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Special Section Papers

Subwavelength Direct Laser Nanopatterning Via Microparticle Arrays for Functionalizing Metallic Surfaces

[+] Author and Article Information
Jean-Michel Romano

School of Engineering,
University of Birmingham,
Edgbaston, Birmingham B15 2TT, UK
e-mail: jean-michel.romano@gadz.org

Rajib Ahmed

Bio-Acoustic MEMS in Medicine
(BAMM) Laboratory,
School of Medicine,
Stanford University,
Palo Alto, CA 94304;
School of Engineering,
University of Birmingham,
Edgbaston B15 2TT, Birmingham, UK
e-mail: rajibah@stanford.edu

Antonio Garcia-Giron

School of Engineering,
University of Birmingham,
Edgbaston, Birmingham B15 2TT, UK
e-mail: AXG616@bham.ac.uk

Pavel Penchev

School of Engineering,
University of Birmingham,
Edgbaston, Birmingham B15 2TT, UK
e-mail: P.Penchev@bham.ac.uk

Haider Butt

School of Engineering,
University of Birmingham,
Edgbaston, Birmingham B15 2TT, UK;
Department of Mechanical Engineering,
Khalifa University,
P.O. Box 127788,
Abu Dhabi, United Arab Emirates
e-mail: H.Butt@bham.ac.uk

Olivier Delléa

Laboratoire des Composants pour la Conversion
de l'Energie (L2CE),
Laboratoire d'Innovation pour les Technologies
des Energies Nouvelles et des Nanomatériaux
(LITEN),
Commissariat á l'Energie Atomique et aux
énergies alternatives (CEA),
Grenoble 38054, France;
CEA/LITEN,
Laboratoire d'Innovation pour les Technologies
des Energies Nouvelles et des nanomatériaux,
Grenoble 38000, France
e-mail: olivier.dellea@cea.fr

Melissa Sikosana

Max Bergmann Center of Biomaterials,
Leibniz Institute of Polymer Research Dresden,
Dresden 01069, Germany
e-mail: sikosana@ipfdd.de

Ralf Helbig

Max Bergmann Center of Biomaterials,
Leibniz Institute of Polymer Research Dresden,
Dresden 01069, Germany
e-mail: helbig@ipfdd.de

Carsten Werner

Max Bergmann Center of Biomaterials,
Leibniz Institute of Polymer Research Dresden,
Dresden 01069, Germany
e-mail: werner@ipfdd.de

Stefan Dimov

School of Engineering,
University of Birmingham,
Edgbaston, Birmingham B15 2TT, UK
e-mail: S.S.Dimov@bham.ac.uk

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MICRO-AND NANO-MANUFACTURING. Manuscript received September 14, 2018; final manuscript received February 8, 2019; published online April 11, 2019. Assoc. Editor: Martin Jun.

J. Micro Nano-Manuf 7(1), 010901 (Apr 11, 2019) (11 pages) Paper No: JMNM-18-1033; doi: 10.1115/1.4042964 History: Received September 14, 2018; Revised February 08, 2019

Functionalized metallic nanofeatures can be selectively fabricated via ultrashort laser processing; however, the cost-effective large-area texturing, intrinsically constrained by the diffraction limit of light, remains a challenging issue. A high-intensity near-field phenomenon that takes place when irradiating microsized spheres, referred to as photonic nanojet (PN), was investigated in the transitional state between geometrical optics and dipole regime to fabricate functionalized metallic subwavelength features. Finite element simulations were performed to predict the PN focal length and beam spot size, and nanofeature formation. A systematic approach was employed to functionalize metallic surface by varying the pulse energy, focal offset, and number of pulses to fabricate controlled array of nanoholes and to study the generation of triangular and rhombic laser-induced periodic surface structures (LIPSS). Finally, large-area texturing was investigated to minimize the dry laser cleaning (DLC) effect and improve homogeneity of PN-assisted texturing. Tailored dimensions and densities of achievable surface patterns could provide hexagonal light scattering and selective optical reflectance for a specific light wavelength. Surfaces exhibited controlled wetting properties with either hydrophilicity or hydrophobicity. No correlation was found between wetting and microbacterial colonization properties of textured metallic surfaces after 4 h incubation of Escherichia coli. However, an unexpected bacterial repellency was observed.

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Figures

Grahic Jump Location
Fig. 1

The modeling results of light focusing through silica microspheres. Irradiation wavelength was fixed at 1030 nm while the microspheres' radii were varied. (a) Intensity mapping for three cases of x = 2r/λ, especially equal to 1.0, 1.9, and 2.9. The color scales are independent for each case, in particular from blue (low intensity) to red (peak intensity). (b) The intensity evolution along the vertical axis, normalized with the sphere's radius for four cases of x. The dashed circle and line indicate the normalized sphere's dimension and surface position. (c) Peak intensity estimations for the considered cases of x from 0.5 to 8. (d) Paraxial focal length and PN length as a function of x. The red colored area suggests combinations of wavelength and radius where the focal point is outside microspheres. (e) FWHM normalized in regard to the irradiation wavelength for the considered x values. (f) Irradiation surface density calculated for a close-packed array of spheres as a function of x. Estimations are taken at the peak intensity positions z = z(Imax) on the substrate surface. Analytical PN waists were plotted according to Arnold [30].

