Evaluation of the mechanical properties of sol-gel-deposited titania filmsusing ultra-micro-indentation method

In the present work, we have investigated the use of ultra micro-indentatio n for the determination of mechanical properties of thin films. Here, we pr esent results obtained for sol-gel-deposited titania (TiO2). The films were deposited on glass ("hard") and copper ("soft") substrates using the sol-g el process. The film thickness was varied from about 50 to over 200 nm by t he number of dips. The indentation experiments were performed using UMIS 20 00, with spherically tipped indentor with nominal radius of 10 mu m. The ap plied indentation force was varied systematically from the contact force of 0.1 mN to a maximum of 10 mN and the maximum indentation depths were of th e order of 100 nm. Indentation stress-strain curves were obtained, from whi ch the values of hardness (H), and elastic modulus (E) for the film is deri ved. The results obtained indicated that the values of H and E determined w ere independent of the film thickness. The measured hardness values average d about 1.2 GPa for as-deposited film, while E was in the range of 55-65 GP a. Higher values of H (1.5 GPa) and E(similar to 85 GPa) were obtained for films heat-treated at 550 degrees C. These higher values of E and H are att ributed to the thermally induced crystallisation of the initial amorphous p hase and possibly due to the elimination of the chemisorbed CH-group charac teristic of sol-gel films. The value of this method as a non-destructive pr ocedure for the characterisation of the mechanical properties of thin films on either hard or soft substrates is discussed. (C) 2000 Elsevier Science S.A. All rights reserved.