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1977 |
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A Novel Microfabrication Technique for Three-dimensional Metal Structures by Photocatalysis |
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Equipment, Machines & Instruments: MEMS, LIGA & Nanotechnology |
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A Novel Microfabrication Technique for Three-Dimensional Metal Structures by Photocatalysis
Masaki Okuno, Tasuku Aso, Satoru Takahashi, Kiyoshi Takamasu
Recently microfabrication technology has been developing along with increasing demand. In particular, micro devices such as Micro Electro Mechanical System (MEMS), Micro Total Analysis System (µ-TAS) and microscopic optical devices as typified by a photonic crystal are in the limelight. To fabricate these devices, there needs to be a microfabrication technique that can deal with three-dimensional submicrometer structure. Presently there are two effective approaches to three-dimensional microfabrication, Focused Ion Beam (FIB) machining [1] and micro stereolithography [2]. FIB can fabricate a wide variety of three-dimensional nanostructures directly, but it requires an expensive apparatus and time-consuming process. Micro stereolithography can fabricate complicated structures, but it cannot fabricate metal structures directly. Therefore, there needs to be a new three-dimensional microfabrication technique that can fabricate metal structures directly.
In this study, we propose a novel microfabrication method that can fabricate three-dimensional metal structures directly. This method uses reduction of metal ions by photocatalysis of titanium oxide (TiO2) [3]. Photocatalysis results from internal photoelectric effect, the phenomenon that when a semiconductor receives a photon, a hole-electron pair is generated. In TiO2 suspension, metal ions get reduced by ultraviolet light exposure and deposition of the metal appears. Controlling the exposure point in three-dimensional space in submicrometer dimension, we can fabricate three-dimensional metal micro-scale structures freely.
In this report, we developed a microfabrication system based on proposed principle mentioned above. This apparatus consists of a laser diode with 405 nm wavelength, high-power objective lenses with 0.90 numerical aperture and a motorized three-axis stage with about 100 nm positioning accuracy. This system was designed so that laser spot, which causes photocatalytic reduction locally inside the TiO2 suspension, could be automatically manipulated in all directions under computer control. Then in order to verify the feasibility of our proposed method, we carried out some fundamental experiments by using this developed system. In these experiments, we employed silver nitrate solution as metal ion solution and brookite TiO2 nanoparticle with sizescale of 10nm as photocatalyst. Output of laser power was adjusted at 7mW / cm2 and laser spot diameter was set at about 0.5 µm. As a result, we succeeded in fabricating of three-dimensional silver skeleton structure with sizescale of about 100 µm in several minutes. This result indicates that our method has potential to fabricate micro-scale three-dimensional metal structure.
[1] S. Matsui, K. Kaito, J. Fujita, M. Komuro, K. Kanda, and Y. Haruyama, J. Vac. Sci.. Technol., B18, 3168, (2000)
[2] S. Shoji, S. Kawata, Photofabrication of three-dimensional photonic crystals by multibeam laser interference into a photopolymerizable resin, Appl. Phys. Lett., 76, 2668-2670, (2000)
[3] A. Fujishima and K. Honda, Electrochemical Photolysis of Water at a Semiconductor Electrode, Nature, 238(5358), 37, (1972)
Key Words: Microfabrication, Micromachine, Three-Dimensional Structure, Metal Structure, Photocatalyst
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