Carbon Nanotube Forests Research Articles

Light‐Actuated Anisotropic Microactuators from CNT/Hydrogel Nanocomposites

AbstractOver the past decades, functional hydrogels that respond to a variety of mechanical and chemical stimuli with a volume change of more than 100% have been developed. Despite this impressive behavior, practical applications of conventional hydrogels are limited by the need to transform their isotropic swelling/contraction into useful deformations, as well as their slow response times. Here, these challenges are addressed by combining poly(N‐isopropylacrylamide) (PNIPAM), a widely used temperature‐responsive polymer, with carbon nanotubes (CNTs). To ensure strong PNIPAM−CNT cohesion, the hydrogel is synthesized directly on the CNT surfaces using in situ redox polymerization. The anisotropy of vertically‐aligned CNT forests is used to transform the isotropic (de)swelling of PNIPAM into anisotropic motion. This material combination is particularly attractive because the high optical absorption and heat conductivity of carbon nanotubes converts light irradiation into PNIPAM actuation. A wide variety of CNT‐skeleton microstructures are tested to reveal a range of actuation behaviors. The authors demonstrate fast reversible movement, active switching from low to high light absorption states, lattice shape changes, and good cycling stability.

Enhancement of catalytic activity by addition of chlorine in chemical vapor deposition growth of carbon nanotube forests

In carbon nanotube (CNT) growth, the role of catalytic nanoparticles involves complex processes of feedstock gas decomposition, carbon feedstock transport, and CNT crystal precipitation. We report on the improvement of the catalytic activity by chlorine addition during the CNT forest growth process. The addition of Cl2 enhanced the diffusion rate of carbon in the catalysts, and thus changed the rate-limiting step from iron diffusion in the catalyst to the feedstock gas decomposition on the catalyst surface, leading to a higher growth rate and longer catalyst lifetime. The addition of Cl2 directly affected numerous CNT structural parameters, including the CNT diameter, number of walls, and crystal quality. Furthermore, the Cl2 addition made the CNT forest super-aligned, and it enhanced the dry spin capability of the CNT forests, allowing CNT webs to be continuously drawn from the forests.

Carbon nanotubes/polyethylenimine/glucose oxidase as a non-invasive electrochemical biosensor performs high sensitivity for detecting glucose in saliva

With the aim of improving the life quality for diabetics, we develop a novel electrode for the noninvasive glucose sensor which can determine the glucose levels in saliva. In this work, carbon nanotubes (CNTs) are directly grown on a fluorine-doped tin oxide (FTO) coated glass substrate through chemical vapor deposition, followed by the immobilization of glucose oxidase (GOx) via electrostatic force with the aid of polyethylenimine (PEI). The results confirm that the CNT forest can substantially enhance the charge transferability, and considerable quantities of GOx can be stably immobilized on the rough surface of the electrode because of the networked structure of the CNT forest. With a fast electron transfer rate and short electron transfer distance, both the current difference of the oxygen consumption and enzyme reduction reaction are detected for glucose sensor using the cyclic voltammetry method. The FTO-CNTs/PEI/GOx electrode exhibits the high sensitivity of 63.38 µA/mMcm2 with a wide linear range of 70–700 µM glucose. Furthermore, the FTO-CNTs/PEI/GOx electrode shows good stability as well as high selectivity towards glucose. Finally, the glucose sensing performance of the FTO-CNTs/PEI/GOx electrode is investigated in artificial saliva, which exhibits great sensitivity even under high-viscosity conditions such as artificial saliva, thus, reveals excellent potential for use in practical applications.

On the interplay between a novel iron and iron-carbide atomic layer deposition process, the carbon nanotube growth, and the metal–carbon nanotube coating properties on silica substrates

The fabrication of iron and iron carbide nanoparticles (NPs) for catalytic reactions such as the growth of carbon nanotubes (CNTs) compete with the challenge of covering a wide range of substrates with perfect control of the NP reactivity. We present in this work a novel atomic layer deposition (ALD) process to grow Fe/Fe3C thin films over silica flat substrates. The depositions were carried out exposing the surface through various number of ALD cycles, resulting in Fe-based films with thicknesses ranging from 4 nm to almost 40 nm. After a thermal treatment, the film dewetts into nanoparticles, where the efficiency to grow CNTs will depend on the average size distribution of the nanocatalyst. X-ray diffraction and x-ray photoelectron spectroscopy were used to track the elemental, phase, and shape (film to particles) transformation in order to identify the key features of the nanocatalyst, thereby controlling the CNT nucleation and growth. Thin film thickness of around 5 nm promotes the growth of a dense CNT forest. Furthermore, the metal–CNT films reveal optical properties that are totally tailored by the initial number of ALD cycles.

