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Short Course: NanotribologyHong Liang
Texas A&M [email protected]
Nanotribology Technical CommitteeMay 15, 2016
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Acknowledgements
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• Tribology: dealing with interacting surfaces in relative motion.• Nanotribology: dealing with high energy surfaces.
Wolfgang Ernst Pauli (4/25/1900 – 12/5/1958), Nobel Laureate, (physics, 1945).
God made materials; devil made surfaces.
Nanotribology
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Topics
A. Introduction
B. Characterization
C. In-situ analysis
D. Applications
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Surface Science Laboratory, Texas A&M University
Historic Development
Courtesy by The University of Arizona Mineral Museum
Courtesy by The University of Tartuensis, Keemia Institute
Primitive
10000 B.C.
Theophrastus
300 B.C.
Fire-by-Friction
Agricola
16th Century
Faraday
19th Century
Carey Lea
19th Century
Ostwald
19th~20th Century
HgS + Cu Hg + CuSRubbing
Milling and metallurgical operation
mortar milling
2AgCl + Zn
2Ag + ZnCl2
Decomposition of metal halides during milling
Thermochemistry
Electrochemistry
Photochemsitry
Mechanochemistry
At nanoscale
. friction alters rubbing surfaces
. measurement is affected by contact
A-1
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What are surfaces
Definition of surfaces:
The exterior or upper boundary of an object or body. A plane or curved two-
dimensional locus of points (as the boundary of a three-dimensional region).
Definition of an interface:
A surface forming a common boundary of two bodies, spaces, or phases. The
place at which independent systems meet and act on or communicate with each
other.
Examples: earth, universe
phase boundaries
what’s the difference between surfaces and interfaces
where are surfaces at a critical point
what are we measuring
A-2
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Cam shaft, Bagson
Wear, Novak
Roughing of a stepped
surface
Continued stepped
surface
Ideal vicinal
crystal
Rough is only relative…
A-3
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SPM image of a thin film of
single-atom-high step (100 nm)
TLK model – terrace, ledge, kink
Why a surface is more active than its bulk
A-4
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Touthankamon statue, 1200 -1300 BC
The glass appears green in daylight (reflected light), but red when light is
transmitted from the inside of the vessel. Lycurgus Cup, 4th & 5th BCBritish Museum
Rose Window, Cathedral of Notre Dame. red & purple colors - AuNPs
At the nanometer length scale,
materials different properties
A-5
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1 A, atoms colorless
1 n, gold clusters, nonmetallic, orange
30 n, gold nanoparticles, red
550 n, gold nanoparticles, metallic
bulk gold
Size matters - optical properties
A-6
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Size matters - physical properties
Cortie et al., Matls. Forum, 2002. A-7
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Shape matters…
Huitink & Liang et al., JPCC, 2011.A-8
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Kellar Autumn, Lewis & Clark College
Water strider. MSN.com
Nature lives with surfaces
A-9
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Kellar Autumn, Lewis & Clark College
Tokay Gecko toe
Geim et al., Nature Matls.,
Vol. 2, July 2003, p.461-463.
Gecko biomimetic dry adhesive tape.
Natural surface inspires engineering innovation
A-10
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Topics
A. Introduction
B. Characterization
i. STM
ii. AFM
iii. Nanoindentation
C. In-situ analysis
D. Applications
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B-1
There are many surface characterization techniques
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Scanning Tunneling Microscope
• Gerd Binnig & Heinrich Rohrer, 1982
• Nobel Prize in Physics 1986
• Under vacuum and conductive materials
nobelprize.org
• Vacuum (Binning & Rohrer, 1982)
• Cryogenic temperatures (Elrod et al. 1984)• He
• Air (Park and Quate, 1986)
• Water (Sonnnenfeld and Hansma, 1986)• Any fluid
• Biosamples
B-2
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Components• Three main parts:
• Tunneling assembly
• Control system and power supply
• Display device
wikipedia.org
• Tip approaches sample
• Tunneling current detected
• Piezo scans point-by-point
• Points are collected
• Generate 3D surface
Operation
B-3
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Tunneling Effect
• Quantum-mechanical effect
• Particle jumps the energy barrier
• Probability: R+T=1
• T e-βw
• β is barrier and particle constant
• w is width of barrier
Perella & Plisch, Intro. STM.
