranked qualitatively. Here the authors develop a quantified triboelectric series for a wide range of polymers by measuring triboelectric charge density with respect to a liquid metal at well-defined conditions.

Accurate estimation of global solar radiation (Rs) is essential to the design and assessment of solar energy utilization systems. Existing empirical and machine learning models for estimating Rs from sunshine duration were comprehensively reviewed. The performances of 12 empirical model forms and 12 machine learning algorithms for estimating daily Rs were further evaluated in different climatic zones of China as a case study, i.e. the temperate continental zone (TCZ), temperate monsoon zone (TMZ), mountain plateau zone (MPZ) and (sub)tropical monsoon zone (SMZ). The best-performing model at each station and the overall best model for each climatic zone were selected based on six statistical indictors, a global performance index (GPI) and computational costs (computational time and memory usage). The results revealed that the machine learning models (RMSE: 2.055–2.751 MJ m−2 d−1; NRMSE: 12.8–21.3%; R2: 0.839–0.936) generally outperformed the empirical models (RMSE: 2.118–3.540 MJ m−2 d−1; NRMSE: 12.1–27.5%; R2: 0.834–0.935) in terms of prediction accuracy. The cubic model (M3), modified linear-logarithmic model (M5) and power model (M10) attained generally better ranks among empirical models based on GPI. M3 was the top-ranked model in TMZ and MPZ, while general best performance was obtained by M5 and M2 in SMZ and TCZ, respectively. ANFIS, ELM, LSSVM and MARS obtained generally better performance among machine learning models, with the overall best ranking by ANFIS in TCZ and SMZ and by ELM in MPZ and SMZ. XGBoost (8.1 s and 74.2 MB), M5Tree (11.3 s and 29.7 MB), GRNN (12.3 s and 295.3 MB), MARS (14.4 s and 42.6 MB), MLP (22.4 s and 41.3 MB) and ANFIS (29.8 s and 23.1 MB) showed relatively small computational time and memory usage. Comprehensively considering both the prediction accuracy and computational costs, ANFIS is highly recommended, while MARS and XGBoost are also promising models for daily Rs estimation.

Establishing reasonable water and fertilizer inputs is of great importance to improve crop yield and water and fertilizer use efficiency in greenhouses. This experiment was conducted in 2013 to investigate the effects of different levels of irrigation and nitrogen (N) fertilizer on the yield, fruit quality, and water and nitrogen use efficiency of cucumbers under fertigation systems in a greenhouse in China. The least square method and multiple regression analysis were used to select the largest single target and multi-objective optimum in this study. The treatments comprised three drip irrigation levels (with ET0 as the reference crop evapotranspiration, W1: 60% ET0; W2: 80% ET0 and W3: 100% ET0) and four N fertilizer levels (N0: 0 kg/ha; N1: 180 kg/ha; N2: 360 kg/ha and N3: 540 kg/ha). The results revealed that the single factors of irrigation and N had an extremely significant effect on the yield. The fruit yield increased with the amount of irrigation water and reached 55.9 t/ha and 51.6 t/ha with the use of N 540 kg/ha and 360 kg/ha, respectively. The yield of 49.6 t/ha, the highest water use efficiency (WUE) of 55.8 kg/m3 and vitamin C of 128.4 mg/kg were obtained from conditions involving medium irrigation levels (80% ET0) with the application of 360 kg/ha N. The highest soluble sugar content at 2.8% was achieved when the irrigation level was 60% ET0 and the application of N was 360 kg/ha. The nitrogen production efficiency (NPE) and partial factor productivity of nitrogen (PFPN) decreased with the increase in the nitrogen application rate. The highest NPE and PFPN of 263.4 kg/kg and 265.9 kg/kg were obtained from irrigation levels of 80% ET0 and 100% ET0, respectively. The yield response factor ky of the cucumbers was 0.94. Taking into account the yield, quality, and water and nitrogen use efficiency, the irrigation level of 80% ET0 with the nitrogen level of 360 kg/ha were the best fertigation strategy. Within a 90% confidence interval, it was concluded that when the irrigation interval was 124–151 mm and the nitrogen interval was 318–504 kg/ha, the yield, WUE, and Vitamin C reached ≥90% of their maximum values at the same time. The determination of this region is of great significance to the management of water and fertilizer in greenhouse cucumis sativus.

