theta probe: a tool for characterizing ultra thin films...

Theta Probe: A tool for characterizing ultra thin films and self assembled monolayers using parallel angle resolved XPS (ARXPS)

C. E. Riley, P. Mack, T. S. Nunney and R. G. White Thermo Fisher Scientific

2

Contents

Introduction Angle Resolved XPS

4

Introduction

• ARXPS provides 3 types of non-destructive depth information:- • 1. Relative depth plots (RDPs)

• Using logarithmic ratios • 2. Film thickness measurement of single and multiple overlayers

• Using derivatives of the Beer-Lambert Equation, I = I ∞exp(-d/λcosθ) • 3. Reconstructed depth profiles

• Using Maximum Entropy Methods

• ARXPS measures electron signals at different angles from sample

• by sample tilting (regular ARXPS) • by parallel angle detection (Theta Probe ARXPS)

5

Attenuation Length, λ, in electron spectroscopy

Ref.: M. P. Seah and W.A. Dench, Surface and Interface Analysis 1 (1979) 2

• Each data point represents a different element or transition

• Photoelectron peak intensity as a function of depth

• 65% of the signal from

6

60o

Collection Angle and angle resolved XPS (ARXPS)

• Information depth varies with collection angle

• I = I∞exp(-d/λcosθ) • 95% intensity from 3λcosθ

• Spectra from thin films on substrates

are affected by the collection angle

0o

SiO2 on Si, gate oxide

Alkane thiol SAM on Au

60o

4.5

nm

9.0

nm

7

Thermo Scientific Theta Probe

• Monochromated XPS • Non-destructive, surface sensitive technique

(0-9nm depth) • Elemental identification and quantification • Chemical bonding identification and quantification

• Parallel angle resolved XPS (PARXPS)

• Depth distribution information non-destructively • Molecular bonding orientation

• 60° collection angle

• (20° - 80°) • NO tilting the sample

• Two Dimensional Detector

• Measures Energy and Angle simultaneously • 112 channels for snapshot spectroscopy • 96 angle channels

XPS and PARXPS

8

• Full range of angles collected simultaneously

• Fast parallel acquisition • No sample tilting • Advantages for constant

transmission • No change in analysis area • No change is sample height

off the tilt axis

2-D Detector snapshot image

112 energy channels - collected simultaneously 96 angle channels

- collected simultaneously - banded into 16 Spectra

- 3.75o interval from 20o to 80o

Parallel angle resolved XPS

9

ARXPS yields depth information non-destructively

• ARXPS provides 3 types of non-destructive depth information:- • 1. Relative depth plots (RDPs)

• Using logarithmic ratios • 2. Film thickness measurement of single and multiple overlayers

• Using derivatives of the Beer-Lambert Equation, I = I ∞exp(-d/λcosθ) • 3. Reconstructed depth profiles

• Using Maximum Entropy Methods

• All 3 methods are integrated within Avantage Data System

10

BulkAngle

leSurfaceAng

II

ln

• Construction: • Collect ARXPS spectra • For each element, calculate:

• Information • Reveals the ordering of the

chemical species • Advantages

• Fast • Model independent, no

assumptions • Limitation

• No depth scale

Provides Information about layer ordering

Treatment of ARXPS Data – 1. Relative Depth Plot

• Relative depth plot from silicon oxide on Silicon substrate:

• C 1s on top surface (contaminant) • Oxidised Si 2p at surface • Elemental Si 2p at substrate

Incr

easi

ng d

epth

Surface

Bulk

11

• Two layer model • Signal from A

• IA = I∞A[1-exp(-d/λA,Acos θ)] • Signal from B

• IB = I∞B exp(-d/λB,Acosθ) • Ratio

• where R0 = I∞a/ I∞b • Simplify

• If λA,A = λB,A = λA then • ln[1+R/ R0] = d/(λA cosθ)

• This assumption is suitable for an

oxide on its own metal (e.g. SiO2 on Si)

−

−−

==

θλ

θλ

cos,exp

cos,exp1

0

ABd

AAd

RRBIAI

0

1

2

3

4

5

0 0.5 1 1.5 2 1/cos( θ )

ln(1

+R/R

∞ )