• Electrons on tip or sample
• Tip and sample are approached
• Apply voltage to detect tunneling current
• e- flow from lower to higher voltage
• Sample at 0V and tip at –1V
• e- will flow from tip to sample
• Signal is amplified for improved resolution
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Operation Modes
• Constant height• Faster
• Used for smoother surfaces
San Diego State Univ.
• Constant current (I~1nA)• Depends on feedback system
B-5
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Constant Current
• Measure current as it scans
• Adjust tip height
• Plot Δz vs. ΔxΔy
Institut für Experimentelle und Angewandte Physik B-6
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Constant Height
• Tip height unchanged
• Tunneling current changes with height
• Plot ΔI vs. ΔxΔy
uni-duesseldorf.deB-7
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Tip Preparation
Making a tip:• 7 mm (1/4 inch)
• ~300 to 400 μm diameter wire
• Make a 45-degree cut on one end of the tip wire.
• Pull upward to create the sharpest tip possible.
• Electro-chemical etching (optional)• Decreases size
• Increases resistance
• Functionalize• Atom manipulation
Materials• Tungsten
• Platinum – iridium
• Platinum
• Gold
• Nickel
www.fys.kuleuven.ac.be/iks/nvsf/Pictures/STM3.gif B-8
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Image Generation
http://www.almaden.ibm.com/vis/stm/lobby.html
• 2D with color gradient• 3D Images
B-9
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Factors Affecting Resolution
• Vibrations• Noise
• Air
• Interference
• Tip geometry• Diameter
• Tip angle
Marti, Othmar., Matthias Amrein. STM and SFM in Biology. Academic Press. San Diego. 1993.
B-10
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Atom Manipulation
• Atom manipulation• Moving atoms
• Ionizing atoms • STM and TOF
• Laser pulse and voltage variation
• Ionized gold particle• Good for memory storage
http://physicsweb.org/articles/news/8/7/13/1#Repp3B-11
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STM - dislocationB-12
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O on Single Crystal
STM image of oxygen atom lattice on
rhodium single crystal; part of study of
electrocatalysis. 4nm scan courtesy
Purdue University.
Human skin tissue, 2.9mm x3.8mm.
B-13
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Topics
A. Introduction
B. Characterization
i. STM
ii. AFM
iii. Nanoindentation
C. In-situ analysis
D. Applications
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LaserSurface
profile
Probe
Detector
Laser Surface
profile
Probe
Cantilever
Detector
Contact mode: Probe follows the topography of the surface
Non contact mode: Change in vibrational amplitude indicates change in material
Atomic Force Microscope
B-14
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Image Artifacts
Four primary sources of artifacts in images measured w. AFM:
• Probes (Major Artifacts)
• Scanners
• Image Processing
• Vibrations
Pacific Nanotechnology B-16
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Artifacts – tip morphology
B-17
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Artifacts - scanner
probe sample angle
B-18
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Artifacts
However, a line profile of the test pattern shows overshoot at the top of each of the lines.
Overshoot may be observed in the line profile at the leading and trailing edge of the structure
The AFM image of a test pattern appears to have no artifacts
B-19
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Artifacts – imaging processing
http://www.pacificnanotech.com/afm-artifacts_single.html
Fourier Filtering
B-20
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Artifacts - vibration
B-21
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Carbon fibers in epoxy matrix
Contact AFM image of an AL/Cu alloy film
Image examples
B-22
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Force Measurement
B-23
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40
Adhesion Measurement
B-24
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Comparison of Adhesion for Ta & TaOxAdhesion under Different Environment and Condition
0
50
100
150
200
250
300
350
400
Air
0.4 wt KCL
Water
KCL
fd-1
Native Oxide
TaO
x b
y
H2O
2in
air Nati
ve T
aO
x
in a
ir
After Oxidation
After Polishing
Adhesio
n (
nN
)
Hu
itin
k, D
., e
t al
. (2
01
0).
Sca
nn
ing,
32
:3
36
–34
4.
