IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research
IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research
IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research
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IGC<br />
<strong>Annual</strong> <strong>Report</strong> 2007<br />
VI.3. Synthesis and Characterisation of<br />
Nanostructured Tin Coatings By Reactive Pulsed<br />
Laser Deposition Technique<br />
Pulsed Laser Deposition (PLD)<br />
is a versatile technique to grow<br />
high quality nanostructured<br />
coatings <strong>for</strong> several<br />
technological applications.<br />
Reactive Pulsed Laser<br />
Deposition (RPLD) offers<br />
additional advantage of<br />
synthesizing transition metal<br />
oxides, nitrides and carbides<br />
with tailored stoichiometric<br />
composition from elemental<br />
metallic target circumventing<br />
the need to prepare highly<br />
dense ceramic targets. In this<br />
technique, an ultra high pure<br />
reactive gas like nitrogen is<br />
bled into the ultra high vacuum<br />
(10 -7 mbar) deposition<br />
chamber through a high<br />
conductance molecular leak<br />
valve. Interaction of nitrogen<br />
gas with highly energetic<br />
axisymmetric<br />
and<br />
supersonically expanding laser<br />
plume containing titanium<br />
vapour plasma produces TiN<br />
clusters ranging from 10-15 nm<br />
size. Impact of such clusters on<br />
a silicon substrate produces<br />
well adherent nanostructured<br />
TiN coatings. It is also possible<br />
to synthesize functionally<br />
gradient nitride coatings<br />
through control of partial<br />
pressure of nitrogen in the<br />
vacuum chamber which in turn<br />
decides the N/Ti ratio.<br />
In order to implement the<br />
above experimental philosophy,<br />
an UHV compatible RPLD setup<br />
was indigenously set up. A<br />
photograph of the<br />
facility is shown in<br />
Fig. 1. The PLD chamber was<br />
pumped by a turbomolecular<br />
pumping system to a base<br />
pressure of 10 -7 mbar. The all<br />
metal chamber contains<br />
necessary optically transparent<br />
view ports <strong>for</strong> the transmission<br />
of laser beam. A Q-switched<br />
Nd:YAG laser with a<br />
wavelength of 1064 nm,<br />
repetition rate of 10 Hz, pulse<br />
energy up to 900 mJ and pulse<br />
width of 7 ns was used <strong>for</strong><br />
executing ablation of high pure<br />
metallic target in a reactive<br />
environment obtained from<br />
mass flow controlled delivery of<br />
gases. In a typical experiment<br />
aimed at optimizing synthesis<br />
conditions <strong>for</strong> nano-structured<br />
functionally gradient TiN<br />
coating, 4 layers of TiN coating<br />
were grown sequentially on a<br />
silicon substrate kept at 473 K.<br />
For each TiN layer extending to<br />
a thickness of 100 nm, a<br />
distinct partial pressure of N 2<br />
was used. In successive<br />
advancing layers, a gradually<br />
Fig.1 Reactive Pulsed Laser Deposition facility <strong>for</strong> synthesis of multilayer<br />
hard coatings (Insert) A-RPLD in progress B-RPLD grown TiN film<br />
BASIC RESEARCH 149
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