Grahic Jump Location
Fig. 2

A direct laser ablation-based nanopatterning by irradiating a HCP CPLA of 1 μm-diameter spheres with a NI 30 μm-diameter Gaussian fs-laser beam. (a) The used experimental setup for processing substrates with a focal offset. ((b) and (c)) The schematic steps of the texturing process. The microspheres are partially removed from the textured area and its surroundings. Micrographs of morphologies achieved with 310 fs laser pulses at 1032 nm wavelength: (d) nanobumps fabricated employing a 2 mm focal offset and 100 irradiations at 1.3 μJ; array of nanoholes fabricated with a single irradiation of (e) 1.3 μJ at focus, (f) 6.3 μJ at focus, and (g) 6.3 μJ at 1 mm focal offset, respectively. ((h)–(j)) Distributions of nanoholes' diameters corresponding to ((e)–(g)). The nanoholes are gathered in clusters of 0.1 μm and a normal distribution is extrapolated from the distribution. Profiles of nanobumps (k) and honeycomb structures (i) are given with two representative AFM cross sections.

Grahic Jump Location
Fig. 3

A large area texturing with nanoholes after NI irradiation (λ = 1032 nm, circular polarization, 30 μm focal spot size) of a CPLA of 1-μm-spheres. (a) The diameters of DLC spots compared with the diameter of those covered with PJ-induced holes, as a function of pulse energy at focus. Mean diameters and their standard deviation were calculated based on five measurements. (b) Schematic representation of textured areas that result from varying hatching and pulse-to-pulse distances, σ and δ, respectively. Micrographs depict the effects on surface morphologies when varying σ and δ, in particular: (c) σ = δ = 25 μm, (d) δ = 22.5 μm and σ = 25 μm, (e) δ = 15 μm and σ = 25 μm, (f) σ = δ = 10 μm and (g) σ = δ = 5 μm, with 3.6 μJ pulses at focus. LIPSS generation upon multiple irradiations of prefabricated arrays of nanoholes: (h) hexagonal LIPSS fabricated at 1 mm focal offset by 100 2.5 μJ pulses. Further evolution of LIPSS over nanoholes fabricated with 3.9 μJ pulses at focus: (i) rhombic-shaped LIPSS after 28 0.5 μJ pulses at focus and (j) ripples-like LIPSS after 177 1.5 μJ pulses at focus. The Fourier transformed micrographs indicating LIPSS periodicity and orientation are depicted in the insets.

Grahic Jump Location
Fig. 4

Optical characterization of nanotextured stainless steel. The evolution of broadband reflection with the increase of pulse numbers with two different pulse energies (a) 0.9 μJ and (b) 6.6 μJ. (c) The reflection evolution for three selected wavelengths, 440 nm (blue), 540 nm (green), and 640 nm (red), with pulse numbers (constant pulse energy of 4.8 μJ). The evolution of reflection properties with the pulse-to-pulse distance for (d) fixed σ = 25 μm and (e) σ = δ. (f) The reflection evolution for selected blue, green, red wavelengths, with the pulse-to-pulse distance σ = δ. (g) Light scattering properties under normal illumination of the surfaces, projected on a 30 mm-hemispherical semitransparent surface. (h) Light scattering properties under different illumination angles, from 10 deg to 80 deg.

Grahic Jump Location
Fig. 5

Wettability and microbiological characterizations of subwavelength surface structures. (a) The evolution of static water CA with the pulse-to-pulse distance (σ = δ) on stainless steel. (b) Advancing and receding water CA for polished and σ = δ = 5 μm textured stainless steel. (c) A tilting test illustrating the sticking effect of water drops onto the σ = δ = 5 μm textured stainless steel. (d) The evolution of normalized adherent E. coli cells after 4 h incubation on perfluoropolyether replicas with the fabricated pulse-to-pulse distance, for (d) σ = 25 μm and (e) σ = δ. Data are shown in box-whisker plots with half of all data points within the box and 100% within the whiskers; black diamonds in the boxes indicate mean values and the black horizontal line the median value (n = 14). (f) Representative SEM images of adhered E. coli on replica of (from left to right): nonstructured reference, σ = 25 μm and δ = 22.5 μm, σ = 25 μm and δ = 15 μm, σ = δ = 10 μm, σ = δ = 5 μm. The adhered E. coli cells are highlighted in green halos.

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