NiPN/Ni Nanoparticle-Decorated Carbon Nanotube Forest as an Efficient Bifunctional Electrocatalyst for Overall Water Splitting in an Alkaline Electrolyte

NiPN/Ni Nanoparticle-Decorated Carbon Nanotube Forest as an Efficient Bifunctional Electrocatalyst for Overall Water Splitting in an Alkaline Electrolyte

Robust Joule-heating induced transmittance modulation of CNT-sheet-paraffin based smart window

Intelligent window with transmittance change has enabled significant advantages for the smart building. Moreover, such a window with the user’s control to ensure privacy could be obtained by the electrical power. Thanks to the horizontally aligned carbon nanotube (CNT)-sheet-like-film from drawable CNT forest, the CNT-sheet was employed as the Joule-heating induced transparent heater to modulate the transmittance change of paraffin corresponding to its solid to liquid phase change. A facile approach was used to fabricate the sandwich-like smart window cell from the CNT-sheet-paraffin nanocomposite. CNT-sheet from the CNT forest was transferred on the glass substrate and then densified by ethanol. Optical microscopy, scanning electron microscopy (SEM), and infrared (IR) thermal mapping microscopy were carried out to characterize the uniformity of the aligned-CNT-sheet. Significantly, the IR microscopy results showed its homogenous Joule-heating generation without any hot spot. The sandwich cell was made from the CNT-coated substrates and was infiltrated by the melted paraffin in between the substrates. UV–vis spectra with electrical power DC application were used to measure such smart window structures. The results showed the Joule-heating induced uniform heat generator of CNT sheet driving the solid to liquid phase change of paraffin, increasing the transmittance of the intelligent window cell six times in the visible light range. Those results have shown promise for developing the facile smart window, especially for the curve window of vehicles.

Waste-induced pyrolytic carbon nanotube forest as a catalytic host electrode for high-performance aluminum metal anodes

A multivalent aluminum metal anode (AMA) can deliver high specific/volumetric capacities of 2,980 mA h g−1/8,040 mA h cm−3 in an ionic liquid-AlCl3 electrolyte system. However, the large concentration overpotential of AMA induced by its distinctive anion-mediated aluminum metal redox mechanism causes poor rate capabilities and insufficient round-trip efficiencies, limiting its application in rechargeable aluminum batteries (RABs). In this paper, we report a novel strategy of using a carbonaceous catalytic host electrode for high-performance AMA. The targeted carbon electrode should have a high active surface area, strong interaction with ionic charge carriers, well-developed electronic pathways, and macroporous internal structures to accommodate incessantly deposited metals. In this regard, a 3D-structured carbon nanotube forest (CNT-F) was fabricated from waste polyolefins by a simple pyrolysis process as an optimal candidate for the catalytic host electrode. The waste-induced pyrolytic CNT-Fs (WP-CNT-F) had large open surface areas covered with multitudinous intrinsic carbon defects, on which uniform aluminum reduction reactions occurred concurrently, leading to significantly lower concentration overpotentials. In addition, the WP-CNT-Fs exhibited high coulombic efficiencies of 99.4–99.8% over a wide range of current densities (0.5–4.0 mA cm−2) and great cycling stabilities over 1,000 cycles. The superior electrochemical performances of the WP-CNT-F-based AMA were demonstrated in the RAB full cells with a commercial graphite cathode, affording a high specific energy and a high power density of ∼ 132.2 W h kgelectrode-1 and 10,230 W kgelectrode-1, respectively, along with outstanding cycling stabilities over 2,500 cycles.