9.0 nm

6.4 nm

4.3 nm

3.6 nm 2.3 nm

1.9 nm

Silicon dioxide on silicon - 6 samples of varying thickness

• Plot: ln[1+R/ R ∞] vs. 1/cos(θ) • Fit through the origin

• Gradient = d/λ

Treatment of ARXPS Data – 2a. Thickness Calculation

12

*AMC = Airborne molecular contamination

Thickness Calculation, comparison with ellipsometry

• SiO2 on Si • Excellent linearity • Unity gradient • Intercept at 0.9 nm because

ellipsometry included AMC* in thickness

y = 1.077x - 0.914R2 = 0.999

0

2

4

6

8

10

0 2 4 6 8 10

Ellipsometry Measurements (nm)

AR

XP

S M

easu

rem

ents

(nm

)

13

XPS Thickness map of Graphene layers on SiO2

5-6

4-5

3-4

2-3

1-2

0

Bilayer

Trilayer

Gra

phen

e la

yers

By using the 2 layer model, the attenuation of the Si

signal reveals the thickness of the graphene sheet that the

Si2p photoelectrons are passing through. This allows a

thickness image of the surface to be generated,

showing the number of layers present in each structure

Optical Image

14

Substrate

n

2 1

• The ratio of the ith peak to that of the substrate will be:

• (λij is the attenuation length of photoelectrons characteristic of layer i in layer j)

• The ratio of peaks between adjacent layers, i and i+1:

• Knowing R0 and λ, fit the angle resolved data to obtain thickness of each layer, values for d

−

−−= ∑ ∑

=

=

−=

=

nj

j

ij

j ij

j

sj

j

ii

ii

s

i dddRII

1

1

1

0

cos1exp

cosexp1

λλθθλ

−

−−

−−

= ∑ ∑=

=

−=

=+

++

+++

ij

j

ij

j ij

j

ji

j

ii

i

ii

i

i

i

i

i dd

d

d

RR

II

1

1

1,1

1,1

10

1

0

1 cos1exp

cosexp1

cosexp1

λλθθλ

θλ

Treatment of ARXPS Data – 2b. Multi Overlayer Thickness Calculator

15

Multi Overlayer Thickness Calculation

• Al2O3 Growth curve in close agreement with

• TEM • Ellipsometry

• Measured SiO2 thickness independent of number of ALD cycles

Si

SiO2 Al2O3 C

16

Treatment of ARXPS Data – 3. Depth Profile Generation Maximum Entropy Method

Sample

Generate random trial

Profile Calculate expected

ARXPS data (Beer Lambert Law) Tj(θ) = exp(-t/λcosθ)

Si

SiO2 Al2O3

HfO2

O1s Si2p

Hf4fAl2p Si2p(O)

0 1 2 3 Depth (nm)

100

80

60

40

20

0

Atom

ic C

once

ntra

tion

(%)

0

2

3

4

5

6

7

O1s

Si2p

Hf4fAl2p Si2p(O)

20 40 60 80 Angle (o)

0.6

0.5

0.3

0.2

0.1

0

0.4

0.7

Rel

ativ

e in

tens

ity (a

rb. u

nit)

Hf4fO1sAl2pSi2pOSi2p

0 1 3 2 Depth (nm)

Atom

ic C

once

ntra

tion

(%)

100

80

60

40

20

0

Take average profile from

5 cycles

Determine error between experimental

and calculated data

Repeat Process 20,000 x.

choose most likley profile

Hf 4f (Oxide)

Al 2p (Oxide)

Si 2p (Oxide)

O 1s

Si 2p (Element)

Initial RDP (for reference)

C1s Ha4f O1s Al2p Si2pO Si2p

Non-destructive depth profile

Non-destructive depth profile consistent with RDP

17

Treatment of ARXPS – Summary of 3 types 2. Overlayer Thickness

3. Non-destructive Depth Profile

BulkAngle

leSurfaceAng

II

ln.1

EntropyMaximum.3

1. Relative Depth Plot (RDP)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

20 40 60 80Angle (°)

Rel

ativ

e In

tens

ity (%

)

O1s

Si2p Hf4f

Al2p Si2p(O)

Si

SiO2 Al2O3

HfO2 0.7 nm

0.8 nm 0.5 nm

ARXPS original data

0

20

40

60

80

100

0 1 2 3 Depth (nm)

Atom

ic C

once

ntra

tion

(%)

O1s Al2p Hf4f Si2pO Si2pE

Hf 4f (Oxide)

Al 2p (Oxide)

Si 2p (Oxide)

O 1s

Si 2p (Element)

CalculatorThickness.2

ARXPS analysis of Graphene on SiC

19

Analysis summary ARXPS analysis of Graphene on SiC

Theta Probe analysis summary • Experimental The Thermo Scientific Theta Probe was used to analyse a

sample of graphene on SiC The sample was mounted on the standard 70 x 70mm

Theta Probe sample holder with conductive carbon tape The monochromated X-ray source was used for XPS

analysis. This offers a selectable spot size from 15- 400µm. The 400µm X-ray spot was used for higher sensitivity and rapid analysis.

