Monolithic integrated optoelectronic chip for vector force detection.

Sensors with a small footprint and real-time detection capabilities are crucial in robotic surgery and smart wearable equipment. Reducing device footprint while maintaining its high performance is a major challenge and a significant limitation to their development. Here, we proposed a monolithic integrated micro-scale sensor, which can be used for vector force detection. This sensor combines an optical source, four photodetectors, and a hemispherical silicone elastomer component on the same sapphire-based AlGaInP wafer. The chip-scale optical coupling is achieved by employing the laser lift-off techniques and the flip-chip bonding to a processed sapphire substrate. This hemispherical structure device can detect normal and shear forces as low as 1 mN within a measurement range of 0-220 mN for normal force and 0-15 mN for shear force. After packaging, the sensor is capable of detecting forces over a broader range, with measurement capabilities extending up to 10 N for normal forces and 0.2 N for shear forces. It has an accuracy of detecting a minimum normal force of 25 mN and a minimum shear force of 20 mN. Furthermore, this sensor has been validated to have a compact footprint of approximately 1.5 mm2, while maintaining high real-time response. We also demonstrate its promising potential by combining this sensor with fine surface texture perception in the fields of compact medical robot interaction and wearable devices.

Non-equilibrium compression achieving high sensitivity and linearity for iontronic pressure sensors.

Flexible pressure sensors with high sensitivity and linearity are highly desirable for robot sensing and human physiological signal detection. However, the current strategies for stabilizing axial microstructures (e.g., micro-pyramids) are mainly susceptible to structural stiffening during compression, thereby limiting the realization of high sensitivity and linearity. Here, we report a bending-induced non-equilibrium compression process that effectively enhances the compressibility of microstructures, thereby crucially improving the efficiency of interfacial area growth of electric double layer (EDL). Based on this principle, we fabricate an iontronic flexible pressure sensor with vertical graphene (VG) array electrodes. Ultra-high sensitivity (185.09 kPa-1) and linearity (R2 = 0.9999) are realized over a wide pressure range (0.49 Pa-66.67 kPa). It also exhibits remarkable mechanical stability during compression and bending. The sensor is successfully employed in a robotic gripping task to recognize the targets of different materials and shapes based on a multilayer perception (MLP) neural network. It opens the door to realizing haptic sensing capabilities for robotic hands and prosthetic limbs.

Effect of robbing intensity on reproductive success of Symphytum officinale (Boraginaceae).

The intervention of nectar robbers in plant pollination systems will cause some pollinators to modify their foraging behavior to act as secondary robbers, consequently adopting a mixed foraging strategy. The influence of nectar robbing on pollinator behavior may be affected by spatio-temporal difference of robbing intensity, and consequently, may have different effects on the pollination of host plants. However, whether and how the nectar robbing might influence pollinators under different robbing intensity still needs further investigation. In this study, Symphytum officinale was used to detect the effect of nectar robbers on pollinators under different robbing intensity as well as their effects on plant reproductive success. Six robbing levels and three bumblebees with mixed foraging behaviors were used to evaluate the effect of different robbing intensity on pollinator behavior, visitation rate, flower longevity and pollen deposition. Our results indicated that the robbing rate increased gradually with the proportion of robbed flowers, but which did not affect the frequency of legitimate visits. The increase of robbing rate promoted the corolla abscission, and then enhanced the self-pollen deposition, but which had no significant effect on cross-pollen deposition. These results indicate that the overall fitness of S. officinale was improved by combined self and cross-pollination modes when visited by both pollinators and nectar robbers simultaneously. Although nectar robbing is not uncommon, its consequences for pollination in the interaction web have not been well studied. Our results emphasize the significance of indirect impacts in mediating the adaptive outcomes of species interactions.

Giant intrinsic photovoltaic effect in one-dimensional van der Waals grain boundaries.

