We present results on near-field ablation using Mie resonance high dielectric constant particles with small size parameter
for establishing a new downsizing technique for nanopatterning. In this article, we first describe a comparative study of
near-field properties on substrates using metallic and dielectric nanoparticle. The results indicate that combination of
particle and substrate for efficient localized near-field nano-processing is important for selecting either metallic or
dielectric particle. We then demonstrate nanoablation using a Mie resonance high dielectric constant small particle.
Theoretical calculations clarified that the maximal enhancement factor and spot diameter close to the smallest size are
obtainable on both low-refractive-index (SiO2) and high-refractive-index (Si) substrates using a 200 nm Mie resonance
dielectric particle (n~2.7) at magnetic quadrupole mode with 400 nm excitation wavelength. Experimental results with
200 nm amorphous TiO2 particles (n=2.66+0.024i) by 400 nm femtosecond laser irradiation verified that clear circular
nanoholes with about 100 nm in diameter were fabricated on both substrates even with laser fluence lower than a half
ablation threshold of the bare substrates. As for nanopatterning with two-dimensionally arrayed 200 nm amorphous TiO2particles, cohesion of nanoholes was observed in high laser fluence regime due to inter-particle near-field interaction.
For plasmonic surface optical applications, localized optical field distribution properties in the vicinity of gold particles
on a silicon substrate by backward and forward irradiation are presented. It is technically difficult to fabricate
nanostructure on the surface by conventional forward laser incidence to the substrate because gold nanoparticles easily
aggregate to form double-layered particle arrays. We calculated enhanced optical field properties in order to pattern the
substrate surface only with a template of the bottom-layered particle arrays in case that the backward irradiation of
femtosecond laser is used in the system of aggregated double-layered gold nanoparticle arrays. With the backward
irradiation, the optical field intensity in the substrate for the double-layered hexagonal arrays is found to be only 30%
lower than the mono-layered system. Moreover, near-field cannot be generated with the forward irradiation. As a result,
only the backward irradiation scheme is found to be effective for uniform surface nanopatterning at enhanced plasmonic
near-field zones.
This paper describes two topics. (1): Nano-processing by near-field optics can fabricate nano-scale structures even with
near-infrared 800 nmTi:saphire laser. New phenomena using particles, leading to a new nano-processing technique via
plasmonics, even with the use of dielectric particles is reported. The physics of nano-hole fabrication process is
switchable simply by the laser fluence. (2): ZnO nanorod arrays on Si (100) substrate were grown by pulsed laser
deposition (PLD) method, and then coated with Au. Two samples of Au-coated nanorod arrays with different average
diameters of 150 nm and 400 nm were prepared to investigate the size dependence of the surface enhanced Raman
scattering (SERS). The diameter of the nanorods was well controllable by the substrate position during PLD. High SERS
enhancement was observed from both Au-coated ZnO nanorod arrays. The Raman spectra of Rhodamine 6G (R6G) as
low as 1 nM were measured with average diameter of 400 nm at an excitation wavelength of 532 nm.
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