Highly Sensitive Capacitive Flexible Pressure Sensor Based on a High-Permittivity MXene Nanocomposite and 3D Network Electrode for Wearable Electronics.

With the fast development of consumer electronic and artificial intelligence equipment, flexible pressure sensors (FPSs) have become a momentous component in the application of wearable electronic, electronic skin, and human-machine interfacing. The capacitive FPS possesses the merits of low energy consumption, high resolution, and fast dynamic response, so it is ideal for mobile and wearable electronics. However, capacitive FPS is vulnerable to electromagnetic interference and parasitic capacitance due to its low sensitivity. Microstructure or porous dielectric materials have been applied to improve the sensitivity of the capacitive FPS, but the high sensitivity is just limited to a narrow region. In this work, we propose a different strategy that incorporates a high-permittivity MXene nanocomposite dielectric with a 3D network electrode (3DNE) to improve the sensing performance of the capacitive FPS. Thanks to the high permittivity of the dielectric layer and hierarchical deformation of the electrode, the fabricated capacitive FPS exhibits a high sensitivity of 10.2 kPa-1 in the low pressure range (0-8.6 kPa) and still maintains a relatively high sensitivity of 3.65 kPa-1 with a near-linear response in a wide pressure range (8.6-100 kPa). In addition, the capacitive FPS can withstand over 20,000 times pressure loads without significant signal damping. Furthermore, the working mechanism of the capacitive FPS is illustrated by the finite element analysis (FEA) method and theoretical calculation. The application potential of the sensor in wearable electronics was demonstrated by human pulse wave monitoring and pressure mapping tests with a 4 × 6 sensor microarray.

Directly writing flexible temperature sensor with graphene nanoribbons for disposable healthcare devices.

Disposable temperature sensors have great advantages in public health security and infectious disease control. However, complicated fabrication processes and poor performances persistently restrict their practical applications. In this paper, a flexible temperature sensor is firstly developed by directly writing or mask spraying commonly-used paper with a highly thermo-sensitive graphene nanoribbon (GNR) ink. The inexpensive, green materials and process endow the GNR sensors with the properties of being low cost, degradable and pollution free. The band gap and the local traps of GNRs, caused by the nanoscale effect and oxygen doping, make the sensor highly thermo-sensitive. The sensor also shows fast response, precise resolution and good bendable properties. As demonstrated, the sensor achieves monitoring of respiratory rate, measurement of body temperature, identification of human touch and constituting a 5 × 5 array for temperature mapping. These results demonstrate that the GNRs sensor is highly promising as an economical disposable device for personal healthcare and disease monitoring.

High-Performance Self-Powered Ultraviolet Photodetector Based on Nano-Porous GaN and CoPc p-n Vertical Heterojunction.

Gallium nitride (GaN) is a superior candidate material for fabricating ultraviolet (UV) photodetectors (PDs) by taking advantage of its attractive wide bandgap (3.4 eV) and stable chemical and physical properties. However, the performance of available GaN-based UV PDs (e.g., in terms of detectivity and sensitivity) still require improvement. Fabricating nanoporous GaN (porous-GaN) structures and constructing organic/inorganic hybrids are two effective ways to improve the performance of PDs. In this study, a novel self-powered UV PD was developed by using p-type cobalt phthalocyanine (CoPc) and n-type porous-GaN (CoPc/porous-GaN) to construct a p-n vertical heterojunction via a thermal vapor deposition method. Under 365 nm 0.009 mWcm-2 light illumination, our device showed a photoresponsivity of 588 mA/W, a detectivity of 4.8 × 1012 Jones, and a linear dynamic range of 79.5 dB, which are better than CoPc- and flat-GaN (CoPc/flat-GaN)-based PDs. The high performance was mainly attributed to the built-in electric field (BEF) generated at the interface of the CoPc film and the nanoporous-GaN, as well as the nanoporous structure of GaN, which allows for a higher absorptivity of light. Furthermore, the device showed excellent stability, as its photoelectrical property and on/off switching behavior remained the same, even after 3 months.

A nanocomposite consisting of ZnO decorated graphene oxide nanoribbons for resistive sensing of NO2 gas at room temperature.

