Short Course: Nanotribology Hong Liang Texas A&M University Hliang@Tamu.Edu

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Short Course: Nanotribology Hong Liang Texas A&M University [email protected]

Nanotribology Technical Committee May 15, 2016 Acknowledgements Nanotribology

• 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. Topics

A. Introduction B. Characterization C. In-situ analysis D. Applications Historic Development

Fire-by-Friction

Primitive 10000 B.C. Faraday Carey Lea Ostwald 19th Century 19th Century 19th~20th Century

2AgCl + Zn Thermochemistry mortar milling Decomposition of Electrochemistry 2Ag + ZnCl2 metal halides during milling Photochemsitry Mechanochemistry Agricola 16th Century Milling and metallurgical At nanoscale operation . friction alters rubbing surfaces Theophrastus HgS + Cu Rubbing Hg + CuS . measurement is affected by contact 300 B.C.

Surface Science Laboratory, Texas A&M University Courtesy by The University of Arizona Mineral Museum Courtesy by The University of Tartuensis, Keemia Institute 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 Rough is only relative…

Cam shaft, Bagson Continued stepped surface

Wear, Novak

Ideal vicinal Roughing of a stepped crystal surface A-3 Why a surface is more active than its bulk

TLK model – terrace, ledge, kink

SPM image of a thin film of single-atom-high step (100 nm) A-4 At the nanometer length scale, materials different properties

Rose Window, Cathedral of Notre Dame. red & purple colors - AuNPs

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 BC British Museum A-5 Size matters - optical properties

1 A, atoms colorless

1 n, gold clusters, nonmetallic, orange

30 n, gold nanoparticles, red

550 n, gold nanoparticles, metallic

bulk gold

A-6 Size matters - physical properties

Cortie et al., Matls. Forum, 2002. A-7 Shape matters…

Huitink & Liang et al., JPCC, 2011. A-8 Nature lives with surfaces

Water strider. MSN.com

Kellar Autumn, Lewis & Clark College A-9 Natural surface inspires engineering innovation

Tokay Gecko toe

Geim et al., Nature Matls., Vol. 2, July 2003, p.461-463.

Gecko biomimetic dry adhesive tape. Kellar Autumn, Lewis & Clark College A-10 Topics

A. Introduction B. Characterization i. STM ii. AFM iii. Nanoindentation C. In-situ analysis D. Applications There are many surface characterization techniques

B-1 Scanning Tunneling Microscope

• Gerd Binnig & Heinrich Rohrer, 1982 • Nobel Prize in Physics 1986 • Under vacuum and conductive materials

• Vacuum (Binning & Rohrer, 1982) • Cryogenic temperatures (Elrod et al. 1984) • He • Air (Park and Quate, 1986) • Water (Sonnnenfeld and Hansma, 1986) • Any fluid • Biosamples

nobelprize.org B-2 Components • Three main parts: • Tunneling assembly • Control system and power supply • Display device

Operation • Tip approaches sample • Tunneling current detected • Piezo scans point-by-point • Points are collected wikipedia.org • Generate 3D surface

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

• 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 Perella & Plisch, Intro. STM. Operation Modes

• Constant current (I~1nA) • Constant height • Depends on feedback system • Faster • Used for smoother surfaces

San Diego State Univ. 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.de B-7 Tip Preparation Materials Making a tip: • Tungsten • 7 mm (1/4 inch) • Platinum – iridium • ~300 to 400 μm diameter wire • Platinum • Make a 45-degree cut on one end of the tip wire. • Gold • Pull upward to create the sharpest tip possible. • Nickel • Electro-chemical etching (optional) • Decreases size • Increases resistance • Functionalize • Atom manipulation

www.fys.kuleuven.ac.be/iks /nvsf/Pictures/STM3.gif B-8 Image Generation

• 2D with color gradient • 3D Images http://www.almaden.ibm.com/vis/stm/lobby.html 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#Repp3 B-11 STM - dislocation B-12 O on Single Crystal

Human skin tissue, 2.9mm x3.8mm.

STM image of oxygen atom lattice on rhodium single crystal; part of study of electrocatalysis. 4nm scan courtesy Purdue University.

B-13 Topics

A. Introduction B. Characterization i. STM ii. AFM iii. Nanoindentation C. In-situ analysis D. Applications Atomic Force Microscope

Detector Detector

Laser Cantilever Laser Surface Surface profile profile

Probe Probe

Contact mode: Probe follows the Non contact mode: Change in vibrational topography of the surface amplitude indicates change in material

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

The AFM image of a test pattern appears to have no artifacts

Overshoot may be observed in the line profile at the leading and trailing edge of the structure

However, a line profile of the test pattern shows overshoot at the top of each of the lines.

