Elastic properties of diamond-like amorphous carbon films grown by computer simulation of ion-beam deposition process

The unique mechanical properties of ta-C films such as high hardness and Young modulus are directly related to the atomic structure of amorphous carbon. Atomic-scale modeling is a valuable tool to study both growth mechanisms of amorphous carbon films and the properties sensitive to details of their structure, primarily to the content of sp ³-bonded atoms. As it has been recently demonstrated, the steady-state growth of ta-C thin films can be modeled using the molecular dynamics method with realistic empirical interatomic potentials. It was shown that the experimentally observed high contents of i>sp ³-bonded atoms ( up to 90%) can be achieved using a potential function of Brenner with a slightly increased interaction radius. This provides a possibility to investigate the mechanical properties of amorphous carbon networks generated by a realistic growth process simulation, rather than by quenching the liquid carbon at high pressures as was done in previous
studies.

In this contribution we present results of the investigation of average and atomic-level elastic moduli of amorphous carbon networks with different sp ³-contents, corresponding to C⁺ ion energies of E = 30-80 eV in the ion-beam deposition process.
For the sake of comparison, the calculation of the elastic moduli was performed using not only the potential functions of Brenner, but also the potential function of Tersoff. The relaxational part of elastic moduli was computed using 3D-supercells with about
1000 atoms and an accurate iterative method for the solution of large linear systems. The elastic moduli tensor was found to show only small deviations from the elastic isotropy. Taking into account that the Brenner potential functions underestimate the bulk modulus of crystalline diamond, the results are in an agreement with experimental measurements.