Role of Fe and Ni nanoparticles on mechanical properties of alumina thin films deposited by laser ablation

Abstract

This paper reports our recent work on the improved mechanical properties of alumina thin films with embedded Fe and Ni nanopaiticle layers. The Fe/Ni nanoparticles-alumina composite thin films have been deposited using a multi-target pulsed laser ablation technique. Every film consists of 10 layers of alumina and 9 intermediate layers of Fe or Ni nanoparticles. Alumina layer thickness kept constant (∼22 nm) and total thickness of multilayered films was in range 220-280 nm depending on metal deposition lime. Composite thin films were deposited at six different substrate temperatures in the range 200-800°C. The mechanical properties measurements, performed by nanoindentation in continuous stiffness mode and applying Nix-Bhattacharya (hardness H) and King's model (Young's modulus E) for film-only properties, have shown that pure alumina films deposited at temperatures 200-500°C are relatively soft (H =15 GPa, E = 190 GPa), while films deposited at ≥600°C are significantly harder (H = 32 GPa, E = 320 GPa). Grazing incidence XRD (GIXRD) data indicated that γ-alumina peaks exist in high temperature samples while alumina films deposited at ≤500°C were amorphous. Embedding Ni and Fe nanoparticle layers at 500°C led to significant increase of H and E (31 GPa and 365 GPa with Fe and 33 GPa and 380 GPa with Ni) and appearance of γ-alumina peaks in GIXRD. Embedding on metal nanoparticle layers does not change mechanical properties of alumina films deposited at 200°C, and significant hardening of metal containing films starts at 400°C. These results suggest that metal nanoparticles have a catalytic effect on the growth of alumina thin films with enhanced crystallinty. The effect of Ni and Fe nanoparticle size on mechanical properties of thin films has been studied times at substrate temperature 500°C using eight different metal deposition. HRTEM data have shown that metal nanopartiles have uniform particle size distribution and inter-particle separation in the layer. Size of Ni and Fe nanoparticles with highest effect on mechanical properties was 4 -6 nm. © 2006 Materials Research Society.