2D materials have a wide range of interesting properties. Among them, transition metal dichalcogenides and 2D heavy metals, with the availability of valley and spin degree of freedom, are the candidates for the conceptual spintronics and valleytronics. Substitutional doping can further functionalize the materials for more applications. Properties like magnetism could be brought and tuned directly by the dopants. Or the dopants can facilitate physisorption or chemisorption, which provides a way to realize materials by design through judicious choice from an enormous amount of molecules and ligands, making the 2D material a "motherboard" for unlimited use.

In this report, I will show my study using density functional theory on the effects of substitutional doping on transition metal dichalcogenides as well as magnetism and photoemission properties of selected 2D materials. Specifically, Nb doping in MoS2 can facilitate ligand covalent bonding by ~1 eV per Nb/bonding pair. This material also shows ~50 larger signal-to-noise ratio and lower detection limit, compared to pristine MoS2, to triethylamine in the form of chemiresistor due to stronger binding with the molecule and more effective charge transfer from the molecule to the plane. V dopant introduces magnetism in WS2 forming a room-temperature dilute magnetic semiconductor. The magnetic moment quenching effect due to defect states hybridization when the two dopants are close to each other results in a non-monotonicity in saturation magnetization which is verified by experiments. The effective Zeeman splitting for this material corresponds to an external magnetic field to the order of 100T. 1T-CrTe2 is an intrinsic room-temperature ferromagnet and my study shows that the magnetic anisotropy energy can be tuned to the extent of changing its easy axis through biaxial strain and charge doping. The calculated phase diagram of 2D Pb in the graphene/SiC interface is consistent with the experiments to be a full coverage monolayer. The simulated ARPES indicates the two "truncated" bands in the experiment are due to the matrix element effect.