Publications

The microstructure of a magnetron sputtered Cr(20 nm)/Sm–Co(20 nm)/Fe(20 nm)/Cr(5 nm) exchange spring magnet was studied using an advanced analytical transmission electron microscopy to better understand the relationship between its chemistry and structure to enhance the energy product. It is shown that the Fe atoms diffuse into the well textured Sm–Co layer, causing a transition from the stoichiometric Sm2Co7 near the Sm–Co/Cr interface to a defected Sm(Co,Fe)5 in the Sm–Co–Fe intermixed area. The graded intermixed layer between Sm–Co and pure Fe gives rise to a compositionally enhanced energy product.

Abstract Triboelectric nanogenerator (TENG) which harvests ubiquitous ambient mechanical energy is a promising power source that can meet the distributed energy demand in the internet of things, wearable electronics, etc. However, the available output of TENG is severely limited by the saturated polarized charge density, small intrinsic capacitance, and large matching impedance. Herein, an effective power management strategy is proposed that flips the free charges on the conductive layer through a controlled LC oscillating circuit composed of the diode, switch, inductor, and the intrinsic capacitor of TENG. In this way, the equivalent charge density reaches a level higher than the saturated polarized charge density. The simulation and experiments show that the limit of energy output can be exceeded under arbitrary load resistance, especially for the low‐impedance common electronics. It is believed that such a general, low‐cost, and highly effective strategy can further broaden the applications of TENG devices across the fields and probably be a new performance evaluation standard for TENG.

No abstract is provided for this article.

AbstractWe systematically investigate the best process conditions that ensure synthesis of different types of one-dimensional cadmium selenide nanostructures with high yield and reproducibility. Through a designed experiment and rigorous statistical analysis of experimental data, models linking the probabilities of obtaining specific morphologies to the process variables are developed. A new iterative algorithm for fitting a multinomial generalized linear model is proposed and used. The optimum process conditions, which maximize the preceding probabilities and make the synthesis process robust (i.e., less sensitive) to variations in process variables around set values, are derived from the fitted models using Monte Carlo simulations.Cadmium selenide has been found to exhibit one-dimensional morphologies of nanowires, nanobelts, and nanosaws, often with the three morphologies being intimately intermingled within the as-deposited material. A slight change in growth condition can result in a totally different morphology. To identify the optimal process conditions that maximize the yield of each type of nanostructure and, at the same time, make the synthesis process robust (i.e., less sensitive) to variations of process variables around set values, a large number of trials were conducted with varying process conditions. Here, the response is a vector whose elements correspond to the number of appearances of different types of nanostructures. The fitted statistical models would enable nanomanufacturers to identify the probability of transition from one nanostructure to another when changes, even tiny ones, are made in one or more process variables. Inferential methods associated with the modeling procedure help in judging the relative impact of the process variables and their interactions on the growth of different nanostructures. Owing to the presence of internal noise, that is, variation around the set value, each predictor variable is a random variable. Using Monte Carlo simulations, the mean and variance of transformed probabilities are expressed as functions of the set points of the predictor variables. The mean is then maximized to find the optimum nominal values of the process variables, with the constraint that the variance is under control.KEY WORDS: Cadmium selenide nanostructuresGeneralized linear modelMultinomialNanotechnologyRobust designStatistical modeling

BaTiO3 thin films were grown epitaxially on (100) MgO substrates by metalorganic chemical vapor deposition (MOCVD) at a temperature of 600 °C. This substrate temperature is the lowest reported temperature for the growth of epitaxial BaTiO3 films by an MOCVD process. The films had a cube–cube orientation relationship with the substrate and were oriented with an a-axis perpendicular to the substrate plane. Nanoscale energy dispersive x-ray spectrometry measurements showed no evidence of interdiffusion between the film and substrate.

No abstract is provided for this article.

Abstract Energy harvesting system based on triboelectric nanogenerators (TENGs) has aroused wide interest from many researchers since it integrates multiple disciplines together including electromagnetics, electric circuit theory, materials science and mechanical engineering. Accurate modeling of a TENG is an indispensable part for revealing the relationships and interactions among physical quantities from different areas. Here, a three-dimensional mathematical model of a contact-mode freestanding TENGs (CF-TENGs) is built with a combination of physical abstraction and geometry configuration, which makes it possible to dynamically analyze the variations of the field and circuit quantities. An accurate Norton’s equivalent circuit model that consists of a current source in parallel with a pure capacitive reactance is proposed. Based on this model the reason for identifying the displacement current as the driving force of TENGs is elucidated, and quantitatively determine the current flowing through the external load resistor and the internal equivalent capacitor. More importantly, a universal dynamic simulation model consisting of a quasi-electrostatic model and a circuit model for the TENG-based energy harvesting system is presented. The presented composite model exhibits an obvious advantage in terms of revealing the dynamic output of TENGs with arbitrary geometry and charge distribution. Finally, based on the characteristics of linearity and time-invariance of the CF-TENG, general optimization strategies are pinpointed, which allow us to accurately predict the maximum output efficiency (close to 82.5%).

With the fast development of the Internet of Things, the requirements of system miniaturization and integration have accelerated research on multifunctional sensors. Based on the triboelectric nanogenerator, a self-powered multifunctional motion sensor (MFMS) is proposed in this work, which is capable of detecting the motion parameters, including direction, speed, and acceleration of linear and rotary motions, simultaneously. The MFMS consists of a triboelectric nanogenerator (TENG) module, a magnetic regulation module, and an acrylic shell. The TENG module is formed by placing a free-standing magnetic disk (MD) on a polytetrafluorethylene (PTFE) plate with six copper electrodes. The movement of the MFMS causes the MD to slide on the PTFE plate and hence excites the electrodes to produce a voltage output. The carefully designed six copper electrodes (an inner circle electrode, an outer circle electrode, and four arc electrodes between them) can distinguish eight directions of movement with the acceleration and determine the rotational speed and direction as well. Besides, the magnetic regulation module is applied here by fixing a magnetic cylinder (MC) in the shell, right under the center of the PTFE plate. Due to the magnetic attraction applied by the MC, the MD will automatically return to the center to prepare for the next round of detection, which makes the proposed sensor much more applicable in practice.

By seamlessly integrating the wearing comfortability of textiles with the biomechanical energy harvesting function of a triboelectric nanogenerator (TENG), an emerging and advanced intelligent textile, i.e., smart textile TENG, is developed with remarkable abilities of autonomous power supply and self-powered sensing, which has great development prospects in the next-generation human-oriented wearable electronics. However, due to inadequate interface contact, insufficient electrification of materials, unavoidable air breakdown effect, output capacitance feature, and special textile structure, there are still several bottlenecks in the road towards the practical application of textile TENGs, including low output, high impedance, low integration, poor working durability, and so on. In this review, on the basis of mastering the existing theory of electricity generation mechanism of TENGs, some prospective strategies for improving the mechanical-to-electrical conversion performance of textile TENGs are systematically summarized and comprehensively discussed, including surface/interface physical treatments, atomic-scale chemical modification, structural optimization design, work environmental control, and integrated energy management. The advantages and disadvantages of each approach in output enhancement are further compared at the end of this review. It is hoped that this review can not only provide useful guidance for the research of textile TENGs to select optimization methods but also accelerate their large-scale practical process.