Surface modification of aluminium by plasma immersion ion implantation

Nitrogen plasma immersion ion implantation (PIII) into pure aluminium was performed at voltages of −10 to −30 kV. Different temperatures, from 250 to 500°C and incident fluences of 1.2–3.6×1018 nitrogen atoms/cm2 were used to investigate the diffusion behaviour and AlN phase formation. X-Ray diffraction (XRD) shows the formation of cubic AlN at temperatures below 300°C, whereas hexagonal AlN appears beyond 390°C. No observable diffusion was measured, using ion beam techniques, at temperatures below 300°C, limiting the retained dose to approximately 10% of the incident ion flux. At higher temperatures, thermally activated diffusion with an activation energy of approximately 1 eV leads to an inward diffusion, albeit not the formation of thick stoichiometric AlN layers. The retained dose is increased to approximately 35% for 500°C and a fluence of 1.2×1018 nitrogen atoms/cm2. A long diffusion tail of nitrogen, below the solubility limit is detectable with SIMS, correlated with a lattice expansion of the native Al by approximately 0.7%.