The isostructural and isoelectronic transition-metal-dichalcogenides 1T-TaS₂ and 1T-TaSe₂ are layered materials with intricate electronic structures. Combining the molecular beam epitaxy growth, scanning tunneling microscopy measurements and first-principles calculations, we prepare monolayer 1T-TaS₂ and TaSe₂ and explore their electronic structures at the atomic scale. Both two-dimensional (2D) compounds exhibit commensurate charge density wave phase at low temperature. The conductance mapping identifies the contributions from different Ta atoms to the local density of states with spatial and energy resolution. Both 1T-TaS₂ and 1T-TaSe₂ monolayer are shown to be insulators, while the former has a Mott gap and the latter is a regular band insulator.

We report the growth and characterization of atomically thick NbS₂, TaS₂, and FeS films on a 6H-SiC(0001) substrate terminated with monolayer or bilayer epitaxial graphene. The crystal and electronic structures are studied by scanning tunneling microscopy and reflection high-energy electron diffraction. The NbS₂ monolayer is solely in the 2H structure, while the TaS₂ monolayer contains both 1T and 2H structures. Charge-density waves are observed in all phases. For the FeS films, the tetragonal structure coexists with the hexagonal one and no superconductivity is observed.