engleski

Topography of Thin Film Buckling Patterns

Morphology and topography of buckling patterns in residually compressed thin film, during or after its delamination from the substrate, were studied by a home made Digital Optical Holographic Microscope. For tungsten thin films deposited by magnetron sputtering, it is well known that argon pressure significantly affects the film internal stress. In the case of tensile residual stress a network of through-thickness cracks forms in the film, while the residually compressed thin films may delaminate from substrate and buckle. A number of buckling patterns such as disordered surface wrinkles, regular herringbone, straight-sided or telephone cord buckles and circular blisters has been studied are analysed. Delamination usually starts as straight-sided linear wrinkle, but then deviate to the the telephone cord (TC) periodic wavy geometry due to the fact that the compressive residual stress in the film is biaxial. In general, buckling profiles can be characterized, by scanning electron microscopy, mechanical or laser-scanning profilometry, optical interferometry, or depending on scale - by using an atomic force microscope. Our home-adapted Digital Optical Holographic Microscope is a commercial metallurgical instrument with sophisticated extensions. The extended set-up consists of two lines for traditional imaging and digital hologram recording, plus a line for “real time” hologram reconstruction. It provides simultaneous or alternative white-light or monochromatic illumination of the very same area of a specimen. By traditional imaging and optical processing in holographic mode, one can display interferometric fringes patterns that reveal lateral and vertical buckling features with precision: Δl ≈ Δh ≈ 0.3 μm. Correlation of traditional microscopy and holographic interferometry provides topography data basis for quantitative 3-D modeling of TC buckling morphology and associated stress-strain mechanics.

Topography; Thin Film; Buckling Patterns

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