Triboelectric nanogenerators (TENGs) have attracted increasing attention because of their excellent energy conversion efficiency, the diverse choice of materials, and their broad applications in energy harvesting devices and self-powered sensors. New materials have been explored, including green materials, but their performances have not yet reached the level of that for fluoropolymers. Here, a high-performance, fully green TENG (FG-TENG) using cellulose-based tribolayers is reported. It is shown that the FG-TENG has an output power density of above 300 W m

Despite recent progress in producing perovskite nanowires (NWs) for optoelectronics, it remains challenging to solution-print an array of NWs with precisely controlled position and orientation. Herein, we report a robust capillary-assisted solution printing (CASP) strategy to rapidly access aligned and highly crystalline perovskite NW arrays. The key to the CASP approach lies in the integration of capillary-directed assembly through periodic nanochannels and solution printing through the programmably moving substrate to rapidly guide the deposition of perovskite NWs. The growth kinetics of perovskite NWs was closely examined by in situ optical microscopy. Intriguingly, the as-printed perovskite NWs array exhibit excellent optical and optoelectronic properties and can be conveniently implemented for the scalable fabrication of photodetectors.

Rydberg atoms have been extensively utilized in microwave measurement with high sensitivity, which has great potential in the field of communication. In this study, we discuss the digital communication based on a Rydberg atomic receiver under simultaneously coupling by resonant and near detuning microwaves. In addition, we verify the feasibility of the Rydberg atom-based frequency division multiplexing (FDM) in microwave communication. We demonstrate the principle and performance of the atom-based FDM receiver by applying amplitude modulation (AM) and frequency modulation (FM), respectively. To demonstrate the actual communication performance at different data transfer rates, we consider monochromatic images as an example. The experimental results show that the maximum acceptable data transfer rate of both AM and FM is about 200 kbps, whereas their maximum bit error rates (BER) is less than 5%. When compared with the traditional electronic receiver, this atomic receiver, which is compatible with FDM, has numerous advantages, such as small size, low power consumption, and high sensitivity. Furthermore, this receiver has a strong ability of anti-electromagnetic interference, and the signals transmitted do not interfere with each other in different channels.

Triboelectric nanogenerators (TENGs) have attracted increasing attention because of their excellent energy conversion efficiency, the diverse choice of materials, and their broad applications in energy harvesting devices and self-powered sensors. New materials have been explored, including green materials, but their performances have not yet reached the level of that for fluoropolymers. Here, a high-performance, fully green TENG (FG-TENG) using cellulose-based tribolayers is reported. It is shown that the FG-TENG has an output power density of above 300 W m-2 , which is a new record for green-material-based TENGs. The high performance of the FG-TENG is due to the high positive charge density of the regenerated cellulose. The FG-TENG is stable after more than 30 000 cycles of operations in humidity of 30%-84%. This work demonstrates that high-performance TENGs can be made using natural green materials for a broad range of applications.

