Carrier Doping of Few-Layer MoS2 with Ionic Polymers and MoS2 Quantum Dots with Atmospheric Water

Tuesday, 26 May 2015: 14:00
Lake Ontario (Hilton Chicago)
D. Briggs, P. Nguyen, C. Fager, S. Sreenivasan, and V. Berry (University of Illinois at Chicago)
Thin layered MoS2 has emerged as a remarkable 2D semiconductor material with great potential due to its direct band gap (thickness dependent), photoluminescence, and high on/off FET rectification.  Additionally, molecular gating has proven to be an effective technique to dope nanomaterials for specific electronic applications. Here, we show two avenues for molecular gating: (A) Carrier doping and electrical properties of few layer MoS2 were controllably modulated by interfacing it with the polyanionic polymer, polystyrene sulfonate (PSS) and the polycationic polymer, polyallylamine hydrochloride (PAH); and (B) MoS2 quantum dots interfaced with a microfiber of PAH were reversibly doped with water molecules by altering the local humidity. PSS interfacing with few layer MoS2 resulted in a blue shift of the Raman E12g and A1g Raman peaks in MoS2 corresponding to hole doping, as expected for negative potential gating. PAH adsorption on PSS doped MoS2 led to a recovery of the A1g peak, while the E12g peak red shifted slightly attributed to over compensation by PAH and electron doping. Similar results were attained with PAH interfacing on MoS2 few layer sheets resulting in electron doping. Electrical characterization confirmed the carrier doping observed by Raman. MoS2 quantum dots interfaced with a microfiber of PAH were reversibly doped with water molecules by changing the local humidity. The p-doping of water absorbed by the polymer microfiber reduced the electron density in n-type MoS2 quantum dots. The change in the carrier concentration (5.24 x 1011 cm-2) was confirmed by electrical measurements and Raman spectra were analyzed to understand the lattice bonding of MoS2 during the self-assembly process onto PAH microfibers. Both of these avenues demonstrate chemical modification or interfacing providing a path for tuning the electronic properties of MoS2 for use in future electronic devices.