  Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDCs)
and black phosphorus (BP) have beneficial electronic, optical, and physical
properties at the few-layer limit. As atomically thin materials, 2D TMDCs and
BP are highly sensitive to their environment and chemical modification,
resulting in a strong dependence of their properties on substrate effects,
intrinsic defects, and extrinsic adsorbates. Furthermore, the integration of 2D
semiconductors into electronic and optoelectronic devices introduces unique
challenges at metal-semiconductor and dielectric-semiconductor interfaces.
Here, we review emerging efforts to understand and exploit chemical effects to
influence the properties of 2D TMDCs and BP. In some cases, surface chemistry
leads to significant degradation, thus necessitating the development of robust
passivation schemes. On the other hand, appropriately designed chemical
modification can be used to beneficially tailor electronic properties, such as
controlling doping levels and charge carrier concentrations. Overall, chemical
methods allow substantial tunability of the properties of 2D TMDCs and BP,
thereby enabling significant future opportunities to optimize performance for
device applications.