Triboelectric nanogenerator (TENG) can convert mechanical energy into electrical energy and has been regarded as a promising portable power source. However, the low output power restricts TENG’s applications in energy harvesters and sensors. Herein, we developed an effective way of increasing TENG’s output power by combining ferroelectricity and conduction of the triboelectric materials. For this purpose, a conductive interlayer modulated ferroelectric nanocomposite was used as the negative triboelectric material. Compared with the conventional ferroelectric nanocomposites based TENG, the transferred triboelectric charge density of the conductive interlayer modulated ferroelectric nanocomposite based TENG can reach 105.70 μC m−2 from 17.50 μC m−2, while the output power density increases to 7.21 W m−2 from 0.11 W m−2. The boosted output performance can be attributed to the existence of a conductive intermediate layer in the negative triboelectric material, which induces charge trapping and enhances ferroelectric polarization of the nanocomposites. Apart from being used as wearable energy harvesters, the TENG device also exhibits a promising application in parachuting surveillance for preventing potential injuries. Furthermore, TENG device has numerous possible application scenarios for future airborne troops. This work provides a brand-new strategy for enhancing contact electrification, showing strong potential in design of high output TENGs.

Triboelectric nanogenerators (TENGs) are attracting more and more attention since they can convert various mechanical energies into electric energy. However, in traditional TENGs for harvesting rotation energy, most of the contacts between two triboelectric materials are rigid-to-rigid contact with very large friction force, which limits their practical application. Here, we report an ultra-low-friction triboelectric-electromagnetic hybrid nanogenerator (NG). A freestanding mode TENG and a rotating electromagnetic generator (EMG) are integrated together to realize the complementary individual merits. The very soft and elastic contact between the two triboelectric materials in the TENG results into very small friction force. The influences of the type and the dimensions of the dielectric material on the performance of the TENG are studied systematically from theory to experiments. The results indicate that the open-circuit voltage and the transfer charge of the TENG increase with the rotation speed, which is very different from a traditional rotary TENG and is due to the increase of the contact area. The optimized TENG has a maximal load voltage of 65 V and maximal load power per unit mass of 438.9 mW/kg under a speed rotation of 1000 rpm, while the EMG has a maximal load voltage of 7 V and maximal load power density of 181 mW/kg. This demonstration shows that the hybrid NG can power a humidity/temperature sensor by converting wind energy into electric energy when the wind speed is 5.7 m/s. Meanwhile, it can be used as a self-powered wind speed sensor to detect wind speed as low as 3.5 m/s.

Atomic vapor cell which is one of the core devices of quantum sensing has a very important impact on the accuracy of detection, especially in the Rydberg-atom based electromagnetic field sensing. Metamaterials provide a feasible scheme for improving the performance of the vapor cell because of their excellent ability to control electromagnetic waves. In this paper, a new type of vapor cell with low perturbation for measuring electric field is proposed to eliminate the field distortion in presence of the vapor cell. The vapor cell is composed of three sets of parallel metamaterials with characteristics of perfect-electric-conductor (PEC), perfect- magnetic-conductor (PMC) and low permittivity (LPM), respectively. At the same time, the effects of vapor cell size and wall thickness on the electric field inside the vapor cell are compared. Finally, a preparation scheme of LPM with a limited size on a glass substrate is proposed.

Ocean waves are one of the most power dense energy sources in the environment. Triboelectric nanogenerators (TENGs) have been demonstrated to effectively harvest mechanical energy carried by low frequency, random/irregular actuation, such as from ocean waves. In this work, a novel design of triboelectric nanogenerator based on the Pelamis snake energy harvester is presented. The sea snake based TENG, with its lightweight structure, was able to harvest energy effectively at low amplitude ocean wave by utilizing charged polytetrafluroethylene balls that would roll due to the wave's curvature. With the integration of springs to connect different segments, the segments are able to bend easily, allowing the enclosed balls to move faster, producing higher output power. The design of an air gap structure allows each segments of the sea snake based TENG to minimize electrostatic induction from ions in sea water, and solve the effect of dielectric shielding from the water on the device performance, as the water, if it is close to the TENG's electrodes, has a detrimental effect causing an increase of the TENG's internal capacitance, which would result in a low voltage with the same amount of charge being transformed. Thus, this illustrates the importance of the air gap structure to minimize low voltage due to high internal capacitance. This further shows the sea snake based triboelectric nanogenerator could be used in actual ocean conditions, such as in high salinity water environment. The added tampered spring to replace the air gap was able to allow the balls on the TENG to move more quickly, as it increased the rotational angle, and the TENG has a maximum power density of 3 W/m3 under actuation. Due to the minimization of dielectric shielding of device performance, the sea snake TENG exhibits a high voltage in simulated water wave conditions.

