Mechanochemistry of Stable Diamane and Atomically Thin Diamond Films Synthesis from Bi- and Multilayer Graphene: A Computational Study

Mono- and few-layer graphenes exhibit unique mechanical, thermal, and electrical properties. However, their hardness and in-plane stiffness are still not comparable to the other allotrope of carbon, i.e., diamond. This makes layered graphene structures to be less suitable for application in harsh environments. Thus, there is an unmet need for the synthesis of atomically thin diamond films for such applications that are also stable under ambient conditions. Here, we demonstrate the possibility for the synthesis of such diamond films from multilayer graphene using the molecular dynamics approach with reactive force fields. We study the kinetics and thermodynamics of the phase transformation as well as the stability of the formed diamond thin films as a function of the layer thickness at different pressures and temperatures for pristine and hydrogenated multilayer graphene. The results indicate that the transformation conditions depend on the number of graphene layers and surface chemistry. We revealed a reduction in the transformation strain by up to 50%, whereas the transformation stress has reduced by as much as 5 times upon passivation with hydrogen atoms. Although the multilayer pristine graphene to diamond transformation is shown to be reversible, hydrogenated multilayer graphene structures had formed a metastable diamond film. Our simulations have further revealed the temperature independence of the transformation strain, whereas transformation stresses are strong functions of temperature.