Determination of mechanical properties of thin films is a difficult task since the substrate usually influences the mechanical response of the film and makes the determination of the "pure" film parameters difficult. However, those properties are increasingly important not only in case of hard and protective layers but also for thin films used in other areas such as microelectronics or optics.
We are developing an own approach to mechanical properties of a thin film system on a substrate which consists of the combination of theoretical modelling and high-accuracy nanoindentation using either spherical or pointed indenters. Our method is suited for the determination of mechanical parameters of thin films as well as for the identification of failure mechanisms in thin film/substrate systems in contact with a counterpart. If the mechanical parameters have been determined and the relevant failure mechanism identified, the behaviour of a certain thin film system under mechanical load can be predicted by modelling. In addition, from this kind of "experiments in the computer" conclusions can be drawn about the design of an optimum film stack which withstands a certain loading condition best.
In the talk, the following new results will be presented:
a) Determination of Young´s modulus of extremely thin films (e.g. ta-C films down to 4.3 nm thickness) as well as for films of cubic boron nitride and diamond, i.e. materials which have (nearly) the same stiffness as the indenter,
b) Determination of yield strength in ultra thin coatings below 100 nm or in extremely soft and pliant materials such as aerogels,
c) Performance of a high-sensitivity load-displacment experiment not only
perpendicular to the surface - as it is the usual way in nanoindentation - but also in lateral direction. This technique [3], which is now available in form of a special device, in principle provides two independent load-displacement curves which can be utilized for instance to determine intrinsic stresses in thin films from nanoindentation experiments.
[1] G.M. Pharr, A. Bolshakov, J. Mater. Res. 17 (10) (2002 Oct.) 2660.
[2] N. Schwarzer, Phil. Mag. 86 (33-35) Nov/Dec 2006, 5153-5767, Special Issue.
[3] T. Chudoba, V.Linss, M. Karniychuk, F. Richter, Surf. Coat. Technol. 200 (2005) 315-320. |