Evaluation of the mechanical properties of sol–gel-deposited titania films using ultra-micro-indentation method

In the present work, we have investigated the use of ultra micro-indentation for the determination of mechanical properties of thin films. Here, we present results obtained for sol–gel-deposited titania (TiO2). The films were deposited on glass (“hard”) and copper (“soft”) substrates using the sol–gel process. The film thickness was varied from about 50 to over 200 nm by the number of dips. The indentation experiments were performed using UMIS 2000, with spherically tipped indentor with nominal radius of 10 μm. The applied 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 the order of 100 nm. Indentation stress–strain curves were obtained, from which the values of hardness (H), and elastic modulus (E) for the film is derived. The results obtained indicated that the values of H and E determined were independent of the film thickness. The measured hardness values averaged about 1.2 GPa for as-deposited film, while E was in the range of 55–65 GPa. Higher values of H (1.5 GPa) and E (∼85 GPa) were obtained for films heat-treated at 550°C. These higher values of E and H are attributed to the thermally induced crystallisation of the initial amorphous phase and possibly due to the elimination of the chemisorbed CH-group characteristic of sol–gel films. The value of this method as a non-destructive procedure for the characterisation of the mechanical properties of thin films on either hard or soft substrates is discussed.