Applied Physics

Buckle Up

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Science  30 Jul 2004:
Vol. 305, Issue 5684, pp. 577
DOI: 10.1126/science.305.5684.577c

Thin films made from soft materials such as polymers are increasingly finding use as coatings, filters, and lithographic resists. Although nanoindentation can be used to measure the mechanical properties of thin films of hard materials, such as metals or ceramics, it is far less accurate for soft viscous materials, and it tends to tell you more about the underlying substrate than the film itself.

Stafford et al. have developed a technique for the rapid and quantitative measure of the elastic modulus of a thin stiff film by placing it on a thick softer substrate and then gently applying stress. This causes the film to buckle, with the resulting periodicity and amplitude dependent on the material properties of both the film and the substrate. The buckling pattern is measured as a diffraction pattern from a scattered laser beam. The authors validated their method using polystyrene films on a polydimethylsiloxane substrate, which included films with varying thickness across their length. They also showed that the method could be applied to more technically challenging porous organosilicate films, which are difficult to analyze but of considerable interest as low-k dielectric materials. — MSL

Nature Mater. 10.1038/nmat1175 (2004).

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