Surface Chemistry of Glass: Interfacial water and mechanochemical properties

Hongtu He, Laura C. Bradley, Zachary R. Dilworth,

Carlo G. Pantano, and Seong H. Kim

Materials Research Institute, Pennsylvania State University

Engineering Conferences International Functional Glasses

January 6 -11, 2013 Sicily, Italy

Acknowledgement

• Laura Bradley, Zach Dilworth – undergraduate REU through support from NSF IMI for New Functionality in Glass (Grant No. DMR-0844014).

• Hongtu He – an exchange student from China through support from NSF IMI for New Functionality in Glass (Grant No. DMR-0844014).

• This work was supported by National Science Foundation (Grant No. DMR-1207328).

Surface properties in ambient conditions are not

intrinsic properties of materials;

they are sensitive to extrinsic factors… (often, unpredictable & difficult to understand)

vacuum

Effects of vapor adsorption on SiO2/Si wear

0 100 200 300 400 500 600-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

He

igh

t (

m)

Width (m)

dry

humid

n-pentanol vapor

(Nominal PHertzian = 360 MPa)

Optical profilometry

0.7 N load on 3mm dia fused silica ball sliding on SiO2/Si

Barnette, Asay, Kim, Guyer, Lim, Janik, and Kim, Langmuir 2009, 25, 13052–13061

In alcohol vapor

In dry

In humid

MEMS Reliability Taxonomy

Romig, et. al. Acta Materialia 51 (2003) 5837

6

Unreliable Dynamic Interfaces have Limited the Development of Complex MEMS

mechanical lock: enabled by 24 independent A/B events

500 m

500 m

M. T. Dugger

"Courtesy Sandia National Laboratories, SUMMiT™ Technologies, www.sandia.gov/mstc"

MEMS side-wall tribometer

20m

Initially coated with “lubricious” fluorinated self-assembled monolayer

In collaboration with M. Dugger (Sandia)

100

101

102

103

104

105

106

107

0.0

0.2

0.4

0.6

0.8

1.0

Fri

ctio

n C

oef

f.

Cycles

Device fails once the lubricious coating layer is worn off

and the adhesion of the newly exposed bare surfaces

becomes larger than the actuation force.

Device fails when

Fadhesion > Facuation

2 Minutes @100 Hz operation

D. B. Asay, M. T. Dugger, and S. H. Kim, Tribol. Lett. 2008, 29, 67.

In the presence of alcohol vapor, the device

does not fail …

MEMS

tribometer

Load

Slide

100

m

10 m

1 00

1 01

1 02

1 03

1 04

1 05

1 06

1 07

1 08

0 .0

0 .2

0 .4

0 .6

0 .8

1 .0

1 0-7

1 0-6

1 0-5

1 0-4

1 0-3

1 0-2

1 0-1

1 00

1 01

D a ys o f O p era tio n

Fric

tio

n C

oe

ff.

C yc le s

NO Device

Failure -

Dry Dev 1

Dry Dev. 2

Dry Dev. 3

15 ±5% P/Psat

95 ±3 % P/Psat

95 ±3 % P/Psat

Dry Dev 1

Dry Dev. 2

Dry Dev. 3

15 ±5% P/Psat

95 ±3 % P/Psat

95 ±3 % P/Psat

Device

Failure

In alcohol vapor

D. B. Asay, M. T. Dugger, and S. H. Kim, Tribol. Lett. 2008, 29, 67.

D. B. Asay, M. T. Dugger, J. A. Ohlhausen, and S. H. Kim, Langmuir 2008, 24, 155.

1~2 min

continuous operation for 2 weeks

Micro-scale lubrication with a

molecular adsorbate film

12

Increased Operating Life of Gear Train with Vapor Phase Lubrication

gear train on aging module

500 m

gear 1 (output gear)

gear 6

left/right

actuator

up/down

actuator

50 m gear 3

assembly

contacts:

dimples

hubs

teeth

1/2 DMS with uengine actuator

(90V square wave)