A self-adhesion criterion for slanted micropillars

Micropillar arrays see use in many fields such as biochemistry, mechanobiology, microfluidics, and micro/nanotechnology via applications like carbon nanotube forests and bioinspired fibrillar adhesives. In these fields, it is commonly desirable to either pack the micropillars as densely as possible or manufacture them to be as long/compliant possible. A barrier to either aim is the phenomenon of self-adhesion, where adjacent micropillars adhere to each other due to Van der Waals forces. In this paper, with self-adhesion as the limiting constraint, we show that longer, more compliant, and/or more densely packed micropillar arrays can be made by slanting the micropillars. From their typical orthogonal configuration, small inclinations produce an increment in micropillar packing and length up to a critical (optimum) angle, beyond which significant slanting produces a reduction in both. For parameter values typical of bioinspired fibrillar adhesives, we estimate that slanted micropillars arranged in a rectangular (triangular) lattice can improve in density by 10% (20%). Slanted micropillars also have increased compliance to loads applied orthogonally to the substrate (we refer to this as ‘orthogonal compliance’), achieved by engaging bending over axial deformation modes. This is particularly useful in fibrillar adhesives for conformation to surface roughness, hence increasing the overall adhesive strength. Our model provides a quantitative tool for the design of slanted micropillar arrays and computes the resulting enhanced array-properties.

Continuous growth of carbon nanotubes on the surface of carbon fibers for enhanced electromagnetic wave absorption properties

As electromagnetic wave (EMW) pollution has become a serious problem in daily life, lightweight, efficient, and mass-produced EMW-absorbing materials are urgently needed. Herein, we developed a novel method for the continuous growth of carbon nanotubes (CNTs) on the surface of polyacrylonitrile (PAN)-based carbon fibers (CFs) by chemical vapor deposition (CVD), which can be applied to mass production. The obtained CF/CNT composites demonstrate outstanding EMW absorption capability, exhibiting a -58.75 dB reflection loss (RL) at a thickness of 1.54 mm. An effective absorption bandwidth (RL < -10 dB) of 4.24 GHz (13.76–18.00 GHz) was achieved at a thickness as low as 1.25 mm, which almost covers the entire Ku band. The excellent EMW-absorbing performance can be attributed to the 3D conductive network constructed by the CNT forest, which effectively promotes multiple reflections and scattering, and further favors dipole and interface polarizations. The mechanical properties of CF, CF-electrochemical anodic oxidation (EAO), and CF/CNT composites were examined, the results showed that the single-filament tensile strength of CF/CNT@0.07 and CF/CNT@0.09 was effectively improved. Our work suggests that the novel CF/CNT composite is a promising material for EMW absorption and strength enhancement owing to its light weight, high strength, low thickness, and good scale-up ability.

Curvature-induced defects on carbon-infiltrated carbon nanotube forests.

A morphological study of the micro-scale defects induced by growing a carbon-infiltrated carbon nanotube (CICNT) forest on concave substrates was conducted. Two CICNT heights (roughly 60 μm and 400 μm) and 4 curvatures (1–4 mm ID) were studied in order to test the geometric limitations. Defects were categorized and quantified by scanning electron microscopy (SEM) of the tops and cross-sections. These deformities were categorized as increased roughness on the top surface, a corrugated (also called wavy or rippled) forest, a curved forest, an inside crevice where the forest separates, and increased forest density on the top surface. Roughness increased nearly 3-fold with the taller forest heights no matter the substrate curvature. Due to the geometric limitations of CICNT height and substrate curvature, all other microscale defects were significantly more present on samples with a small radius of curvature and a tall CICNT forest (p < 0.05). These buckling and warping types of defects were attributed to the increase in circumferential compression as the forest grows as well as the van der Waals interactions between the nanotubes. Because the fabrication process for CICNT involves growing a CNT forest and then infiltrating it with pyrolytic carbon, this work may be applicable to other CNT forests on concave substrates within these forest heights and substrate curvatures.

Flexible and Robust Ultrablack Elastomers with a Dual‐Gradient Design for Broadband and Efficient Light Management

AbstractEngineering flexible broadband light absorbers is crucial to various applications ranging from dark‐level reduction to light harvesting. However, developing solvent free, ultrablack elastomers with high light‐absorption performance and broad absorption band remains a challenge. Here, a class of composite elastomers is fabricated for ultrablack sheet materials. The fabrication process involves a fast photo‐polymerization of acrylates in the presence of gradient deposited polypyrrole (PPy) nanoparticles. The resultant film shows a dual‐gradient structure (i.e., lower side features lower polymer chain density while higher concentration of deposited PPy). Such structure design critically contributes to the formation of bio‐mimetic, hierarchical surface microstructures for efficient light trapping. As a result, lower side of the film exhibits incident‐light‐angle independent, high light absorptivity of 98.43% at 250–2400 nm. Moreover, flexible and mechanically robust absorbers have been demonstrated to offer versatile solar energy related applications, such as sunlight heater, photoactuator, pattern display, and anticounterfeiting. Rather than tedious processing ways generally used in carbon nanotube forests or plasmonic involved ultrablack materials, dual‐gradient design principle is concise and compatible with polymer thin‐film fabrication process, and applicable to various elastic substrates, thus will provide guidance for fabricating various flexible ultrablack sheet materials and devices in a cost‐effective and large scalable way.

