3D Strain in 2D Materials: To What Extent is Monolayer Graphene Graphite?

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Graphene, a 2D material, is structurally related to graphite.
• Understanding graphene's mechanical properties is crucial for its applications.
• Direct measurement of graphene's out-of-plane stiffness is challenging due to its 2D nature.

Purpose of the Study:

• To determine the extent to which graphene's mechanical properties mirror those of graphite.
• To quantify the out-of-plane stiffness of unsupported monolayer graphene.
• To compare the in-plane phonon frequency shift rates of graphene and graphite.

Main Methods:

• Obtained unambiguous Raman spectra from unsupported monolayer graphene under applied pressure.
• Utilized Raman spectroscopy to measure phonon frequency shifts.
• Quantified out-of-plane stiffness and in-plane phonon frequency shift rates.

Main Results:

• Determined a physically meaningful out-of-plane stiffness for monolayer graphene, consistent with graphite.
• Reported an in-plane phonon frequency shift rate for unsupported monolayer graphene of 5.4 cm⁻¹ GPa⁻¹, closely matching graphite's 4.7 cm⁻¹ GPa⁻¹.
• Observed that monolayer graphene exhibits similar in-plane and out-of-plane stiffnesses and anharmonicities to graphite.

Conclusions:

• Monolayer graphene shares significant mechanical properties with graphite.
• Graphene's mechanical behavior is comparable to its bulk counterpart, graphite.
• The findings provide critical insights into graphene's mechanical response under stress.