The ubiquitous sensors have accelerated the realization of Internet of Things (IoT) but also raised challenges to the current overcrowding radio frequency (RF) based communications. The optical wireless communication (OWC) that utilizes the wide optic bandwidth can well solve the spectrum crisis and is an appealing complementary solution to the IoT applications. However, the additional direct current (DC) power supply and complicated modulating and power management circuits may limit the large-scale deployment of OWC systems. In this paper, by integrating with triboelectric nanogenerators (TENGs), the light-emitting diode (LED) could be directly transformed into a wireless transmitter that conveys the information associated with mechanical stimuli without additional power supply. With the customized TENG devices and the help of advanced image processing and machine learning techniques, three demonstrations with functions of optical remote control, pressure sensing, and security authentication, were demonstrated. The concept and results in this paper may greatly broaden the application of IoT through the integration of OWC and TENG.

Piezoelectric generators (PEGs) are a promising power source for future self-powered electronics by converting ubiquitous ambient mechanical energy into electricity. However, most of the high-output PEGs are made from lead zirconate titanate, in which the hazardous lead could be a potential risk to both humans and environment, limiting their real applications. III-Nitride (III-N) can be a potential candidate to make stable, safe, and efficient PEGs due to its high chemical stability and piezoelectricity. Also, PEGs are preferred to be flexible rather than rigid, to better harvest the low-magnitude mechanical energy. Herein, a high-output, lead-free, and flexible PEG (F-PEG) is made from GaN thin film by transferring a single-crystalline epitaxial layer from silicon substrate to a flexible substrate. The output voltage, current density, and power density can reach 28 V, 1 μA·cm–2, and 6 μW·cm–2, respectively, by bending the F-PEG. The generated electric power by human finger bending is high enough to light...

This study investigated the effects of different combinations of irrigation and nitrogen levels on the growth of greenhouse sweet peppers, assessing yield, quality, water use efficiency (WUE), and partial factor productivity from applied N (PFPN). By using controlled drip irrigation, the optimal conditions for efficient, large-scale, high-yield, and high quality production of sweet peppers in Northwest China were determined. Using the local conventional irrigation and nitrogen regime as a control (105% ET0, N: 300 kg·hm−2), three alternative irrigation levels were also tested, at 90%, 75%, and 60% ET0. These were combined with nitrogen levels at 100%, as the control, and 75%, 50%, and 25%, resulting in 16 combination treatments. The results show that different supplies of water and nitrogen nutrition had a significant impact on the growth, yield, WUE, PFPN, and quality of fruit. The treatments of W0.90N0.75, W0.90N0.50, W0.75N0.75, and W0.75N0.50can better maintain the “source-sink” relationship of peppers. They increased the economic yield, WUE, and PFPN. A principal component analysis was performed to evaluate indicators of fruit quality, revealing that the treatment of W0.75N0.50resulted in the best fruit quality. For greenhouse sweet peppers produced in Northwest China, the combination of W0.90N0.75resulted in the highest economic yield of 34.85 kg·hm−2. The combination of W0.75N0.75had the highest WUE of 16.50 kg·m−3. The W0.75N0.50combination treatment had the highest fruit quality score. For sustainable ecological development and in view of limited water resources in the area, we recommend the W0.75N0.50combination treatment, since it could obtain the optimal fruit quality, while its economic yield and WUE were 9% and 4% less than the maximum, respectively. This study provides a theoretical basis for the optimal management of water and nitrogen during production of greenhouse sweet peppers in Northwest China.

