Multistability of graphene nanobubbles.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Graphene nanobubbles are formed by encapsulating atoms within a graphene sheet on a substrate.
• The behavior and stability of these nanostructures are crucial for understanding their potential applications.

Purpose of the Study:

• To investigate the multistability of graphene nanobubbles using noble gas atoms as a model system.
• To determine the factors influencing the structural configurations and stability of nanobubbles.
• To analyze the impact of temperature and pressure on nanobubble states.

Main Methods:

• Utilized noble gas atoms (He, Ne, Ar, Kr, Xe) as a model system for simulations.
• Performed numerical simulations of thermal vibrations to study nanobubble dynamics.
• Analyzed the effect of varying numbers of encapsulated atoms (N) on layer formation (l).

Main Results:

• Graphene nanobubbles are multistable systems, with stable states characterized by the number of encapsulated atom layers (l).
• The maximum number of layers (l_m) increases with the number of atoms (N), reaching l_m=6 for N=4000.
• Internal pressures reach ~1 GPa due to graphene membrane compression.
• A ground state always exists, transitioning to a liquid state upon heating; other states transform to the ground state at characteristic temperatures (T_l).
• For N=4000, the ground state is the four-layer packing (l=4).
• Nanobubble shape (H/R ratio) is not universal, varying from 0 to 0.28, with H/R ~ 0.2 specific to ground states.
• External hydrostatic pressure does not alter multistability but can induce crystallization, decreasing the H/R ratio.

Conclusions:

• Graphene nanobubbles exhibit complex multistability dependent on encapsulated atom configurations.
• The observed structural diversity challenges the notion of a universal nanobubble shape.
• Understanding these states is key for controlling nanobubble properties in potential applications.