Superior Self-Powered Room-Temperature Chemical Sensing with Light-Activated Inorganic Halides Perovskites

Hybrid halide perovskite is one of the promising light absorber and is intensively investigated for many optoelectronic applications. Here, the first prototype of a self-powered inorganic halides perovskite for chemical gas sensing at room temperature under visible-light irradiation is presented. These devices consist of porous network of CsPbBr3 (CPB) and can generate an open-circuit voltage of 0.87 V under visible-light irradiation, which can be used to detect various concentrations of O2 and parts per million concentrations of medically relevant volatile organic compounds such as acetone and ethanol with very quick response and recovery time. It is observed that O2 gas can passivate the surface trap sites in CPB and the ambipolar charge transport in the perovskite layer results in a distinct sensing mechanism compared with established semiconductors with symmetric electrical response to both oxidizing and reducing gases. The platform of CPB-based gas sensor provides new insights for the emerging area of wearable sensors for personalized and preventive medicine.H.C. and M.Z. contributed equally to this work. A.T. gratefully acknowledges the support of Australian Research Council (ARC) DP150101939, ARC DE160100569, and Westpac 2016 Research Fellowship. M.Z., S.H., and A.W.Y. H.-B. acknowledge the support of the Australian government via financial support from the ARC through the DP160102955 program and the Australian Renewable Energy Agency. K.R.C. acknowledges the support of an ARC Future Fellowship. The financial support from ARC through DP160102955 is also acknowledged

Three-dimensional nano-heterojunction networks: A highly performing structure for fast visible-blind UV photodetectors

Visible-blind ultraviolet photodetectors are a promising emerging technology for the development of wide bandgap optoelectronic devices with greatly reduced power consumption and size requirements. A standing challenge is to improve the slow response time of these nanostructured devices. Here, we present a three-dimensional nanoscale heterojunction architecture for fast-responsive visible-blind UV photodetectors. The device layout consists of p-type NiO clusters densely packed on the surface of an ultraporous network of electron-depleted n-type ZnO nanoparticles. This 3D structure can detect very low UV light densities while operating with a near-zero power consumption of ca. 4 × 10-11 watts and a low bias of 0.2 mV. Most notably, heterojunction formation decreases the device rise and decay times by 26 and 20 times, respectively. These drastic enhancements in photoresponse dynamics are attributed to the stronger surface band bending and improved electron-hole separation of the nanoscale NiO/ZnO interface. These findings demonstrate a superior structural design and a simple, low-cost CMOS-compatible process for the engineering of high-performance wearable photodetector

Fabrication, mechanical properties, and multifunctionalities of particle reinforced foams:A review

In the past decade, particle reinforced foams have been intensively studied and applied in diverse fields owing to their low weight-to-strength ratio, low cost, and tailorable physical properties using various matrix materials and additives. In particular, the thin-walled microstructures in foams and certain particles provide excellent energy absorption capacity compared with the solid materials. A considerable number of research findings on particle reinforced foams have been reported from various aspects, including fabrication techniques, matrices and reinforcement types, mechanical responses as well as other physical properties. Up to date, several review articles have been published to partially cover the stated aspects on hollow particles reinforced foams (i.e., syntactic foams). However, discussion on different types of nano/micro-scale solid particles and millimeter-scale porous particles reinforced foams remains insufficient. Therefore, this article aims to provide a comprehensive review on particle (e.g., solid/porous/hollow particles) reinforced foams (made up of metal/polymer/ceramic matrices) covering fabrication techniques, mechanical responses and their multifunctionalities. Particularly, different reinforcing mechanisms and modifications to physical functions of foams with different matrices using various types of particle additives are reviewed. The opportunities for future explorations of particle reinforced foams in the aspects of manufacturing, modeling and applications are discussed lastly

Low-Voltage High-Performance UV Photodetectors: An Interplay between Grain Boundaries and Debye Length

