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Modifying the Band Gap of Semiconducting Two-Dimensional Materials by Polymer Assembly into Different Structures

Liao, Chih-Kai, Phan, Jasmine, Herrera, Maura, Mahmoud, Mahmoud A.
Langmuir 2019 v.35 no.14 pp. 4956-4965
nanoparticles, optical properties, photoluminescence, polyethylene glycol, strength (mechanics), thiols, tungsten
Polyethylene glycol (PEG) assembled on the surface of two-dimensional tungsten disulfide (WS₂) into a limited number of nanoislands (NIs), nanoshells (NSs), and granular nanoparticulates (GNPs) depending on its chain length. NI assemblies showed a nonmeasurable shift of photoluminescence (PL) and the A and B absorption peaks of WS₂. This confirmed that the electronic doping by thiol is not effective. The PEG NS assembly displayed a smaller red shift of the PL and a slight decrease of the energy difference between the A and B absorption peaks of WS₂. However, increasing the dielectric function on the surface of WS₂ has a small influence on their optical properties. The PEG NP assembly on WS₂ exhibited a significant red shift of the PL spectrum and a large decrease of the energy difference between A and B absorption peaks. Deforming the WS₂ sheet by the PEG NP assembly decreased the orbital coupling and lowered the electronic direct band gap significantly. Raman bands of WS₂ are shifted to a higher frequency on improving its mechanical strength after the PEG assembly.