The photovoltaic effect lies at the heart of eco-friendly energy harvesting. However, the conversion efficiency of traditional photovoltaic effect utilizing the built-in electric effect in p-n junctions is restricted by the Shockley-Queisser limit. Alternatively, intrinsic/bulk photovoltaic effect (IPVE/BPVE), a second-order nonlinear optoelectronic effect arising from the broken inversion symmetry of crystalline structure, can overcome this theoretical limit. Here, we uncover giant and robust IPVE in one-dimensional (1D) van der Waals (vdW) grain boundaries (GBs) in a layered semiconductor, ReS2. The IPVE-induced photocurrent densities in vdW GBs are among the highest reported values compared with all kinds of material platforms. Furthermore, the IPVE-induced photocurrent is gate-tunable with a polarization-independent component along the GBs, which is preferred for energy harvesting. The observed IPVE in vdW GBs demonstrates a promising mechanism for emerging optoelectronics applications.

Strong bulk photovoltaic effect in engineered edge-embedded van der Waals structures.

Bulk photovoltaic effect (BPVE), a second-order nonlinear optical effect governed by the quantum geometric properties of materials, offers a promising approach to overcome the Shockley-Quiesser limit of traditional photovoltaic effect and further improve the efficiency of energy harvesting. Here, we propose an effective platform, the nano edges embedded in assembled van der Waals (vdW) homo- or hetero-structures with strong symmetry breaking, low dimensionality and abundant species, for BPVE investigations. The BPVE-induced photocurrents strongly depend on the orientation of edge-embedded structures and polarization of incident light. Reversed photocurrent polarity can be observed at left and right edge-embedded structures. Our work not only visualizes the unique optoelectronic effect in vdW nano edges, but also provides an effective strategy for achieving BPVE in engineered vdW structures.

Giant Negative Thermopower Enabled by Bidirectionally Anchored Cations in Multifunctional Polymers.

The lack of high-quality ionic thermoelectric materials with negative thermopowers has stimulated scientists' broad research interest. The effective adjustment of the interaction between ions and a polymer network is an important way to achieve high-quality ion thermoelectric properties. Integrating different types of ion-polymer interactions into the same thermoelectric device seems to lead to unexpected gains. In this work, we propose a strategy for bidirectionally anchoring cations to synergistically generate a giant negative thermopower and high ionic conductivity. This is mainly achieved through synergistic ion-polymer coordination and Coulomb interactions. An ionic thermoelectric material was prepared by infiltrating a polycation electrolyte [poly(diallyldimethylammonium chloride)] with CuCl2 into the poly(vinyl alcohol)-chitosan aerogel. The confinement effect of copper-coordinated chitosan on cations, the repulsive property of the polycationic electrolyte on cations, and the unique chemical configuration of a transition metal chloride anion ([CuCl4]2-) are the fundamental guarantees for achieving a thermopower of -28.4 mV·K-1. Moreover, benefiting from the high charge density of the polycationic electrolyte, we obtain an ionic conductivity of 40.5 mS·cm-1. These findings show the application prospect of synergistic different types of ion-polymer interactions in designing multifunctional ionic thermoelectric materials.

Revealing the Effect of High Ni Content in Li-Rich Cathode Materials: Mitigating Voltage Decay or Increasing Intrinsic Reactivity.

Li-rich layered oxides are considered as one of the most promising cathode materials for secondary lithium batteries due to their high specific capacities, but the issue of continuous voltage decay during cycling hinders their market entry. Increasing the Ni content in Li-rich materials is assumed to be an effective way to address this issue and attracts recent research interests. However, a high Ni content may induce increased intrinsic reactivity of materials, resulting in severe side reactions with the electrolyte. Thus, a comprehensive study to differentiate the two effects of the Ni content on the cell performance with Li-rich cathode is carried out in this work. Herein, it is demonstrated that a properly dosed amount of Ni can effectively suppress the voltage decay in Li-rich cathodes, while over-loading of Ni, on the contrary, can cause structural instability, Ni dissolution, and nonuniform Li deposition during cycling as well as severe oxygen loss. This work offers a deep understanding on the impacts of Ni content in Li-rich materials, which can be a good guidance for the future design of such cathodes for high energy density lithium batteries.

Effects of continuous variation in vertical and lateral herkogamy on reproductive success in Euphorbia fischeriana (Euphorbiaceae).

