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Flexible ultraviolet (UV) light sensor was developed using ZnO thin film based surface acoustic wave (SAW) deposited onto low cost, commercial and thin aluminum foil (50 um thickness). ZnO nanorods were further grown on the surface of the device by a simplified hydrothermal process for enhancing the sensitivity. The zero order antisymmetric (A0) and symmetric (S0) lamb wave modes were identified at 13 MHz and 30 MHz respectively. These modes were used to obtain their frequency responses at various UV light intensities. UV sensing performance was investigated at different flexible/bending positions. The results showed good sensitivity in various flexible positions, moreover, the nanorods improved the sensitivity of the sensor by 59% and 44% for A0 and S0 modes, respectively. In addition, they possessed very good repeatability and stability, hence they have great potential for flexible and wearable UV light sensing applications.

High-precision gas sensors operated at room temperature are attractive for various real-time gas monitoring applications, with advantages including low energy consumption, cost effectiveness and device miniaturization/flexibility. Studies on sensing materials, which play a key role in good gas sensing performance, are currently focused extensively on semiconducting metal oxide nanostructures (SMONs) used in the conventional resistance type gas sensors. This topical review highlights the designs and mechanisms of different SMONs with various patterns (e.g. nanoparticles, nanowires, nanosheets, nanorods, nanotubes, nanofilms, etc.) for gas sensors to detect various hazardous gases at room temperature. The key topics include (1) single phase SMONs including both n-type and p-type ones; (2) noble metal nanoparticle and metal ion modified SMONs; (3) composite oxides of SMONs; (4) composites of SMONs with carbon nanomaterials. Enhancement of the sensing performance of SMONs at room temperature can also be realized using a photo-activation effect such as ultraviolet light. SMON based mechanically flexible and wearable room temperature gas sensors are also discussed. Various mechanisms have been discussed for the enhanced sensing performance, which include redox reactions, heterojunction generation, formation of metal sulfides and the spillover effect. Finally, major challenges and prospects for the SMON based room temperature gas sensors are highlighted.

Multi-shape memory effect (multi-SME) in amorphous polymers has attracted great attention due to their complex thermal transitions and multi-step recovery behavior. Many experimental studies have been reported for synthesis, characterization, testing and demonstration of the multi-SME. However, theoretical approaches have seldom been applied although they are critically needed to understand the principles and predict the behavior of the multi-SME in various amorphous polymers. In this study, a new thermomechanical model was proposed to describe the thermo-/chemo-responsive multi-SME of amorphous polymers with tunable segment compositions. Based on the Weibull statistical model, a new constitutive framework was established to describe temperature-, stretch ratio- and strain-dependent behaviors of thermo-/chemo-responsive multi-SME. Finally, this newly proposed model was applied to quantitatively identify the crucial factors for the thermo-/chemo-responsive shape recovery behaviors, which have been verified by the reported experimental data.

Deep ultraviolet (DUV) photodetectors have wide-range applications in satellite communications, air purification, and missile-plume detection. However, the critical barriers for the currently available wide-band gap semiconductor film-based DUV photodetectors are their low efficiency, complicated processes, and lattice mismatch with the substrate. Quantum dot (QD) devices prepared using solution-based methods can solve these problems. However, so far, there are no reports on photovoltaic-type DUV photodetectors using QDs. In this study, we propose a novel methodology to construct a hybrid zero-/two-dimensional DUV photodetector (p-type graphene/ZnS QDs/4H-SiC) with photovoltaic characteristics. The device exhibits excellent selectivity for the DUV light and has an ultrafast response speed (rise time: 28 μs and decay time: 0.75 ms), which are much better than those reported for conventional photoconductive photodetectors.

By integrating phase transition theory and Takayanagi principle, we have developed a thermodynamic model to describe working mechanism and thermomechanical behavior of shape memory polymers (SMPs) with tunable multi-shape memory effect (multi-SME). Thermodynamics and state/phase transitions of different segments in the SMPs were modeled by considering their cooperative relaxation, which is defined as a process where a group of segments undergo relaxation simultaneously, based on the Takayanagi principle. Dependences of thermomechanical behavior of amorphous polymers on volume fraction, cooperative relaxation and glass transition temperatures of both hard and soft segments were theoretically investigated. Working mechanisms of the multi-SME and cooperative relaxation of the amorphous polymers have well been explained using this newly proposed model, which offers an effective approach for designing new SMPs with multi-segments.

Graphene/epoxy resin nanocomposites were prepared using an in-situ polymerization process, and their formation mechanisms, microstructures, mechanical properties and electrical conductivity were characterized. Results showed that graphene is well dispersed in the epoxy matrix, and covalent cross-links are formed between graphene and epoxy matrix. Tensile strength and modulus of the graphene/epoxy composites were found to increase firstly and then decrease with the increase of graphene loading contents. When the graphene content was 0.3 wt%, tensile strength, tensile modulus and elongation were found to increase by 46.8%, 47.3% and 24.0% compared with those of pure epoxy resin. When the graphene content was 1.38 vol%, the conductivity of the composite was 3.28 × 10−4 S m−1 with a low percolation threshold of 0.47 vol%. Enhancement mechanisms for the properties of composites were identified to be dispersion strengthening, effective transfer of stress and bridging of graphene.

For carbon fiber reinforced metal matrix composites, there are many potential problems such as severe agglomeration of carbon fibers (CFs), their poor interfacial wettability with the matrix, and poor mechanical strength. To solve these problems, we proposed to use electroless plating to coat a layer of Ni onto the CFs, and then studied their interfacial structures, fracture strain/strength and wettability. The coated Ni layer was uniformly distributed onto and well bonded with the CFs. The maximum strain of the CFs coated with the Ni layer was increased by 23.4%, though their average fracture strength was slightly decreased from 3.5 GPa to 2.25 GPa. The wettability of the Ni-coated fiber was significantly improved, verified from testing results using both a dip coating method and a fiber reinforced composite simulation test.

