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[Display omitted] • Inherent micropore-cracks on the MAO surface are eliminated by the femtosecond laser; • The alumina nanocrystallines (γ-Al 2 O 3 and α-Al 2 O 3) are formed and embedded into the original amorphous layer; • Material surface becomes the intrinsically superhydrophobic even at high temperatures; • The measured corrosion current falls to an unprecedent value of 1.46 × 10-13 A/cm2. Microarc oxidation (MAO) is a widely employed technology for the corrosion protection of metal surfaces due to the formation of thick-layer ceramic substances. However, its practical effectiveness is strictly limited by the inevitable concomitant generation of numerous microscale pores/cracks on the oxidation surface to directly expose the substrate materials. As concerning this problem, we here introduced a novel method of the femtosecond laser irradiation to completely eliminate the above MAO defects on aluminum alloys, which consequently modulates the passivation layer into the dense and the superhydrophobic. Meanwhile, with the deep insights into the phase composition variations of the oxide layer, we can find that the laser treatments enable the development of both γ-Al 2 O 3 and α-Al 2 O 3 nanocrystallines with embedment in the amorphous substances to significantly improve the chemical stability of materials. Such laser modifications eventually result in the ultra-corrosion-resistant surface of aluminum alloys, with the measured corrosion current density of 1.46 × 10-13 A/cm2 as well as the impedance value over 112 GΩ∙cm2, about two orders of magnitude enhancement in the anticorrosion compared to the initial MAO sample. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nanopores and micropillars are prepared on polyetheretherketone surfaces. • Surface structures adhere more silver nanoparticles and chelate more zinc ions. • Surface structures and zinc ions greatly enhance osteogenic activity. • Zinc-silver synergy enhances the antibacterial effects. The disadvantages of polyetheretherketone (PEEK) implant materials include lack of osseointegration and antimicrobial properties, which are the main reasons for implant failure. In this study, we propose a strategy of a three-dimensional nanoporous micropillar structure constructed on PEEK surfaces by integrating sulfonation treatment with femtosecond laser processing and chelating zinc-silver dual ions with polydopamine. The results show that the increased number of sites on the surface structure increases the total amount of zinc ions and silver particles adsorbed on the surface. Under the synergistic effect of the dual ions, PEEK shows good inhibitory effects on both Escherichia coli and Staphylococcus aureus. In addition, in vitro cell culture experiments show that the surface structures promote cell attachment and play a positive role in the cell mineralization. The increased cell proliferation, cell differentiation and mineralization capacity further confirm the excellent osteogenic properties of the modified PEEK. This surface strategy of imparting antibacterial and bone-promoting properties to PEEK by surface structural modification and ion co-implantation, has significant potential for bone implant applications. [ABSTRACT FROM AUTHOR]

With femtosecond (fs) laser pulse irradiation, a simple but efficient technique to fabricate bi- and quad-directional low spatial frequency laser-induced periodic surface structures (BD- and QD-LSFLs) is suggested on metals. By inserting a quartz wedge achromatic depolarizer prior to the focusing optics, we change the polarization of fs laser pulses periodically in one dimension within the laser spot, and find that this method leads to the creation of BD- and QD-LSFLs by simply raster scanning fs laser pulses on Ni. It is also demonstrated that the interval of orientation change of BD-LSFLs can be manipulated with defocus. • LSFLs with multiple orientations were fabricated on metals within a single raster scanline. • Interval of orientation change in bi-directional LSFLs was controlled with defocus. • Formation mechanism of BD- and QD-LSFLs was discussed with the superposition of two orthogonally polarized fs laser pulses. [ABSTRACT FROM AUTHOR]

