Transcript Nanogeoscience and Nanotechnology – Applications of SIMS

Elias Chatzitheodoridis
National Technical Univ. of Athens
TOF-SIMS Instruments: Isotope Geochemistry & Cosmochemistry Group
Collaboration: Dr Ian Lyon, Reader, Univ. of Manchester
School of Earth, Atmospheric & Environmental Sciences

Primary ions
Generation inside an ion gun
• Acceleration at energies equal or higher than 10keV
• Formed into a beam and focused onto the sample’s surface at a small
spot (a few microns to a few nm)
•

Secondary ions
Atoms of the sample’s surface are sputtered away or recoil
• Some are ionised –secondary ions
• Secondary ions are extracted, accelerated and formed into a beam
•

Mass analysis
•
Secondary ions are focused into the mass spectrometer and analysed by
mass
Sputtered atoms and ionisation
Damage of the sample’s surface
Recoiling and internal damage
During impact the energy is thermalised
that is
The atoms look like they are being
produced from a hot plasma with a
characteristic temperature
(e.g. T≅9600K for 25keV Ga+)
1000
Relative Sensitivity Factor (Si)
Exponential Fit
100
RSF [Si=1]
10
 Less
than 1% of
the sputtered ions
are ionised
1
Si ionisation
(RSF=1)
0.1
Temperature from slope:
9590 ± 710 K
0.01
0.001
Easy ionisation 
 Difficult ionisation
0.0001
2
4
6
8
10
12
14
First Ionization Potential [eV]
 Ions
Measured relative sensitivity factors of different elements in silicate
standards as a function of the first ionisation potential of those elements
with low
first ionisation potential are easily ionised
 Ions with high first ionisation potential form
positive ions much less efficiently
 Ions
with high electron affinities (e.g. halogens)
form negative ions easily.
16
Secondary Ion Energy Spectrum
Ion Intensity (arbitrary units)
14
Highest population of ions
12
10
8
6
4
2
0
0
20
40
60
80
Ion Energy (eV)
100
120
140
160
 Ionisation
is prone to matrix effects
(chemical composition of the materials)
 Instrumental
effects cause fractionation of
elemental or isotopic ratios
(compared to real abundances)
TOF-SIMS
Static/Dynamic SIMS
Post ionisation of Neutrals -SNMS
One TOF-SIMS
A second TOF-SIMS
instrument
instrument
Power supplies
Laser system
& Acquisition unit
An operator
(Torston Henkel)
Vacuum
controllers
Power
supplies
& Acquisition
unit
A hand
A cup of tee


Ion source for analysis & e-gun for charge compensation
Primary column: A column of electrostatic lenses to form
charged ions into a beam

The sample

Secondary column: The extraction lens system and secondary
ion beam formation
Energy filtering (for magnetic analysers)
The mass analyser/spectrometer
Detection system (single- or multi-)




System is supported by a heavy duty vacuum system, capable
of achieving typically down to 10-10mbar (using combinations
of turbo-molecular and ion pumps).
TOF reflectron chamber
Electron gun
(for charge compensation)
Sample analysis
chamber (under vacuum)
Preparation
vacuum &
sample carousel
Vacuum systems
(pumps)
Ion gun
(primary ions -behind)
Ion detection
system
Sample insertion
t1
t2
t3
Pulsed Primary
ion beam (<20ns
pulse)
Sample
Secondary ion
beam
m1 < m2 < m3 < mv
Collector
Travel time: less than10 to >100μs
m1
m3
m2
t0
t0+Δt
t0+2 Δt
mν
t0+ν Δt
Electrostatic
reflector
Magnetic
analyser
1
B
2m u
e
m3>m2>m1
Collector
Ion population
R
Electrostatic
analyser
Energy
window
Monoatomic
Molecular
Energy (eV)
+ or
-
Secondary
ion beam
Electric
potential
Sample
Primary
Ion beam
Crater
formation
 More
than 99% of sputtered atoms are neutrals
 Lasers can be used to pos-ionise these atoms and
enhance ion yield
 Matrix effects are reduced
Secondary
Neutrals
and ions
Primary ion
beam
Laser beam
Magnetic sector SIMS instruments:
• single-collector instruments: one isotope at a time
• multi-collector instruments: up to 7 isotopes in parallel
TOF-SIMS instruments:
• All possible masses in a cycles (a full mass spectrum)
A TOF-SIMS mass spectrum
TOF-SIMS
Chemical bonding and
molecular information
Elemental information
Dynamic SIMS
Imaging information
Thickness & Density information
Evans Analytical Group
 Spatial
resolution at the nanoscale: primary ion
beams can be focused to spot sizes down to the
nanoscale (typically 200nm, ranging between
50nm and 2mm)
 It
is pulsed to a short (ns) ion pulse, typically 2 to
20ns for high mass resolution, achieving also
high depth resolution.
 Timescale
range.
for producing secondary ions at the ps
Duoplasmatron
ions guns
C60 ions guns
Metal ion guns
Best for Biomaterials &
organic materials
(Cs+, Ga+, Au+, Au2+, Au3+)
Best for Elemental &
Isotopic analysis
Elemental analysis
A Cs+ ion
gun
An
Au+
ion gun