1000

10000

100000

Cumulative Percent Failed

Ac

cu

mu

late

d C

yc

les

to

Fa

ilu

re

10 20 9080705030

t50 = 46.6 Kcycles

sigma = 0.069

t50 = 31.0 Kcycles

sigma = 0.304100 Hz

500 Hz

FOTAS monolayer alone, t50 = 4.7x104

With VPL, device was stopped at 4.8x108

cycles without failure

• 1000 ppm pentanol, <100 ppm H2O

M. T. Dugger

13

VPL is Effective on MEMS Devices with Thermal Actuators

VPL with pentanol produces extraordinary operating life in a variety of MEMS devices

single crystal silicon Fiber Switch

100 m100 m

5x106 cycles in air 5x106 cycles in 20% Psat pentanol

M. T. Dugger

Understanding

accelerated wear of SiO2 by water

and wear prevention by alcohol

Density Functional Theory (DFT) calculation of

Si-O-Si bond dissociation by rxn with gas molecule

Model System:

β-cristobalite (111)

Si-O-Si Rupture via Methanol

Red – O

Yellow – Si

White – H

Grey – C

CH3OH(gas)

Stable & low density

form of SiO2

Ea

Barnette, Asay, Kim, Guyer, Lim, Janik, and Kim, Langmuir 2009, 25, 13052–13061

DFT calculation of activation energy for

different surface terminations

Transition State for Si-O-Si break

R1

R2

Si

RT

ErateRxn aexp

R1 R2 Ea (kJ/mol)

H H 114

CH3 H 151

H CH3 112

CH3 CH3 154

propyl propyl 224

Alcohol termination (OR) increases the activation barrier necessary to break Si-O-Si linkages…

Barnette, Asay, Kim, Guyer, Lim, Janik, and Kim, Langmuir 2009, 25, 13052–13061

“Amorphous oxide of Si is boring; multicomponent silicate glasses

are more complicated & interesting”

Water adsorption and penetration can cause ion-exchange with mobile/leachable ions and hydrolysis of Si-O-Si network

Si-O- Na+ + H2O

Si-OH + Na+ + OH-

Si-O-Si + OH- Si-OH + Si-O-

Si-O- + H2O Si-OH + OH-

Si-O-Si + H2O Si-OH + HO-Si

R.A.Schaut, C.G.Pantano. 2005

Molecules possessing proton donor sites and lone-pair orbitals can enhance the crack growth rate by coupling across the Si-O bond to form an activated complex…

Charles & Hillig Theory

Influence of water vapor on crack propagation in soda lime glass

S. M. Wiederhorn J. Am. Ceram. Soc. 50, 407-414 (1967)

Stress-intensity factor, KI (MPam1/2) 0.4 0.8 0.7 0.6 0.5

RH

I

II

III

Freiman, Wiederhorn, & Mecholsky, J. Am. Ceram. Soc. 92, 1371 (2009)

How does water adsorption affect scratch behaviors of glass?

Scratching glass surface in humid conditions

Applied load

Friction force

Load: 0.2 N

Sliding speed:~4.2mm/s

Hertzian Pressure: ~200 MPa

Gas with controlled humidity

Carrier gas

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 100 200 300 400

Fric

tio

n C

oe

ffic

ien

t

Number of Passes

20% RH

40% RH

90% RH

-21000 m3 -32000 m3 -30000 m3 Total displaced volume

20% RH 40% RH 90% RH

Humidity dependence of wear of fused quartz surface rubbed with pyrex ball

Optical profilometry images of the substrate

20% RH

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 100 200 300 400

Fric

tio

n C

oe

ffic

ien

t

Number of Passes

20% RH

40% RH

90% RH

-13000 m3 +25000 m3 -18500 m3

Humidity dependence of wear of soda lime glass surface rubbed with pyrex ball

40% RH 90% RH

Total displaced volume

Optical profilometry images of the substrate

Optical profilometry image of pyrex ball rubbed in 20% RH Deposition of substrate wear debris

