Effect of layer and stacking sequence in simultaneously grown 2H and 3R WS₂ atomic layers

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Layer number and stacking order critically influence properties of 2D layered materials.
• Tungsten disulfide (WS₂) typically exists in the 2H phase, but other structures like 3R are possible.
• Understanding structural influences is key for novel electronic and optical applications.

Purpose of the Study:

• To achieve simultaneous large-scale growth of 2H and 3R stacked multilayer WS₂ crystals.
• To investigate the effects of layer number and stacking order on WS₂ optical and electronic properties.
• To explore spin or valley polarization in CVD-grown WS₂.

Main Methods:

• Simultaneous large-scale growth of 2H and 3R WS₂ using chemical vapor deposition (CVD).
• Characterization using Raman spectroscopy and photoluminescence (PL) measurements.
• Investigation of circularly polarized luminescence under circularly polarized excitation.

Main Results:

• Both 2H and 3R WS₂ showed similar PL and Raman peak variations with increasing layer number.
• 3R stacked WS₂ exhibited distinct red/blue shifts in Raman peaks and lower energy PL peaks compared to 2H WS₂.
• Circularly polarized luminescence confirmed spin or valley polarization in the synthesized WS₂ crystals.

Conclusions:

• Optical and electronic properties of multilayer WS₂ are dependent on both layer number and stacking order.
• The study provides a method for synthesizing WS₂ with controlled stacking for tailored properties.
• Demonstrated spin/valley polarization in CVD-grown WS₂ opens avenues for spintronic and valleytronic devices.