Accurate detection of UV light by wearable low-power devices has many important applications including environmental monitoring, space to space communication, and defense. Here, we report the structural engineering of ultraporous ZnO nanoparticle networks for fabrication of very low-voltage high-performance UV photodetectors. Record high photo- to dark-current ratio of 3.3×105 and detectivity of 3.2×1012 Jones at ultra-low operation bias of 2 mV and low UV-light intensity of 86 μW⋅cm-2 are achieved by controlling the interplay between grain boundaries and surface depletion depth of ZnO nanoscale semiconductors. An optimal window of structural properties is determined by varying the particle size of ultraporous nanoparticle networks from 10 to 42 nm. We find that small electron-depleted nanoparticles (≤ 40 nm) are necessary to minimize the dark-current, however, the rise in photo-current is tampered with decreasing particle size due to the increasing density of grain boundaries. These findings reveal that nanoparticles with a size close to twice their Debye’s length are required for high phototo dark-current ratio and detectivity, while further decreasing their size decreases the photodetector performanceA.T. gratefully acknowledges the support of Australian Research Council DP150101939, Australian Research Council DE160100569, and Westpac2016 Research Fellowshi

Self-assembly of Au Nano-islands with Tuneable Organized Disorder for Highly Sensitive SERS

Aggregates of disordered metallic nano-clusters exhibiting long-range organized fractal properties are amongst the most efficient scattering enhancers, and they are promising as high performance surface-enhanced Raman scattering (SERS) substrates. However, the low reproducibility of the disordered structures hinders the engineering and optimization of well-defined scalable architectures for SERS. Here, a thermophoretically driven Au aerosol deposition process is used for the self-assembly of thin films consisting of plasmonic nano-islands (NIs) with a controllable and highly reproducible degree of disorder. The intrinsic Brownian motion of the aerosol deposition process results in long-range periodicity with self-similar properties and stochastically distributed hot-spots, providing a facile means for the reliable fabrication of crystalline Au substrates with uniform disorder over large-surfaces. These morphological features result in the generation of a high density of hot-spots, benefitting their application as SERS substrates. NI substrates with an optimal uniform disorder demonstrate a SERS enhancement factor (EF) of 107–108 with nanomolar concentrations of Rhodamin-6G. These findings provide new insights into the investigation of light scattering with disordered structures, paving the way toward low-cost scalable self-assembly optoelectronic materials with applications ranging from ultrasensitive spectroscopy to random lasing and photonic devices

Structural engineering of nano-grain boundaries for low-voltage UV-photodetectors with gigantic photo- to dark-current ratios

Ultraporous networks of ZnO nanoparticles (UNN) have recently been proposed as a highly performing morphology for portable ultraviolet light photodetectors. Here, it is shown that structural engineering of the nanoparticle grain boundaries can drastically enhance the performance of UNN photodetectors leading to gigantic photo to dark current ratios with operation voltages below 1 V. Ultraporous nanoparticle layers are fabricated by scalable low-temperature deposition of flame-made ZnO aerosols resulting in highly transparent layers with more than 95% visible light transmittance and 80% UV-light absorption. Optimal thermally induced necking of the ZnO nanoparticles increased the photo- to dark-current ratio, at a low light density of 86 μW cm−2, from 1.4 × 104 to 9.3 × 106, the highest so far reported. This is attributed to the optimal interplay of surface depletion and carrier conduction resulting in the formation of an open-neck grain boundary morphology. These findings provide a robust set of guiding principles for the design and fabrication of nanoparticle-based optoelectronic devices.A.T. gratefully acknowledges the support of Australian Research Council DP150101939, Australian Research Council DE160100569, and Westpac 2016 Research Fellowship

Self-assembly of noble metal-free graphene-copper plasmonic metasurfaces

The strong light confinement and near field enhancement by metallic scatters enabled the development of a large family of plasmonic-based technologies, including broadly used gold metasurfaces. Despite progress, the engineering of non-precious metal plasmonic devices remains challenging, due to the limited chemical stability of most nanostructured metals. Here, we report the preparation of earth-abundant plasmonic metasurfaces by the engineering of copper-graphene nano-resonators, and their use as localized surface plasmon resonance (LSPR) sensors. We achieve the large-scale self-assembly of Cu nanocrystals, featuring a protective graphene film, by one-step reduction of CuO nanoparticle networks in a hydrocarbon-containing atmosphere. Microscopic and spectroscopic investigations reveal that coalescence and reduction of the CuO nanoparticles during graphene growth result in the formation of graphene-encapsulated metallic Cu nano-islands (NIs). These Cu-graphene metasurfaces can detect down to 1% concentrations of toluene gas at room temperature, displaying a reproducible and rapid LSPR shift of 0.2 nm. Finite-difference time-domain (FDTD) simulation and structural characterization reveal that the graphene layer significantly improves the Cu crystals’ long-term stability, leading to a prolonged LSPR performance over periods of three months. These insights provide promising directions for the development of earth-abundant plasmonic materials with applications ranging from biosensing to photo-catalysis and other optoelectronic devices.</p