<50nm beam diameter

High energy ions

High currents

Faster depth profiles

Lower projectile energy
(compared to ionic ion
beams)

Energy is released in a
wider area (per
molecule)  higher
depth resolution
Small spot size (<300nm)


Runs with O2, CN-, Ar,
He, H or Xe pure gases

High energy, high
current ion beams

Minimum spot size
<300nm
Polypeptide analysis
• Material is removed
• Rate depends on the density of the primary ion beam
• Can range from a monolayer/hour to microns/min
Ion population (cps)
Energy distribution of:
• Atomic ions is broad
• Molecular ions is narrow
Molecular ion energy distribution
Atomic ion energy distribution
Energy distribution
A
fractionation effect occurring mainly at
the very first moments of the analysis, then
reaches a steady state which is not the real
value
 Can
be solved by starting the acquisition
after some time of bombardment
 Comparison
with standards assists in
reducing the effect
Formula to calculate mass
fractionation in per mil (‰) values
Common mass fractionation values (in per mil)
relative to the natural abundance of the
isotopes of the elements.
 Use
of Standards with chemistry similar to
the sample
 Use
of Relative Sensitivity Factor sets (RSFs)
• Numbers produced using standards with
chemistry similar to the sample
• Each element is calibrated to one high abundance
element (such as Si for silicates)
Secondary Ion Energy Spectrum
 Ions
A
14
Ion Intensity (arbitrary units)
leave the surface
with a range of
energies, e.g. for a 2kV
biased sample the
energy range is
2 to 2.2kV
12
10
8
6
4
2
0
0
20
40
60
80
Ion Energy (eV)
reflectron would correct for this
difference
100
120
140
160
Ions arrive at
the same time
Reflectron with
suitably set
retarding field
Energy distribution
Detector
Slow ions, e.g. 2.2kV
Sample
Fast ions, e.g. 2.2kV
Path difference
Ions start at
the same time
Energy distribution
 Surface
topography can affect the yield of
secondary ions
 Perfectly
flat/polished samples should be
analysed
 Carbon
or gold coating would reduce
charging effects, however cleaned prior to
analyses using the ion beam in DC mode
Point analysis
Line scan (horizontal profile)
2D Elemental/Isotopic maps
(by scanning the beam)
Sample surface
Depth profile
(due to sputtering)
Volume (3D)
Elemental/Isotopic maps
(scanning & depth profiling)
- Negative ions
+ Positive ions
Oxygen, Sulphur & halogens
Metal, alkaline & REEs
1400
1000
1000
Mg
K
41
K
Na
800
800
Αριθμός ιόντων.
Αριθμός ιόντων.
1200
Αριθμός ιόντων.
23
24
M
24g
40
1000
600
600
400
400
800
24
25
M
25g
Mg
200
200
0
0
23.5
23.5
600
24
24.5
24.5
24
25
25
Μάζα (amu)
Μάζα (amu)
Mg
26
M
26g
Mg
25.5
25.5
26
26.5
26.5
26
400
39
1
200
2
0
0
27
H
7
H
5
12
Li
10
K
Al
C
15
20
25
Μάζα (amu)
30
35
40
45
•
•
•
•
Scaling of the time slice and the time offset is required
This gives the correct position of the masses on the mass axis
Allocation of the right peak to the right mass is the possible
Discrepancies may exist between:
• Atomic and molecular ions
• Different parts of the spectrum
 The
measure of separation of two closely
positioned masses
 It is defined as m/Δm
• m is the mass of the atom of interest
• Δm is the Full Width at Half Maximum of a fully
 It
Gaussian peak
differs at the different parts of the spectrum
 Improves by faster primary pulses, however
secondary signal is reduced
• Minimum pulse rate: ~10kHz
• Time difference between pulses: 100μs
• Faster pulse rates would overlap successive spectra
2500
26
One peak contributes to
the intensity of the other
Mg
Αριθμός ιόντων.
2000
1500
1000
25
12
Mg1H
C2 1 H2
500
0
25.9
25.92
25.94
25.96
Μάζα (amu)
25.98
26
 Molecular
 Isobaric
 Twin
interference (e.g. C4H9 with 57Fe)
interferences (e.g. 48Ca and 48Ti)
or cluster ions (e.g. 40Ca2+ with 80Se+ )
 Doubly-charged
mass (e.g. 28Si2+)
 Primary
ions which appear at half the
ions combining with sample’s
elements (e.g. Ga2+ at mass 138 interferes
with 138Ba and Ga3+ at 207 with 207Pb)
 Magnetic
sector instruments
• Powerful magnets
 TOF-SIMS
instruments
• Ultra-fast electronics: shorter pulses, better time
slicing
• Optimal travel distances (long TOF tubes):
increased mass resolution
 Hydrides:
form from always abundant
hydrogen
 Only 1.007 mass
and 24MgH
 Requires
resolve
units heavier, e.g. 25Mg
more like ~4000MRP to properly
25Mg
24MgH
Spot size
DC beam current
Number of ions in 20ns pulse
Number of secondary ion
produced (assuming sputter yield of 10
and a generous secondary ionization
efficiency of 1% (yields are more usually
10-3-10-4)
5mm
1mm
100nm
10nm
50nA
5nA
1nA
0.1nA
60,000
6000
1200
120
600
60
12
1
With decreasing spot size all values are decreased,
especially secondary ion yields

