Comprehensive analysis of the surface and crystal properties has been performed at clean c-plane sapphire substrates, sapphire layers after nitridation, and subsequently grown InN layers deposited by metal-organic vapor phase epitaxy. The (1 x 1) surface of clean sapphire reconstructs into a (root 31 x root 31)R +/- 9 degrees structure after annealing at 1050 degrees C, which was performed prior to the nitridation process. The formation of crystalline AIN was observed for nitridation above 800 C. X-ray photoelectron spectroscopy performed on the nitridated layers shows that N-Al chemical bonds dominate this structure, while the number of N-O bonds is negligibly small. Amorphous AlNxOy, layers form during nitridation below 800 C, where N-O bonds dominate. All layers formed by nitridation show defects associated with N bonds. The morphology of the nitridated layers affects the surface and crystal quality of the subsequently grown polar InN layers. N-polar InN layers with a smooth surface and single crystalline structure were grown on the AIN nitridated layers, while In-polar InN layers with a rough surface and a polycrystalline structure were grown on the amorphous nitridated layers. (c) 2014 Elsevier B.V. All rights reserved.