Coatings

Bressanone Sept. 2006

Coatings

1

Choice of a Suitable Coating Method

• 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

Bressanone Sept. 2006

Coatings

2

1

Comparison Sol-Gel Processing / CVD

Sol-Gel Processing

CVD

• larger variety of precursors

• non-oxidic materials can also be deposited

• many processing options

• no shrinkage during annealing

• preparation of inorganic-organic hybrid materials possible

• epitactic growth and selective deposition possible

• generation of complex micro- and nanostructures (incl. porosity) possible

• better control of film growth

• low thermal stress of the substrat • simple coating techniques

Bressanone Sept. 2006

Coatings

3

Preparation of Lead Zirconate Titanate (PZT) – A Comparison Solid state reaction

Sol-gel processing

PbO + TiO2 + ZrO2

Pb(OAc)2 · 3 H2O + Ti(OPr)4 + Zr(OPr)4 + acetylacetone

750 - 1100 °C several h

PZT Sol

Pb(Zr0.53Ti0.47)O3

Bressanone Sept. 2006

700 °C / 2 min

Coatings

4

2

Sol-Gel Processing Scheme

Gel

Sol Solvent Evaporation

Powders

Supercritical Extraction

Gelation Evaporation

Xerogel Xerogel Film

Aerogel

Dry Heat

Materials costs no big issue Shinkage can be controlled (< ca. 5 μm)

Heat

Dense Ceramic Film

Dense Glass

Bressanone Sept. 2006

Coatings

5

Application of Sol-Gel Coatings Metal Alkoxides Metal Salts + water (ev. catalyst or additives) - alcohol

Precursors Hydrolysis Condensation

Sol Coating

substrate

Wet film Drying, Hardening (thermal or uv)

Coating Bressanone Sept. 2006

Coatings

6

3

Which materials can be coated Glasses Ceramics Metals Polymers

Coating techniques Dipping Spraying Doctor blading Painting Rolling Flow coating …..

Curing methods Thermal Photochemical

Coating materials inorganic (ceramic materials) inorganic-organic hybrid materials nanoparticles

Variation of the film properties Chemical composition Porosity Micro-/Nanostructure (texture)

Bressanone Sept. 2006

Coatings

7

Coating Techniques Spray coating

Spin coating

Application of the coating solution

Bressanone Sept. 2006

Spreading of the film

Coatings

Solvent evaporation

8

4

Coating Techniques Dip coating

Dipping

Coating of Solvent the substrat evaporation

Flow coating

Industrial dip coating plant (up to 1.15 x 1.60 m2) (Prinz Optics GmbH)

Bressanone Sept. 2006

Coatings

9

Tailoring of Sol-Gel Coatings An example for a deliberate tailoring of the materials properties (RO)3Si

(ButO)

O O

3Al

Formation of a dual inorganicorganic network Hardness

(MeO)3SiCH2CH2CH3

Reduction of brittleness

Addition of solvents (alcohol) and lacquer additives

Sol 1) Conventional coating techniques 2) Curing (130°C, 45 min)

Scratch-resistant and corrosion-protecting coating for brass

Bressanone Sept. 2006

Coatings

10

5

Limits of Sol-Gel Coatings

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

Bressanone Sept. 2006

Coatings

11

Protection of sensitive surfaces Scratch- and abrasion-resistant coatings Improvement of wear

Coatings with optical properties Coatings with barrier properties Modification of surface polarity Electroactive layers Sensor layers

Bressanone Sept. 2006

Coatings

12

6

Surface Protection 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%. Scratch-resistant coating: 1. Sol-gel processing of Si(OMe)4, Ti(OEt)4 and (RO)3Si

O

O

2. Spin coating on CR39 lenses 3. Thermal curing at 110°C for several h

polycarbonate disk with scratch-resistant coating

High scratch and abrasion resistance due to the formation of titanium oxo clusters and high degree of organic crosslinking (polymerization of the epoxy groups)

Rupp & Hubrach

Bressanone Sept. 2006

Coatings

13

Surface Protection 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.

Bressanone Sept. 2006

Coatings

14

7

Surface Protection UV curable hard coatings O O Si O

based on

O Si O O

SH +

O O Si O

S

O Si O O

high throughput and short processing times magnifying PMMA lenses with scratchresistant sol-gel coating

Increase of nD (1.49 to 1.52) by addition of 12 mol% methacrylate-substituted Zr(OPr)4

scratch-resistant and easy-to-clean coating for PMMA earmoulds

Bressanone Sept. 2006

Coatings

15

Surface Protection 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

X

O (RO)2MeSi

X

Me

O

O O

S

X

X = Br or H

Me

X

1.56 – 1.60

0 – 20 MPa

1.52

1400 MPa

O

O

Et S

Young’s modulus

O

O (RO)2MeSi

Refractive index

O

O O

Bressanone Sept. 2006

Coatings

16

8

Surface Protection Wear-improving coating

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 and hydrophobicity of coated and uncoated leather

