Effects of He+ ion implantation on optical and structural properties of MgAl2O4

Single crystals of magnesium-aluminate spinel were implanted with 170 keV H et ions to fluences ranging from 1 x 10(16) to I x 10(21) ions/m(2) at 120 K. The effects of ion implantation were studied using Optical Absorption Sp ectroscopy, Rutherford Backscattering Spectroscopy and Ion Channeling (RBS/ C) and Transmission Electron Microscopy (TEM). In absorption spectra obtain ed from the implanted samples, growth of an F-center band at 5.3 eV was obs erved. At the fluence of 3 x 10(20) ions/m(2), the growth of this band not only ceases but the intensity suddenly decreases. This may be due to format ion of a new phase at this fluence. This is partially confirmed by the fact that at this and higher ion doses, a modulated absorbance becomes apparent in the absorption spectrum of spinel. This effect is caused by formation o f a buried layer with refraction index lower than that of an unimplanted sa mple. RBS/C and TEM measurements show that spinel is not amorphized over th e fluence range examined in this study. TEM microdiffraction observations s how that in the damaged region the intensities of superlattice spots decrea se significantly, suggesting that ion beam irradiation induces either an or der-disorder phase transition or a transformation into the so-called "metas table" phase of spinel. (C) 2000 Elsevier Science Ltd. All rights reserved.