Single-crystal, large-area, fold-free monolayer graphene

Area of Science:

• Materials Science
• Nanotechnology
• Surface Science

Background:

• Chemical vapor deposition (CVD) on metal substrates is key for scalable graphene synthesis.
• Graphene films often contain imperfections like grain boundaries, adlayers, and folds, degrading performance.
• Graphene folds have been less studied compared to other defects.

Purpose of the Study:

• Investigate the formation mechanism of graphene folds during CVD growth.
• Identify conditions to produce large-area, high-quality, fold-free graphene films.
• Optimize the CVD process for reproducible and scalable graphene synthesis.

Main Methods:

• Graphene growth using ethylene precursor on single-crystal Cu-Ni(111) foils.
• Controlled variation of initial growth temperature.
• Analysis of film morphology and defect formation during cooling.
• Fabrication and characterization of graphene field-effect transistors.

Main Results:

• A critical growth temperature of 1,030 Kelvin was identified, above which folds form during cooling.
• Folds are triggered by compressive stress release via step bunching on the Cu-Ni foil.
• Restricting growth temperature between 1,000-1,030 Kelvin yields fold-free, single-crystal monolayer graphene.
• Resulting films exhibit high-quality transport properties with average mobilities of (7.0 ± 1.0) × 10³ cm²/Vs.
• The process is scalable for simultaneous growth on multiple foils and allows foil reuse.

Conclusions:

• Controlling CVD growth temperature is crucial for preventing graphene folds.
• The identified temperature window enables scalable production of high-quality, fold-free graphene.
• This method enhances graphene's potential for electronic applications due to uniform transport properties.