Fabricating AC/DC nanogenerators based on single ZnO nanowires by using a nanomanipulator in a scanning electron microscope

Single zinc oxide nanowires(ZnO NWs)are promising for nanogenerators because of their excellent semiconducting and piezoelectric properties,but characterizing the latter efficiently is challenging.As reported here,an electrical breakdown strategy was used to construct single ZnO NWs with a specific length.With the high operability of a nanomanipulator in a scanning electron microscope,ZnO-NW-based twoprobe and three-probe structures were constructed for fabricating AC/DC nanogenerators,respectively.For a ZnO NW,an AC output of between−15.31 mV and 5.82 mV was achieved,while for a DC nanogenerator,an output of24.3 mV was realized.Also,the three-probe structure’s output method was changed to verify the distribution of piezoelectric charges when a single ZnO NW is bent by a probe,and DC outputs of different amplitudes were achieved.This study provides a low-cost,highly convenient,and operational method for studying the AC/DC output characteristics of single NWs,which is beneficial for the further development of nanogenerators.

Pick-up strategies for and electrical characterization of ZnO nanowires with a SEM-based nanomanipulator

Because of their unique mechanical and electrical properties,zinc oxide(ZnO)nanowires are used widely in microscopic and nanoscopic devices and structures,but characterizing them remains challenging.In this paper,two pick-up strategies are proposed for characterizing the electrical properties of ZnO nanowires using SEM equipped with a nanomanipulator.To pick up nanowires efficiently,direct sampling is compared with electrification fusing,and experiments show that direct sampling is more stable while electrification fusing is more efficient.ZnO nanowires have cut-off properties,and good Schottky contact with the tungsten probes was established.In piezoelectric experiments,the maximum piezoelectric voltage generated by an individual ZnO nanowire was 0.07 V,and its impedance decreased with increasing input signal frequency until it became stable.This work offers a technical reference for the pick-up and construction of nanomaterials and nanogeneration technology.

Analysis of load and adaptability of disc cutters during shield tunneling in soft-hard varied strata

The disc cutters of shield machines exhibit unsatisfactory adaptability and performance during the soft–hard varied strata tunneling process.To analyze the rotation state,cutting performance,and adaptability of disc cutters during shield tunneling in soft–hard varied strata,the Holmquist Johnson Cook and Federal Highway Administration constitutive models are introduced to numerically simulate the failure process of materials on the excavation face and to calculate the load of disc cutters.Additionally,the parameters of the models are modified based on laboratory disc cutter excavation test results.The results of numerical calculation can reflect the load level and the behavior of the disc cutters during operation.The tangential loads of the disc cutters during the cutting of four typical soft-strata excavation face models are numerically calculated,thus providing reference values for the starting torque of the disc cutters.A greater penetration is suggested for soft-strata tunneling to allow the disc cutters to rotate smoothly and continuously as well as to guarantee a better cutting effect.The disc cutters in the center of the cutterhead should be specified with a lower starting torque to prevent uneven wear,rotation stagnation,cutterhead clogging,and other adverse phenomena.

Probabilistic analysis of secant piles with random geometric imperfections

The failure to achieve minimum design overlap between secant piles compromises the ability of a structure to perform as designed,resulting in water leakage or even ground collapse.To establish a more realistic simulation and provide guidelines for designing a safe and cost-effective secant-pile wall,a three-dimensional model of a secant pile,considering the geometric imperfections of the diameter and direction of the borehole,is introduced.An ultrasonic cross-hole test was performed during the construction of secant piles in a launching shaft in Beijing,China.Based on the test results,the statistical characteristics of the pile diameters and orientation parameters were obtained.By taking the pile diameter D,inclination angleβ,and azimuth angleαas random variables,Monte Carlo simulations were performed to discuss the influence of different design parameters on the probability density functions of the overlap of secant piles.The obtained results show that the randomness of the inclination angle and pile diameter can be well described by a normal distribution,whereas the azimuth angle is more consistent with a uniform distribution.The integrity of the secant-pile wall can be overestimated without considering the uncertainty of geometric imperfections.The failure of the secant-pile wall increases substantially with increasing spatial variability in drilling inclination and diameter.A design flowchart for pile spacing under the target safety level is proposed to help engineers design a safe and economical pile wall.