Molecular Dynamics Simulations of Hydrocarbon Film Growth from Acetylene Monomers and Radicals: Effect of Substrate Temperature
M Zarshenas and K Moshkunov and B Czerwinski and T Leyssens and A Delcorte, JOURNAL OF PHYSICAL CHEMISTRY C, 122, 15252-15263 (2018).
In an attempt to rationalize the mechanisms occurring during plasma polymerization of acetylene, classical molecular dynamics computer simulations investigating the deposition and reaction of a mixed gas of acetylene molecules and radicals on the Ag(111) substrate were performed for a wide range of substrate temperatures. Prior to that, this article establishes a methodology for film deposition and identifies the appropriate potentials for hydrocarbons by comparison with electronic calculations using density functional theory. On the basis of this preliminary study, simulations of film growth are carried out at different temperatures using the reactive empirical bond order potential. Our results show that the rates of formation of new C-C and C-H bonds are higher at the beginning of the film growth when the substrate is still exposed than when it is covered with polymeric chains, and these initial reaction rates are proportional to temperature. The analysis of the hybridization of carbon atoms in the films shows that the substrate temperature increase leads to the formation of coatings containing more carbon atoms in the sp(2) and sp(3) configurations and less in the sp configuration with sp(2) becoming dominant at high temperatures. We establish a polymerization connectivity formalism that describes the structural transformation of the film during the deposition on the basis of each atom hybridization and bonding. Within this formalism, the evolution of the polymerization and the connection character of the polymers is observed and discussed.
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