Bressanone Sept. 2006

Coatings

17

Protection of sensitive surfaces Coatings with optical properties Decorative (colored) coatings Photochromic coatings Interference layers Antireflective coatings Reflective coatings Optoelectronic components Photocatalysis

Coatings with barrier properties Modification of surface polarity Electroactive layers Sensor layers

Bressanone Sept. 2006

Coatings

18

9

Coatings with Optical Properties Decorative coatings

O

Si(OMe)4 + Ti(OEt)4 + (EtO)3Si-CH=CH2 + (RO)3Si addition of organic dye UV and/or thermal curing

• • • •

O

wide variety of colours improved mechanical properties of the glass as easy to recycle as uncoloured glass dishwasher-safe

Research Laboratory for Packaging, Japan

Bressanone Sept. 2006

Coatings

19

Coatings with Optical Properties Decorative coatings on glass

Bressanone Sept. 2006

Coatings

20

10

Coatings with Optical Properties

Wavelength-selective absorption films to raise the color purity of luminiscence and improve contrast in high-performance cathode ray glass tubes Et2N

NEt2+

O

Rhodamine B is soluble in water and alcohols ⇒ dye seeps out when film is wiped SO3-

⇒ chemical bonding of the dye to the SiO2 network

O

S O

Bressanone Sept. 2006

Si(OEt)3

N H

Coatings

21

Coatings with Optical Properties Photochromism: fast for optical switches, for eye protection, privacy shields slow for optical data storage, energy conserving coatings, etc... Example: Spirooxazine derivative

hν1

N N

O

Δ or hν2

N N

O

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 the sol-gel matrix → higher chromophore concentrations can be achieved without affecting the mechanical integrity of the sol-gel matrix

Si(OEt)3 HN

O N N

O

O

Photochromic coating on paper

Bressanone Sept. 2006

Coatings

22

11

Antireflexion Layers on Glass

Bildquelle: Fa. Schott AG

Requirements improved transmission high band width low angle dependence colorless residual reflexion high mechanical stability Materials and microstructures gradient layers (index) interference layers (λ/4 single layers) interference multiple layers (SiO2-TiO2) Anwendungen Architectural glass, displays, solar cells, optical components

Bressanone Sept. 2006

Coatings

23

Antireflexion Layers on Glass λ/4 single layer nLuft

= 1,00

multilayers (interference)

effective

Glas

nGlas = 1,52

Band width: Angle dependence: Residual reflections: Mechanical. stability:

effective:

SiO2 TiO2 SiO2

nSchicht= 1,26

Material:

gradient layers

medium medium

dense, alternating refractive index niedrig high

dense, glassy, nanostructured (< λ/4) high low

colored

colored

colorless

low - good

very good

good

porous, glassy

Bressanone Sept. 2006

Coatings

24

12

Coatings with Optical Properties Porous anti-reflection sol-gel coatings on glass 100%

100% 8%

n0, air

n0, air

nfilm, coating

nglass, glass

nglass, glass

n0, air

0%

n0, air 92%

100%

Uncoated glass

Coated glass No reflexions for a given λ, if optical thickness = λ /4 nfilm = √n0·nglass ≈ 1.22

Bressanone Sept. 2006

Coatings

25

Coatings with Optical Properties Antireflective coating: Structuring by deposition of small particles Si(OR)4

(TMOS, TEOS) EtOH, MeOH H2O NH3

Hydrolysis/ Condensation

Thermal toughening (400550°C ⇒ wipe-proof, weatherresistance porous SiO2 layer

Stöber particles

Bressanone Sept. 2006

Nanoporous SiO2 layer

Coatings

MERCK, FLABEG

26

13

Coatings with Optical Properties Interference Filter Alternating SiO2 and TiO2 layers

50 nm

80 nm

Increasing withdrawal speed during dip coating: increasing film thickness (60 nm → 120 nm) change of optical properties color effect filter

Bressanone Sept. 2006

Coatings

27

Coatings with Optical Properties Structuring by embossing (gradient layers) Antireflective coating 1. Polysiloxane chains from

O

Me O

Si O

O

O S

O O

2. Embossing 3. UV curing = fixing the imprinted structure

O

Optoelectronic components

Bressanone Sept. 2006

Coatings

28

14

Coatings with Optical Properties

Reflective coatings

ZrO2 / PVP

.. ..

210 nm SiO2 ZrO2 / PVP 210 nm SiO2 substrate

15 nm ZrO2 particles (from ZrOCl2) in PVP binder (15 wt%); nD 1.70 SiO2 from Si(OEt)4; nD 1.22

20 layers SiO2 / ZrO2

a: theoretical, b:experimental Pohl Institute of Solid State Physics, Shanghai

Bressanone Sept. 2006

Coatings

29

Coatings with Optical Properties Optical Waveguides Hybrid materials from Ph2Si(OH)2 and CH2=C(Me)OC(O)(CH2)3Si(OMe)3 photopatternable core layer (high refractive index)

cladding (lower refractive index)

buffer layer (lower refractive index)

Bressanone Sept. 2006

Coatings

30

15

Coatings with Optical Properties TiO2 photocatalysis

Creation of porosity (high surface area) by embossing or by deposition of particles

UV irradiation (λ< 388 nm) promotes degradation of organic compounds alters the polarity of the surface („photoinduced super-hydrophilicity“)

SEM and AFM micrograph of a porous TiO2 sol-gel thin film

Bressanone Sept. 2006

Coatings

31

Coatings with Optical Properties Anti-fogging

A TiO2-coated surface is rendered more hydrophilic by UV irradiation (right).

