Publications

Abstract Triboelectric nanogenerator (TENG)’s use is constrained by their surface charge density and alternating current output. This study therefore proposes a coupling output method combining charge excitation and phase shift to realize an almost constant high‐performance direct‐current (DC) and DC‐TENG is designed to harvest the energy of flowing water. The output characteristic of the DC‐TENG with or without charge excitation is thoroughly investigated in the experiment. The impact on the effectiveness of phases ( P ) and groups ( G ) is further proven by comparing and quantifying the current wave. The operation capability in a water environment is further demonstrated by the transmitted charge's attenuation of roughly 10.84% after the environment's humidity is increased to 90% RH. According to the findings of the investigation, DC‐TENG with 3P4G can reach almost constant DC with the root mean square value of 29.1 μ A and the crest factor of 1.23. And the 220 μ F capacitor can be charged to 5 V within 63 s and the peak output power of 9.18 mW is obtained. Finally, an experimental platform is established to simulate the water environment and the thermography is steadily powered. This scheme has reference significance to realize high‐performance DC output in the water environment.

Using the piezoelectric polarization charges created atthe metalGaNnanobelt (NB)interfaceunder straintomodulate transport of local charge carriers across the Schottky barrier, the piezotroniceffectisutilizedtoconvertmechanicalstimuliappliedon the wurtzite-structured GaN NB into electronic controlling signals, basedonwhichtheGaNNBstrain-gatedtransistors(SGTs)havebeen fabricated. By further assembling and integrating GaN NB SGTs, universal logic devices such as NOT, AND, OR, NAND, NOR, and XOR gates have been demonstrated for performing mechanicalelec- tricalcoupledpiezotronic logicoperations. Moreover,basicpiezotronic computationsuchasone-bitbinary addition overtheinput mechanical strains with corresponding computation results in an electrical domain by half-adder has been implemented. The strain-gated piezotronic logic devices may find applications in humanmachine interfacing, active flexible/stretchable electronics, MEMS, biomedical diagnosis/therapy, and prosthetics.

Abstract In recent years, tremendous effort is devoted to developing platforms, such as implantable drug delivery systems (IDDSs), with temporally and spatially controlled drug release capabilities and improved adherence. IDDSs have multiple advantages: i) the timing and location of drug delivery can be controlled by patients using specific stimuli (light, sound, electricity, magnetism, etc.). Some intelligent “closed‐loop” IDDS can even realize self‐management without human participation. ii) IDDSs enable continuous and stable delivery of drugs over a long period (months to years) and iii) to administer drugs directly to the lesion, thereby helping reduce dosage and side effects. iv) IDDSs enable personalized drug delivery according to patient needs. The high demand for such systems has prompted scientists to make efforts to develop intelligent IDDS. In this review, several common stimulus‐responsive mechanisms including endogenous (e.g., pH, reactive oxygen species, proteins, etc.) and exogenous stimuli (e.g., light, sound, electricity, magnetism, etc.), are given in detail. Besides, several types of IDDS reported in recent years are reviewed, including various stimulus‐responsive systems based on the above mechanisms, radio frequency‐controlled IDDS, “closed‐loop” IDDS, self‐powered IDDS, etc. Finally, the advantages and disadvantages of various IDDS, bottleneck problems, and possible solutions are analyzed to provide directions for subsequent research.

High density bulk FePt/Fe3Pt nanocomposite magnets have been prepared by high-pressure warm compaction of chemically synthesized FePt and Fe3O4 nanoparticles. It is found that the density increases with the compaction pressure and temperature. Density of the bulk samples up to 95% theoretical value has been obtained while the nanostructured morphology is retained. It is also observed that a high pressure expedites the FePt phase transition from the disordered face-centered-cubic structure to the L10 structure, leading to the phase transition temperature in the compacts one hundred degrees lower than usual. This phase transition in turn facilitates the consolidation of the compacts. Magnetic characterizations showed that interphase exchange coupling is enhanced upon the compaction. Post-annealing of the compacts results in further improved magnetic performance of the compacts owing to interface modification. Energy products up to 16.3 MG Oe of the isotropic bulk nanocomposite magnets have been achieved, which is significantly higher than the theoretical limit for fully dense single-phase FePt magnets.