Systematic investigation of experimental parameters on nitrogen incorporation into carbon nanotube forests

Nitrogen doping carbon nanotubes can enhance their beneficial physical and chemical properties, rendering them more desirable for various applications, e.g., in electronics. In this study, we used catalytic chemical vapor deposition to synthesize carbon na-no-tube forests on different substrates. The samples were prepared in the presence of compounds containing nitrogen (ammonia, acetonitrile, tripropylamine, and their mixture with acetone) that were introduced into the reactor by bubbling or injection. Of the two different nitrogen introduction methods, the direct injection of a liquid nitrogen precursor promoted the synthesis of bamboo-structured carbon nanotube forests more efficiently. It was found in the injection experiments that the amount of precursor affected the extent of nitrogen incorporation. The presence of various nitrogen species in CNTs was also identified, and the manner in which temperature and the presence of hydrogen both influence nitrogen incorporation into the carbon na-no-tubes was observed.

In-situ growth of bamboo-shaped carbon nanotubes and helical carbon nanofibers on Ti3C2Tx MXene at ultra-low temperature for enhanced electromagnetic wave absorption properties

The potential of two-dimensional layered MXenes in electromagnetic wave (EMW) absorption needs further development. Herein, we carried out the in situ growth of carbon nanotubes (CNTs) on the surface of Ti3C2Tx MXene at ultra-low temperature via chemical vapor deposition. The obtained CNTs exhibited a bamboo-like structure and were accompanied by helical carbon nanofibers. The ultra-low temperature solved the problem that the high temperature required in the traditional CNT growth process would destroy the structural integrity of MXene. The lush CNT forest cross-linked the MXene layers, transforming the two-dimensional layered structure into a three-dimensional conductive network, providing abundant conductive channels for carriers, optimizing the impedance matching of the CNT/MXene hybrid, and resulting in a significant dielectric loss. The as-prepared CNT/MXene hybrid exhibited a minimal reflection loss of −52.56 dB (99.9994% EMW absorption) in the X-band. This work proposes a new idea to enhance the EMW absorption properties of Ti3C2Tx MXene and fabricate high-performance MXene-based EMW absorbers.

Maximizing Energy Density of Nanostructured Electrochemical Capacitors: From Proof of Concept to Reliable Manufacturing

