Surface texturing is the process of applying a specific type of pattern of roughness onto the surface in order to change its properties

1. LASER
TEXTURING
Suresh Lal S R
Assistant Professor
Department of Mechanical Engineering
Government Engineering College, Wayanad

2. Contents
O Introduction
O Production of hydrophobic surfaces
O Pulsed UV laser ablation
O Femtosecond laser texturing
O Enhancing optical performance
O Improving tribological characteristics of
surfaces
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3. Surface texturing
O Surface texturing is the process of applying a
specific type of pattern of roughness onto the
surface in order to change its properties.
O Applications
O Inducing hydrophobicity
O Improving optical performance of solar cells
O Improving tribological characteristics of surfaces
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4. Hydrophobicity
O Hydrophobic surfaces have property to repel
the water droplets and during the rolling of
these droplets, dirt and foreign particles
adhered to the surface flush out.
O micro protrusions (pillars) and nano-hair on the
leaf surface provides very low surface-energy.
This low surface-energy get dominated by the
surface tension of the water droplets and
droplets try to maintain their spherical shape.
O Micro-protrusions supports the water droplets
and don't allow the droplets to get punctured.
These protrusions provide contact angle of
126°. Nano-hair (height range 300 to 1000 nm)
are flexible and soft in nature and provide wax
like surface resulting in additional increase of
contact angle by 16°.
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1Courtesy: Directions 2015 Vol. 15 No.1, IIT, Kanpur

5. Applications of hydrophobicity
O Impeller casing and blades of centrifugal
pumps
O Aerofoils and aircraft engine surfaces
O Power transmission lines
O Pipes of air conditioners and refrigerators
O Radar and telecommunication antennas
O Weather proof infrastructures
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6. Production of Hydrophobic
Surfaces
Using
O Laser texturing
O Nano casting based on soft lithography
O Electrochemical surface texturing
techniques
O Superhydrophobic coatings
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7. Pulsed UV Laser Ablation
O Super-hydrophobic surfaces are directly
fabricated on the metal (brass) surfaces using a
high power pulsed UV laser.
O Third harmonic diode-pumped solid state laser
O Wavelength - 355 nm
O Pulse repetition rate – 30 kHz
O Pulse duration – 20 ns
O Focused spot size ~ 40 µm
O Laser fluence ~ 10.5 J/cm2
O Scanning field – 60 X 60 mm
O Scanning speed – 200 mm/s
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8. 8
Pulsed UV Laser Ablation
3Technical Digest. Summaries of papers presented at the Conference on Lasers and
Electro-Optics. Post-conference Technical Digest (IEEE Cat. No.01CH37170)
Publication Year: 2001

9. Pulsed UV Laser Ablation
O The laser beam is coupled into a galvanometer after
passing through a 10 X beam expander and focused
by an f-theta lens with focal length of 100 mm and
then focused on the brass sample surface.
O The brass sample surface is initially polished to a
surface roughness of 400 nm.
O The UV laser beam writes designed patterns on the
brass substrates.
O The morphology of the brass surface is examined with
a field emission scanning microscope.
O Surface roughness was measured by a 3D topography
device.
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10. Pulsed UV Laser Ablation
O Spike shape micro-structures are
formed on the brass substrates.
O The pitch of the grid equates the spot
size of laser beam ~ 40 µm with a height
of ~20 µm.
O The surface roughness obtained is ~5
µm.
O Plenty of nano-structures are also
formed and scattered on the surface.
O It is also observed that plenty of nano-
structures are also formed and
scattered on the surface of the micro-
structures.
O The phenomenon is due to Gaussian
distribution of the laser beam at the
focus points so that the energy density
at the border of the laser beam is lower
than that of the centre.
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2JLMN-Journal of Laser Micro/Nano engineering Vol. 6, No. 1, 2011

