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Modifying the Band Gap of Semiconducting Two-Dimensional Materials by Polymer Assembly into Different Structures
Langmuir : the ACS Journal of Surfaces and Colloids
|March 16, 2019
Summary
Polyethylene glycol (PEG) assembly on tungsten disulfide (WS2) affects its optical properties. Nanoparticulate PEG significantly alters WS2
Area of Science:
- Materials Science
- Condensed Matter Physics
- Nanotechnology
Background:
- Two-dimensional materials like tungsten disulfide (WS2) possess unique electronic and optical properties.
- Surface functionalization is crucial for tuning these properties for specific applications.
- Polyethylene glycol (PEG) is a versatile polymer for surface modification.
Purpose of the Study:
- To investigate the impact of different polyethylene glycol (PEG) assembly morphologies on the optical properties of two-dimensional tungsten disulfide (WS2).
- To understand how PEG chain length influences the formation of nanoislands (NIs), nanoshells (NSs), and granular nanoparticulates (GNPs) on WS2.
- To correlate structural changes induced by PEG assembly with alterations in WS2's photoluminescence (PL) and absorption spectra.
Main Methods:
- Synthesis of WS2 with varying PEG chain lengths to form different nanostructures (NIs, NSs, GNPs).
- Photoluminescence (PL) spectroscopy to measure emission shifts.
- Absorption spectroscopy to analyze changes in A and B absorption peaks.
- Raman spectroscopy to assess mechanical properties and structural integrity.
Main Results:
- PEG nanoisland (NI) assembly showed minimal impact on WS2 optical properties, indicating ineffective electronic doping.
- PEG nanoshell (NS) assembly resulted in a slight red shift in PL and a minor decrease in the energy difference between A and B absorption peaks.
- PEG granular nanoparticulate (NP) assembly caused a significant red shift in PL, a large decrease in the A-B peak energy difference, and a substantial reduction in the electronic direct band gap due to WS2 sheet deformation.
- Raman bands shifted to higher frequencies, suggesting enhanced mechanical strength of WS2 after PEG assembly.
Conclusions:
- The morphology of PEG assembly on WS2 dictates its effect on optical and electronic properties.
- PEG granular nanoparticulate (NP) assembly significantly deforms WS2, leading to substantial changes in its band gap and optical response.
- PEG assembly can enhance the mechanical robustness of WS2, as evidenced by Raman spectroscopy shifts.
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