*2.1.2. Advantages of thin film deposition via PLD*

when ablation was conducted with fs pulses. The smoothness of these film surfaces is a consequence of the removal of ablated material with reduced expulsion of melted particles [17].

10 Applications of Laser Ablation - Thin Film Deposition, Nanomaterial Synthesis and Surface Modification

**Figure 6.** SEM images of Mg thin films deposited by PLD in different regimes: ns (a) ps (b) and fs (c) (Reproduced with

The laser pulse fluence can be defined as the optical energy that is delivered to a selected area on the target. Therefore, the fluence can be varied by changing the laser energy or the dimen‐

The coupling of the laser energy to the target surface is dependent on pulse parameters (duration and energy profile), and target characteristics (surface roughness, porosity and density). The fusion and vaporization processes occur only when the laser beam intensity is higher that a *threshold value* defined as the minimal energy of the laser pulse per surface unit

**Figure 7.** Typical SEM micrographs of TiO2 nanoparticles deposited on carbon cloth substrate at a laser fluence of 5 (a)

For a fixed wavelength and a chosen material, the fluence on the target will have a major effect on the particulate size and density [1]. We present an example where in order to obtain a porous gas diffusion layer, TiO2 nanoparticles have been deposited at two different laser fluences on carbon

(b) respectively (Reproduced with permission from Ref. [20]).

permission from Ref. [17]).

*2.1.1.2.2. Influence of the laser fluence*

sion of the spot area on target.

that generates plasma ignition.

and 1 J/cm2

**1.** A major advantage of PLD is related to its large versatility, that is, by control of the deposition parameters, one can obtain thin films with a completely different morphology, structure and/or functionality [20].

We return again to our example of ZnO thin films synthesized by PLD in a vacuum or in oxygen ambient. Just by changing the ambient not only the aspect, but also the wettability behaviour of the films was completely different (**Figure 8**). The thin films were hydrophilic when deposited in an oxygen flux and superhydrophobic (157°) when synthesized in a vacuum. Different conditions changed the Zn and O arrangement in the crystal lattice that influenced the electrical behaviour of the surface [13, 21].


We provide an example with profiles of TiN films synthesized by PLD by applying to a TiN target 5,000, 10,000 or 20,000 laser pulses [24]. TiN is a hard material, quite difficult to ablate, so the thicknesses of films were quite low, even for a high number of applied pulses. A progressive increase of the TiN films thickness is evidenced in the profiles of **Figure 9**. Films synthesized with 5,000 pulses were of ~60 nm thickness, for 10,000 pulses the thickness was of ~86 nm, while for 20,000, it increased to ~133 nm.

**4.** Any type of material can be ablated, so the method is not limited to special classes of compounds.

Ceramic, metallic and organic materials have been deposited by PLD. An exhaustive list can be found in the subchapter 2.1.4.

**5.** Using a carousel system with targets of different compositions, multi‐layer films can be obtained. The combinations are endless and new structures with complementary prop‐ erties can be obtained.

**Figure 8.** Textile material partially coated with ZnO nanostructures: (a) hydrophobic nanoparticle deposited in vac‐ uum, (b) hydrophilic thin film deposited in 13 Pa oxygen flux, and (c) hydrophobic thin film deposited in vacuum. Inset (a) and (c): water droplet in static mode and the measured CA images were acquired with a EOS 50D digital cam‐ era (Canon).

**Figure 9.** Thickness profiles of TiN layers recorded by profilometry (Reproduced with permission from Ref. [24]).

**Figure 10.** SEM/EDX images recorded for ZrC/TiN multi‐layers deposited by PLD (Reproduced with permission from Ref. [26]).

A relevant case of multi‐structures ZrC/ZrN and ZrC/TiN is given for exemplification (**Figure 10**). The purpose of this research was to increase the hardness and the elastic modulus of protective coatings. Out of ZrC, ZrN, and TiN single layers, the best results were obtained in case of ZrC with a hardness of 27.6 GPa and a reduced modulus of 228 GPa [25]. For multi‐ structures, the hardness and reduced modulus increased to similar values between 32.4 and 33.2 GPa and between 251 and 270 GPa, respectively [26].
