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The use of two‐photon polymerization (TPP) initiated by a photosensitizer's non‐linear two‐photon absorption in two‐ and three‐dimensional (2D and 3D) microfabrications for various photonic applications has been intensively studied. Since TPP emerged as a new technology over a decade ago, a large variety of micro‐objects including 3D micro‐optical components, micromechanical devices, and 3D photonic crystals have been fabricated using TPP with a high spatial resolution of approximately submicron scale to 100 nm. Recent efforts have been made to improve the fabrication efficiency and precision of micro‐objects obtained with TPP; in particular, many studies have been carried out with the aim of developing efficient two‐photon absorbing chromophores. In this article, efforts to develop highly efficient two‐photon absorbing materials and also describe recent attempts to enhance the resolution and improve the fabrication efficiency of nanofabrications based on two‐photon polymerization are discussed. Copyright © 2006 John Wiley & Sons, Ltd.

We report a newly synthesized inorganic polymer photoresist with a high ceramic yield by the functionalization of polyvinylsilazane (KiON VL20) with 2‐isocyanatoethyl methacrylate via linkage or insertion reaction routes. The chemistry of the synthesis and the pyrolytic conversion as well as the mechanical evaluation were investigated by using various analytical instruments. We show for the first time that this photosensitive resin is a novel precursor for the fabrication of complex 3D SiCN ceramic microstructures with a 210 nm resolution via a two‐photon absorbed crosslinking process and subsequent pyrolysis at 600 °C under a nitrogen atmosphere. Moreover, the dimensional deformation during pyrolysis was significantly reduced by adding silica nanoparticles as a filler. In particular, the ceramic microstructures containing 40 wt % silica nanoparticles exhibited a relatively isotropic shrinkage owing to its sliding free from the substrate during pyrolysis.

Two-photon stereolithography (TPS) provides many advantages for achieving two-dimensional (2D) and threedimensional (3D) micrometer-scale polymeric, ceramic and metallic structures applicable to complicated optical and neoelectronic microdevices. In the fabrication of high-resolution 3D microstructures, TPS has significant advantages over conventional microelectromechanical system (MEMS) processing, which involves time-consuming multistep indirect fabrication processes. Many studies have recently been made to develop and improve the TPS process, focusing on creating greater efficiency, higher resolution, and greater productivity, which are essential requirements of a practical TPS process. For the first time, an artistic microstructure has recently been successfully produced with an ultraprecise spatial resolution, sub-30 nm nanofibers, 3D multilayer imprint stamps for mass production, and ceramic 3D microstructures. In this review, we report the progress of twophoton polymerization based on 3D microfabrication, including the results obtained from the original research. This report is presented in three sections: improvement of resolution, precise design schemes, and applications of 3D microstructures.Precise micro 3D pattern fabricated by two-photon lithography.

Experimental studies on the fabrication of sub-30-nm nanofibers using two-photon initiated photopolymerization ͑TPP͒ have been carried out. To generate nanofibers at the interior region of microstructures, a photopolymerization method involving a long laser-exposure technique ͑LET͒ is proposed. A multitude of nanofibers with a notably high resolution ͑about 22 nm͒ in TPP were produced using the LET. Furthermore, it is also demonstrated that thin interconnecting networks were created regularly in a weakly polymerized region existing around the boundary of a densely polymerized voxel, allowing for the creation of various embossing patterns. By controlling the distance between adjacent voxels or lines, a selective generation of nanofibers in a local area is possible, which leads to the fabrication of high-functional filters and mixers. Embossing patterns and microchannels including nanofibers inside were fabricated by the LET so as to demonstrate the practical feasibility of this approach. These sub-30-nm nanofibers may find meaningful applications such as biofilters, mixers, and photon emitters in diverse research fields.

We present the replication of polyethylene (PE) nano-micro hierarchical structures and their application for superhydrophobic surfaces. A commercial ultrasonic welding system was used to apply ultrasonic vibration energy to the forming of nano-micro hierarchical structures. To evaluate ultrasonic formability, Ni nanomold and nano-micro hierarchical mold were designed and fabricated. The optimal weld times were 1.5 s and 3.0 s for PE nanoprotrusions and nano-micro hierarchical structures, respectively. The forming process was conducted at atmospheric pressure. The PE structures were well replicated without a vacuum. The trapped air in the microcavity of the nano-micromold was dispersed and absorbed into the molten PE. Ultrasonic nano-microreplication technology showed an extremely short processing time and did not require a vacuum environment. To investigate the applicability of ultrasonic forming, the fabricated nanoprotrusions and nano-micro hierarchical structures were coated with plasma polymerized fluorocarbon (PPFC) of a hydrophobic nature and were applied to modify superhydrophobic surfaces. The contact angle was increased from 106 • (smooth surface) to 125 • (nanostructured surface) and finally to 160 • (nano-microstructured surface) so that the surface became superhydrophobic.

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