Mesoporous silica membranes by self-assembled nanospheres and mediated laser ablation

Monodisperse silica nanospheres with sizes ranging from 250 to 515 nm have been synthesized and self-assembled to produce laser hot spots at the surface of oxidized silicon substrates. Illumination with single UV nanosecond laser pulses produces direct local ablation of the silica membrane. By preparing self-assembled nanosphere monolayers, the resulting nanoholes take the form of two-dimensional arrays in hexagonal close packed (hcp) configuration. Periodicity of the arrays is determined by the size of the assembled spheres. While the local field enhancement is strongly dependent on the sphere size, the morphology of the produced features can be maintained for all tested situations by balancing the change in local fields with the laser pulse energy. This work demonstrates the fabrication of 100-nm thick porous membranes with pore size of about 100nm and periodicity ranging from 250 to 650 nm.