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Graphene, with a carrier mobility achieving up to 140,000 cm 2 /Vs at room temperature, makes it an ideal material for application in semiconductor devices. However, when the metal comes in contact with the graphene sheet, an energy barrier forms at the metal-graphene interface, resulting in a drastic reduction of the carrier mobility of graphene. In this review, the various methods of forming metal-graphene covalent contacts to lower the contact resistance are discussed. Furthermore, the graphene sheet in the area of metal contact can be cut in certain patterns, also discussed in this review, which provides a more efficient approach to forming covalent contacts, ultimately reducing the contact resistance for the realization of high-performance graphene devices.

Exploring beyond monoelemental and binary two-dimensional (2D) nanomaterials is an important step to further engineer and functionalize well-known 2D nanomaterials for the next-generation technologies. In this work, using state-of-the-art first-principles electronic structure calculations and statistical sampling of structural configurations, we examine the influence of anionic exchange in two monolayer group IV (namely, Ge- and Sn-based) monochalcogenides. Using chemical bonding analysis, we demonstrate the link between anisotropic lattice properties and band structure-derived characteristics. We also show how this structural anisotropy and iono-covalency chemical bonding may both strongly influence the direction-dependent optical responses and have a milder effect on direction-dependent thermoelectric power factor in these monolayer group IV alloys. This allows one to consider the linear Vegard’s relation for anionic engineering of monolayer group IV alloys and further explore strong (and weak) anisotropy in their direction-dependent material properties.

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