Abstract

Tightly focused femtosecond laser beam can initiate multiphoton absorption and result in ultralocalized (within the femtoliter volume) chemical crosslinking of the liquid or gel state photopolymer. Translating the sample or changing the position of the focus beam enables pin-point photo-patterning of true three-dimensional micro/nanostructures with sub-diffraction spatial resolution [1]. However, further increase of resolution is of high importance for this direct laser writing technique to produce features with spatial dimensions less than < 100 nm in order to enter the realm of nanotechnology. As the laser multiphoton polymerization technique enables to the reproducibly achievable feature dimensions of tens of nanometers consisting of tens of initial monomer molecules, the effect of non-local polymerization arises, which is usually treated as a limiting factor. This non-local poly-merization greatile depends on specific laser excitation conditions, material properties, development, as well as dimensions and geometry of the structure itself. Non-local growth of the polymer chains away from the exposed areas leads to loss of resolution and structure definition [2]. This is commonly interpreted as an underdevelopment artifact, since it prevents from achieving ultra fine features separated with a thin gap in between. If there are rigid supports of densely polymerized regions nearby, non-locally growing polymer chain gets entangled one end in one support and the other end in the other. This way a suspended self-formed nanofiber or nanomembrane can originate. On the other hand, control of non-local polymerization opens a way for achieving higher resolution, which is not reachable using direct laser writing approach. In our experimental work, we present results of self-formed nanofibers and nanomembranes in acrylate based photosensitive material AKRE (tris(2-hydroxy ethyl) isocyanurate triacrylate) with < 100 nm diameter or thickness, respectively. Other widely used materials, such as Ormocomp (Micro Resist), PEG-DA-258 (Sigma-Aldrich) and SCR-500 (Japan Synthetic Rubber Company) were also tested for the comparison.

© 2011 Optical Society of America