Ph. D. THESIS 2009
Ph. D. THESIS 2009
Ph. D. THESIS 2009
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In fact, this unusual phenomenon is caused by the collective action of multiple<br />
pulses.<br />
Nucleation<br />
10 mW 20 mW<br />
12<br />
40 mW<br />
Growth<br />
a b<br />
Nucleation<br />
40 mW<br />
Figure 17. Competition between (a)nucleation and (b) growth processes<br />
during the gold fabrication at different laser power<br />
4.3.3. The influence of the operating parameters<br />
The deposition of gold nanowires is performed at the active layersubstrate<br />
interface in order to recover the metallic deposit at the substrate surface after<br />
removing the unreacted matrix.<br />
The chemical reaction path of the salt-PSS-ferric citrate system is expected to<br />
be dependent on the initial molar ratios between reactants and on viscosity of<br />
solutions, on the reaction parameters, such as laser power and nature of the<br />
substrate used for the active layer deposition.<br />
4.3.3.1. The laser power<br />
The delivered power of femtosecond laser was varyed in order to establish how<br />
it can modify the characteristics of double nanowire. Typical laser powers are<br />
in the tens of milliwats, measured at the laser output.<br />
Under our experimental conditions, no gold lines were observed for laser<br />
powers below 10 mW.<br />
Higher laser powers, ranging from 30 to 40 mW, are required to initiate the<br />
process for other metals such as silver, copper or nickel. This can be attributed<br />
to a higher reactivity of gold (III) ions (oxidative power) when compared to<br />
others metallic ions.<br />
There were obtained similar structures as shape, but various as size, at two<br />
different powers of the laser (80 mW and 120 mW), the results suggesting that