Ultraviolet (UV) detectors have attracted considerable attention in the past decade due to their extensive applications in the civil and military fields. Wide bandgap semiconductor-based UV detectors can detect UV light effectively, and nanowire structures can greatly improve the sensitivity of sensors with many quantum effects. This review summarizes recent developments in the classification and principles of UV detectors, i.e., photoconductive type, Schottky barrier type, metal-semiconductor-metal (MSM) type, p-n junction type and p-i-n junction type. The current state of the art in wide bandgap semiconductor materials suitable for producing nanowires for use in UV detectors, i.e., metallic oxide, III-nitride and SiC, during the last five years is also summarized. Finally, novel types of UV detectors such as hybrid nanostructure detectors, self-powered detectors and flexible detectors are introduced.

The construction of heterojunctions has been widely applied to improve the gas sensing performance of composites composed of nanostructured metal oxides. This review summarises the recent progress on assembly methods and gas sensing behaviours of sensors based on nanostructured metal oxide heterojunctions. Various methods, including the hydrothermal method, electrospinning and chemical vapour deposition, have been successfully employed to establish metal oxide heterojunctions in the sensing materials. The sensors composed with the built nanostructured heterojunctions were found to show enhanced gas sensing performance with higher sensor responses and shorter response times to the targeted reducing or oxidising gases compare with those of the pure metal oxides. Moreover, the enhanced gas sensing mechanisms of the metal oxide-based heterojunctions to the reducing or oxidising gases are also discussed, with the main emphasis on the important role of the potential barrier on the accumulation layer.

Recently, the nanogenerators which can convert the mechanical energy into electricity by using piezoelectric one-dimensional nanomaterials have exhibited great potential in microscale power supply and sensor systems. In this paper, we provided a comprehensive review of the research progress in the last eight years concerning the piezoelectric nanogenerators with different structures. The fundamental piezoelectric theory and typical piezoelectric materials are firstly reviewed. After that, the working mechanism, modeling, and structure design of piezoelectric nanogenerators were discussed. Then the recent progress of nanogenerators was reviewed in the structure point of views. Finally, we also discussed the potential application and future development of the piezoelectric nanogenerators.

An easy and flexible two-step approach consisting of annealing and subsequently selective pitting corrosion has been developed to prepare porous carbonyl iron flakes (CIFs). Based on the dependence of the morphologies and compositions of the resultant CIFs on the annealing temperature and corrosion time, a formation mechanism for the porous CIFs has been substantiated. In our protocol, the annealing process carried out as the first step in the formation process causes an increase in the grain size and forces the Fe nanocrystals to react with the N impurities in the raw CIFs to generate dispersed Fe₄N domains. These domains subsequently induce selective pitting corrosion, resulting in porous CIFs. As a result of the porous structure, the as-obtained porous CIFs have a specific surface area of 16.92 m² g⁻¹, a saturation magnetization of 140 emu g⁻¹ and a coercivity of 61 Oe. Compared with the raw CIFs, they have a large permeability at high frequencies and a modest permittivity. Consequently, composites containing 20 vol% of the porous CIFs in paraffin wax display a reflection loss ≤−20 dB over a wide frequency range of 2.9–20 GHz when the thickness is varied between 0.9 and 4.5 mm. The results reported here suggest a facile approach to preparing porous nanocrystalline metals. Our results offer a promising strategy for the fabrication of absorbents for thin-thickness and strong-absorption microwave absorbing materials with working frequencies adjustable over a wide range simply by varying the thickness.