Currently, portable energy storage devices are lacking in the overall performance characteristics needed to meet desired energy and power density performance demands. Furthermore, these performance demands for long-lasting energy storage devices for portable electronics continue to constantly increase. Batteries remain the main source of portable energy storage, but they generally lack the pulsed-power delivery capability required by many applications, as well as have limited cycle life. Thus, improvements in devices that show a high operational cycle life in addition to delivering high energy and power densities are extremely desirable over a wide range of physical sizes, footprints, and power delivery capabilities. Conventional electrostatic capacitors provide some of these benefits compared to batteries, including high power density and extended cycle life, but are lacking in the energy density capability required to replace batteries in many applications.Electrochemically-based double-layer capacitors (EDLCs) or ultracapacitors offer a promising solution to bridging the gap between maintaining the high-power density capability of electrostatic capacitors while providing a path to improving the energy density to be comparable to batteries –significantly broadening their applicability. An EDLC’s power density and energy density are based on the highly reversible surface charge adsorption-based mechanism of energy storage. This provides benefits in terms of high frequency responses as well as providing a route to supply power for longer duration pulses. Additionally, since the stored capacity is based on the surface charge adsorption-based energy storage, it provides an essentially indefinite lifespan as long as the materials do not degrade. However, current EDLC technologies still provide significantly lower energy density than is available from batteries. This energy density gap must be narrowed if the EDLCs are going to make further inroads toward replacing batteries.The capacitance and energy density are driven by the electrode’s available solution-accessible surface area. Thus, our approach to increasing the energy density of electrochemical capacitors is through the development of carbon nanotube-based electrode structures with a precise, highly controlled and ordered nanostructured porosity. To further improve power and energy density, these electrode structures are used in combination with an ionic liquid electrolyte with high voltage window, thus providing an increased operating voltage. While traditional electrode materials are generally comprised of randomly ordered porous structures, we have developed electrodes with an adjustable and highly controlled pore structure that provide very high surface area. These electrodes are produced using a nanotemplated approach that allows for preparation of high surface area aligned and vertically oriented carbon nanotube (CNT)-based electrodes. The templated approach has the added benefit of a achieving a greater areal CNT density than available in traditional carpet-grown CNT forests as well as providing more uniform and controllable CNT outer and inner diameters. The ability to control these dimensions allows for tailoring the electrode geometry for a specific electrolyte.Ionic liquids are becoming increasingly popular in a variety of applications as a result of their unique properties and highly tailorable chemistry. In electrochemical applications, their large voltage stability window, low vapor pressure, excellent thermal stability at temperatures above most organic solvents’ boiling points, and lower temperature conductivity make them an excellent electrolyte choice. Ionic liquids are ideal for use in higher temperature electronics applications, especially in small-scale microelectronics formats where confined spaces make efficient heat removal very difficult. By making use of ionic liquid electrolytes and optimizing the interaction of the electrolyte with our templated CNT electrodes, we have developed an energy storage technology with high-energy density and high-power density.In this talk, we will discuss the challenges and solutions to scaling up the fabrication and testing of reproducible, nanostructured electrodes from 3.14 cm2 or smaller single-sided lab cells to multiple 200 cm2 electrodes on both sides of an aluminum current collector. We will discuss the electrode fabrication scale-up and performance validation from small coin or disc cells tested in a glove box to larger area sealed pouch cells with integration of an optimized ionic liquid electrolyte. We discuss cell fabrication challenges and solutions including verifying the performance of the electrodes as they are scaled up, and the cell fabrication including ensuring the electrode and separator are reliably wetted with the ionic liquid electrolyte. The challenges of optimizing the practical tradeoff of electrode active depth and minimizing the current collector thickness as we move the electrode and overall cell design to a fully packaged cell while maintaining the optimized electrochemical performance characteristics will be discussed.[DISTRIBUTION STATEMENT A. Approved for public release; Distribution is unlimited 412TW-PA-21154]

A simple method to grow millimeters long vertically aligned carbon nanotube forests

Growing long vertically aligned carbon nanotube (VACNT) forests have been achieved so far. However, it requires some additional steps or use of etchants to keep catalyst nanoparticles (NPs) active during VACNT growth in chemical vapor deposition (CVD). Here, we were able to grow a 2.6 mm long VACNT forest with a very simple and cost effective method without using an etchant or other complicated systems. Reducing the catalyst at lower temperature than the growth temperature before VACNT growth provided dense and uniform NPs formation. We observed that NPs, formed after low temperature reduction, did not coarsen at growth temperature at least for 20 min which extends catalyst NP lifetime. Moreover, we find that time varying forest height of VACNT is accurately represented by the Gompertz model of height evolution as a result of low temperature catalyst reduction otherwise it is represented by the monomolecular model. Additionally, use of very low carbon feedstock (10 sccm C2H4) enabled us to prevent carbon coating of active catalyst NPs and ensured a longer NP lifetime. Low carbon use also provided a cost effective and an eco-friendly synthesis of VACNT.

Proposal of Analytical Model of Tensile Property of Untwisted Carbon Nanotube Yarn and Estimation of Tensile Property of Carbon Nanotube

Spinnable carbon nanotubes enable us to produce carbon nanotube assemblies such as yarn and sheet without binder. Untwisted carbon nanotube yarn is one of the assemblies. Untwisted carbon nanotube yarns are composed of unidirectionally aligned carbon nanotubes along with the yarn axis, and thus untwisted carbon nanotube yarns are an ideal preform for composite fabrication with high mechanical performance. In this study, untwisted carbon nanotube yarns with varied densities were prepared by using spinnable carbon nanotube forests, and the tensile properties were examined. Furthermore, an analytical model of tensile properties for untwisted carbon nanotube yarns was proposed based on the shear-lag model. The proposed model can predict the tensile behavior of an untwisted yarn from the tensile modulus and strength of a carbon nanotube, the volume packing fraction of carbon nanotubes for the untwisted yarn, and shear stress exerted on the slipped region of a carbon nanotube. Then, the proposed model was applied to estimate the elastic modulus and tensile strength of a carbon nanotube from the tensile properties of untwisted carbon nanotube yarns. In our case, the estimated tensile elastic modulus of a carbon nanotube was about 200 GPa, and the estimated tensile strength of a carbon nanotube was about 1.9 GPa.

