High quality poly(methyl methacrylate) (PMMA) thin nanocomposite films doped with different concentration of silver (Ag) nanoparticles are demonstrated. SEM and TEM confirmed the presence of Ag-PMMA nanocomposites with excellent dispersion of Ag nanoparticles into the PMMA matrix and nanoparticles with an average size of 9 nm. By using a direct Laser writing system with a continuous wave 405 nm diode Laser source the films were exposed, allowing the formation of hole-like or linear patterns in the sub 200nm regime, using a 280nm FWHM sized laser spot, demonstrating, for the first time, the potential for sub-diffraction limit laser processing in such 2-material composite systems.
In this work, direct-write, high-resolution multiphoton photolithography using doped random methacrylic co-polymer thin films is demonstrated, using a continuous wave ultraviolet (UV) 375 nm diode laser source. The random copolymers are specifically designed for enhancing resolution and addressing issues arising from laser ablation processes, such as the berm-formation around the created holes in the film, which can be accessed by tuning the polymeric material properties including Tg, surface adhesion etc. The methacrylic copolymer is composed of monomers, each of them especially selected to improve individual properties. The material formulations comprise perylene molecules absorbing at the exposure wavelength where the polymeric matrix is transparent. It was found that if the radiation intensity exceeds a certain threshold, the perylene molecules transfer the absorbed light energy to the acrylate polymer matrix leading to polymer degradation and ablation of the exposed areas. The non-linear nature of the light absorption and energy transfer processes resulted in the creation of holes with critical dimensions well below the used wavelength reaching the sub 50 nm domain. Arrays of holes having various dimensions were fabricated in the laser ablation experiments using a directwrite laser system developed specifically for the purposes of this project.
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