Molecular Dynamics simulations of plasma sputtered ZrxCu1-x amorphous metallic glass thin film growth. Effects of composition and kinetic energy
Résumé
Recently, there has been a huge interest in the atomic-level structure and structure-property relationship in metallic glasses (MGs). These materials have been studied for 40 years because of their promising properties belonging to both metals (electron, heat conductivity, ductility...) and glasses (hardness...). To stabili e an amorphous phase in metallic alloys, atomic diffusion must be prevented. This could be achieved by playing with the chemical composition (mixing of elements with different atomic sizes) or by freezing low ordered phases during the synthesis process. It has been shown that deposition of thin films by condensation onto substrates, even at ambient temperature, allows to synthesize metallic glasses even in binary systems. In this work, we employed classical molecular dynamics simulations model to study ZrxCu100-x (3 ≤ x ≤ 9 ) metallic alloy films deposited on a silicon (100) substrate. Input data were chosen to fit with typical experimental operating conditions of magnetron sputter deposition process. The evolution is monitored with variable compositions of deposited atoms. The Zr-Zr, Cu-Cu and Zr-Cu interactions are modelled with the Embedded Atom Method (EAM), the Si-Si interaction with Tersoff potential, the Zr-Si and Cu-Si interactions with Lennard-Jones (12-6) potentials. Snapshots are created for vizualization purposes. X-Ray Diffraction patterns and Radial Distribution Functions are calculated for direct comparison with sputter deposition experiments. Different film morphologies and structures are evidenced when the Zr/Cu composition ratio and the argon sputtering gas pressure are varied. Varying the argon sputtering pressure results in the variation of the Zr and Cu kinetic energies which in turn modifies the input parameters for carrying out the MD simulations. The results are compared with X-Ray Diffraction and Scanning Electron Microscopy analyses of experimentally deposited thin films by magnetron co-sputter deposition. Both simulation and experimental results show that the structure of the ZrxCu100-x film varies from crystalline to amorphous depending on the Zr concentration. The kinetic energy affects the layer morphology : below a threshold kinetic energy the film is nanostructured and above it becomes continuous.