Scientific Advisory Board - Erich Schmid Institute

ERICH SCHMID INSTITUTE OF MATERIALS SCIENCE
testing with the Afm is a good method to study the deformation behavior of ductile films and to
be able to compare them with other films on soft substrates.
further fragmentation experiments include in situ synchrotron tensile tests operated at the
Kmc ii beam line at the Berliner elektronenspeicherring-gesellschaft für Synchrotronstrahlung
(BeSSY ii) in Berlin. the common sin²ψψ method was used to obtain the copper lattice strains in
longitudinal (parallel to straining direction) and transverse (perpendicular to straining direction)
directions to measure the stresses in the films during straining. the results of the film stresses
of 50, 100 and 200 nm cu films are shown in fig. 14 for both directions. All curves of the
longitudinal direction exhibit nearly the same progression (fig. 14a). the film stresses initially
rise with increasing strain up to a peak stress, after which the stresses decrease due to the
plastic deformation and crack formation until a plateau is reached at about 5-8% strain. the
stresses decrease into the compressive region during the unloading of the sample. Because
of the mismatch of the poisson ratios between copper and polyimide, the film stresses of all
different thicknesses show lower values in the transverse direction than in the longitudinal
(fig. 14b). All samples exhibit the same film thickness tendency: the higher the film thickness
the higher are the film stresses. the stresses can be directly compared to Sem and Afm
fragmentation experiments and the peak stresses correspond to the initial yielding of the films.
the plateau stresses relate to when crack saturation is reached.
Fig . 14 Results of the film stresses for the 50, 100 and 200 nm thick Cu films in (a) longitudinal
and (b) transverse sample direction. The plateaus were indicated by straight lines. The images
in the left edge show the cracked sample strained in tension with the measured x-ray direction
(white arrows).
Mechanically Robust Film-Substrate System
mechanical properties of metal films on polymer substrates are normally studied in terms of
the fracture and adhesion of the film, while the properties of the polymer substrate and testing
conditions were overlooked. Substrate orientation and thickness, as well as strain rate and
temperature effects are examined using cr films deposited onto polyethylene terephthalate
(pet) substrates. the effects of substrate orientation and thickness, strain rate and temperature
have been examined for cr films on pet. only temperature alters the film fracture and buckling
behavior when strained at higher temperatures of 70nm and 150nm thick cr films on pet. the
average crack spacing of the films increased when strained at 80°c or 180°c and the buckle
shape changed from a sharp to a smooth, rounded cross-section with increased temperature
(fig. 15). the change in buckle size and shape corresponded to a qualitative decrease in
the adhesion energy and no substrate deformation underneath buckles at high temperatures
Scientific RepoRt 2012 page 29