Ultrafast laser induced periodic sub-wavelength aluminum surface structures and nanoparticles in air and liquids

Abstract

In this communication, we demonstrate the generation of laser-induced periodic sub-wavelength surface structures (LIPSS) or ripples on a bulk aluminum (Al) and Al nanoparticles (NPs) by femtosecond (fs) laser direct writing technique. Laser irradiation was performed on Al surface at normal incidence in air and by immersing in ethanol (C2H5OH) and water (H2O) using linearly polarized Ti:sapphire fs laser pulses of ∼110 fs pulse duration and ∼800 nm wavelength. Field emission scanning electron microscope is utilized for imaging surface morphology of laser written structures and it reveals that the spatial periodicity as well as the surface morphology of the LIPSS depends on the surrounding dielectric medium and also on the various laser irradiation parameters. The observed LIPSS have been classified as low spatial frequency LIPSS which are perpendicularly oriented to the laser polarization with a periodicity from 460 to 620 nm and high spatial frequency LIPSS which spectacles a periodicity less than 100 nm with the orientation parallel to the polarization of the incident laser beam. Fabricated colloidal solutions, which contain the Al NPs, were characterized by UV-Vis absorption spectroscopy and transmission electron microscopy (TEM). TEM results reveal the formation of internal cavities in Al NPs both in ethanol and water. Formation mechanism of LIPSS and cavities inside the nanoparticles are discussed in detail.

The Role of the Laser-Induced Oxide Layer in the Formation of Laser-Induced Periodic Surface Structures

“…Their periodicity (Λ LIPSS ) usually ranges from hundreds of nanometers up to some micrometers and it is used to classify them into the general categories as low-spatial frequency LIPSS (LSFL), when Λ LSFL ∼ λ, and high-spatial frequency LIPSS (HSFL) for Λ HSFL λ, where λ is the laser wavelength [2]. Suitable manufacturing strategies have been identified, including the optimization of laser processing parameters (laser fluence, wavelength, repetition rate, angle of incidence, number of pulses per spot area) [3][4][5][6][7][8], material properties (optical, thermal and mechanical properties) [9][10][11], and the ambient medium in which they are generated (air, vacuum, reactive atmospheres) [12][13][14][15] for applications in optics, medicine, fluid transport and tribology among others [1].…”

3D Microfluidic Surface‐Enhanced Raman Spectroscopy (SERS) Chips Fabricated by All‐Femtosecond‐Laser‐Processing for Real‐Time Sensing of Toxic Substances

“…This periodicity was significantly smaller than the laser wavelength (≈25%). A LIPSS nanograting having a periodicity less than 40% of the laser wavelength is referred to as a high‐spatial‐frequency LIPSS (HSFL) . Such structures can only be obtained with a femtosecond laser having a fluence close to the ablation threshold.…”

Nonlinear optics on nano/micro-hierarchical structures on metals: focus on symmetric and plasmonic effects

“…with the grooves formed normal to the electric field direction [26,27,42]. Here, λ is the incident light wavelength, and ε ' and ε d are the dielectric constants of the real part and of the surrounding dielectric material, respectively.…”

“…Incidentally, to remove NSs perfectly, laser irradiation was also tested on the Ni surface at normal incidence in water [42] using the experimental setup shown in Figure 2(b). However, as seen in Figure 17(e,f), we could neither remove the NSs nor fabricate the cube structures.…”