Continuous variation in herkogamy has been well reported, however, less attention has been paid to the phenomena that the consecutive expression of two types of herkogamy in the same flower. Euphorbia fischeriana, which have both vertical and lateral herkogamy, show vertical herkogamy during the female phase. However, their gynophores bend to one side with the male phase and show lateral herkogamy. In this study, we observed the effect of successive sexual organs movement on variation in herkogamy traits. By artificially manipulating the flower to present gynophore straightened in the floral center or bend to one side, we attempted to investigate whether herkogamy movement affects pollinator access efficiency, pollen removal and deposition, and seed set ratio. Furthermore, we conducted artificial pollination in the female phase to evaluate the effect of changes in pollination environment on the variations in herkogamy traits. The results showed that gynophore straightened in female phase favors pollen deposition, whereas gynophore bending in male phase was conducive to the removal of pollen. Visitation frequency, pollen deposition and removal, and seed set ratio decreased significantly when the gynophore movement was manipulated. Finally, the bending of gynophore was obviously promoted by pollination. Therefore, the continuous variation of herkogamy in the same flower of E. fischeriana caused by the bending of the gynophore could improve the accuracy of pollination and avoid the interference of the ovary with access efficiency. That may be an adaptive strategy when pollinators are scarce. Furthermore, our study also provides good support for the hypothesis that variations in herkogamy traits are strongly selected by differences in pollination environments.

Wearable Pressure Sensors with Capacitive Response over a Wide Dynamic Range.

At present, there are mainly two types of capacitive pressure sensors based on ordinary capacitance and electrical double layer (EDL) capacitance. However, few researchers have combined these two types of capacitors in pressure sensing to improve the dynamic range of a sensor under pressure. Here, we fabricated a capacitive pressure sensor with an asymmetric structure based on poly(vinylidene fluoride-co-hexafluoropropylene) using a simple electrospinning process. A layer of mixed ionic nanofiber membrane and a layer of pure nanofiber membrane were stacked and used as the dielectric layer of the sensor. Due to the porous structure and non-stickiness of the pure nanofiber membrane, it can be penetrated by the mixed ionic nanofiber membrane under pressure, realizing the reversible conversion from ordinary capacitance to EDL capacitance, thereby achieving a great change in the capacitance value. The sensitivities of the sensor are 55.66 and 24.72 kPa-1 in the pressure ranges of 0-31.11 and 31.11-66.67 kPa, respectively, with good cycle stability, fast loading-unloading response time, and an ultra-low pressure detection limit as low as 0.087 Pa. Finally, this sensor was used for the detection of human physiological signals, and the sensor would have potential applications in the fields of human tactile sensing systems, bionic robots, and wearable devices.

A Decrease in the Staminode-Mediated Visitor Screening Mechanism in Response to Nectar Robbers Positively Affects Reproduction in Delphinium caeruleum Jacq. ex Camb. (Ranunculaceae).

Nectar-robbing insects, which are frequently described as cheaters in plant-pollinator mutualisms, may affect plant reproductive fitness by obtaining nectar rewards without providing pollination services. The negative effects of nectar robbing on plant reproductive success have been widely reported, but the reasons for possible positive effects demand further investigation. The goal of the study was to evaluate the effects of nectar robbing on the reproductive success of Delphinium caeruleum. Two staminodes cover the stamens and pistils in the flowers of D. caeruleum, forming a "double door" type of structure that compels pollinators to physically manipulate the staminodes to access the sex organs. In order to explore whether the operative strength required to open the staminodes is affected by actions associated with nectar robbing, we set up five different treatment groups: no nectar robbing, natural nectar robbing, artificial nectar robbing, hole making, and nectar removal. A biological tension sensor was used to measure the operative strength required to open the staminodes in the flowers. We also assessed the effect of nectar robbing on the flower-visiting behavior of pollinators and the effect of nectar robbing on reproductive fitness by the flower. The results showed that the operative strength needed to open staminodes was reduced by nectar robbers but not by artificial nectar robbing, hole making, or nectar removal. The flowers' continuous visitation rate and visitation frequency by pollinators decreased significantly in robbed flowers. Both the pollen export and pollen deposition in naturally robbed flowers were significantly higher than those in nonrobbed flowers. Our results demonstrate that nectar robbers play an indirect positive role in the reproductive fitness of D. caeruleum flowers by reducing the operative strength of staminodes to promote pollen transfer. The reduction in operative strength of staminodes might be an adaptive mechanism that responds to nectar robbing.

