1. Role of swift heavy ion irradiation in
materials science
V.Krishnakumar
Department of Physics
Periyar University
Salem- 636 011
Tamil Nadu, India.
2. Use of heavy ions
This presentation is a short review of the results in the last
years.
The pelletron facility is available at Inter University
Accelerator Centre (IUAC), New Delhi , India.
Inter-University Accelerator Centre
(IUAC) is an autonomous
organization which provides
accelerator facilities to universities
for basic and applied research in
nuclear physics, atomic physics,
materials science biosciences and other
allied fields.
Inter-University Accelerator Centre
has a running Pelletron, a tandem Van
de graaf type accelerator.
A Linear accelerator is planned as a booster accelerator
3. 15 UD Pelletron facility @ IUAC
The Pelletron accelerator can be operated upto 15 MV of terminal potential
and can produce dc as well as pulsed beam of a variety of elements. The
pelletron has been operational since July 1991.
4. The 15 UD pelletron is a versatile, heavy ion
tandem type of electrostatic accelerator. In this
machine, negative ions are produced and
preaccelerated to ~300KeV in Ion Source and
injected into strong Electrical field inside an
accelerator tank filled with SF6 insulating gas.
At the centre of the tank is a terminal shell
which is maintained at a high voltage (~15
MV).The negative ions on traversing through
the accelerating tubes from the column top of
the tank to the positive terminal gets
accelerated.
On reaching the terminal they pass through a
stripper which removes some electrons from
the negative ions, thus transforming the
negative ions into positive ions.
5. These positive ions are then repelled away from the positively
charged terminal and are accelerated to ground potential to the
bottom of the tank. In this manner same terminal potential is used
twice to accelerate the ions.
On exiting from the tank, the ions are bent into horizontal plane by
analyzing magnet, which also select a particular beam of ion.
The switching magnet diverts the high energy ion beams into
various beam lines into the different experimental areas of the
beam hall. The entire machine is computer controlled and is
operated from the control room
6. ENERGETIC IONS BEAM IN MATERIALS SCIENCE
Materials Synthesis Materials
Modification
Materials
Characterization
10’s keV to MeV < MeV to Sn
dominates
> 10 MeV
Sn dominates
A few MeV 10’s to 100’s Mev
PIXE
NRA
RBS
Channeling
eV to a few kev
Doping
Implantation
Compound phase
IBM
IBAD
Plasma deposition
DCsputtering
Rf sputtering
Magnetron
Sputtering
ECR plasma based
deposition
ERDA
Channeling
Blocking
7. HHiigghh eenneerrggyy iioonn iirrrraaddiiaattiioonn--IImmppoorrttaannccee
Energetic ion beams play a vital role in the field of
research in Materials Science.
modification of the surface and the bulk structure of
solids – control over the specific properties
A trail of defects
point defects, defect
optical wave guides and wave
clusters, structural phase
guide lasers for tailoring the
transformation occurs
electro-optic and non-linear
In Semiconductors
optical properties of important
HTS
materials of modern optics.
CMR
Metallic targets
Polymers
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
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. 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] (dE/dx)e
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] (dE/dx)n
Dominant at low energies (few tens of KeV to MeV)
10. 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.
11. 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.
12. 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.
13. NNuucclleeaarr ssttooppppiinngg
Causes damage and dislocation of nuclei from
their lattice sites due to elastic collisions
Always produce lattice defects (permanent
atomic displacements - in the form of vacancy +
self-interstitial atom = Frenkel pair)
(Interstitial atoms, anionic or cationic vacancies)
Damage areas – modify material properties
Ex: change of color of diamonds produce
interesting alloys
14. Two main models:
- Thermal spike model : excited electrons rapidly transfer
energy to phonons. Very large energy (heat) deposition
leading to localized melting & rapid cooling ® high defect
densities or amorphization.
- Coulomb explosion model: large positive space charge
resulting from electronic excitation leads to strong atomic
repulsion, atomic displacements and a cylindrical shock
wave.
