Nanoribbons of molybdenum disulfide (MoS2) are interesting 1D nanostructures with intriguing electronic properties, consisting of a semiconducting bulk bounded by edges with metallic character. Edges of similar character can also be expected in other transition-metal dichalcogenide (TMDC) nanostructures. We report first-principles electronic structure calculations for the total energy and the band structure of four representative TMDCs, MoS2, MoSe2, WS2, WSe2, in various 1D nanoribbon configurations. We compare the thermodynamic stability and the electronic structure of the 2D bulk and 35 different quasi 1D nanoribbons for each of the four materials. In each case, we consider the reconstructions of the zig-zag metal-terminated edge by adding different amounts of chalcogen adatoms. The 1D structures we investigated have positive edge energies when the chalcogen chemical potential is close to the energy of the bulk chalcogen phase, and negative edge energies for higher chemical potential values. We find that the reconstruction with two chalcogen adatoms per edge metal atom is the most stable under usual experimental conditions and that all 1D nanoribbon structures exhibit metallic character.

No abstract

2D semiconducting transition metal dichalcogenides (TMDs) have attracted interest for optoelectronics, catalysis, and energy applications. Control over TMD electronic and optical properties, which depend on dimensionality and are modified by nanostructuring and adsorbates, is important for the development and deployment of reliable nanoscale devices for such applications. Density functional theory calculation results for the atomic structure, energetics, and electronic structure of the metal edges of 2D MX2 (M = Mo, W and X = S, Se) with several coverages of adsorbed hydrogen, oxygen, hydroxyl radicals, and water are presented. Using zigzag nanoribbon models, it is found that compared with the basal planes of MX2, edges are more active and exhibit a rich adsorbent behavior. In general, the thermodynamically stable M‐edges, with two X adatoms, weakly bind hydrogen, oxygen, and water and strongly bind hydroxyl. However, adsorption energies depend on the adsorbate type and coverage and may be tuned for the catalysis of important chemical reactions such as water splitting and hydrogen evolution. The electronic band structure calculations show that, besides bandgap energy modifications and gap states, the well‐established robust metallic character of the edge states is preserved, albeit Fermi‐level shifts that depend both on adsorbates and adsorbents.

Nanoribbons of MoS2 present a unique electronic structure that consists of a semiconducting bulk bounded by metallic edges; same holds for other Transition-Metal Dichalcogenides (TMDs) (Mo-,W-,S2,Se2). We perform first-principles calculations for TMD nanoribbons with reconstructed zig-zag metal terminated edges that contain chalcogen adatoms. All nanorobbons have possitive edge energies when the chemical potential of chalcogens is close to the energy of solids, and negative edge energies for high chemical potential. The reconstruction with two chalcogen adatoms is expected to be the most stable one. In all nanoribbons, a metallic phase is found near their edges, with the Fermi level of this metallic phase being lower than the Fermi level of the 2D material.