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Bressanone Sept. 2006 Coatings 1
Coatings
Bressanone Sept. 2006 Coatings 2
• Requirements to the coating material (chemical composition, purity, crystallinity, materials properties)
• Thermal stability of the substrate material• Adhesion of the coating under certain conditions
(temperature, humidity, sunlight, etc.)• Throughput• Costs for investments, running costs• Environmental aspects
Choice of a Suitable Coating Method
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Bressanone Sept. 2006 Coatings 3
• non-oxidic materials can also be deposited
• larger variety of precursors
• simple coating techniques
• low thermal stress of the substrat
• better control of film growth• generation of complex micro- and nanostructures (incl. porosity) possible
• epitactic growth and selective deposition possible
• preparation of inorganic-organic hybrid materials possible
• no shrinkage during annealing• many processing options
CVDSol-Gel Processing
Comparison Sol-Gel Processing / CVD
Bressanone Sept. 2006 Coatings 4
Solid state reaction Sol-gel processing
PbO + TiO2 + ZrO2 Pb(OAc)2 · 3 H2O + Ti(OPr)4 +
Zr(OPr)4 + acetylacetone
PZT Sol
Pb(Zr0.53Ti0.47)O3
750 - 1100 °Cseveral h
700 °C / 2 min
Preparation of Lead Zirconate Titanate (PZT) – A Comparison
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Bressanone Sept. 2006 Coatings 5
Xerogel Film
Powders
Dense Ceramic Film
Heat
Sol
GelationEvaporation
Gel
SolventEvaporation
Supercritical Extraction
Xerogel Aerogel
Dense Glass
Dry Heat
Materials costs no big issueShinkage can be controlled (< ca. 5 μm)
Sol-Gel Processing Scheme
Bressanone Sept. 2006 Coatings 6
Precursors Metal AlkoxidesMetal Salts
Sol
Wet film
+ water (ev. catalyst or additives)- alcohol
HydrolysisCondensation
Coating
substrateCoating
Drying,Hardening (thermal or uv)
Application of Sol-Gel Coatings
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Coating materials
inorganic (ceramic materials)inorganic-organic hybrid materialsnanoparticles
Variation of the film properties
Chemical compositionPorosityMicro-/Nanostructure (texture)
Coating techniques
DippingSprayingDoctor bladingPaintingRollingFlow coating…..
Curing methods
ThermalPhotochemical
Which materialscan be coated
GlassesCeramicsMetalsPolymers
Bressanone Sept. 2006 Coatings 8
Application of thecoating solution
Spreading of the film Solvent evaporation
Spray coating
Spin coating
Coating Techniques
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Bressanone Sept. 2006 Coatings 9
Industrial dip coating plant(up to 1.15 x 1.60 m2)(Prinz Optics GmbH)
Dip coating
Flow coating
Dipping Coating of Solventthe substrat evaporation
Coating Techniques
Bressanone Sept. 2006 Coatings 10
O(RO)3SiO
Formation of a dual inorganic-organic network
(ButO)3Al Hardness
Reduction of brittleness(MeO)3SiCH2CH2CH3
Sol
Addition of solvents (alcohol) and lacquer additives
Scratch-resistant and corrosion-protecting coating for brass
1) Conventional coating techniques2) Curing (130°C, 45 min)
An example for a deliberate tailoring of the materials properties
Tailoring of Sol-Gel Coatings
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Bressanone Sept. 2006 Coatings 11
Crackability• stresses develop during drying due to shrinkage• thermal expansion mismatches• plastic deformation of substrate
Thickness limits(Thick films required for thermal barriers, and abrasion and wear protection)
Reasons:Cracks develop during drying more likely in thicker films
Possible solutions:• multilayer deposition• use of fillers to reduce shrinkage
Limits of Sol-Gel Coatings
Bressanone Sept. 2006 Coatings 12
Protection of sensitive surfacesScratch- and abrasion-resistant coatingsImprovement of wear
Coatings with optical propertiesCoatings with barrier propertiesModification of surface polarityElectroactive layersSensor layers
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Bressanone Sept. 2006 Coatings 13
polycarbonate disk with scratch-resistant coating
Scratch-resistant coatings for polycarbonate lenses
Most successful material for optical lenses: CR39® (PPG Industries). nD 1.498, Abbé number 59, density 1.31 g/cm3, luminous transmittance 91%.
