The ultrathin body of two-dimensional (2D) materials provides potential for next-generation electronics and optoelectronics. The unavoidable atomic defects substantially determine the physical properties of atomic-level thin 2D materials, thus enabling new functionalities that are impossible in three-dimensional semiconductors. Therefore, rational design of atomic defects provides an alternative approach to modulate the physical properties of 2D materials. In this review, we summarize the recent progress of defect engineering in 2D materials, particularly in device performance enhancement. Firstly, the common defects in 2D materials and approaches for generating and repairing defects, including synthesis and post-growth treatments, are systematically introduced. The correlations between defects and optical, electronic, and magnetic properties of 2D materials are then highlighted. Subsequently, defect engineering for high performance electronics and optoelectronics is emphasized. At last, we provide our perspective on challenges and opportunities in defect engineering of 2D materials.

Group-VI elemental two-dimensional (2D) materials (e.g., tellurene (Te)) have unique crystalline structures and extraordinarily physical properties. However, it still remains a great challenge to controllably grow 2D Te with good repeatability, uniformity, and highly aligned orientation using vapor growth method. Here, we design a Cu foil-assisted alloy-buffer-controlled growth method to epitaxially grow aligned single-crystalline 2D Te on an insulating mica substrate. The in-situ formation of Cu-Te alloy plays a key role on 2D Te growth, alleviating the spatial and temporal non-uniformity of precursor in conventional vapor deposition process. Through transmission electron microscopy (TEM) analysis combined with theoretical calculations, we unveil that the alignment growth of Te in the [110] direction is along the [600] direction of mica, owing to the small lattice mismatch (0.15%) and strong binding strength. This work presents a method to grow aligned high-quality 2D Te in a controllable manner.

The inferior electrical contact to two-dimensional (2D) materials is a critical challenge for their application in post-silicon very large- scale integrated circuits. Electrical contacts were generally related to their resistive effect, quantified as contact resistance. With a systematic investigation, this work demonstrates a capacitive metal-insulator-semiconductor (MIS) field-effect at the electrical contacts to 2D materials: The field-effect depletes or accumulates charge carriers, redistributes the voltage potential, and gives rise to abnormal current saturation and nonlinearity. On one hand, the current saturation hinders the devices' driving ability, which can be eliminated with carefully engineered contact configurations. On the other hand, by introducing the nonlinearity to monolithic analog artificial neural network circuits, the circuits' perception ability can be significantly enhanced, as evidenced using a coronavirus disease 2019 (COVID-19) critical illness prediction model. This work provides a comprehension of the field-effect at the electrical contacts to 2D materials, which is fundamental to the design, simulation, and fabrication of electronics based on 2D materials.

Physically unclonable crypto primitives have potential applications for anti-counterfeiting, identification, and authentication, which are clone proof and resistant to variously physical attack. Conventional physical unclonable function (PUF) based on Si complementary metal-oxide-semiconductor (CMOS) technologies greatly suffers from entropy loss and bit instability due to noise sensitivity. Here we grow atomically thick MoS₂ thin film and fabricate field-effect transistors (FETs). The inherently physical randomness of MoS₂ transistors from materials growth and device fabrication process makes it appropriate for the application of PUF device. We perform electrical characterizations of MoS₂ FETs, collect the data from 448 devices, and generate PUF keys by splitting drain current at specific levels to evaluate the response performance. Proper selection of splitting threshold enables to generate binary, ternary, and double binary keys. The generated PUF keys exhibit good randomness and uniqueness, providing a possibility for harvesting highly secured PUF devices with two-dimensional materials.