Pulsed laser deposition of thin films HASNAIN JAVED BS HONS. DEPARTMENT OF PHYSICS UNIVERSITY OF GUJRAT, GUJRAT
What is thin film? A thin film is a layer of material ranging from fractions
of a nanometer to several micrometer (1 nm - µm) in thickness.
Thin film is used to modifyPhysical characteristics
Electrical conductivity Chemical inertnessChemical characteristicsdecoration
Thin Film Deposition
The act of applying thin film on a substrate. Transfer atoms from target to a vapour and
then deposite on a substrate
optics electricity computer magnetics Solar cells
Applications of thin films
Ways to deposit thin films
Chemical deposition Plating Chemical solution
deposition Spin coating Chemical vapor
deposition Atomic layer deposition
Physical deposition
Sputtering Pulse laser deposition
target
substrate
Evaporation
target
substrate
Chemical vapor deposition
Ar+
substrate
gas
Sputtering
Target:! (metals, semiconductors…)Laser: (UV, 10 ns)Vacuum: Atmospheres to ultrahigh vacuum or inert gas
Pulsed Laser DepositionWith the pulsed laser deposition (PLD) method, thin films are prepared by the ablation of one or more targets illuminated by a focused pulsed-laser beam.
Gas and ultra high vacume
Ultra high vacume In vacuum, the plume
does not expand unidirectionally
The ejected species diffuse in the plume and collide with each other, which leads to a rapid thermalization of the particle cloud.
Gas Ambient gas scatters and
attenuates the plume changing its spatial
distribution the deposition rate kinetic energy
distribution of the different species.
Process in PLD
The removal of atoms from the bulk material is done by vaporization of the bulk at the surface region in a state of non-equilibrium.
Thus transferring some of their energy to the lattice of the target.The surface of the target is then heated up and vaporized.
Creation of plasma
Laser Beam
e-
e-
e-
e-e-
e-
e-
solid
Cont…
Melting (tens of ns), Evaporation, Plasma Formation (microseconds), Resolidification
Dynamic of the plasma Material expands in a plasma parallel to the normal
vector of the target surface towards the substrate. The spatial distribution of the plume is dependent on the
background pressure inside the PLD chamber. The dependency of the plume shape on the pressure can be described by The vacuum stage, where the plume is very narrow and
forward directed; The intermediate region where a splitting of the high and
less energetic species can be observed
Deposition of the ablation material The high energetic species ablated from the target are
bombarding the substrate surface It may cause damage to the surface by sputtering off atoms from
the surface.
Nucleation and growth of the film
The nucleation process and growth kinetics of the film depend on several growth parameters including:
Laser parameters Surface temperature Substrate surface Background pressure
Types of deposited film
three-dimensional island growth
two-dimensional monolayer
growth of separate islands on top of a full monolayer
Conclusion· Flexible, easy to implement · Exact transfer of complicated materials · Variable growth rate · Atoms arrive in bunches, allowing for much more controlled
deposition· When compared to other thin film techniques (e.g. chemical
vapour deposition, sol-gel, sputtering, etc), PLD does not need expensive or corrosive precursors,large volume targets.
· Neither it need very high temperature and/or pressure