Nanofabrication of hexagonally arrayed holes on an aluminum surface using femtosecond laser pulses

Nano-processing using a near-field generated by irradiating a laser to the nano-particle is becoming a new emerging nanotechnology, because it can fabricate nano-size structures of sub-laser-wavelength. In this paper, we would like to report on the nanohole fabrication on an aluminum (Al) surface by femtosecond lasers due to near-field enhanced effects. The particle size used experimentally is 450 nm and 820 nm (PS, n=1.59) in diameter. The used laser fluence ranges from the bellow-ablation-threshold fluence to the above-threshold fluence of Al films. The ablation threshold of Al films is 400 mJ/cm² approximately. The Al films were deposited on the silicon substrate by conventional vacuum evaporation method. Particles were successfully arrayed in an hexagonal closed-packed structure (hep) so that the near-field generates uniformly on each particle