Overview of Auger Spectroscopy in Materials Characterization
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Auger Spectroscopy
E. Haimi, SEM lecture
Auger electrons were named after
Pierre Auger who, together with
Lise Meitner, discovered Auger
electron emission in 1920s.
Leng, Yang. Materials Characterization :
Introduction to Microscopic and
Spectroscopic Methods, John Wiley &
Sons, Incorporated, 2013. ProQuest
Ebook Central,
http://ebookcentral.proquest.com/lib/a
alto-
ebooks/detail.action?docID=1333091.
Created from aalto-ebooks on 2018-11-
26 01:42:43.
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Incident electron beam hits the surface
• Produces core-level vacancy
• Relaxation of the ionised state by emission
of an x ray
photon
• Detection of an x ray
W.R. Runyan, T.J. Saffner, Semiconductor measurements
and instrumentation, McGraw Hill, 2nd Ed. 1998, Chapter
14.
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The relaxation of the ionized state by an Auger electron
If you know the
kinetic
energy
E
K
, we can calculate
the
binding energy
of the
atom’s photoelectron (
E
B
)
based on the following
relationship
The kinetic energy of an
Auger electron in Figure
7.1b is given by the
following equation.
A typical AES spectrum is a
plot of intensity versus
kinetic energy
typical XPS spectrum is a
plot of intensity versus
binding energy.
The intensity of Auger electrons are relatively small
compared with those of primary and secondary
electrons that have escaped from a solid surface.
The primary electrons ejected from a solid surface by
inelastic scattering comprise the background of an
AES spectrum in the region of high kinetic energies,
while the secondary electrons comprise the
background in the region of low kinetic energies.
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Rare event
1 Auger electron for every 1 000 secondary electrons
(SEM)
-> development for a special detectors
• Auger transition is more probable
with lighter elements
– starting Li ->
– Observes well C, N and O
– Are often also contaminants
– Requires ultra high vacuum (UHV)
W.R. Runyan, T.J. Saffner, Semiconductor measurements
and instrumentation, McGraw Hill, 2nd Ed. 1998, Chapter
14.
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y
•
Auger electrons originated from different
electron shells
are labelled with three letter: ABC
A = initial ionization shell
B = replacement electron shell
C = Auger electron shell
Most probable are KLL, LMM, MNN
W.R. Runyan, T.J. Saffner, Semiconductor measurements
and instrumentation, McGraw Hill, 2nd Ed. 1998, Chapter
14.
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•
Incident electron beam 3 -5 keV
• Auger electrons are adsorbed into
the solid sample
• Only few monolayers detected
– > High surface sensitivity
W.R. Runyan, T.J. Saffner, Semiconductor measurements
and instrumentation, McGraw Hill, 2nd Ed. 1998, Chapter
14.
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•
Applied negative voltage
for the outer plate
• Inner plate to ground
• Applied a voltage ramp
by time
• Maximize the detection
of Auger electrons
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What can I analyse?
S
a
m
p
l
e
s
•
When interested of the outer most
monolayers on a surface
• Interest of light elements
• Or contamination (organic)
• Samples need to tolerate and be suitable for ultra high
vacuum!
• Is non-destructive, however, needs sample preparation,
so often the sample is lost
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•
Only few monolayers, often we have organic
impurities
•
Ionized inert gas (Ar+) with focus beam of 3-5
keV
•
The removal rate of material ~10 nm per
minute
W.R. Runyan, T.J. Saffner, Semiconductor measurements
and instrumentation, McGraw Hill, 2nd Ed. 1998, Chapter
14.
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Example of
AlGaAs:SF
6
Having S and F impurities +
organic contamination (C,O)
After sputter etching, the
peaks of Ga, As and Al more
visible
Also, a small indication of Ar
W.R. Runyan, T.J. Saffner, Semiconductor measurements
and instrumentation, McGraw Hill, 2nd Ed. 1998, Chapter
14.
