Out-of-plane surface patterning by subsurface processing of polymer substrates with focused ion beams

Abstract This work explores a new technique for the out-of-plane patterning of nanostructures prefabricated on the surface of a polymer substrate. The technique is based on ion-beam-induced material modification in the bulk of a polymer. Effects of subsurface and surface processes on the surface morphology have been studied for three polymer materials (Polymethylmethacrylate, Polycarbonate and Polydimethylsiloxane) by using irradiations with He+, Ne+ and Ga+ focused ion beams. Thin films of a Pt60Pd40 -alloy and of pristine Au were used to mimic nanostructured thin films. We show that the height of thin Pt60Pd40 films deposited on Polymethylmethacrylate and Polycarbonate substrates can be patterned by He+ ion beam with nanometer precision while preserving nanometric features of the pre-deposited films. Ion irradiation of the Au-coated samples results in Au-film delamination, bulging and perforation, which is attributed to accumulation of radiolysis gases at the film-substrate interface. The irradiation with Ne+and Ga+ ions destroys the films and roughens the surface due to dominating sputtering processes. A very different behavior, resulting in the formation of complex, multiscale 3D- patterns, is observed for Polydimethylsiloxane samples. The roles of the metal film structure, elastic properties of the polymer substrate and irradiation-induced mechanical strain in the patterning process are elaborated and discussed.