The rates of unlayered graphene formation in a supercooled carbon melt at low pressure

Five-Membered Loop-Initiated Nucleation of Unlayered Graphene Sheets in a Carbon Melt, with Diffusion Barrier Possibilities

“…From a look at stellar atmosphere temperature and ejection models, as well as simple constraints operating during our laboratory synthesis, we estimate that the cooling for these presolar droplets was at least 7 orders of magnitude slower than the cooling rate of condensed droplets in the lab . Using a two-dimensional (2D) extension of classical nucleation theory, as well as some atomistic work with semi-empirical potentials, we now have a model for liquid-to-solid nucleation and growth which fits reasonably well with the observations on sheet size and number density in both types of specimens …”

“…That in turn may be key to the diffusion barrier properties of that composite, since diffusion through van der Waals bonded layers (e.g., in mica and graphite but not in this material) is a well-known mechanism for the transport of materials over geologic times. , Pentagons are the seed cluster on which the observed faceted pentacones are likely based, just as a unit cell might be the minimum size seed structure on which a precipitated three-dimensional (3D) crystal is based. The precipitation model research then easily adapts this focus on the stability of a particular structure to a focus on the critical stability temperature of single loops as a way to infer the lowest temperature below which supercooling cannot survive . Of static focus on the abundance of 5- vs 6-member loops examined the possibility, inferred from observation, that 5-member loop nucleation may be a competitive path to the formation of the larger structures observed.…”

A Semi-empirical Model for the Containerless Solidification of Liquid Carbon

“…In this work we derive 2D nucleation and growth models for graphene sheets from a carbon melt to study the solidification processes, undercooling for liquid carbon, and the saturation process when considering different cooling rates. The nucleation model builds on the classic and modern approaches of nucleation theory − but begins with ring nucleation because high binding-energy hex-rings are a key component of graphene which has been observed in unlayered form in both astrophysical and lab specimens, in the former case in likely faceted pentacone form. The growth model follows a single fixed Arrhenius activation energy model, starting with our independent DFT and experimental work predictions of 5- and 6-atom critical nucleus rings .…”