Probing interlayer shear thermal deformation in atomically-thin van der Waals layered materials.

Atomically-thin van der Waals layered materials, with both high in-plane stiffness and bending flexibility, offer a unique platform for thermomechanical engineering. However, the lack of effective characterization techniques hinders the development of this research topic. Here, we develop a direct experimental method and effective theoretical model to study the mechanical, thermal, and interlayer properties of van der Waals materials. This is accomplished by using a carefully designed WSe2-based heterostructure, where monolayer WSe2 serves as an in-situ strain meter. Combining experimental results and theoretical modelling, we are able to resolve the shear deformation and interlayer shear thermal deformation of each individual layer quantitatively in van der Waals materials. Our approach also provides important interlayer coupling information as well as key thermal parameters. The model can be applied to van der Waals materials with different layer numbers and various boundary conditions for both thermally-induced and mechanically-induced deformations.

Giant Thermopower of Hydrogen Ion Enhanced by a Strong Hydrogen Bond System.

Ionic thermoelectric materials based on organic polymers are of great significance for low-grade heat harvesting and self-powered wearable temperature sensing. Here, we demonstrate a poly(vinyl alcohol) (PVA) hydrogel that relies on the differential transport of H+ in PVA hydrogels with different degrees of crystallization. After the inorganic acid is infiltrated into the physically cross-linked PVA hydrogel, the ionic conductor exhibits a huge ionic thermopower of 38.20 mV K-1, which is more than twice the highest value reported for hydrogen ion transport thermoelectric materials. We attribute the enhanced thermally generated voltage to the movement of H+ in the strong hydrogen bond system of PVA hydrogels and the restrictive effect of the strong hydrogen bond system on anions. This ionic thermoelectric hydrogel opens up a new way for thermoelectric conversion devices using H+ as an energy carrier.

Giant negative thermopower of ionic hydrogel by synergistic coordination and hydration interactions.

The design of ultrasensitive ionic thermopiles is important for low-grade heat collection and temperature sensing. However, high-quality ionic thermoelectric materials with negative thermopower have been rarely reported to date. Effective adjustment of the interaction between the polymer network and the electrolyte anion/cation is an important method to achieve notable thermopower. Here, we demonstrate an ionic hydrogel thermoelectric material with giant negative thermopower obtained by synergistic coordination and hydration interactions. The ionic hydrogel, made of polyvinyl alcohol and sodium hydroxide, is prepared by simple dry-annealed process and exhibits a thermopower of up to −37.61 millivolts per kelvin, an extremely high absolute thermopower for electronic and ionic conductors. This ionic hydrogel is promising for the design of high-thermopower ionic thermoelectric materials and the low-grade heat energy harvesting.

Corolla Abscission Triggered by Nectar Robbers Positively Affects Reproduction by Enhancing Self-Pollination in Symphytum officinale (Boraginaceae).

Nectar robbers, which affect plant fitness (directly or indirectly) in different degrees and in different ways, potentially constitute a significant part of mutualistic relationships. While the negative effects of nectar robbing on plant reproductive success have been widely reported, the positive effects remain unknown. The target of our study was to evaluate the effects of nectar robbers on the reproductive success of Symphytum officinale (Boraginaceae). We observed the behavior, species and times of visitors in the field, and we assessed the effect of nectar robbers on corolla abscission rate and time. To test the fitness of corolla abscission, we detected the changes in stigma receptivity, pollen viability, pollen amount and appendage opening size along with the time of flower blossom. The flowering dynamics and floral structure were observed to reveal the mechanism of self-pollination. Finally, pollen deposition seed set rate and fruit set rate were determined to estimate the effect of nectar robbers on reproduction success. We observed 14 species of visitors and 2539 visits in 50 h of observation; 91.7% of them were nectar robbers. The pressure and nectar removal of nectar robbers significantly promoted corolla abscission during a period when pollen grains are viable and the stigma is receptive. In addition, corolla abscission significantly increased the pollen deposition and seed setting rate. Our results demonstrate that nectar robbing contributes to enhancing seed production and positively and indirectly impacts the reproductive success of S. officinale. This mechanism involved the movement of anthers and indirect participation by nectar robbers, which was rarely investigated. Considering the multiple consequences of nectar robbing, understanding the impact of nectar robbers on plant reproduction is essential to comprehend the evolutionary importance of relationships between plants and their visitors.

