Dear Jinkee The colour might be due to the thickness as there is N2 in the chamber there might be N2 in the film. Why dont you analyse the film using Ellipsometry, SEM-EDS or XPS. If you have the facility. Thanks Sarfaraz Moh Thin film centre University of Paisley UK ___________________________________________________________ALL-NEW Yahoo! Messenger - all new features - even more fun! http://uk.messenger.yahoo.com