Publications

Microstructure analysis of a SmCo/Fe exchange spring bilayer

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.

Piezo-Phototronic Effect on Electrochemical Processes and Energy Storage

Grain boundary studies of high-temperature superconducting materials using electron backscatter Kikuchi diffraction

Nanogenerators for blue energy

Boost the Performance of Triboelectric Nanogenerators through Circuit Oscillation

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.

Piezoelectricity of single-atomic-layer MoS2 for energy conversion and piezotronics

No abstract is provided for this article.

Statistical Modeling and Analysis for Robust Synthesis of Nanostructures

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

Piezoelectric Nanogenerators for Self-Powered Nanodevices

A novel approach converts nanoscale mechanical energy into electric energy for self-powering nanodevices.In our own work, we've used piezoelectric zinc-oxide nanowire (ZnO NW) arrays to demonstrate a novel approach for converting nanoscale mechanical energy into electric energy. Here, we review the fundamental principle behind the nanogenerator, present an approach for improving its performance, and discuss some of the challenges we face in pushing this technology to reach its potential.

Epitaxial growth of <i>B</i> <i>a</i> <i>T</i> <i>i</i> <i>O</i>3 thin films at 600 °C by metalorganic chemical vapor deposition

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.

A flexible lithium-ion battery with quasi-solid gel electrolyte for storing pulsed energy generated by triboelectric nanogenerator

Piezo-phototronic and pyro-phototronic effects enhanced broadband photosensing

MRS volume 32 issue 2 Front matter

No abstract is provided for this article.

Self-Powered Sensing in Wearable Electronics─A Paradigm Shift Technology

With the advancements in materials science and micro/nanoengineering, the field of wearable electronics has experienced a rapid growth and significantly impacted and transformed various aspects of daily human life. These devices enable individuals to conveniently access health assessments without visiting hospitals and provide continuous, detailed monitoring to create comprehensive health data sets for physicians to analyze and diagnose. Nonetheless, several challenges continue to hinder the practical application of wearable electronics, such as skin compliance, biocompatibility, stability, and power supply. In this review, we address the power supply issue and examine recent innovative self-powered technologies for wearable electronics. Specifically, we explore self-powered sensors and self-powered systems, the two primary strategies employed in this field. The former emphasizes the integration of nanogenerator devices as sensing units, thereby reducing overall system power consumption, while the latter focuses on utilizing nanogenerator devices as power sources to drive the entire sensing system. Finally, we present the future challenges and perspectives for self-powered wearable electronics.

Three-dimensional mathematical modelling and dynamic analysis of freestanding triboelectric nanogenerators

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%).

Antibiotic Resistance of Helicobacter pylori Strains Isolated From Pediatric Patients in Southwest China

The number of antibiotics that are appropriate for Helicobacter pylori eradication in children is limited. Profiling regional or population-specific antibiotic resistance is essential in guiding the H. pylori eradication treatment in children. The aim of this study was to evaluate the antibiotic resistance in H. pylori strains isolated from children and adolescents in Southwest China. Gastric biopsies from 157 pediatric patients with or without previous H. pylori eradication treatment were collected for H. pylori culture. Susceptibility to amoxicillin (AML), clarithromycin (CLR), metronidazole (MTZ), levofloxacin (LEV), tetracycline (TET), furazolidone (FZD), and rifampicin (RIF) was determined by E-test or a disk diffusion assay. A total of 87 patients from three ethnic groups (Han/Tibetan/Yi) were H. pylori culture positive (55.4%). The overall resistance rates were 55.2% for CLR, 71.3% for MTZ, 60.9% for RIF, and 18.4% for LEV. No isolate was found to be resistant to AML, TET, and FZD. Among the 53 treatment-naïve pediatric patients, primary resistance rates to clarithromycin, metronidazole, levofloxacin, and rifampicin were 45.3, 73.6, 15.1, and 60.4%, respectively. Among the 34 treatment-experienced patients, secondary resistance rates to clarithromycin, metronidazole, levofloxacin, and rifampicin were 70.6, 67.6, 23.5, and 61.8%, respectively. Isolates exhibiting simultaneous resistance to clarithromycin and metronidazole were 28.3 and 52.9% among the treatment-naïve and treatment-experienced patients, respectively. In conclusion, among pediatric patients in Southwest China, resistance rates were high for clarithromycin, metronidazole, levofloxacin, and rifampicin, whereas nil resistance was found to amoxicillin, tetracycline, and furazolidone. Our data suggest that the standard clarithromycin-based triple therapy should be abandoned as empiric therapy, whereas the bismuth quadruple therapy (bismuth/PPI/amoxicillin/tetracycline) would be suitable as first-line empiric treatment regimen for this pediatric population. Tetracycline and furazolidone may be considered for treating refractory H. pylori infections in adolescent patients.

Self-Powered Multifunctional Motion Sensor Enabled by Magnetic-Regulated Triboelectric Nanogenerator

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.

Highly-sensitive and highly-correlative flexible motion sensors based on asymmetric piezotronic effect

Smart Textile Triboelectric Nanogenerators: Prospective Strategies for Improving Electricity Output Performance

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.

Digital Information Storage Mechanical Metamaterials

Abstract Information storage is an important functionality to produce a sense-decide-respond loop in active mechanical metamaterial systems. Here, we propose a new class of mechanical metamaterials with self-powered digital information storage capability. In the so-called mechanically-responsive data storage metamaterials, data is incorporated into a set of self-recovering unit cells that form the material lattice. As the metamaterial structure is loaded, the cells in each layer generate electrical signals that are coded as binary bits to represent the stored data. We show how the proposed designs can serve as sequential access memory data storage devices, where the stored data can be accessed in a deformation sequential order under mechanical stimulations. The stiffness of the metamaterial structure can be rationally designed to create either a flexible/soft or hard data storage system. We further discuss the potential of the proposed technology to create low-cost, non-volatile, and long-term storage solutions for data storage applications.