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In this work, we monitor in situ the movement of ZnO piezoelectric nanowires by using a conductive atomic force microscope integrated into a scanning electron microscope. This setup allows seeing the bending of the nanowires and simultaneously measuring the currents generated. We conclude that the currents generated not only come from piezoelectric effect, but also from contact potential and triboelectric effect. These contributions have been ignored in all previous reports in this field, meaning that the power conversion efficiency of these devices may have been systematically overestimated. Our study helps to clarify the working mechanism of piezoelectric nanogenerators based on ZnO nanowires.

Two-dimensional laser-induced periodic surface structures with a deep-subwavelength periodicity (80 nm ≈ λ/10) are obtained for the first time on diamond surfaces. The distinctive surface nanotexturing is achieved by employing a single step technique that relies on irradiation with two temporally delayed and cross-polarized femtosecond-laser pulses (100 fs duration, 800 nm wavelength, 1 kHz repetition rate) generated with a Michelson-like interferometer configuration, followed by chemical etching of surface debris. In this Letter, we demonstrate that, if the delay between two consecutive pulses is ≤2 ps, the 2D periodicity of nanostructures can be tuned by controlling the number of pulses irradiating the surface. Under scanning mode, the method is effective in treating uniformly large areas of diamond, so to induce remarkable antireflection properties able to enhance the absorptance in the visible up to 50 times and to pave the route toward the creation of metasurfaces for future diamond-based optoelectronic devices.