Substrate-related optical activity in monolayer WS 2 ${\rm WS}_2$ and MoSe 2 ${\rm MoSe}_2$ : A tip-enhanced Raman...

Area of Science:

• Materials Science
• Nanotechnology
• Spectroscopy

Background:

• Two-dimensional materials, such as transition metal dichalcogenides (TMDs), exhibit properties highly sensitive to substrate interactions.
• Conventional Raman spectroscopy has limited spatial resolution, obscuring local variations in strain and doping that impact TMD behavior.
• Understanding these substrate effects is crucial for tailoring TMD properties for advanced applications.

Purpose of the Study:

• To investigate the influence of substrate interactions on the vibrational properties of monolayer tungsten disulfide (WS2) and molybdenum diselenide (MoSe2) at the nanoscale.
• To overcome the resolution limitations of conventional Raman spectroscopy by employing tip-enhanced Raman spectroscopy (TERS).
• To correlate nanoscale topographical features with local variations in strain, doping, and dielectric screening.

Main Methods:

• Utilized tip-enhanced Raman spectroscopy (TERS) to achieve nanometric spatial resolution.
• Investigated monolayer WS2 and MoSe2 samples on glass and glass/hexagonal boron nitride (hBN) substrates.
• Analyzed the relationship between Raman spectral features and substrate-induced topographical inhomogeneities.

Main Results:

• TERS enabled direct correlation between Raman signals and nanoscale structural features like wrinkles.
• Observed local variations in strain, doping, and dielectric screening across the substrate interface.
• Demonstrated that nanoscale structural features locally modulate the vibrational response of WS2 and MoSe2.

Conclusions:

• TERS is a powerful technique for probing local variations in 2D materials, overcoming limitations of conventional methods.
• Substrate interactions, including topographical features, significantly influence the vibrational properties of TMDs at the nanoscale.
• The findings provide insights into controlling and optimizing 2D material properties through substrate engineering.