Refractive indices of metastable and amorphous phases in Ne+-ion irradiated magnesium–aluminate spinel

Abstract Single-crystal MgAl2O4 was subjected to 180 keV Ne+-ion irradiation to fluences of (1, 5, and 10)×10 20 ions/m 2 . The metastable and amorphous phases induced by irradiation were studied using transmission electron microscopy (TEM) and optical transmission spectroscopy. The thicknesses of implantation-induced layer structures were obtained from TEM observations. This information was then used in conjunction with optical transmission results to deduce the refractive indices of individual structures. It was found that the lowest ion fluence produces a metastable layer with a reduced index of refraction (n=1.70±0.005) relative to the pristine substrate (n=1.72), whereas the intermediate fluence induces an amorphous region (n=1.61±0.01) bounded by metastable regions. The effect of the highest fluence is to increase the thickness of the amorphous layer (n=1.60±0.01) at the expense of the metastable regions.