Halide perovskites have great potential for use in high‐performance light‐emitting diodes (LEDs) and displays. Here, a perovskite LEDs (PeLEDs) fabricated directly on an elastomer substrate, in which ...every single layer in the device from bottom anode to top cathode is patterned solely using a highly scalable inkjet printing process, is reported. Compared to PeLEDs made using conventional microfabrication processes, the printing process significantly shortens the fabrication time by at least tenfold (from over 5 h to less than 25 min). The all‐printed PeLEDs have a novel 4‐layer structure (bottom electrode, perovskite emissive layer, buffer layer, top electrode) without separate electron or hole transporting layers. For flexible PeLEDs printed directly in ambient conditions, a turn‐on voltage, maximum luminance intensity, and maximum current efficiency of 3.46 V, 10227 cd m−2, and 2.01 cd A−1, respectively, is achieved. The devices also exhibit excellent robustness and stability even when bent to a curvature radius of 2.5 mm. The reported device structure and fabrication processes can enable high‐performance flexible PeLEDs to be manufactured over a larger area at extremely low cost and fast speed, which can facilitate the adoption of the promising PeLED technology in the emerging foldable displays, smart wearables, and many other applications.
Inkjet‐printing approaches are used to fabricate flexible organometallic halide perovskite light‐emitting diodes on elastic substrates from the bottom anode to the top cathode under ambient conditions. The fabrication time is significantly shortened by at least tenfold. The device has a novel simplified 4‐layer structure without conventional electron‐ and hole‐transport‐layer, but still exhibits extremely high performance even under aggressive bending tests.
A stretchable conductor is one of the key components in soft electronics that allows the seamless integration of electronic devices and sensors on elastic substrates. Its unique advantages of ...mechanical flexibility and stretchability have enabled a variety of wearable bioelectronic devices that can conformably adapt to curved skin surfaces for long-term health monitoring applications. Here, we report a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)-based stretchable polymer blend that can be patterned using an inkjet printing process while exhibiting low sheet resistance and accommodating large mechanical deformations. We have systematically studied the effect of various types of polar solvent additives that can help induce phase separation of PEDOT and PSS grains and change the conformation of a PEDOT chain, thereby improving the electrical property of the film by facilitating charge hopping along the percolating PEDOT network. The optimal ink formulation is achieved by adding 5 wt % ethylene glycol into a pristine PEDOT:PSS aqueous solution, which results in a sheet resistance of as low as 58 Ω/□. Elasticity can also be achieved by blending the above solution with the soft polymer poly(ethylene oxide) (PEO). Thin films of PEDOT:PSS/PEO polymer blends patterned by inkjet printing exhibits a low sheet resistance of 84 Ω/□ and can resist up to 50% tensile strain with minimal changes in electrical performance. With its good conductivity and elasticity, we have further demonstrated the use of the polymer blend as stretchable interconnects and stretchable dry electrodes on a thin polydimethylsiloxane (PDMS) substrate for photoplethysmography (PPG) and electrocardiography (ECG) recording applications. This work shows the potential of using a printed stretchable conducting polymer in low-cost wearable sensor patches for smart health applications.
There is an increasing interest in the development of memristive or artificial synaptic devices that emulate the neuronal activities for neuromorphic computing applications. While there have already ...been many reports on artificial synaptic transistors implemented on rigid substrates, the use of flexible devices could potentially enable an even broader range of applications. In this paper, we report artificial synaptic thin-film transistors built on an ultrathin flexible substrate using high carrier mobility semiconducting single-wall carbon nanotubes. The synaptic characteristics of the flexible synaptic transistor including long-term/short-term plasticity, spike-amplitude-dependent plasticity, spike-width-dependent plasticity, paired-pulse facilitation, and spike-time-dependent plasticity have all been systematically characterized. Furthermore, we have demonstrated a flexible neurological electronic skin and its peripheral nerve with a flexible ferroelectret nanogenerator (FENG) serving as the sensory mechanoreceptor that generates action potentials to be processed and transmitted by the artificial synapse. In such neurological electronic skin, the flexible FENG sensor converts the tactile input (magnitude and frequency of force) into presynaptic action potential pulses, which are then passed to the gate of the synaptic transistor to induce change in its postsynaptic current, mimicking the modulation of synaptic weight in a biological synapse. Our neurological electronic skin closely imitates the behavior of actual human skin, and it allows for instantaneous detection of force stimuli and offers biological synapse-like behavior to relay the stimulus signals to the next stage. The flexible sensory skin could potentially be used to interface with skeletal muscle fibers for applications in neuroprosthetic devices.