Angle resolved data was taken from the central point of the sample to obtain depth information from the sample

Using the angle resolved data, it is possible to find the thickness of the graphene layer


20

Surface sensitive

Bulk sensitive

Angle resolved

Proprietary and confidential

Angle resolved Using the Theta Probe’s unique angle

resolved capabilities, information can be obtained from the sample non-destructively

Angle resolved data was acquired for carbon, oxygen and silicon

The 2D detector has 96 angle channels For analysis, these angle channels were

binned into 16 discrete angle ranges of 3.75°angular resolution

The higher the angle, the more surface sensitive that spectra are

The data on the left is an example of how the carbon spectra change throughout the angle range. The highest angle and the lowest angle this can be seen on the next slide

Sample Analysis

21

C1s spectra


Bulk vs. Surface angle The two spectra for the lowest angle and

the highest angle are compared here The higher the angle, the more surface

sensitive that spectra are From the bulk angle spectra it is possible

to see a similar intensity of SiC to graphene

On the surface angle spectra the intensity of SiC is much lower than the graphene

As the ratio of SiC to graphene is much lower on the surface angle; this points to graphene being predominantly on the surface, with SiC the substrate

278 280 282 284 286 288 290 292 294 296 298

Inten

sity

Binding Energy (eV)

Bulk angle vs. Surface angle Bulk angle Surface angle

SiC Graphene

Spectra normalised for clarity

Graphene on SiC As-received

22

Relative depth plot


O1s C1s Graphene C1s SiC

Peaks (Peaks) Relative Depth Plot

Relative depth plot Avantage software can produce a relative

depth plot from ARXPS data Rapid and ‘model free’ method for

describing depth ordering of chemical states and elements

Provides qualitative information The plot of the graphene on SiC sample

shows clear structure • Oxygen on the surface • Graphene underneath • SiC substrate


23

Integrated Avantage layer thickness calculation software

ARXPS film thickness measurement • Avantage software for thickness analysis

Avantage software, combined with ARXPS analysis on Theta Probe, can be used to measure the thickness of up to three layers on a substrate Example of film thickness recipe shown to left

• Thickness measurements for graphene Surface oxygen is a very low concentration. This

points to there being a small amount of dilute oxygen spread out over the surface A density of 2.27 g/cm3 was used for graphene.

This is a reference density of graphite A band gap of 0.01eV was used for graphene Using these values and the obtained spectra the

thickness of graphene can be calculated Graphene = 0.857nm

Graphene on SiC As-received ARXPS film thickness measurement

24

ARXPS non-destructive depth profile Avantage data system allows concentrations

of various elements/ chemical states to be constrained

Results on previous slide were used to determine the ARXPS depth profile of graphene on SiC

The sample was modelled as a mixture of graphene, oxygen and SiC

• No SiC on surface • Small amount of oxygen on surface • 0.857nm of graphene

The 0.857nm of graphene is the approximate correct distance for two graphene layers on the surface of the sample

The reconstructed profile shows the presence of oxygen at the surface, suggesting that there maybe some oxygen content in the first layer


0

10

20

30

40

50

60

70

80

90

100

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1

Relat

ive In

tensit

y (%

)

Depth (nm)

ARXPS profile C graphene O SiC

ARXPS depth profile

ARXPS analysis of a Fluoropolymer Catheter

26

Fluoropolymer catheter • ARXPS from a curved, insulating surface

• Live optical view for easy alignment of sample • Analysis area DOES NOT change as a function of photoemission angle • Charge neutralisation conditions DO NOT change as a function of

photoemission angle • Depth distribution of carbon bonding states

ARXPS Applications

Live optical view from Theta Probe camera

Fluropolymer Catheter

27

ARXPS Applications

Live optical view from Theta Probe camera Fluoropolymer catheter

• ARXPS from a curved, insulating surface • Live optical view for easy alignment of sample • Analysis area DOES NOT change as a function of photoemission angle • Charge neutralisation conditions DO NOT change as a function of


