Strain-induced conduction gap in vertical devices made of misoriented graphene layers

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Graphene's unique electronic properties are sensitive to its atomic structure.
• Moiré superlattices in twisted bilayer graphene offer tunable electronic band structures.
• Strain engineering is a promising route to modify graphene's properties.

Purpose of the Study:

• To investigate the impact of uniaxial strain on the transport properties of twisted bilayer graphene.
• To explore the formation and tunability of a conduction gap in strained twisted graphene.
• To assess the potential of strain-induced effects for electronic device applications.

Main Methods:

• Fabrication of vertical devices using partially overlapping, misoriented graphene layers.
• Application of controlled uniaxial strain to the graphene devices.
• Measurement and analysis of electrical transport properties, including conductance and Seebeck coefficient.
• Theoretical analysis of strain-induced shifts and separations of Dirac points in reciprocal space.

Main Results:

• Uniaxial strain effectively displaces and separates the Dirac points of misoriented graphene layers in k-space.
• A significant conduction gap (up to hundreds of meV) is achieved with small strain (<5%).
• The conduction gap exhibits clear dependence on strain magnitude, direction, channel orientation, and twist angle.
• Strong modulation of conductance and a notable improvement in the Seebeck coefficient were observed.

Conclusions:

• Strain engineering provides a powerful method to tune the electronic properties of twisted bilayer graphene.
• The observed strain-induced conduction gap and improved transport properties highlight potential for novel graphene-based devices.
• These findings suggest promising applications for strained twisted graphene in transistors, strain sensors, and thermal sensors.