Optical profilometry image of pyrex ball rubbed in 90% RH Wear of ball

-200 -150 -100 -50 0 50 100 150 200

-12

-8

-4

0

4

Hig

ht

(m

)

Distance (m)

-200 -150 -100 -50 0 50 100 150 200

-12

-8

-4

0

4

Heig

ht

(m

)

Distance (m)

-100 -50 0 50 100

-1.6

-1.2

-0.8

-0.4

0.0

0.4

0.8

20%RH

40%RH

90%RH

Sodium silicateFused quartz

90%RH

40%RH

He

igh

t (

m)

Position (m)

20%RH

-100 -50 0 50 100

-1.6

-1.2

-0.8

-0.4

0.0

0.4

0.8

Heig

ht

(m

)

Position (m)

-200 -150 -100 -50 0 50 100 150 200

-12

-8

-4

0

4

Hig

ht

(m

)

Distance (m)

-200 -150 -100 -50 0 50 100 150 200

-12

-8

-4

0

4

He

igh

t (

m)

Distance (m)

Pyrex ball rubbed against sodium silicate substrate

20% RH

90% RH

L. Bradley, Z. Dilworth,,, C. G. Pantano, & S. H. Kim “Hydronium Ions in Soda-lime Silicate Glass Surfaces” J. Am. Ceram. Soc. (DOI: 10.1111/jace.12136)

(Article first published online: 24 DEC 2012)

In 20% RH

A small increase in humidity from dry air drastically

change the surface scratch behavior of glass

-100 0 100

20

10

0

-10

Distance (m)

In dry N2

-100 0 100

20

10

0

-10

Distance (m)

100 200 300 4000.0

0.5

1.0

20%RH

Frictio

n C

oe

ffic

ien

t

Sliding cyles

Dry N2

8.8m 4.3m

Pyrex ball

SLG substrate

Pyrex ball

SLG substrate

Hei

ght

(m

)

-100 0 10010

0

-10

Distance (m)

100 200 300 4000.0

0.5

1.0

90%RH

40%RH

20%RH

Frictio

n C

oe

ffic

ien

t

Sliding cyles

As RH approaches saturation, the SLG surface becomes

“wear-resistant”…

-11.8m

-100 0 10010

0

-10

Distance (m)

SLG substrate

Pyrex ball Pyrex ball Pyrex ball

In 20% RH In 40% RH In 90% RH

-100 0 10010

0

-10

Distance (m)

4m

SLG substrate SLG substrate

4.3m

Hei

ght

(m

)

0 100 200 300 400

-1.2

-0.8

-0.4

0.0

400 cycles

200 cycles

100 cycles

50 cycles 20 cycles

He

igh

t(m

)

Distance(um)

10 cycles

0 100 200 300 400

-1.2

-0.8

-0.4

0.0

400cycles

200cycles

100cycles50cycles

20cycles

He

igh

t (

m)

Distance (m)

10cycles

In 20% RH, the wear of the SLG substrate continues as the # of scratch cycles increases

In 90% RH, the damage to the SLG substrate is made initially by a few asperity contacts; but it does not grow.

Water adsorption on glass surface matters…

If the substrate is SiO2, it’s easy to measure water adsorption isotherm…

vent

IR

Humid gas

Silicon ATR Crystal

Penetration depth @ 3000 cm-1 = ~ 300 nm

detect adsorbed molecules only

heated

bubbler

1

carrier gas (Ar or dry clean air)

heated

bubbler

2

condenser

Water adsorption on SiO2 in humid ambience

D. B. Asay and S. H. Kim, J. Phys. Chem. B 2005, 109, 16760

3230cm-1

solid-like (ice-like)

3400cm-1

liquid-like

ATR-IR measurement

0.5

1.0

3.0

2.0

2.5

1.5

Av

era

ge t

hic

kn

ess (

nm

)

3800 3600 3400 3200 3000 2800 2600

3390

3360

PM

-RA

IRS

inte

nsity (

au) 2850

2918

Wavenumber (cm-1)

Dry

15%

35%

55%

75%

95%

0 20 40 60 80 1000

1

2

3

4

Water adsorbed

upon increase of humidity

Strongly bound water

not removable by Ar purging

Alcoholic hydroxyl

O

H /

CH

inte

nsity (

au)

Relative Humidity (%)

A. Tu, H. R. Kwak, A. L. Barnette, S. H. Kim, Langmuir 2012, 28, 15263–15269.

Water contact angle alone cannot tell you much about the structure of water on the solid surface.

