Surface Functionalization (LiM 2017)

Applying laser dispersion and laser ablation to generate functional layers for deep drawing tools
Freiße, Hannes; Vetter, Konstantin; Seefeld, Thomas; Vollertsen, Frank

Avoiding lubricants in forming processes would reduce the demand of minimal oil in production processes. Cleaning
processes would not be necessary any more. This would offer the possibility to optimize the cost efficiency of the
process chain. However, forming without lubrication would lead to a significant change in the tribological system. So,
new approaches for tool surfaces must be developed to ensure process reliability in dry metal forming. In this work a
laser generated tool surface is presented to form high alloy steel without lubrication. Laser dispersion is applied to inject
spherical fused tungsten carbide particles into the surface of the aluminum bronze substrate. Afterwards, ultra-short
pulse laser is deployed to ablate the matrix of the metal matrix composite (MMC). Subsequently, the hard particles
stand out of the matrix with a defined depression and form a supporting plateau, which is in direct contact with the
sheet material during the forming process.

Keywords: laser dispersion; laser ablation; forming technology


Femtosecond laser micropatterning of diamond-like nanocomposite coatings to improve friction on the microscale
Pimenov, Sergei; Zavedeev, Evgeny; Arutyunyan, Natalia; Zilova, Olga; Shupegin, Mikhail; Jaeggi, Beat; Neuenschwander, Beat

We report on femtosecond laser micropatterning of diamond-like nanocomposite (DLN) coatings (SiOx containing
diamond-like carbon films) and investigation of the frictional properties of laser-patterned films on the nano and
microscale. The DLN films of 2-3
μm thickness were irradiated using a femtosecond laser (λ=1030 nm, τ=320 fs) at low fluences (below the single-pulse damage threshold) corresponding to the conditions of surface graphitization and incipient ablation developing during multipulse irradiation. The low-fluence multipulse irradiation was applied to produce periodic linear micropatterns (graphitized strips of <10 μm width and 20 μm period) on the DLN films. Microfriction properties of the laser-patterned films were studied using atomic force microscopy (AFM) in the lateral force mode. It was found that transition from nano to microscale (by increasing an AFM tip radius from 10 nm to 1.5 μm) was characterized by significant changes in the friction behaviour of laser-patterned films, demonstrating much lower friction forces within laser-irradiated areas than on the original film. The laser-patterned surface was found to exhibit changes in the wettability due to enlarged hydrophobicity of laser-graphitized surface. This resulted in a strong influence
of capillary forces on the friction forces under the ‘nano’ loads and lowering of the friction forces on the laser-modified surface. The relative role of laser-induced surface modifications (graphitization, spallation, ablation, nanostructuring) in the observed microfriction behaviour is discussed.

Keywords: Diamond-like nanocomposite film; femtosecond laser; graphitization; ablation; micropatterning; friction force microscopy


Influence of Pulse Duration and Scanning Direction on the Deformation of Edges during Laser Micro Polishing
Nüsser, Christian; Schneider, Simon

Laser micro polishing with pulsed laser radiation has been investigated regarding the smoothing of surfaces. It is often
described that this process influences the geometry of the surface less than conventional polishing techniques, which
are often based on abrasive smoothing. But it is currently unknown how much the geometry of parts is influenced during
laser micro polishing. The edges are of particular interest since they often determine the function of surfaces and it is
known that they are significantly rounded during laser macro polishing with continuous wave laser radiation.
Therefore, in this paper the influence of the pulse duration and the scanning direction on the deformation of edges
during laser micro polishing is investigated. Milled test samples made of TiAl6V4 are used for the examinations. Three
different pulse duration regimes (tP 200 ns, tP = 285-660 ns, tP = 1.22-1.60 μs) as well as three scanning directions are
investigated. The analysis is performed with laser scanning microscopy for the geometry of the edges and white-light
interferometry for the roughness of the surfaces. The results show that the pulse duration has minor influence and that
the deformation of edges presumably depends more on the beam dimensions. Additionally, scanning of the surface in a
meandering pattern perpendicular to the edge leads to less deformation than scanning parallel to the edge.

Keywords: Laser Micro Polishing, Laser Polishing, Edge Deformation, Edge Rounding, Surface Functionalization


Tamper-proof holographic markings for high-value goods
Wlodarczyk, Krystian L.; Ardron, Marcus; Waddie, Andrew; Taghizadeh, Mohammad; Weston, Nick; Hand, Duncan P.

