**6. Conclusions**

280 Recent Advances in Nanofabrication Techniques and Applications

The dependence of the holes diameter versus the depth at different fluences, obtained by AFM measurements, is showed in the figure 13c. As expected, with the decrease of the laser energy from the central zone to the edges of the irradiated area, the depth of the holes is decreasing. In the case of multilayer structures, the hole depth decrease depending on the laser fluence corresponds to the ablation of the first, second or third layer. This type of planar metal/dielectric interfaces with a selective distribution of layers can open new perspective in the excitation of propagating surface plasmons and, consequently, in creating

Laser Induced Forward Transfer (LIFT) represents a challenging technique to the conventional etching microfabrication techniques. It becomes particularly interesting when a very small quantity of material has to be deposited on a substrate. Many kinds of materials such as metallic films, semiconductors, polymers, or even biological material can be transferred (Thomas et al, 2007; Sanz et al, 2010; Colina et al, 2005). The material to be transferred is initially deposited in thin films on a transparent substrate named donor substrate, or "ribbon" (transparent at laser radiation used for LIFT process). Usually, but not necessarily, a very thin metallic layer is deposited as buffer between the donor substrate and the film to be transferred. The donor sample, is placed at a short distance, parallel to another acceptor substrate (virtually any material). The donor film is backward irradiated with a

The laser is focused on the donor thin film at the interface with the donor substrate. Then, a small amount of buffer material is ablated and transformed in gaseous faze. This gas expands pushing forward the rest of the material which is projected to the acceptor substrate. If the parameters are correctly chosen, the ejected material is deposited on the acceptor's surface. The role of the buffer layer is only to protect the material to be transferred and is used especially in the case of organic materials susceptible to be affected by a direct exposure to the laser beam. Otherwise, in absence of a buffer layer, the material itself can be vaporized at the interface with the donor substrate, the pressure of the created gas

transferring a small quantity of material from a substrate to another.

transducers for sensing of biomolecular recognition reactions.

**5. Femtosecond laser induced forward transfer** 

pulsed laser, like in figure 14.

Fig. 14. The schematic of LIFT principle.

Various experimental techniques for materials micro-processing based on ultra-short pulsed lasers are presented.

Direct femtosecond laser writing technique by two-photon photo-polymerization was used to produce microstructures in the volume of transparent materials. By this technique, photonic devices such as photonic crystals, optical couplers, diffractive elements, 3D structures for microfluidics, scaffolds for tissue engineering, and other MEMS can be fabricated.

Femtosecond laser ablation was used to produce 2D microstructures on different materials surface. Electronic devices, based on CRLH transmission lines having metamaterials characteristics in the tens-GHz frequency range, such as band-pass filters, antennas, and directional couplers were manufactured by combined photo-lithography and femtosecond laser ablation techniques. A microprinting method, based on laser induced forward transfer

Ultrashort Pulsed Lasers – Efficient Tools for Materials Micro-Processing 283

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of a small quantity of ablated material from a donor substrate to an acceptor substrate, was demonstrated.

Using self-assembled monolayers of colloidal micro-spheres on glass and metallic thin film substrates, nano-patterning was obtained by ultrashort pulse laser ablation in the nearsurface enhanced laser field irradiation regime. Formation of ordered areas of nano-holes in a multilayer structure was demonstrated by selective near-field laser ablation.

Ultrashort pulsed laser micro/nanostructures writing technique could be considered as an alternative to the classical techniques based on photo-lithography. New micro/nanoprocessing technologies can be developed by combining femtosecond laser writing techniques with already proved lithography techniques.