Water adsorption on OH-SAM on Au; the “strongly bound” water on organic OH surface does not form ice-like structure

380036003400320030002800 180016001400

1738

1412

1467

15761712

2848

2918

PM

-RA

IRS

In

ten

sity (

a.u

.)

Wavenumber (cm-1)

3430

Dry

5%

15%

45%

75%

95%

0 20 40 60 80 1000

1

2

3

4

5

6

7

O

H /

C

H in

ten

sity (

au

)

Relative Humidity (%)

Although COOH-SAM/Au also show a water contact angle is <5o, it behaves quite different from OH-SAM/Au and OH/SiO2.

A. Tu, H. R. Kwak, A. L. Barnette, S. H. Kim, Langmuir 2012, 28, 15263–15269.

Water contact angle alone cannot tell you much about the structure of water on the solid surface.

Sum-Frequency-Generation (SFG) Vibration Spectroscopy

2800 2850 2900 2950 3000

SFG

sig

nal

(a.

u.)

Frequency, cm -1

2000~4000 cm-1

532nm w1

w2 w1+w2

SFG occurs at the interface or in the bulk

with no inversion symmetry (2)2 0

IRVISeffSFG III www2

)2(

To generate SFG signals:

Random Inversion symmetry

No inversion symmetry in both molecular and optical length scales

Amorphous polymers Bulk water & vapor Glass

Piezoelectric crystals Crystalline biopolymers

Interfaces

Centrosymmetric crystals (such as NaCl)

Symmetrically arranged groups (such as CH2 in well-packed SAM or lipid bilayer)

χeff(2)

≠ 0

χeff(2)

= 0

2800 2900 3000 3300 3600

Lo

g(1

/R)

Wavenumber cm-1

Propanol mole fraction

in the vapor mixture

of proanol & water

y=1.00

y=0.88

y=0.60

y=0.40

y=0.36

y=0.35

y=0.35

y=0.24

y=0.00

2800 2900 3000 3300 3600

SF

G inte

nsity (

au

)

Wavenumber cm-1

Propanol mole fraction

in the vapor mixture of

propanol & water

y=1.00

y=0.88

y=0.60

y=0.50

y=0.40

y=0.36

y=0.35

y=0.35

y=0.35

y=0.24

y=0.00

0.0 0.2 0.4 0.6 0.8 1.02.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

Vapor

xWater,yWater

Pre

ssure

(kP

a)

xPropanol,yPropanol

Liquid

Azeotrope

1.0 0.8 0.6 0.4 0.2 0.0

Co-adsorption of water & alcohol on SiO2 A. L. Barnette and S. H. Kim, J. Phys. Chem. C 2012, 116, 9909-9916.

ATR-IR spectra SFG spectra

A. L. Barnette and S. H. Kim J. Phys. Chem. C 2012, 116, 9909−9916

0.0 0.2 0.4 0.6 0.8 1.00.0

0.5

1.0

1.5

Th

ickn

ess o

f p

rop

an

ol (n

m)

Vapor mole fraction (y) of propanol

0

2

4

6

8

Thic

kness o

f wa

ter (n

m)

Co-adsorption of water & alcohol on SiO2

Silica surface

3000 3200 3400 3600 3800

SF

G I

nte

nsity (

au

)

Wavenumber cm-1

Dry

40% RH

60% RH

80% RH

Saturation

Water adsorption on Glass as ftn of RH (glass cleaning = ethanol rinsed, and then soaked/aged in water for 3 hr)

3000 3200 3400 3600 3800

SF

G in

ten

sity (

au

)

