d s a - tu wien...by scanning force microscopy the following mechanical (surface) properties can be...
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Repetition: Thickness Measurement
Amd
S
d = ThicknessS = DensityA = Substrate surface
Attention:The coating density, S , is in most cases different from the bulk density, D .
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Optical Methods: Photometer
Operation:ReflexionTransmission
1 Modulated light source2 Detector f. reflected light3 Detector f. transmitted light4 Controller5 Substrate holder6 Beam deflection
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Photometer: Transmission of Metals
T ... Transmission degreed ... Coating thickness
= 550 nm
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Photometer: ReflexionPrinziple:Two beaminterference
Example:Multiple coatingOptical thickness:
alReOptical dndn
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Interferometer: Multi-Beam Interference
cosd2sinF1
1II2
0t
Transmitted Intensity It
2)R1(R4F
Fineness FI , A0 0
A0r
A0t
d
A1t
A1r
R...Reflectivity
d
It
F small
F large
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Tolansky-Interferometer: Interference Wedge
d(x)
x
d(x)
d(x)
x
d(x)
N
2ND
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FECO: White Light InterferometryFringes of Equal Chromatic Order
t=const (no interference wedge)
= variable (white light)
Principle: Interferograms:
d = 0t = 2 µm
d = 100 nmt = 2 µm
d = 0t = 1 µm
d = 100 nmt = 2 µm
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Other Optical Methods
Nomarski-Interferometry+ Uses polarization and birefringence+ Can easily be integrated into optical microscope
VAMFO (Variable Angle Monochromatic Fringe Observation)+ Variation of light impingement angle+ Simultaneous determination of n and d+ In Situ-method
Ellipsometry+ Variation of light impingement angle+ Simultaneous determination of n and d+ Determination of roughness+ In Situ-method
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Friction and Wear
Friction:No removal of material
Wear:Removal of material associated with weight loss
F =mgg Fg
FgFgF=μr
Fg
nr FF No dependence on the
extension of theinteracting surfaces!
=>microscopic interaction unclear!µ = Friction coefficient
0 < µ < 4 - 5(!); µ is not confined to values smaller 1
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Friction and Wear: Measurement
Wear:+ All above methods with analysis of transfer
films and abraded coatings+ Abrasion measurement by thickness control+ Slurry-abrasion+ Special test rigs
Friction:+ Linear load (scratch-test)+ Pin on disc+ Disc on disc+ Special tribometers
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Micro Hardness
Defined by the residual deformation of a material due to the penetration of an (ideally) undeformable test body.
Test body material:+ Diamond
Test body geometries:+ Vickers: Pyramid with diagonal vs. height 1:7+ Knoop: three sided pyramid+ Rockwell: sphere+ Wedge
Test loads: + 10-5 – 2 N
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Micro Hardness: Test GeometryUltra micro hardness-tester, Vickers geometry:
a) Strain gageb) Samplec) Double springd) Coile) Clutchf) Base plate
Test body
This type of hardness tester can easily be implemented into an optical or a scanning electron microscope.
Micro hardness impressions
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NanoindenterThe Nanoindenter also allows the determination of the elastic (reversible) deformation (i. e. of the elastic modulus) of the sample.
In the case of coatings care has to be taken that the indentation depth of the test body is less than 1/3 of the film thickness.
Only under this condition the influence of the substrate can be neglected.
Penetration depthResidual deformation
load
Elasti
c m
odul
us
unload
Forc
e
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Non-Destructive Hardness MeasurementHertzian contact:
w(r) corresponds to the indentation depth of the test body.G and
result from
the elastic constants of the sample:
r
z
0 w(r)
w(r)=f(F,G, )F
Point force acting ontoan ideally elastic half-plain:
G...Shear modulus...Poisson ratio
G c 44
cc c
12
44 122( )
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Determination of Elastic Constants
Elastic constants can be determined by the measurement of the sound velocity of longitudinal und transversal vibrational modes wthin a solid body.
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Surface Acoustic WavesExciatation of longitudinal and transversal surface modes by a defined laser pulse:
From the runtime of the wave package the sound velocity can be determined. From this the elastic constants can be deduced.The excitation of surface waves allows the application of this principle to thin films.
