transparent, and wearable electronics and optoelectronics due to their reduced dimensions that offer flexibility and transparency with proper band gap, high carrier mobility, and highly efficient light absorption. [1][2][3] In addition, their ideally dangling-bond-free surface and atomic thickness are promising for ideal heterogeneous contact and reduced short channel effect, [4] thus making them suitable for future nano-scaled electronic and optoelectronic devices. An ideal field-effect transistor based on an molybdenum disulfide (MoS 2 ) channel is theoretically predicted to reach large on/off ratio (>10 9 ), room temperature mobility of 410 cm 2 (Vs) −1 , and near-ideal subthreshold swing of 60 meV per decade. [5,6] However, most of experimental results significantly differ from the aforementioned theoretical predictions. One of dominant factors degrading the overall performance of 2D materials based devices arises from unwanted chemical interactions between deposited metal electrodes and 2D TMDC channel. These chemical interactions originate from incomplete/imperfect covalent/surface bonds of TMDCs and unwanted damages from the direct deposition of metal layers and precursors, which are used during the device fabrication processes. These lead to the creation of unfavorable interface states and pinning of fermi energy levels, which Contact engineering for monolayered transition metal dichalcogenides (TMDCs) is considered to be of fundamental challenge for realizing highperformance TMDCs-based (opto) electronic devices. Here, an innovative concept is established for a device configuration with metallic copper monosulfide (CuS) electrodes that induces sulfur vacancy healing in the monolayer molybdenum disulfide (MoS 2 ) channel. Excess sulfur adatoms from the metallic CuS electrodes are donated to heal sulfur vacancy defects in MoS 2 that surprisingly improve the overall performance of its devices. The electrode-induced self-healing mechanism is demonstrated and analyzed systematically using various spectroscopic analyses, density functional theory (DFT) calculations, and electrical measurements. Without any passivation layers, the self-healed MoS 2 (photo)transistor with the CuS contact electrodes show outstanding room temperature field effect mobility of 97.6 cm 2 (Vs) −1 , On/Off ratio > 10 8 , low subthreshold swing of 120 mV per decade, high photoresponsivity of 1 × 10 4 A W −1 , and detectivity of 10 13 jones, which are the best among back-gated transistors that employ 1L MoS 2 . Using ultrathin and flexible 2D CuS and MoS 2 , mechanically flexible photosensor is also demonstrated, which shows excellent durability under mechanical strain. These findings demonstrate a promising strategy in TMDCs or other 2D material for the development of high performance and functional devices including self-healable sulfide electrodes.

Monolayered, semiconducting MoS2 and their transition metal dichalcogenides (TMDCs) families are promising and low-cost materials for hydrogen generation through electrolytes (HER, hydrogen evolution reaction) due to their high activities and electrochemical stability during the reaction. However, there is still a lack of understanding in identifying the underlying mechanism responsible for improving the electrocatalytic properties of theses monolayers. In this work, we investigated the significance of controlling carrier densities in a MoS2 monolayer and in turn the corresponding electrocatalytic behaviors in relation to the energy band structure of MoS2. Surface functionalization was employed to achieve p-doping and n-doping in the MoS2 monolayer that led to MoS2 electrochemical devices with different catalytic performances. Specifically, the electron-rich MoS2 surface showed lower overpotential and Tafel slope compared to the MoS2 with surface functional groups that contributed to p-doping. We attributed such enhancement to the increase in the carrier density and the corresponding Fermi level that accelerated HER and charge transfer kinetics. These findings are of high importance in designing electrocatalysts based on two-dimensional TMDCs.

Electronic devices in highly integrated and miniaturized systems demand electromagnetic interference shielding within nanoscale dimensions. Although several ultrathin materials have been proposed, satisfying various requirements such as ultrathin thickness, optical transparency, flexibility, and proper shielding efficiency remains a challenge. Herein, we report an ultrahigh electromagnetic interference (EMI) SSE/t value (>10 6 dB cm 2 /g) using a conductive CuS nanosheet with thickness less than 20 nm, which was synthesized at room temperature. We found that the EMI shielding efficiency (EMI SE) of the CuS nanosheet exceeds that of the traditional Cu film in the nanoscale thickness, which is due to high conductivity and the presence of internal dipole structures of the CuS nanosheet that contribute to absorption due to the damping of dipole oscillation. In addition, the CuS nanosheet exhibited high mechanical stability (10 4 cycles at 3 mm bending radius) and air stability (25 °C, 1 atm), which far exceeded the performance of the Cu nanosheet film. This remarkable performance of nanometer-thick CuS proposes an important pathway toward designing EMI shielding materials for wearable, flexible, and next-generation electronic applications.

Engineering energy levels of MoS2 monolayers via halide atom doping can greatly contribute to the charge kinetics and the catalytic activities.

The 2D semimetallic electrodes have been employed to show outstanding contact properties with 2D semiconducting transition‐metal dichalcogenides (TMDCs) channel, leading to large enhancement of 2D transistor and phototransistor performance. Herein, an innovative concept is established for a unique 2D semimetallic electrode‐2D TMDC channel (2D–2D) device configuration where the electronic structures of 2D semimetallic electrodes are systematically modulated to improve the contact properties with 2D monolayer molybdenum disulfide (MoS2) channel. The 2D semimetallic copper sulfide (CuS) electrodes are doped with iodine atoms by a direct exposure of iodine gas. The contact properties and charge‐transport behavior in the 2D–2D field‐effect transistors (FETs) are highly improved, which is attributed to the favorable energy band alignment and associated material properties between the iodine‐doped CuS (CuS–I) electrodes and 2D channel. The 2D–2D FETs show a high on current, high on/off ratio, and twofold improvement in mobility. Furthermore, 2D–2D phototransistors and flexible/transparent photodetectors are fabricated using the CuS–I/MoS2, which also performed outstanding photoresponsivity characteristics and mechanical durability under external bending strain conditions. These findings demonstrate a promising pathway that under the 2D–2D configuration, the electronic modulation by the iodine atoms may enable the development of future 2D electronic applications.