Fabrication Of Functional Surfaces With Controllable Reflectivity And Wettability By Laser Interference Lithography

The properties of the material surface can be effectively improved by altering the surface structure on the nano-and micro-scales.The improvement of the optical and wetting characteristics of the material surface that is an important research topic in the surface engineering,which has great values for applications in aeronautics,astronautics,biology,medicine and energy materials.Fabricating large-area micro-/ nano-structures in controllable manners is the key technical bottleneck of its practical application,which has been a hot topic in the field of surface engineering.This thesis focuses on the fabrication of functional surfaces with controllable reflective and wettability through multi-beam laser interference lithography(LIL).The main work completed and results achieved are in the following.First,an asymmetric configuration of three-beam interference with the azimuth angles of0°,90° and 180° and the corresponding polarization vectors of TE-TM-TE was designed and developed based on the analysis of the influences of the azimuth angles and the polarization vectors.The asymmetric three-beam interference system was built for experimental verification.The system is simple with respect to the design of optical paths and is able to effectively control the formation of interference patterns so that makes it easier to fabricate the periodic structures with high duty cycles.Second,the effect of exposure process parameters of the asymmetric three-beam LIL system on the morphology of the structures was studied,and the shape,height and duty cycle of structures were able to be adjusted through the control of exposure doses.The fabrication of large-area,micro-and nano-structure masks was achieved in a controllable manner based on the study.Finally,it was studied that the formations of micro-and nano-structures depend on experimental conditions during the inductively coupled plasma reactive ion etching(ICP-RIE)process.The consumed masks and accumulated ions are the two main reasons which cause the isotropic etching.Based on the findings,a cyclic plasma etching technique was developed to solve the difficulty of generating periodic structures with high aspect ratios on the sub-micron scale and to effectively control the morphologies of the structures at the same time.Based on LIL and the cyclic plasma etching technique,the functional surfaces with controllable reflectivity and wettability have been studied.The main work completed and results achieved are in the following.1.In the wettability of micro-and nano-structures,periodic structures with different geometric parameters were fabricated using the asymmetric three-beam LIL and the cyclic plasma etching technique.The superhydrophobic structures were achieved,and their contact angles exceeded 160?,and the rolling angle was less than 5?.This thesis revealed the proportional relationship of the top area ratio of period structures on the adhesionproperty of the surface.The controllable fabrication of the superhydrophobic structures with tunable adhesion was realized based on the findings,and the adhesive force was able to be adjusted from 2.36 ?N to 30 ?N.The controllable adhesion of different superhydrophobic structures makes it possible to implement the transportations of micro-droplets.The studies have important applications in many fields such as targeted drug delivery,biomolecular quantitative detection,selective liquid transportation and oil /water separation.2.In the antireflection of micro-and nano-structures,the structural geometric parameters of simulated moth-eye structures that produced satisfied antireflectivity in the ultra-wide spectral region were obtained through studying on the effects of the structural geometric parameters on optical properties using the FDTD software.The bionic moth-eye structures with ultra-broadband antireflective properties were fabricated via the asymmetric three-beam LIL and the cyclic plasma etching.The antireflection efficiency of the bionic moth-eye structure was less than 2% reflectivity in the range from the visible(400 nm)to the mid-infrared(11 ?m)region.The bionic moth-eye structures have great significance for developing optical devices in the working range of visible light,near-infrared and mid-infrared bands.3.Research was extended into multifunctional surfaces with both wettability and antireflective properties.With the asymmetric three-beam LIL,the modification methods of nanostructures on the surface of hierarchic structures were studied during the cyclic plasma etching process,and the multifunctional structures antireflection with superhydrophobicity were fabricated.The reflectivity of multifunctional structures was maintained at 1% in the range from the visible to the near-infrared wavelength range,and its water contact angle exceeded 150 ?.The antireflective structures with superhydrophobicity have great advantages for long-term use in harsh environments.In addition,the superhydrophobic structures with anisotropic adhesion were fabricated by two-beam LIL and cyclic plasma etching.It is revealed that the structural morphology is the key factor affecting the wetting anisotropy of the grating structures,thereby achieving three states of anisotropic wetting:anisotropic hydrophobicity,anisotropic hydrophilicity,and anisotropic adhesive wetting.The study offers design insights for applications such as liquid manipulation,directional liquid transportation,and liquid collections.