Size scaling of mesoporous silica membranes produced by nanosphere mediated laser ablation

Monodisperse silica nanospheres with sizes ranging from 250 to 725 nm were prepared and assembled into monolayers to produce regularly distributed light hot spots at the surface of oxidized silicon substrates when illuminated by a laser. Single UV nanosecond laser pulses were employed with energies above the local ablation threshold for the silicon dioxide layer, resulting in the direct formation of 2D periodically porous membranes on top of the silicon. The periodicity of the array was driven by the size of the self-assembled nanospheres. While the local field enhancement was strongly dependent on the sphere size due to Mie resonances, the size and morphology of the produced features could be maintained for all tested situations by balancing the change in local fields with the laser pulse energy. This work demonstrates the fabrication of 90 nm thick porous membranes with pore size of about 100 nm and periodicity ranging from 250 to 725 nm.