Wavenumber cm-1

Dry

20% RH

40% RH

60% RH

80% RH

Satruation

Soda lime glass Fused quartz glass

3000 3200 3400 3600 3800

Air/water

Air/0.1MNaOH

0 20 40 60 80 100

Square

root of S

FG

inte

nsity (

a.u

)

Relative humidity (%)

FQ:3760cm-1

SL:3430cm-1

L. Bradley, Z. Dilworth,,, C. G. Pantano, & S. H. Kim “Hydronium Ions in Soda-lime Silicate Glass Surfaces”

J. Am. Ceram. Soc. (DOI: 10.1111/jace.12136) (Article first published online: 24 DEC 2012)

Na+

Na+

Na+

Na+

Na+

Na+

Na+ Na+

Na+ Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+ leach

during aging in liquid water

Equili-brium with

adsorbed water layer

Na+

Na+

Na+

Na+

H3O+

H3O+

H3O+

H3O+

H3O+

H3O+

H3O+ H2O

H3O+

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H3O+

H3O+

In water or near-saturation humidity Pristine Na-silicate glass

H3O+

H3O+

H3O+

Na+

Na+

Na+

Na+

H+

H3O+

H+

H3O+

H3O+

H3O+

H3O+

In dry ambient

H3O+

H3O+

H3O+

H+

H+

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H+

The water molecules diffusing into the glass surface may find protons in the Na+-leached sites and form hydronium ions.

Arun K. Varshneya et al. 2010

Na+ = 0.1nm K+ = 0.14nm H3O+ = 0.14nm

2800 3000 3200 3400 3600 3800

SF

G in

ten

sity (

au

)

Wavenumber cm-1

high humidity

high humidity

Soda lime glass

Laura Bradley, Zach Dilworth, et al. J. Am. Ceram. Soc. (DOI: 10.1111/jace.12136)

Low humidity

Si

O

Si

H H O

Si

O

Si

O H

H

Si

O

H H

Si

O

Hydrolysis & network corrosion

Michalske and Bunker. 1984.

L. C. Bradley et al. JACERS 2013

Solvation of H+ in the leached Na+ site forming H3O+

Water ingression into glass

Formation of H3O+ formation in the Na+-leached site??

Searching for more supporting evidences..

Dry N2

20%RH

40%RH

90%RH -100 0 100

-1.2

-0.8

-0.4

0.0

90%RH

40%RH

He

igh

t(m

)Distance(m)

20%RH

-100 0 100

-10

-5

0

He

igh

t (

m)

Distance (m)

-100 0 100

5

0

-5

-10

He

igh

t (

m)

Distance (m)

2.2 m

-100 0 100

5

0

-5

-101.6 m

He

igh

t (

m)

Distance (m)

-100 0 100

5

0

-5

-10

He

igh

t (

m)

Distance (m)

4.2 m

-100 0 100

5

0

-5

-10

He

igh

t (

m)

Distance (m)

7.3 m

The wear resistance at 90% RH is not observed for pyrex glass substrate rubbed with pyrex glass ball

Pyrex ball Pyrex glass 100 200 300 400

0.0

0.3

0.6

0.9

90%RH

40%RH

20%RH

Friction

Co

effic

ien

t

Sliding cyles

Dry N2

In dry N2

The wear resistance at 90% RH is not observed for AF45 alkali-free borosilicate glass rubbed with pyrex glass ball

Dry N2 20%RH 40%RH 90%RH

-100 0 100

-15

-10

-5

0

He

igh

t (

m)

Distance (m)-100 0 100

-0.8

-0.4

0.0

90%RH

40%RH

He

igh

t(m

)

Distance(m)

20%RHIn dry N2

How about chemically-strengthened glasses?