C-C C-O

CF3

CF2

C-*C=O O-*C=O

Depth distribution of carbon bonding states • Depth integrated carbon chemistry

• High energy resolution spectrum of C1s region shows carbon bonding states within total XPS sampling depth (~10 nm)

• Fluorocarbon states easily observed • Excellent resolution due to high performance charge

neutralisation system

C1s spectrum


28

ARXPS Applications



photoemission angle • Depth distribution of carbon bonding states ARXPS C1s spectra

Surface

Bulk

Depth distribution of carbon bonding states • Depth distribution of carbon chemistry

• ARXPS C1s spectra acquired simultaneously at all angles • Constant charge neutralisation conditions at all angles • Constant analysis area at all angles • ARXPS data was peak fit with the components shown on the

previous slide to generate a Relative Depth Plot


29

ARXPS Applications




Depth distribution of carbon bonding states • Depth distribution of carbon chemistry

• Relative depth plot shows the layer ordering of elements and chemical states

• Method is model independent • Instant conversion of ARXPS data into depth information

CF3 C-*C=O

CF2

C-C

O-*C=O

C-O

Layer ordering of carbon bonding states


Relative Depth Plot

Measuring the quality of Self-Assembled Monolayers of alkane thiols on gold

31

Alkane Thiol SAMs on Au for Biological Applications

• Functionalising SAMs grown on substrate surfaces • Potential for well controlled design of biomaterials

• Modified functionalised groups for immobilisation of proteins, etc.

• Wide variety of potential applications • eg Biosensors in diagnosis, lab-on-chip, micro-contact

printing, etc • Need reliable characterisation technique (XPS, ARXPS)

• Identification and quantification of the functional groups • Probe chemistry of overlayer with nano-scale depth resolution • Provide information about orientation and structure

Protein of interest

SNAPS

6

O

OO

NH

ON

NN

NH

NH2

SAu

CH3

SAu

S

O

O CH3

Au

3

S

O

O CH3

Au

3

S

O

O CH3

Au

3

S

O

O CH3

Au

3

S

O

O CH3

Au

3

We acknowledge Karlsruhe Institute of technology for the use of the diagram

32

Self-assembled monolayers

Self-assembled monolayers • Non-destructive depth profiling of single molecule

• Self-assembled monolayers allow controlled modification of surface properties by controlled functionalisation

• Possible application in molecular electronics and biomaterials

• Organo-sulphur chemistry often used to form layers on gold • Layer thickness as a function of organic chain length

• Molecular orientation information and depth profile of single molecules

Schematic of self-assembled monolayer

Theta Probe ARXPS measurement • Experimental advantages • Data from all angles comes from same

analysis point • Imaging ARXPS is possible, allowing

film uniformity to be studied • Rapid snapshot acquisition reduces

X-ray spot dwell time • Lower X-ray power on sensitive

monolayer samples

3 mm

Imaging ARXPS of undecane thiol sample damaged in transit

33

Alkane thiol self-assembled monolayers on Au



• Possible application in molecular electronics and biomaterials • Organo-sulphur chemistry often used to form layers on gold • Layer thickness as a function of organic chain length



Nonanethiol

Dodecanethiol

Hexadecanethiol

Images from AsemblonTM, 15340 NE 92nd Street, Suite B, Redmond, WA

98052-3521, USA. www.asemblon.com

Self-assembled monolayer materials

used in this work

Hydroxy undecanethiol

1-mercapto-11-undecyl-tri(ethylene glycol)

Undecanethiol

34








0

0.5

1

1.5

2

2.5

0 5 10 15 20

Number of Carbon AtomsLa

yer

Thic

knes

s

Theta Probe measured layer thickness

Non-destructive ARXPS thickness measurement • Thickness as a function of organic chain length

• Film thickness measured on Theta Probe • Thickness increases linearly with organic chain length

35

Proposed mechanism of SAM growth

Reproduced from ‘Asemblon Self-Assembled Monolayers (SAMs) Handbook’

