The advent of two-dimensional (2D) materials has ushered in a new era for electronic and optoelectronic devices. However, their atomic-scale thickness presents a fundamental contact interface challenge: the formation of a Schottky barrier at the 2D material–metal contact interface, which often leads to Schottky barrier and high contact resistance (R_C). While detrimental for conventional transistor scaling, this inherent Schottky barrier is also a critical functional element, actively harnessed in devices like photodetectors. This duality defines the central theme of contact interface engineering in 2D electronics. This review comprehensively examines recent advances in understanding and engineering these critical interfaces. We first elucidate the core physical principles governing contact formation, including Fermi level (E_F) pinning (FLP), charge transfer, and Schottky barrier modulation. We then distinguish strategic pathways for engineering contacts: routes toward ultralow-resistance Ohmic contacts (van der Waals (vdW) integration, interfacial doping, and edge contacts) and methods for tailoring Schottky contacts through barrier-height tuning. Insights from advanced characterization techniques and theoretical models for extracting Schottky barrier height (SBH) and R_C are also integrated. Finally, we outline unresolved challenges and future directions, providing a roadmap toward rationally designed 2D contact interfaces for unlocking full device potential.

The emerging two-dimensional (2D) materials exhibit strong exciton effects with rich exciton types, dominating their optical and optoelectronic properties. The modulation of the interlayer van der Waals (vdW) gap in 2D materials significantly influences interlayer coupling, enabling the manipulation of the excitonic binding energy (E_B), electronic band structure, etc. However, the impact of the vdW gap between 2D materials and their substrates on excitonic behavior is seldom explored, and the physical mechanism remains unclear. Here, we experimentally demonstrate the vdW gap between 2D materials and substrates can effectively tune the excitonic E_B and electronic bandgap, owing to the change in the local dielectric environment and the Coulomb screening effect. The vdW gap between monolayer WS₂ and SiO₂/Si substrate reduced from ~ 6 to 3 nm by the simple annealing process enhances the Coulomb screening effect, decreases the excitonic E_B by ~ 20 meV, redshifts the bandgap by ~ 14 meV and thus strongly suppresses the trion formation. Our findings elucidate the underlying physical interaction mechanisms between 2D materials and substrates, offering valuable insights for designing and optimizing optical and optoelectronic devices by utilizing these supported 2D materials.

Given its intriguing band structure and unique tunable bandgap, AB-stacked bilayer graphene has great potentials in the applications of high-end electronics, optoelectronics and semiconductors. The epitaxial growth of AB-stacked single-crystal bilayer graphene films requires a strict AB-stacked lattice, identical orientations and seamless stitching of bilayer graphene islands. However, the particles inevitably present on the metal surface that produced during high temperature growth would induce random orientations, twisted stacking islands, and uncontrollable multilayers, which is a great challenge to overcome. Here, we propose a heat-resisting-box assisted strategy to produce nearly pure AB-stacked bilayer graphene single-crystal films on Cu/Ni (111) foils. With our technique, the particles on the Cu/Ni (111) surface are effectively eliminated, which greatly minimizes the occurrence of randomly twisted islands and uncontrollable multilayers. The as-grown AB-stacked bilayer graphene films show > 99% alignment and > 99% AB stacking order. Our work provides a promising method towards the growth of pure AB-stacked bilayer graphene single crystals and would accelerate its device applications.

The state-of-the-art semiconductor industry is built on the successful production of silicon ingot with extreme purity as high as 99.999999999%, or the so-called "eleven nines". The coming high-end applications of graphene in electronics and optoelectronics will inevitably need defect-free pure graphene as well. Due to its two-dimensional (2D) characteristics, graphene restricts all the defects on its surface and has the opportunity to eliminate all kinds of defects, i.e., line defects at grain boundaries and point or dot defects in grains, and produce intrinsically pure graphene. In the past decade, epitaxy growth has been adopted to grow graphene by seamlessly stitching of aligned grains and the line defects at grain boundaries were eliminated finally. However, as for the equally common dot and point defects in graphene grain, there are rare ways to detect or reduce them with high throughput and efficiency. Here, we report a methodology to realize the production of ultrapure graphene grown on copper by eliminating both the dot and point defects in graphene grains. The dot defects, proved to be caused by the silica particles shedding from quartz tube during the high-temperature growth, were excluded by a designed heat-resisting box to prevent the deposition of particles on the copper surface. The point defects were optically visualized by a mild-oxidation-assisted method and further reduced by etching-regrowth process to an ultralow level of less than 1/1, 000 μm². Our work points out an avenue for the production of intrinsically pure graphene and thus lays the foundation for the large-scale graphene applications at the integrated-circuit level.