Three-dimensional hierarchically porous MoS2 foam as high-rate and stable lithium-ion battery anode.

Architected materials that actively respond to external stimuli hold tantalizing prospects for applications in energy storage, wearable electronics, and bioengineering. Molybdenum disulfide, an excellent two-dimensional building block, is a promising candidate for lithium-ion battery anode. However, the stacked and brittle two-dimensional layered structure limits its rate capability and electrochemical stability. Here we report the dewetting-induced manufacturing of two-dimensional molybdenum disulfide nanosheets into a three-dimensional foam with a structural hierarchy across seven orders of magnitude. Our molybdenum disulfide foam provides an interpenetrating network for efficient charge transport, rapid ion diffusion, and mechanically resilient and chemically stable support for electrochemical reactions. These features induce a pseudocapacitive energy storage mechanism involving molybdenum redox reactions, confirmed by in-situ X-ray absorption near edge structure. The extraordinary electrochemical performance of molybdenum disulfide foam outperforms most reported molybdenum disulfide-based Lithium-ion battery anodes and state-of-the-art materials. This work opens promising inroads for various applications where special properties arise from hierarchical architecture.

Graphdiyne-Based Nanofilms for Compliant On-Skin Sensing.

Thin-film electronics pliably laminated onto the epidermis for noninvasive, specific, and multifunctional sensing are ideal wearable systems for health monitoring and information technologies. However, it remains a critical challenge to fabricate ultrathin and compliant skin-like sensors with high imperceptibility and sensitivities. Here we report a design of conductive hydrogen-substituted graphdiyne (HsGDY) nanofilms with conjugated porous structure and inherent softness for on-skin sensors that allow minimization of stress and discomfort with wear. Dominated by the subtle deformation-induced changes in the interdomain tunneling conductance, the engineered HsGDY sensors show continuous and accurate results. Real-time noninvasive spatial mapping of dynamic/static strains in both tensile/compressive directions monitors various body motions with high sensitivity (GF ∼22.6, under 2% strain), fast response (∼60 ms), and long-term durability (∼5000 cycles). Moreover, such devices can dynamically distinguish between the temperature difference and frequency of air inhaled and exhaled through the nostril, revealing a quantitative assessment of the movement/health of the human body. The proof-of-concept strategy provides an alternative route for the design of next-generation wearable organic bioelectronics with multiple electronic functionalities.

Flexible Nanoporous Template for the Design and Development of Reusable Anti-COVID-19 Hydrophobic Face Masks.

Since the outbreak of the severe respiratory disease caused by the novel coronavirus (COVID-19), the use of face masks has become ubiquitous worldwide to control the rapid spread of this pandemic. As a result, the world is currently facing a face mask shortage, and some countries have placed limits on the number of masks that can be bought by each person. Although the surgical grade N95 mask provides the highest level of protection currently available, its filtration efficiency for sub-300 nm particles is around 85% due to its wider pore size (∼300 nm). Because the COVID-19 virus shows a diameter of around 65-125 nm, there is a need for developing more efficient masks. To overcome these issues, we demonstrate the development of a flexible, nanoporous membrane to achieve a reusable N95 mask with a replaceable membrane and enhanced filtration efficiency. We first developed a flexible nanoporous Si-based template on a silicon-on-insulator wafer using KOH etching and then used the template as a hard mask during a reactive ion etching process to transfer the patterns onto a flexible and lightweight (<0.12 g) polymeric membrane. Pores with sizes down to 5 nm were achieved with a narrow distribution. Theoretical calculations show that airflow rates above 85 L/min are possible through the mask, which confirms its breathability over a wide range of pore sizes, densities, membrane thicknesses, and pressure drops. Finally, the membrane is intrinsically hydrophobic, which contributes to antifouling and self-cleaning as a result of droplets rolling and sliding on the inclined mask area.

Heterogeneous Cubic Multidimensional Integrated Circuit for Water and Food Security in Fish Farming Ponds.

Among major food production sectors, world aquaculture shows the highest growth rate, providing more than 50% of the global seafood market. However, water pollution in fish farming ponds is regarded as the leading cause of fish death and financial losses in the market. Here, an Internet of Things system based on a cubic multidimensional integration of circuit (MD-IC) is demonstrated for water and food security applications in fish farming ponds. Both faces of the silicon substrate are used for thin-film-based device fabrication. The devices are interconnected via through-silicon-vias, resulting in a bifacial complementary metal-oxide-semiconductor-compatible electronics system. The demonstrated cubic MD-IC is a complete, small, and lightweight system that can be easily deployed by farmers with no need for specialists. The system integrates on its outer sides simultaneous air and water quality monitoring devices (temperature, electrical conductivity, ammonia, and pH sensors), solar cells for energy-harvesting, and antenna for real-time data-transfer, while data-management circuitry and a solid-state battery are integrated on its internal faces. Microfluidic cooling technology is used for thermal management in the MD-IC. Finally, a biofriendly polymeric encapsulation is used to waterproof the embedded electronics, improve the mechanical robustness, and allow the system to float on the surface of the water.

