Tuning the Optical Bandgap of Semiconducting Two-Dimensional Materials by Different Techniques
The liquid and mechanical exfoliation techniques are merged in a mechanical exfoliation assisted by molecular tweezers technique (MEAMT). Semiconducting 2-dimensional materials (S2DM), on comparing to the typical liquid exfoliation technique, the MEAMT resulted in a higher yield percentage and higher photoluminescence (PL) quantum efficiency which is attributed to the increased surface homogeneity of the sheets and reduced defect density. Polyethylene glycol (PEG) assembled on the surface of two-dimensional tungsten disulfide (WS2) into a limited number of nanoislands (NIs), nanoshell (NS), and granular nanoparticulates (GNPs) depending on its chain length. Deforming the S2DM by PEG NPs assembly decreased the orbital coupling and lowered the electronic direct band gap significantly. Conjugated polymers (CP) are used for tuning the optical band gap of S2DM. The acceptable reason for the modification of the band gap of MoS2 by CPs is the generation of interlayer excitons (ILE) at their interface. The optical band gap of S2DM is further changed by introducing an inert polymer spacer of different thickness to separate MoS2 from CP. This is attributed to the reduction of the efficiency of excitonic interactions and lowering the exciton binding energy, which is induced by the increase of the dielectric function at the CP-S2DM interface. Plasmonic Janus nanoparticles are also used to tune the band gap of S2DM. Due to the large Plasmonic Janus nanoparticles/S2DM Schottky barrier, the plasmon-induced hot-electron transfer (PHET) from Plasmonic Janus nanoparticles. Pauli blocking and phase-space filling are responsible for the blue shift of S2DM assembled with Plasmonic Janus nanoparticles.