Self-cleaning

Bressanone Sept. 2006

Coatings

32

16

Protection of sensitive surfaces Coatings with optical properties Coatings with barrier properties Corrosion protection (water and oxygen barriers) Barrier against diffusion of organic compounds

Modification of surface polarity Electroactive layers Sensor layers

Bressanone Sept. 2006

Coatings

33

Barrier Coatings Corrosion Protection of Aluminum Pigment Uncoated Al pigments

Immediate reaction 2Al + 6H2O 2Al(OH)3 + 3H2 SiO2

Al

Bressanone Sept. 2006

After sol-gel hybrid coating

☺ Neutral water test: 150°; „superhydrphilic“: θ = 0°

Bressanone Sept. 2006

Coatings

46

23

(Super-)Hydrophobic Surfaces While alkyl chains provide hydrophobicity, fluoroalkyl chains also provide oleophobicity

Lotus effect

Examples for fluorinated silanes (RO)3Si (RO)3Si

C6F13 O N H

O

C8F16H

Superhydrophobicity: + nanostructured surface

Bressanone Sept. 2006

Coatings

47

Modification of Surface Polarity Superhydrophobic Coatings Silicone mould

Gel from Si(OMe)4

drop diameter 0.2 mm

G. M. Whitesides et al. , 1998

Bressanone Sept. 2006

Hydrophobization by a monolayer of Cl3SiCH2CH2(CF2)9CF3 contact angle before: 118°, after: 170°) J. Bico et al. , 1999

Coatings

48

24

Modification of Surface Polarity Hydrophobic or Oleophobic Coatings • less adhesion of dust particles • easier to clean • anti-wetting behavior of paints = anti-graffiti coatings glass slide not coated

Easy-to-clean coating black paint

glass slide coated

Anti-grafiti coating

Anti-soiling coating

Antiadhesive coating

Bressanone Sept. 2006

Coatings

49

Protection of sensitive surfaces Coatings with optical properties Coatings with barrier properties Modification of surface polarity Electroactive layers Antistatic coatings Transparent conducting coatings Dielectric layers Piezoelectric layers Electrochromic layers

Sensor layers

Bressanone Sept. 2006

Coatings

50

25

Electroactive Layers Antistatic Coatings Antistatic properties can be obtained by • increasing the proportion of polar groups • incorporating ionic compounds Best results for: Si

+ H2O

O

Si

CH2OH

O

OH

O

Si

+ H2O

O

O O

Si

O

O

Si

Bressanone Sept. 2006

Polar goups

Partially coated polycarbonate tile (ash test)

COOH COOH

Ionic groups

NMe3+

Coatings

51

Electroactive Layers 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

Bressanone Sept. 2006

Transmission (— ) and reflectance spectra (- -) of dip-coated ATO and AZO (layer on both sides) and ITO coatings (layer on one side)

Coatings

52

26

Electroactive Layers Inorganic-organic hybrid materials as dielectric layers in microelectronics Good adhesion to various substrates Patternable by direct laser-writing or laser ablation 5. Pentrium® chip set 4. I.-O. layer with 2nd signal plane 3. I.-O. layer with 1st signal plane 2. I.-O. layer with power plane 1. Ground plane

Test structure by direct laser writing

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

Bressanone Sept. 2006

Coatings

53

Electroactive Layers Piezoelectric Layers Pb(OAc)2 · 3 H2O + Ti(OPr)4 + Zr(OPr)4 + acetylacetone

Film thickness on a metal substrate about 0.8 μm. Piezoelectric charge:

Pb(Zr0.53Ti0.47)O3

sensor

piezoelectric actuator

Bressanone Sept. 2006

Coatings

54

27

Electroactive Layers Electrochromic Devices Applications • "Smart Windows" • Automotive glazing and sunroofs • Active and passive displays

ITO = indium tin oxide FTO = fluorine-doped tin oxide tungsten trioxide inorganic-organic hybrid polymer CeO2/TiO2

Bressanone Sept. 2006

Coatings

55

Protection of sensitive surfaces Coatings with optical properties Coatings with barrier properties Modification of surface polarity Electroactive layers Sensor layers

Bressanone Sept. 2006

Coatings

56

28

Sensors Fiber-optical sensors Ormocer® sensor layer optical fiber

Phase shift [deg]

Sensor fiber in a CFK-composite (photo: DaimlerChrysler AG)

signal of an optical sensors with CO2-sensitive ORMOCER® layer at different humidities hours

Bressanone Sept. 2006

Coatings

57

29