Controllable, Wide‐Ranging n‐Doping and p‐Doping of Monolayer Group 6 Transition‐Metal Disulfides and Diselenides

Abstract

Developing processes to controllably dope transition-metal dichalcogenides (TMDs) is critical for optical and electrical applications. Here, molecular reductants and oxidants are introduced onto monolayer TMDs, specifically MoS , WS , MoSe , and WSe . Doping is achieved by exposing the TMD surface to solutions of pentamethylrhodocene dimer as the reductant (n-dopant) and "Magic Blue," [N(C H -p-Br) ]SbCl , as the oxidant (p-dopant). Current-voltage characteristics of field-effect transistors show that, regardless of their initial transport behavior, all four TMDs can be used in either p- or n-channel devices when appropriately doped. The extent of doping can be controlled by varying the concentration of dopant solutions and treatment time, and, in some cases, both nondegenerate and degenerate regimes are accessible. For all four TMD materials, the photoluminescence intensity; for all four materials the PL intensity is enhanced with p-doping but reduced with n-doping. Raman and X-ray photoelectron spectroscopy (XPS) also provide insight into the underlying physical mechanism by which the molecular dopants react with the monolayer. Estimates of changes of carrier density from electrical, PL, and XPS results are compared. Overall a simple and effective route to tailor the electrical and optical properties of TMDs is demonstrated.

High‐Performance Monolayer MoS2 Films at the Wafer Scale by Two‐Step Growth

“…However, ML films that were grown at 600, 700, and 1000 °C possess much lower electron doping densities. Moreover, Figure g indicates that the reported n el values derived from electronic device drain currents exhibit almost one order of magnitude less than that of PL spectra, which is a recently reported phenomenon . Through analysis of the PL characterization above, we demonstrated that the electron doping level of the wafer‐scale ML MoS 2 film could be engineered by simply varying the experimental parameters in the two‐step growth process.…”

“…Figure g provides a comparison of n el values in this work versus previous reports. The red points are the n el values as derived by PL photoexcitation . The black points are the n el values obtained through electronic device drain currents .…”

“…The red points are the n el values as derived by PL photoexcitation . The black points are the n el values obtained through electronic device drain currents . Notably, all of these reports used single crystalline ML MoS 2 flakes (exfoliated or CVD grown) as research objects.…”

Quasi-two-dimensional magnon identification in antiferromagneticFePS3via magneto-Raman spectroscopy

“…While significant research has been dedicated thus far to studying the optical, mechanical, and electrical properties of 2D materials, 3,[5][6][7][8][9] exploring magnetism is still in its infancy, even though 2D magnetic materials provide a solid-state platform to experimentally access fundamental, low-dimensional physics. 10,11 Additionally, any 2D magnetic material would likely still possess the captivating properties of 2D materials, including extremely large mechanical flexibility, 12,13 efficient tuning of transport properties with an electric field, [14][15][16][17] relative ease of chemical modification, 18,19 as well as the ability to create van der Waals stacked heterostructures. 20 These myriad of tuning parameters could unlock opportunities for customengineered magnetoelectric and magneto-optical devices, where 2D magnets coupled with other technologically relevant materials could realize unprecedented capabilities in fields such as spintronics.…”

Demonstration of the key substrate-dependent charge transfer mechanisms between monolayer MoS2 and molecular dopants

“…Various methods have been proposed for tuning E F within the band gap of TMDCs, including substitution with dopant atoms 15 , stacking with other 2D materials 16 , exposure to gases [6][7][8]17 , adsorption of alkali metals 18,19 , and adsorption of organic molecules [20][21][22][23][24][25][26] . In accordance with this approach, deposition of molecular electron acceptors or donors on TMDCs has been suggested as a very effective strategy for controlling the E F position via doping, and accordingly high-performance TFTs were realized 22,24,26 . However, the extent to which the changes in electrical TFT characteristics were indeed due to electron transfer between the dopant molecules and the monolayer TMDC (ML-TMDC) was not unambiguously demonstrated, and mostly changes of photoluminescence intensity of excitons versus trions were interpreted as signature of charge transfer (CT).…”