11. Pulsed UV Laser Ablation
O The surrounding area of laser ablation
absorbs less laser energy, therefore only
central part of metal is melted and formed
liquid pools where the heating temperature
is not high enough to vaporize the metal.
O During this process, the ripples are
generated on the surfaces of metal liquid
pools, which create plenty of nano-
structures since the metal liquid is splashed
and shrunk into nano-particles during the
re-solidification.
O When the laser irradiation ends, the metal
surface layer is cooled down rapidly by
heat conduction into the metal substrate
and nano-structures are remained on the
surfaces of the micro-structure.
O These nano-structures are in the size of
200~600 nm.
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2JLMN-Journal of Laser Micro/Nano engineering Vol. 6, No. 1, 2011

12. Pulsed UV Laser Ablation
O A high resolution camera is employed to measure the
static contact angles of water droplet on metal
samples.
O The volume of water droplet for the testing is 1 μl.
O After the laser treatment, the water contact angle of the
laser textured brass surface was ~ 110°.
O The contact angle of the laser textured brass surface
increases when exposing to air.
O After two weeks, the contact angle of the laser
textured brass sample reaches a plateau and the
surface become super-hydrophobic surface with a
contact angle of ~ 161°.
O Materials of the outer layer on the brass surface are
converted into stoichiometric ZnO and CuO, which are
hydrophobic materials.
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2JLMN-Journal of Laser Micro/Nano engineering Vol. 6, No. 1, 2011

13. Femtosecond Laser Texturing
O An amplified Ti:sapphire laser system is used to
texture the platinum sample with an array of
parallel microgrooves covered by extensive
nanostructures.
O Wavelength - 800 nm
O Pulse repetition rate – 1 kHz
O Pulse duration – 65 fs
O Laser flounce ~ 9.8 J/cm2
O A scanning electron microscope and 3D laser
scanning microscope are used to examine the
surface textures.
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14. Femtosecond Laser Texturing
14
O The laser textured titanium surface
appeared as an array of parallel
microgrooves covered by extensive
nanostructures.
O The microgroove spacing is about 100
µm and the depth is about 75 µm.
O The smallest nanoscale features are
about 5-10 nm.
O Exposure of the textured surface
makes it superhydrophobic, due to the
chemical interaction with the CO2
present in the atmosphere.
O The water contact angle is measured
as 1580.
4J . Appl. Phy. 117,033103 (2015)

15. Enhancing Optical Properties
15
O To minimise reflection from the flat surface, the
multi-crystalline silicon wafers in solar panels are
textured.
O This means creating a roughened surface so that
incident light may have a larger probability of being
absorbed into the solar cell.
5journal of materials processing technology 2 0 1 ( 2 0
0 8 ) 291–296

16. Enhancing Optical Properties
16
O Material used as a substrate was “as
cut”, p-type, boron doped multi-
crystalline silicon wafers manufactured
by casting method.
O Experiments were carried out on wafers
of thickness ∼330 µm, area 5 cm×5 cm
and resistivity 1 Ωcm.
O Texturization of wafers was performed
by means of ALLPRINT DN50A Q-
switched Nd:YAG laser (λ=1064 nm)
O Successive grooves were scribed with
constant spacing within consecutive
scanning of the wafer surface by laser
beam in the opposite directions. 5journal of materials processing technology 2 0 1 (
2 0 0 8 ) 291–296

17. Enhancing Optical Properties
17
O maximum output power (P=50W)
O speed of laser beam v = 20 mm/s
O pulse repetition frequency f = 15 kHz.
O The texture consisting of parallel grooves as well as a criss-cross of
perpendicular grooves with spacing of 90 µm was produced.
O A wet etching treatment after laser texturisation was performed in
20% KOH at 80 ◦C for 10 and 20 min to remove laser damaged layer
(ablation slag).
O The topography of laser-textured surfaces was investigated using
scanning electron microscopes.
O The reflectance of produced textures was measured by PerkinElmer
Lambda spectrophotometer with an integrating sphere.
O The illuminated I–V parameters were measured under standard AM
1.5 radiation

