Publications

Abstract Mechanical system with adjustable stiffness and damping (ASAD) shows great potential in vibration suppression of aircraft, vehicle, precise instrument, etc. However, current ASAD systems consist of power, sensing, and controlling components, which bring huge challenges of system reliability and integrability, and critically limit its application diversity. Herein, we proposed the first strategy for regulating ASAD system that is system simplification, self‐powered and no‐delay by deeply coupling triboelectric nanogenerator (TENG) and electrorheological fluid (ERF). Under the time‐varying mechanical triggering, the local and time correlated output of TENG instantaneously applied on the ERF regulates the entire mechanical system dynamically and “in‐phase”. As an illustration, the resonance of a cantilever system is effectively suppressed naturally without complicated controlling strategy, and the vibration isolating efficiency reaches up to 85.2%. Finally, a mechanical transmission system is demonstrated utilizing a rotary TENG and ERF, excellent soft‐start performance is enabled by this self‐regulating ASAD strategy. This work may provide the opening arsenal of methodologies used in self‐powered and self‐regulating mechanical systems.

Abstract It is commonly accepted that batteries perform better at low current densities below the mass‐transport limit, which restricts their current rate and capacity. Here, it is demonstrated that the performance of Zn metal electrodes can be dramatically enhanced at current densities and cut‐off capacities exceeding the mass‐transport limit by using pulsed‐current protocols. These protocols achieve cumulative plating/stripping capacities of 11.0 Ah cm −2 and 3.8 Ah cm −2 at record‐high current densities of 80 and 160 mA cm −2 , respectively. The study identifies and understands the promoted (002)‐textured Zn growth and suppressed hydrogen evolution based on the thermodynamics and kinetics of competing reactions. Furthermore, the over‐limiting pulsed‐current protocol enables long‐life Zn batteries with high mass loading (29 mg cathode cm −2 ) and high areal capacity (7.9 mAh cm −2 ), outperforming cells using constant‐current protocols at equivalent energy and time costs. The work provides a comprehensive understanding of the current‐capacity‐performance relationship in Zn plating/stripping and offers an effective strategy for dendrite‐free metal batteries that meet practical requirements for high capacity and high current rates.

Abstract Contact electrification (CE) is one of the oldest topics in physics, which has been discussed for more than 2600 years. Recently, an overlapped electron‐cloud (OEC) model was proposed by Wang to explain all types of CE phenomena for general materials in which a deep overlapping of electron clouds belonging to two atoms results in a lowered potential barrier for electron transfer from one to the other by applying a compressive force, which is simply referred to as Wang transition for CE. Here, the degree of electron‐cloud overlap between two atoms is controlled by using tapping mode atomic force microscopy. A temperature difference and electric field are applied between atoms of two surfaces. It is found that electron transfer only occurs when the contact tip and sample interact in the repulsive‐force region, which corresponds to a strong overlap of the electron clouds. Such a fact even preserves if the tip is at a higher temperature than the sample for 120 K. Alternatively, by applying a bias, electron tunneling would occur when the tip is in the attractive‐force region within which normal electron transfer would not occur. These studies solidify the overlapped electron‐cloud model first proposed by Wang. Further, the temperature and bias effects on the CE are explained based on a modified OEC model.

Impurity doping is the most important technique to functionalize semiconductor nanowires. The crucial point is how the states of impurity atoms can be detected. The chemical bonding states and electrical activity of boron (B) and phosphorus (P) atoms in germanium nanowires (GeNWs) are clarified by micro-Raman scattering measurements. The observation of B and P local vibrational peaks and the Fano effect clearly demonstrate that the B and P atoms are doped into the crystalline Ge region of GeNWs and electrically activated in the substitutional sites, resulting in the formation of p-type and n-type GeNWs. This method can be a useful technique for the characterization of semiconductor nanowire devices. The B-doped GeNWs showed an increasingly tapered structure with increasing B concentration. To avoid tapering and gain a uniform diameter along the growth direction of the GeNWs, a three step process was found to be useful, namely growth of GeNWs followed by the deposition of an amorphous Ge layer with high B concentration and then annealing.

A cross-linked triboelectric nanogenerator with high performance is designed for the first time, which harvests vibrational energy to self-power the electrochemical oxidation of organic molecules. This system lays the groundwork for applications to an environmentally friendly production of important organic molecules and the waste treatment of organic pollutants. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Active mechanical metamaterials have shown a glimpse of their capacity to create the foundation for intelligent matter. This study presents the concept of mechanical metamaterial electronics (meta-mechanotronics) to design intelligent matter with information processing capability. This advanced functionality is achieved by fusing the mechanical metamaterials, digital electronics and nano energy harvesting technologies. Electronic mechanical metamaterials explored under the meta-mechanotronics paradigm rely merely on their constituent components to perform self-powered mechanical-electrical-logic operations. A proof-of-concept digital unit cell is presented as the 2-bit building block for electronic mechanical metamaterials. The digital unit cell is rationally designed as a monostable origami-inspired metamaterial with twist buckling behavior and specific multi-motion properties to synthesize discrete mechanical configurations and realize digital logic gates. Experimental studies are performed to evaluate the digital computing performance of the designed mechanical metamaterial logic gate.

