Recently, as applications based on triboelectricity have expanded, understanding the triboelectric charging behavior of various materials has become essential. This study investigates the ...triboelectric charging behaviors of various 2D layered materials, including MoS2, MoSe2, WS2, WSe2, graphene, and graphene oxide in a triboelectric series using the concept of a triboelectric nanogenerator, and confirms the position of 2D materials in the triboelectric series. It is also demonstrated that the results are obviously related to the effective work functions. The charging polarity indicates the similar behavior regardless of the synthetic method and film thickness ranging from a few hundred nanometers (for chemically exfoliated and restacked films) to a few nanometers (for chemical vapor deposited films). Further, the triboelectric charging characteristics could be successfully modified via chemical doping. This study provides new insights to utilize 2D materials in triboelectric devices, allowing thin and flexible device fabrication.
A triboelectric series of 2D layered materials is confirmed using the concept of a triboelectric nanogenerator. The position of 2D materials in the triboelectric series is obviously related to the output signal obtained from the triboelectric nanogenerator and the effective work function. These results provide new insights for realizing 2D‐materials‐based high‐performance energy harvesting and wearable devices.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Wearable and implantable devices require conductive, stretchable and biocompatible materials. However, obtaining composites that simultaneously fulfil these requirements is challenging due to a ...trade-off between conductivity and stretchability. Here, we report on Ag-Au nanocomposites composed of ultralong gold-coated silver nanowires in an elastomeric block-copolymer matrix. Owing to the high aspect ratio and percolation network of the Ag-Au nanowires, the nanocomposites exhibit an optimized conductivity of 41,850 S cm
(maximum of 72,600 S cm
). Phase separation in the Ag-Au nanocomposite during the solvent-drying process generates a microstructure that yields an optimized stretchability of 266% (maximum of 840%). The thick gold sheath deposited on the silver nanowire surface prevents oxidation and silver ion leaching, making the composite biocompatible and highly conductive. Using the nanocomposite, we successfully fabricate wearable and implantable soft bioelectronic devices that can be conformally integrated with human skin and swine heart for continuous electrophysiological recording, and electrical and thermal stimulation.
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The preparation of ferroelectric polymer–metallic nanowire composite nanofiber triboelectric layers is described for use in high‐performance triboelectric nanogenerators (TENGs). The electrospun ...polyvinylidene fluoride (PVDF)–silver nanowire (AgNW) composite and nylon nanofibers are utilized in the TENGs as the top and bottom triboelectric layers, respectively. The electrospinning process facilitates uniaxial stretching of the polymer chains, which enhances the formation of the highly oriented crystalline β‐phase that forms the most polar crystalline phase of PVDF. The addition of AgNWs further promotes the β‐phase crystal formation by introducing electrostatic interactions between the surface charges of the nanowires and the dipoles of the PVDF chains. The extent of β‐phase formation and the resulting variations in the surface charge potential upon the addition of nanowires are systematically analyzed using X‐ray diffraction (XRD) and Kelvin probe force microscopy techniques. The ability of trapping the induced tribocharges increases upon the addition of nanowires to the PVDF matrix. The enhanced surface charge potential and the charge trapping capabilities of the PVDF–AgNW composite nanofibers significantly enhance the TENG output performances. Finally, the mechanical stability of the electrospun nanofibers is dramatically enhanced while maintaining the TENG performances by applying thermal welding near the melting temperature of PVDF.
High‐performance triboelectric nanogenerators (TENG) are successfully demonstrated using electrospun polyvinylidene fluoride (PVDF)–silver nanowire (AgNW) composite nanofibers. It is found that an electrospinning process and the addition of AgNWs to the PVDF promote the effective formation of the polar crystalline β‐phase. The enhanced surface charge potential and charge trapping properties of the PVDF–AgNW composite nanofibers significantly enhance the TENG performances.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
A stretchable polyaniline nanofiber temperature sensor array with an active matrix consisting of single‐walled carbon nanotube thin‐film transistors is demonstrated. The integrated temperature sensor ...array gives mechanical stability under biaxial stretching of 30%, and the resultant spatial temperature mapping does not show any mechanical or electrical degradation.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Stretchable electronics have recently been extensively investigated for the development of highly advanced human‐interactive devices. Here, a highly stretchable and sensitive strain sensor is ...fabricated based on the composite of fragmentized graphene foam (FGF) and polydimethylsiloxane (PDMS). A graphene foam (GF) is disintegrated into 200–300 μm sized fragments while maintaining its 3D structure by using a vortex mixer, forming a percolation network of the FGFs. The strain sensor shows high sensitivity with a gauge factor of 15 to 29, which is much higher compared to the GF/PDMS strain sensor with a gauge factor of 2.2. It is attributed to the great change in the contact resistance between FGFs over the large contact area, when stretched. In addition to the high sensitivity, the FGF/PDMS strain sensor exhibits high stretchability over 70% and high durability over 10 000 stretching‐releasing cycles. When the sensor is attached to the human body, it functions as a health‐monitoring device by detecting various human motions such as the bending of elbows and fingers in addition to the pulse of radial artery. Finally, by using the FGF, PDMS, and μ‐LEDs, a stretchable touch sensor array is fabricated, thus demonstrating its potential application as an artificial skin.