Based on theoretical analysis, finite element simulation and experimental verifications, we have systematically investigated evolution, hybridization and decoupling of multiple acoustic wave modes and vibration patterns generated from piezoelectric film acoustic wave devices fabricated on flexible thin foils/plates. ZnO piezoelectric films deposited on flexible and bendable Al foil and plates were selected for this particular study. The ZnO/Al acoustic wave devices were chosen with wavelengths varied from 12 to 800 μm, ZnO film thickness from 2 to 10 μm and Al foil/plate thickness from 10 to 600 μm. Multiple acoustic wave modes (including symmetrical and asymmetrical Lamb waves, Rayleigh waves and higher harmonic/Sezawa wave modes) were generated, hybridized occasionally with each other, and then easily decoupled by changing the ratios of the substrate/film thicknesses to wavelengths. Ratios between device wavelength and substrate/film thickness have been identified to be the dominant parameter in determining the evolution and hybridization of multiple wave modes and their vibration patterns, which provide useful design guidance for both sensing and microfluidic applications using these flexible and bendable acoustic wave devices.

A dual functional sensor for detecting both UV light and H2S gas was fabricated using the hexagonal phase porous In2O3 nanoparticles, which were prepared using the hydrothermal and calcination process. The porous In2O3 nanoparticles with large surface areas and pore volumes could provide plenty of active sites to produce much active oxygen species, which were beneficial for the UV light and H2S gas sensing reactions, thus resulting in a good sensing performance. At room temperature, the dual functional sensor based on porous In2O3 nanoparticles exhibited ultra-high responses for sensing both UV light (with a wavelength of 365 nm) and H2S gas. As a UV sensor, its response was 12886.0 for a UV power intensity of 1.287 mW/cm2 and its detection limit was 0.013 mW/cm2. As a H2S gas sensor, the sensor exhibited an ultra-high response (26268.5–1 ppm H2S) and a very low detection limit (1 ppb of H2S), and it also have excellent selectivity, reversibility and stability.

One of the critical issues for the conventional TENGs for applications in biomechanical and blue energy harvesting is to develop adaptive, simple-structured, high performance but low-cost TENGs for the complex excitation conditions. To solve this problem, we propose an origami-inspired TENG integrated with folded thin film electret, which can be facilely formed from two pieces of liquid crystal polymer (LCP) strips through high degrees of paper folding. It has been proved efficient for harvesting energy from both sinusoidal vibrations and impulse excitations which are universally existed in the ambient environment. Double-side corona discharging process is employed to maximize the charge density generated by the electret thin films. Attributing to the excellent elastic property of self-rebounding spring structures based on the origami design, the flexible TENGs can be readily integrated into smart shoes, floors, watches and clothes for wearable and energy harvesting applications. Triggered by impulse excitation of gentle finger tapping, instantaneous open-circuit voltage and short-circuit current of 1000 V and 110 μA, respectively, have been obtained with a remarkable peak power density of 0.67 mW/cm3 (or 1.2 mW/g). A spherical floating buoy generator integrating multiple origami TENGs is further developed to harvest ocean wave energy at various frequencies and amplitudes as well as in arbitrary directions. The outcomes of this work offer new insights of realizing single structured TENG designs for multifunctional applications. Accepted version This research is supported by National Natural Science Foundation of China Grant (No. 51705429 & No. 61801525), National Natural Science Foundation of Shaanxi Province No. 2018JQ5030, the Fundamental Research Funds for the Central Universities No. 31020190503003, Laboratory fund of Science and Technology on Micro-system Laboratory No. 614280401010417, Science, Technology and Innovation Commission of Shenzhen Municipality JCYJ20170815161054349, Guangdong Natural Science Funds Grant (2018A030313400), Space Science and Technology Foundation, UK Engineering and Physical Sciences Research Council (EPSRC) for support under grant EP/P018998/1, Newton Mobility Grant (IE161019) through Royal Society.

Smart materials with self-growing and tailorable mechanical strength have wide-range potential applications in self-healing, self-repairing, self-assembly, artificial muscle, soft robots and intelligent devices. However, their working mechanisms and principles are not fully understood yet and mathematically and physical modeling is a huge challenge, as traditionally synthesized materials cannot self-grow and reconstruct themselves once formed or deformed. In this study, a phenomenological constitutive model was developed to investigate the working mechanisms of self-growing and tailorable mechanical strength in double-network (DN) hydrogel composites, induced by mechanochemical transduction of dynamic-modal mechanophore. An extended Maxwell model was firstly employed to characterize the mechanical unzipping of hydrogel composites, and then mechanochemically induced destruction and reconstruction processes of brittle network in the hydrogel composite were formulated. The enhanced mechanical strength of brittle network has been identified as the key driving force to generate self-growing and tailorable mechanical strength in the hydrogel composite. Finally, a stress-strain constitutive relationship was developed for the dynamic-modal mechanophorein the hydrogel composite. Simulation results obtained from the proposed model were compared with the experimental data, and a good agreement has been achieved. This study provides an effective strategy for modelling and exploring the working mechanism in the mechanoresponsive DN hydrogel composites with self-growing and tailorable mechanical strength.

Titanium alloys have been applied for many lightweight structural components in the fields of aerospace, automobiles and biomedical implants owing to their light-weight, good mechanical properties and biocompatibility. However, poor tribological performance often restricts their wide-range applications. In this study, we synthesized Cu modified Ti-6Al-4 V (TC4) powders with various Cu contents (0, 1, 3, 5, 10 wt%), which was further strengthened with 0.3 wt% graphene oxide nanosheets (GONs) using a powder metallurgy technology. These composite powders were then synthesized into titanium matrix composites using spark plasma sintering. Effects of Cu contents on microstructure evolution, phase composition and tribological properties of Ti matrix composites were systematically investigated. The synthesized composites were consisted of α-Ti, β-Ti, Ti2Cu, in-situ-formed TiC and remained GONs, and showed better tribological properties than those of TC4 alloy. The average coefficient of friction was reduced from 0.168 to a minimum value of 0.120 as the copper content increased from 0 to 3 wt%, meanwhile the wear volume loss was reduced by 49.3%. Whereas further increasing Cu contents resulted in the increases of both coefficients of friction and wear volume loss. These improvements are mainly attributed to the hardness strengthening effects by Ti-Cu intermetallics and TiC@GONs structure, as well as the self-lubricating effect of GONs. Compared with traditional surface modification processes, the new method proposed in this work is cost-effective and promising for improving the tribological performance of titanium alloys in industry applications.

