Nucleation stages and surface morphology evolution of epitaxial SrBi2Ta2O9 thin films on SrTiO3 (001) substrates have been studied by ultra-high vacuum atomic force microscopy. The SrBi2Ta2O9 nucleates and grows half-unit-cell by half-unit-cell as well-defined 2D islands at low coverage. After 2D growth stage, which proceeds up to several half unit-cell layers, a transition from 2D to 3D island growth is observed. After coalescence of small 3D islands into larger islands, clear columnar structures, consisting of spirals, emerge. The surfaces of films with their thickness above 1500 A exhibit round hills consisting of curved terraces with sizes of steps ranging from 6 Å to 12.5 Å.
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