Conductance anisotropy in epitaxial graphene sheets generated by substrate interactions

Area of Science:

• Materials Science
• Condensed Matter Physics
• Surface Science

Background:

• Epitaxial graphene grown on silicon carbide (SiC) is a promising material for electronic applications.
• Understanding charge transport properties at the nanoscale is crucial for device development.
• Substrate interactions can significantly influence graphene's electronic behavior.

Purpose of the Study:

• To investigate the microscopic charge transport properties of epitaxial graphene on SiC.
• To identify the origins of observed conductivity anomalies.
• To develop a model explaining substrate-induced effects on graphene conductivity.

Main Methods:

• Utilized an ultrahigh vacuum four-probe scanning tunneling microscope for microscopic transport measurements.
• Performed in-situ characterization of epitaxial graphene on SiC.
• Developed and applied a theoretical model to interpret experimental results.

Main Results:

• Observed anisotropic conductivity in epitaxial graphene, deviating from isotropic behavior.
• Identified a correlation between conductivity anisotropy and substrate step edges.
• Demonstrated that charge buildup at step edges causes local scattering of charge carriers.

Conclusions:

• Substrate interactions, specifically at step edges, play a critical role in the electronic transport of epitaxial graphene on SiC.
• A model involving charge buildup and carrier scattering at step edges successfully explains the observed anisotropic conductivity.
• Future device designs utilizing patterned graphene on insulating substrates must account for these substrate effects.