Ions Scattering Spectroscopy (ISS)
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Ions Scattering Spectroscopy (ISS)
STKK 6104 Laboratory Skill Practices
Norfarhana Abdul Samad P59341
Nur Khairul Nabila Kamarudin P59342
Mohd Razali Shamsuddin P61352
Serawati Jafirin P62181
Siti Zarina Zakwan P62981
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General Principles
a) Classical binary collisionsIn a first approximation, ion scattering can be described by elastic binary hard-sphere collisions
Due to the law of conservation ofenergy and momentum one obtains the following relations for the scattered atom (E1) and the recoiled atom (E2):
2
21
122
12211
01
sincos
mm
mmmEE
221
22
2102 )(
cos4
mm
mmEE
In the case of 90° or 180° scattering detection the equation for E1 simplifies to:
90°: 180°:12
1201 mm
mmEE
2
12
1201
mm
mmEE
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When a parallel ion beam impinges on a target atom, the trajectories are bent due to the repulsive forces, leading to so called shadow cones. These cones depend on the primary energy and the electronic charge of the involved particles
There is a critical angle c above which the scattered projectile can hit a second atom.
An additional phenomenon of shadowing is the blocking. A blocking cone is formed behind blocking atoms.
This blocking can be nicely seen in the experiment,e.g. backscattering of 150 keV protons from a W(100) crystal
Shadowing and blocking
1
2
3
4
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Channeling
When an ion beam is aligned along a high symmetry of a single crystal, most of the ions can penetrate deep into the crystal (thousands of Å).
This is due to the fact that the shadow cones are small for high energetic and light ions (e.g. 1MeV He+).
During their way through the crystal electronic interaction leads to a continuous energy loss: electronic stopping power. For 1 MeV He+ in Si it is about 60 eV per monolayer.
Sputtering
Impinging ions may produce a number of recoiling atoms and in form of a cascade process some sample atoms may be ejected from the surfaces: sputtering
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Sputter yield
The number of sputtered atoms per impinging ions depends on the primary energy, the mass of the ions and the target atoms and the angle of incidence.
The maximum yield is at about 30 keV. At higher energies ion implantation is
prevalent.The sputter yield also increases with
increasing angle
The application of sputtering is manifold:
a) Detection and identification of ions in the SIMS techniqueb) Combined sputtering and surface analysis by AES or XPS for depth
profilingc) Sputtering for thin film productiond) Sputtering for surface etching
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Ion Scattering Spectroscopies
LEIS (Low Energy Ion Scattering) spectroscopy is referred to primary energies in the range of 100 eV to 10k eV.
Medium Energy Ion Scattering (MEIS) to a range from 100 to 200k eV.
High Energy Ion Scattering (HEIS) to energies between 1 and several MeV.
HEIS technique is best known as Rutherford Backscattering Spectroscopy (RBS).
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Low-energy ion scattering (LEIS)
Low-energy ion scattering (LEIS) is an analytical tool that provides information on the atomic composition of the outer surface, when noble gas ions are used as projectiles.
quantitative composition analysis is currently done on a huge variety of materials, including catalysts and organic materials.
LEIS (Low Energy Ion Scattering) spectroscopy is referred to primary energies in the range of 100 eV to 10 keV
Often the LEIS technique is called Ion Scattering Spectroscopy (ISS)
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Instrumentation
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LEIS is based on simple principles: the laws of mechanics. The surface under investigation is targeted by light noble gas ions (often He+).
When such an ion collides with a surface atom, momentum and energy are transferred, depending on the mass of the surface atom and the collision angle.
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The light ion is scattered backwards with ahigh energy after a collision with a heavy surface atom and with a low energy after a collision with a light atom.
By measuring the energy of the backscattered ions in an energy spectrum while keeping the angle fixed the mass of the surface atoms can be determined and this leads to the elucidation of the atomic composition of the surface.
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Figure 3 shows an example of an application of LEIS in catalysis. It shows how platinum in an automotive exhaust catalyst is covered with coke during use.This deteriorates the performance of the catalyst. The coke can be removed in a regeneration step and the platinum isavailable for the reaction.
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Medium Energy Ion Scattering (MEIS)
E0= 100 keV -200 keV
• MEIS more surface sensitive and more complex instrument• High depth resolution of the atomic composition in MEIS is useful for
studies of all solids1) crystalline,2) nanocrystalline3) semiconducting4) insulating
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MEIS-Instrumentation
DUOPLASMATRON
ION SOURCE
X-Y
STEERER
EINZEL LENS
ACCELERATION
TUBE
Q-LENS
X-Y STEERER
BENDING
MAGNET
COLLIMATOR
CHOPPING
ELECTRODECHOPPING
APERTURE
POSCHENRIEDER ELECTROSTATIC
DEFLECTOR
MCP
SCATTERED-ION
DECELERATION TUBE
SAMPLE
AMPLIFIER CFD
TIME
ANALYZER
PULSEGENERATOR
DELAY
DELAY
(a)
(b) (d)
a) Ion beam source in combination with a 100 k eV accelatorb) Beam chopping systemc) Target on a 3-axis goniometerd) TOF energy analyzer located at scattering angle of 180o
(c)
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High Energy Ion ScatteringRutherford Backscattering Spectroscopy (RBS)
• Usually protons, 4He, and sometimes lithium ions are used as projectiles at backscattering angles of typically 150– 170◦.
• Different angles or different projectiles are used in special cases.
E0=1 and several MeV
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RBS-INSTRUMENTATION
1. An ion source, usually alpha particles (He2+ ions) or, less commonly, protons.2. A linear particle accelerator capable of accelerating incident ions to high
energies, usually in the range 1-3 MeV.3. A detector capable of measuring the energies of backscattered ions over some
range of angles.
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ISS Application
Coatings – LEIS can be used to: Detection and quantification of pinholes Root cause analysis of adhesion failure Quantification of initial growth Cleaning Surface modification
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Example: Detection of bad wetting of coated surface
With a normal ion beam the surface composition
of the coating is determined.
With a microbeam in the line scan mode the composition of the outer surface inside the pinholes
and the distribution of the pinholes is determined.
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ISS ApplicationOxygen membranes and Solid Oxide Fuel Cells (SOFC)
The performance of oxygen membranes and Solid Oxide Fuel Cells (SOFC) relies on the oxygen transport through an electrolyte.
A popular electrolyte is yttria stabilized zirconia (YSZ). Using LEIS it has been found that at the operation
temperature trace impurities in the YSZ segregate to the surface and block the oxygen diffusion. This impurity segregation was found to be typical for YSZ samples heated in oxygen at temperatures of 700°C or higher.
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YSZ after calcination
The main surface constituents are calcium- and hafniumoxide. Since there is no Y or Zr peak, these elements are not present in the outer surface. The strong increase in the background at energies below 2700 eV demonstrates that the 2nd and deeper layers do consist of yttria and zirconia.
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ADVANTAGES
Non-destructive depth profiling
Quantitative determination of amorphization and defect density without standards
Whole wafer analysis (150, 200, 300 mm) as well as irregular and large samples
Conductor and insulator analysis
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DISADVANTAGES
Large analysis area (~2 mm) Useful information limited to top ~1 μm of
samples
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APPLICATIONS
ideal use for:Crystallographic analysis of thin filmsCrystal damage/defect profilingDetermining percent amorphizationDetermining thickness of amorphous layers
Relevant industries DefenseSemiconductorTelecommunications