B-25
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0
2
4
6
8
10
12
14
16
18
20
0 50 100 150 200 250 300 350
Time (s)
Ad
hes
ion
(n
N)
0
10
20
30
40
50
60
70
80
Adhesion
Current
Cu
rrent (µ
A)
Adhesion and Surface Condition
Hu
itin
k, D
., e
t al
. (2
01
0).
Sca
nn
ing,
32
:3
36
–34
4.
42 B-26
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Albers et al., Nature Nanotechnology, 2009.
AFM measurement of force and energy
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Lantz et al., Science, 2001.
Measure short-ranged chemical bonding forces
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B-29
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Topics
A. Introduction
B. Characterization
i. STM
ii. AFM
iii. Nanoindentation
C. In-situ analysis
D. Applications
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Nanoindentation
Nanoindentation developed in the 1970’s
B-30
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B-31
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B-32
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Hardness and Reduced Modulus
𝐻 =𝑃𝑚𝑎𝑥𝐴𝑟
Indention head and force-displacement curve
B-33
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Ceramic Matrix Composite
Multi-Phase Materials
Indentation cups in ferrite (alpha-Fe)
(dark) and cementite (light)
Gold Wire.
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Nano-scratch
Ingole et al., J. Trib., 2007. B-35
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Topics
A. Introduction
B. Characterization
C. In-situ analysis
In situ TEM – onset of wear
In-process surface morphology
D. Applications
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in situ TEM
to see the onset of wear
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Materials and Conditions
Substrate: Si (100)
Indenter: diamond (Berkovitch)
Au film: 1 μm
Mohr hardness: Si 7.0, Au 2.5-3
Sliding speed: 14 nm/sec
60
mm
In Situ TEM
C-1
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1600
1400
1200
1000
800
600
400
200
Au Si %wt
0 20 40 60 80 100
Tem
pera
ture
(o
C)
AuSi3
Figure 3, Equilibrium phase diagram of Au-Si. C-2
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In situ TEM analysis
during nanoindentation
Au
Si
200
111222
Si (011)Huitink et al., APL, 2011.
C-3
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After indent
After indent - Au After indent -Si
C-4
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Aft. Ind. 6, BF
C-5
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After Indent
File name: Au-SiaftInd2-diff1.tifThis file shows the same
AuSi3. After the same indent.
AuSi3
Area of X-ray Diffraction
C-6
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In-process observation of surface
morphology in a tribological process
remains to be a challenge
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In Situ Surface Measurement
63
Time: 0-5 min Time: 5-10 min Time: 10-15min
Time: 15-20 min Time: 20-25 min Time: 25-30 min Time: 30-35 min
D. H
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Height image
2.5 um area scan
C-7
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-15 nm
+15 nm
0 nm
Huitink & Liang et al., JES 2010.
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-15 nm
+15 nm
0 nm
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-15 nm
+15 nm
0 nm
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-15 nm
+15 nm
0 nm
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-15 nm
+15 nm
0 nm
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-15 nm
+15 nm
0 nm
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0 – 5 min 5 – 10 min 10 – 15 min
15 – 20 min 20 – 25 min 25 – 30 min
-15 nm
+15 nm
0 nm
Surface Topography Variation: 2V Potential
Hu
itin
k, D
., e
t al
. (2
01
0).
Sca
nn
ing,
32
:3
36
–34
4.
70
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Time: 0-5 min Time: 5-10 min Time: 10-15min
Time: 15-20 min Time: 20-25 min Time: 25-30 min Time: 30-35 min
D. H
uit
ink
et a
l. (2
01
0)
Elec
tro
chem
. So
lid-S
tate
Let
t.,
Vo
lum
e 1
3, I
ssu
e 9
, pp
. F1
6-F
19
.Height image
2.5 um area scan
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-2
-1
0
1
2
3
0 10 20 30 40 50 60
Time (min)
Ra (
+)
an
d S
ke
w (
-) (
nm
)
No Potential 2V Potential 4V Potential
No Potential Skew 2V Potential Skew 4V Potential Skew
Surface Statistics: Ra and Skewness
72
Hu
itin
k, D
., e
t al
. (2
01
0).
Sca
nn
ing,
32
:3
36
–34
4.