Self-powered wireless sensor systems are highly sought for the forthcoming Internet of Things era. However, most of the technologies take the route of energy harvesting, storage, and power regulation to power wireless sensor systems, which has a limited operation duration due to the low energy utilization efficiency of the multiple energy conversions involved. Here, we propose a triboelectric nanogenerator (TENG) based fully self-powered, instantaneous wireless sensor system which yet does not contain electronic devices and chips, but the passive components only. By integrating a capacitive sensor and an inductor coil with TENG, the pulse voltage output of the TENG is converted into a sinusoidal signal containing the sensing information with a resonant frequency and is transmitted to the receiver in distance wirelessly and continuously. A precise analytical model is developed for the capacitive sensor system with general implication; the oscillating signal generated by the model shows excellent agreement with experimental results. A capacitive humidity sensor is then utilized for sensing demonstration, showing that the maximum transmission distance of the sensor system is 50 and 90 cm for a 1 cm diameter magnetic-core coil pair and 20 cm diameter air-core coil pair, respectively. The wireless humidity sensor exhibits a sensitivity of 1.26 kHz/%RH, fast response speed, and excellent linearity, demonstrating its great application potential of the self-powered technology.

Nanoparticles have been widely used to enhance mechanical properties of polymer matrix, however, the complex mechanisms of interfacial entanglements, coupled confinements and coordinative motions among the polymer macromolecules and nanoparticles have not been well understood. In this study, we develop a coupling model to describe the thermodynamic entanglements and confinement effects within nanoparticle reinforced shape memory polymer (SMP) nanocomposites. We found that thermodynamic relaxation of the SMP nanocomposite is determined by cooperative effects of sub-entanglement and topological entanglement of macromolecule chains, which selectively enhance the relaxation behaviors and enable a high recovery stress of SMP nanocomposites. Finally, the effectiveness of this model is demonstrated by applying it to predict the constitutive relationships and shape memory behaviors, and this fundamental approach can reveal toughening mechanisms of shape recovery strength in the SMP nanocomposites by nanoparticles.

Graphene quantum dots decorated zinc oxide nanowires (GQDs@ZnO-NWs) were applied to enhance sensing performance of highly flexible and transparent surface acoustic wave (SAW) ultraviolet (UV) photodetectors made on ultra-thin flexible glass. The developed flexible SAW sensors possess better performance than that of the previously developed polymer based flexible SAW devices, due to insignificant acoustic loss of flexible glass substrate. UV sensitivity of the flexible glass based SAW sensors was enhanced by three times, and the response time was shorten by four times after the sensor was coated with the GQDs@ZnO-NWs hybrid nanomaterials. These improvements are mainly attributed to: (1) large specific surface areas of ZnO NWs which can generate a large number of photon-generated carriers; (2) introduction of GQDs which can reduce the carrier recombination rate. The resonant frequency of flexible glass SAW UV photodetectors exhibited a good repeatability and stability in responses to cyclic changes of the UV lights at different wavelengths. They also maintained a good performance under a bending angle of ∼30° for 200 times without apparent degradation, showing the excellent flexibility and stability of the UV photodetector.

Ball milling process has become one of the effective methods for dispersing graphene nanoplates (GNPs) uniformly into matrix; however, there are often serious issues of structural integrity and interfacial reactions of GNPs with matrix. Herein, GNPs/Ti‐6Al‐4V (GNPs/TC4) composites are synthesized using high energy ball milling (HEBM) and spark plasma sintering. Effects of ball milling on microstructural evolution and interfacial reactions of GNPs/TC4 composite powders during HEBM are investigated. As ball milling time increase, particles size of TC4 is first increased (e.g., ≈104.15 μm, 5 h), but then decreased to ≈1.5 μm (15 h), which is much smaller than that of original TC4 powders (≈86.8 μm). TiC phases are in situ formed on the surfaces of TC4 particles when ball milling time is 10Thinsp;h. GNPs/TC4 composites exhibit 36–103% increase in compressive yield strength and 57–78% increase in hardness than those of TC4 alloy, whereas the ductility is reduced from 28% to 7% with an increase of ball milling time (from 2 to 15 h). A good balance between high strength (1.9 GPa) and ductility (17%) of GNPs/TC4 composites is achieved when the ball milling time is 10 h, attributing to the synergistic effects of grain refinement strengthening, solid solution strengthening, and load transfer strengthening from GNPs and in situ formed TiC.

Spatial distribution of biological cells plays a key role in tissue engineering for reconstituting the cellular microenvironment, and recently, acoustofluidics are explored as a viable tool for controlling structures in tissue fabrication because of its good biocompatibility, low-power consumption, automation capability, nature of non-invasive, and non-contact. Herein, a reusable acoustofluidic device is developed using surface acoustic waves for manipulating microparticles/cells to form a 3D matrix pattern inside a scaffold-based hydrogel contained in a millimetric chamber. The 3D patterned and polymerized hydrogel construct can be easily and safely removed from the chamber using a proposed lifting technique, which prevent any physical damages or contaminations and promote the reusability of the chamber. The generated 3D patterns of microparticles and cells are numerically studied using a finite-element method, which is well validated by the experimental results. The proposed acoustofluidic device is a useful tool for in vitro engineering 3D scaffold-based artificial tissues for drug and toxicity testing and building organs-on-chip applications. Ministry of Education (MOE) Nanyang Technological University The authors gratefully acknowledge the support of 1) Nanyang Technological University and the Ministry of Education of Singapore through a Ph.D. Scholarship and AcRF Tier 1 research grant (RG 96/18); 2) the UK Engineering and Physical Sciences Research Council (EPSRC) grants (EP/P018998/1); and 3) Special Interesting Group of Acoustofluidics funded by UK Fluids Network (EP/N032861/1).

