The chemical, structural, mechanical and optical properties of thin aluminum oxide films deposited at room temperature (RT) and 800 degrees C on (100) Si and Si-SiO2 substrates by pulsed laser deposition and plasma enhanced chemical vapor deposition are investigated and compared. All films are smooth and near stoichiometric aluminum oxide. RT films are amorphous, whereas gamma type nano-crystallized structures are pointed out for films deposited at 800 degrees C. A dielectric constant of similar to 9 is obtained for films deposited at room temperature and 11-13 for films deposited at 800 degrees C. Young modulus and hardness are in the range 116-254 GPa and 6.4-28.8 GPa respectively. In both cases, the results show that the deposited films have very interesting properties opening applications in mechanical, dielectric and optical fields. (C) 2007 Elsevier B.V. All rights reserved.