Ultra-thin diamond films, diamanes, represent a diamond with a thickness of one unit cell. As a method for their preparation, the effect of a chemically induced phase transition was proposed, according to which multilayer graphene can be converted into a diamond film only under the action of chemical adsorption of adatoms on the surface (hydrogen, fluorine, etc.). We have studied the stability of diamanes and constructed a phase diagram of the transition of multilayer graphene to diamane depending on the thickness of the films and the type of surface.
A controlled tuning the structure of nanomaterials at the atomic level is the most important problem of modern materials science. Description of nanostructures stability requires to take into account their size and surface effects. This problem is especially clearly seen in the study of the phase transformation of nanomaterials, when the phase transition depends not only on external conditions, but also on the contribution of surface effects. For example, the classical Bundy’s carbon phase diagram changes with decreasing carbon film thickness, the graphite-diamond phase transition pressure increases, which reflects an increase in the instability of diamond with size reduction. Upon reaching the atomic thickness, diamond films should demonstrate a number of extremely attractive physical properties, but their synthesis requires fundamentally different approach. Two ways of synthesis of nanomaterial usually considered: the “top-down” and “bottom-up” approaches. The top-down paradigm, when macroscopic material is separated to the required nanostructure probably is not the case, since it is impossible to obtain diamond films of nanometer thickness by separating the bulk diamond. The bottom-up approach (the required nanostructure is synthesized from smaller nanostructures) seems to be the most relevant for this case, although it certainly requires overcoming a number of non-trivial scientific problems. The traditional method of chemical vapor deposition is not applicable for solving the problem of obtaining diamond films of atomic thickness due to the high growth rate and their imperfection at the atomic level. In this project, we will consider another option for producing diamond films, when the initial material is not gas, but a bilayer graphene film. Their formation occurs through a controlled chemical reaction of two graphene sheets with reference atoms, mainly hydrogen and fluorine. We will try this method in an experiment, and we will study theoretically in details the mechanism of transformation of graphene layers not only in the case of bilayer graphene, but also other structures based on weakly coupled layers, double-walled carbon nanotubes and other related nanomaterials.
The project PI is Dr. habil. Pavel Sorokin.