15. Nature of materials modification depends on
Properties of the target material
Electrical
Thermal
Structural
Mass of the projectile ion
Irradiation parameters
Ion energy
Fluence rate
Ion species
16. 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
17. The aim of the investigations
The physical mechanisms responsible for defect formation
(point defects, tracks)
The threshold energies of point defects, track and surface
defect formation.
The mechanism of amorphization (if there is any) in the ion
tracks.
The mechanisms of the annihilation of crystal defects during
irradiation.
- The types of crystal defects and their proportion depending
on the type and energy of the ion.
18. NNoonn--lliinneeaarr ooppttiiccss
Linear optics- Optical properties of a medium are
independent of intensity of light radiation
Non- linear phenomena- available from high
intensity lasers
Non-linear optical processes have led to
generation of frequencies that are not available
with the existing laser sources
Mathematically the NLO effect can be described
on the molecular scale by the following total
polarization
19. Ptot- Total polarization of the molecule.
m- the permanent dipole moment.
E- the electric field.
c(1) – linear polarizibility.
c(2), c(3) – first and second hyperpolarizibility co-efficients.
Possess the most important property of second
harmonic generation (frequency doubling).
Useful for the fabrication of tunable lasers,opto
electronic and photonic devices.
20. Issues rreellaatteedd ttoo nnoonn--lliinneeaarr ooppttiiccss
The frequency conversion processes include
Frequency doubling
Sum frequency generation (SFG)
Differential-frequency generation (DFG)
Optical parametric generation (OPG)
Electro-optic modulation(EOM)
21. OObbjjeeccttiivveess ooff oouurr wwoorrkk..
Growth of good quality non – linear optical crystals.
Characterization of crystals by applying various
vibrational, optical and fluorescence spectroscopic tools
before and after swift heavy ion irradiation.
These studies will help us to understand the
fundamental aspects of these materials and what
needs to be pursued vigorously in the exploitation of
their device applications.
22. 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
23. 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
24. 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.
25. 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
26. Electro-optic co-efficient is directly proportional
to dielectric constant of the material.
Ion irradiation enhances the electro-optic
co-efficient of NLO crystals
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.
27. Materials ttrriieedd bbyy iioonn iirrrraaddiiaattiioonn
Irradiation of heavy ions has been carried out in some of
the following NLO materials and arrived at better results
Aceto acetanilide
Potassium titanyl phosphate
Barium strontium borate
Para - hydroxy acetophenone
Para - hydroxy benzoate
Benzoyl glycine
Bismuth triborate
Ammonium dihydrogen phosphate
Potassium dihydrogen phosphate
28. STUDY OF THE DAMAGE PRODUCED IN
K [CS (NH2) 2] 4 BR ( KTTB) - A NONLINEAR OPTICAL SINGLE
CRYSTAL BY SWIFT HEAVY ION IRRADIATION
Metal coordinated semiorganic NLO crystals thiourea CS(NH2)2 –
organic ligand – dominant in NLO effect
Free thiourea is in a centrosymmetric Pbnm space group and
SHG inactive.
large dipole moment and its ability to form an extensive network
of hydrogen bonds
Substitutions that reduce the symmetry of thiourea molecule
enhance NLO properties
Forms coordinate bonds through sulphur.- Sulphur to metal
bonding
29. Selected ion beam
parameters
Used
Pelletron 15 UD @ IUAC ,
New Delhi
Ion beam Li3+
Energy 40 MeV
Fluence 1x1010 to 1x1012 ions/cm2
Current 1 pna
Electronic energy loss (Se) 0.4432 KeV/nm
Nuclear energy loss (Sn) 2.5 x 10-4 KeV/nm
HIVAC chamber Diameter 1.5 m
Vaccum in the chamber 3x10-6mbars
Justification
The transition metal ions like Li3+, have incomplete electronic d-shell ,
should affect the ion-solid interaction to a greater extent than non-transition
metal ions
They have promising effects of doping when it is added in the host solid.
30. Five-position water or liquid nitrogen
cooled sample holder is used for small
sample irradiations.