We present a fast and reliable laser-based process for the generation of ‘tamper-proof’ security markings on the surface
of metals, such as stainless steel, nickel and nickel-chromium Inconel® alloys. The markings are in the form of phase
computer generated holograms (CGHs) and are produced using 35ns long laser pulses of 355nm wavelength. The CGHs
contain an array of very shallow (< 0.5μm deep) optically-smooth deformations; each deformation is produced by a
single laser pulse that locally melts and evaporates the metal surface. Binary and multi-level CGHs are possible. The
holographic structures are designed to form diffractive images containing alphanumeric characters and simple images.
The flexibility of the process allows each hologram to be unique. Moreover, the laser-generated holograms can possess
additional security features and enhanced appearance. The holographic structures are resistant to abrasion and
tampering because they are generated directly on the metal surface. As demonstrated, these structures can be used as
security markings for commercially-available (high value) metal goods, e.g. luxury watches.

Keywords: Laser marking; security markings; diffractive optics; phase holograms; metals


Generation of functional sub-µm sphere patterns on quartz substrates using fs-laser
Stroj, Sandra; Matylitskaya, Volha; Matylitsky, Victor; Kasemann, Stephan; Domke, Matthias

In recent years, the formation of laser-induced periodic surface structures (LIPSS) has attracted many researches in the
field of laser microprocessing. The formation of LIPSS can be observed for a big variety of materials where e.g. silicon is
prone to form more distinctive structures than e.g. glasses. Moreover, LIPSS usually appear in form of sinusoidal parallel
structures. Spherical shaped patterns, especially with undercut, could enable several new surface functionalities and
In this work we utilize LIPSS formation to generate sub-micron-size quartz spheres, distributed in a specific pattern and
fixed on a quartz surface. As a first step, a thin layer of amorphous silicon (a-Si) was selectively structured on a quartz
substrate. Due to the crystallinity of the material and the limited layer thickness small silicon droplets form instead of
the usually observed parallel LIPSS structures. This pattern can now be transferred into SiO2 by a thermal oxidation step.
The final device is all quartz with a functional surface showing a pattern of spheres with undercut where the appearance
can be controlled by the laser process parameters. The surface exhibits water contact angles of up to 163° and a contact
angle hysteresis of up to 151° (θa = 163°, θr = 12°). Additional, the transparency show values close to 80 %.

Keywords: femtosecond laser, functional surface, wetting properties, contact angle ;


Ultra-fast multi-spot-parallel processing of functional micro- and nano-structures on embossing dies with ultrafast lasers
Brüning, Stephan; Jarczynski, Manfred; Mitra, Thomas; Du, Keming; Fornaroli, Christian; Gillner, Arnold

Functionalization of surfaces is of ma jor inte rest for several applica tions , e .g. tooling indus try, printing i ndus try and for
consume r products . I n sui table mass production appli ca tions , like inje ction molding or roll -to -roll processing for di ve rse
ma rke ts , the final product could be equipped with new features, like hydrophilic behavior, adjus table gloss le vel , soft -
touch beha vior, light manage ment prope rties and so on. For the gene ra tion of functionalities at reasonable costs, dies
and molds can be complemented with an additional structure in mi cro/nano s cale using laser abla tion te chnologies .
Through the a vailability of USP-lase rs , fea tures sizes down to the diffra ction limi t could be trans fe rred in a digi tal wa y
(pi xel by pi xel / voxel by voxel ) to a tool , like a cylinde r for a roll-to -roll mass production. In re cogni tion of an indus trial
implementa tion, an ultra -hi gh resol ved di re ct digi tal transfe r is a limi ting factor. Shorte r processing times by furthe r
increasing the spot- or workpie ce-movements a re limi ted. By kee ping the a chie ved s tate -of-the -a rt pe rformance ,
s caling-up indi vidual modula ted lase rs/laser-spots ena ble a less challenging wa y of increasing the producti vi ty. In this
work, the pa rallel process of indi vi dual modulate d mul ti laser sources is compa red wi th a lase r source spli t by Diffra cti ve
Opti cal Ele ments (DOE) for applica tions in a cylinde r micro structuring system. With spotsizes down to approx. 2 μm and
depth resolution of 50 nm per pulse, diffractive elements are processed on a me tal plate (e .g. s tainless steel plate , shim).
Thi s shim could be used as a n e mbossing die for mass production roll -to-roll processes.

Keywords: ultrashort laser pulse; 3D μm machining; ablation; Soft-Touch-Structures; hydrophobic surfaces; antibacterial surfaces; diffractive optical elements (DOE); ultra-short pulsed lasers; functional surfaces; light management; micro prisms; Fresnel lenses; lenticular lenses; micro processing; roll-to-roll production; embossing dies; shim


Scanning strategy of high speed shifted laser surface texturing
Moskal, Denys; Martan, Jiri; Kucera, Martin