Apple iPad glass

-100 0 1005

0

-5

-10

He

igh

t (

m)

Distance (m)

0.3 m

-100 0 1005

0

-5

-10

He

igh

t (

m)

Distance (m)

3.6 m

-100 0 1005

0

-5

-10

He

igh

t (

m)

Distance (m)

1.8 m

-100 0 1005

0

-5

-10

He

igh

t (

m)

Distance (m)

9.3 m

Dry N2

20%RH

40%RH

90%RH

-100 0 100-0.8

-0.4

0.0

Dry N2 90%RH

40%RH

He

igh

t(m

)Distance(m)

20%RH

HTC cellphone glass

-100 0 1005

0

-5

-10

He

igh

t (

m)

Distance (m)

2.2 m

-100 0 1005

0

-5

-10

He

igh

t (

m)

Distance (m)

3 m

-100 0 1005

0

-5

-10

He

igh

t (

m)

Distance (m)

3.7 m

-100 0 1005

0

-5

-10

He

igh

t (

m)

Distance (m)

4.8 m

Dry N2

20%RH

40%RH

90%RH -100 0 100

-0.8

-0.4

0.0

90%RH

40%RH

He

igh

t(m

)Distance(m)

20%RH

-100 0 100

-6

-3

0

He

igh

t (

m)

Distance (m)

48

The surface chemistry of counter-surface sliding against glass

matters…

Not only vapor environment, but also counter surface of rubbing matter…

Diamond tip (curvature=200nm) When Pcontact < Hardness hillock (surface protrusion) When Pcontact > Hardness wear (material removal)

SiO2 ball (diameter=1000nm) Pcontact << Hardness

Substrate = Si wafer with native SiO2

J. Yu, S. H. Kim, B. Yu, L. Qian, and Z. , ACS Appl. Mater. Interfaces 2012, 4, 1585-1593.

We expect a soft material would get

easily damaged when rubbed with

a hard material…

Hardness:

Ball Substrate

Al2O3 = 20GPa

Si3N4 = 14.5GPa

SiO2 = 6.0GPa

pyrex = 4.3GPa

Soda lime glass

= 5.9GPa vs.

SiO2 ball Soda lime glass

-100 0 100-15

-10

-5

0

He

igh

t (

m)

Distance (m)

-100 0 10015

10

5

0

-5

He

igh

t (

m)

Distance (m)

12 m

Si3N4 ball Soda lime glass

-100 0 100-15

-10

-5

0

He

igh

t (

m)

Distance (m)

-100 0 10015

10

5

0

-5

He

igh

t (

m)

Distance (m)

10.4 m

-100 0 100

5

0

-5

-10

He

igh

t (

m)

Distance (m)

5.1 m

-100 0 100-15

-10

-5

0

He

igh

t (

m)

Distance (m)

Al2O3 ball

No surprise in dry N2 environment…

Soda lime glass

In 90% RH, SiO2 ball wears and the scratch in soda lime glass is negligible.

SiO2 ball Soda lime glass

-100 0 100

5

0

-5

He

igh

t (

m)

Distance (m)

6.3 m

-100 0 100

5

0

-5

He

igh

t (

m)

Distance (m)

2 m

-100 0 100

-1.6

-1.2

-0.8

-0.4

0.0

90%RH

40%RH

He

igh

t(m

)Distance(m)

20%RH

-100 0 100-15

-10

-5

0

He

igh

t (

m)

Distance (m)

-100 0 10015

10

5

0

-5

He

igh

t (

m)

Distance (m)

12 m

-100 0 100

5

0

-5

-10

He

igh

t (

m)

Distance (m)

6.6 m

Dry N2

20%RH

40%RH

90%RH

100 200 300 4000.0

0.3

0.6

0.9 90%RH

40%RH

20%RH

Friction

Co

effic

ien

t

Sliding cyles

Dry N2

In all humidity, the “hard” Si3N4 ball wears and the “soft” soda lime glass is almost intact.