Classification of Cognitive Impairment and Healthy Controls Based on Transcranial Magnetic Stimulation Evoked Potentials.

Backgrounds: Nowadays, risks of Cognitive Impairment (CI) [highly suspected Alzheimer's disease (AD) in this study] threaten the quality of life for more older adults as the population ages. The emergence of Transcranial Magnetic Stimulation-Electroencephalogram (TMS-EEG) enables noninvasive neurophysiological investi-gation of the human cortex, which might be potentially used for CI detection. Objectives: The aim of this study is to explore whether the spatiotemporal features of TMS Evoked Potentials (TEPs) could classify CI from healthy controls (HC). Methods: Twenty-one patients with CI and 22 HC underwent a single-pulse TMS-EEG stimulus in which the pulses were delivered to the left dorsolateral prefrontal cortex (left DLPFC). After preprocessing, seven regions of interest (ROIs) and two most reliable TEPs' components: N100 and P200 were selected. Next, seven simple and interpretable linear features of TEPs were extracted for each region, three common machine learning algorithms including Support Vector Machine (SVM), Random Forest (RF), and K-Nearest Neighbor (KNN) were used to detect CI. Meanwhile, data augmentation and voting strategy were used for a more robust model. Finally, the performance differences of features in classifiers and their contributions were investigated. Results: 1. In the time domain, the features of N100 had the best performance in the SVM classifier, with an accuracy of 88.37%. 2. In the aspect of spatiality, the features of the right frontal region and left parietal region had the best performance in the SVM classifier, with an accuracy of 83.72%. 3. The Local Mean Field Power (LMFP), Average Value (AVG), Latency and Amplitude contributed most in classification. Conclusions: The TEPs induced by TMS over the left DLPFC has significant differences spatially and temporally between CI and HC. Machine learning based on the spatiotemporal features of TEPs have the ability to separate the CI and HC which suggest that TEPs has potential as non-invasive biomarkers for CI diagnosis.

Tailoring of Gradient Particles of Li-Rich Layered Cathodes with Mitigated Voltage Decay for Lithium-Ion Batteries.

Voltage decay during cycling is still a major issue for Li-rich cathodes in lithium ion batteries. Recently, the increase of Ni content has been recognized as an effective way to mitigate this problem, although it leads to lower-capacity materials. To find a balance between voltage decay and high capacity, particles of Li-rich materials with concentration gradients of transition metals have been prepared. Since voltage decay is caused by oxygen loss and phase transition that occur mainly on the particle surface, the Ni content is designed with a negative gradient of concentration from the surface to the bulk of particles. To do so, microsized Li1.20Ni0.13Co0.13Mn0.54O2 particles are mixed with much smaller LiNi0.8Co0.1Mn0.1O2 particles to form deposits of small particles onto larger particles. The concentration gradient of Ni is achieved as the Ni ions in LiNi0.8Co0.1Mn0.1O2 penetrate into Li1.20Ni0.13Co0.13Mn0.54O2 during a calcination post-treatment. Gradient samples show superior cycling performance and voltage retention as well as improved safety. This systematic study explores a material model combining Li-rich and high-Ni layered cathodes that is shown to be effective in creating a balance between mitigated voltage decay and high energy density.

Black phosphorus-based van der Waals heterostructures for mid-infrared light-emission applications.

