Xingxing Zhang

In article number 1804508, Sang Ouk Kim and co‐workers present a reliable and effective nanopatterning strategy for 2D transition metal dichalcogenides via block copolymer (BCP) lithography. By exploiting various BCP templates, diverse nanostructures, including nanomeshes, nanodots, and nanowire arrays, are demonstrated with wafer‐scale scalability. Edge‐exposed MoS₂ nanomeshes exhibit superior sensitivity and reversibility for NO₂ gas sensing.

An improved method for the synthesis of wafer‐scale continuous PtSe₂ films with an effective doping strategy in a controllable manner is developed. Nearly symmetric n‐type and p‐type field‐effect transistors have been fabricated, based on which logic inverter and vertically stacked p–n junction arrays are successfully demonstrated in wafer scale, which enable potential applications in future 2D material circuits.

Abstract

Semiconductive transition metal dichalcogenides (TMDs) have been considered as next generation semiconductors, but to date most device investigations are still based on microscale exfoliation with a low yield. Wafer scale growth of TMDs has been reported but effective doping approaches remain challenging due to their atomically thick nature. This work reports the synthesis of wafer‐scale continuous few‐layer PtSe₂ films with effective doping in a controllable manner. Chemical component analyses confirm that both n‐doping and p‐doping can be effectively modulated through a controlled selenization process. The electrical properties of PtSe₂ films have been systematically studied by fabricating top‐gated field effect transistors (FETs). The device current on/off ratio is optimized in two‐layer PtSe₂ FETs, and four‐terminal configuration displays a reasonably high effective field effect mobility (14 and 15 cm² V⁻¹ s⁻¹ for p‐type and n‐type FETs, respectively) with a nearly symmetric p‐type and n‐type performance. Temperature dependent measurement reveals that the variable range hopping is dominant at low temperatures. To further establish feasible application based on controllable doping of PtSe₂, a logic inverter and vertically stacked p–n junction arrays are demonstrated. These results validate that PtSe₂ is a promising candidate among the family of TMDs for future functional electronic applications.

Synthesis and characterization of 2D transition metal dichalcogenides are reported. These materials show excellent catalytic activity in oxygen reduction and evolution reactions in an aprotic medium containing ionic liquid and Li salt. These findings open a way to seek highly efficient bifunctional catalysts, which have been rarely studied for core electrochemical reactions and energy storage systems.

Abstract

The optimization of traditional electrocatalysts has reached a point where progress is impeded by fundamental physical factors including inherent scaling relations among thermokinetic characteristics of different elementary reaction steps, non‐Nernstian behavior, and electronic structure of the catalyst. This indicates that the currently utilized classes of electrocatalysts may not be adequate for future needs. This study reports on synthesis and characterization of a new class of materials based on 2D transition metal dichalcogenides including sulfides, selenides, and tellurides of group V and VI transition metals that exhibit excellent catalytic performance for both oxygen reduction and evolution reactions in an aprotic medium with Li salts. The reaction rates are much higher for these materials than previously reported catalysts for these reactions. The reasons for the high activity are found to be the metal edges with adiabatic electron transfer capability and a cocatalyst effect involving an ionic‐liquid electrolyte. These new materials are expected to have high activity for other core electrocatalytic reactions and open the way for advances in energy storage and catalysis.

The disassembly of 2D vertical heterostructures (2DVHs) is successfully achieved. As a demonstration, ReS₂/WS₂ 2DVHs is disassembled into WS₂ and ReS₂ via Te disassembly promoters on the basis of microscopic and spectroscopic characterizations, which gives inspiration for the modification and functionalization of 2DVHs.

Abstract

As one of the most widely discussed fields, the assembly of nanomaterials has always been extensively studied. However, its inverse process, namely disassembly, is still limited in the ambit of biomolecules. Specifically, in the emerging 2D research field, disassembly still remains unexplored. Inspired by the disassembly of DNA molecules via breaking intermolecular hydrogen bonds, the disassembly of 2D vertical heterostructures (2DVHs) is first achieved through the weakening of the interlayer van der Waals interactions. As a demonstration, ReS₂/WS₂ VHs is successfully disassembled into individual building blocks. Density functional theory calculations are performed to study the disassembly of the 2DVHs, which simulate that 2DVHs are first activated by the disassembly promoters and then disassembled with weakened interlayer van der Waals interactions. Such a disassembly process demonstrates that it has great potential to be expanded as a general strategy to achieve the disassembly of other 2D superstructures.

The electronic and optical properties, as well as related applications of 2D transition metal carbides, carbonitrides, and nitrides (MXenes) are reviewed. This very large and rapidly growing family of 2D materials has demonstrated attractive electrical, optical, electrochemical, and mechanical properties, which lead to numerous plasmonic, optoelectronic, and other applications.

Abstract

2D transition metal carbides, carbonitrides, and nitrides, known as MXenes, are a rapidly growing family of 2D materials with close to 30 members experimentally synthesized, and dozens more studied theoretically. They exhibit outstanding electronic, optical, mechanical, and thermal properties with versatile transition metal and surface chemistries. They have shown promise in many applications, such as energy storage, electromagnetic interference shielding, transparent electrodes, sensors, catalysis, photothermal therapy, etc. The high electronic conductivity and wide range of optical absorption properties of MXenes are the key to their success in the aforementioned applications. However, relatively little is currently known about their fundamental electronic and optical properties, limiting their use to their full potential. Here, MXenes' electronic and optical properties from both theoretical and experimental perspectives, as well as applications related to those properties, are discussed, providing a guide for researchers who are exploring those properties of MXenes.