Metal-Organic Frameworks/Conducting Polymer Hydrogel Integrated Three-Dimensional Free-Standing Monoliths as Ultrahigh Loading Li-S Battery Electrodes

The lithium-sulfur (Li-S) system is a promising material for the next-generation of high energy density batteries with application extending from electrical vehicles to portable devices and aeronautics. Despite progress, the energy density of current Li-S technologies is still below that of conventional intercalation-type cathode materials due to limited stability and utilization efficiency at high sulfur loading. Here, we present a conducting polymer hydrogel integrated highly performing free-standing three-dimensional (3D) monolithic electrode architecture for Li-S batteries with superior electrochemical stability and energy density. The electrode layout consists of a highly conductive three-dimensional network of N,P codoped carbon with well-dispersed metal-organic framework nanodomains of ZIF-67 and HKUST-1. The hierarchical monolithic 3D carbon networks provide an excellent environment for charge and electrolyte transport as well as mechanical and chemical stability. The electrically integrated MOF nanodomains significantly enhance the sulfur loading and retention capabilities by inhibiting the release of lithium polysulfide specificities as well as improving the charge transfer efficiency at the electrolyte interface. Our optimal 3D carbon-HKUST-1 electrode architecture achieves a very high areal capacity of >16 mAh cm-2 and volumetric capacity (CV) of 1230.8 mAh cm-3 with capacity retention of 82% at 0.2C for over 300 cycles, providing an attractive candidate material for future high-energy density Li-S batteries.</p

Paper-Like Writable Nanoparticle Network Sheets for Mask-Less MOF Patterning

Geometrical structuring of monolithic metal-organic frameworks (MOFs) components is required for their practical implementation in many areas, including electronic devices, gas storage/separation, catalysis, energy storage as well as bio-medical applications. Despite progress in structuring MOFs, an approach for the precise patterning of MOF functional geometries in the millimeter- to micro-meter depth is lacking. Here, a facile and flexible concept for the microfabrication of complex MOF patterns on large surfaces is reported. The method relies on the engineering of easily-writable sheets of precursor metal oxide nanoparticles. The gas-phase conversion of these patterned ceramic nanoparticle sheets results in monolithic MOF objects with arbitrarily shaped geometries and thicknesses of up to hundreds of micrometers. The writing of complex patterns of zeolitic imidazolate framework-8 (ZIF-8) is demonstrated by a variety of approaches including ion beam, laser, and hand writing. Nanometer-scale patterns are achieved by focused ion beam (FIB). Artless handwritings are obtained by using a pen in a similar fashion to writing on a paper. The pure ZIF-8 composition of the resulting patterns is confirmed by a series of physical and chemical characterization. This facile MOF precursor-writing approach provides novel opportunities for the design of MOF-based devices with applications ranging from micro-fluidics to renewable energy systems.</p

Flexible Impact-Resistant Composites with Bioinspired Three-Dimensional Solid–Liquid Lattice Designs

The ubiquitous solid–liquid systems in nature usually present an interesting mechanical property, the rate-dependent stiffness, which could be exploited for impact protection in flexible systems. Herein, a typical natural system, the durian peel, has been systematically characterized and studied, showing a solid–liquid dual-phase cellular structure. A bioinspired design of flexible impact-resistant composites is then proposed by combining 3D lattices and shear thickening fluids. The resulting dual-phase composites offer, simultaneously, low moduli (e.g., 71.9 kPa, lower than those of many reported soft composites) under quasi-static conditions and excellent energy absorption (e.g., 425.4 kJ/m3, which is close to those of metallic and glass-based lattices) upon dynamic impact. Numerical simulations based on finite element analyses were carried out to understand the enhanced buffering of the developed composites, unveiling a lattice-guided fluid–structure interaction mechanism. Such biomimetic lattice-based flexible impact-resistant composites hold promising potential for the development of next-generation flexible protection systems that can be used in wearable electronics and robotic systems