Band Gap Engineering and Layer-by-Layer Mapping of Selenium-Doped Molybdenum Disulfide

Abstract

Ternary two-dimensional dichalcogenide alloys exhibit compositionally modulated electronic structure, and hence, control of dopant concentration within each individual layer of these compounds provides a powerful tool to efficiently modify their physical and chemical properties. The main challenge arises when quantifying and locating the dopant atoms within each layer in order to better understand and fine-tune the desired properties. Here we report the synthesis of molybdenum disulfide substitutionally doped with a broad range of selenium concentrations, resulting in over 10% optical band gap modulations in atomic layers. Chemical analysis using Z-contrast imaging provides direct maps of the dopant atom distribution in individual MoS2 layers and hence a measure of the local optical band gaps. Furthermore, in a bilayer structure, the dopant distribution is imaged layer-by-layer. This work demonstrates that each layer in the bilayer system contains similar local Se concentrations, randomly distributed, providing new insights into the growth mechanism and alloying behavior in two-dimensional dichalcogenide atomic layers. The results show that growth of uniform, ternary, two-dimensional dichalcogenide alloy films with tunable electronic properties is feasible.

Phosphorous doped p-type MoS2 polycrystalline thin films via direct sulfurization of Mo film

“…Among them, the direct grown method of TMDs (e.g. MoS 2 ) synthesis via sulfurization of transition metal films has great advantages for a large scale to have possibilities for the band gap engineering, 29 hetero-structures, 30 and doping. 25 Laskar et al 25 first reported on in situ p-type doping in cation-site by Nb diffusion in direct grown MoS 2 thin films.…”

Growth of Transition Metal Dichalcogenides and Directly Modulating Their Properties by Chemical Vapor Deposition

“…[57,62,63] Ajayan et al also achieved synthesis of MoS2(1-x)Se2x alloy, Se component can be controlled from 0 to 75% by changing ratio of S and Se precursors before growth procedure, and prolonged growing time could result to film growth due to increased nucleation density. [64] However, the optical bandgap of the alloy can be turned over 200 meV. Except for common Raman and PL measurements, X-ray photoelectron spectroscopy (XPS) is valid to confirm Se content by comparing Se 3p3/2 and 3d peak intensity revolution, while atomic annular dark field (ADF) imaging is useful to analyze dopant distribution.…”

“…Except for common Raman and PL measurements, X-ray photoelectron spectroscopy (XPS) is valid to confirm Se content by comparing Se 3p3/2 and 3d peak intensity revolution, while atomic annular dark field (ADF) imaging is useful to analyze dopant distribution. [64] Different from doping in the growth process, atom substitution can be conducted after growth of MoS2, and annealing using the dopant sources in the furnace is also efficient to turn band structure of the material. [65] Except for chalcogenide atom substitution, transition metal atoms can also be substituted using CVT methods to modulate properties of MoS2 and these alloys shows good thermodynamic stability at ambient conditions.…”

Band Gap Engineering of Hybrid 2-D Nanomaterials Some Recent Developments

“…Band gap engineered nanosheets were successfully produced using precursors from mechanically exfoliated MoS 2 (1-x) Se 2x bulk alloy showing triangular nanosheets (SEM) with the edge lengths of 30-80 micron. Lateral composition-graded 2D-MoS 2(1-x) Se 2x nano layers were also synthesized employing a simple moving source thermal evaporation method of an improved CVD [55][56][57][58][59][60][61][62][63][64][65][66][67][68]. Subsequently, 2D-WS 2x Se 2(1-x) alloys were prepared from WO 3 (monoclinic crystal) to WS 2 (1-x) Se 2x (hexagonal crystal) through simultaneous sulfurization and selenization, in which, the chemical activity of S made it easy to tune the value of x by varying the weight of sulfur powder [69].…”