Two-dimensional transition metal carbides/nitrides, known as MXenes, have recently received significant attention for gas sensing applications. However, MXenes have strong adsorption to many types of volatile organic compounds (VOCs), and therefore gas sensors based on MXenes generally have low selectivity and poor performance in mixtures of VOCs due to cross-sensitivity issues. Herein, we developed a Ti3C2Tx-based virtual sensor array (VSA) which allows both highly accurate detection and identification of different VOCs, as well as concentration prediction of the target VOC in variable backgrounds. The VSA’s responses from the broadband impedance spectra create a unique fingerprint of each VOC without a need for changing temperatures. Based on the methodologies of principal component analysis and linear discrimination analysis, we demonstrate highly accurate identifications for different types of VOCs and mixtures using this MXene based VSA. Furthermore, we demonstrate an accuracy of 93.2% for the prediction of ethanol concentrations in the presence of different concentrations of water and methanol. The high level of identification and concentration prediction shows a great potential of MXene based VSA for detection of VOCs of interest in the presence of known and unknown interferences.

This paper reports significant enhancement of corrosion resistance and electrical properties of waterborne epoxy coatings through additions of ceria modified graphene. Results showed that ceria particles were uniformly distributed and covalently bonded onto the surface of graphene. A dense interface layer was formed between the ceria modified graphene and epoxy matrix by aliphatic ether bonds. The composite coating with a modified graphene content of 0.5 wt% exhibited the best corrosion resistance with the highest impedance modulus (e.g., 103 Ω cm2 for the damaged coating) and the lowest corrosion rate (e.g., 0.002 mm/year). The excellent corrosion resistance of the composite coating is related to the barrier effect of graphene and the inhibition effect of ceria on metal corrosion. Moreover, the coating showed a low percolation threshold of 0.231 vol% and its electrical conductivity reached 10−5 S/m when the content of modified graphene was 0.5 wt%.

Poor wettability and weak interfacial bonding between Cu and Al2O3 have been critical issues for sintering of high-quality Ni@Al2O3/Cu composites. In this paper, we explore an interfacial engineering design methodology to achieve good mechanical properties of Ni@Al2O3/Cu composites using spark plasma sintering method. The Ni coated powders were prepared using a heterogeneous precipitation method, which can significantly improve wettability between Cu and Al2O3 and enhance their interfacial bonding. The sintered Ni@Al2O3/Cu composites with a copper content of 15 vol% showed a compact network structure of alumina well-infiltrated with metallic Cu, and achieved good mechanical (e.g., fracture toughness of 6.72 MPam1/2) and physical properties (e.g., relative density of 99.3% and electrical resistivity of 1.2810−3 Ω m). The key mechanisms for the enhanced properties of the composites synthesized using the Ni coated composite powders have been identified as: (1) well-formed ceramic/metal interfacial structures which improve wettability of Al2O3 with Cu, and promote the formation of a homogeneous network structure; (2) enhanced elemental diffusion and interfacial reactions, which result in formation of Cu2O and CuAlO2 and thus improve interfacial wetting and bonding properties.

A new phenomenon, electric field enhanced adsorption and diffusion of lithium, magnesium and aluminum ions in a MoS2 monolayer, was investigated using density functional theory in this study. With the electric field increased from 0 to 0.8 V/Å, the adsorption energies of the Li, Mg and Al atoms in the MoS2 monolayer were decreased from −2.01 to −2.49 eV, from −0.80 to −1.28 eV, and −2.71 to −3.01 eV, respectively. The corresponding diffusion barriers were simultaneously decreased from 0.23 to 0.08 eV, from 0.15 to 0.10 eV, and 0.24 to 0.21 eV for the Li, Mg and Al ions, respectively. We concluded that the external electric field can increase the charging speed of rechargeable ion batteries based on the MoS2 anode materials.

CeO2 nanowires were synthesized using a facile hydrothermal process without any surfactant, and their morphological, structural and gas sensing properties were systematically investigated. The CeO2 nanowires with an average diameter of 12.5 nm had a face-centered cubic fluorite structure and grew along [111] of CeO2. At the room temperature of 25 °C, hydrogen sulfide (H2S) gas sensor based on the CeO2 nanowires showed excellent sensitivity, low detection limit (50 ppb), and short response and recovery time (24 s and 15 s for 50 ppb H2S, respectively).

Based on density functional theory computation, we systematically investigated diffusion behavior of Mg ions in β-tin (Sn), bismuth (Bi), and their magnesiation compounds of Bi2Mg3 and Mg2Sn. Results showed that the β-Sn and Bi are good candidates for the anode materials for Mg ion batteries with small diffusion barriers. The dynamic simulations and the obtained energy barriers showed that compared with β-Sn, Bi is a better anode candidate with fast charge/discharge rates for the Mg ion batteries.

This paper reported that functionalization of carbon nanotube (CNT) nanopaper with beta-cyclodextrins (β-CD) enhanced the thermo-mechanical properties and shape recovery of shape memory polymer (SMP) nanocomposite. The functionalized CNT nanopaper showed a remarkable capability to enhance interfacial bonding strength between SMP matrix and the cyclodextrin molecules, where the inclusion complex was formed by interaction of the β-CD with epoxy-based SMP matrix. Electrically induced shape recovery behavior of the nanocomposite were characterized, and a high efficiency of shape recovery of SMP nanocomposite incorporated with the CNT-β-CD nanopaper was demonstrated.

Synergistic effects of self-assembled carboxylic acid-functionalized carbon nanotube (CNT) and nafion/silica nanofiber on the electro-activated shape recovery behavior of shape memory polymer (SMP) nanocomposite were investigated. Carboxylic acid-functionalized CNTs were self-assembled onto the carbon fiber mat to enhance their bonding reliability and achieve efficient electrical actuation for SMP matrix. Nafion/silica nanofibers were electrospun onto surfaces of the carbon fiber mat to prevent electrically resistive heat dissipation. The combination of electrically/thermally conductive CNTs and thermally resistive nafion/silica nanofibers results in improvement for both electrically induced shape recovery and actuation efficiency in the SMP nanocomposite.