Laser pulseat time t0
Surface wavepackage
Piezoelectr.transducer
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Hardness: Important Influences
The follwing material parameters may influence hardness:
+ Sress state+ Temperature+ Grain size+ Impurities+ Degree of deformation
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Mechanical Properties: Spatial Resolution
By Scanning Force Microscopy the following mechanical (surface) properties can be determined spatially resolved on the nanometer scale:
+ Elastic modulus+ Hardness + Adhesion strength
This is possible by the so-called force spectroscopy
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Force-Distance curves:
a/b: Approach
b/c: “Snap-on”
c/d: Repulsive region
d/f: Pull-back
e: Zero transient
f/g: Detatchment of tip
g/h: Force free pull-back
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Pulsed Force Mode
free cantileveroscillation
Repated recording of force/distance curves during an AFM-scan with electronic analysis:
Topography
Adhesion
Stiffness
Polymer chains:Force-distance curve:
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ArtifactsImportant artifact of force spectroscopy: Formation of a water meniscus between tip and surface under regular envronmental conditions.
Preventive measures:+ Work under dry nitrogen+ Work in liquids+ Work under inert gas+ Work under HV
The meniscus primarily modifies the values for the adhesion of the tip to the surface due to the high surface tension of water.
AFM-tip
Water meniscus
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DuctilityBulk material: breaking strain b [%]
Thin film: 3-point-bending test
0
0ZB l
ll
lZ = Sample length at breaking pointl0 = Length of uncharged sampleB = Breaking strain [%]
dR2d100
B d = Film thickness
R = Radius of curvature for first crack formation
Cracks
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StressesKinds of stress:
Mechanical Stress:
MECH T I
MECHCan be triggered by clamping the substrate and subsequent relaxation
Thermal stress:Triggered by different coefficients of thermal expansion (CTE) of substrate and coating
)TT)((E MBUSST ES ... Elastic modulus coatingS ... CTE, coatingU ... CTE. substrateTB ... Coating temperatureTM ... Temperature of stress measurement
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Stresses and Film Structure
Intrinsic stress:
IIntrinsic stresses are a direct consequence of the coating structure and the deposition conditions.
Tensile stressCompressive stressVariable
Tensile stress
Compressive stress
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Intrinsic Stress: Sputtering
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Stress Measurement: FundamentalsCurved Substrate:
Tensile stress Compressive Stress
a) Substrateb) Coatingc) Reference plate
Total stress
of a thin film:
2s1sFs
2ss
R1
R1
d)1(6dE
ES ... Elastic Modulus substrateS ... Poisson Ratio substratedS ... Substrate thicknessdF ... Film thicknessRS1 , RS2 ... Radius of curvature before/after coating, respectively
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Stress Measurement: Interference Optics
a) Substrateb) Coatingc) Reference plate
(plane glass)d) Beam dividere) Light sourcef) to acquisition optics
DM ... Diameter m-th Newton-fringeDN ... Diameter n-th Newton-fringe
... Wavelength of incident light
RD D
m nsm n
2 2
4( )
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Stress Measurement: Geometric Optics
a) Coated substrateb) Glass plate with reflecting coatingc) Beam dividerd) Displaye) Image uncoated substratef) Image coated substrateg) Incident light
y ... Sample diametery+ ... Image diameter uncoated sampley' ... Image diameter coated sampleD ... Distance sample/display
RyD
y y
2'
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Stress Measurement: Cantilever
Principle:
CoatingSubstrate
Geometry:
l
RS
l
H
H)2tan(
Htana
21
SRlsin
lH2
Htana
l2RS
Neglections and assumptions:a) no lateral displacement of cantileverb) no vertical displacement of cantilever()c) low /H
Compressive stress
Tensile stress
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Stress Measurement: X-RaysPrinciple:
Measurement of the global deformationof the elementary cell by:+ Interstitials+ Vacancies
Advantages:+ Non-destructive+ In Situ possible
Disadvantages:Numerous error sources:+ Lattice defects+ Dislocations+ Impurities+ Impurity phases