Self-polymerization of nano-fibres and nano-membranes induced by two-photon absorption

Laser Two-Photon Polymerization (LTPP) is a technique enabling formation of 3D nanostructures in photosensitive resins with sub-wavelength resolution and unmatched flexibility. However, controllable fabrication of sub-100 nm features by this technique is still a challenge. Self-polymerization, also known as non-local polymerization, is considered to be promising in this ultra-high resolution structure formation. Recent observation of fragile self-polymerized fibres with diameter within tens of nanometres (nano-fibres) encourages the use of self-polymerization to produce nanometre scale structures other than fibres and to define the conditions for controllable fabrication. “X”-shaped polymerized supports are used as rigid structures to produce suspended self-polymerized features of different nature (shape and dimensionality) in-between the walls of “X”. By laser writing lines parallel to the substrate and perpendicular to the long symmetry axis of “X” under different conditions, selfformation of periodic nano-fibres (diameter <100 nm) and nano-membranes is induced in acrylate photopolymer AKRE37. Depending on introduced exposure dose, spatial density threshold behaviour of non-structure, nano-fibre, nano-membrane, and laser written lines is deduced. Preliminary model including laser intensity, concentration of radicals, collapse force, and distance between supports as variables having threshold effect on final self-polymerized structure’s geometry is proposed to explain non-local self-polymerization. Keywords: femtosecond laser, multi-photon absorption polymerization, acrylate photopolymer, self-assembly, nanotechnology