Effects of dopants on structural stability of monoclinic WO 3 were studied using density functional theory. Transformation from monoclinic to cubic crystal structures was obtained by gradually increasing doping concentrations of both rhenium (Re) and electrons inside the monoclinic WO 3 , whereas a large distortion of WO 6 octahedra was observed by gradually increasing doping concentrations of both niobium (Nb) and holes inside the monoclinic WO 3 . It was verified that Re x W 1-x O 3 has a cubic structure if x is larger than 0.375, and the transformation from monoclinic to cubic structure is mainly dependent on the occupancy of the W 5 d orbital. The elastic characteristics of the Re x W 1-x O 3 decrease with the increase of the content of Re in the range of 0.375 ≤ x ≤ 0.875.

The effect of the transfer rate of signal molecules on coupled chemical oscillators arranged on a two-dimensional plane was systematically investigated in this paper. A microreactor equipped with a surface acoustic wave (SAW) mixer was applied to adjust the transfer rate of the signal molecules in the microreactor. The SAW mixer with adjustable input powers provided a simple means to generate different mixing rates in the microreactor. A robust synchronization of the oscillators was found at an input radio frequency power of 20 dBm, with which the chemical waves were initiated at a fixed site of the oscillator system. With increasing input power, the frequency of the chemical waves was increased, which agreed well with the prediction given by the time-delayed phase oscillator model. Results from the finite element simulation agreed well with the experimental results.

In wireless communication an orthogonal frequency division multiplexing (OFDM) system is efficiently used in recent years. The OFDM method in wireless channels can create deep fades, as a result of multipath dispersive spreading. Thus, a channel state information is essential when coherent detection is involved in OFDM system. Therefore, in many coherent communication systems, a good channel estimation method is necessary for OFDM receiver design. And semi-blind channel estimation is one of these good channel estimation methods. Conventionally, a semi-blind channel estimation uses least square (LS) technique. In our paper, we applied the scaled least square (SLS) to enhance the performance of the semi-blind channel estimator. The SLS requires less knowledge of the channel second-order statistics and has improved performance than the LS technique. Simulation results show that the proposed SLS semi-blind channel estimation method enhances the performance reasonably than conventional semi-blind channel estimation.

In this study, we report hierarchical TiO2 sphere–sulfur frameworks assisted with graphene as a cathode material for high performance lithium–sulfur batteries. With this strategy, the volume expansion and aggregation of sulfur nanoparticles can be effectively mitigated, thus enabling high sulfur utilization and improving the specific capacity and cycling stability of the electrode. Modification of the TiO2–S nanocomposites with graphene can trap the polysulfides via chemisorption and increase the electronic connection among various components. The graphene-assisted TiO2–S composite electrodes exhibit high specific capacity of 660 mA h g−1 at 5C with a capacity loss of only 0.04% per cycle in the prolonged charge–discharge processes at 1C.

In this research work, for the first time, we introduced amino-substituted perylene diimide derivative (N-PDI) as an alternative electron transport layer (ETL) to replace the commonly used TiO2 in planar heterojunction perovskite solar cells. Two types of device structures i.e., glass/FTO/N-PDI/CH3NH3PbI3-xClx/spiro-MeOTAD/Au, and polyethylene terephthalate (PET)/ITO/N-PDI/CH3NH3PbI3-xClx/spiro-MeOTAD/Au, were fabricated on both rigid and flexible substrates using room-temperature solution processing technique. Based on the proposed device structures, the power conversion efficiency (PCE) of 17.66% was obtained based on glass/FTO rigid substrates, and a PCE of 14.32% was achieved based on PET/ITO flexible substrates. Results revealed that the terminal amino group in N-PDI resulting in the enhanced wetting capability of surfaces to perovskite, and the lower the surface work function of FTO substrate as well as passivate the surface trap states of perovskite films. Our results confirm that small molecule semiconductor N-PDI can serve as an effective electron-transport material for achieving high-performance perovskite solar cells and draw molecular design guidelines for electron-selective contacts with perovskite.

Polydopamine (PDA) is applied to natural rubber (NR)/clay nanocomposites through a facile dip-coating approach, which is inspired by the mussel adhesion proteins. This novel modification of clay perfectly captures the interfacial tailoring reinforcement principles for rubber/filler compounds. The hydrophilic PDA coating assists clay platelets to disperse uniformly in aqueous NR latex with respect to TEM observations. Furthermore, PDA modified montmorillonite (PDA-MMT) interacts with NR chains by robust hydrogen-bonding adhesion, which serves as an efficient physical cross-linker demonstrated with transverse magnetization decay analyses. The expectable enhancements are directly visualized in strengthened tensile properties with 46% increasement of tensile strength by adding 6 phr PDA-MMT and only 18% increasement without PDA modification. Besides, the Eα→0 values of NR based composites follow such sequence: NR/MMT < NR < NR/PDA-MMT. Synthetic substitute of natural melanin as PDA is, PDA-MMT layers remarkably stabilize the NR matrix via radical-scavenging pathway during heat-treatment.

Surface acoustic wave and chemiresistor based gas sensors integrated with a sensing layer of sol-gel CuO-Al2O3 composite film were fabricated and their performance and mechanisms for H2S sensing were characterized and compared. In the composite film, CuO nanoparticles provide active sites for adsorption and reaction of H2S molecules while Al2O3 nanoparticles help to form a uniform and mesoporous film structure, both of which enhance the sensitivity of the sensors by providing numerous active CuO surfaces. Through the comparative studies, the SAW based H2S sensor operated at room temperature showed a lower detection limit, higher sensitivity, better linearity and good selectivity to H2S gas with its concentration ranging from 5 ppb to 100 ppm, compared with those of the chemiresistor sensor, which are mainly attributed to the effective mass sensing properties of the SAW sensor, because a minor change in the mass of the film caused by adsorbed H2S molecules would lead to a significant and monotonous change of the resonant frequency of the SAW devices.

