Ph. D. THESIS 2009

Part B
Fabricatio n o f 3 D Metallic Micro - an d n an o stru ctu re s
by Lase r In d u ced Pho to ch e m istry
1. Principle of nanostructuration by two-photon induced photochemistry
In the last decade, two-photon absorption (TPA) processes have been
intensively studied and improved for 1D, 2D and 3D micro/nanostructures
fabrication. The main aspect consists of a spatial confinement of the chemical
process in a small volume at the focal laser point. In spite of this advantage, the
first attempts have been done only in 1992 by Wu et all [1] who observed the
possibility of two-photon excitation by a femtosecond laser of some resins used
in microelectronics.
Five years later, in 1997, Maruro [2] have presented different threedimensional
structures obtained by this approach through a radical mechanism.
TPA technique has been applied succesfully for 3D polymer fabrication process
[3] but not for metals. For the first time Wu et all achieved to obtained threedimensional
metallic structures using a photographic-like approach within a
sol-gel dielectric matrix [4]. The 3D latent image was generated by a
femtosecond laser irradiation inside the photographic medium thanks to the use
of a high numerical aperture objective.
a a
Figure 1. Three-dimensional spiral structure produced within silver-doped solgel
materials by two-photon absorption (the latent image)
Continuous laser radiation does not induce the reduction, whereas
increasing the pulse width, in certain conditions of exposure, the rate of
reduction is reduced, suggesting the decisive role of multiphoton absorption
process.