The Study Of Femtosecond Laser Induced Micro/Nanostructures On Solid Materials Surfaces And Their Wettabilities

In recent years,as a kind of advanced ultra-precision machining,femtosecond laser micro/nano fabrication has attracted much interest in the field of science and research.With ultrashort irradiation periods and ultrahigh power intensities,femtosecond laser presents unique advantages over conventional laser.Femtosecond laser can fabricate almost all kinds of materials via a noncontact and nonthermal process.In addition,femtosecond laser machining can improve the precision significantly.Both sub-micron structures and three dimensional complex structures can be fabricated by femtosecond laser,which also has the characteristic of low-energy-consumption.A large number of experimental research results show that a variety of extraordinary micron and nanoscale surface structures such as ripples,micron-sized conical structures and nano-column structures are formed when the femtosecond laser processing the solid materials.These special surface micro/nanostructures have significant effects on the surface functional properties of the materials.The surface wettabilities,optical properties and so on of the materials can be improved remarkably owing to these unique phenomena,which injects much vitality into the field of preparing novel multifunctional materials.Wettability is a kind of important property of the surface of solid materials.According to many theoretical and experimental research results,the microstructures of the surface(affecting its surface roughness)and the chemical composition of the surface(affecting its surface energy)have significant and determined effects on the wettability of the surface of solid materials.A large number of researchers have obtained superhydrophobic surface on the different kinds of materials through changing the micron surface morphology of the materials or reducing the surface energy of the surfaces via a variety of processing methods.Femtosecond laser machining has became a kind of important and efficient method for preparing superhydrophobic surfaces due to its capability of fabricating varieties of micro/nanostructures on the surfaces of solid materials.Surface silanization is a relatively common and typical surface modification method for reducing the surface energy of solid materials.In this thesis,two typical solid materials-silicon and copper are selected to be the object of our study.Firstly,we fabricate different kinds of surface micro/nanostructures on the materials through designing different laser processing parameters with the method of femtosecond laser scanning line by line.Following the principle of single variable of controlling variable method,we design and perform a series of systematic experiments to investigate the effects of main processing parameters including pulse energy,scanning velocity,repetition rate,scanning spacing and pulse distance on the formed micron surface morphology of the materials.Then we use the same machining parameters and enlarge the processing areas of the materials.After laser processing,we perform surface silanization for these processed samples to reduce the surface energy of them.Combining femtosecond laser scanning and surface silanization,we fabricate a series of Si and Cu surfaces with different levels of wettabilities including hydrophobic even superhydrophobic surfaces.And we systematically investigate the effects of different kinds of surface morphology on the wettabilities of corresponding materials respectively.In addition,we also investigate the relations between surface wettabilities of these two kinds of materials and laser scanning spacing and pulse distance.The experimental results show that the surface micro/nanostructures formed on the silicon and copper wafers are all affected by the different laser processing parameters in a certain extent.Under the constant pulse energy,only through the proper combination of other laser processing parameters including scanning velocity,repetition rate and scanning spacing can we fabricate the ideal surface micro/nanostructures on the solid materials such as Si and Cu.Finally we obtain robust superhydrophobic Si and Cu surface through performing surface silanization to those Si and Cu wafers with surface micro/nanostructures.