A highly stretchable and sensitive strain sensor based on a composite of fragmentized graphene foam (FGF) and polydimethylsiloxane (PDMS) is fabricated in a facile process. The FGF/PDMS sensor demonstrates high stretchability up to 70% and high durability over 10 000 stretching cycles with gauge factor in the range of 15–29 depending on the maximum strain applied and the FGF content.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Wafer‐scale growth of transition metal dichalcogenides with precise control over the number of layers, and hence the electronic state is an essential technology for expanding the practical ...application of 2D materials. Herein, a new growth method, phase‐transition‐induced growth (PTG), is proposed for the precisely controlled growth of molybdenum disulfide (MoS2) films consisting of one to eleven layers with spatial uniformity on a 2 in. wafer. In this method, an energetically unstable amorphous MoSxOy (a‐MoSxOy) phase is effectively converted to a thermodynamically stable crystalline MoS2 film. The number of MoS2 layers is readily controlled layer‐by‐layer by controlling the amount of Mo atoms in a‐MoSxOy, which is also applicable for the growth of heteroatom‐inserted MoS2. The electronic states of intrinsic and Nb‐inserted MoS2 with one and four layers grown by PTGare are analyzed based on their work functions. The work function of monolayer MoS2 effectively increases with the substitution of Nb for Mo. As the number of layers increases to four, charge screening becomes weaker, dopant ionization becomes easier, and ultimately the work function increases further. Thus, better electronic state modulation is achieved in a thicker layer, and in this respect, PTG has the advantage of enabling precise control over the film thickness.
Phase‐transition‐induced growth is effective for synthesizing layer‐controlled and electronic‐state‐modulated MoS2 films. The energetically unstable amorphous MoSxOy is efficiently converted to a thermodynamically stable crystalline MoS2 film on a wafer scale with excellent uniformity. The number of layers is precisely controlled layer‐by‐layer from one to eleven layers, which is applicable in the growth of both intrinsic and heteroatom‐inserted MoS2.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
This paper proposes a large-signal stabilization method for the dc power system with a constant power load (CPL), which is detrimental to system stability due to its negative incremental resistance ...(NIR). The proposed method utilizes a shunt active damper at the point of common coupling of the dc bus and controls it as a parallel set of a virtual capacitor, virtual inductor, and resistor. The Takagi-Sugeno fuzzy model is employed with the Lyapunov stability theorem to verify the asymptotic stability of the system and to estimate the region of asymptotic stability. Improvements on the dc-bus voltage stability are evaluated based on dc-bus voltage deviation or dc-bus capacitance reduction. The performance of the proposed shunt active damper is verified by simulation and experimental results.
A highly stretchable hybrid nanogenerator has been developed using a micro‐patterned piezoelectric polymer P(VDF‐TrFE), PDMS‐CNT composite, and graphene nanosheets. Mechanical and thermal energies ...are simultaneously harvested from a single cell of the device. The hybrid nanogenerator exhibits high robustness behavior even after 30% stretching and generates very stable piezoelectric and pyroelectric power outputs due to micro‐pattern designing.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Highly stretchable 2D fabrics are prepared by weaving fibers for a fabric-structured triboelectric nanogenerator (FTENG). The fibers mainly consist of Al wires and polydimethylsiloxane (PDMS) tubes ...with a high-aspect-ratio nanotextured surface with vertically aligned nanowires. The fabrics were produced by interlacing the fibers, which was bonded to a waterproof fabric for all-weather use for fabric-structured triboelectric nanogenerator (FTENG). It showed a stable high-output voltage and current of 40 V and 210 μA, corresponding to an instantaneous power output of 4 mW. The FTENG also exhibits high robustness behavior even after 25% stretching, enough for use in smart clothing applications and other wearable electronics. For wearable applications, the nanogenerator was successfully demonstrated in applications of footstep-driven large-scale power mats during walking and power clothing attached to the elbow.
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