Energy harvesters based on the tribovoltaic effect that can convert mechanical energy into electricity offer a potential solution for the energy supply of decentralized sensors. However, a substantial disparity in output current, exceeding 106 times, exists between micro- and macro-contact tribovoltaic nanogenerators (TVNGs). To tackle this challenge, we develop a quantification method to determine the effective contact efficiency of conventional large-scale TVNGs, revealing a mere 0.038% for a TVNG of 1 cm2. Thus, we implement an optimization strategy by contact interface design resulting in a remarkable 65-fold increase in effective contact efficiency, reaching 2.45%. This enhancement leads to a current density of 23 A m-2 and a record-high charge density of 660 mC m-2 for the TVNG based on Cu and p-type silicon. Our study reveals that increasing the effective contact efficiency will not only address the existing disparities but also have the potential to significantly enhance the output current in future advancements of large-scale TVNGs.

Vibrations in living environments are generally distributed over a wide frequency spectrum and exhibit multiple motion directions over time, which renders most of the current vibration energy harvesters unpractical for their harvesting purposes. Here, a 3D triboelectric nanogenerator (3D‐TENG) is designed based on the coupling of the triboelectrification effect and the electrostatic induction effect. The 3D‐TENG operates in a hybridization mode of conjuntioning the vertical contact‐separation mode and the in‐plane sliding mode. The innovative design facilitates harvesting random vibrational energy in multiple directions over a wide bandwidth. An analytical model is established to investigate the mechano‐triboelectric transduction of 3D‐TENG and the results agree well with experimental data. The 3D‐TENG is able to harvest ambient vibrations with an extremely wide working bandwidth. Maximum power densities of 1.35 W m ‐2 and 1.45 W m ‐2 are achieved under out‐of‐plane and in‐plane excitation, respectively. The 3D TENG is designed for harvesting ambient vibration energy, especially at low frequencies, under a range of conditions in daily life and has potential applications in environmental/infrastructure monitoring and charging portable electronics.

Multifunctional Metamaterial Implants In article number 2203533, Amir H. Alavi and co-workers present a new generation of patient-specific metamaterial orthopedic implants that can detect the bone healing progress. The so-called "self-aware implants" can respond to their environment, empower themselves, and self-monitor their condition. Bench-top tests are performed using synthetic biomimetic and human cadaver spine models to evaluate the electrical and mechanical performance of the metamaterial implants.

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.

Catalyst-free, direct heteroepitaxial growth of vertical InAs nanowires on Si(111) substrates was accomplished over a large area by metal−organic chemical vapor deposition. Nanowires showed very uniform diameters and a zinc blende crystal structure. The heterojunctions formed at the interface between the n-type InAs nanowires and the p-type Si substrate were exploited to fabricate vertical array photodiode devices which showed an excellent rectification ratio and low reverse leakage current. Temperature-dependent current transport across the heterojunctions was studied theoretically and experimentally in the dark and under AM 1.5 illumination. When operated in photovoltaic mode, the open-circuit voltage was found to increase linearly with decreasing temperature while the energy conversion efficiency changed nonmonotonically with a maximum of 2.5% at 110 K. Modeling of the nanowire/substrate heterojunctions showed good agreement with the experimental observations, and allowed determining the conduction band offset between the InAs nanowires and Si to be 0.10−0.15 eV. The external quantum efficiency and photoresponsivity profiles of the device showed a broad spectral response from the visible to the infrared region, indicating potential applications as a broad band photovoltaic cell or a visible−infrared dual-band photodetector.