B-19 Artifacts – imaging processing

Fourier Filtering

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

B-20 Artifacts - vibration

B-21 Image examples

Carbon fibers in epoxy matrix

Contact AFM image of an AL/Cu alloy film

B-22 Force Measurement

B-23 Adhesion Measurement

40 B-24 Comparison of Adhesion for Ta & TaOx Adhesion under Different Environment and Condition After Oxidation

400

344. –

350 336

300 x 250 Air After Polishing 0.4 wt KCL

200 Water in air in

KCL Adhesion (nN) Adhesion

150 TaO Native fd-1

by by in air in

x x Native Oxide 2

100 O

Huitink, D., et al. (2010). Scanning, 32: Scanning, (2010). al.et Huitink, D.,

TaO H

0 B-25 Adhesion and Surface Condition

20 80

344. – 16 60 336 14

50 (µA) Current 12 Adhesion 10 40 Current

8 30

Adhesion (nN) 6 20

4 32: Scanning, (2010). al.et Huitink, D.,

10 2

0 0 0 50 100 150 200 250 300 350 42 Time (s) B-26 AFM measurement of force and energy

Albers et al., Nature Nanotechnology, 2009. Measure short-ranged chemical bonding forces

Lantz et al., Science, 2001. 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

푃 퐻 = 푚푎푥 퐴푟

Indention head and force- displacement curve

B-33 Gold Wire.

Multi-Phase Materials Ceramic Matrix Composite Indentation cups in ferrite (alpha-Fe) (dark) and cementite (light) 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 In Situ TEM

60 mm

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

C-1 1600

1400

1200 C) o o 1000

800

Temperature ( Temperature 600 AuSi3 400

200 0 20 40 60 80 100 Au Si %wt

Figure 3, Equilibrium phase diagram of Au-Si. C-2 In situ TEM analysis during nanoindentation

200

111 222

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

Area of X-ray Diffraction

AuSi3

This file shows the same AuSi3. After the same indent. File name: Au-SiaftInd2-diff1.tif C-6

In-process observation of surface morphology in a tribological process remains to be a challenge In Situ Surface Measurement

Time: 0-5 min Time: 5-10 min Time: 10-15min

State Lett., Lett., State

F19. - Height image 2.5 um area scan

Time: 15-20 min Time: 20-25 min Time: 25-30 min Time: 30-35 min

D. Huitink et al. (2010) Electrochem. Solid Electrochem. (2010) al. Huitink et D. F16 pp. 9, Issue 13, Volume

63 C-7 +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

-15 nm Surface Topography Variation: 2V Potential

0 – 5 min 5 – 10 min 10 – 15 min

+15 nm

344.

– 336

15 – 20 min 20 – 25 min 25 – 30 min 0 nm Huitink, D., et al. (2010). Scanning, 32: Scanning, (2010). al.et Huitink, D.,

70 -15 nm

Time: 0-5 min Time: 5-10 min Time: 10-15min

State Lett., Lett., State -

Height image

2.5 um area scan

F19. -

Time: 15-20 min Time: 20-25 min Time: 25-30 min Time: 30-35 min

D. Huitink et al. (2010) Electrochem. Solid Electrochem. (2010) al. Huitink et D. F16 pp. 9, Issue 13, Volume Surface Statistics: Ra and Skewness

344. –

2 336

(+) and Skew (-) (nm) Skew (-) (+) and 0 10 20 30 40 50 60

-1 Huitink, D., et al. (2010). Scanning, 32: Scanning, (2010). al.et Huitink, D.,

-2 Time (min) No Potential 2V Potential 4V Potential 72 No Potential Skew 2V Potential Skew 4V Potential Skew C-8 Abbott-Firestone Curves 15 15 1 hr 1 hr 1 hr 11 10 10 9

9 8 344.

8 7 – 7 10 Time 10 Time 6 Time 6 5 336 5 4 4 3 3 2 2 0 0 1 0 5 1 5

0 0 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1

Depth (nm) Depth

-5 -5 Huitink, D., et al. (2010). Scanning, 32: Scanning, (2010). al.et Huitink, D.,

-10 -10 No Potential 2V 4V

73 C-9 -15 Bearing Ratio -15 Bearing Ratio 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 CMP is an important step in IC fab

SemiSource.

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

Slurry Wafer holder dispenser

Polishing pad IBM.

