Patterning Buckles in Polymer/Metal Thin Films By Laser Irradiation

Patterning Buckles in Polymer/Metal Thin Films by Laser Irradiation

Kunal Mondal^#, Ying Liu^#, Michael D Dickey*, Jan Genzer*

Department of Chemical & Biomolecular Engineering, NC State University, Raleigh, NC 27695-7905

Abstract

Buckling of thin films is a promising way to fabricate micro-scale structures without the use of expensive lithographic processes or clean rooms. Laminated films on a rigid substrate will form buckled topography to accommodate the stresses arising from the mismatch in thermal expansion of the individual layers. Buckles form over the entire film if heated uniformly. Here, we induce buckles at specified locations of a metal/polymeric laminate (supported by a silicon wafer) by delivering heat locally to the surface of the film via a laser beam. Upon exposure with a laser beam, the thin bilayer film buckles locally. Rastering the laser beam across the surface can form shapes such as circles, lines, and squares. The characteristic buckling wavelength is 43 µm, as measured by atomic force microscopy and image analysis. Although the wavelength of the CO₂ laser is 10 µm, the resolution of features formed by conventional laser ablation is closer to 100 µm; thus, buckling offers a way of patterning structures with ‘sub-ablation’ dimensions. Buckles have prospective applications in optoelectronics, biology, biomedical engineering, and small-scale fabrication.

*Corresponding authors E-mail: jan_genzer@ncsu.edu, mddickey@ncsu.edu

^#Contributed equally to this work