The piezotronic effect and piezo-phototronic effect on materials and devices have been widely studied in binary semiconductors. Wide-band ternary semiconductors are a great class of materials with potential application in nano/microdevices, because of their continuously tunable physical properties with composition. Here, we first demonstrate the piezo-photronics effect of ternary wurtzite structured nanowires (NWs), opening an innovative materials system. Single-crystal ternary CdSxSe1–x (x = 0.85, 0.60, and 0.38) NWs were synthesized with site-controlled compositions via a chemical vapor deposition process, and high-performance visible photodetectors (PDs) with fast response speed (

Rapid advancements in stretchable and multifunctional wearable electronics impose a challenge on corresponding power devices that they should have comparable portability and stretchability. Here, we report a highly stretchable and washable all-yarn-based self-charging knitting power textile that enables both biomechanical energy harvesting and simultaneously energy storing by hybridizing triboelectrical nanogenerator (TENG) and supercapacitor (SC) into one fabric. With the weft-knitting technique, the power textile is qualified with high elasticity, flexibility, and stretchability, which can adapt to complex mechanical deformations. The knitting TENG fabric is able to generate electric energy with a maximum instantaneous peak power density of ∼85 mW·m–2 and light up at least 124 light-emitting diodes. The all-solid-state symmetrical yarn SC exhibits lightweight, good capacitance, high flexibility, and excellent mechanical and long-term stability, which is suitable for wearable energy storage devices. The ...

Developing lightweight, flexible and sustainable sensor networks with miniaturized integration and functionality for the Internet of Things (IoT) remains a challenge and an urgent demand for the next-generation electronic devices. Paper-based electronics, which represents one of the main green electronics in the future, have been considered as one of the most exciting technologies to meet the consumption of the frequently upgraded electronics. Here, we presented an ultrathin (about 200 µm) and lightweight paper-based self-powered system that consists of a paper-based triboelectric/piezoelectric hybrid nanogenerator and a paper-based supercapacitor. Under human motions such as flipping the page and moving the book/document, the as-fabricated self-powered system built-in the smart book/document was capable of sustaining power for portable devices, such as continuously driving LEDs and the temperature/humidity sensor. With the signal-processing circuit, the paper-based system was further developed into a wireless human-machine interaction system for documents management and smart reading. The ultrathin and highly flexible characteristics of the self-powered system not only endow the device with power generation feature for portable devices, but also build up the wireless human-machine interactions in developing potential applications for the IoT.

Although silicon (Si) devices are the backbone of modern (opto-)electronics, infrared Si-photosensing suffers from low-efficiency due to its limitation in light-absorption. Here, we demonstrate a large improvement in the performance, equivalent to a 366-fold enhancement in photoresponsivity, of a Si-based near-infrared (NIR) photodetector (PD) by introducing the piezo-phototronic effect via a deposited CdS layer. By externally applying a −0.15‰ compressive strain to the heterojunction, carrier-dynamics modulation at the local junction can be induced by the piezoelectric polarization, and the photoresponsivity and detectivity of the PD exhibit an enhancement of two orders of magnitude, with the peak values up to 19.4 A/W and 1.8 × 1012 cm Hz1/2/W, respectively. The obtained maximum responsivity is considerably larger than those of commercial Si and InGaAs PDs in the NIR waveband. Meanwhile, the rise time and fall time are reduced by 84.6% and 76.1% under the external compressive strain. This work provides ...

Achievement of p–n homojuncted GaN enables the birth of III-nitride light emitters. Owing to the wurtzite-structure of GaN, piezoelectric polarization charges present at the interface can effectively control/tune the optoelectric behaviors of local charge-carriers (i.e., the piezo-phototronic effect). Here, we demonstrate the significantly enhanced light-output efficiency and suppressed efficiency droop in GaN microwire (MW)-based p–n junction ultraviolet light-emitting diode (UV LED) by the piezo-phototronic effect. By applying a −0.12% static compressive strain perpendicular to the p–n junction interface, the relative external quantum efficiency of the LED is enhanced by over 600%. Furthermore, efficiency droop is markedly reduced from 46.6% to 7.5% and corresponding droop onset current density shifts from 10 to 26.7 A cm–2. Enhanced electrons confinement and improved holes injection efficiency by the piezo-phototronic effect are revealed and theoretically confirmed as the physical mechanisms. This stud...