A composite prepared from zinc oxide and graphene oxide nanoribbons (ZnO/GONR) is demonstrated to enable improved room temperature (RT) detection of nitrogen dioxide (NO2). Low-cost hydrothermal synthesis is used to construct the composite. The properties of the resistive sensor, including the sensitivity, response and recovery times, repeatability and selectivity, were investigated in the NO2 concentration range from 1 to 50 ppm at RT. The sensor, typically operated at a voltage of 5 V, exhibits a low detection limit of 1 ppm, a fast response-recovery time, and excellent repeatability which outperforms that of pure ZnO sensors. The sensing mechanism is explained in terms of a redox reaction between NO2 and oxygen anions on the surface of the ZnO/GONR composite. Graphical abstract Schematic representation of the NO2 sensing mechanisms on the surface of the ZnO/GONR composite and overall improved NO2 gas-sensing performance.

Electrodeposition of Pd-Pt Nanocomposites on Porous GaN for Electrochemical Nitrite Sensing.

In recent years, nitrite pollution has become a subject of great concern for human lives, involving a number of fields, such as environment, food industry and biological process. However, the effective detection of nitrite is an instant demand as well as an unprecedented challenge. Here, a novel nitrite sensor was fabricated by electrochemical deposition of palladium and platinum (Pd-Pt) nanocomposites on porous gallium nitride (PGaN). The obtained Pd-Pt/PGaN sensor provides abundant electrocatalytic sites, endowing it with excellent performances for nitrite detection. The sensor also shows a low detection limit of 0.95 µM, superior linear ampere response and high sensitivity (150 µA/mM for 1 to 300 µM and 73 µA/mM for 300 to 3000 µM) for nitrite. In addition, the Pd-Pt/PGaN sensor was applied and evaluated in the determination of nitrite from the real environmental samples. The experimental results demonstrate that the sensor has good reproducibility and long-term stability. It provides a practical way for rapidly and effectively monitoring nitrite content in the practical application.

A ZnO/porous GaN heterojunction and its application as a humidity sensor.

A heterojunction of ZnO/porous GaN (ZnO/PGAN) was fabricated and directly applied to a diode-type humidity sensor. ZnO disks were loaded onto PGAN using a spraying process. The structure and surface morphology of the ZnO/PGAN were characterized using X-ray diffraction and scanning electron microscopy. The heterojunction displayed an excellent diode nature, which was investigated using photoluminescence spectra and I-V characteristics. The excellent transport capability of ZnO/PGAN contributes to enhanced electron transfer, and hence results in high sensitivity and quick response/recovery properties under different relative humidity (RH) levels. In the range of 12-96% RH, a fast sensing response time as low as 7 s and a recovery time of 13 s can be achieved. The simple design of a ZnO/PGAN based humidity sensor highlights its potential in various applications.

Flexible Highly Sensitive Pressure Sensor Based on Ionic Liquid Gel Film.

Flexible, semitransparent ionic liquid gel (ionogels) film was first fabricated by in situ polymerization. The optimized ionogels exhibited excellent mechanical properties, high conductivity, and force sensing characteristics. The multifunctional sensor based on the ionogel film was constructed and provided the high sensitivity of 15.4 kPa-1 and wide detection range sensing from 5 Pa to 5 kPa. Moreover, the aforementioned sensor demonstrated excellent mechanical stability against repeated external deformations (for 3000 cycles under 90° bending). Importantly, the sensor showed advantages in detection of environmental changes to the external stimulus of subtle signals, including a rubber blower blowing the sensor, gently touching, torsion, and bending.

Fabrication of a cobalt phthalocyanine free-standing film on an ionic liquid surface for memory device applications.

The fabrication of a metal phthalocyanine (MPc) film with good transferability and exploitation of its properties are very important for further application. In this study, a continuous free-standing film of CoPc was obtained on an ionic liquid (IL) surface via a physical vapor deposition (PVD) method. The as-obtained film has a ß-phase structure and is constructed with one dimensional CoPc to form a network structure. The morphology of the film could be easily tuned by tunning the flow rate of the carrier gas. More importantly, the device based on these films shows obvious electrical switching and negative differential resistance (NDR) characteristics. The maximum ON/OFF current ratio of two distinctive conductivity states is ∼100 at a reading voltage of +30 V. The conductivity and conductive switching behavior of the NW constructed device are better than the device constructed with NRs. The NDR effect and electrical switching conduction mechanism can be explained by the charge trap elements of the CoII/CoI redox couples. The above results open up the possibility of CoPc as a memory medium for information storage and logic circuits applications.

Wearable Wide-Range Strain Sensors Based on Ionic Liquids and Monitoring of Human Activities.

