Graphene-WS₂ heterostructures by a lithography free method: their electrical properties

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Two-dimensional (2D) materials offer unique electronic properties.
• Fabricating complex heterostructures from these materials often requires intricate lithography techniques.
• Graphene and transition metal dichalcogenides like WS₂ are promising building blocks for novel electronic devices.

Purpose of the Study:

• To develop and demonstrate a lithography-free method for fabricating 2D material heterostructures.
• To investigate the electrical and magnetotransport properties of graphene-WS₂ heterostructures.
• To understand the underlying charge transport mechanisms in these fabricated devices.

Main Methods:

• Utilized a transmission electron microscope (TEM) grid as a shadow mask for lithography-free fabrication.
• Synthesized graphene via radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD).
• Prepared WS₂ by depositing WO₃ followed by sulfurization.
• Performed variable temperature and magnetic field-dependent electrical transport measurements.

Main Results:

• Successfully fabricated graphene-WS₂ heterostructures without using traditional lithography.
• Observed temperature-dependent resistance and magnetoresistance in individual components and the heterostructure.
• Identified variable-range hopping (VRH) as the dominant transport mechanism at low temperatures, consistent with 2D Mott VRH theory (R ∝ T⁻¹/³).
• Confirmed 2D Mott VRH transport through quadratic low-field magnetoresistance dependence (∼B²).

Conclusions:

• The developed shadow mask technique is a viable lithography-free approach for 2D heterostructure fabrication.
• Graphene-WS₂ heterostructures exhibit characteristic 2D Mott VRH transport behavior at low temperatures.
• This method offers a simpler route for producing advanced 2D material-based electronic devices.