Analysis of the standard

Choice of an element of
high abundance
(e.g. Si in silicates and
glasses)

Correct for possible
background

We apply the formula to
the right
Measured Intensity
of the unknown (X)
Requested value, the
RSF of the unknown (X)
compared to Si
Measured Intensity
of Silicon
Atomic abundance
of Silicon in nature
Atomic abundance
of unknown in
nature
This is explained with a
thermal ionisation model
(plasma formation)
EX = First Ionisation potential of
unknown element
ER = First Ionisation potential of the
reference element
k = Boltzmann's constant
Tav = Average temperature for all
elements; typical values between
6,000 and 10,000 Kelvin.
Not all elements fit such a model, e.g. some
elements that preferentially ionise as oxides
rather than atomic ions
Most successful model is
the Local Thermal
Equilibrium Model (LTE)
256 points
Array of Spectra
Voxels = volume pixels

Magnetic sector SIMS data can be small
• Ratios, line and depth profiles, elemental and isotopic maps,
maps of ratios

TOF-SIMS data can be very large, generally 50150Mbytes, sometimes exceeding 0.5Gbytes
• A microscale volume of the sample with nanoscale volume
resolution is digitised
• All chemical information is known for each voxel (volume
pixel)
• Specialised software should
 manipulate the data
 produce a variety of maps and profiles
 assist in geochemical interpretation
 SIMS
data are very complicated due to
multiple interferences
 SIMS produces any kind of charged
particles: random clusters of elements
 Instrumental effects can distort spectra
 Quantitative analysis is getting very
difficult due to fractionation and matrix
effects
A powerful software system is required to
assist in interpretation