Mid-infrared (MIR) light-emitting devices play a key role in optical communications, thermal imaging, and material analysis applications. Two-dimensional (2D) materials offer a promising direction for next-generation MIR devices owing to their exotic optical properties, as well as the ultimate thickness limit. More importantly, van der Waals heterostructures-combining the best of various 2D materials at an artificial atomic level-provide many new possibilities for constructing MIR light-emitting devices of large tuneability and high integration. Here, we introduce a simple but novel van der Waals heterostructure for MIR light-emission applications built from thin-film BP and transition metal dichalcogenides (TMDCs), in which BP acts as an MIR light-emission layer. For BP-WSe2 heterostructures, an enhancement of ~200% in the photoluminescence intensities in the MIR region is observed, demonstrating highly efficient energy transfer in this heterostructure with type-I band alignment. For BP-MoS2 heterostructures, a room temperature MIR light-emitting diode (LED) is enabled through the formation of a vertical PN heterojunction at the interface. Our work reveals that the BP-TMDC heterostructure with efficient light emission in the MIR range, either optically or electrically activated, provides a promising platform for infrared light property studies and applications.

S-Doped Carbon Fibers Uniformly Embedded with Ultrasmall TiO2 for Na+ /Li+ Storage with High Capacity and Long-Time Stability.

Building a rechargeable battery with high capacity, high energy density, and long lifetime contributes to the development of novel energy storage devices in the future. Although carbon materials are very attractive anode materials for lithium-ion batteries (LIBs), they present several deficiencies when used in sodium-ion batteries (SIBs). The choice of an appropriate structural design and heteroatom doping are critical steps to improve the capacity and stability. Here, carbon-based nanofibers are produced by sulfur doping and via the introduction of ultrasmall TiO2 nanoparticles into the carbon fibers (CNF-S@TiO2 ). It is discovered that the introduction of TiO2 into carbon nanofibers can significantly improve the specific surface area and microporous volume for carbon materials. The TiO2 content is controlled to obtain CNF-S@TiO2 -5 to use as the anode material for SIBs/LIBs with enhanced electrochemical performance in Na+ /Li+ storage. During the charge/discharge process, the S-doping and the incorporation of TiO2 nanoparticles into carbon fibers promote the insertion/extraction of the ions and enhance the capacity and cycle life. The capacity of CNF-S@TiO2 -5 can be maintained at ≈300 mAh g-1 over 600 cycles at 2 A g-1 in SIBs. Moreover, the capacity retention of such devices is 94%, showing high capacity and good stability.

New Insights on the Fast Response of Poly(Ionic Liquid)s to Humidity: The Effect of Free-Ion Concentration.

The swelling mechanism is widely used to explain the response of ionic liquids (ILs) or poly(ionic liquid)s (PILs) to moisture. While a fairly broad consensus has been attained, there are still some phenomena that are not well explained. As a complement to the swelling mechanism, we systematically studied the free volume theory in the rapid response and recovery of PIL humidity performance. We chose poly(1-ethyl-3-vinylimidazolium bromide) (PIL-Br), poly(1-ethyl-3-vinylimidazolium tetrafluoroborate) (PIL-BF4) and poly(1-ethyl-3-vinylimidazolium bis(trifluoromethane sulfonimide)) (PIL-TFSI) as model materials and investigated the impact of PIL structure including anion type, film thickness and affinity to moisture on performance to obtain the humidity sensing mechanism for PILs based on free volume theory. Hence, we can combine free volume theory with the designed PIL structures and their affinity with moisture to obtain a high concentration of free ions in PIL sensing films. Furthermore, the PIL humidity sensors also show fast, substantial impedance changes with changing humidity for real-time monitoring of the human respiratory rate due to a fast response and recovery performance. Therefore, our findings develop a new perspective to understand the humidity performance of PILs based on free volume theory, resulting in fast response and recovery properties realized by the rational design of PIL sensing films.

A highly selective and sensitive H2S sensor at low temperatures based on Cr-doped α-Fe2O3 nanoparticles.

Cr-doped α-Fe2O3 nanoparticles were synthesized by a low-cost and environmentally friendly hydrothermal route. Their gas sensing properties were investigated and the sensor showed high sensitivity and selectivity to H2S gas. Different Cr doping levels from 0 to 8.0 wt% were studied, and the sensor of 4.0 wt% Cr-doped α-Fe2O3 showed the largest response, with a response of 213 to 50 ppm H2S at 100 °C. The incorporation of Cr ions within α-Fe2O3 nanocrystals increases the specific surface area, and promotes the oxidation of H2S and oxygen adsorption in the air. Thus, the doping of Cr into α-Fe2O3 nanostructures would be a promising method for designing and fabricating high performance H2S gas sensors.