Si3N4 ball Soda lime glass

-100 0 100

-0.4

0.0

0.4

90%RH

40%RH

He

igh

t(m

)Distance(m)

20%RH

-100 0 100

-10

-5

0

He

igh

t (

m)

Distance (m)

-100 0 10015

10

5

0

-5

He

igh

t (

m)

Distance (m)

10.4 m

-100 0 100

0

-5

1.8 m

He

igh

t (

m)

Distance (m)

-100 0 100

0

-5

He

igh

t (

m)

Distance (m)

1.6 m

-100 0 100

2

0

-2

-4

-6

He

igh

t (

m)

Distance (m)

1.5 m

Dry N2

20%RH

40%RH

90%RH

100 200 300 4000.0

0.3

0.6

0.9 90%RH

40%RH

20%RH

Friction

Co

effic

ien

t

Sliding cyles

Dry N2

In intermediate humidity, Al2O3 ball wears and the scratch into soda lime glass by is very small.

-100 0 100

2

0

-2

-4

-6

He

igh

t (

m)

Distance (m)

0.2 m

-100 0 100

0

-5

He

igh

t (

m)

Distance (m)

1.1 m

-100 0 100

5

0

-5

-10

He

igh

t (

m)

Distance (m)

5.1 m

-100 0 100

0

-5

He

igh

t (

m)

Distance (m)

1.1 m

-100 0 100-6

-3

0

He

igh

t (

m)

Distance (m)

-100 0 100

-0.4

-0.2

0.0

90%RH

40%RH

He

igh

t(m

)Distance(m)

20%RH

Dry N2

20%RH

40%RH

90%RH

SL glass Al2O3 glass 100 200 300 400

0.0

0.3

0.6

0.9

90%RH

40%RH

20%RH

Frictio

n C

oe

ffic

ien

t

Sliding cyles

Dry N2

Protecting glass from being scratched using “simple” alcohol adsorption

57 -100 0 100

0

10

20

30

n-propanol vaporn-pentanol vapor

90%RH

He

igh

t (

m)

Distance (m)

Dry N2

1 10 1000.0

0.3

0.6

0.9

n-propanol vapor

n-pentanol vapor

90%RH

Frictio

na

l co

eff

icie

nt

Sliding cycles(N)

dry N2

Pyrex ball

Dry N2

SLG substrate

90% RH

n-pentanol

vapor

The wear of SLG / pyrex glass interface can be shut off by one monolayer-thic alcohol adsorption

n-propanol

vapor

Mechanical property of surface region of glass ???

Indentation load–displacement curve

pA

FH max

pA

SEr

2

dh

dFS

Reduced elastic modulus

Hardness

Nanoindentation test

Contact stiffness

0

10

20

30

40

Ha

rdn

ess (

GP

a)

Indent depth(nm)

air side of glass

tin side

aged wiht water

annealed glass

140nm90nm40nm0

50

100

150

200

140nm90nm

Ela

stic m

odu

lus (

GP

a)

Indent depth(nm)

air side of glass

tin side

aged with water

annealed glass

40nm

Indentation depth dependence of elastic modulus and harness of Asahi soda-lime glass surface

Humidity = 40 – 60%

J.A. Howell et al. J. Non-Cryst. Solids, 354 (2008) 1891–1899

Does the surface have better mechanical strength than the bulk?

A. Bolshakov, G.M. Pharr, J. Mater. Res. 13 (1998) 1049. K. O. kese, Z. C. Li, & B. Bergman, Mater. Sci. Eng. A 204 (2005) 1.

0.0 0.5 1.0 1.5 2.0-150

-100

-50

0

50

He

igh

t(n

m)

Distance(um)

Or is it just a measurement artifact?

Conclusions

• Water activity at glass surface – equilibrium with the gas phase water – Quite different from that at SiO2 surface – At high RH, H3O+ ions seem to be formed in the

interfacial region

• Scratch resistance under shear – Mechanochemical effects; not just mechanical. – Different from stress corrosion or crack propagation – Functions of vapor condition and counter-surface

chemistry

Nano-indentation of Diamond-like carbon (DLC)

Hf (nm) Er (GPa) H (GPa)

120 59.3 0.5 5.6 0.1

90 58.6 0.6 5.6 0.1

50 43.2 1.1 4.6 0.2