Rupp & Hubrach
High scratch and abrasion resistance due to the formation of titanium oxo clusters and high degree of organic crosslinking (polymerization of the epoxy groups)
Scratch-resistant coating:1. Sol-gel processing of Si(OMe)4, Ti(OEt)4 and
2. Spin coating on CR39 lenses3. Thermal curing at 110°C for several h
O(RO)3SiO
Surface Protection
Bressanone Sept. 2006 Coatings 14
Subsequent improvements of scratch resistant coatings on polycarbonate
by replacement of Ti(OEt)4 for Zr(OR)4 or Al(OR)3, or by addition of boehmite (AlOOH) nanoparticles
Increase of haze during abrasive treatment (Tumble test): × noncoated CR39, + titanium containing coating, □ coating containing AlOOH nanoparticles.
Surface Protection
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Bressanone Sept. 2006 Coatings 15
scratch-resistant and easy-to-clean coating for PMMA earmoulds
UV curable hard coatings
based on SHSiO
OO Si
O
OO+ SSi
O
OO
SiO
OO
magnifying PMMA lenses with scratch-resistant sol-gel coating
high throughput and short processing times
Increase of nD (1.49 to 1.52) by addition of 12 mol% methacrylate-substituted Zr(OPr)4
Surface Protection
Bressanone Sept. 2006 Coatings 16
Optical fibers coatings for protection against scratching
Tailoring the organic spacer between the inorganic species allows tailoring both the refractive index and Young’s modulus in a wide range
Me
MeO
X
X
X
X
O
OO
O
S(RO)2MeSi
X = Br or H
O
O
S(RO)2MeSiEt
O
O
O
O
Refractive Young’s index modulus
1.56 – 1.60 0 – 20 MPa
1.52 1400 MPa
Surface Protection
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Bressanone Sept. 2006 Coatings 17
wear and hydrophobicity of coated and uncoated leather
Thin (≤ 4 μm) inorganic-organic hybrid coating:
• natural, optical and haptic properties are preserved• high hydrophobicity• high water vapour permeability and water vapor up-take• very good scratch resistancy and improved wear properties• good temperature- and light-proof
Wear-improving coating
Surface Protection
Bressanone Sept. 2006 Coatings 18
Protection of sensitive surfacesCoatings with optical properties
Decorative (colored) coatingsPhotochromic coatingsInterference layersAntireflective coatingsReflective coatingsOptoelectronic componentsPhotocatalysis
Coatings with barrier propertiesModification of surface polarityElectroactive layersSensor layers
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• wide variety of colours• improved mechanical properties of the
glass• as easy to recycle as uncoloured glass• dishwasher-safe
Si(OMe)4 + Ti(OEt)4 + (EtO)3Si-CH=CH2 +addition of organic dyeUV and/or thermal curing
O(RO)3Si
ODecorative coatings
Research Laboratory for Packaging, Japan
Coatings with Optical Properties
Bressanone Sept. 2006 Coatings 20
Decorative coatings on glass
Coatings with Optical Properties
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Bressanone Sept. 2006 Coatings 21
O NEt2+Et2N
SO3-
SO
ONH
Si(OEt)3
Wavelength-selective absorption films
to raise the color purity of luminiscence and improve contrast in high-performance cathode ray glass tubes
Rhodamine B is soluble in water and alcohols⇒ dye seeps out when film is wiped
⇒ chemical bonding of the dye to the SiO2 network
Coatings with Optical Properties
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Photochromism: fast for optical switches, for eye protection, privacy shieldsslow for optical data storage, energy conserving coatings, etc...
Example: Spirooxazine derivative
Embedding in sol-gel coatings:For sufficient photochromism: dye concentration > 25 wt% → mechanical stability of sol-gel film is deteriorated.
Grafting of the dye to thesol-gel matrix → higher chromophoreconcentrations can be achievedwithout affecting the mechanical integrityof the sol-gel matrix
O
N
N
O
O
HN
Si(OEt)3
O
N
N O
N
N
hν1
Δ or hν2
Photochromic coating on paper
Coatings with Optical Properties
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Bressanone Sept. 2006 Coatings 23
Requirementsimproved transmissionhigh band widthlow angle dependence
colorless residual reflexionhigh mechanical stability
Materials and microstructuresgradient layers (index)interference layers (λ/4 single layers)interference multiple layers (SiO2-TiO2)
AnwendungenArchitectural glass, displays, solar cells, optical components
Bildquelle:Fa. Schott AG
Antireflexion Layers on Glass
Bressanone Sept. 2006 Coatings 24
Material:
Band width:Angle
dependence:Residual
reflections:Mechanical.
