Reversal in Output Current Direction of 4H-SiC/Cu Tribovoltaic Nanogenerator as Controlled by Relative Humidity.

Tribovoltaic nanogenerators (TVNG) represent a fantastic opportunity for developing low-frequency energy harvesting and self-powered sensing, by exploiting their real-time direct-current (DC) output. Here, a thorough study of the effect of relative humidity (RH) on a TVNG consisting of 4H-SiC (n-type) and metallic copper foil (SM-TVNG) is presented. The SM-TVNG shows a remarkable sensitivity to RH and an abnormal RH dependence. When RH increases from ambient humidity up to 80%, an increasing electrical output is observed. However, when RH rises from 80% to 98%, the signal output not only decreases, but its direction reverses as it crosses 90% RH. This behavior differs greatly from that of a Si-based TVNG, whose output constantly increases with RH. The behavior of the SM-TVNG might result from the competition between the built-in electric field induced by metal-semiconductor contact and a strong triboelectric electric field induced by solid-liquid triboelectrification under high RH. The authors also demonstrated that both SM-TVNG and Si-based TVNG can work effectively as-is even fully submerged in deionized water. This mechanism can affect other devices and be applied to design self-powered sensors working under high RH or underwater.

Enhanced Piezoelectricity of MAPbI3 by the Introduction of MXene and Its Utilization in Boosting High-Performance Photodetectors.

Recently, perovskite photodetectors (PDs) are risen to prominence due to substantial research interest. Beyond merely tweaking the composition of materials, a cutting-edge advancement lies in leveraging the innate piezoelectric polarization properties of perovskites themselves. Here, the investigation shows utilizing Ti3C2Tx, a typical MXene, as an intermediate layer for significantly boosting the piezoelectric property of MAPbI3 thin films. This improvement is primarily attributed to the enhanced polarization of the methylammonium (MA+) groups within MAPbI3, induced by the OH groups present in Ti3C2Tx. A flexible PD based on the MAPbI3/MXene heterostructure is then fabricated. The new device is sensitive to a wide range of wavelengths, displays greatly enhanced performance owing to the piezo-phototronic coupling. Moreover, the device is endowed with a greatly reduced response time, down to millisecond level, through the pyro-phototronic effect. The characterization shows applying a -1.2% compressive strain on the PD leads to a remarkable 102% increase in the common photocurrent, and a 76% increase in the pyro-phototronic current. The present work reveals how the emerging piezo-phototronic and pyro-phototronic effects can be employed to design high-performance flexible perovskite PDs.

Wear-Resisting and Stable 4H-SiC/Cu-Based Tribovoltaic Nanogenerators for Self-Powered Sensing in a Harsh Environment.

Tribovoltaic nanogenerators (TVNGs) are an emerging class of devices for high-entropy energy conversion and mechanical sensing that benefit from their outstanding real-time direct current output characteristics. Here, a self-powered TVNG was fabricated using a small-area 4H-SiC semiconductor wafer and a large-area copper foil. Thus, the cost of materials remains low compared to devices employing large-scale semiconductors. The 4H-SiC/metal-TVNGs (SM-TVNGs) presented here are sensitive to vertical force and sliding velocity, making them appropriate for mechanical sensing. Notably, owing to the modulated bindingtons and surface states, these SM-TVNGs performed well in a harsh environment, namely, in high-temperature and high-humidity conditions. In addition, the SM-TVNGs exhibited an excellent wear-resisting property. On these bases, we designed a self-powered and real-time monitoring device able to estimate the number of staff present in various areas of a deep mining site, a high-temperature and high-humidity environment. This work not only discloses basic physics behind the tribovoltaic effect but also sheds light on possible applications of SM-TVNGs for wear-resisting and stable mechanical sensors in harsh environments.

Triboelectric Leakage-Field-Induced Electroluminescence Based on ZnS:Cu.

The related studies and applications of ZnS-based phosphorescent materials involve various aspects such as lighting, display, sensing, electronic signatures, and confidential information. Here, triboelectrification-induced electroluminescence (TIEL) of the ZnS:Cu due to the triboelectric leakage field is discovered via a gently horizontal sliding between a ZnS:Cu particle-doped polydimethylsiloxane (PDMS) film and a polytetrafluoroethylene (PTFE) or fluorinated ethylene propylene (FEP) film, whose intensity is positively correlated with the temperature, the doping ratio of ZnS:Cu, the pressure, and the frequency. It is also demonstrated that the TIEL mainly occurs inside the bulk film, where the ZnS:Cu phosphor particles can be polarized instantaneously by the leakage electric field of triboelectrification. The polarization will lead to a tilted energy band of the ZnS, resulting in an emitting of green light due to electrons detrapped into the conduction band and recombined with holes in the impurity state. This study not only reveals great fundamental physics for understanding of luminescence induced by a simple sliding between two triboelectric materials but also indicates another way for triboelectrification to be used in advanced optoelectronic devices.

Phosphorus released from sediment of Dianchi Lake and its effect on growth of Microcystis aeruginosa.

Phosphorus stored in lake sediments is an inner nutrient source and can be released into overlying water to exacerbate algal blooms. A simulated microcosm of Dianchi Lake was built to investigate phosphorus release from sediments to overlying water and its effect on the growth of Microcystis aeruginosa. The sediments of Dianchi Lake had a total phosphorus (TP) content of 1.7-1.8 mg g(-1) with Ca bound phosphorus (Ca-P, 50-54 %) and organic phosphorus (Org-P, 28-32 %) as the main fractions. The sediments released 8 % of TP into the overlying water with Fe/Al bound phosphorus (Fe/Al-P, 26 %) and Org-P (65 %) being the main fractions released. The phosphorus concentration of the overlying water increased from 0.14-0.16 to 0.28-0.33 mg L(-1). The biomass density of M. aeruginosa was positively correlated (R (2) = 0.825) with the concentration of orthophosphate, which was the predominant bioavailable phosphorus fraction for algal growth. Org-P can be partly utilized by M. aeruginosa but will not cause a bloom. A good understanding of the geochemical cycles of phosphorus is needed for regulating phosphorus release from sediments and thereby reducing the risk of cyanobacterial blooms.