Atomistic study of the solid state inside graphene nanobubbles

Abstract

A two-dimensional (2D) material placed on an atomically flat substrate can lead to the formation of surface nanobubbles trapping different types of substances. In this paper graphene nanobubbles of the radius of 7–34 nm with argon atoms inside are studied using molecular dynamics (MD). All modeled graphene nanobubbles except for the smallest ones exhibit an universal shape, i.e., a constant ratio of a bubble height to its footprint radius, which is in an agreement with experimental studies and their interpretation using the elastic theory of membranes. MD simulations reveal that argon does exist in a solid close-packed phase, although the internal pressure in the nanobubble is not sufficiently high for the ordinary crystallization that would occur in a bulk system. The smallest graphene bubbles with a radius of 7 nm exhibit an unusual “pancake” shape. Previously, nanobubbles with a similar pancake shape were experimentally observed in completely different systems at the interface between water and a hydrophobic surface.

The Gas in Graphene Bubbles: An Improved van der Waals Equation Description

“…Figure shows that the value of h / a from eq is 0.15, which is in good agreement with the MD simulation results. A similar value has also been obtained by previous work for the height-to-radius ratio. ,, The value for the height-to-radius ratio in the experiment is in the range of 0.1 to 0.15 . It shows that the theoretical prediction from the membrane theory agrees with both MD simulations and the experiment, so the membrane theory can provide a good description for the height-to-radius ratio.…”

“…This additional equation is to describe the state of the gas inside the bubble. Several experiments have observed very high pressure for the gas in the graphene bubble, which is typically on the order of 1 GPa. , The gas pressure is so high that it may cause phase transition for the trapped substance, − or induce some high-pressure chemical reactions . It is thus important to investigate how to describe the gas inside the graphene bubble.…”

Universal shape of graphene nanobubbles on metallic substrate

“…3(b), the observed aspect ratios are notably larger than the results of previous experiments 8 and simulations. 39 To theoretically estimate the ratio H / R we use the model proposed in work 8 neglecting the bending rigidity:where γ GS , γ GB , and γ SB are the adhesion energies between graphene-substrate, graphene-substance, and substrate-substance, respectively; Y is the Young modulus; c 1 is the dimensionless parameter. In the case of the dome graphene membrane and round base the Young modulus Y = 22 eV A −2 and the parameter c 1 = 1.7 are known from.…”

Intercalation, decomposition, entrapment – a new route to graphene nanobubbles

“…Pressures within these bubbles have been reported to be in the order of MPa [4][5][6][7] , with one report achieving up to 1 GPa 8 . The small volumes of gas contained within GNBs are therefore a route to study gas-phase reactions in small volumes or under high pressures, potentially producing new exotic phases of matter 9 . GNBs, and larger micro-scale bubbles, are regularly found between the graphene and silicon-oxide substrate, believed to have formed due to the trapping of air upon the transfer of mechanically exfoliated graphene flakes onto the flat substrate 10,11 .…”