stability:
porous, glassy
mediummedium
colored
low - good
dense, alternating refractive index
niedrighigh
colored
very good
dense, glassy, nano-structured (< λ/4)
highlow
colorless
good
λ/4 single layer
effectivenLuft = 1,00
nSchicht= 1,26
nGlas = 1,52
multilayers(interference)
Glas
SiOTiOSiO
2
2
2
gradient layerseffective:
Antireflexion Layers on Glass
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Bressanone Sept. 2006 Coatings 25
Porous anti-reflection sol-gel coatings on glass
92%
100%
8%
nglass, glass
n0, air
n0, air
Uncoated glass
nglass, glass
nfilm, coating
n0, air
n0, air
100%
100% 0%
Coated glass
No reflexions for a given λ, if optical thickness = λ /4nfilm = √n0·nglass ≈ 1.22
Coatings with Optical Properties
Bressanone Sept. 2006 Coatings 26
Hydrolysis/Condensation
Si(OR)4(TMOS, TEOS)
EtOH, MeOHH2ONH3
Nanoporous SiO2 layerMERCK, FLABEGStöber particles
Thermal toughening (400-550°C ⇒ wipe-proof, weather-resistance porous SiO2 layer
Antireflective coating: Structuring by deposition of small particles
Coatings with Optical Properties
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Bressanone Sept. 2006 Coatings 27
Interference Filter
Alternating SiO2 and TiO2 layers
Increasing withdrawal speed during dip coating:increasing film thickness (60 nm → 120 nm)change of optical propertiescolor effect filter
Coatings with Optical Properties
50 nm 80 nm
Bressanone Sept. 2006 Coatings 28
OO
OO
OSSi
OMe
OO
Structuring by embossing (gradient layers)
Antireflective coating1. Polysiloxane chains from
2. Embossing3. UV curing = fixing the imprinted structure
Coatings with Optical Properties
Optoelectronic components
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Bressanone Sept. 2006 Coatings 29
Reflective coatings
SiO2 from Si(OEt)4; nD 1.22
substrate
210 nm SiO2
ZrO2 / PVP210 nm SiO2
ZrO2 / PVP....
15 nm ZrO2 particles (from ZrOCl2) in PVP binder (15 wt%); nD 1.70
20 layers SiO2 / ZrO2a: theoretical, b:experimental
Pohl Institute of Solid State Physics, Shanghai
Coatings with Optical Properties
Bressanone Sept. 2006 Coatings 30
buffer layer(lower refractive index)
photopatternable core layer(high refractive index) cladding
(lower refractive index)
Optical WaveguidesHybrid materials from Ph2Si(OH)2 and CH2=C(Me)OC(O)(CH2)3Si(OMe)3
Coatings with Optical Properties
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Bressanone Sept. 2006 Coatings 31
Coatings with Optical Properties
TiO2 photocatalysis
UV irradiation (λ< 388 nm)promotes degradation of organic compounds alters the polarity of the surface („photoinduced super-hydrophilicity“)
Creation of porosity (high surface area) by embossing or by deposition of particles
SEM and AFM micrograph of a porous TiO2 sol-gel thin film
Bressanone Sept. 2006 Coatings 32
Coatings with Optical Properties
A TiO2-coated surface is rendered more hydrophilic by UV irradiation (right).
Anti-fogging
Self-cleaning
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Bressanone Sept. 2006 Coatings 33
Protection of sensitive surfacesCoatings with optical propertiesCoatings with barrier properties
Corrosion protection (water and oxygen barriers)Barrier against diffusion of organic compounds
Modification of surface polarityElectroactive layersSensor layers
Bressanone Sept. 2006 Coatings 34
Uncoated Al pigments After sol-gel hybrid coating
Immediate reaction2Al + 6H2O 2Al(OH)3 + 3H2
☺ Neutral water test: <1ml H2 from 3gAl in 3 days
☺ Boiling test (time to react 50% of the Al in boiling water): 13h Not stable at pH 9
Al
SiO2
RSiO3/2
Corrosion Protection of Aluminum Pigment
Barrier Coatings
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Bressanone Sept. 2006 Coatings 35
Coatings on Metals
Corrosion protectionAbrasion resistanceAdhesion promotion for paints
Barrier Coatings
Bressanone Sept. 2006 Coatings 36
Replacement of conversion coatings (especially chromating)
AIMg1 alloy
Top: wet coating system (poxyprimer and polyurethane top layer) after 1000 h ESS test.
