Publication

Results of the work in the Laser4Fun project has been published as:

Jean-Michel Romano, Antonio Garcia-Giron, Pavel Penchev, Stefan Dimov. Triangular self-organized surface textures produced by femtosecond laser irradiation on stainless steel and titanium alloy. 2nd World Congress on Micro and Nano Manufacturing (September 2018); doi: 10.3850/978-981-11-2728-1_09

Abstract

The large area uniformity of laser-induced periodic surface structures (LIPSS) on ferritic stainless steel and titanium alloy is studied. A single-step process was designed to generate low spatial frequency LIPSS (LSFL) over relatively large areas. For the first time, a new LIPSS morphology is fabricated using near-infrared ultrashort pulsed laser. Extraordinarily uniform self-organized triangular structures in hexagonal arrangements were fabricated in the subwavelength range. The generation of such LSFL was found to be highly repeatable, not material dependent but very sensitive to the used laser processing settings. Therefore, the sensitivity of triangular-LSFL formation to pulse fluence and scanning speed were investigated.

Results of the work in the Laser4Fun project has been published as:

Andrés Fabián Lasagni, Sabri Alamri, Alfredo Ismael Aguilar-Morales, Florian Rößler, Bogdan Voisiat and Tim Kunze. Biomimetic Surface Structuring Using Laser Based Interferometric Methods. Appl. Sci. 2018, 8(8), 1260

Abstract

This review investigates the capabilities of laser-based interferometric methods for producing structures with multiple-scaled surface features imitating natural examples. Firstly, laser interference lithography is used to produce hierarchical patterns with length-scales in the micrometer and sub-micrometer range. Different strategies are discussed to produce a wide variety of periodic arrays, depending on the number of resist lasers used as well as the way in which the exposure steps are organized. After that, periodic patterns are fabricated on polymers using ns laser pulses from an UV-laser system. Additionally in this case, multiple-scale patterns are produced by using different strategies. A similar approach is described to treat metallic surfaces of steel X6Cr17 and a titanium alloy Ti6Al4V. The geometry of the produced microstructures was characterized using scanning electron microscopy and confocal microscopy. Measurement of water contact angle is performed for both polymer and metallic surfaces..

Link(s)

• http://www.mdpi.com/2076-3417/8/8/1260
• https://doi.org/10.3390/app8081260

Results of the work in the Laser4Fun project has been published as:

Alfredo I. Aguilar-Morales, Sabri Alamri, Tim Kunze, Andrés Fabián Lasagni. Influence of processing parameters on surface texture homogeneity using Direct Laser Interference Patterning. Optics & Laser Technology. Volume 107, November 2018, Pages 216–227.

Abstract

Surface functionalities in the field of tribology, wettability, biocompatibility and holographic marking introduced by well-defined surface structures strongly depend on the surface texture homogeneity and quality. This work presents strategies for the fabrication of homogeneous periodic surface microstructures employing the Direct Laser Interference Patterning (DLIP) technology with the fundamental transverse mode (TEM00) emitted from a nanosecond laser source. Ti6Al4V substrates are structured using line-like patterns with spatial periods of 7.20 µm, 5.82 µm and 4.31 µm. The impact of various DLIP process parameters such as laser fluence, pulse overlap, hatch distance and spatial period on the produced surface microstructures is introduced and the consequences on the surface texture homogeneity are discussed. Large-area analysis of micro structures is carried out through white light interferometry and scanning electron microscopy. A quantitative measurement scheme of the pattern homogeneity, based on topographical properties such as kurtosis, standard deviation and mean structure height was introduced. Furthermore, the influence of a second modulation arising from the employed hatch distance has been identified. A quantitative parameter, the surface error percentage, has been introduced and employed for the characterization of pattern homogeneity. It was found that specially for larger spatial periods and surfaces treated at high laser fluence, pulse-to-pulse overlaps and a short hatch distance, the overall surface texture homogeneity could be improved up to ∼80–90%.

Link(s)

• https://www.sciencedirect.com/science/article/pii/S0030399218303347
• https://doi.org/10.1016/j.optlastec.2018.05.044

Results of the work in the Laser4Fun project has been published as:

Fotis Fraggelakis, Girolamo Mincuzzi, Inka Manek-Hönninger, John Lopez and Rainer Kling(2018) Generation of micro- and nano-morphologies on a stainless steel surface irradiated with 257 nm femtosecond laser pulses. RSC Adv., 2018, 8, 16082-16087. DOI: 10.1039/C8RA01774C.

