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29 June 2001 Tungsten microcone arrays grown by nanosecond pulsed Nd: YAG laser irradiation
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Tungsten microcone arrays with a high aspect ratio, which protrude from the initial surface of a target material, have been formed by Nd:YAG laser irradiation of tungsten in a low pressure inert gas atmosphere. The laser fluences were 1.5- 9.6 J/cm2 at SHG. The tungsten substrate was irradiated with 1-3600 pulses. The microcone growth was strongly affected by the number of laser pulses. The microcones were up to 20 micrometers tall and had about a 1.5 micrometers diameter at the tip. Several ten or several hundred pulses caused only a rough surface while subsequent pulses created the microcone arrays. Silicon, polymer, and oxides were used as the target materials in the former studies. The growth on these substrates could be attributed to the presence of various impurities and chemical gases. However, we used no impurities or chemical gases in this experiment. We believe that the growth mechanism of the microcones might be different from this study. It was concluded that the melted/solidification tungsten tip induced by the repetition of the pulsed laser irradiation on the top surface plays a significant role in the formation of the microcones. These tall tungsten microcone arrays might be very attractive for various industrial applications.
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Yuji Kawakami and Eiichi Ozawa "Tungsten microcone arrays grown by nanosecond pulsed Nd: YAG laser irradiation", Proc. SPIE 4274, Laser Applications in Microelectronic and Optoelectronic Manufacturing VI, (29 June 2001);

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