C-8
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-15
-10
-5
0
5
10
15
0 0.2 0.4 0.6 0.8 1
Bearing Ratio
Depth
(nm
)11
10
9
8
7
6
5
4
3
2
1
-15
-10
-5
0
5
10
15
0 0.2 0.4 0.6 0.8 1
Bearing Ratio
10
9
8
7
6
5
4
3
2
1
Abbott-Firestone Curves
Time
0
1 hr
Time
0
1 hr
Time
0
1 hr
No Potential 2V 4V
73
Hu
itin
k, D
., e
t al
. (2
01
0).
Sca
nn
ing,
32
:3
36
–34
4.
C-9
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Topics
A. Introduction
B. Characterization
C. In-situ analysis
D. Applications
CMP – intro.
wear dynamics
wear kinetics
Other examples
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Chemical-mechanical Polishing (CMP) – a scalable nanotribochemical process
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SemiSource.
CMP is an important step in IC fab
Little room for error: wafer at exit had traveled 10 miles in 30-45 days, undergone 200-500 processing steps.
Larger wafers, smaller line width, more automation, low cost consumables. D-1
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CMP Technology Development
Chow et al., US Patent, 1987. Kanta et al., IEEE VLSI Intcon. Conf., 1988.
Yeh et al., Vacuum, 1988. Jeffrey et al., US Patent, 1990.
IBM.
Polishing
pad
Wafer holderSlurry
dispenser
Polishing
pad
Wafer holderSlurry
dispenser
D-2
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Common Chemicals in Cu CMP Slurries
Oxidizing agents
Complexing
agents Inhibitors Surfactants
Ferric nitrate Glycine Benzotriazole Triton-X
Nitric acid Citric acid Benzimidizole DTAB
Hydrogen peroxide Ethylenediamine Polytriazole CTAB
Ammonium
persulfate
Ammonium
hydroxide Phenyltriazolthion
Potassium
permanganate
D-3
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An example of a polishing slurry
Particles:
e.g. SiO2, surface area 55 m2/g
aggregated particle size: 80 nm
Typical composition:
abrasives, SiO2, Al2O3, or CeO2
DI water
oxidizer (for metals)
other additives
D-4
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Etch Region Passivation Region
H2O2 Concentration
MR
R (
A/m
in)
Add glycineOr catalyst
AddBTA
Add glycineOr catalyst
Add BTA
The chemistry in a hydrogen peroxide system
D-5
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Polished Fumed SiO2
New Fumed SiO2New Fumed SiO2
Liang et al., J. Elec. Matls., 2005. D-6
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Polishing Mechanisms:
Chemical wear:
Liang et al., J. Elec. Matls., Vol.30, No.4, 2001.Liang et al., J. Elec. Matls., Vol.31, No.8, 2002.
metalinsulator
Passivating film
Kaufman et al., J. Electrochem. Soc., Vol. 138, No.11, 1991.
After polishing
Passivating film:
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CMP is the synergy betw.chemical & mechanical removal
L
e0
k*L/2
H(t)
hm(t
hc,top(t)
hc,valley(t)
ld(t)
B(t)
x0(t)
INIT
IAL P
AR
AM
ET
ER
S
DY
NA
MIC
PA
RA
ME
TE
RS
h0
Estragnat et al., 2006. D-8
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High Roughness Low Roughness
0
500
1000
1500
2000
2500
3000
0 10 20 30 40 50 60 70
Time (mn)
RR
(A
/mn
)
'Calculated RR Experimental RR Trend of experimental RR
Estragnat et al., 2006.
0
200
400
600
800
1000
1200
1400
0 10 20 30 40 50 60 70
Time (mn)
RR
(A
/mn)
Calculated RR Experimental RR Trend of experimental RR
D-9
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Ng and Liang, J. Trib., 2007
Wear in CMP: non-equilibrium & multi-mode
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wear dynamics
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H2O2.
Time (second)
Fri
ctio
n C
oe
ffic
ien
t
0V
+ 2.4 V
off
Time (second)
Fri
ctio
n C
oe
ffic
ien
t
0V
+ 2.4 V
off
H2O.
Time (second)
0 V
+2.4 V +4.4V
Fri
ctio
n C
oe
ffic
ien
t
off
Acidic acid.
