Theta Probe: A tool for characterizing ultra thin films...
Transcript of Theta Probe: A tool for characterizing ultra thin films...
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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
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Contents
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Introduction Angle Resolved XPS
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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)
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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
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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
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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
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• 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
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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
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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
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• 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
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*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
)
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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
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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
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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
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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
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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
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ARXPS analysis of Graphene on SiC
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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
Thermo Scientific Theta Probe
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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
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C1s spectra
Proprietary and confidential
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
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Relative depth plot
Proprietary and confidential
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
Graphene on SiC As-received
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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
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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
Graphene on SiC As-received
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
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ARXPS analysis of a Fluoropolymer Catheter
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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
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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
photoemission angle • Depth distribution of carbon bonding states
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
Fluropolymer Catheter
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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
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
Fluropolymer Catheter
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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
photoemission angle • Depth distribution of carbon bonding states
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
Fluropolymer Catheter
Relative Depth Plot
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Measuring the quality of Self-Assembled Monolayers of alkane thiols on gold
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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
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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
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Alkane thiol self-assembled monolayers on Au
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
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
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Alkane thiol self-assembled monolayers on Au
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
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
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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
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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
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Coverage versus bonding
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
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Coverage versus bonding
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
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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
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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
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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
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Alkane thiol self-assembled monolayers on Au
Schematic of self-assembled monolayer
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
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
Nonanethiol
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0
20
40
60
80
100
Con
cent
ratio
n/%
Alkane thiol self-assembled monolayers on Au
Schematic of self-assembled monolayer
Non-destructive ARXPS profile of alkanethiol on Au
C Au
S
Dodecanenanethiol 0 1 2
Depth / nm
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
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
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0
20
40
60
80
100
Con
cent
ratio
n/%
Alkane thiol self-assembled monolayers on Au
Schematic of self-assembled monolayer
Non-destructive ARXPS profile of alkanethiol on Au
C Au
S Hexadecanenanethiol
Depth / nm 0 1 2
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
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
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0
20
40
60
80
100
Con
cent
ratio
n/%
Alkane thiol self-assembled monolayers on Au
Schematic of self-assembled monolayer
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
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
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0
20
40
60
80
100
Con
cent
ratio
n/%
Alkane thiol self-assembled monolayers on Au
Schematic of self-assembled monolayer
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
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
Functionalised alkanethiol non-destructive depth
profiles • Thickness and molecular orientation information
• Confirms that organic bonds to gold at sulphur • Chemical state information is preserved
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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
Thermo Scientific Theta Probe
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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!