Laser Surface Texturing (LST) is one of the perspective ways for creating of functional surfaces: low frictional, hydrophobic or
hydrophilic, photonic structures, thermal spray substrates and so on. There are several methods for laser surface texturing of large
areas, but they have some physical limitations, such as heat accumulation, plasma shielding and achieving high precision at fast laser
beam scanning speed. In this paper a new method called shifted Laser Surface Texturing (sLST) is presented. This sLST method is able to
overcome mentioned physical limitations. The sLST method is based on formation of large array of microobjects by collecting them from
short/ultrashort laser pulses, which are distant in time and processing plane. It is achieved by application of a series of laser scanning of
linear raster which contains a lot of single pulses. Each single pulse in one raster belongs to different object from the textured area. The
linear raster is shifted by small distance between each repetition. The high precision of the shape and position of every textured object
(< 2 μm) is achieved by control of laser spots position electronically by using of constant repetition frequency of laser pulse generation.
In this way the mirrors movement has no control of object position directly, but supply only continuous movement of the laser spot
position. The method of sLST has great potential for polygonal, resonant or hybrid scanning system, where laser beam scanning speed
reached up to 1000 m/s and high precision of microobjects formation becomes difficult task. In this paper there is described the
principle of the method along with its applications on functional surfaces. In discussion there are presented physical and technical
parameters of high speed sLST in comparison with classical texturing methods.

Keywords: laser surface texturing, scanning strategy, high speed, functional surfaces


Fabrication of bionic surfaces with mixed superhydrophobic and superhydrophilic properties using fs-lasers
Domke, Matthias; Kostal, Elisabeth; Kasemann, Stephan; Matylitsky, Victor; Stroj, Sandra

The exciting functionalities of natural superhydrophobic and superhydrophilic surfaces, e.g. the extreme water
repellency of the lotus flower, served as inspiration for a variety of bionic designs. In contrast, little attention has been
paid to combine superhydrophobic and superhydrophilic wetting properties to micropatterns. However, as the example
of the Namib desert beetle shows, such micropatterns improve e.g. the water collection efficiency from fog. With this in
mind, the patent-pending ClearSurfaceTM process by Spectra-Physics® was developed, which enables the
functionalization of nearly all kind of substrates with mixed wetting properties of arbitrary shape. In this way,
superhydrophilic micropatterns (contact angle < 5°) can be fabricated fast and flexible on a superhydrophobic
background (contact angle > 150°). This process enables the design of novel devices for biomedical and microfluidic

Keywords: ultrafast, laser, patterning, superhydrophobic, superhydrophilic, surfaces;


A novel method of laser doping to poly-Si thin films using XeF excimer laser irradiation in acid solution
Tanaka, Nozomu; Suwa, Akira; Goto, Tetsuya; Nakamura, Daisuke; Sadoh, Taizoh; Ikenoue, Hiroshi

In this paper, we propose a new method that achieves implantation of phosphorus (P) to poly-silicon (poly-Si) thin films
and dopant activation simultaneously at room temperature. We crystallized amorphous-silicon (a-Si) into poly-Si by
xenon fluoride (XeF) excimer laser annealing under atmospheric condition. Then the poly-Si film was irradiated by a XeF
excimer laser in a phosphoric acid solution. After laser irradiation in the phosphoric acid solution, the concentration of P
atoms in the poly-Si films was approximately 6.7×1018 cm-3, and the resistivity of the poly-Si films decreased dramatically
from 4.3×104 Ω
cm to 1.4 Ωcm. Through this method, the implantation of P atoms and dopant activation can be performed simultaneously.

Keywords: Laser Doping ; XeF Excime Laser ; Poly-Si ; Flexible Display ; Thin Film Transistor(TFT)


Application specific intensity distributions for laser functionalization of (nano-)ceramic coatings as wear protection
Völl, Annika; Wollgarten, Susanne; Stollenwerk, Jochen; Loosen, Peter

The l aser based functionalization of thin s ol-gel based (nano -)ceramic coatings re quires a two -step thermal process.
Fi rs t, the s olvent material, in which the ce ramic i s applied, needs to be re move d i n a dryi ng process. Afterwards, during a
s e cond step th at re moves the last organic constituents, the ce ramics full potential as wear protection coating is
a chi eved via cross-linking. As both steps re quire s ignificantly different processing te mperatures, the material usually is
tre a te d i n two consecutive l aser based processes. Thus, the process efficiency ca n be increased to a great e xtent by
us i ng application specific beam profiles. These beam profiles can be designed i n such a way tha t they combine both
s te ps into a single one by ra ising the induced material te mperature stepwise. To this e nd, we present a me thod to obtain
a n a pplication specific intensity distribution that i nduces a prescribed te mperature profile in a laye red s ystem consisting
of a me tal s ubstrate and a thin (nano -)ceramic coating. This is done by s olving a n inverse heat conduction problem using
the conjugate gra dient approach with a djoint problem. Afte rwards, we give the design of a free -form optic that
produces the obtained intensity distribution i n an experimental s etup. We conclude our work by ve ri fyi ng our a pproach
us i ng the commercial FEM software ANSYS.

Keywords: Surface Functionalization; Process Simulation;