Abstract Transient electronics that disintegrate via material dissolution or depolymerization under certain stimuli have great potential in biomedical and military applications. The triboelectric nanogenerator (TENG), an emerging mechanical energy harvesting technology with great flexibility in material choices, is promising in offering transient power sources. Previously reported transient energy harvesters using biodegradable polymers require solution‐based degradation and have limited applications in non‐biological scenarios. A short time span, sunlight‐triggered degradable TENG is developed. The main substrate includes an acid‐sensitive poly(phthalaldehyde) (PPHA), a photoacid generator (PAG), and a photosensitizer (PS). Through photo‐induced electron transfer, the ultraviolet radiation absorbed by the PS is transferred to the PAG to generate photoacids that trigger the depolymerization of PPHA. Transient TENG‐based mechanical energy harvesters and touch/acoustic sensors are successfully demonstrated by embedding silver nanowires onto the PPHA‐based films. The fabricated devices degrade rapidly under winter sunlight. The degradation rate can be further tuned via changing the ratio of photosensitive agents. This work not only broadens the applicability of TENG as transient power sources and sensors, but also extends the use of transient functional polymers toward advanced energy and sensing applications.

We have devised a novel vertical-cavity surface-emitting laser structure. The epitaxial layers have been grown by molecular beam epitaxy (MBE). The bottom mirror consists of 30.5 pairs of multilayer distributed Bragg reflector (DBR). The top mirror is a hybrid reflector consisting of 8.5 pairs of multilayer and a semi-transparent metal film. The structure is obtained by two He ion implantations using tungsten wires as an implant mask. The lowest threshold current is 8.2 mA, and the highest peak light output power is 1.8 mW under room-temperature cw conditions.

Molybdenum disulfide (MoS 2 ) has attracted a great attention as an excellent 2D material for future optoelectronic devices. Here, a novel MoS 2 tribotronic phototransistor is developed by a conjunction of a MoS 2 phototransistor and a triboelectric nanogenerator (TENG) in sliding mode. When an external friction layer produces a relative sliding on the device, the induced positive charges on the back gate of the MoS 2 phototransistor act as a “gate” to increase the channel conductivity as the traditional back gate voltage does. With the sliding distance increases, the photoresponsivity of the device is drastically enhanced from 221.0 to 727.8 A W −1 at the 100 mW cm −2 UV excitation intensity and 1 V bias voltage. This work has extended the emerging tribotronics to the field of photodetection based on 2D material, and demonstrated a new way to realize the adjustable photoelectric devices with high photoresponsivity via human interfacing.

Quasi-spherical VO2 nanoparticles with uniform size and high crystallinity are ideal functional materials for applications in field-effect transistors, smart window coatings and switches. However, the synthesis of these VO2 nanoparticles has long been a challenge. This article presents a novel doping strategy for the simultaneous control of the size, morphology and polymorphology of VO2 nanoparticles. Doping can induce the change in crystal structure and exhibits a significant promoting effect on the formation of doped monoclinic VO2 (VO2 (M)). Specifically, by antimony (Sb3+) doping, hexagonal-shaped, well crystalline monoclinic VO2 nanoparticles with tunable sizes (8–30 nm) and controllable polymorphs were synthesized via a one-pot, hydrothermal method. Sb3+ dopants, which are larger in radius and lower in valence than V4+ ions, can introduce extra oxygen vacancies during the nucleation and growth of VO2 nanoparticles. These positively charged nuclei may suppress the adsorption of VO2+ aqua ions, and therefore inhibit the growth of the VO2 (M) nanoparticles. Comparably, Sb5+ dopants that possess higher valence counts than V4+ ions can induce the growth of VO2 (M) particles to 200–300 nm width and above 500 nm length. The Sb3+-doped VO2 (M) nanoparticles exhibit excellent properties in metal–semiconductor transformation at transition temperatures ranging from 55–68 °C. Films obtained by casting these nanoparticles show excellent optical properties (both visible transmittance and infrared regulation), compared with those prepared from gas phases, such as sputtering. This synthetic strategy that involves the doping of an element with a different valence count than the matrix cation may be useful for controlling the solution growth of some technologically significant nanomaterials. In addition, the formation mechanism of solid and crystalline transformation was also studied by designing a specific reaction autoclave.

Electric-field-based stimulation is emerging as a new cancer therapeutic modality through interfering with cell mitosis. To address its limitations of complicated wire connections, bulky devices, and coarse spatial resolution, an improved and alternative method is proposed for wirelessly delivering electrical stimulation into tumor tissues through designing an implantable, biodegradable, and wirelessly controlled therapeutic triboelectric nanogenerator (ET-TENG). With the excitation of ultrasound (US) to the ET-TENG, the implanted ET-TENG can generate an alternating current voltage and concurrently release the loaded anti-mitotic drugs into tumor tissues, which synergistically disrupts the assembly of microtubules and filament actins, induces cell cycle arrest, and finally enhances cell death. With the assistance of US, the device can be completely degraded after the therapy, getting free of a secondary surgical extraction. The device can not only work around those unresectable tumors, but also provides a new application of wireless electric field in cancer therapy.