Gallium nitride (GaN) is a compound semiconductor which shows advantages in new functionalities and applications due to its piezoelectric, optoelectronic, and piezo-resistive properties. This study develops a thin film GaN-based acoustic tweezer (GaNAT) using surface acoustic waves (SAWs) and demonstrates its acoustofluidic ability to pattern and manipulate microparticles. Although the piezoelectric performance of the GaNAT is compromised compared with conventional lithium niobate-based SAW devices, the inherited properties of GaN allow higher input powers and superior thermal stability. This study shows for the first time that thin film GaN is suitable for the fabrication of the acoustofluidic devices to manipulate microparticles with excellent performance. Numerical modelling of the acoustic pressure fields and the trajectories of mixtures of microparticles driven by the GaNAT was performed and the results were verified from the experimental studies using samples of polystyrene microspheres. The work has proved the robustness of thin film GaN as a candidate material to develop high-power acoustic tweezers, with the potential of monolithical integration with electronics to offer diverse microsystem applications.

Miscible polymer blends offer great designability on shape memory effect (SME) with adjustable mechanical properties and stimuli-responsiveness, by simply changing the constituent compositions. However, the thermodynamics understanding behind those SMEs on miscible polymer blends are yet to be explored. This paper describes an approach to achieve highly designable SMEs with adjustable glass transition temperature (Tg) and width of glass transition zone by dynamically coordinating components in miscible blends. An extended domain size model was formulated based on the Adam-Gibbs theory and Gaussian distribution theory to study the synergistic coordination of component heterogeneities on conformational entropy, glass transition and relaxation behavior of the miscible blend. The effectiveness of model was demonstrated by applying it to predict dual- and triple-SMEs in miscible polymer blends, where the theoretical results show good agreements with the experiment results. We expect this study provide an effective guidance on designing advanced miscible polymer blends based on the SME.

Zirconium pentatelluride (ZrTe5) single crystal has recently received significant attention because of its quantum electronic transport properties and is regarded as a promising candidate for low-temperature thermoelectric cooling and spintronic applications. However, single crystal of ZrTe5 has generally small sizes and can only be produced in small quantities using a complicated process, whereas ZrTe5 polycrystals are easily produced and their properties are easily adjusted. In this study, we focus on the magneto-transport properties at low temperatures of nanocomposites of ZrTe5 produced using both hand-milling and ball-milling processes to investigate the impact of the microstructure. The ball-milled sample shows a low thermal conductivity of 1 W m−1 K−1, which is almost a constant below 300 K. However, due to its small grain sizes, the electron mobility is significantly decreased, thus their thermoelectric performances are not as good as that of the hand-milled sample. Also, below 25 K, the resistivity and the Seebeck coefficient of the ball-milled sample are decreased, which is associated with the energy barrier at their grain boundaries. Due to the larger grain sizes and fewer defects in the hand-milled sample, the external magnetic field shows a significant influence on its thermoelectric properties at low temperatures. These results indicate that polycrystalline ZrTe5 with large grain sizes may exhibit similar quantum properties as those of single crystals.

In this study, titanium matrix composites reinforced by graphene nanoplates (GNPs) were successfully prepared via an in-situ processing strategy. Both TiC nanoparticles and TiC@GNPs strips are in-situ formed at the grain boundaries, and enhance interfacial bonding strength between GNPs and Ti matrix by acting as rivets in the microstructure. The GNPs can be retained in the center of TiC layer, which provides a shielding protection effect for the GNPs. These in-situ formed TiC nanoparticles are linked together to form a discontinuous and three-dimensional (3D) network structure. Due to the formation of 3D network architecture and improved interfacial bonding, the composites show both high strength and good ductility. The significant strengthening effect reinforced by the GNPs can be attributed to a homogeneous distribution of in-situ formed TiC nanoparticles and TiC@GNPs strips, resulting in TiC interface/particle strengthening and excellent interfacial load transfer capability.

In this work, ZnO/Al thin film based flexible acoustic wave devices are demonstrated for their applications in gas flow rate measurements based on the changes in temperature of the devices. A good sensitivity of gas flow rate can be achieved, mainly because thin film based device has a large temperature coefficient of frequency of ~280 ppm/K, owing to the large coefficient of thermal expansion of aluminum foil. A heat source is used to enhance the sensitivity of the thin film device by introducing a temperature offset. The flexible acoustic wave device shows a high sensitivity, fast response times, and a good repeatability for measurement of the flow rate of nitrogen. When the flexible acoustic wave device is bent and attached onto the inner wall of a pipe, the device exhibits good performance for monitoring the gas flow rate, demonstrating its applications of flow rate measurement on curved or randomly shaped surfaces.

Conventional acoustofluidics are restricted to manipulation of droplets on a flat surface, and there is an increasing demand for acoustofluidic devices to be performed at inclined surfaces to facilitate multilayered microfluidic device design and enhance system compactness. This paper reports theoretical and experimental studies of acoustofluidic behaviors (including transportation/pumping and jetting) along inclined surfaces using AlN/Si Rayleigh surface acoustic waves (SAWs). It has been demonstrated that for droplets with volume smaller than 3 μL, they could be efficiently transported on arbitrary inclined surfaces. The gravity effect would play a more and more important role in uphill climbing with the increased inclination angle. When the inclination angle was increased up to 90°, a higher threshold power was needed to transport the droplet and the maximum droplet volume which can be pumped also reached its minimum value. Effects of surface inclination angle on droplet jetting angles could be neglected for their volumes less than 2 μL. Moreover, microfluidic and acoustic heating performances of AlN/Si SAWs were further studied and compared with those conventional ZnO/Si SAWs with the same electrode configurations.

