Ph. D. THESIS 2009

Our goal is to develope a lasser asisted technique to fabricate continuous
and well defined gold nanostructures inspiring by the iron-based photographic
technique in gold and its photochemical process.
Taking in account that the process has been validated both in solution and in
the solid state, preliminary two-photon induced photoprecipitation experiments
have been performed.
4.3.1. PSS- matrix for gold microfabrication
The TPA iradiation of a gold salt aqueous solution can form gold nanoparticles,
insoluble in water, which aggregate short time after generation. On Figure 44
can be seen the optical image of two huge gold colloids obtained in a 0.1 M
gold salt solution, when irradiating by a femtosecond laser at 40 mW.
Figure 13. Optical image recorded in transmitted light for two huge gold colloids
generated in aqueous solution of gold salt at 40 mW.
The key point of our experiment was to increase the solution viscosity using
different matrices such as xanthane, polyethyleneoxide, gelatine, and poly (4styrenesulfonate
acid) as stabilizers. These compounds allow to controll the rate
of reduction and to keep the metallic deposition localized in the small volume
at the focal point during the laser action and after it stops. From this point of
view is required a hydrosoluble and relative chemical stable polymer host, good
electrons donor which allow an homogeneus dispersion of high gold salt
concentrations without phase separation in the solid state. In this respect we
chose the poly (4-styrenesulfonic acid), denoted PSS, which embodies all these
properties, as a system stabilizer.
Thus, it offers the possibility to fabricate continuous and well defined silver
nanostructures by two-photon absorption. Figure 14a) shows gold lines
fabricated by TPA at the same laser power when PSS matrix is added to the
previous gold salt aqueous solution.
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