[Display omitted] • We firstly propose applying FLI to improve the wetting of Al/B 4 C system. • We systematically explored the micro structural changes of B 4 C under different irradiation parameters. • Femtosecond laser can enhance the interfacial wetting between Al and B 4 C, reducing the contact angle of 24° compared to the untreated one. • Our method identifies a novel and sustainable way to fabricate a good wetting of Al/B 4 C system, offering a promising application for mass production. The Al/B 4 C composites are widely used in aerospace, automotive, military and energy industries, which combine the mechanical properties of Al metal and B 4 C ceramics. To achieve the best composite performance, it is crucial to overcome the poor wetting between the two materials. It is well known that surface micro-nano structures can affect wetting. However, the high brittleness and hardness of B 4 C make it challenging to process. In this paper, we proposed a novel approach to create hierarchical micro-nano surface structures on B 4 C by femtosecond laser irradiation. Surface morphology, phase change, and valence bond structure before and after irradiation were characterized respectively. The wetting of B 4 C was characterized in terms of high-temperature metal melt wetting. Under high photon energy impact, carbon elements were precipitated, leading to forming a boron-rich phase. This new phase possesses higher chemical reactivity and is capable of promoting reactions with Al. Compared with the contact angle of the untreated sample, the contact angle decreased by 24°. This work demonstrates that femtosecond laser irradiation is a sustainable and concise technology to improve high-temperature wetting, providing a new idea for enhancing the wetting of metal/ceramic systems. [ABSTRACT FROM AUTHOR]

Laser-induced periodic surface structures (LIPSS) formation on the surface of mono-crystalline silicon is reported for a specific fabrication regime of large-area structuring. Using a femtosecond laser at 1030 nm wavelength, a particular range of fluence and beam overlap in two-dimensional scanning scheme has been identified where LIPSS-covered areas organize into stripes perpendicular to the scanning direction. The stripes, where the LIPSS appear, are regularly spaced and located in between the centers of two subsequent Gaussian pulses while the regions receiving the peak pulse fluence are free of LIPSS. The formation of the LIPSS stripes is examined by analyzing local integrated fluence, N-on-1 pulse damage geometry and thresholds of modifications. Processes at play in the generation of such stripes of LIPSS are discussed and an explanation based on interpulse feedback from amorphized areas is proposed. [Display omitted] • Regular stripes of LIPSS are formed by femtosecond laser beam scanning on Si surface. • The stripes of low spatial frequency LIPSS are perpendicular to scanning direction. • By tuning of the laser scanning conditions, other structure types can be formed. • A mechanism of LSFL stripes formation, based on amorphization, is proposed. [ABSTRACT FROM AUTHOR]

Laser-induced periodic surface structures (LIPSS, ripples) were processed on steel (X30CrMoN15-1) and titanium (Ti) surfaces by irradiation in air with linear polarized femtosecond laser pulses with a pulse duration of 30 fs at 790 nm wavelength. For the processing of large LIPSS covered surface areas (5 mm × 5 mm), the laser fluence and the spatial spot overlap were optimized in a sample-scanning geometry. The laser-processed surfaces were characterized by optical microscopy (OM), white light interference microscopy (WLIM) and scanning electron microscopy (SEM). Spatial LIPSS periods between 450 and 600 nm were determined. The nanostructured surface regions were tribologically tested under reciprocal sliding conditions against a 10-mm diameter ball of hardened 100Cr6 steel. Paraffin oil and engine oil were used as lubricants for 1000 sliding cycles at 1 Hz with a normal load of 1.0 N. The corresponding wear tracks were analyzed by OM and SEM. In particular cases, the laser-generated nanostructures endured the tribological treatment. Simultaneously, a significant reduction of the friction coefficient and the wear was observed in the laser-irradiated (LIPSS-covered) areas when compared to the non-irradiated surface. The experiments reveal the potential benefit of laser surface structuring for tribological applications. [ABSTRACT FROM AUTHOR]

Highlights: [•] Porous structures are obtained on biopolymer films upon fs laser irradiation. [•] Higher ablation thresholds are observed for temporally shaped pulses. [•] Control via different contributions of multi-photon and avalanche ionization processes. [Copyright &y& Elsevier]