Herein, presents a novel method for the preparation of a Love mode SAW biosensor for the selective detection of carcinoembryonic antigen (CEA) using a transuding polymer nanocomposite thin film based bioreceptor. Graphene oxide (GO) was synthesized using modified Hummers' method and flower-like MoS2 nanoparticles were allowed to grow on the 2D layers GO. The rGO-MoS2 was further used as a host for the synthesis of Au nanoparticles (AuNP) and the final three-component nano-cluster was introduced to the previously synthesized polyamic acid diethyl ethanolamine salt precursor. The uniform mixture was coated on the delay line area of SAW device and conducted thermal imidization process to obtain polyimide nanocomposite. The thickness of the thin film was optimized based on the insertion loss and centre frequency response of the SAW device. Further, anti-CEA self-assembled monolayer (SAM) based bioreceptor was prepared on the polyimide nanocomposite thin film through thioglycolic acid – EDC/NHS immobilization mechanism. The bioreceptor was tested for immunoassay analysis with CEA solution with varying concentrations. The LOD of the biosensor was estimated at 0.084 ng/ml. The real-time applicability of the biosensor was validated using clinical serum sample analysis and the selectivity was evaluated through the affinity test towards other common tumour marking proteins. The biosensor also showed excellent stability, only 10% reduction activity was observed till 80th day of storage. The antigen-antibody adsorption parameters were also evaluated through Langmuir and Freundlich adsorption isotherms.

Cu–Cr–Zr alloys are often subjected to premature failures due to arc erosion at moment of their breakdown. In this paper, a series of simulated high-voltage arc ablation experiments were conducted to systematically investigate arc ablation characteristics of Cu–Cr–Zr alloys, their microstructure evolutions and anti-ablation properties after plastic deformation and microalloying. Results showed that during their arc ablation processes, a halo pattern was firstly formed on the surface under the action of high-temperature arc. This is followed by partial melting and splashing of Cu, forming of uneven and rough surfaces, and finally significant burning of the alloy. The degree of ablation of alloy is aggravated with the increased breakdown voltage. Due to a combined effect of solid solution strengthening, fine grain strengthening and deformation strengthening, the ablation resistance of the micro-alloyed and plastically deformed alloy has been significantly improved. The breakdown field strengths of commercial Cu–Cr–Zr alloy, heat-treated and deformed one, micro-alloyed and heat-treated one are 1.46 × 106 V/m, 1.67 × 106 V/m and 1.90 × 106 V/m, respectively. However, the breakdown strength of alloys after microalloying is unstable. Results show that there are no preferred phases for the first breakdown of arc ablation of Cu–Cr–Zr alloys. The second-phase particles with high-hardness and high-melting temperature hinder the splashing and flow of the molten copper, and inhibit the movement of the cathode spots during the ablation process.

Surface acoustic wave (SAW)-based formaldehyde gas sensor using bi-layer nanofilms of bacterial cellulose (BC) and polyethyleneimine (PEI) was developed on an ST-cut quartz substrate using sol-gel and spin coating processes. BC nanofilms significantly improve the sensitivity of PEI films to formaldehyde gas, and reduces response and recovery times. The BC films have superfine filamentary and fibrous network structures, which provide a large number of attachment sites for the PEI particles. Measurement results obtained using in situ diffuse reflectance Fourier transform infrared spectroscopy showed that the primary amino groups of PEI strongly adsorb formaldehyde molecules through nucleophilic reactions, thus resulting in a negative frequency shift of the SAW sensor due to the mass loading effect. In addition, experimental results showed that the frequency shifts of the SAW devices are determined by thickness of PEI film, concentration of formaldehyde and relative humidity. The PEI/BC sensor coated with three layers of PEI as the sensing layer showed the optimal sensing performance, which had a frequency shift of 35.6 kHz for 10 ppm formaldehyde gas, measured at room temperature and 30 % RH. The sensor also showed good selectivity and stability, with a low limit of detection down to 100 ppb.

A nano-patterning process is reported in this work, which can achieve surface acoustic wave (SAW) devices with an extremely high frequency and a super-high mass sensitivity. An integrated lift-off process with ion beam milling is used to minimize the short-circuiting problem and improve the quality of nanoscale interdigital transducers (IDTs). A specifically designed proximity-effect-correction algorithm is applied to mitigate the proximity effect occurring in the electron-beam lithography process. The IDTs with a period of 160 nm and a finger width of 35 nm are achieved, enabling a frequency of ∼30 GHz on lithium niobate based SAW devices. Both centrosymmetric type and axisymmetric type IDT structures are fabricated, and the results show that the centrosymmetric type tends to excite lower-order Rayleigh waves and the axisymmetric type tends to excite higher-order wave modes. A mass sensitivity of ∼388.2 MHz × mm2/ μ g is demonstrated, which is ∼109 times larger than that of a conventional quartz crystal balance and ∼50 times higher than a conventional SAW device with a wavelength of 4 μm.

Recently, various materials have been explored for their potential applications in homojunction solar cells, which have distinct advantages of good lattice matching at the junction interfaces with minimum recombination losses of carriers. This paper presents an overview of design, technique, and materials in the advanced homojunction solar cells with their latest reported efficiencies. We review the development of homojunction solar cells with two-dimensional (or thin film) based materials, one-dimensional materials (nanowire/nanorods/nanotube), and zero-dimensional (nanodots and quantum dots) based materials. Among the thin film materials explored for homojunction solar cells, we mainly focus this review on CuInS2, InGaN, and InP based homojunction solar cells.

Mucosal-like ZnS nanostructures were synthesized on surface of ST-cut quartz surface acoustic wave (SAW) device using a chemical bath deposition method for ammonia sensing applications. Results showed the SAW device with ZnS mucosal nanostructures achieved a good sensitivity, e.g., with a frequency shift of ~190 Hz upon exposure to 1 ppm ammonia gas. This is mainly attributed to the large specific surface areas and more active sites on the surfaces of the ZnS mucosal nanostructures. Selectivity of the SAW device with the ZnS mucosal nanostructure for ammonia sensing was excellent in comparisons with those for other types of gases such as hydrogen sulfide, hydrogen, nitrogen dioxide, carbon monoxide and ethanol.

