Two-dimensional (2D) materials including graphene and transition metal dichalcogenides (TMDs) have been intensively explored for fundamental research and technological applications. The ultrathin nature and large surface area of 2D materials enable their optical and electrical properties to be tuned through surface modification. In this study, redox-active molecules were introduced onto the surface of 2D materials to achieve strong and nondestructive n- and p- doping effects. A series of monolayer TMDs, including MoS2, WS2, MoSe2, and WSe2, were tested. Doping was achieved by exposing the TMD surface to solutions of pentamethylrhodocene dimer as the molecular reductant and “Magic Blue,” [N(C6H4-p-Br)3]SbCl6, as the molecular oxidant. The degree of doping can be finely controlled by the choice of dopants, treatment time, and the concentration of doping solution. Notably, current-voltage characteristics of TMD-based 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. Detailed physical characterizations were conducted to study the doping effect. Photoluminescence (PL) properties of the doped monolayer TMDs were measured; for all four materials the PL intensity is enhanced with p-doping but reduced with n-doping. X-ray photoelectron spectroscopies (XPS) was performed to investigate the impact of doping on the TMDs chemical structure and energy levels. The coverage of absorbed doping product was also calculated based on the XPS data. Estimates of changes of carrier density from electrical, PL, and XPS results were compared. In summary, this technique provides a simple yet effective route to tailor the band structure of the 2D materials and control the resulting electrical and optical properties.

Controllable, wide-ranging n- and p-doping of monolayer transition-metal disulfides and diselenides

2019 Spring National Meeting

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