Effect of heavy ion irradiation on materials

1. Swift Heavy ion irradiation
Prof. V. Krishnakumar
Professor and Head
Department of Physics
Periyar University
Salem – 636 011, India

2. HHiigghh eenneerrggyy iioonn iirrrraaddiiaattiioonn--IImmppoorrttaannccee
 Energetic ion beams play a vital role in the field of
research in Materials Science.
 Energetic ions are suitable means for the modification
of the surface and the bulk structure of solids.
 All classes of materials can be modified and analyzed
with ion beam in order to know about the
improvements of their physico-chemical properties
such as electrical, electronic, optical, mechanical,
magnetic, catalytic structural and metallurgical etc.

3. When energetic ions passes through
matter,it looses its energy in two ways
Electronic energy loss due to inelastic collision
with electrons(Se)[Electronic stopping]
 Dominant at higher energies (few tens of MeV
and higher)-Swift heavy ion Irradiation(SHI)
Nuclear energy loss due to elastic collision with
atoms of the solid(Sn)[Nuclear stopping]
Dominant at low energies (few tens of KeV to
MeV)

4. • Low energy ions <2MeV – elastic
collision – nuclear energy loss
• High energy ions > 2MeV – Inelastic
collision – electronic energy loss -
SHI.

5. EElleeccttrroonniicc ssttooppppiinngg
 Interaction of heavily charged ions with
electrons of the target material through
Coulomb forces, produce track of ionization
and highly kinetic electrons along the path of
the primary ion - latent track (Se>Sth) – Sth
depends on the material - Electronic energy
loss.

6.  When SHI passes through the materials Se
increases with energy and mass of the ions. The
effect of Sn is very small( range of the particle >
sample thickness).
 The desirable defects can be generated in
materials by locking sufficient energy into the
lattice - favors huge possibilities in tailoring of
materials.

7. Energy loss can be varied by choosing proper
ions and doses.
This remarkable flexibility coupled with new
cluster beams provides new outlook in many
fields.
Ion implantation is a crucial method for dopant
incorporation in device fabrication which
produces lattice disorder – detrimental for device
performance.

8. Crystal defects due to electronic
stopping
• If the heat conductivity is low enough (insulators),
then the energy of the exited electrons is
transferred to the target atoms in the vicinity of the
ion trajectory. As a result crystal defects are
formed.
• This swift heavy ion collision displacement
damage manifests itself in the form of
1. Point defect (defect cluster) generation and
2. dislocation loop formation at the periphery of the
ion trajectory.
3. Disordered and even amorphous ion track cores.
4. High energy heavy ion collisions (elastic and
inelastic) in a variety of solids create radiation
damage on the target surface.

9. NNuucclleeaarr ssttooppppiinngg
 Causes damage and dislocation of nuclei from
their lattice sites due to elastic collisions
 Always produce lattice defects
(Interstitial atoms, anionic or cationic vacancies)
 Damage areas – modify material properties
 Ex: change of color of diamonds produce
interesting alloys

10. Nature of materials modification depends on
Properties of the target material
o Electrical
o Thermal
o Structural
Mass of the projectile ion
Irradiation parameters
o Ion energy
o Fluence rate (ion concentration)
o Ion species

11. DDiiffffeerreennccee ooff mmaatteerriiaallss mmooddiiffiiccaattiioonn bbyy
eenneerrggeettiicc iioonnss
LLooww eenneerrggyy iioonnss HHiigghh eenneerrggyy iioonnss
 Embedded into the material Not embedded into the
material (large
range)
 Modification due to cascade Modification due to
collision of impinging ions electronic excitation
 Modification in the Modification in the
presence of embedded ion absence of embedded ion
 Nuclear stopping Electronic stopping
 Produce point defects Columnar defects

12. Impacts of heavy ion irradiation
• Ion beams play a significant role in engineering
the properties of materials.
• To alter and tailor many materials properties like
electronic and optical
• Energetic ions are suitable means for the
modifications of the surface and the bulk
structure of solids
• Possible to create optical wave guides in organic
crystals.

13. Ion induced eeffffeeccttss oonn NNLLOO mmaatteerriiaallss
Irradiation of heavy ions is expected to bring
following changes
Formation of gray tracks (coloration) on the
irradiated samples of high fluences irrespective of ion
beam and its energy.
Efficient generation of harmonic frequencies requires a
non-linear medium with following desirable properties
High Thermal stability
Large transparency window
High optical damage threshold
High mechanical hardness

14. Due to these facts, wave guide structures can be obtained
Light guidance demands adjacent regions of different
refractive indices
Two methods to create wave guide structures
Heavy ion exchange- causes increased refractive
indices
MeV irradiation of light elements forms a layer of
reduced refractive index due to high nuclear energy
deposition

15.  This will increase the single mode spectral bandwidth
for efficient SHG in wave guiding lasers.
Modifications in the refractive index of the
materials on ion irradiation leads to the formation
of wave guides.
Formation of wave guides will guide to modify the
essential property of second harmonic generation,
which widens their scope in photonic and opto-electronic
applications.

16. Also, Post treatment after SHI irradiation into
insulator leads to the nano-cluster formation and
change of optical property.
Dielectric constant of a material is related to
polarizability (ionic, electronic, oriental and space
charge)of the material.
Disordering of the crystal lattice by ion
irradiation causes increase in dielectric constant

17. Electro-optic co-efficient is directly proportional
to dielectric constant of the material.
o Ion irradiation enhances the electro-optic co-efficient
of NLO crystals
o Irradiated crystals can be a good EO modulator
of light.
Ion irradiation also affects the transmittance
properties of crystals, hence, it is also expected
to influence the SHG property.