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l
y
s
i
s
A derivative display is
used to help in the
characterization
Data obtained from the
experiment
- Has high background of
secondary electrons
W.R. Runyan, T.J. Saffner, Semiconductor measurements
and instrumentation, McGraw Hill, 2nd Ed. 1998, Chapter
14.
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–
S
I
M
S
•
Ions are also charged
particles (like electrons)
•
Can be deflected with
electric or magnetic field
•
Focused small ion probe at
the sample surface
•
Incident ions are capable to
knock of
secondary ions
S
I
M
S
• Provides
–
Detection of All element (also
H and other light ones)
– Different Isotopes
– Detection for one to two most
top atomic layers (< 1 nm)
– Detection of elements in Concentration as low
as 10
-6
possible
[Auger and XPS 0.1 at%]
• Many of the non
Charged
products
-> can not be
detected
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n
t
a
t
i
o
n
Ultra high vacuum needed
Electromagnetic lenses
Y. Leng, Materials Characterization : Introduction to
Microscopic and
Spectroscopic Methods, Publisher,
Wiley-VCH
S
I
M
S
• Ions
– Large mass
O- ion 10 000 more mass than
electron
– Can be destructive for the
surface
– “Sand blaster”
• Ions commonly used
Ar
+
, Xe
+
, O
2+
, Ga
+
, Cs
+
Y. Leng, Materials Characterization : Introduction to
Microscopic and
Spectroscopic Methods, Publisher,
Wiley-VCH
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?
• Method still under development [especially data
analysis] - > qualitative method (currently)
• Two different modes of operation
– Dynamic SIMS
• Destructive
• High flux of primary ions (sputtering)
• Similar to Auger and XPS
– Static SIMS
• Non-destructive
• Low flux of primary ions [changing the analysis place]
Y. Leng, Materials Characterization : Introduction to
Microscopic and
Spectroscopic Methods, Publisher,
Wiley-VCH
S
I
M
S
• Not a measure of mass but
rather
mass to charge ratio
• Sensitive
– Very little background
– Depth of 1-2 nm (from surface)
– Ppm or Ppb detection limits
– Qualitative technique
Boron doped Silicon
Y. Leng, Materials Characterization : Introduction to
Microscopic and
Spectroscopic Methods, Publisher,
Wiley-VCH
S
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M
S
A
n
a
l
y
s
i
s
• Mass-to-charge ratio
– Individual ions
– Ion clusters
– Molecular fragments
• Spectrum of positive or negative
ions
• More complex than(Auger/XPS),
more peaks
Y. Leng, Materials Characterization : Introduction to
Microscopic and
Spectroscopic Methods, Publisher,
Wiley-VCH
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2
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Imaging Method
SEM OM TEM
AFM
Elemental Analysis
TEM (Crystal) EDS Raman
XPX Augur SIMS
Surface properties
XPS (roughness) AFM
SEM SIMS Nanoindentation
Unknown
Other knowledge
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x
a
m
1.
X-ray Diffractometry (XRD)
2.
Scanning Electron Microscopy (SEM)
3.
Electronic Transport in semiconductors (Basics of
semiconductors, Four Probe Resistvity, Hall effect)
4.
Raman Spectroscopy
5.
Nanoindentation
O
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x
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F
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a
s
k
• Describe a method
–
From all the methods (major topics) learned at the
course are in my doctoral hat –
you will take one and answer to questions:
1. What does the method provide and how does it work?
(0-3 p.)
2. What kind of samples can be analysed? (0-3 p.)
3. What could a possible result look and how is it
analysed? (0-3
p.)
+ Additional point possible (1 p.)
O
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l
E
x
a
m
S
e
c
o
n
d
t
a
s
k
• A case:
–
Real case (from a published paper):A material
has been created
Make a presentation
1.
How the material synthesized (2p)
2.
What are the methods used for
characterization (2p)
3.
