| Femtosecond pulsed laser with nonlinear and non-equilibrium interaction processes has extremely short duration and ultrahigh peak power so that it is very important in the field of manufacturing. In recent years, femtosecond laser micro/nano fabrication has become the hot spot of research. Specially, the fabrication of large-area, uniform strcutures has been concerned gradually by researchers. Therefore, this paper is intended to study how to fabricate uniform, repeatable and large-area micro-nano structures by a femtosecond laser. We focus on changing material properties and laser parameters to investigate the control of femtosecond laser to surface micro-nano structures. Based on this, the fabricated structures would be used in various fields, such as color effects, wetting characteristics.Major contributions and innovations in this paper are summarized as followed:(1) In view of material properties, coating film assisted femtosecond laser fabrication is proposed to substitute traditional processing in order to control the local transient electronic dynamic during the interaction between laser and material. Take silicon as an example, the comparison test of gold film coated silicon and silicon is conducted to investigate the change of repeatability and uniformity when fabricating same structures. The results show that when 20 nm Au film is coated on silicon, the cross-links and broken structures of laser induced periodic surface structures(LIPSS or ripples) are significantly reduced. And the boundary between LIPSS covered area and the unprocessed area on Au-coated silicon is clear. The good consistency between the scanning lines facilitates the formation of large-area, uniform LIPSS.(2) In view of the laser parameters, take ZnO as an example, our study mainly investigate the influence of laser fluence and scanning speed to struture morphology. An abnormally asymmetrical grating-splitting phenomenon is discovered. At relatively high laser fluences(F=0.51- 0.63J/cm2), near-wavelength ripples are split asymmetrically to create subwavelength laser-induced periodic surface structures with dual gaps(~230nm and ~430nm) on the primary grooves. At relatively low laser fluences(F=0.4- 0.45J/cm2), nearwavelength ripples are split symmetrically, leading to the formation of uniform subwavelength structures with a period of ~340nm. Although the LIPSS on ZnO have been extensively studied in recent years, the interesting phenomenon of asymmetrical gratingsplitting forming bi-periodic structures is reported here for the first time. The observation of a special transition provides morphological evidence that would be helpful for us in further understanding basic physical mechanisms. The splitting phenomena further imply that excitation of surface plasmon polaritons(SPP) and second harmonic generation(SHG) may respectively play the dominate role for LIPSS formation under different conditions. However, further study is required to understand the detailed fundamentals of the LIPSS formation on ZnO.(3) The obtained large-area, uniform and repeatable LIPSS have wide applications. Our study mainly takes Ti and Ni as examples to study the optical properties and wetting characteristics of LIPSS under different laser parameters. Among them, the micro-nano structures obtained on Ni surface can not only realize the super-hydrophobic effect, but also can present various colors under different view angles. It should be pointed out that the change of LIPSS will also make the color change. Therefore, the color can be finely adjusted through the control of LIPSS, such as the periods of structures. In the experiment of processing Ti, we also realize the super-hydrophobic effect and the contact angle can reach above 160°. Moreover, we preliminarily explore the switchable superoleophobicitysuperoleophilicity on laser modified surfaces, which has important research meaning in the application fields of femtosecond laser induced micro-nano structures. |
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