A　magnesium　wetting　layer　was　used　to　modify　the　surface　structure　of　MgAl2O4　(111)　substrate　to　achieve　growth　of　high-quality　ZnO　film　by　radio　frequency　plasma-assisted　molecular　beam　epitaxy.　It　is　found　that　this　magnesium　layer　plays　a　crucial　role　in　30　degrees　rotation　domain　elimination,　defect　density　reduction,　and　polarity　control　of　ZnO　film,　as　demonstrated　by　in　situ　reflection　high-energy　electron　diffraction　and　ex　situ　transmission　electron　microscopy.　Atomic　force　microscopy　observation　shows　smooth　ZnO　surfaces　with　clearly　resolved　atomic　steps　of　the　films.　(c)　2007　American　Institute　of　Physics.