basics sputtering, ion beam

1. Reference Paper: Ghosh, S.; Avasthi, D.K.; Som, T.; Tripathi, A.; Srivastava, S.K.; Gruner,
F.; Assmann, W.; Ion velocity, charge state and substrate dependent electronic sputtering of
fullerene, Nuclear Instruments and Methods in Physics Research B ,212, 2003, 431–435.

2. Layout of Presentation
Sputtering- Fundamental
Effect of Ion Velocity
Effect of Charge State
Effect of Substrate

3. What is
sputtering? Its Types
Basic Principle
Its need

4. The ejection of atoms from the surface of a material (the target) by
bombardment with energetic particles is called sputtering.
• Used to modify the properties of the materials.
• Use of solid targets makes it possible to control the type and composition
of the material
• Formation of alloy material.
• It avoids the use of complicated process chemistry.
Sputtering1
Usefulness2

5. Energetic ion when penetrates solid, it causes –
-electronic excitations
-nuclear collisions
Atoms emission from the surface occurs if the energy transfer in such collisions is
enough to overcome surface binding energy.
Sputter yield:
The average number of atoms
ejected from the target per
incident ion.
Depends on –
•ion incident angle
•energy of the ion
•masses of the ion and target atoms
•surface binding energy of atoms in
the target
Basic Principle3

6. Electronic
Sputtering
Nuclear
Sputtering
Potential
Sputtering
• Governed by the electronic energy loss process
• Governed by nuclear energy loss
• Material removal occurs due to atomic collision cascade
• Highly charged ion (HCI) has stored potential energy.
• HCI can be quite high and produce sputtering in Insulator
Types of Sputtering4

7. Electronic Sputtering
study in fullerene
Systematic study was done to see the effect of:
 Ion Velocity
 Charge state
 Substrate Dependence

8. Experimental Section
Fullerene films deposited by resistive heating evaporation technique
Thickness- 20 nm
To study ion velocity dependence:
• 130 MeV Ag11+
• 80 MeV Au6+
To study charge state effect:
Irradiation by 200 MeV Au 15+ and 32+ charge states.
To study substrate dependence:
Irradiation by 200 MeV Au15+ ion on substrate-
• Si (1 0 0)
• Borosilicate glass
Similar Se value in C60
1
2
3

9. ION VELOCITY DEPENDENCE1
Electronic sputtering yields-
Au- 1.8 x 104 atoms/ion (more decrease in C content)
Ag- 9.8 x103 atoms/ion
Au
Ag

10. Explanation
low incident ion velocity - higher
density of energy deposition
(in narrow cylindrical
zone around the ion path)
Damaged zone more extended in
case of Au (low velocity).
And electronic sputtering yield is
directly proportional to
the area of the ion damaged zone

11. CHARGE STATE DEPENDENCE2
Decrease of NC with fluence in both the cases appears to be of similar kind
200 MeV Au
Stopping power is
dependent on
charge state but
due to the
possibility of
equilibration of
the charge state
its effect becomes
minimal.

12. SUBSTRATE DEPENDENCE3
Electronic sputtering yields-
Si- 2.9 x 104 atoms/ion
Glass- 4.5 x104 atoms/ion (more decrease in C content)

13. Additional heat coming from the substrate will be higher in the case of glass
as compared to silicon.
Thermal spike generated in films is same
Due to ion passage- thermal spike is formed in the substrate (below the C60
film )
This temperature addition results in higher erosion.
Reason-
•Temperature in Si - smear out more efficiently (higher thermal conductivity,
nearly 40 times more)
Influencing energy confinement of the film and hence the
sputtering yield
•Poor crystallinity of glass (electron-phonon coupling strength will be stronger,
resulting in high temperature rise).
Explanation

14. Concluding Remarks
• Se is 1000 times more than Sn, attributing that the observed
loss of C from fullerene films is predominantly due to Se.
• On the basis of thermal spike mechanism-
Excitation energy of electrons of the material gets coupled to
the lattice via electron–phonon coupling mechanism
Results in rapid thermal spike (typically more than thousands of
Kelvin) is generated in the lattice.
It will cause vaporization of materials inside a very narrow zone
(nanodimensional) and that get released from the surface.

15. References-
 Avasthi, D.K.; Mehta, G.K.; Swift Heavy Ions
for Materials Engineering and Nanostructuring;
Springer Series in materials science, 2011, 145.