Short Course: NanotribologyHong Liang

Texas A&M Universityhliang@tamu.edu

Nanotribology Technical CommitteeMay 15, 2016

Acknowledgements

• 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

Topics

A. Introduction

B. Characterization

C. In-situ analysis

D. Applications

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

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

Cam shaft, Bagson

Wear, Novak

Roughing of a stepped

surface

Continued stepped

surface

Ideal vicinal

crystal

Rough is only relative…

A-3

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

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

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

Size matters - physical properties

Cortie et al., Matls. Forum, 2002. A-7

Shape matters…

Huitink & Liang et al., JPCC, 2011.A-8

Kellar Autumn, Lewis & Clark College

Water strider. MSN.com

Nature lives with surfaces

A-9

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

Topics

A. Introduction

B. Characterization

i. STM

ii. AFM

iii. Nanoindentation

C. In-situ analysis

D. Applications

B-1

There are many surface characterization techniques

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

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

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

Operation Modes

• Constant height• Faster

• Used for smoother surfaces

San Diego State Univ.

• Constant current (I~1nA)• Depends on feedback system

B-5

Constant Current

• Measure current as it scans

• Adjust tip height

• Plot Δz vs. ΔxΔy

Institut für Experimentelle und Angewandte Physik B-6

Constant Height

• Tip height unchanged

• Tunneling current changes with height

• Plot ΔI vs. ΔxΔy

uni-duesseldorf.deB-7

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

Image Generation

http://www.almaden.ibm.com/vis/stm/lobby.html

• 2D with color gradient• 3D Images

B-9

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

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

STM - dislocationB-12

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

Topics

A. Introduction

B. Characterization

i. STM

ii. AFM

iii. Nanoindentation

C. In-situ analysis

D. Applications

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

Image Artifacts

Four primary sources of artifacts in images measured w. AFM:

• Probes (Major Artifacts)

• Scanners

• Image Processing

• Vibrations

Pacific Nanotechnology B-16

Artifacts – tip morphology

B-17

Artifacts - scanner

probe sample angle

B-18

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

Artifacts – imaging processing

http://www.pacificnanotech.com/afm-artifacts_single.html

Fourier Filtering

B-20

Artifacts - vibration

B-21

Carbon fibers in epoxy matrix

Contact AFM image of an AL/Cu alloy film

Image examples

B-22

Force Measurement

B-23

40

Adhesion Measurement

B-24

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

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

Albers et al., Nature Nanotechnology, 2009.

AFM measurement of force and energy

Lantz et al., Science, 2001.

Measure short-ranged chemical bonding forces

B-29

Topics

A. Introduction

B. Characterization

i. STM

ii. AFM

iii. Nanoindentation

C. In-situ analysis

D. Applications

Nanoindentation

Nanoindentation developed in the 1970’s

B-30

B-31

B-32

Hardness and Reduced Modulus

𝐻 =𝑃𝑚𝑎𝑥𝐴𝑟

Indention head and force-displacement curve

B-33

Ceramic Matrix Composite

Multi-Phase Materials

Indentation cups in ferrite (alpha-Fe)

(dark) and cementite (light)

Gold Wire.

Nano-scratch

Ingole et al., J. Trib., 2007. B-35

Topics

A. Introduction

B. Characterization

C. In-situ analysis

In situ TEM – onset of wear

In-process surface morphology

D. Applications

in situ TEM

to see the onset of wear

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

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

In situ TEM analysis

during nanoindentation

Au

Si

200

111222

Si (011)Huitink et al., APL, 2011.

C-3

After indent

After indent - Au After indent -Si

C-4

Aft. Ind. 6, BF

C-5

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

In-process observation of surface

morphology in a tribological process

remains to be a challenge

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

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

C-7

-15 nm

+15 nm

0 nm

Huitink & Liang et al., JES 2010.

-15 nm

+15 nm

0 nm

-15 nm

+15 nm

0 nm

-15 nm

+15 nm

0 nm

-15 nm

+15 nm

0 nm

-15 nm

+15 nm

0 nm

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

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

-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

-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

Topics

A. Introduction

B. Characterization

C. In-situ analysis

D. Applications

CMP – intro.

wear dynamics

wear kinetics

Other examples

Chemical-mechanical Polishing (CMP) – a scalable nanotribochemical process

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

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

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

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

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

Polished Fumed SiO2

New Fumed SiO2New Fumed SiO2

Liang et al., J. Elec. Matls., 2005. D-6

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:

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

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

Ng and Liang, J. Trib., 2007

Wear in CMP: non-equilibrium & multi-mode

wear dynamics

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

Friction only

E-potential only

Friction andE-potential

Friction dominates surface chemistry & morphology

Friction and E-potentialE-potential only

Friction only

Friction + environment => surface chemistry & morphology

D-13

Ta1+ to 5+Ta2+ to 5+

Kar et al., Electrochimca Acta, 2008; ECS Lett., 2008.

In Ta CMP, friction stirs surfaces

D-14

-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

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

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

wear kinetics

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

D-19

D-20

D-21

Friction-triggered reactions

• Potentiodynamic test

• Potentiostatic EIS test

The friction coefficient is

affected by the applied

potential.

The surface is passivated

after ECMP

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

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

• Faraday’s law shows how many Ta atoms were oxidized.

• Oxidation state is dependent of mechanical force.

Summary

A. Introduction

B. Characterization

C. In-situ analysis

D. Applications

Polishing

pad

Wafer holderSlurry

dispenser

Polishing

pad

Wafer holderSlurry

dispenser

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

Tetrahedron, cube, octahedron, dodecahedron, icosahedron, sphere

Exercise Problem – use the following tips to measure friction

What techniques were used

to make these images?

E. coli Füzik et al.

C40 (hex)MoSi2

120A

What techniques were used to make these images?