Fully interactive environment
Database of all ions of all elements of the periodic table
Database of common interferences, updated on the spot
Includes a parser: Spreadsheet style calculations between
images
Data Mining and Automated image extraction and
comparison
Stoichiometry calculator
Clever Interference calculators
Fully interactive peak deconvolution
Image matching with other images (e.g. SEM) with common
cursor, moving in parallel at all open image windows
Spectrum interpretation assistants
Masking capabilities for looking at the chemistry/spectrum of a
certain area (e.g. a certain mineral)
Histogram plot capabilities, also of complicated spreadsheetstyle functions
xxZr16O
xxZr
isotopes
and combinations
with hydrogen
isotopes
91Zr+90Zr1H
92Zr1H
94Zr1H
96Zr1H
1
xxZr16O
isotopes
and combinations
with hydrogen
2
Stalactite with
high content of
organic material
Stalactite with
low content of
organic material
Trace element mapping on Zircons
Oral talk and Poster at Goldschmidt 2007
SEM image
89Y+ (red)
on 28Si+ (blue)
Detrital
core
Y goes to garnet through
a melt phase
Monazite
inclusion
UHP rim
1070°C
High Lithium concentration at the rims of zircon
Enhanced contrast 7Li+ ion map
Overlay of three TOF-SIMS ion maps:
(Red) Lithium and (Green) Potassium on a blue
background, which is silicon and defines the crystal
area.
Yield of 16O- from feldspar is higher
than zircon (centre of circle)
16O-
Zircon
Diamond
Feldspar
Diamond
Yield of 16O1H- from feldspar is
lower than zircon (centre of circle)
16O1H-
35Cl-
12C 2
Diamond
Diamond
32S-
Carbonate globules (rosettes) in the ALH84001 Martian meteorite
Unpublished data
40Ca
24Mg
28Si
A complicated
relationship
between the
carbonate and the
silica glass is
revealed from the
overlapping maps
Mesostasis & Carbonates of the Nakhla Martian meteorite
Unpublished data
Total image (69Ga is subtracted)
BS-SEM image
Pyx
Mn-Crb
Ilm
Plag
Mn-Crb
Mn-Crb
Plag
Mn-Crb
Plag
KFelds
SEM compositional
map of Silicon
Fe-Mn-Mg ion map
BS-SEM image
Pyx
Mn-Crb
Ilm
Plag
Mn-Crb
Mn-Crb
Plag
Mn-Crb
Plag
KFelds
Na-K-Fe ion map
BS-SEM image
Pyx
Mn-Crb
Ilm
Plag
Mn-Crb
Mn-Crb
Plag
Mn-Crb
Plag
KFelds
Lithium ion map
BS-SEM image
Pyx
Mn-Crb
Ilm
Plag
Mn-Crb
Mn-Crb
Plag
Mn-Crb
Plag
KFelds
Ca- electron probe map
Ca- ion map
Biomarkers and biosignatures
IDPs
Data from References

The signs left behind by living forms
Biochemicals
• PAHs –Polycyclic Aromatic
Hydrocarbons
• Lipids
• Terpenoids
• Hopanes
• Recognisable organic fragments
PAHs

Enrichment in certain elements

Certain isotopic variations

Biominerals (magnetites, sulfides, amorphous Mn oxides,
Todorokite, Jarosite, Vaterite etc.)




Benzene-based multi-rings / similar to graphite
single layer fragments
Formed by incomplete combustion of any
organic material
Very common on Earth, some carcinogenic
Present also in interstellar medium in high
abundances (probably broken graphite after
interstellar dust grain collision, which contain
graphite)
Lack of certain PAHs from
fresh surfaces of Martian
meteorites (ALH84001),
demonstrated by TOF-SIMS,
shows non-biogenic origin
of Martian organic content.
• Silicon carbide grains of ≤2μm diameter
• Stardust of stellar sources (Red Giants,
AGB-stars, Supernovae, and Novae)
• Found inside meteorites or collected
during NASA’s STARDUST project
• Identified by their exotic isotopic ratios
• Supernovae shockwaves implant Li, B and
noble gases
Depth profiling in the nanoscale is
necessary to find out the composition
of the interstellar medium, the most
primitive matter in the solar system
NanoSIMS
isotope maps of
300nm presolar
silicon grains, 17O
enriched, in
interstellar grains
• Are seen as the Milky-way
• Probably, the most primitive materials of
our solar system (indicated by presolar
silicates found in them)
• Collected as clusters but very fragile,
break apart during preparation for
measurements
• Final sizes less than 1μm
• Chemically, very heterogeneous
• Mineralogy: Mg-olivine, pyroxene, Fesulphide
• Useful to study, giving clues on the
molecular synthesis (such as H2, CO2) in
the universe
Positive ions
Negative ions
 Ancient
glass contained
mineral-rich colourants
 Checking
the trace
elements of these
colourants, provenance of
glass can be inferred
 Important
archaeological
consequences 
interaction of civilisations
Inclusions and matrix in 14th century BC opaque yellow
glass excavated in Tel el-Amarna, Egypt. TOF-SIMS
images and mass spectra of major and trace elements.
 TOF-SIMS
instruments are very sensitive
 Nano-analysis is possible
 Instruments are becoming easier to use
 New ion sources enhance analytical results
 Intelligent software is required for
• Spectrum analysis interpretation
• Clever map extraction and manipulation
• Data mining
• Combine spatial and spectral info for
interpretation