Soft wearable sensors are essential components for applications such as motion tracking, human–machine interface, and soft robots. However, most of the reported sensors are either specifically ...designed to target an individual stimulus or capable of responding to multiple stimuli (e.g., pressure and strain) but without the necessary selectivity to distinguish those stimuli. Here we report an elastomeric sponge-based sensor that can respond to and distinguish three different kinds of stimuli: pressure, strain, and temperature. The sensor utilizes a porous polydimethylsiloxane (PDMS) sponge fabricated from a sugar cube sacrificial template, which was subsequently coated with a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) conductive polymer through a low-cost dip-coating process. Responses to different types of stimuli can be distinguished by simultaneously recording resistance and capacitance changes. Because pressure, tensile strain, and temperature change result in different trends in resistance and capacitance change, those stimuli can be clearly distinguished from each other by simultaneously measuring the resistance and capacitance of the sensor. We have also studied the effect of the pore size on the sensor performance and have found that the sponge sensor with smaller pores generally offers greater resistance change and better sensitivity. As a proof-of-concept, we have demonstrated the use of the porous sponge sensor on an artificial hand for object detection, gesture recognition, and temperature sensing applications.
Soft pressure sensors may find a wide range of applications in soft robotics, biomedical devices, and smart wearables. Here, an inkjet‐printed resistive pressure sensor that offers high sensitivity ...and can be fabricated using a very simple process is reported. The device is composed of a conductive silver nanoparticle (AgNP) layer directly printed onto a polydimethylsiloxane substrate and encapsulated by a VHB tape. The pressure is measured through change in electrical resistance caused by pressure‐induced strain in the printed AgNP thin film. The influence of substrate stiffness and thickness on the sensitivity and achieved sensors with an optimized configuration that exhibit highly repeatable response with a sensitivity of up to 0.48 kPa−1 is systematically studied. It is further demonstrated that such a printed soft sensor patch is capable of measuring arterial pulse waveforms or detecting acoustic vibrations under various sound pressure levels. With its simple and low‐cost fabrication process and high sensitivity, the inkjet‐printed resistive pressure sensor is promising for future biomedical and smart wearable device applications.
A soft resistive pressure sensor fabricated on elastomer substrate using a very simple printing process is demonstrated. The printed sensor patch offers high sensitivity and can be used in a variety of applications, such as arterial pulse waveform measurement or audio signal recording.
Inhibitory control is a cognitive process that inhibits a response. It is used in everyday activities, such as driving a motorcycle, driving a car and playing a game. The effect of this process can ...be compared to the red traffic light in the real world. In this study, we investigated brain connectivity under human inhibitory control using the phase lag index and inter-trial coherence (ITC). The human brain connectivity gives a more accurate representation of the functional neural network. Results of electroencephalography (EEG), the data sets were generated from twelve healthy subjects during left and right hand inhibitions using the auditory stop-signal task, showed that the inter-trial coherence in delta (1-4 Hz) and theta (4-7 Hz) band powers increased over the frontal and temporal lobe of the brain. These EEG delta and theta band activities neural markers have been related to human inhibition in the frontal lobe. In addition, inter-trial coherence in the delta-theta and alpha (8-12 Hz) band powers increased at the occipital lobe through visual stimulation. Moreover, the highest brain connectivity was observed under inhibitory control in the frontal lobe between F3-F4 channels compared to temporal and occipital lobes. The greater EEG coherence and phase lag index in the frontal lobe is associated with the human response inhibition. These findings revealed new insights to understand the neural network of brain connectivity and underlying mechanisms during human response inhibition.
