| Budget Amount *help |
¥15,000,000 (Direct Cost: ¥15,000,000)
Fiscal Year 2005: ¥7,200,000 (Direct Cost: ¥7,200,000)
Fiscal Year 2004: ¥7,800,000 (Direct Cost: ¥7,800,000)
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| Research Abstract |
A nanoscale waveguide is required as a far/near-field conversion device in advanced nanoscale photonic devices. One possible device, a metallic nanoparticle plasmon waveguide, was proposed and near-field energy transfer was observed along the lithographically patterned metallic nanodot chain. Here, we developed the self-assembly of a size- and position-controlled ultra-long nanodot chain using a novel effect of near-field optical desorption.
We fabricated a nanodot chain using radio frequency (RF) sputtering under illumination on glass substrate with a 100-nm wide and 30-nm deep groove. During the deposition of Al, illumination of 2.33-eV light (50 mW) with linear polarization perpendicular to the groove (E_<90>) resulted in the formation of a 99.6-nm-diameter Al nanodot chains with 27.9-nm separation that were as long as 100 μm in a highly size- and position-controlled manner. The deviation of both nanodot size and the separation were as small as 5 nm. To identify the position of the c
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hain, we compared topographic atomic force microscopy (AFM) images of the surface of the glass substrate before and after Al deposition. Comparison of the profiles showed that the nanodot chain was formed around edge. Furthermore, no dot structure was obtained with parallel polarization E_0. Since the near-field intensity with E_<90> was strongly enhanced at the edge of the groove in comparison with E_0 owing to edge enhancement of the electrical field, a strong near-field intensity results in nanodot chain formation. The dot formation at the one-sided edge originates from the asymmetric electric-field intensity distribution, owing to the slanted illumination. This prediction is supported by calculations.
Al-dot chain formation was also observed with RF sputtering of Al under illumination of a 2.62-eV light (100 mW) with E_<90>, which resulted in the formation of 84.2-nm nanodot with 48.6-nm separation. Although the period was similar to that fabricated under 2.33-eV illumination, the dot size was reduced in proportion to the increase in the photon energy, indicating that the size- and position-controlled dot-chain formation originates from desorption of the deposited metallic nanoparticles. A metallic dot has a strong optical absorption due to plasmon resonance, which strongly depends on particle size. This can induce desorption of the deposited metallic nanodot when it reaches the resonant diameter. As the deposition of metallic dots proceeds, the growth is governed by a trade-off between deposition and desorption, which determines their size, depending on the photon energy of the incident light.
Since the nanodot chain forms at the size based on plasmon resonance, the resulting structure should have high transmission efficiency of optical near-field energy. Furthermore, since our deposition method is based on a photo-desorption reaction, it could be widely used to fabricate size- and position-controlled nanoscale structures with other metals or semiconductors. Less
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