Wearable sensors for detection of human activities have encouraged the development of highly elastic sensors. In particular, to capture subtle and large-scale body motion, stretchable and wide-range strain sensors are highly desired, but still a challenge. Herein, a highly stretchable and transparent stain sensor based on ionic liquids and elastic polymer has been developed. The as-obtained sensor exhibits impressive stretchability with wide-range strain (from 0.1% to 400%), good bending properties and high sensitivity, whose gauge factor can reach 7.9. Importantly, the sensors show excellent biological compatibility and succeed in monitoring the diverse human activities ranging from the complex large-scale multidimensional motions to subtle signals, including wrist, finger and elbow joint bending, finger touch, breath, speech, swallow behavior and pulse wave.

Direct physical vapor deposition and flexible photoelectrical properties of large-area free-standing films of metal octaethylporphyrin on ionic liquid surface.

Free-standing films of metal octaethylporphyrins (MOEPs) were prepared for the first time by a physical vapor deposition on surface of an ionic liquid (IL). Different from those on solid surfaces, the as-obtained films were very compact and with plannar structure. The monitoring of time-dependent process indicated that the high surface energy of IL and the strong π…π interaction between MOEP molecules played key roles in forming such films. Furthermore, the as-obtained film showed good transferability, which made it possible to be easily transferred to any substrates for further device application. More importantly, the prototype photodetectors based on free-standing films of MOEP showed ultra flexibility, mechanical stability, and durability.

Electrosynthesis of bismuth nanodendrites/gallium nitride electrode for non-enzymatic hydrogen peroxide detection.

Bismuth nanodendrites (BiNDs) were electrodeposited on planar gallium nitride (GaN) electrode via a differential pulse voltammetric technique to fabricate the non-enzymatic hydrogen peroxide (H2O2) sensor. SEM images revealed that the as-obtained BiNDs had numerous dendrite sub-branches, whose diameters ranged from 136 to 152nm. The BiNDs/GaN electrode showed linear amperometric responses for H2O2 in the concentration range from 10µM to 1mM with the sensitivity of 60.0µAmM-1cm-2. Another linear range was from 1 to 10mM with the sensitivity of 23.3µAmM-1cm-2. The limit of detection (LOD) was 5µM with the signal-to-noise ratio of 3. The applicability of the sensor was investigated to the H2O2 detection in real samples such as fetal bovine serum and milk, and the sensor exhibited excellent anti-interference capacity. The achieved results indicate that the as-prepared BiNDs/GaN sensor with good reproducibility and long-term stability was promising for detecting H2O2 in practical environments.

Porous GaN electrode for anodic stripping voltammetry of silver(I).

Here we demonstrate porous GaN electrode can be applied for trace Ag(I) detection. Compared to traditional planar electrodes, porous GaN electrode can detect lower concentration of Ag(I) as it possesses more deposition sites (crystal defects) and larger surface area. Under the optimum conditions, porous GaN electrode shows a linear voltammetric response in the Ag(I) concentration range from 1 to 100ppb with the detection limit of 0.5ppb. Such an unmodified, high-porosity and chemically stable electrode is promising to operate in real samples.

Correction: Large-size nanosheets of 9,10-bis(phenylethynyl)anthracene with high photoresponse and light emission anisotropy.

Correction for 'Large-size nanosheets of 9,10-bis(phenylethynyl)anthracene with high photoresponse and light emission anisotropy' by Juan-Ye Wang et al., Phys. Chem. Chem. Phys., 2016, DOI: 10.1039/c5cp05507e.

Electrochemical fabrication and interfacial charge-transfer process of Ni/GaN(0001) electrodes.

The electrodeposition of Ni on single-crystal n-GaN(0001) film from acetate solution was investigated using scanning electron microscopy, X-ray diffraction, energy dispersive X-ray analysis, atomic force microscopy, and electrochemical techniques. The as-deposited Ni/n-GaN(0001) had a flat band potential of Ufb = -1.0 V vs. Ag/AgCl, which was much lower than that of bare GaN(0001). That is, a more feasible charge-transfer process occurred at the Ni/n-Ga(0001) interface. On the basis of a Tafel plot, an exchange current density of ∼1.66 × 10(-4) mA cm(-2) was calculated. The nuclei density increased when the applied potential was varied from -0.9 V to -1.2 V and, eventually the whole substrate was covered. In addition, the current transient measurements revealed that the Ni deposition process followed instantaneous nucleation in 5 mM Ni(CH3COO)2 + 0.5 M H3BO3.

