Publications

Electrical discharge is generally considered as a negative effect in the electronic industry and often causes electrostatic discharge (ESD) and thus failure of electronic components and integrated circuits (IC). However, this effect was recently used to develop a new energy-harvesting technology, direct-current triboelectric nanogenerator (DC-TENG). In this chapter, its fundamental mechanism and the working modes of the nanogenerator will be presented. They are different from the general alternating current TENG (AC-TENG) invented in 2012, which is based on triboelectrification and electrostatic induction. Taking advantage of the electrostatic discharge, it can not only promote the miniaturization trend of TENG and self-powered systems, but also provide a paradigm shifting technique to in situ gain electrical energy.

Maximizing TENGs’ energy cycle by analyzing the dynamic charge transfer process and suppressing air breakdown.

Abstract Ferroelectret nanogenerators were recently introduced as a promising alternative technology for harvesting kinetic energy. Here we report the device’s intrinsic properties that allow for the bidirectional conversion of energy between electrical and mechanical domains; thus extending its potential use in wearable electronics beyond the power generation realm. This electromechanical coupling, combined with their flexibility and thin film-like form, bestows dual-functional transducing capabilities to the device that are used in this work to demonstrate its use as a thin, wearable and self-powered loudspeaker or microphone patch. To determine the device’s performance and applicability, sound pressure level is characterized in both space and frequency domains for three different configurations. The confirmed device’s high performance is further validated through its integration in three different systems: a music-playing flag, a sound recording film and a flexible microphone for security applications.

The synthesis of high quality ZnO nanowire (NW) arrays on a range of conventional conductive substrates has important applications in LEDs, nanogenerators and piezotronics. In this paper, using ammonium hydroxide as the reactant, together with zinc nitrate hexahydrate, ZnO NW arrays have been grown on various patterned metal layers, such as Au, Ag, Cu and Sn, without pre-depositing a seed layer. The mechanism for this novel synthesis route has been discussed and the effect of parameters such as ammonia concentration and solution/container volume ratio on the nanowire growth has also been investigated. Preferentially selective nucleation and the subsequent growth of ZnO NW arrays was demonstrated on patterns of different metals without a ZnO seed. Electrical characterization was subsequently performed to reveal the characteristics of the contacts formed between the ZnO NWs and the underlying metal layer . Further demonstration of the as-fabricated ZnO NW arrays on flexible substrates as an electromechanical switch in response to externally applied strain exhibits the potential applications of the demonstrated seedless synthesis of patterned ZnO NW arrays in areas ranging from sensing, and energy harvesting to interfacing piezotronics with silicon based technologies.

Abstract With the improvement of the airtightness of modern buildings, installing ventilation systems indoors is becoming increasingly important, which works for a long time continuously and needs to be monitored in real‐time. However, the complex wiring of monitoring sensors makes assembly and maintenance more difficult. This work reports a hybridized triboelectric‐electromagnetic nanogenerator (HNG) as a power supply of a self‐powered wireless monitoring system for ventilation systems. The HNG integrates an air inlet cover, a stator with coils and interdigitated copper electrodes, a rotor with magnets, fluorinated ethylene propylene films, and optimized built‐in wind blades. The HNG scavenges wind energy from a ventilation system and serves as a power supply for electric applications. Under the wind speed of 6.5 m s −1 in the ventilation system, the maximum stabilized voltage and maximum instantaneous current of the HNG are 177.5 V and 0.049 A, which can charge smartphones and light up a bulb. Furthermore, the HNG realizes the self‐powered wireless transmission of temperature and humidity sensing nodes. This work demonstrates an effective wind energy harvester, providing an innovative strategy for monitoring the condition of the ventilation system and broadening the thoughts of prospective energy harvesting.

