In situ Study of Cracking and Buckling of Chromium Films on PET Substrates

Abstract

Chromium (Cr) films are widely used as interlayers to promote the adhesion of copper or gold to substrates. However, the Cr interlayer usually fractures at lower strains than the ductile metal films. In this paper, the cracking and buckling behavior of Cr films on polyethylene terephthalate (PET) substrates were studied in situ under tensile loading with the Atomic Force Microscope (AFM) and optical microscope imaging. Cr films with three nominal thicknesses of 15, 70 and 140 nm were studied. The depth and width of the cracks, as well as the height and width of the buckles, were measured from AFM images acquired at incremental loading steps. The buckle shapes at different strain levels were carefully examined using AFM line profile. It was found that at large strain levels the measured buckle shapes usually deviated from the elastic buckling mode shapes. Further in situ AFM imaging of the buckles at a smaller scan area revealed that in some cases the buckles were cracked at the apex. These in situ nanoscale measurements provided experimental observations and data for further model development and more accurate measurement of the interfacial fracture energy at the Cr-PET interface.

Ductile film delamination from compliant substrates using hard overlayers

“…Additionally, the CuTi film was strained in situ under the atomic force microscope (AFM) [25,30–33] to better observe the surface deformation (necking) and crack formation as a function of strain. For this, a miniaturized screw-driven tensile stage was utilized with a 25 μm × 25 μm scan size at 1 Hz and a 512 dpi resolution.…”

Robust mechanical performance of chromium-coated polyethylene terephthalate over a broad range of conditions

“…Samples were strained to crack and buckle saturation at room temperature in the MD. Other studies of Cr films on compliant substrates have observed similar channel cracking and buckles forming between cracks [6,10,29,30]. The evolution of the crack density (1/) with ex situ straining is shown in Figure 5 for the 15-and 150-nm Cr films strained at 4 Â 10 À4 s À1 on PET substrates in the MD Crack spacings at saturation are also the same in both orientations for the 150-nm film: ¼ 9.5 AE 3.2 mm in the MD and ¼ 9.1 AE 1.3 mm in the TD.…”

Fracture behavior and adhesion energy of nanostructured Cu/Mo multilayer films

“…3(b), where one can see that the average buckle heights and widths generally increased with increasing the modulation period λ . Jin et al [22] found that, in the single layer Cr films on flexible polyethylene terephthalate substrate, both the buckle widths and heights markedly increased when the film thickness was varied from 15 nm to 140 nm. Similar results were observed in Pundt et al's work [17,23] on polymer-supported Nb films.…”