An investigation of ion implantation-induced near-surface stresses and their effects in sapphire and glass

Using both cantilever bending and indentation fracture techniques, the generation of near-surface compressive stresses by ion-implantation into sapphire and glass has been monitored and characterized. In all cases, the surface stresses initially increase with ion dose until a critical dose (dependent on material and ion species/ energy) is reached. Beyond this dose, stress relief has been observed and, for sapphire implanted with both Y⁺ and Ti⁺, this has been attributed to the formation and growth of an amorphous layer as monitored by hardness testing. The stress relief has been simply modelled and values estimated for the mechanical strength of the amorphous layer produced. For sapphire, the integrated stress produced over the near-surface volume was found to increase linearly with dose; values of the integrated stress produced by the two different species were similar when considered in terms of energy deposition. Estimates of the contribution to the integrated stress of both the implantation-induced damage and the implanted species profile suggest that the implanted profile makes a minor but significant (20%) contribution. Broadly similar behaviour was observed for soda-lime-silica glass specimens implanted with both C⁺ and N⁺. While the origins of the compressive stress produced are probably similar to those in crystalline materials (i.e. defect production and ion-stuffing), no microstructural explanations for both the observed hardening with increasing dose and stress relief have been forthcoming. However, high-dose implantation of N⁺ into glass leads to blistering and concomitant softening.