Predicting carbon nanotube forest attributes and mechanical properties using simulated images and deep learning

Understanding and controlling the self-assembly of vertically oriented carbon nanotube (CNT) forests is essential for realizing their potential in myriad applications. The governing process–structure–property mechanisms are poorly understood, and the processing parameter space is far too vast to exhaustively explore experimentally. We overcome these limitations by using a physics-based simulation as a high-throughput virtual laboratory and image-based machine learning to relate CNT forest synthesis attributes to their mechanical performance. Using CNTNet, our image-based deep learning classifier module trained with synthetic imagery, combinations of CNT diameter, density, and population growth rate classes were labeled with an accuracy of >91%. The CNTNet regression module predicted CNT forest stiffness and buckling load properties with a lower root-mean-square error than that of a regression predictor based on CNT physical parameters. These results demonstrate that image-based machine learning trained using only simulated imagery can distinguish subtle CNT forest morphological features to predict physical material properties with high accuracy. CNTNet paves the way to incorporate scanning electron microscope imagery for high-throughput material discovery.

Electrical conductivity across the alumina support layer following carbon nanotube growth

Several electrical devices are formed by growing vertically aligned carbon nanotube (CNT) structures directly on a substrate. In order to attain high aspect ratio CNT forest growths, a support layer for the CNT catalyst, usually alumina, is generally required. In many cases, it has been found that current can pass from a conductive substrate, across the alumina support layer, and through the CNTs with minimal resistance. This is surprising in the cases where alumina is used because alumina has a resistivity of ρ&amp;gt;1014 Ω cm. This paper explores the mechanism responsible for current being able to cross the alumina support layer with minimal resistance following CNT growth by using scanning transmission electron microscopy imaging, energy dispersive x-ray spectroscopy, secondary ion mass spectroscopy, and two-point current-voltage (I-V) measurements. Through these methods, it is determined that exposure to the carbonaceous gas used during the CNT growth process is primarily responsible for this phenomenon.

Rational Construction of Fluffy CNT on Binary FeCo‐NC as High‐Efficiency S Host for Li−S Battery

AbstractDeveloping functional porous carbon materials that are efficient for hosting S and catalytically converting Li polysulfide (LiPS) is of great importance to ease the LiPS shuttle effect, which is the main obstacle against the practical applications of Li−S batteries. Herein, we developed a porous binary FeCo‐NC material functionalized by dual‐site catalytic FeCo species and delicately introduced carbon nanotube (CNT) forest on FeCo‐NC surface. The successful decoration of highly dispersed binary Fe and Co species and heavily introduced N species up to 10 at.%, are critical to improve the quality of host interfaces for high‐efficiency anchoring/conversion of polar LiPS and electrolyte wetting. The fluffy CNT forest on particulate FeCo‐NC can serve as highway for electron conducting and reservoir for confining S/LiPS when physically stacked. Electrochemical measurements indicated binary FeCo‐NC/CNT composite serving as host for a 70 wt.% S loading. It showed enhanced absorption and conversion kinetics of LiPS, and improved rate capability and stability of Li−S half‐cell.

Electronic Skin With Embedded Carbon Nanotubes Proximity Sensors

We present an electronic skin with proximity sensing capabilities. Through a simple and cheap fabrication process, we integrate carbon nanotube forests, which serve as the sensing element, into soft, flexible, and transparent artificial skin. Numerical simulations demonstrate the operational principle of the electronic skin proximity sensors. Experimental characterization reveals excellent repeatability and performance of the electronic skin proximity sensors, which are unaffected by the applied strain. Mounting the electronic skin on experimenter's finger further demonstrates its high performance, variability, and potential to interface with humans. Thus, the cheap and simple fabrication process of this electronic skin, together with its straightforward operation, high reliability, and excellent performance under large deformations and different working conditions, set the stage for the development of a new generation of high-end flexible sensory electronic skin, which is attractive in a wide range of engineering fields, such as autonomous soft robotics, biomedicine, and the Internet of Things.