Up to now, the measurement of radio-frequency (RF) electric field achieved using the electromagnetically-induced transparency (EIT) of Rydberg atoms has proved to be of high-sensitivity and shows a potential to produce a promising atomic RF receiver at resonance between two chosen Rydberg states. In this paper, we study the extension of the feasibility of digital communication via this quantum-based antenna over a continuously tunable RF-carrier at off-resonance. Our experiment shows that the digital communication at a rate of 500 kbps can be performed reliably within a tunable bandwidth of 200 MHz near a 10.22 GHz carrier. Outside of this range, the bit error rate (BER) increases, rising to, for example, 15% at an RF-detuning of ±150 MHz. In the measurement, the time-varying RF field is retrieved by detecting the optical power of the probe laser at the center frequency of RF-induced symmetric or asymmetric Autler-Townes splitting in EIT. Prior to the digital test, we studied the RF-reception quality as a function of various parameters including the RF detuning and found that a choice of linear gain response to the RF-amplitude can suppress the signal distortion. The modulating signal can be decoded at speeds up to 500 kHz in the tunable bandwidth. Our test consolidates the physical basis for reliable communication and spectral sensing over a wider broadband RF-carrier, which paves a way for the concurrent multi-channel communications founded on the same pair of Rydberg states.

It is known that contact-electrification (or triboelectrification) usually occurs between two different materials, which could be explained by several models for different materials systems ( Adv. Mater. 2018, 30, 1706790; Adv. Mater. 2018, 30, 1803968). But contact between two pieces of the chemically same material could also result in electrostatic charges, although the charge density is rather low, which is hard to understand from a physics point of view. In this paper, by preparing a contact-separation mode triboelectric nanogenerator using two pieces of an identical material, the direction of charge transfer during contact-electrification is studied regarding its dependence on curvatures of the sample surfaces. For materials such as polytetrafluoroethylene, fluorinated ethylene propylene, Kapton, polyester, and nylon, the positive curvature surfaces are net negatively charged, while the negative curvature surfaces tend to be net positively charged. Further verification of the above-mentioned trends was obtained under vacuum (∼1 Pa) and higher temperature (≤358 K) conditions. Based on the received data acquired for gentle contacting cases, we propose a curvature-dependent charge transfer model by introducing curvature-induced energy shifts of the surface states. However, this model is subject to be revised if the mutual contact mode turns into a sliding mode or more complicated hard-pressed contact mode, in which a rigorous contact between the two pieces of the same material could result in nanoscale damage/fracture and possible species transfer. Our study provides a primitive step toward understanding the basics of contact-electrification.

Silicon photonics is now widely accepted as a key technology in a variety of systems. But owing to material limitations, now it is challenging to greatly improve the performance after decades of development. Here, we show a high-performance broadband photodetector with significantly enhanced sensitivity and responsivity operating over a wide wavelength range of light from near-ultraviolet to near-infrared at low power consumption. The specially designed textured top ceiling electrode works effectively as an antireflection layer to greatly improve the absorption of near-infrared light, thereby overcoming the absorption limitation of near-infrared light. Instead of the conventional p-n junction and p-intrinsic-n junction, we introduce a ∼15 nm thick alumina insulator layer between a p-type Si substrate and n-type ZnO nanowire (NW) arrays, which significantly enhances the charge carrier separation and collection efficiency. The photosensing responsivity and sensitivity are found to be nearly 1 order of magnitude higher than that of a reference device of p-Si/n-ZnO NW arrays, significantly higher than the commercial silicon photodiodes as well. The light-induced charge carriers flow across the appropriate thickness of insulator layer via the quantum mechanical Fowler-Nordheim tunneling mechanism. By virtue of the piezo-phototronic effect, the charge density at the interfaces can be tuned to alter the energy bands and the potential barrier distance for tunneling. Additionally, along with the use of incident light of different wavelengths, the influence of the insulator layer on the transport of electrons and holes separately is further investigated. The demonstrated concepts and study would lead to sensitivity improvement, quality enhancement of data transfer, decrease of power consumption, and cost reduction of silicon photonics.