Results and their conclusion (10 p)
4.
What methods would you use to
characterize this sample? What more
information can you get (6 p)
Auger spectroscopy is a powerful technique used for materials characterization, involving the emission of Auger electrons to analyze the elemental composition of a sample. Named after Pierre Auger, this method provides valuable information about the surface properties of materials. The technique is commonly used in conjunction with other spectroscopic methods like EDS to enhance analytical capabilities. Understanding the principles behind Auger spectroscopy is essential for researchers and scientists working in the field of materials science.
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Presentation Transcript
CHEM CHEM- -E5140 Materials Materials Characterization Characterization Laboratory Laboratory Auger + SIMS Course summary 29.11.2021 E5140
Auger Spectroscopy Auger electrons were named after Pierre Auger who, together with Lise Meitner, discovered Auger electron emission in 1920s. Leng, Yang. Materials Characterization : Introduction to Microscopic and Spectroscopic Methods, John Wiley & Sons, Incorporated, 2013. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/a alto- ebooks/detail.action?docID=1333091. Created from aalto-ebooks on 2018-11- 26 01:42:43. E. Haimi, SEM lecture
EDS Characteristic x-rays Incident electron beam hits the surface Produces core-level vacancy Relaxation of the ionised state by emission of an x ray photon Detection of an x ray W.R. Runyan, T.J. Saffner, Semiconductor measurements and instrumentation, McGraw Hill, 2nd Ed. 1998, Chapter 14.
Auger spectroscopy Auger electron emission The kinetic energy of an Auger electron in Figure 7.1b is given by the following equation. If you know the kinetic energy EK, we can calculate the binding energy of the atom s photoelectron (EB) based on the following relationship A typical AES spectrum is a plot of intensity kinetic energy versus typical XPS spectrum is a plot of intensity versus binding energy. The relaxation of the ionized state by an Auger electron
The intensity of Auger electrons are relatively small compared with those of primary and secondary electrons that have escaped from a solid surface. The primary electrons ejected from a solid surface by inelastic scattering comprise the background of an AES spectrum in the region of high kinetic energies, while the secondary electrons background in the region of low kinetic energies. comprise the
Auger electrons Rare event 1 Auger electron for every 1 000 secondary electrons (SEM) -> development for a special detectors Auger transition is more probable with lighter elements starting Li -> Observes well C, N and O Are often also contaminants Requires ultra high vacuum (UHV) W.R. Runyan, T.J. Saffner, Semiconductor measurements and instrumentation, McGraw Hill, 2nd Ed. 1998, Chapter 14.
Auger electron terminology Auger electrons originated from different electron shells are labelled with three letter: ABC A = initial ionization shell B = replacement electron shell C = Auger electron shell Most probable are KLL, LMM, MNN W.R. Runyan, T.J. Saffner, Semiconductor measurements and instrumentation, McGraw Hill, 2nd Ed. 1998, Chapter 14.
High surface sensitivity Incident electron beam 3 -5 keV Auger electrons are adsorbed into the solid sample Only few monolayers detected > High surface sensitivity W.R. Runyan, T.J. Saffner, Semiconductor measurements and instrumentation, McGraw Hill, 2nd Ed. 1998, Chapter 14.
Auger equipment The cylindrical mirror analyser Applied negative voltage for the outer plate Inner plate to ground Applied a voltage ramp by time Maximize the detection of Auger electrons
Auger spectroscopy What can I analyse? Samples When interested of the outer most monolayers on a surface Interest of light elements Or contamination (organic) Samples need to tolerate and be suitable for ultra high vacuum! Is non-destructive, however, needs sample preparation, so often the sample is lost
Surface cleaning Sputter etching Only few monolayers, often we have organic impurities Ionized inert gas (Ar+) with focus beam of 3-5 keV The removal rate of material ~10 nm per minute W.R. Runyan, T.J. Saffner, Semiconductor measurements and instrumentation, McGraw Hill, 2nd Ed. 1998, Chapter 14.