Abstract: Ultra-high-molecular-weight polyethylene (UHMWPE) is a polymer with mechanical and corrosion properties, which make it appropriate for using in biomedical devices such as hip and knee prostheses. The surface morphology and chemistry of UHMWPE influence its biocompatibility. A laser with wavelength at 1027nm delivering 450fs pulses at a repetition rate of 1kHz is used to modify the surface of UHMWPE samples with 0.45μm root mean square surface roughness. Micrometric resolution is achieved with the use of a focusing lens of 0.25NA and pulse energies of few microjoules. The study focuses in the influence of different pulse energies and pulse overlaps on the laser-induced surface roughness and ablation yield. Confocal microscopy is used to characterize changes in the morphology of the irradiated surfaces, and their chemical structure is analyzed by attenuated total reflectance infrared and Raman spectroscopies. The roughness increases as the pulse energy increases until it reaches a maximum. The ablation yield increases with the pulse energy and pulse overlap. However, the ablation yield per pulse is lower for higher pulse overlap. Pulses of 6μJ have the highest ablation efficiency. Infrared and Raman spectra of samples irradiated with low energy pulses are similar to those of the pristine sample. However, some Ce:glyph name="dbnd" />O bonds can be detected after irradiation with the highest pulse energies. [Copyright &y& Elsevier]

Transform an Al alloy 6061 material into long-term stable anticorrosive by femtosecond laser induced microstructure with the phase change. [Display omitted] • The femtosecond laser is employed to locally modify the mineral components and morphology of Al alloy surfaces for the significant enhanced anticorrosion property with long-term stability of more than 2 months under seawater. • The femtosecond laser-induced thick protective layers (of tens of micrometres) such as Al 2 O 3 , MgO and Al 3 Mg 2 on the Al alloy surfaces can introduce a high corrosion resistance in the order of MΩ, thus significantly limit the corrosion current up to 3.0 nA cm−2. As per the best of our knowledge, it is one of the lowest reported value using ultrafast laser fabricated protective surfaces. • The laser-induced amorphization of the metal surface is deeply explored, and it is attributed to the increment of crystalline dislocation density caused by femtosecond laser-induced stress and compressive strain. It plays a key role in improving the anticorrosion property by significantly decrease the free energy with the amorphized material, thus increase the metal alloy's chemical stability and decrease the reactivity of its elements. • The laser-fabricated micro and nano-structures having low surface energy can exhibit the efficient air-trapping capability and decrease the contact between the metal surface and corrosive solution after annealing. Through adopting a technique of femtosecond laser micro/nano-structuring, we successfully modify the surface of aluminium alloy material into the long-term stable anti-corrosive properties, exhibiting the measured corrosion rate two orders of magnitude smaller than that of the bare sample. The underlying mechanisms are attributed to both the surface micro/nano-structure formation with the thick stable oxide layers and the significant phase change from crystalline to amorphous by the laser-induced stress and compressive strain, which consequently reduce the free energy and chemical activity of the structured surface. Such investigations may open a new eco-friendly way to produce anti-corrosive metal surfaces for deep seawater applications. [ABSTRACT FROM AUTHOR]

Abstract: In this work, the nanostructuring induced in femtosecond (fs) laser irradiation of biopolymers is examined in self-standing films of collagen and gelatine. Irradiation by single 90fs pulses at 800, 400 and 266nm is shown to result in the formation of a modified layer with submicrometric size structures. The size and uniformity of the observed features are strongly dependent on irradiation wavelength and on the characteristics of the biopolymer (water content and mechanical strength). Examination of the films by laser induced fluorescence serves to assess the chemical modifications induced by laser irradiation, revealing changes in the emission bands assigned to the aromatic amino acid tyrosine and its degradation products. The results are discussed in the framework of a mechanism involving the generation of large free-electron densities, through multiphoton and avalanche ionization, which determine the temperature and stress distribution in the irradiated volume. [Copyright &y& Elsevier]

