Surface chemical effects of low-energy N-2(+) ion bombardment on single crystalline alpha-Al2O3

Composition changes and chemical structure alterations initiated by ion bea ms on metal oxide surfaces have been widely studied. Significant difference s in the effect of low-keV inert (Ar+) and reactive (N-2(+)) ion impact on a series of metal oxides have been published recently by the present author s. In this work the effect of 0.5-5 keV N-2(+) bombardment on single crysta lline alpha-Al2O3 was studied by quantitative XPS. Clarifying the existing ambiguity, experimental evidence is presented that supports the preferentia l oxygen loss and build-up of nitrogen. The oxygen Loss increased with incr easing N-2(+) ion energy until approaching an atomic ratio saturation value of O/Al similar to 1 on 3.5 keV bombardment with the concomitant build-up of N at N/Al similar to 0.5. In contrast to other oxides, for alpha-Al2O3 t wo major types of nitrogen were detected on N-2(+) impact; the two N 1s lin es were separated by 7 eV, The one at 396.4 eV binding energy corresponds t o a nitride-type N-Al environment, similar to that found in bulk AlN, Forma tion of the nitride is interpreted as the result of replacement of lattice oxygen around Al by implanted nitrogen in a two-stage process. The 403.4 eV component is assigned to nitrogen trapped in the cation-deficient lattice of alpha-Al2O3 in empty octahedral sites surrounded by oxygen atoms bonded to Al. Both of these chemical states of nitrogen were stable on heating up to 550-650 degrees C, Copyright (C) 2000 John Wiley & Sons, Ltd.