The rapid development of microscaled piezoelectric energy harvesters has provided a simple and highly efficient way for building self-powered sensor systems through harvesting the mechanical energy from the ambient environment. In this work, a self-powered microfluidic sensor that can harvest the mechanical energy of the fluid and simultaneously monitor their characteristics was fabricated by integrating the flexible piezoelectric poly(vinylidene fluoride) (PVDF) nanofibers with the well-designed microfluidic chips. Those devices could generate open-circuit high output voltage up to 1.8 V when a droplet of water is flowing past the suspended PVDF nanofibers and result in their periodical deformations. The impulsive output voltage signal allowed them to be utilized for droplets or bubbles counting in the microfluidic systems. Furthermore, the devices also exhibited self-powered sensing behavior due to the decreased voltage amplitude with increasing input pressure and liquid viscosity. The drop of output voltage could be attributed to the variation of flow condition and velocity of the droplets, leading to the reduced deformation of the piezoelectric PVDF layer and the decrease of the generated piezoelectric potential.

It has been noticed that for ultrashallow ion implanted dopant profiles, the metallurgical junction is not at the same location as the peak of the spreading resistance profile, i.e., the on-bevel junction. This can be attributed to the carrier redistribution effect. Furthermore, the pressure under the spreading resistance probes causes band-gap narrowing of the material under the probes. This pressure-induced band-gap narrowing effect increases the intrinsic carrier concentration of the semiconductor material. An inverse algorithm used to convert spreading resistance profiles into the electrically active dopant profiles, taking both carrier redistribution and band-gap narrowing into account, is presented in this article. Using this algorithm, the depth of the metallurgical junction of a shallow ion implanted p ϩ n profile is determined to be 0.121 m from the surface, whereas the on-bevel junction depth is 0.089 m. The recovered dopant concentration profile agrees very well with that obtained from secondary ion mass sepctrometry. The algorithm is shown to work very well also for an n ϩ p junction.

The research and development of low-powerconsumption and room-temperature hydrogen sensors are of great significance for the safe application of hydrogen energy. Herein, orthorhombic Nb 2 O 5−x nanobelts are prepared through a combined procedure of hydrothermal, ion exchange, and annealing treatment in Ar. The topological transformation process results in the formation of abundant surface defects including chemical defects such as Nb 4+ , oxygen vacancies, and disordered microregions, which lead to the abnormal p-type conducting and hydrogen sensing behavior. Moreover, the orthorhombic Nb 2 O 5−x nanobelts exhibit fast and sensitive room-temperature hydrogen sensing performance, which shows greater advancement than the monoclinic, tetragonal, and hexagonal Nb 2 O 5 one-dimensional (1D) nanostructures. The response time and lowest limit of detection of the as-fabricated room-temperature sensor decrease to 28 s and 3.5 ppm, respectively. The sensor also exhibits a highly selective hydrogen response against CO, CH 4 , ethanol, H 2 S, and NH 3 . The hydrogen response of the Nb 2 O 5−x nanobelts can be attributed to the redox reaction between hydrogen and preadsorbed oxygens. The defective surface structure and the prolonged dimension of the nanobelts give rise to the highly reactive surface and the suppression of the negative nanojunction effect, which greatly improves the sensing performance. The orthorhombic lattice structure can also promote gas adsorption and diffusion behavior due to its specific catalytic and pathway effect. The results of this work can be helpful for the rational design and defect engineering of the Nb 2 O 5 -based 1D nanostructures for room-temperature hydrogen sensing applications.

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