Effect of Li concentration-dependent material properties on diffusion induced stresses of a Sn anode.

Sn is one of the promising Li ion battery anode materials with high theoretical capacity and mechanical properties that allow for effective relaxation of Li diffusion-induced stresses. Sn is a low melting point metal with a low modulus and strength and has the ability to relax stresses via plasticity and creep deformations. In this study, concentration-dependent material properties are used in numerical simulations to model the Li diffusion-induced stress evolution in Sn micropillars. Simulation results using concentration-dependent material properties resulted in a completely different failure mode in comparison to that of concentration-independent simulation results. Tensile hoop stress needed for crack propagation was analyzed to be at the core for concentration-independent material properties, and switched to being at the surface for concentration-dependent simulation results. In addition, by incorporating these maximum tensile DIS results, the critical size for the failure of Sn micropillars was determined to be 5.3 µm at C/10 charging rate. This was then correlated with experimental observations, where fracture occurred in Sn micropillars with sizes larger than 6 µm, while 4.4 µm sized Sn micropillars survived the lithiation cycle.

Noninvasive Featherlight Wearable Compliant "Marine Skin": Standalone Multisensory System for Deep-Sea Environmental Monitoring.

Advances in marine research to understand environmental change and its effect on marine ecosystems rely on gathering data on species physiology, their habitat, and their mobility patterns using heavy and invasive biologgers and sensory telemetric networks. In the past, a lightweight (6 g) compliant environmental monitoring system: Marine Skin was demonstrated. In this paper, an enhanced version of that skin with improved functionalities (500-1500% enhanced sensitivity), packaging, and most importantly its endurance at a depth of 2 km in the highly saline Red Sea water for four consecutive weeks is reported. A unique noninvasive approach for attachment of the sensor by designing a wearable, stretchable jacket (bracelet) that can adhere to any species irrespective of their skin type is also illustrated. The wearable featherlight (<0.5 g in air, 3 g with jacket) gadget is deployed on Barramundi, Seabream, and common goldfish to demonstrate the noninvasive and effective attachment strategy on different species of variable sizes which does not hinder the animals' natural movement or behavior.

Size-dependent hardness of five-fold twin structured Ag nanowires.

In this study, the size dependent hardness of silver nanowires with a five-fold twin structure was examined using nanoindentation. As the diameter of the nanowires is reduced, the five-fold twin boundaries restrict the dislocation motion, and therefore a size dependent plasticity is expected for these uniquely structured nanowires. The polyol reduction method with modifications was used to synthesize silver nanowires with different diameters in the range of 70 nm to 144 nm. The nanoindentation experiments were performed on silver nanowires deposited on a stiff MgO substrate, and the resulting h, P, and S data were analyzed using the analytical double contact model for nanowire indentation. The hardness of the nanowires determined using the double contact model showed an increase in the hardness with reduction in the diameter of the nanowires, as expected due to the presence of the twin boundaries. The hardness values determined using the analytical double contact model compared favorably to the hardness values calculated from the contact areas that were extracted from finite element method simulations of an elastic indentation into the silver nanowires on the MgO substrate.

Vertically aligned P(VDF-TrFE) core-shell structures on flexible pillar arrays.

PVDF and P(VDF-TrFE) nano- and micro- structures have been widely used due to their potential applications in several fields, including sensors, actuators, vital sign transducers, and energy harvesters. In this study, we developed vertically aligned P(VDF-TrFE) core-shell structures using high modulus polyurethane acrylate (PUA) pillars as the support structure to maintain the structural integrity. In addition, we were able to improve the piezoelectric effect by 1.85 times from 40 ± 2 to 74 ± 2 pm/V when compared to the thin film counterpart, which contributes to the more efficient current generation under a given stress, by making an effective use of the P(VDF-TrFE) thin top layer as well as the side walls. We attribute the enhancement of piezoelectric effects to the contributions from the shell component and the strain confinement effect, which was supported by our modeling results. We envision that these organic-based P(VDF-TrFE) core-shell structures will be used widely as 3D sensors and power generators because they are optimized for current generations by utilizing all surface areas, including the side walls of core-shell structures.