The surface of one side of the sample
holder is as large as 32 cm2.
The samples to be irradiated are fixed on
this surface by conductive glue.
During the irradiation the sample holder
is in vacuum better than 10-6 torr.
The ion current is measured by a Faraday
cup.
Sample Holder
31. Experimental
KBr + 4 CS (NH2) 2 ® K [CS (NH2) 2] 4 Br
Grown in saturated aqueous solution by slow
evaporation in mixed solvent Acetone & Water(1:1).
PH condition 4.25 , 2 to 3 weeks
32. Empirical formula K [CS (NH2) 2] 4Br
Formula Weight 422
Crystal: Color
Shape
Size
Transparent colorless
Rectangular
1X0.4x0.3 cm3
Crystal System Tetragonal
Space group P41
Unit cell parameters
a =7.28 Å, a = b = g = 90
°
b= 7.28 Å, c= 16.42 Å
Point group symmetry C V 2
(Å3): 870.233, Z : 2 4
Density 0.431 g/cm3
Diffractometer ENRAF NONIUS CAD 4
Radiation Mo Ka
Wavelength 0.71–0.73Å
Hygroscopicity Non- hygroscopic
U-V absorption (cut off) 350 nm
Hardness Good
Band gap 3.53 eV
Elements Calculate
d (%)
Experime
ntal (%)
Sulphur 34.87 30.33
Potassiu
10.65 9.24
m
Bromine 21.77 20.72
Structural and compositional analysis
EDAX
33. Comparison of free ligand thiourea and other metal bromide
complexes
Free
ligand
TUa
Cu(TU)6
Brb
2
Ni(TU)6B r2
b Co(TU)6 Br2
b
K(TU)4Br a Assignments
3384 3460 3400 3422 3571 n s (NH2) and nas(NH2)
3278 3300 3365 3383 3367 n s (NH2) and nas(NH2)
3175 3253 3279 3288 3263 n s (NH2) and nas(NH2)
3093 3180 3180 3200 3167 n s (NH2) and nas(NH2)
1617 1604 1617 1617 1625 d(N-H)
1472 1477 1483 1530 1468 n(N-C-N)
1413 1422 1440 1420 1429 r(NH2) n(C-N) n(C-S)
1388 1398 1422 1385
1083 1089 1089 1099 1091 r(NH2)n(C-N) n(C-S)
730 712 710 700 720 n(C-N) ,n(C-S)
a - present work
b -G.M.S. El-Bahy, B.A. Sayed El, A.A. Shabana, Vib. Spectrosc. 31 (2003) 101.
34. Photoluminescence
He- Cd Laser – 442 nm
520 nm p-p* transitions - metal to ligand molecules – defect
centre
Fluence increases – emission decreases and blue shifts - lattice
deformation – displacement of anion and cation
37. The dielectric constant decreases as frequency is increased and
almost saturated - governance of various polarization
mechanisms.
generally active at low frequencies and high temperature -
indicates the perfection of the crystals.
The increase in dielectric constant with increase in
temperature and fluence indicates increase in amorphization
induced by high-energy heavy ion irradiation from the trapping and
detrapping of the charge carriers under the influence of electric field
at defect sites
As fluence increases, amorphization increases which in turn
decrease the number of crystalline dipoles per unit volume are
available to enter into the relaxation process and the original
relaxation phase is suppressed because its combined
motion is obstructed by the appearance of amorphous phase.
Increase in DE – Electro optic modulator – can be
recommended
40. CONCLUSIONS
The defects produced due to irradiation have been studied
in detail by defect sensitive techniques like Photoluminescence
and optical absorption spectra.
The microhardness decreases which in turn increases the
crack length. It is attributed to the amorphization induced due to
irradiation.
Also increase in dielectric constant and decrease in
dielectric loss may be due to the disordering of crystal lattice by
ion beam. This is also due to the dominance of various
polarization mechanisms.
A notable increase in dielectric constant is the hallmark of
the electro-optic property of the irradiated crystals - fabrication
of electro-optic modulators using KTTB crystal.
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