Reversible Rectification of Microscale Ferroelectric Junctions Employing Liquid Metal Electrodes

A liquid metal/carbon nanotubes complex enabling ultra-fast polymerization of super-robust, stretchable adhesive hydrogels for highly sensitive sensor

Carbon nanotubes (CNTs) usually served as conductive and reinforcing nanofillers for making nanocomposites have never been reported to play a role in accelerating fabrication of hydrogels. Herein, we report an important discovery that by involving CNTs and liquid metal (LM) to form a complex (LM@CNTs), multifunctional hydrogels are rapidly prepared from vinyl monomers without heating or adding any initiators and crosslinkers. Study results demonstrate that LM@CNTs not only performs as both initiator and crosslinker for synthesizing hydrogels, but also dramatically reduces the polymerization duration from 3 days to minute levels, compared with that of only LM involved in hydrogel fabrication. Specifically, the complex initiates (<60 s) and crosslinks (<8min) monomers to form the high-performance hydrogels, which significantly reduces energy consumptions. The resulting polyacrylic acid (PAA) hydrogel possesses super stretchability (∼1200 %), high tensile strength (0.96 MPa), outstanding strain sensitivity (Gauge factor = 15.40 at 300-500 % strain), and excellent adhesion to various substrate surfaces. Additionally, the injectable molding performance will benefit the mass production of the hydrogels, which exhibits great potential for applications of wearable flexible sensors. This study provides an environmentally friendly, rapid polymerization, and energy-saving strategy by effectively applying nano-fillers for viable fabrication and application of multifunctional hydrogels.

In Situ Active Switching of Bipolar Current Rectification in 2D Semiconductor Vertical Diodes

Two-dimensional semiconducting transition-metal dichalcogenides (TMDCs) have attracted extensive attention as building blocks of miniaturized electronic and optical devices. However, as the characteristics of TMDC devices are predominately determined by their device structures, the function of TMDC devices is fixed once fabricated, leaving the reconfigurable active device and circuit a challenge. Here, we have demonstrated the current rectification switching in TMDC vertical diodes using a liquid metal (EGaIn) top electrode with a reconfigurable contact area. The rectification switching is closely related to the ultrathin gallium oxide layer on the surface of EGaIn. Under the small contact, with the existence of gallium oxide, photocurrent dominates the electrical transport showing a negative rectification, while as the contact increases, the broken gallium oxide leads to rectification switching to the positive bias direction. Such rectification switching applies to thin TMDC flakes down to 3 nm, benefitting from the soft electrical contact between the TMDC and the EGaIn electrode. Our work shows the new possibility of actively reconfigurable TMDC vertical diodes enabled by the liquid metal electrode and will promote promising applications of flexible and tunable TMDC-based nanoelectronic devices.

Smart Eutectic Gallium-Indium: From Properties to Applications

Eutectic gallium-indium (EGaIn), a liquid metal with a melting point close to or below room temperature, has attracted extensive attention in recent years due to its excellent properties such as fluidity, high conductivity, thermal conductivity, stretchability, self-healing capability, biocompatibility, and recyclability. These features of EGaIn can be adjusted by changing the experimental condition, and various composite materials with extended properties can be further obtained by mixing EGaIn with other materials. In this review, not only the are unique properties of EGaIn introduced, but also the working principles for the EGaIn-based devices are illustrated and the developments of EGaIn-related techniques are summarized. The applications of EGaIn in various fields, such as flexible electronics (sensors, antennas, electronic circuits), molecular electronics (molecular memory, opto-electronic switches, or reconfigurable junctions), energy catalysis (heat management, motors, generators, batteries), biomedical science (drug delivery, tumor therapy, bioimaging and neural interfaces) are reviewed. Finally, a critical discussion of the main challenges for the development of EGaIn-based techniques are discussed, and the potential applications in new fields are prospected.