(45e) Laser Induced Buckling for Micrscale Patterning

Buckling of thin films is a simple way to fabricate micro-scale structures without the use of expensive lithographic processes or clean rooms. It is possible to form buckles on a surface by heating a film stack of two or more layers. Buckles form over the entire surface due to the stresses arising from mismatch in thermal expansion between the layers. Here, we induce buckles only at specified locations of an aluminum/polystyrene/silicon film-stack by delivering heat locally to the surface of the film via a laser beam. Buckles form without the need for additional heating. Rastering the laser beam across the surface can form shapes such as circles, lines, and squares composed of individual buckles. The buckles have wavelengths ranging from 3.5 mm-11.2 mm depending on the polymer film thickness. Conventional buckling theory predicts these wavelength values, suggesting that they are indeed driven by thermal expansion. The resolution of features formed by conventional laser ablation is closer to 50 µm; thus, buckling offers a way of patterning structures with ‘sub-ablation’ dimensions. The ability to pattern buckles may find applications in optoelectronics, biology, biomedical engineering, and microfabrication.