Abstract
High-speed flexible circuits are required in flexible systems to realize real-time information analysis or to construct wireless communication modules for emerging applications. Here, we ...present scaled carbon nanotube-based thin film transistors (CNT-TFTs) with channel lengths down to 450 nm on 2-μm-thick parylene substrates, achieving state-of-the-art performances of high on-state current (187.6 μA μm
−1
) and large transconductance (123.3 μS μm
−1
). Scaling behavior analyses reveal that the enhanced performance introduced by scaling is attributed to channel resistance reduction while the contact resistance (180 ± 50 kΩ per tube) remains unchanged, which is comparable to that achieved in devices on rigid substrates, indicating great potential in ultimate scaled flexible CNT-TFTs with high performance comparable to their counterparts on rigid substrates where contact resistance dominates the performance. Five-stage flexible ring oscillators are built to benchmark the speed of scaled devices, demonstrating a 281 ps stage delay at a low supply voltage of 2.6 V.
Abstract
Next‐generation shortwave infrared (SWIR) imaging systems generally require a multidimensional information sensing capability (including intensity, wavelength, polarization, phase, etc.), a ...highly integrated photodetector unit, and information processing, allowing for miniaturization and low‐cost production. However, traditional polarized SWIR imaging systems with integrated polarizer arrays as supplementary filters and silicon‐based amplifying circuits are complicated and very expensive. Here, a SWIR polarization‐sensitive photodetector and a monolithic integrated polarization amplification system (MIPAS) based on well‐aligned carbon nanotube (CNT) arrays are demonstrated. The polarization‐sensitive CNT photodetector exhibits anisotropic ratios of ≈5.18 and ≈7.56 at 1800 and 2000 nm wavelengths, respectively, and high‐resolution characteristics that can be utilized to image SWIR laser spots with a radius of less than 10 µm. Furthermore, MIPAS including a CNT field‐effect transistor, a CNT loading resistor, and a polarization‐sensitive CNT photodetector is used to increase the anisotropic ratio of the CNT photodetector. The amplified anisotropic ratio is improved up to 173 and 243 at 1800 and 2000 nm wavelengths, respectively, which is the maximum reported in the SWIR band. Our work demonstrates that the CNT polarization‐sensitive photodetector has the potential for SWIR polarization imaging with a monolithic integrated polarization amplification system.
Epidermal electronic systems that simultaneously provide physiological information acquisition, processing, and storage are in high demand for health care/clinical applications. However, these ...system-level demonstrations using flexible devices are still challenging because of obstacles in device performance, functional module construction, or integration scale. Here, on the basis of carbon nanotubes, we present an epidermal system that incorporates flexible sensors, sensor interface circuits, and an integrated flash memory array to collect physiological information from the human body surface; amplify weak biosignals by high-performance differential amplifiers (voltage gain of 27 decibels, common-mode rejection ratio of >43 decibels, and gain bandwidth product of >22 kilohertz); and store the processed information in the memory array with performance on par with industrial standards (retention time of 10
8
seconds, program/erase voltages of ±2 volts, and endurance of 10
6
cycles). The results shed light on the great application potential of epidermal electronic systems in personalized diagnostic and physiological monitoring.
A CNT-based epidermal system is proposed for physiological signal capturing, processing, and storage.
There is increased interest in ultrathin flexible devices with thicknesses of <1 micrometers due to excellent conformability toward advanced laminated bioelectronics. However, because of limitations ...in materials, device structure, and fabrication methodology, the performance of these ultrathin devices and circuits is insufficient to support higher-level applications. Here, we report high-performance carbon nanotube-based thin-film transistors (TFTs) and differential amplifiers on ultrathin polyimide films with a total thickness of <180 nanometers. A dual-gate structure is introduced to guarantee excellent gate control efficiency and mechanical stability of the ultrathin TFTs, which exhibit high transconductance (8.96 microsiemens per micrometer), high mobility (127 square centimeters per volt per second), and steep subthreshold swing (84 millivolts per decade), and can sustain a bending radius of curvature of <10 micrometers. The differential amplifier achieves the highest gain-bandwidth product (1.83 megahertz) among flexible differential amplifiers, enabling higher-gain amplification of weak signals over an extended frequency spectrum that is demonstrated by amplification of electromyography signals in situ.There is increased interest in ultrathin flexible devices with thicknesses of <1 micrometers due to excellent conformability toward advanced laminated bioelectronics. However, because of limitations in materials, device structure, and fabrication methodology, the performance of these ultrathin devices and circuits is insufficient to support higher-level applications. Here, we report high-performance carbon nanotube-based thin-film transistors (TFTs) and differential amplifiers on ultrathin polyimide films with a total thickness of <180 nanometers. A dual-gate structure is introduced to guarantee excellent gate control efficiency and mechanical stability of the ultrathin TFTs, which exhibit high transconductance (8.96 microsiemens per micrometer), high mobility (127 square centimeters per volt per second), and steep subthreshold swing (84 millivolts per decade), and can sustain a bending radius of curvature of <10 micrometers. The differential amplifier achieves the highest gain-bandwidth product (1.83 megahertz) among flexible differential amplifiers, enabling higher-gain amplification of weak signals over an extended frequency spectrum that is demonstrated by amplification of electromyography signals in situ.
