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.

Layout of Presentation

Sputtering- Fundamental

Effect of Ion Velocity

Effect of Charge State

Effect of Substrate

What is

sputtering? Its Types

Basic Principle Its need

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.

Sputtering 1

Usefulness 2

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 Principle 3

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 Sputtering 4

Electronic Sputtering

study in fullerene

Systematic study was done to see the effect of:

Ion Velocity

Charge state

Substrate Dependence

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

ION VELOCITY DEPENDENCE 1

Electronic sputtering yields-

Au- 1.8 x 104 atoms/ion (more decrease in C content)

Ag- 9.8 x103 atoms/ion

Au

Ag

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

CHARGE STATE DEPENDENCE 2

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.

SUBSTRATE DEPENDENCE 3

Electronic sputtering yields-

Si- 2.9 x 104 atoms/ion

Glass- 4.5 x104 atoms/ion (more decrease in C content)

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

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.

References-

Avasthi, D.K.; Mehta, G.K.; Swift Heavy Ions

for Materials Engineering and Nanostructuring;

Springer Series in materials science, 2011, 145.