Doping of graphene exfoliated on SrTiO3

Area of Science:

• Materials Science
• Surface Science
• Condensed Matter Physics

Background:

• Graphene's unique electronic properties make it a promising material for advanced applications.
• Understanding the work function of graphene on different substrates is crucial for device engineering.

Purpose of the Study:

• To determine the work function of single-layer and bilayer graphene exfoliated on crystalline strontium titanate (SrTiO3) substrates.
• To investigate the influence of substrate interactions on graphene's electronic properties.

Main Methods:

• Atomic Force Microscopy (AFM) and Scanning Kelvin Probe (SKP) measurements were performed under ultra-high vacuum (UHV) conditions.
• Contact Potential Difference (CPD) was systematically measured as a function of graphene layer number.

Main Results:

• The CPD monotonically increased with the number of graphene layers, reaching saturation after five layers.
• The work function of single-layer graphene (SLG) was determined to be 4.409 ± 0.039 eV, and bilayer graphene (BLG) was 4.516 ± 0.035 eV.
• The measured work functions are higher than that of free-standing graphene, indicating electron accumulation.

Conclusions:

• The work function of exfoliated graphene on SrTiO3 increases with layer number and saturates at approximately five layers.
• Single-layer graphene exhibits a work function of 4.409 eV, suggesting n-type doping due to electron accumulation.
• These findings provide critical data for utilizing graphene-based heterostructures in electronic devices.