Ph. D. THESIS 2009

Figure 5 shows the SEM image of a silver double wire, recorded at 1.0 μm
scale and 20000x magnification, which indicates a line width of almost 500 nm
and a distance between lines of 1.2 μm.
Taking in account that the distance between lines is 1.2 μm and the diameter of
the laser spot at the focal point is evaluated to 700 nm, we may point out that
the local thermal effect plays a decisive role among the shape of the metallic
features in the deposition process. The lack of deposition at the line center
suggested that thermal effect induced further the metallic particles ablation
after deposition process.
From this point of view the chemical system containing ammonium ferric
citrate as sensitizer and reducing agent reveals a limitation induced by the local
thermal effect that will generate the double wire and will decrease the purity of
silver structures.
3.6. TPA fabrication of 2D and 3D silvermicro/nanostructures
Metallic silver 2D and 3D structures have been fabricated using the
chemical system that contains silver nitrate dispersed into a PSS matrix.
When the laser is moved in the x-y plane of the sample we can fabricate lines.
As a result when the laser is not moved during the fabrication we obtain a dot
instead of a line. The photo-reduction of silver ions was performed within a 48
hours old thin film, obtained by spin-coating. The surface of a 2.5x2.5 cm
microscope slide was modified with polyimide in order to improve the
attachement of silver structure onto the surface during the fabrication [7]. The
2D structures were written using a 100xPH3 immersed-oil objectiv with 1.25
NA.
A dots network with a period of 5 m was designed using increasingly
exposure times from 1s to 7s, and powers ranging from 1 mW to 8 mW, at
0.5m/s and DT of 2 ms (Figure 6).
a b
Figure 6. Optical images recorded with a x100Ph3 oil-immersed objective
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