Nitrogen (N) fertilizer is known to improve the quality and biomass of vegetables, but it is unclear how to manage the large amount of NO3-N that accumulates in the soil after vegetable harvest. In this study, we examined the influence of irrigation level and irrigation frequency on the growth and soil residual NO3-N of the catch crop mini Chinese cabbage (Brassica pekinensis) in a greenhouse. Using conventional border irrigation with adequate water supply as a control (CK), three irrigation levels (WH: 160% crop evapotranspiration (ETc), WM: 120% ETc and WL: 80% ETc) and three irrigation frequencies (intervals of F2: 2 days, F4: 4 days, and F8: 8 days) were assessed in 2014, 2015 and 2016 in northwest China. The results showed that the weight of the leaves and leaf stalks was the primary determinant of yield, and that these are the primary N-containing vegetative organs of the plants. At the same irrigation level, the total N content of the plants increased in the order F8 &lt, F2 &lt, F4. The trend in the total N content in the mini Chinese cabbage plants among different treatments was synchronized with the yield. The highest total N content in the plants was observed in the WMF4 treatment during all three years. The three-year averages of mini Chinese cabbage aboveground biomass, yield and water use efficiency (WUE) in the WMF4 treatment were 60%, 64.5% and 119.2% higher respectively than in the CK treatment. The residual NO3-N content in the soil in the WMF4 treatment was only 1.3% higher than that in the CK treatment. The total N uptake in the WMF4 treatment was 79.2% higher than that in the CK treatment, and the N loss in the WMF4 treatment was 46.3% lower than that in the CK treatment. Under these experimental conditions, the WMF4 treatment can be recommended as an appropriate irrigation regime for mini Chinese cabbage under fallow greenhouse management in northwest China.

Nanocomposites consisting of a flexible piezoelectric polymer and a reinforcing phase have shown great potential for constructing high-performance piezoelectric nanogenerators (PENGs). However, the weak interface and poor dispersion of piezoelectric reinforcing phase significantly impair the electromechanical properties (e.g., effective stress/strain, piezoelectric coefficients) of the nanocomposites, thus severely restricting the performance enhancement of the PENGs. In this study, we hydrothermally synthesized the piezoelectric reinforcing phase of BaTiO3 nanowires, and grafted a layer of high-modulus polymethyl methacrylate (PMMA) onto the nanowire surface via surface-initiated polymerization. The PMMA coating layer forms a strong interface between BaTiO3 nanowires and the polymer matrix [i.e., poly(vinylidenefluoride-co-trifluoroethylene)], which efficiently improves dispersion of the BaTiO3 nanowires and stress transfer at the interface, therefore resulting in an enhanced output performance in the fibrous nanocomposite PENGs. The output voltage and current of the PMMA encapsulated BaTiO3 (PMMA@BaTiO3) nanowires-based PENG can reach to 12.6 V and 1.30 μA, with a maximum output power of 4.25 μW, which is 2.2 times and 7.6 times higher than the PENG with unmodified BaTiO3 nanowires and the PENG without BaTiO3 nanowires, respectively. Furthermore, the flexible PENG exhibits great stability that could continuously generate stable electrical pulses for 6000 cycles without any decline. This study provides a feasible approach of interface tailoring for achieving high-performance piezoelectric nanocomposite and shows the promising potential of the fibrous nanocomposites in biomechanical energy harvesters and smart wearable sensors.