The relatively poor dynamic response of current flexible strain gauges has prevented their wide adoption in portable electronics. In this work, we present a greatly improved flexible strain gauge, where one strip of Au nanoparticle (NP) monolayer assembled on a polyethylene terephthalate film is utilized as the active unit. The proposed flexible gauge is capable of responding to applied stimuli without detectable hysteresis via electron tunneling between adjacent nanoparticles within the Au NP monolayer. Based on experimental quantification of the time and frequency domain dependence of the electrical resistance of the proposed strain gauge, acoustic vibrations in the frequency range of 1 to 20,000 Hz could be reliably detected. In addition to being used to measure musical tone, audible speech, and creature vocalization, as demonstrated in this study, the ultrafast dynamic response of this flexible strain gauge can be used in a wide range of applications, including miniaturized vibratory sensors, safe entrance guard management systems, and ultrasensitive pressure sensors.

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A flexible strain gauge is an essential component in advanced human-machine interfacing, especially when it comes to many important mobile and biomedical appliances that require the detection of finger touches. In this paper, we report one such strain gauge made from a strip of nanoparticle monolayer onto a flexible substrate. This proposed gauge operates on the observation that there is a linear relationship between electrical conduction and mechanical displacement in a compressive state. Due to its prompt temporal response, the gauge can accurately track various mechanical stimuli running at the frequencies of interest. Experiments have confirmed that the proposed strain gauge has a strain detection limit as low as 9.4 × 10(-5), and its gauge factor can be as large as 70, making this device particularly suitable for sensitive finger touch sensing. Furthermore, negligible degradation in the gauge's output electrical signal is observed even after 9000 loading/unloading cycles.

Material used in flexible devices may experience anisotropic strain with identical magnitude, outputting coherent signals that tend to have a serious impact on device reliability. In this work, the surface topography of the nanoparticles (NPs) is proposed to be a parameter to control the performance of strain gauge based on tunneling behavior. In contrast to anisotropic tunneling in a monolayer of spherical NPs, electron tunneling in a monolayer of urchin-like NPs actually exhibits a nearly isotropic response to strain with different loading orientations. Isotropic tunneling of the urchin-like NPs is caused by the interlocked pikes of these urchin-like NPs in a random manner during external mechanical stimulus. Topography-dependent isotropic tunneling in two dimensions reported here opens a new opportunity to create highly reliable electronics with superior performance.

We study the effects of film thickness on lattice parameters, direct band gap and photovoltaic outputs in the sol-gel derived BiFeO3 thin films. With the change of the film thickness, the great transitions will take place in the preferred orientation and lattice parameters. Furthermore, the photovoltaic outputs are significantly dependent on the film thickness. The results show that the open circuit voltage gradually increases and the short circuit current reciprocally decreases with the increase of film thickness. In particular, we demonstrate for the first time that there are tunable photovoltaic outputs with external electric field polarization switching in the polycrystalline BiFeO3 film, which is critical for the future device applications based on the photovoltaic properties of BiFeO3 films.