Bottom: sol-gel inorganic-organic hybrid coating
CEA
Corrosion protection for aluminum sheets
Barrier Coatings
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Bressanone Sept. 2006 Coatings 37
Corrosion protection of silver reflector in laser cavities• Protection against oxidation to preserve the high reflectivity • Protection against mechanical and chemical attack during handling, cleaning or weathering
10-50 nm dense, hydrophobic or hydrophilic films from Si(OEt)4 / RSi(OR)3 at pH 2. nD 1.445-1.449
CEA / Le Ripault
Specular reflectance variation with oxidative medium timeexposure
Barrier Coatings
Bressanone Sept. 2006 Coatings 38
1. One or two silanes with epoxy and methacrylate groups → adhesion to polymeric substrates, curing at low temperatures or by UV.
2. Tri- or tetraethoxysilane for high inorganic crosslinking → reduction of water vapor permeation, adhesion to metallic substrates.
3. Diorganosilane (e.g. Ph2Si(OH)2) → modification of Young’s modulus, improvement of dielectric properties, influence on hydrophobicity and solubility of water in the material.
days
rela
tive
capa
city
(%)
(I) uncoated, (iI) encapsulated, (IiI) ORMOCER-coated thin-film capacitor(95 °C/100 % rel. humidity)
Passivation layers in electronic devices
Barrier Coatings
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Bressanone Sept. 2006 Coatings 39
food packaging foilspackaging of technical products
encapsulation of solar cells
flexible LCDs
100100
10-1 10-1
10-6
10-2
10-6
10-2
State-of-the art with ORMOCER® coatings
High- and ultra-barrier coatings
Requirements
oxygenpermeability[cm3/m2dbar]
water vaporpermeability
[g/m2d]
barrier properties
flexibleOLEDs
organicsolar cells
Barrier Coatings
Bressanone Sept. 2006 Coatings 40
3
3
7
1(MeO)3Si(CH2)3NMe3+ Cl-
1211N(CH2CH2OH)3
1CH2=C(Me)COOH
121Al(OsBu)3
11Zr(OPr)4
23444
Type 3Type 2
a b cType 1
a b
O(RO)3Si
O
Barrier layers on plastics
Barrier Coatings
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Bressanone Sept. 2006 Coatings 41
PET
hybrid polymer
PET / SiOx / hybrid polymer / PET
I
Barrier layers on plasticsBarrier properties of the barrier systems produced by roll-to-roll processes (OR: ORMOCER®, OTR = Oxygen Transmission Rate, WTR = Water Vapor Transmission Rate)
10 µm
PETPEThybrid polymer
II
SiOx
Barrier Coatings
Bressanone Sept. 2006 Coatings 42
Hybrid polymer on SiOx-coated foils for food packaging
Oxygen permeability
reg. cellulose (30 µm) BOPP (30 µm) PET (30 µm)
Foil + SiOx(PVD) (30 nm)
Foil + SiOx(PVD) + hybrid polymer (5 µm)
1.78
1600
25
110
1.01
< 0.
05
< 0.
05
< 0.
05
0.11
[cm³/m²⋅d⋅bar]
regeneratedcellulose
BOPP PET
140.
510.