LOW COVERAGE HIGH COVERAGE

•At LOW COVERAGE we expect to observe a mixture of SAM bonding modes

•At HIGH COVERAGE we expect to see one type of bonding mode

36

Coverage versus bonding

Au Au

C C

S S

Atomic concentration maps of C, Au and S

•Concentration of elements varies across sample

•Carbon / sulphur correlate well

•Three zones

High C, high S, lower Au

Mid C, mid S, mid Au

Low C, low S, high Au

We have a strongly changing coverage of undecanethiol self-assembled monolayer

across sample

S

C

Au

Undecanethiol

37


159 160 161 162 163 164 165 166 167 168

Binding Energy (eV)

Au Au

Sulphur chemistry

SAM SAM

[SB]:[SA] = 1 : 3.11 Sulphur spectrum from black shaded area on image

SA

SA

SB SB

Undecanethiol sulphur chemistry at HIGH COVERAGE

•XPS image has full sulphur spectrum at each pixel

•Retrospective spectroscopy of sulphur from shaded area

•Two chemical states of sulphur observed

•Sulphur chemistry diagnostic of SAM bonding modes

•High proportion of SA compared to SB

38


159 160 161 162 163 164 165 166 167 168

Binding Energy (eV)

Sulphur chemistry

Au Au

SAM SAM

[SB]:[SA] = 1 :1.43 Sulphur spectrum from black shaded area on image

SA

SA

SB

SB

Undecanethiol sulphur chemistry at LOW COVERAGE

•Increased proportion of SB at low coverage region of image

•PARXPS mapping allows us to acquire full angle resolved datasets at each pixel in the map

•Next slide shows sulphur spectra from LOW COVERAGE zone from bulk and surface sensitive angles

39

Coverage versus bonding ARXPS analysis of sulphur bonding

159 160 161 162 163 164 165 166 167 168

Binding Energy (eV)

[SB]:[SA] = 1 : 1.47 Sulphur spectrum from surface sensitive angle

SA

SA

SB

SB

159 160 161 162 163 164 165 166 167 168

Binding Energy (eV)

[SB]:[SA] = 1 : 2.00 Sulphur spectrum from bulk sensitive angle

SA

SA

SB

SB

Angle resolved analysis from LOW COVERAGE zone

•Qualitative analysis of data indicates SB closer to top surface

than SA

40

SB

Coverage versus bonding ARXPS analysis of sulphur bonding

Au Au

SAM SAM

C O

SA

Au

Increasing relative depth

Relative depth plot for LOW COVERAGE zone

Undecanethiol bonding modes

•Angle resolved XPS information easily summarised as Relative Depth Plot

•Shows molecular orientation for SAM bonding

•There are at least two bonding modes for undecanethiol at LOW COVERAGE, with thiol group pointing downwards or

upwards

•At HIGH COVERAGE, most of the bonding is with thiol pointing downwards

41

Influence of head group Sulphur chemistry

159 160 161 162 163 164 165 166 167 168

Binding Energy (eV)

Sulphur spectrum from 1-mercapto-11-undecyl-tri(ethylene glycol) on Au

[SB]:[SA] = 1 : 2.35

SA

SA

SB

SB

159 160 161 162 163 164 165 166 167 168

Binding Energy (eV)

Sulphur spectrum from hydroxyundecanethiol on Au

SA

SA

Sulphur chemistry with different head groups

•PEG SAM shows both chemical states

of sulphur

•Indicates different bonding modes of

PEG SAM

•Hydroxy SAM shows only one bonding

mode

•Steric effect of larger PEG head group

affects SAM bonding modes

•Use mixed PEG / alkanethiol to reduce

steric effect

42



Alkanethiol non-destructive depth profiles • Thickness and molecular orientation information

• Confirms that organic bonds to gold at sulphur at HIGH COVERAGE

• Relative layer thickness is observed in profiles

0

20

40

60

80

100

Con

cent

ratio

n/%

Nonanethiol

C Au

S

0 0.5 1 1.5Depth / nm

Non-destructive ARXPS profile of alkanethiol on Au






Nonanethiol

43

0

20

40

60

80

100

Con

cent

ratio

n/%




C Au

S

Dodecanenanethiol 0 1 2

Depth / nm






Alkanethiol non-destructive depth profiles

• Thickness and molecular orientation information • Confirms that organic bonds to gold at sulphur at HIGH