Abstract

Surface structuring by femtosecond lasers has emerged as an efficient tool to functionalize the surfaces of various solid materials. Laser induced periodic surface structures (LIPSS) can drastically impact the wetting, friction and optical properties of the surface depending on the size, aspect ratio and period of the structures. Morphological characteristics in the nanoscale, such as nano roughness, contributing to a hierarchical surface formation are considered to have a significant impact on those properties. In this study, we demonstrate for the first time to our knowledge the feasibility of inducing ripples and spikes utilizing a 257 nm femtosecond laser. LIPSS with a period smaller than 200 nm were realised. Furthermore, we show the evolution of those structures into conical spikes for this wavelength, and we provide an interpretation on their formation. Finally, we show that sub 200 nm LIPSS can create subwavelength gratings providing non-angular dependent light reflection and non-periodic morphologies showing super hydrophobic behaviour.

Link(s)

• http://pubs.rsc.org/en/Content/ArticleLanding/2018/RA/C8RA01774C#!divAbstract
• http://pubs.rsc.org/en/content/articlehtml/2018/ra/c8ra01774c
• 10.1039/C8RA01774C

Results of the work in the Laser4Fun project has been published as:

Jean-Michel Romano, Antonio Garcia-Giron, Pavel Penchev, Stefan Dimov (2018) Triangular laser-induced submicron textures for functionalising stainless steel surfaces. Applied Surface Science
Volume 440, 15 May 2018, Pages 162–169.

Abstract

Processing technologies that engineer surfaces with sub-micron topographies are of a growing interest to a range of optical, hydrophobic and microbiological applications. One of the promising technologies for creating such topographies employs ultra-short laser pulses to produce laser-induced periodic surface structures (LIPSS) that often result in non-regular, quasi-periodic nanoripples and nanopillars. In this research near infrared ultra-short pulses of 310 fs with a circular polarisation was used to texture ferritic stainless steel workpieces. A single-step process was designed to generate low spatial frequency LIPSS (LSFL) over relatively large areas. Apart from highly regular and homogeneous parallel lines with approximately 900 nm periodicity, extraordinarily uniform triangular-LSFL in hexagonal arrangements was created. The generation of such LSFL was found to be highly repeatable but very sensitive to the used laser processing settings. Therefore, the sensitivity of triangular-LSFL formation to the used laser processing settings, i.e. pulse to pulse distance, pulse fluence and focal plane offsets, were investigated in regard to the resulting morphologies and functional properties, i.e. structural colors and super-hydrophobicity. Finally, the capability of this technology for producing uniform triangular-shaped LSFL on relatively large surface areas of stainless steel plates was studied.

Link(s)

• https://www.sciencedirect.com/science/article/pii/S0169433218300886
• https://doi.org/10.1016/j.apsusc.2018.01.086

Results of the work in the Laser4Fun project has been published as:

F. Fraggelakis, G. Mincuzzi, J. Lopez, Inka Manek-Honninge, R. Kling, “2D laser induced periodic surface structures with double cross-polarized pulses,” Proc. SPIE 10520, Laser-based Micro- and Nanoprocessing XII, 105200L (19 February 2018); doi: 10.1117/12.2287841

Abstract

We present a systematic study on the generation of 2D surface structures on stainless steel, using double, crosspolarized femtosecond pulses with variable interpulse delay. We demonstrate the combined effect of the interpulse delay and key process parameters in order to obtain periodic structures. The sets of double pulses were produced utilizing a modified Michelson interferometer with interpulse delay varying from -100 ps to +2 ns. The study was carried out with an industrial laser having pulse duration of 350 fs, emitting in the near infrared (λ = 1030 nm), operating at 100 kHz coupled with a Galvo scanner. We evaluate the obtained surface morphology and structure period using SEM characterization and Fourier analysis.

Link(s)

• https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10520/105200L/2D-laser-induced-periodic-surface-structures-with-double-cross-polarized/10.1117/12.2287841.full?SSO=1

Results of the work in the Laser4Fun project has been published as:

A.Garcia-Giron, J.M.Romano, Y.Liang, B.Dashtbozorg, H.Dong, P.Penchev, S.S.Dimov (2018) Combined surface hardening and laser patterning approach for functionalising stainless steel surfaces. Applied Surface Science, Volume 439, 1 May 2018, Pages 516-524.

