The field emission and resulting breakdown induced damage in the actuation paths of MEMS capacitive switches are investigated. The effect of asperities burning due to Joule heating and the resulting explosive break down are presented. The breakdown gives rise to almost mirror craters formation on the cathode and anode electrodes. A linear relation between crater diameter and the breakdown current is found when breakdown occurs in vacuum. In ambient atmosphere the breakdown leads to large amplitude current oscillations and the formation of extended damage on both electrodes. © 2020 Elsevier Ltd

We develop ZnO/p-Si photodetectors by atomic layer deposition (ALD) of ZnO thin films on laser-microstructured silicon, and we investigate their electrical and optical behavior, demonstrating high sensitivity and broadband operation. Microstructured p-type silicon was obtained by nanosecond laser irradiation in SF6 gas, which results in the formation of quasi-ordered and uniform microspikes on the silicon surface. The irradiated silicon contains sulfur impurities, which extend its absorbance to the near-infrared. A thin film of ZnO was conformally deposited on the microstructured silicon substrates by ALD. Photoluminescence measurements indicate high crystalline quality of the ZnO film after annealing. Current-voltage (I-V) measurements of the ZnO/p-Si heterodiodes in the dark show a nonlinear behavior with unusual high current values in reverse bias. Under illumination photocurrent is observed for reverse bias, even for wavelengths below the silicon bandgap in the case of the laser-microstructured photodetectors. Higher current values are measured for the microstructured photodetectors compared to planar ones. Photoconductivity measurements show enhanced responsivity across the UV-vis-NIR spectral range for the laser-microstructured devices because of their increased surface area and light absorption. © 2020 American Chemical Society.

Photovoltaic devices based on organic semiconductors and organo-metal halide perovskites have not yet reached the theoretically predicted power conversion efficiencies while they still exhibit poor environmental stability. Interfacial engineering using suitable materials has been recognized as an attractive approach to tackle the above issues. We introduce here a zinc porphyrin-triazine-bodipy donor-πbridge-acceptor dye as a universal electron transfer mediator in both organic and perovskite solar cells. Thanks to its "push-pull" character, this dye enhances electron transfer from the absorber layer toward the electron-selective contact, thus improving the device's photocurrent and efficiency. The direct result is more than 10% average power conversion efficiency enhancement in both fullerene-based (from 8.65 to 9.80%) and non-fullerene-based (from 7.71 to 8.73%) organic solar cells as well as in perovskite ones (from 14.56 to 15.67%), proving the universality of our approach. Concurrently, by forming a hydrophobic network on the surface of metal oxide substrates, it improves the nanomorphology of the photoactive overlayer and contributes to efficiency stabilization. The fabricated devices of both kinds preserved more than 85% of their efficiency upon exposure to ambient conditions for more than 600 h without any encapsulation. © 2019 American Chemical Society.

Photonic crystal structuring has emerged as an advanced method to enhance solar light harvesting by metal oxide photocatalysts along with rational compositional modifications of the materials’ properties. In this work, surface functionalization of TiO2 photonic crystals by blue luminescent graphene quantum dots (GQDs), n–π* band at ca. 350 nm, is demonstrated as a facile, environmental benign method to promote photocatalytic activity by the combination of slow photon-assisted light trapping with GQD-TiO2 interfacial electron transfer. TiO2 inverse opal films fabricated by the co-assembly of polymer colloidal spheres with a hydrolyzed titania precursor were post-modified by impregnation in aqueous GQDs suspension without any structural distortion. Photonic band gap engineering by varying the inverse opal macropore size resulted in selective performance enhancement for both salicylic acid photocatalytic degradation and photocurrent generation under UV–VIS and visible light, when red-edge slow photons overlapped with the composite’s absorption edge, whereas stop band reflection was attenuated by the strong UVA absorbance of the GQD-TiO2 photonic films. Photoelectrochemical and photoluminescence measurements indicated that the observed improvement, which surpassed similarly modified benchmark mesoporous P25 TiO2 films, was further assisted by GQDs electron acceptor action and visible light activation to a lesser extent, leading to highly efficient photocatalytic films. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.