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. D-2 Common Chemicals in Cu CMP Slurries

Complexing Oxidizing agents agents Inhibitors Surfactants

Ferric nitrate Glycine Benzotriazole Triton-X

Nitric acid Citric acid Benzimidizole DTAB

Hydrogen peroxide Ethylenediamine Polytriazole CTAB

Ammonium Ammonium persulfate hydroxide Phenyltriazolthion Potassium permanganate

D-3 An example of a polishing slurry

Particles: 2 e.g. SiO2, surface area 55 m /g aggregated particle size: 80 nm

Typical composition:

abrasives, SiO2, Al2O3, or CeO2 DI water oxidizer (for metals) other additives

D-4 The chemistry in a hydrogen peroxide system

Etch Region Passivation Region Add glycine Or catalyst Add glycine Or catalyst

Add BTA

MRR MRR (A/min) Add BTA

H2O2 Concentration

D-5 New Fumed SiO2

Polished Fumed SiO2

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

Passivating film: Passivating film insulator metal

After polishing

Kaufman et al., J. Electrochem. Soc., Vol. 138, No.11, 1991.

Chemical wear:

Liang et al., J. Elec. Matls., Vol.30, No.4, 2001. Liang et al., J. Elec. Matls., Vol.31, No.8, 2002. CMP is the synergy betw. chemical & mechanical removal

hm(t h0

x0(t)

h (t) c,top H(t)

ld(t)

INITIAL PARAMETERS INITIAL DYNAMIC PARAMETERS DYNAMIC

hc,valley(t)

B(t) k*L/2 L

Estragnat et al., 2006. D-8 High Roughness Low Roughness

3000 1400

2500 1200

1000 2000

800 1500

600

RR (A/mn)RR

RR (A/mn) 1000 400

500 200

0 0 0 10 20 30 40 50 60 70 0 10 20 30 40 50 60 70 Time (mn) Time (mn)

'Calculated RR Experimental RR Trend of experimental RR Calculated RR Experimental RR Trend of experimental RR

Estragnat et al., 2006. D-9 Wear in CMP: non-equilibrium & multi-mode

Ng and Liang, J. Trib., 2007 wear dynamics Friction reflects environmental changes

Ta 2friction+potentialO off friction TaOonly

2.4 V 0 V

+2.4 V +4.4V

Friction Coefficient Friction Coefficient FrictionCoefficient FrictionCoefficient Acidic acid.

H2O2. Time (second) Time (sec)

0V H2O. off + 2.4 V

Friction Coefficient Friction Coefficient

Time (second) Kar et al., Electrochimca Acta, 2008; ECS Lett., 2008. Friction dominates surface chemistry & morphology

Friction and Friction only E-potential Friction only

E-potential only E-potential only Friction and E-potential Friction + environment => surface chemistry & morphology

D-13 In Ta CMP, friction stirs surfaces

2+ to 5+ Ta Ta 1+ to 5+

Kar et al., Electrochimca Acta, 2008; ECS Lett., 2008. D-14 In Ta CMP, non-equilibrium phases exist

Ta2O3, TaO2 2

Ta2O, TaO 0

E(v) Ta2O5

-2 Ta

-4 0 3 6 9 12 15 pH

equilibrium state non-equilibrium state

D-15 Friction promotes non-equilibrium phases in Ta CMP

1E+150 ΔG╪ = 5 eV 1E+100 non-spontaneous 1E+50

k k (sec-1) spontaneous 1E-50

Oxidation Rate Constant Constant Oxidation Rate 1E-100 0 2 4 6 8 10 12 Mechanical Energy (eV)

(G  ) RT k  (kbT / h)e

when -ΔG╪ >ε, the effect of ε is negligible when -ΔG╪ ≤ε, the mechano-chemistry occurs Kar, et al., Eelectrochem. Acta, 2008. non-equilibrium process is easier to get by…

Work done by mechanical force (Ea  ) / RT k  k0e

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

The friction coefficient is affected by the applied potential. • Potentiostatic EIS test

The surface is passivated after ECMP Removal Rate • Single frequency EIS was used.

Z is impedance, thickness R is real part, resistance Z  R i C C is imaginary part, reciprocal of capacitance

Gao et al., JES, 2009. D-23 Faraday’ law bridges between corrosion current and corrosion rate.

Ta+ ITW 107 MRR  QNo A Ta2+ MRR—material removal rate, nm/min. I—current, A. 3+ T—time, 60s. Ta W—atomic weight. Q—elementary charge, 1.6×10-19. 23 No—Avogadro’s number, 6.023×10 . 4+ ρ—density, g/cm. Ta A—area, cm2.

m+ - 1 M M +me Ta5+ MRR 5

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

Slurry Wafer holder dispenser

Polishing pad Conclusion Remarks

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. Exercise Problem – use the following tips to measure friction

Tetrahedron, cube, octahedron, dodecahedron, icosahedron, sphere What techniques were used to make these images? What techniques were used to make these images?

C40 (hex) MoSi2

120A

E. coli Füzik et al.