Abstract

The paper reports a laser patterning method for producing surfaces with dual scale topographies on ferritic stainless steel plates that are hardened by low temperature plasma surface alloying. Nitrogen and carbon based gasses were used in the alloying process to obtain surface layers with an increased hardness from 172 HV to 1001 HV and 305 HV, respectively. Then, a nanosecond infrared laser was used to pattern the plasma treated surfaces and thus to obtain super-hydrophobicity, by creating cell- or channel-like surface structures. The combined surface hardening and laser patterning approach allowed super-hydrophobic surfaces to be produced on both nitrided and carburised stainless steel plates with effective contact angles higher than 150°. The hardened layers on nitrided samples had cracks and was delaminated after the laser patterning while on plasma carburised samples remained intact. The results showed that by applying the proposed combined approach it is possible to retain the higher hardness of the nitrided stainless steel plates and at the same time to functionalise them to obtain super-hydrophobic properties.

Link(s)

• https://doi.org/10.1016/j.apsusc.2018.01.012

Results of the work in the Laser4Fun project has been published as:

Sabri Alamri, Alfredo I. Aguilar-Morales, Andrés F. Lasagni (2018) Controlling the wettability of polycarbonate substrates by producing hierarchical structures using Direct Laser Interference Patterning. European Polymer Journal. Volume 99, February 2018, Pages 27–37.

Abstract

New strategies for the fabrication of surface structures using Direct Laser Interference Patterning are presented in this work, aiming to fabricate hierarchical structures with selective wetting properties. Polycarbonate sheets have been structured employing a two-beam interference arrangement using an ultraviolet (263 nm) nanosecond-pulsed laser, creating line- and pillar-like structures with simple and hierarchical geometries. Two different methods for producing hierarchical structures are here provided, both relying on a pixel-wise structuring technique and able to achieve high structure depths. The produced surface patterns are characterized by confocal microscopy, scanning electron microscopy and the influence of the surface topography on the water contact angle is investigated. The correlation between structure geometry and wettability response, in terms of structure height and directionality of the droplet shape is reported.

Link(s)

• http://www.sciencedirect.com/science/article/pii/S0014305717314003

Results of the work in the Laser4Fun project has been published as:

Antonio Ancona, Gagandeep Singh Joshi, Annalisa Volpe, Michele Scaraggi, Pietro Mario Lugarà and Giuseppe Carbone. Non-Uniform Laser Surface Texturing of an Un-Tapered Square Pad for Tribological Applications. Lubricants 2017, 5, 41.

Abstract

Femtosecond laser surface micro-texturing has emerged as a promising technology to enhance the tribological properties of different kinds of lectromechanical devices. In this research paper, we have exploited the intrinsic flexibility and micrometric accuracy of femtosecond laser ablation to realize complex micro-structural modifications on the surface of a laboratory prototype of a steel thrust bearing (un-tapered) pad. The Bruggeman Texture Hydrodynamics theory (BTH) is employed for the design of the anisotropic and non-uniform texture maximizing the thrust load of the pad prototype. The preliminary experimental results, reported in this work, show that the non-uniform micro-texture largely affects the friction characteristics of the contact. In particular, in agreement with the BTH predictions, the tribo-system shows friction properties that are strongly
sensitive to the direction of the sliding speed, as a consequence of the micro-fluid dynamics which are designed to occur only in a specific sliding direction. We suggest that the joint action of virtual prototyping (BTH lubrication theory) and ultrafast laser micro-prototyping can lead to unconventional and impressive results in terms of enhanced or tailored contact mechanics properties of the generic lubricated tribopair.

Link(s)

• http://dx.doi.org/10.3390/lubricants5040041

Results of the work in the Laser4Fun project has been published as:

Alfredo I. Aguilar-Morales, Sabri Alamri, Andrés Fabián Lasagni. Micro-fabrication of high aspect ratio periodic structures on stainless steel by picosecond direct laser interference patterning. Journal of Materials Processing Technology. Volume 252, February 2018, Pages 313-321.

Abstract

We have studied the fabrication of line-like and pillar-like periodic microstructures on stainless steel by means of direct laser interference patterning. A picosecond (10 ps) pulsed Nd:YAG laser operating at 1064 nm wavelength was used to produce the microstructures with spatial periods ranging from 2.6 μm to 5.2 μm. By varying the laser parameters (laser fluence, pulse-to-pulse overlap) structure depths ranging from 500 nm to nearly 11.5 μm could be obtained. Furthermore, low and high frequency laser induced periodic surface structures (LIPSS) have been generated, resulting in three-level multi-scaled patterns. The orientation of the laser induced periodic structures with respect to the interference patterns could be adjusted by controlling the laser beam polarization. Finally, static water contact angle measurements are performed to investigate its correlation with the surface morphology. The treated surfaces are characterized using confocal and scanning electron microscopy.

Link(s)

• https://doi.org/10.1016/j.jmatprotec.2017.09.039