High-speed flexible circuits are required in wireless flexible systems that perform real-time information analysis for emerging applications, such as next-generation wearables for personal health ...care. Scaling the channel length of the transistors into the sub-μm region is one of the keys. Here, we present scaled carbon nanotube-based thin film transistors (CNT-TFTs) with channel lengths down to 450 nm on 2-μm-thick parylene substrates, achieving state-of-the-art performances of high on-state current (187.6 μA μm -1 ) and large transconductance (123.3 μS μm -1 ). Scaling behavior analyses reveal that the performance hike in scaling is attributed to the channel resistance reduction while the contact resistance remains unchanged. Notably, the contact resistance on a single nanotube basis of 180 ± 50 kΩ/tube is comparable to that achieved in rigid ones, indicating huge potential in ultimate scaled flexible CNT-TFTs with high performance comparable to their rigid counterparts where contact resistance dominates the whole device performance. Five-stage flexible ring oscillators are built to benchmark the speed of scaled devices, in which an oscillation frequency of 356 MHz and a stage delay of 281 ps were achieved at a low supply voltage of 2.6 V.
•Cellulose nanocrystals (CNC) were prepared from stem of Asparagus officinalis L. using the sulfuric acid hydrolysis method.•The prepared CNC were used to form food grade oil/water Pickering ...emulsions.•The Asparagus derived CNC can provide a potential material as a new green emulsifier in food applications.
Nano cellulosic materials as promising emulsion stabilizers have attracted great interest in food industry. In this paper, five different sized cellulose nanocrystals (CNC) samples were prepared from stem of Asparagus officinalis L. using the same sulfuric acid hydrolysis conditions but different times (1.5, 2, 2.5, 3.0, and 3.5h). The sizes of these CNC ranged from 178.2 to 261.8nm, with their crystallinity of 72.4–77.2%. The CNC aqueous dispersions showed a typical shear thinning behavior. In a palm oil/water (30/70, v/v) model solution, stable Pickering emulsions were formed with the addition of CNC, and their sizes are in the range of 1–10μm based on the optical and confocal laser scanning microscopy (CLSM) observation. The CNC sample prepared at 3h hydrolysis time, showed a relative efficient emulsion capacity for palm oil droplets, among these CNCs. Other parameters including the CNC, salt, and casein concentrations on the emulsion stability were studied.
•A greater proportion of copper metal foam (CMF) can enhance the heat transfer of paraffin wax and reduce the temperature gradient.•A theoretical model was built to calculate the comprehensive heat ...transfer coefficient of composite PCMs and to determine the intensity change of heat conduction and natural convection of PCMs with different CMF proportions.•Melting time and heat storage capacity of CMF composite PCMs first increased and then decreased with increasing CMF proportion.•Heat storage rate and comprehensive heat transfer coefficient first decreased and then increased with increasing CMF proportion.•Composite PCMs with a CMF proportion of 0.86% exhibit the best heat storage performance.
Phase-change materials (PCMs) can overcome the low energy density and utilization efficiency of solar energy. However, the low thermal conductivity of PCMs significantly affects the thermal efficiency of solar devices; thus, improving the thermal conductivity of PCMs has been the focus of many recent studies. In this study, copper metal foam (CMF) composite PCMs were prepared using paraffin wax and high-pore-density CMF. The effect of the CMF proportion on heat transfer enhancement in the PCM melting process was analyzed using experimental equipment for heat storage visualization. Comprehensive heat transfer coefficients of CMF composite PCMs were obtained. The experimental results showed that as the CMF proportion increased from 0 to 2.15%, the melting time of the CMF composite PCMs and their heat storage capacity first increased and then decreased, whereas the heat storage rate and comprehensive heat transfer coefficient first decreased and then increased. The minimum temperature gradient of 8.09 K was reached when the CMF proportion was 2.15%. More importantly, as the proportion of CMF increased from 0.43 to 2.15%, the proportion of natural convection decreased from 87.90 to 17.69%, and natural convection was the major heat transfer mechanism in the melting process of composite PCMs with a low CMF proportion. The composite PCMs with a CMF proportion of 0.86% has the best heat storage performance when the heat storage capacity and heat storage rate were both considered.