The polymer-based triboelectric nanogenerator (TENG) has long grappled with the constraint of limited current density (CD), whereas semiconductor-based triboelectric nanogenerators, using the tribovoltaic effect, have shown promising potential for achieving high current density. This study introduces an effective solution─a direct current tribovoltaic nanogenerator with ultrahigh current density─founded on a flexible organic semiconductor textile activated by solvents. By introducing 95% ethyl alcohol, an ultrahigh current density of 8.75 A/m2 and peak power density of 1.07 W/m2 are demonstrated, marking a striking enhancement of 438-fold and 170-fold, respectively, in comparison to the friction surface without 95% ethyl alcohol. The activation mechanism is that the poly(vinyl alcohol) dissolution by solvents exposes more PEDOT:PSS, and the formation of hydrogen bonds with PSS– releases more active PEDOT+. This advancement finds practical utility, as evidenced by successful demonstrations involving cell phone charging and small motor propulsion. The breakthrough unveiled in this work presents vistas for the widespread application of flexible organic semiconductor textile-based tribovoltaic nanogenerators, offering exciting opportunities for biomechanical energy harvesting.

The field emission properties of individual multiwalled carbon nanotubes have been measured simultaneously in correlation to the emitter images and their real work functions at tips by the in situ transmission electron microscopy method. The field emission of a single nanotube still follows the Fowler-Nordheim law. The field enhancement factor has been determined by the real work function rather than a given constant. In situ imaging and measurement show that the work function at the nanotube tip depends strongly on its structure and surface condition. This study provides an approach of direct linking field emission with the in situ emitter structure and the real work function at the emitter tip.

The ultrahigh flexibility and strong mechanical toughness of silicon nanowires (SiNWs) is demonstrated using manipulation and measurements on buckled SiNWs in a scanning electron microscope (see figure). The experimental data and calculated results show that the nanowire can bear a large strain (1.5%), much more than the bulk material, while the elastic constant of the NW is similar to that of the bulk.

'Polymethyl Methacrylate (PMMA)' published in 'Encyclopedia of Nanotechnology'

Contact electrification is about the charge transfer between the surfaces of two materials in a contact-separation process. This effect has been widely utilized in particle separation and energy harvesting, where the charge transfer is preferred to be maximized. However, this effect is always undesirable in some areas such as electronic circuit systems due to the damage from the accumulated electrostatic charges. Herein, we introduced an approach to purposely manipulate the contact electrification process both in polarity and magnitude of the charge transfer through an applied electric field between two materials. Theoretical modeling and the corresponding experiments for controlling the charge transfer between a Pt coated atomic force microscopy tip and Parylene film have been demonstrated. The modulation effect of the electric field on contact electrification is enhanced for a thinner dielectric layer. This work can potentially be utilized to enhance the output performance of energy harvesting devices or nullify contact electric charge transfer in applications where this effect is undesirable.

Abstract Recently, electret‐based triboelectric nanogenerator (E‐TENG) showssignificant advantages for energy harvesting applications, including a largeelectric current and high output stability. Inthis investigation, porous biocompatible polylactide (PLA) film is prepared for E‐TENG applications. They found that thesurface potential of the porous PLA‐based bioelectret film is maintained at2.1 kV after 86 days of decay,. The measurement data from theE‐TENG‐based cantilever beam showed that the E‐TENG reached an open‐circuitvoltage ( V oc ) of 184 V and a short circuit current ( I sc )of 22.4 µAat 13.8 Hz. Furthermore, the E‐TENG and the PVDF‐based piezoelectric nanogenerator (PENG) are combined to create a hybridNG for energy harvesting applications. The data indicate that the maximumoutput power of the hybrid NG reached 73.5 µWat 6 MΩ,which is 30.7% and 1.91‐fold higher than that of the PENG and the E‐TENG,respectively. The hybrid NG is used as a powersource to drive a wireless temperaturetransmission system, which can receive a temperature transmission signal from 20 m away. The advantages of biocompatibility,softness and ease of processing make the porous PLA film a great candidate forwearable devices applications.