The facile synthesis and optical waveguide properties of single-crystal 1,2,3,4,5-pentaphenyl-1,3-cyclopentadiene microrods.

Single-crystalline 1,2,3,4,5-pentaphenyl-1,3-cyclopentadiene (PPCP) microrods were prepared by a facile solution process. The PPCP microrods with smooth surfaces could absorb excitation light and propagate the photoluminescence (PL) emission. They showed excellent properties in the low optical loss of a single rod and feasible transfer between neighboring rods. Moreover, PPCP displayed typical aggregation-induced emission enhancement (AIEE) characteristics in the solution state.

Highly sensitive broadband flexible photodetectors based on a blend film with zinc octaethylporphyrin long nanowires embedded in an insulating polymer.

Blend films with long nanowires of zinc octaethylporphyrin (ZnOEP) embedded in an insulating polymer of poly(methyl methacrylate) (PMMA) have been successfully fabricated by a one-step spin-coating process. Concerning photoactive blends based on small-molecule semiconductors, this is quite a novel strategy and allows us to greatly reduce the issues related to low device performance, such as phase-separation, poor connectivity of the semiconducting layer, and higher densities of interfacial defects. Intensive studies on the correlation between the film morphology and device performance have revealed that excellent photodetector performance is derived from efficient charge transport and good connectivity observed in highly crystalline, interconnected ZnOEP nanowires embedded in an insulating PMMA matrix. To the best of our knowledge, this is the first demonstration of a blend-film-based organic photodetector, which exhibits high sensitivity, high stability, high I(on)/I(off) ratio, excellent mechanical flexibility, and a broadband responsivity region extending up to 1050 nm. The unique characteristics of facile fabrication, high sensitivity, excellent mechanical stability, and broadband responsivity can make the blend film of ZnOEP and PMMA promising in large-area flexible photodetectors.

Large-size nanosheets of 9,10-bis(phenylethynyl)anthracene with high photoresponse and light emission anisotropy.

Large-size single crystalline nanosheets of 9,10-bis(phenylethynyl)-anthracene were prepared by a facile solution process and were fully characterized. The prototype photodetector was then fabricated on the basis of a single nanosheet and exhibited superior performance with the largest photoresponse ratio up to ca. 10(5). Moreover, the nanosheets show obvious light emission anisotropy.

Preparation and Optical Waveguiding Property of Single-Crystal Organic NPB Microsheets.

2D microstructures of N,N'-diphenyl-N,N'-bis(1-naphthyl)-1,1'-biphenyl-4,4'-di-amine (NPB) have been prepared by a facile solution method and fully characterized. The as-prepared NPB microsheets have well-defined shapes and very smooth surfaces, and are ideal building blocks for 2D optical waveguides. The results indicate that the optic losses within NPB microsheets are closely related to the direction of propagation, and the shape of microsheets can change the direction of waveguiding light. Such 2D optical waveguides may have potential applications in future miniaturized light-based circuits serve as interconnectors different from 1 D optical waveguides.

Investigation of transport properties of coronene·TCNQ cocrystal microrods with coronene microrods and TCNQ microsheets.

Coronene·TCNQ cocrystal microrods, coronene microrods, and TCNQ microsheets were constructed by a drop-casting method. Prototype devices were fabricated and their field-effect-transistor (FET) performances were investigated. It is found that coronene·TCNQ microrods had exhibited an n-type characteristic and showed better FET performances than TCNQ microsheets.

Metal Ions Mediated Morphology and Phase Transformation of Chalcogenide Semiconductor: From CuClSe2 Microribbon to CuSe Nanosheet.

Foreign ions are of significant importance in controlling and modulating the morphology of semiconductor nanocrystals during the colloidal synthesis process. Herein, we demonstrate the potential of foreign metal ions to simultaneously control the morphology and crystal phase of chalcogenide semiconductors. The results indicate that the introduction of Al(3+) ions can induce the structural transformation from monoclinic CuClSe2 microribbons (MRs) to klockmannite CuSe nanosheets (NSs) and the growth of large-sized CuSe NSs. The as-prepared micrometer-sized CuSe NSs exhibit a high-conducting behavior, long-term durability, and environment stability. The novel properties enable CuSe NSs to open up a bright prospect for printable electrical interconnects and flexible electronic devices.