Abstract: Investigation of the process of nanohole formation on silicon surface mediated with near electromagnetic field enhancement in vicinity of gold particles is described. Gold nanospheres with diameters of 40, 80 and 200nm are used. Irradiation of the samples with laser pulse at fluences below the ablation threshold for native Si surface, results in a nanosized surface modification. The nanostructure formation is investigated for the fundamental (λ =800nm, 100fs) and the second harmonic (λ =400nm, 250fs) of the laser radiation generated by ultrashort Ti:sapphire laser system. The near electric field distribution is analyzed by an Finite Difference Time Domain (FDTD) simulation code. The properties of the produced morphological changes on the Si surface are found to depend strongly on the polarization and the wavelength of the laser irradiation. When the laser pulse is linearly polarized the produced nanohole shape is elongated in the E-direction of the polarization. The shape of the hole becomes symmetrical when the laser radiation is circularly polarized. The size of the ablated holes depends on the size of the gold particles, as the smallest holes are produced with the smallest particles. The variation of the laser fluence and the particle size gives possibility of fabricating structures with lateral dimensions ranging from 200nm to below 40nm. Explanation of the obtained results is given on the basis simulations of the near field properties using FDTD model and Mie''s theory. [Copyright &y& Elsevier]

Abstract: We compare the foaming characteristics induced by irradiation with single ns and fs laser pulses of UV, VIS and IR wavelengths on gelatines differing in gel strength (bloom values 75 and 225) and in crosslinking degree. We have observed that while laser irradiation with nanoseconds leads to the formation of a microfoam layer at 266nm, and melting and crater formation at longer wavelengths (532 and 1064nm), fs pulse irradiation leads to submicron foaming at all wavelengths studied (266, 400 and 800nm). These results show the possibility of controlling the submicrometric foam structure in this biomaterial and can shed light into the working mechanisms of fs laser nanoprocessing in biomaterials, where increase of temperature, thermoelastic stress generation, and stress-induced bubble formation are mediated by the generated plasma. [Copyright &y& Elsevier]

Abstract: We report that plasma generated during processing of materials with ultrashort pulse lasers and the associated high intensity optical beam have both favourable and unfavourable impact on the machined surface quality. Intensity of the optical beam propagating through ambient air medium enhanced further by self-focusing is sufficiently high to cause gas breakdown forming air plasma. The generated plasma reduces the effect of self-focusing but also distorts the beam profile. Duration of the pulse being too short for thermal equilibrium to establish, ablation occurs largely by direct removal of the material forming another plasma plume. Normally, the scattering effect of plasma results in distortions of the fabricated features. However, for certain parameter ranges, the competing self-focusing and gas plasma plumes supplemented with the material plasma can combine to cause filamentation, eliminating the distortions. Filament of hot plasma also acts as a well-shaped energy source. In the present study, brass is taken as an example for the investigation. Experiments were conducted to capture the spectrum of the light scattered by plasma using a spectrometer. Analysis was done to estimate the material plasma. Theoretical calculation on the intensity distribution in an optical beam propagating through air was then followed for a range of parameter values taking the self-focusing effect of the medium and the impact of the plasma generated by its breakdown. Approximate values of the machining parameters for clean fabrication are deduced from the calculations, which were used to conduct a laser machining test on brass. [Copyright &y& Elsevier]

[Display omitted] • We show controlled Voronoi partitions (VPs) by femtosecond laser processing on Au. • The VPs are formed by controlling the laser fluence. • FDTD and TTM are used to explain the formation of emerging structures. Ultrafast and high intensity laser pulses can drive materials into highly non-equilibrium conditions. At a sufficiently high intensity, femtosecond laser pulses can turn a solid material into a superheated solid or a superheated liquid state. For metals with low electron–phonon coupling strength, e.g., gold (Au), a superheated liquid state can lead to the formation of a family of unique surface structures, the so-called Voronoi partitions (VPs). Although chaotic in nature, we demonstrate here a control of VP formation through varying the laser fluence and pulse number, resulting in a rich variety of VPs. To understand the formation of complex surface geometries under laser irradiation, we utilizes a numerical approach that integrates the finite difference time domain of electromagnetic field method with the two-temperature model. By studying the spatio-temporal distribution of electromagnetic and temperature fields and by analyzing the geometric properties of the VPs, we provide a framework for understanding the emerging surface patterns. With VPs, novel structures are generated with promising potential applications, namely, Gecko-skin-like nano-spikes and nano-cauliflower-like surface structures. [ABSTRACT FROM AUTHOR]