16
611
25 0.81
[g/m²⋅d]
regeneratedcellulose PE
T
Water vapor permeability
Barrier Coatings
22
Bressanone Sept. 2006 Coatings 43
Aroma barrierproperties
43 47
83
230
0.3 120
BOPP 30 µm,uncoated
[µg/m²⋅d]
BOPP 30 µm +coating (9 µm)
O
Diphenyloxid
H3C O CH3
O CH3 CH3CH2
OHH3C
CH3
OH
H3C CH3
CH3
H3C CH2
Linalylacetat
cis-3-Hexenol
Menthol (+)-Limonen
Hybrid polymer on SiOx-coated foils for food packaging
Barrier Coatings
Bressanone Sept. 2006 Coatings 44
Flexible polymer barrier films for the encapsulation of solar cells
Encapsulation system for solar modules: a) the front side, b) the rear side of the solar cell
Barrier Coatings
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Bressanone Sept. 2006 Coatings 45
Protection of sensitive surfacesCoatings with optical propertiesCoatings with barrier propertiesModification of surface polarity
Antigrafiti / antisoiling coatingsHydrophilic / hydrophobic coatings
Electroactive layersSensor layers
Bressanone Sept. 2006 Coatings 46
hydrophilic
hydrophobic
Wetting of inorganic-organichybrid coatings of varyingpolarity by water droplets
Modification of Surface Polarity
“superhydrophobic”: θ > 150°; „superhydrphilic“: θ = 0°
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Bressanone Sept. 2006 Coatings 47
(RO)3Si NH
O
O
C8F16H
C6F13(RO)3Si
While alkyl chains provide hydrophobicity, fluoroalkyl chains also provide oleophobicity
Examples for fluorinated silanes
(Super-)Hydrophobic Surfaces
Superhydrophobicity: + nanostructured surface
Lotus effect
Bressanone Sept. 2006 Coatings 48
Superhydrophobic Coatings
drop diameter 0.2 mm
Gel from Si(OMe)4
Silicone mould
G. M. Whitesides et al. , 1998
Hydrophobization by a monolayer of Cl3SiCH2CH2(CF2)9CF3contact angle before: 118°, after: 170°)
J. Bico et al. , 1999
Modification of Surface Polarity
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Bressanone Sept. 2006 Coatings 49
Hydrophobic or Oleophobic Coatings
• less adhesion of dust particles• easier to clean• anti-wetting behavior of paints = anti-graffiti coatings
Easy-to-clean coating
Anti-grafiti coating Anti-soiling coating
Antiadhesive coating
Modification of Surface Polarity
black paint
glass slidenot coated
glass slidecoated
Bressanone Sept. 2006 Coatings 50
Protection of sensitive surfacesCoatings with optical propertiesCoatings with barrier propertiesModification of surface polarityElectroactive layers
Antistatic coatingsTransparent conducting coatingsDielectric layersPiezoelectric layersElectrochromic layers
Sensor layers
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Bressanone Sept. 2006 Coatings 51
Best results for:
Polar goups
Ionic groups
Partially coated polycarbonate tile (ash test)
Antistatic properties can be obtained by• increasing the proportion of polar groups• incorporating ionic compounds
Antistatic Coatings
OSiO
OSiCH2OH
OH
+ H2O
OSi OSiCOOH
+ H2O
OOO
COOH
NMe3+Si
Electroactive Layers
Bressanone Sept. 2006 Coatings 52
Transparent conducting coatings on glass
Sheet resistance vs. sintering temperature of dip-coated SnO2:Sb (ATO, 10 layers), In2O3(ITO, 2 layers) and ZnO:Al (AZO, 10 layers) on silica glass → adjustable sheet resistance
Transmission (— ) and reflectance spectra (- -) of dip-coated ATO and AZO (layer on both sides) and ITO coatings (layer on one side)
Electroactive Layers
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Bressanone Sept. 2006 Coatings 53
Inorganic-organic hybrid materials as dielectric layers in microelectronics
Good adhesion to various substratesPatternable by direct laser-writing or laser ablation
Test structure by direct laser writing
5. Pentrium® chip set4. I.-O. layer with 2nd
signal plane3. I.-O. layer with 1st signal
plane2. I.-O. layer with power
plane1. Ground plane
Manufacturing stages (bottom to top) for one of the smallest Pentium® Multichip Moduls (MCM-L/D, 40 x 40 x 1.2 mm) by multilayers of inorganic-organic hybrid materials
Electroactive Layers
Bressanone Sept. 2006 Coatings 54
Piezoelectric Layers
Pb(OAc)2 · 3 H2O + Ti(OPr)4 + Zr(OPr)4 + acetylacetone
Pb(Zr0.53Ti0.47)O3
Film thickness on a metal substrate about 0.8 μm. Piezoelectric charge:
piezoelectricsensor actuator
Electroactive Layers
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Bressanone Sept. 2006 Coatings 55
Electrochromic Devices
Applications • "Smart Windows" • Automotive glazing and sunroofs • Active and passive displays
ITO = indium tin oxideFTO = fluorine-doped tin oxide
tungsten trioxide
inorganic-organic hybrid polymer
CeO2/TiO2
Electroactive Layers
Bressanone Sept. 2006 Coatings 56
Protection of sensitive surfacesCoatings with optical propertiesCoatings with barrier propertiesModification of surface polarityElectroactive layersSensor layers
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Bressanone Sept. 2006 Coatings 57
Fiber-optical sensors
Sensor fiber in a CFK-composite (photo: DaimlerChrysler AG)
signal of an optical sensors with CO2-sensitive ORMOCER® layer at different humidities
Ormocer®sensor layer
optical fiber
hours
Phase shift [deg]
Sensors