We describe a method using grazing incidence di€ractometry (GID) with a rotating anode X-ray source to measure the in-plane alignment of $10-nm thick MgO ®lms deposited by ion beam assisted deposition (IBAD). In conjunction with these measurements, we have calibrated the IBAD ®lm growth process by monitoring the ®lm in situ with re¯ected high-energy electron di€raction and comparing the intensity versus time curve with results obtained from the ex situ GID measurements. GID has also been used to identify di€erences in the observed in-plane texture for samples with and without the addition of a homoepitaxial layer. Improvements in texture after the addition of the homoepitaxial layer are attributed to the healing of ion induced damage during growth of the IBAD layer. Further analysis has re-vealed that standard X-ray di€raction measurements of these overcoated ®lms do not suciently quantify the in-plane alignment of the initial IBAD layers. Ó 2001 Elsevier Science B.V. All rights reserved.