Elastic modulus of thin homogeneous films can be determined by indenti
ng the specimen to various depths and extrapolating the measured (appa
rent) E-values to zero penetration. The paper shows the application of
five approximation functions for this purpose: linear, exponential, r
eciprocal exponential, Gao's, and the Doerner and Nix functions. Compa
rison of the results for 26 film/substrate combinations has shown that
the indentation response of film/substrate composites can, in general
, be described by the Gao analytical function. In determining the thin
film modulus from experimental data, satisfactory results can also be
obtained with the exponential function, while linear function may be
used only for thick films where the relative depths of penetration are
small. The article explains the pertinent procedures and gives practi
cal recommendations for the testing.