Time (sec)
Fric
tio
n C
oef
fici
ent
Ta2O
TaO
2.4 V
friction onlyfriction+potential
Time
Fric
tio
n C
oef
fici
ent
Ta2O
TaO
2.4 V
friction onlyfriction+potential
Kar et al., Electrochimca Acta, 2008; ECS Lett., 2008.
Friction reflects environmental changes
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Friction only
E-potential only
Friction andE-potential
Friction dominates surface chemistry & morphology
Friction and E-potentialE-potential only
Friction only
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Friction + environment => surface chemistry & morphology
D-13
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Ta1+ to 5+Ta2+ to 5+
Kar et al., Electrochimca Acta, 2008; ECS Lett., 2008.
In Ta CMP, friction stirs surfaces
D-14
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-4
-2
0
2
4
0 3 6 9 12 15
pH
E(v
)
Ta2O3, TaO2
Ta2O5
equilibrium state non-equilibrium state
Ta
Ta2O, TaO
In Ta CMP, non-equilibrium phases exist
D-15
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1E-100
1E-50
1
1E+50
1E+100
1E+150
0 2 4 6 8 10 12
Mechanical Energy (eV)
Oxid
ati
on
Rate
Co
nsta
nt
k (
sec-1
)
ΔG╪ = 5 eV
non-spontaneous
spontaneous
RTG
b ehTkk)(
)/(
when -ΔG╪ ≤ε, the mechano-chemistry occursKar, et al., Eelectrochem. Acta, 2008.
when -ΔG╪ >ε, the effect of ε is negligible
Friction promotes non-equilibrium phases in Ta CMP
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Kar et al., Electrochimca Acta, 2008; ECS Lett., 2008.
Work done by mechanical force RTEaekk/)(
0
non-equilibrium process is easier to get by…
D-17
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wear kinetics
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Experimental Condition
• Three-electrode system on a tribometer
• Single frequency EIS with 5Hz
• Ta sample polished by the pad (Politex) on the platen
• Slurry
-- H2O2 (1.5wt%)
-- Alumina (0.2wt%)
-- KCL (2wt%)
-- pH=2.60
Gao et al., JES, 2009. D-18
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D-19
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D-20
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D-21
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Friction-triggered reactions
• Potentiodynamic test
• Potentiostatic EIS test
The friction coefficient is
affected by the applied
potential.
The surface is passivated
after ECMP
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Removal Rate• Single frequency EIS was used.
i CRZ Z is impedance, thickness
R is real part, resistance
C is imaginary part, reciprocal of capacitance
Gao et al., JES, 2009. D-23
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Faraday’ law bridges between corrosion current and corrosion rate.
M Mm++me-
Ta+
Ta2+
Ta3+
Ta4+
Ta5+
AQN
ITWMRR
o
710
MRR—material removal rate, nm/min.I—current, A.T—time, 60s.W—atomic weight.Q—elementary charge, 1.6×10-19.No—Avogadro’s number, 6.023×1023.ρ—density, g/cm.A—area, cm2.
MRR5
1
D-24
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• Faraday’s law shows how many Ta atoms were oxidized.
• Oxidation state is dependent of mechanical force.
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Summary
A. Introduction
B. Characterization
C. In-situ analysis
D. Applications
Polishing
pad
Wafer holderSlurry
dispenser
Polishing
pad
Wafer holderSlurry
dispenser
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Wolfgang Ernst Pauli (4/25/1900 – 12/5/1958), Nobel Laureate, (physics, 1945).
God made materials; devil made surfaces.
Nanotribology – measure, control, and fabricate perfect surfaces.
Conclusion Remarks
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Tetrahedron, cube, octahedron, dodecahedron, icosahedron, sphere
Exercise Problem – use the following tips to measure friction
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What techniques were used
to make these images?
![Page 107: Short Course: Nanotribology - Society of Tribologists and](https://reader034.vdocuments.site/reader034/viewer/2022042421/626088140678831c162bfe1f/html5/thumbnails/107.jpg)
E. coli Füzik et al.
C40 (hex)MoSi2
120A
What techniques were used to make these images?