Facile and Versatile Functionalization of Two-Dimensional Carbon Nitrides by Design: Magnetism/Multiferroicity, Valleytronics, and Photovoltaics

Ab initio calculation evidence has shown that two-dimensional (2D) carbon nitrides may enable “facile functionalization” when a domain of carbon nitride is wetted by a solution of metal halides with mobile cations/anions. During the wetting process, each cavity can be functionalized by a unit of metal halide. Compared with prevailing functionalization or doping strategies through either high-temperature diffusion of source ions or ion implantation by using accelerators, such a room-temperature “wet-lab” functionalization approach is more facile and efficient. The wet-lab functionalization not only can facilitate isolation of the 2D monolayer, but also, with applying different metal halides, enable various new and desirable properties for broad applications, e.g., 2D magnetism and 2D ferroelectricity with high piezoelectric coefficient. The latter can be implemented in spin-independent valleytronics for non-volatile electrical manipulations. Notably, tunable bandgaps, ranging from 1.0 to 2.5 eV, can be realized by controlling the metal-halide functionalization density, while the separation of electrons/holes can be facilitated by the ferroelectric polarizations and heterostructure band alignments. Moreover, multifunctional domains like P/N doped or magnetic/ferroelectric domains can be selectively constructed through such solution-processed functionalization with different halides, followed by seamless integration into a single sheet of carbon nitride, akin to the P/N channels in silicon wafers.