An　improved　MBE-grown　ZnO　film　on　nitrided　sapphire　was　obtained　by　introducing　an　MgO　buffer　layer　before　the　ZnO　growth.　The　effect　of　MgO　layer　was　systematically　studied　by　transmission　electron　microscopy　investigations.　It　was　found　that　the　island　feature　of　MgO　buffer　promoted　the　strain　relaxation　of　the　nitrided　layer,　which,　in　turn,　improved　the　quality　of　the　ZnO　film.　(c)　2007　Elsevier　B.V.　All　rights　reserved.