Damage evolution and surface morphology of helium implanted yttria-stabilized zirconia single crystal

The effects of helium ion implantation on the surface morphology of (1 0 0)-oriented yttria-stabilized zirconia (YSZ) single crystals have been studied. Ion implantation at various fluences in the range 0.01–5.1 × 1016 He-atoms/cm2 has been carried out at room temperature using a 2.74 MeV He+ ion beam passing through a 8.0 μm Al foil. The microstructure and surface morphology of the irradiated surface are examined using atomic force microscopy. Rutherford backscattering spectrometry combined with the channeling technique is applied for the investigation of lattice damage and for the thickness determination of the implanted layer. The ion-irradiated areas are found to protrude to different heights in nm scale. The fluence dependence of the magnitude of rms roughness exhibits a very sharp increase with the increase of the ion dose at higher fluences and in a narrow range between 2 × 1016 and 5.1 × 1016 cm−2, which is preceded by a linear increase at lower fluences. Given a sufficient concentration for implanted He, above 2 × 1016 cm−2, surface blistering occurs directly during implantation. The size and distribution of blisters are dependent on the total helium content. For the specimen with a fluence 4.0 × 1016 cm−2, an annealing has been conducted at 300 °C. After the annealing, some of the blisters are found to become larger in size, up to about 10 μm in diameter and 1 μm in height without rupture. Within the present experimental conditions, no signature of any surface exfoliation or flaking in YSZ is observed. A tentative explanation of the results is presented.