| Surface structures with nanoscale size and periodicity are important in controlling the optical property of the surface as well as light-matter interaction,which holds a great promise in solar-energy conversion,photonics,and biomedical fields.The fabrication of periodic nanostructure requires sophisticated and expensive nanofabrication tools that limit the large-scale integration of these structures for practical applications.On the other hand,direct femtosecond(fs)laser processing is a maskless fabrication technique that can effectively modify materials’ optical,electrical,mechanical,and tribological properties with potential applications in biomedical,environmental,and energy fields.Fs-laser processing can alter the properties of treated surfaces either by introducing random surface structures or,interestingly,regular and periodic surface structures.In particular,one-dimensional(1D)femtosecond laser-induced periodic surface structures(fs-LIPSSs)with subwavelength periodicity can be fabricated on a wide range of materials which has attracted considerable attention.However,three major challenges hinder fs-LIPSSs from practical applications,particularly in nano-photonics;(i)The lack of long-range order of spatial uniformity,(ii)the difficulty to produce and control subwavelength periodic surface structures,i.e.,high-spatial frequency LIPSSs(HSFL),and finally(iii)obtaining twodimensional(2D)complex geometries.The long-range nonuniformity stems from the fact that fsLIPSSs formed due to excitations of SPPs from random nanoroughness,so the final fs-LIPSSs structures are often twisted into many bends rather than straight-line.Secondly,the origin of HSFL is mainly suggested via a self-reorganization of the irradiated material,associated with a surface instability as a result of surface erosion and atomic diffusion effects.Therefore,the control in HSFL periodicity and uniformity is difficult.Finally,for two-dimensional surface structures,there should be two beams that can form two grooves in distinct directions.On the other hand,randomly formed surface structures are relatively easier to obtain and can have important applications,e.g.,in structural coloring,increasing the efficiency of incandescent lamps,and creation of superhydrophobic and super-hydrophilic surface structures.However,due to their randomness,it is difficult to control the acquired properties due to fs-laser ablation,for example,fslaser ablation of metals creates black metals,however,the control over the absorption bandwidth,which is of major importance in energy applications,is an unexplored challenge.This thesis aims to address these challenges by exploring novel laser fabrication techniques that allowed us,to some extent,overcome these challenges.By adopting multipulse fs-laser ablation,we demonstrate the fabrication of high-quality 1D fs-LIPSSs structure on nickel,using multiple timedelayed collinear femtosecond laser pulses.We explore the origins of the uniformity of the produced surface structures.In addition,we demonstrated 1D HSFL structures with unusually high aspect ratios(~ 50)compared to existing literature.Finally,we demonstrated a variety of 2D complex geometries,e.g.,spherical,triangular,and rhombic structures on Cobalt surfaces at short time-delays(<12 ps).Using three temporally delayed fs-pulses,we were able to create highly uniform and large scale 2D periodic surface structures on Nickel surface.These structures differ from other 2D laser induced surface structures in terms of the ability to create uniform 2D structures over the entire irradiation region.The first part of the thesis deals with the creation of uniform 1D,2D,and HSFL structures.The main objective of this thesis is to form a controlled surface structures and uncover the applications of subwavelength random and ordered structures in energy and biomedical fields.The second part of the thesis deals with the creation of controlled random and uniform structures by fs-laser pulses that exhibits desirable features for material functionalization,e.g.,perfect light absorption,superhydrophobicity,and superhydrophilicity with many potential applications in biomedical,environmental,and energy fields.In the context of biomedical field,we demonstrated the applications of fs-treated surface structures including subwavelength fs-LIPSSs,fs-LIPSSs covered with nano/microstructures,conic and 1D-rod-like structures,and spherical nanostructures for antibacterial adhesion properties.The results of in-vitro experiments showed the ability of all the fslaser surface structures to reduce the adhesion of Escherichia coli(E.coli)bacteria and further show that fs-LIPSSs enjoys superior antibacterial adhesion properties due to its large-scale coverage.Approximately 99.03% of the Au fs-LIPSSs surface is free from bacterial adhesion.In the context of energy applications,for the first time,we showed a novel femtosecond processing method guided by plasmon-hybridization model to fabricate selective and broadband light absorbers on different metals for solar-energy conversion.We show an improvement of 130% in solar thermoelectric generator(TEGs)efficiency for the treated selective solar absorber tungsten.We also demonstrate the application of fs-laser treatment on heat exchangers by functionalizing the surface ofa common heatsink material,i.e.,Al,to enhance both its radiative and convective cooling performance and demonstrated its effect on improving the output power of a TEG. |