18. Enhancing Optical Properties
18
SEM images of multi-crystalline silicon surface with texture in the form of criss-cross
grooves: (a) after laser texturisation, (b) after laser texturisation and 10min etching and
(c and d) after laser texturisation and 20min etching
5journal of materials processing technology 2 0 1 ( 2 0 0 8 ) 291–296

19. Enhancing Optical Properties
19
5journal of materials processing technology 2 0 1 ( 2 0 0 8 ) 291–296
Reflection curves for wafers with texture in the form of criss-cross grooves

20. Enhancing Optical Properties
20
O To confirm effectiveness of produced textures, total reflection
curves were measured with spectrophotometer equipped with
an integrating sphere for wavelengths covering the range
300–1300 nm.
O The total reflectance curves for the criss-cross texture shows
that etching process did not influence the increase of
reflectance.
O After etching, regions of increased reflectance may be
observed, but there also exist regions where etching
decreases reflectance.
O It can be seen that laser texturing reduced effective
reflectance even more than four times compared with raw and
un-textured wafers.

21. Surface texturing to improve
tribological characteristics
O There is an increasing need to reduce and
control friction and wear in order to
O extend the lifetime of mechanical systems
O to improve their efficiency and reliability
O to conserve scarce material resources and
energy as well as to improve safety
O Surface texturing is one of the existing
methods of friction reduction.
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22. Applications of LST
O Some examples where the technology of
LST has been utilized to improve the
tribological properties are
O In enhancing the performance of
mechanical seals
O sliding bearings of hydraulic machines
O piston ring of diesel engine, cylinder liner,
and thrust bearings.
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23. Laser Surface Texturing (LST)
O As a means for enhancing tribological performance
of contact components, laser surface texturing
(LST) has been in use for many years.
O It involves creation of an artificially distributed
array of micro-dimples or channels on components
surface by a material removal process with a laser
beam.
O The formation of patterned micro-dimples may
affect hydrodynamic lubrication and load carrying
capacity of the textured surface.
O The dimples are expected to help in reducing
friction and at the same time they may trap wear
particles also which is expected to reduce wear.
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24. Laser Surface Texturing for
piston rings
O Developing more fuel-efficient and compact
automobile engines with reduced environmental
impact is one of the biggest challenges in the era
of global warming.
O The friction loss in an internal combustion engine
is a major factor in determining the fuel economy.
Around 20–30% of the friction losses in a
compression-ignition engine are due to the
piston/cylinder system, of which a large part is
attributed to the piston rings.
O Proper lubrication and surface texture are key
issues in reducing friction in a piston/cylinder
system.
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25. References
1. Patel D, Jain V K, Ramkumar J, Surface texturing for inducing hydrophobicity,
Directions 2015 Vol. 15 No.1 (2015), pp. 46-53
2. Tang M, Shim V, Pan Z Y, Choo Y S, Hong M H, Laser ablation of metal substrate for
super-hydrophobicity, Journal of Laser micro/nanoengineering Vol. 6, No. 1 (2011) pp.
6-9
3. McConnell G, Ferguson A.I., Third harmonic generation of a mode-locked laser in a
resonant enhancement cavity, Post-conference Technical Digest (IEEE Cat.
No.01CH37170) Publication Year: 2001, pp. 453-454
4. Vorobyev A Y, Guo C, Multifunctional surfaces produced by femtosecond laser pulses,
Journal of applied physics 117, 033103 (2015), pp. 033103-1 – 033103-5
5. Dobrzan L A, Drygałaa A, Gołombeka K, Panekb P, Bielanskab E, Ziebab P, Laser
surface treatment of multicrystalline silicon for enhancing optical properties, Journal of
materials processing technology 201 (2008), pp. 291–296
6. Etsion I, Sher E, Improving fuel efficiency with laser surface textured piston rings,
Tribology International 42 (2009), pp. 542–547
7. Dangsheng Xiong, et. al., Tribological properties of PTFE/laser surface textured
stainless steel under starved oil lubrication, Tribology International 82 (2015), pp. 305-
310