High entropy alloy nitride coatings (HEAN), showing superior mechanical strength, high oxidation resistance, and thermal stability, have often been used in protective hard coatings field. However, ...the high temperature tribological field of novel HEA nitride films has not yet been well studied. The correlations among tribological properties, compressive residual stress, mechanical properties, and self-lubricating oxide are still limited.
In this research, the novel (AlCrNbSiTiMo)N coatings were fabricated on both Inconel-718 and Si (100) substrate by radio frequency (RF) magnetron sputtering via tuning both substrate bias at 300 °C deposition temperature. The (AlCrNbSiTiMo)N coatings with a specific substrate bias exhibit an outstanding hardness of 34.5±0.8 GPa.
In the wear test at 700 °C, the films deposited at −100 V revealed the lowest wear rate around 1.2 × 10−6 mm3N−1 m−1. With Molybdenum doping, the MoO3 Magnéli phase was observed on the surface at elevated temperature wearing process, and the friction coefficient at high temperature decreased significantly due to a lubricating surface. The coating exhibited the average friction coefficient value of 0.48 in the wear test of 700 °C. The high temperature tribological performance was addressed and related to the mechanical properties, the plastic deformation resistance H3/E2, and the excess residual stress of the films.
This study provides a new design for hard coatings applied to severe wearing conditions. By tuning substrate bias, the (AlCrNbSiTiMo)N coatings exhibit outstanding mechanical and tribological characteristics, which will be a promising candidate for high temperature tribological protective film.
•The high entropy alloy nitride coating (AlCrNbSiTiMo)N revealed favorable hardness of 34.5±0.8 GPa.•The (AlCrNbSiTiMo)N coatings exhibited low friction coefficient of 0.48±0.08 at 700°C owing to the Magnéli phase MoO3.•The optimal wear rate of 1.2×10−1 mm3 N−1m−1 was demonstrated by controlling residual stress via substrate bias tuning.
As the initial stage in the formation of human intelligence, the sensory–memory system plays a critical role for human being to perceive, interact, and evolve with the environment. Electronic ...implementation of such biological sensory–memory system empowers the development of environment-interactive artificial intelligence (AI) that can learn and evolve with diversified external information, which could potentially broaden the application of the AI technology in the field of human–computer interaction. Here, we report a multimodal artificial sensory–memory system consisting of sensors for generating biomimetic visual, auditory, tactile inputs, and flexible carbon nanotube synaptic transistor that possesses synapse-like signal processing and memorizing behaviors. The transduction of physical signals into information-containing, presynaptic action potentials and the synaptic plasticity of the transistor in response to single and long-term action potential excitations have been systematically characterized. The bioreceptor-like sensing and synapse-like memorizing behaviors have also been demonstrated. On the basis of the memory and learning characteristics of the sensory–memory system, the well-known psychological model describing human memory, the “multistore memory” model, and the classical conditioning experiment that demonstrates the associative learning of brain, “Pavlov’s dog’s experiment”, have both been implemented electronically using actual physical input signals as the sources of the stimuli. The biomimetic intelligence demonstrated in this neurological sensory–memory system shows its potential in promoting the advancement in multimodal, user-environment interactive AI.
We demonstrate a polymer-free method that can routinely transfer relatively large-area graphene to any substrate with advanced electrical properties and superior atomic and chemical structures as ...compared to the graphene sheets transferred with conventional polymer-assisted methods. The graphene films that are transferred with polymer-free method show high electrical conductance and excellent optical transmittance. Raman spectroscopy and X-ray/ultraviolet photoelectron spectroscopy also confirm the presence of high quality graphene sheets with little contamination after transfer. Atom-resolved images can be obtained using scanning tunneling microscope on as-transferred graphene sheets without additional cleaning process. The mobility of the polymer-free graphene monolayer is as high as 63 000 cm2 V–1 s–1, which is 50% higher than the similar sample transferred with the conventional method. More importantly, this method allows us to place graphene directly on top of devices made of soft materials, such as organic and polymeric thin films, which widens the applications of graphene in soft electronics.
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