Atomically thin transition metal dichalcogenides (TMDCs) have drawn much interest for their promising applications in electronic, optoelectronic, valleytronic and sensing fields. Controlled growth of large-scale and high-quality TMDC nanostructures is highly desirable but remains challenging. In the present work, large-scale monolayer, bilayer and few-layer MoSe ₂ films have been controllably synthesized by ambient pressure chemical vapor deposition (APCVD). Hydrogen flow rate, growth temperature as well as selenium–metal flux ratio have been systematically investigated, which were demonstrated to play a key role in the synthesis of MoSe ₂ nanostructures. We have also reported the successful growth of MoSe ₂ nanoribbons with controlled width and length on diverse substrates by APCVD with the assistance of sodium chloride and corresponding growth mechanism was proposed. Our findings highlight the prospects for the controlled growth of novel 1D and 2D TMDC nanostructures for nanoelectronic devices and the development of mixed-dimensional heterostructures.

Polymorphic structures of transition metal dichalcogenides (TMDs) host exotic electronic states, like charge density wave and superconductivity. However, the number of these structures is limited by crystal symmetries, which poses a challenge to achieving tailored lattices and properties both theoretically and experimentally. Here, we report a coloring-triangle (CT) latticed MoTe₂ monolayer, termed CT-MoTe₂, constructed by controllably introducing uniform and ordered mirror-twin-boundaries into a pristine monolayer via molecular beam epitaxy. Low-temperature scanning tunneling microscopy and spectroscopy (STM/STS) together with theoretical calculations reveal that the monolayer has an electronic Janus lattice, i.e., an energy-dependent atomic-lattice and a Te pseudo-sublattice, and shares the identical geometry with the Mo₅Te₈ layer. Dirac-like and flat electronic bands inherently existing in the CT lattice are identified by two broad and two prominent peaks in STS spectra, respectively, and verified with density-functional-theory calculations. Two types of intrinsic domain boundaries were observed, one of which maintains the electronic-Janus-lattice feature, implying potential applications as an energy-tunable electron-tunneling barrier in future functional devices.