COVERAGE • Relative layer thickness is observed in profiles

Dodecanethiol

• Layer thickness ~ 1.6 nm • SAM length ~1.8 nm

• SAM tilted by 27o

44

0

20

40

60

80

100

Con

cent

ratio

n/%




C Au

S Hexadecanenanethiol

Depth / nm 0 1 2






Alkanethiol non-destructive depth profiles

• Thickness and molecular orientation information • Confirms that organic bonds to gold at sulphur at HIGH

COVERAGE • Relative layer thickness is observed in profiles

Hexadecanethiol

45

0

20

40

60

80

100

Con

cent

ratio

n/%



Non-destructive ARXPS profile of hydroxy undecanethiol on Au

CH2 Au

S

Depth / nm 0 1 2 3

CH2OH

Functionalised alkanethiol non-destructive depth profiles

• Thickness and molecular orientation information • Confirms that organic bonds to gold at sulphur

• Chemical state information is preserved • Possible to observe CH2OH at top surface, then alkane

chain, then thiol group at Au interface






46

0

20

40

60

80

100

Con

cent

ratio

n/%



Non-destructive ARXPS profile of 1-mercapto-11-undecyl-tri(ethylene glycol) on Au

CH2 Au

S

Depth / nm

CH2OH

0 1 2 3

C2H4O






Functionalised alkanethiol non-destructive depth

profiles • Thickness and molecular orientation information

• Confirms that organic bonds to gold at sulphur • Chemical state information is preserved

47

Alkane thiol SAM study - summary

ARXPS analysis of self-assembled monolayers • Conclusion

• For reliable and complete analysis of SAMs Combination of XPS/PARXPS and mapping should be used

Minimises X-ray flux density • Thickness measurement of different SAMs possible

For a series of alkanethiols, thickness found to be proportional to chain length

Dodecanethiol shown to have thickness of 1.6 nm, 27o tilted • Proposed mechanism of SAM growth has been confirmed Low coverage of SAM is associated with two bonding modes of

alkanethiols to Au substrate • Thiol group or methyl group bound to Au

Thiol / Au bonding is predominantly observed at high coverage • Non-destructive profiling of SAMs with Theta Probe confirms molecular

bonding mode for high coverage

• Acknowledgement: • Thermo Fisher Scientific acknowledge Assemblon Inc., USA and Daniel J. Graham for

providing the alkane-thiol samples and images and for helpful discussions


Thank you for your kind attention!

Theta Probe: A tool for characterizing ultra thin films and self assembled monolayers using parallel angle resolved XPS (ARXPS)幻灯片编号 2Introduction�Angle Resolved XPSIntroductionAttenuation Length, λ, in electron spectroscopyCollection Angle and angle resolved XPS (ARXPS)Thermo Scientific Theta ProbeParallel angle resolved XPSARXPS yields depth information non-destructivelyTreatment of ARXPS Data – 1. Relative Depth PlotTreatment of ARXPS Data – 2a. Thickness CalculationThickness Calculation, comparison with ellipsometryXPS Thickness map of Graphene layers on SiO2Treatment of ARXPS Data – 2b. Multi Overlayer Thickness CalculatorMulti Overlayer Thickness CalculationTreatment of ARXPS Data – 3. Depth Profile Generation Maximum Entropy MethodTreatment of ARXPS – Summary of 3 typesARXPS analysis of Graphene on SiCARXPS analysis of Graphene on SiCSample AnalysisGraphene on SiC As-receivedGraphene on SiC As-receivedGraphene on SiC As-received幻灯片编号 24ARXPS analysis of a Fluoropolymer Catheter幻灯片编号 26幻灯片编号 27幻灯片编号 28幻灯片编号 29Measuring the quality of �Self-Assembled Monolayers of alkane thiols on goldAlkane Thiol SAMs on Au for Biological ApplicationsSelf-assembled monolayersAlkane thiol self-assembled monolayers on AuAlkane thiol self-assembled monolayers on AuProposed mechanism of SAM growthCoverage versus bondingCoverage versus bondingCoverage versus bondingCoverage versus bondingCoverage versus bondingInfluence of head groupAlkane thiol self-assembled monolayers on AuAlkane thiol self-assembled monolayers on AuAlkane thiol self-assembled monolayers on AuAlkane thiol self-assembled monolayers on AuAlkane thiol self-assembled monolayers on AuAlkane thiol SAM study - summaryThank you for your kind attention!

theta probe: a tool for characterizing ultra thin films...

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