We report that cellulose nano-crystals (CNCs) can be used as a sensitive and selective layer in surface acoustic wave (SAW) sensors for in-situ HCl gas detection. CNCs were prepared through directly hydrolysis of cotton fiber and were spin-coated on quartz SAW resonators to form the sensitive layer. The CNCs have been identified to have abundant hydroxyl groups on their surfaces, which can act as the perfect adsorption sites for H2O, which can further act as the active sites for HCl gas adsorption. The absorption of HCl on the CNCs layer, thus leads to an increase of its mass, causing negative responses of the SAW sensors. Ambient humidity and thickness of CNCs layer are found to have significant influences on the responses of the SAW sensor. With an 80-nm-thick CNCs layer, the sensor shows a response of −2 kHz to 1 ppm HCl at 25 °C and relative humidity of 50 % with an excellent selectivity and recovery characteristics.

Correction for ‘Development and characterisation of acoustofluidic devices using detachable electrodes made from PCB’ by Roman Mikhaylov et al., Lab Chip, 2020, 20, 1807–1814, DOI: 10.1039/C9LC01192G.

To prevent early failure of concrete due to infiltration of chloride ions from environment, epoxy resin nanocomposites modified with graphene oxides (GOs) were prepared using a solution blending process and then sprayed onto testing blocks of concrete. Microstructural analysis revealed that the GOs were uniformly dispersed inside the epoxy matrix, and covalent cross-links were formed between the GO and epoxy matrix. Water surface contact angles of concrete coated with the nanocomposites coatings were found to increase firstly but then decrease with the increase of the added GO contents. When the GO content was 0.3 wt%, the contact angle was 96.1°±0.3°, whereas that of pure epoxy resin was 77.5° ±0.3°. At the same GO content, water absorption and chloride diffusion coefficient of the coated concrete are much lower than those of the uncoated samples. The enhancement mechanisms for the chloride ion penetration resistance are attributed to the formation of cross-linking in the composite coating, improved hydrophobicity and shielding effects of the GOs.

Ultra-sensitive H2S sensors operated at room temperature were fabricated using Ag–In2O3 nanorod composites synthesized using sol–hydrothermal method followed by NaBH4 reduction process. TEM proved that the In2O3 was nanorod structures of ~ 110 nm in length and ~ 35 nm in diameter. Ag nanoparticles with diameters from 10 to 15 nm homogeneously decorated on the surfaces of the In2O3 naonorods. XRD and XPS analysis proved that the Ag elements existed as zero-valent metallic silver on the surface of the In2O3 nanorods. Ag nanoparticles could enhance the formation of chemisorbed oxygen species and interactions between H2S molecules and oxygen species due to spillover effect, and the electron transfer between Ag and In2O3 nanorods also enhanced the sensing properties. Therefore, the H2S sensors based on the Ag–In2O3 nanorod composites showed significantly improved sensing performance than those based on the pure In2O3 nanorods. The optimized content of Ag nanoparticles is 13.6 wt%. Operated at room temperature, the H2S sensors made of 13.6 wt% Ag–In2O3 nanorod composites exhibited an ultra-high response of 93719 to 20 ppm H2S and a superior detection limit of 0.005 ppm. The sensor also showed good reversibility, good selectivity, excellent reproducibility and stability for detection of H2S gas.

Nanocomposite powders based on metal-coated graphene were synthesized using an in-situ co-reduction method in order to improve wettability and interfacial bonding between graphene and metal. Graphene oxide (GO) of 2~3 atomic layers was synthesized using the Hummer&rsquo, s method with graphite as a raw material and then dispersed into a dispersing agent solution mixed with N-Methyl pyrrolidone and deionized water to form a homogeneous GO suspension, which was finally added into electroless plating solutions for the reduction process. Copper-coated graphene (Cu@graphene) and nickel-coated graphene (Ni@graphene) were synthesized using this one-step and co-reduction method by mixing salt solutions containing metal ions and GOs into the plating solution. The Cu ions or Ni ions were adsorbed and bonded onto the edges and surfaces of graphene, which was reduced from the GOs using a strong reducing agent of ascorbic acid or sodium borohydride. Crystalline Cu particles with an average size of about 200 nm were formed on the surface of graphene, whereas amorphous or nanocrystalline Ni particles with an average size of 55 nm were formed on the surface of graphene. Distribution of these metal particles on the graphene is homogeneous and highly dispersed, which can effectively improve the sinterability of composite powders. Cohesive energy distribution between graphene and metal interface was analyzed using first-principle calculation method. Formation mechanism of metal coated graphene was identified to be that both the GO and metal ions were simultaneously reduced in the reducing agents and thus a chemical bonding of graphene/metal was formed between the metal particles and graphene.

Ti matrix composites reinforced with 0.6 wt% reduced graphene oxide (rGO) sheets were fabricated using spark plasma sintering (SPS) technology at different sintering temperatures from 800 °C to 1100 °C. Effects of SPS sintering temperature on microstructural evolution and mechanical properties of rGO/Ti composites were studied. Results showed that with an increase in the sintering temperature, the relative density and densification of the composites were improved. The Ti grains were apparently refined owing to the presence of rGO. The optimum sintering temperature was found to be 1000 °C with a duration of 5 min under a pressure of 45 MPa in vacuum, and the structure of rGO was retained. At the same time, the reaction between Ti matrix and rGO at such high sintering temperatures resulted in uniform distribution of micro/nano TiC particle inside the rGO/Ti composites. The sintered rGO/Ti composites exhibited the best mechanical properties at the sintering temperature of 1000 °C, obtaining the values of micro-hardness, ultimate tensile strength, 0.2% yield strength of 224 HV, 535 MPa and 446 MPa, respectively. These are much higher than the composites sintered at the temperature of 900 °C. The fracture mode of the composites was found to change from a predominate trans-granular mode at low sintering temperatures to a ductile fracture mode with quasi-cleavage at higher temperatures, which is consistent with the theoretical calculations.