Monitoring dopants by Raman scattering in an electrochemically top-gated graphene transistor.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Graphene's discovery has spurred advances in 2D physics and devices.
• Current graphene devices predominantly use silicon dioxide (SiO2) back gating.
• Electrochemical gating is established for polymer transistors and carbon nanotubes.

Purpose of the Study:

• To demonstrate a top-gated graphene transistor.
• To achieve significantly higher doping levels than previously reported.
• To investigate the role of gate capacitance in device performance.

Main Methods:

• Fabrication of a top-gated graphene transistor utilizing a solid polymer electrolyte.
• In situ Raman spectroscopy to monitor doping levels.
• Comparison of gate capacitance with traditional SiO2 back gates.

Main Results:

• Achieved doping levels up to 5x10^13 cm^-2, surpassing previous records.
• Demonstrated higher gate capacitance due to a nanometer-thick Debye layer in the polymer electrolyte.
• Observed distinct doping-dependent shifts in Raman G and 2D peaks.
• Identified the G/2D peak intensity ratio as a sensitive doping indicator.

Conclusions:

• Top-gated graphene transistors with solid polymer electrolytes offer superior doping capabilities.
• The high capacitance of the electrolyte gate is key to achieving high doping levels.
• In situ Raman spectroscopy provides effective monitoring of doping in graphene devices.