Indentation response of a thin film on Si (001) probed with a Berkovich indenter at the stated loads. A TiN coating and bulk Si (001) are shown for comparison at 5 and 35 mN.
(a) Composite modulus and (b) hardness of films synthesized at of tested with a Berkovich indenter for a load range from 2 to 35 mN compared to the response of bulk Si (001) and a more compliant FL synthesized at . The film-only hardness and modulus values of the coatings were extrapolated according to Ref. 12.
Cross-sectional TEM images of thin films after indentation at (a) 20 mN and (b) 35 mN. High-resolution images of the marked areas in (b) indicate amorphization around the intact cone of (001) Si. No damage was detected in the films up to 35 mN and in the Si at loads .
von Mises stress along the axis under the intender simulated by FEM considering a linear elastic response of the film as well as a critical yield strength of 11 GPa for the Si substrate (164 GPa) resulting in unrealistically high maximum values as well as substrate failure for loads .
The equivalent normal stress for the stated maximum loads exerted by the effective indenter as fitted from the experimental load-displacement curves with the FILM DOCTOR software. An increasing deviation from the ideal Hertzian shape is most pronounced for higher loads.
von Mises stress along the -axis resulting from the fitted normal stress distribution (Fig. 5) as calculated with the FILM DOCTOR software. The maximum of in the signifies a limit of linear elastic behavior, while the experimentally verified yield strength of Si of (Ref. 22) is reproduced for indentation loads .
Comparison of the experimentally obtained load-displacement curve and the by FEM simulated data considering linear elastic behavior (Fig. 4) as well as an elastic limit of in the coating. The good agreement of the latter is evident; while the deviation at higher loads is attributed to the phase transformation of Si.
(a) von Mises stress, (b) shear stress, and hydrostatic pressure (c) along the interface as analytically calculated by the FILM DOCTOR software and compared to the results obtained by FEM simulations. The shaded area indicates the region were phase transformation of Si is observed in TEM (Fig. 3).
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