Effect of Surface cleaning Sputter etching Example of AlGaAs:SF6 Having S and F impurities + organic contamination (C,O) After sputter etching, the peaks of Ga, As and Al more visible Also, a small indication of Ar W.R. Runyan, T.J. Saffner, Semiconductor measurements and instrumentation, McGraw Hill, 2nd Ed. 1998, Chapter 14.
Data analysis A derivative display is used to help in the characterization Data obtained from the experiment - Has high background of secondary electrons W.R. Runyan, T.J. Saffner, Semiconductor measurements and instrumentation, McGraw Hill, 2nd Ed. 1998, Chapter 14.
Secondary Ion Mass Spectroscopy SIMS Ions are also charged particles (like electrons) Can be deflected with electric or magnetic field Focused small ion probe at the sample surface Incident ions are capable to knock of secondary ions
SIMS Provides Detection of All element (also H and other light ones) Different Isotopes Detection for one to two most top atomic layers (< 1 nm) Detection of elements in Concentration as low as 10-6 possible [Auger and XPS 0.1 at%] Many of the non Charged products -> can not be detected
Instrumentation Ultra high vacuum needed Electromagnetic lenses Y. Leng, Materials Characterization : Introduction to Microscopic and Spectroscopic Methods, Publisher, Wiley-VCH
SIMS Ions Large mass O- ion 10 000 more mass than electron Can be destructive for the surface Sand blaster Ions commonly used Ar+, Xe+, O2+, Ga+, Cs+ Y. Leng, Materials Characterization : Introduction to Microscopic and Spectroscopic Methods, Publisher, Wiley-VCH
SIMS Is the method destructive? Method still under development [especially data analysis] - > qualitative method (currently) Two different modes of operation Dynamic SIMS Destructive High flux of primary ions (sputtering) Similar to Auger and XPS Static SIMS Non-destructive Low flux of primary ions [changing the analysis place] Y. Leng, Materials Characterization : Introduction to Microscopic and Spectroscopic Methods, Publisher, Wiley-VCH
SIMS Not a measure of mass but rather mass to charge ratio Sensitive Very little background Depth of 1-2 nm (from surface) Ppm or Ppb detection limits Qualitative technique Boron doped Silicon Y. Leng, Materials Characterization : Introduction to Microscopic and Spectroscopic Methods, Publisher, Wiley-VCH
SIMS Analysis Mass-to-charge ratio Individual ions Ion clusters Molecular fragments Spectrum of positive or negative ions More complex than(Auger/XPS), more peaks Y. Leng, Materials Characterization : Introduction to Microscopic and Spectroscopic Methods, Publisher, Wiley-VCH
Course summary The first lecture 6.9.2020 Imaging Method SEM OM TEM AFM Elemental Analysis TEM (Crystal) EDS Raman XPX Augur SIMS Other knowledge Unknown Surface properties XPS (roughness) AFM SEM SIMS Nanoindentation
The techniques for the exam 1.X-ray Diffractometry (XRD) 2.Scanning Electron Microscopy (SEM) 3.Electronic Transport in semiconductors (Basics of semiconductors, Four Probe Resistvity, Hall effect) 4.Raman Spectroscopy 5.Nanoindentation
Oral Exam First task Describe a method From all the methods (major topics) learned at the course are in my doctoral hat you will take one and answer to questions: 1. What does the method provide and how does it work? (0-3 p.) 2. What kind of samples can be analysed? (0-3 p.) 3. What could a possible result look and how is it analysed? (0-3 p.) + Additional point possible (1 p.)
Oral Exam Second task A case: Real case (from a published paper):A material has been created Make a presentation 1. How the material synthesized (2p) 2. What are the methods used for characterization (2p) 3. Results and their conclusion (10 p) 4. What methods would you use to characterize this sample? What more information can you get (6 p)
