Triboelectric nanogenerators (TENGs) are widely applied to self‐powered devices and force sensors. TENGs consist of the electrode‐layer frequently made of high‐cost conductors (Ag, Au, ITO) and the tribo‐layer of rigid negative‐triboelectricity fluoropolymers (PTFE, FEP). The surface morpholoy is studied for enhancing performance. Here, a high‐performance Al/PDMS‐TENG is proposed with a complex morphology of overlapped deep two‐height microneedles (OL‐DTH‐MN) fabricated by the integrated process of low‐cost CO2 laser ablation and PDMS casting for self‐powered devices and high‐sensitivity force/pressure sensors. The high open‐circuit voltage and short‐circuit current of the OL‐DTH‐MN‐TENG are 167 V and 129.3 µA. Also, the sensitivity of the force/pressure sensor of the OL‐DTH‐MN‐TENG is very high, 1.03 V N−1 and about 3.11 V kPa−1, at an area of 30 cm2 that is much higher than the sensitivity of about 0.18–0.414 V N−1 and 0.013–0.29 V kPa−1 of conventional TENG sensors. Meanwhile, the high‐performance OL‐DTH‐MN‐TENG not only exhibits the energy storage capability of charging a 0.1 µF capacitor to 2.75 V at 1.19 s, to maximum 3.22 V, but also activates various self‐powered devices including lighting colorful 226 LEDs connected in series, the “2020‐ME‐NCKU” advertising board, a calculator and a temperature sensor. Numerical simulation is also performed to support the experiments.
Low stress silicon carbide films with good uniformity in thickness and composition were deposited by varying the deposition parameters in a plasma enhanced chemical vapor deposition (PECVD) unit. The effects of deposition parameters on structure, chemical state and stress distribution of these films in the as-deposited state were investigated. The as-deposited films were typically amorphous and under compressive stress. A low compressive film with a stress level of -160 MPa was obtained at low substrate temperature (250°C) under an appropriate deposition pressure of 1100 mTorr. The chemical state and stress distribution were studied as a function of annealing temperatures in the range from 400°C to 650°C. The hydrogenated bonds decreased with the increase in annealing temperatures around 500–600°C, causing the outdiffusion of hydrogen. Owing to the breakage of the hydrogenated bonds, the recombination of unsaturated bonds on silicon and carbon atoms was promoted, enhancing the bond density of the Si–C stretching mode. Meanwhile, the stress could be further reduced to achieve a stress-free film (0.7 MPa) by post deposition annealing and shifting from the compressive region to the tensile region. The stress relaxation was ascribed to the dissociation of the hydrogenated bonds and the incorporation of hydrogen. As a result, Si–C bonds were created, leading to the formation of tensile stress.
This study prepared samples with femtosecond(fs)-laser-induced periodic surface structures (LIPSSs) controlled by laser power (or peak fluence, F0) and overlap ratio (OR) to improve the friction and wear behavior of the SKD 61 tool steel sliding against a hard Si3N4 ceramic counterface in oil lubrications. Pin-on-plate (pin: Si3N4; plate: SKD 61 steel) tribological tests were conducted with the reciprocating motion perpendicular to the laser scanning direction and having an incline angle (40°∼50°) with respect to the LIPSSs. The contact angles (θ) formed on the textured surfaces were measured for an oil lubricant. The (θ)oil results were found to have their correlation with the areal surface roughness (Sa), skewness (Sk), and kurtosis (Ku) of the textured surfaces produced at various F0 and OR values. The mean friction coefficient (μ) and wear loss (W) of the steel specimens in oil lubrications are reduced by decreasing contact angle, (θ)oil. The combined effect of F0 and OR on the (θ)oil and the (θ)oil effect on μ and W are thus linked together, and the correlation provides an efficient and convenient way in the choices of laser operating conditions with the minimum μ and W. The minimum values of μ (=0.0089) and W (=2.124 × 104
μm3) were obtained with OR = 50% and a laser power of 17 mW.
Steel specimens are textured by controlling laser peak fluence F0 and overlap ratio, OR. A 3D fractal model with the characteristic (periodic) lengths, Lx and Ly, and fractal dimensions, Dx and Dy, is introduced to solve the morphologies with the same skewness Sk and kurtosis Ku as that of the textured specimen. The product value LxLy shows its correlation with Sk and is used as a surface pattern parameter with its value proportional to asperity's plateau area. Areal mean surface roughness Sa and LxLy, superior than the conventionally used Sa, Sk, and Ku, become the controlling factors that are more efficient to interpret their role on contact angle (θ)oil formed at textured surfaces with various patterns. Effects of F0 and OR on (θ)oil are efficiently evaluated through the correlations of texturing conditions of laser power and overlap ratio with Sa and LxLy. Adhesive energy Ea((θ)oil) is introduced to establish its connection with tribological parameters.
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