In the field of bionics, sophisticated and multifunctional electronic skins with a mechanosensing function that are inspired by nature are developed. Here, an energy-harvesting electronic skin (energy-E-skin), i.e., a pressure sensor with energy-harvesting functions is demonstrated, based on fingerprintinspired conducting hierarchical wrinkles. The conducting hierarchical wrinkles, fabricated via 2D stretching and subsequent Ar plasma treatment, are composed of polydimethylsiloxane (PDMS) wrinkles as the primary microstructure and embedded Ag nanowires (AgNWs) as the secondary nanostructure. The structure and resistance of the conducting hierarchical wrinkles are deterministically controlled by varying the stretching direction, Ar plasma power, and treatment time. This hierarchical-wrinkle-based conductor successfully harvests mechanical energy via contact electrification and electrostatic induction and also realizes self-powered pressure sensing. The energy-E-skin delivers an average output power of 3.5 mW with an open-circuit voltage of 300 V and a short-circuit current of 35 µA; this power is sufficient to drive commercial light-emitting diodes and portable electronic devices. The hierarchical-wrinkle-based conductor is also utilized as a self-powered tactile pressure sensor with a sensitivity of 1.187 mV Pa -1 in both contact-separation mode and the single-electrode mode. The proposed energy-E-skin has great potential for use as a next-generation multifunctional artificial skin, self-powered human-machine interface, wearable thin-film power source, and so on.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted considerable attention owing to their synergetic effects with other 2D materials, such as graphene and hexagonal boron nitride, in TMD-based heterostructures. Therefore, it is important to understand the physical properties of TMD–TMD vertical heterostructures for their applications in next-generation electronic devices. However, the conventional synthesis process of TMD–TMD heterostructures has some critical limitations, such as nonreproducibility and low yield. In this paper, we synthesize wafer-scale MoS2–WS2 vertical heterostructures (MWVHs) using plasma-enhanced chemical vapor deposition (PE-CVD) via penetrative single-step sulfurization discovered by time-dependent analysis. This method is available for fabricating uniform large-area vertical heterostructures (4 in.) at a low temperature (300 °C). MWVHs were characterized using various spectroscopic and microscopic techniques, which revealed their uniform nanoscale polycrystallinity and the presence of vertical layers of MoS2 and WS2. In addition, wafer-scale MWVHs diodes were fabricated and demonstrated uniform performance by current mapping. Furthermore, mode I fracture tests were performed using large double cantilever beam specimens to confirm the separation of the MWVHs from the SiO2/Si substrate. Therefore, this study proposes a synthesis mechanism for TMD–TMD heterostructures and provides a fundamental understanding of the interfacial properties of TMD–TMD vertical heterostructures.

Over the past few years, many researchers have been excited with the advent of two-dimensional (2D) materials such as graphene and molybdenum disulfide (MoS2) because of their intriguing physical and chemical properties. Furthermore, they have great potential in various applications including nanoelectronics, flexible or stretchable devices, energy conversion or storage devices, sensors, nanocomposites, and others. In addition to their electrical, mechanical, optical, and thermal properties, interfacial properties of 2D materials such as adhesion energy have recently attracted attention from researchers since interfacial interactions of 2D materials with others are of great importance in obtaining mechanical integrity of nanomanufacturing processes and related devices. In this respect, this paper reviews the adhesion properties of 2D materials. Measurement methods and characteristics of adhesion behaviors were summarized and discussed mainly for graphene and MoS2.

No abstract

Free-standing graphene-based paper-like materials have garnered significant interest for various applications because of their tunable physical and chemical properties, along with unique multilayered structures. Because of the layered configuration of graphene paper, characterization of the interactions between graphene sheets is critical for understanding its fundamental properties and applications. We investigate the interlayer cohesion energies in graphene papers using the mode I fracture concept with double cantilever beam specimens. Mechanical separation along the middle of the graphene paper thickness enables the evaluation of interlayer bonding strength in the paper. Starting from graphene oxide paper, the chemical reduction using hydroiodic acid tunes the interlayer cohesion energy from 11.30 ± 0.25 to 4.78 ± 0.18 J/m 2 as the reduction time increases. The interlayer cohesion energy is correlated with the oxygen content, interlayer spacing, and electrical conductivity of graphene papers. This work provides a fundamental characterization of the interlayer cohesion energy of graphene paper and establishes the potential for tunability of the interlayer interactions in graphene paper.