A visual experimental system was built to explore the effect of low-pore-density copper metal foam (CMF) on the heat transfer during paraffin wax (PX) melting, and the effective thermal ...conductivities of composite phase change materials (PCMs) were obtained. A three-dimensional mathematical heat transfer model was established, the microstructure of the CMF was characterized using a high-definition camera, and a physical model of the CMF ball was determined. The melting heat transfer mechanism of the composite PCMs was investigated through the experimental and simulation results, including the temperature distribution, velocity vector, solid-liquid interface, volume fraction, heat transfer mechanism, and heat storage performance. The results show that as the CMF filling ratio increased from 0% to 2.13%, the temperature gradients of the composite PCMs were 86.1, 74.6, 29.2, and 12.6 K, indicating that the filling of CMF effectively alleviates the thermal stratification phenomenon during PX melting. Incorporation of the CMF increased the thermal conductivity of the composite PCMs, but suppressed their natural convection. When the CMF filling ratio was less than 1.28%, natural convection dominated the heat transfer type during PX melting; meanwhile, when the CMF filling ratio was greater than 1.28%, heat conduction was the major heat transfer mechanism. The composite PCMs exhibited great heat storage performance when the CMF filling ratio was 1.68%, and the heat storage rate was 13.25% higher than that of pure PX with the same heat storage capacity. In addition, a theoretical calculation model for predicting the heat transfer mechanism of the composite PCMs was established, and the results show that as the CMF filling ratio increased from 0.43% to 2.15%, the natural convection proportion of heat transfer performance decreased from 82.74% to 13.99% during the melting process.
•The mathematical model can well predict the melting heat transfer process of PCMs.•The filling of CMF leads the paraffin temperature distribution more uniform.•Natural convection is dominated as the CMF filling ratio is less than 1.28%.•The composite PCM has better heat storage performance as CMF filling rate is 1.68%.
In this paper we presented a novel water-based nanoparticle printing ink which can easily be used in producing electric-conductive patterns for the microfabrication and microelectronic devices by ...commercial printers. The well-dispersed nanoparticle ink was composed of metallic colloids which had a gold core less than 5
nm in diameter and were protected by two overlapped layers of polymers, poly(N-vinylpyrrolidone) (PVP) and acrylic resin (AR). The double layer protected gold nanoparticle (AuNP) ink was stable against aggregation for more than 1 year even at gold concentration higher than 20%. Viscosity of as-prepared ink was similar to the commercial inks which could be used in producing continuous and smooth lines 10
μm in width and could be printed on various substrates. It has been found that the obtained gold patterns after sintered at 500
°C for 3
h would convert to electrical conductive ones. The density of metallic particles as well as the conductivity of patterns can be controlled by mediating the number of printing layers and the conditions of sintering process. A 50-layer printed line obtained in our experiment showed apparent conductivity of 8.0
×
10
4
S
cm
−1 which was near to the conductivity value of the bulk gold metal.
In this paper, a single tree-type multiple-head surfactant, bis (amidoethyl-carbamoylethyl) octadecylamine (C18N3), which functions as both the reducing and capping agent in the reaction system, has ...been used to fabricate gold nano- and microplates. The triangle and hexagonal plate, polyhedron, and sphere morphology of the gold nanoparticles could be easily controlled simply by changing the molar ratio of C18N3/HAuCl4. Other influences on the morphology of the gold particles, such as Cl− concentration, temperature and time, were also studied. At standard conditions, 80 °C, and a molar ratio C18N3/HAuCl4 of 6.9 in a 0.5 M KCl aqueous solution, the size of the plates could be manipulated from several tens of nanometers to several micrometers just by changing the C18N3 concentration. A crystalline growth process for the nanoplate formation has been observed in this system. At the initiation of the crystalline formation, the predominant morphology was triangular, followed by a mixture of triangular, hexagonal, and truncated triangular structures as the particle grew larger. Ultimately, the structures became primarily hexagonal. As-prepared gold nano- and microplates greatly enhanced the surface enhanced Raman scattering (SERS) of ascorbic acid molecules compared to that of other gold nanoparticle morphologies.
