**2.2. Combinational pulsed laser deposition (CPLD)**

One simple approach to study a binary or ternary system is to map all the possible composi‐ tions of the phase diagram. Of course, one can synthesize and test one composition at a time, but the disadvantages are the large number of experiments and lots of wasted time. By using a multi‐target carousel holder and rhythmically changing the deposition targets during a PLD experiment or two laser beams that irradiate two targets at the same time, one can obtain alternating layers with different periodicities both vertically and horizontally, along the substrate surface (**Figure 12**) [62]. In a single CPLD experiment, thousands of different compositions can be synthesized on a substrate of a few square centimetres [10]. Different stoichiometries can give rise to a variety of different structures and properties. The feasibility and utility of this concept has been demonstrated in the discovery of a number of new materials with much improved physico‐chemical properties than the precursors [63–65]. **Figure 12** shows a schematic of a CPLD deposition experiment. The experimental set‐up can include two independent laser beams or a split laser beam that hits two targets alternatively or one target at a time, the targets being interchanged with the desired frequency via a mobile carousel.

### *2.2.1. Advantages of CPLD*


We give a practical example of IZO (indium‐zinc‐oxide) compositional libraries synthesized by CPLD [66–69]. Due to the reduced availability of indium, in order to minimize costs, Zn is used for partial replacement of this element. Normally, individual thin films should be synthesized by PLD for measuring their conductivity. By CPLD, we synthesise a library with hundreds of IZO compositions, identify the areas with high conductivity and then we assess the IZO composition using a punctual spectroscopic technique (laser induced breakdown spectroscopy‐LIBS). Thus, a significant reduction of time devoted to film deposition and individual analyses could be achieved. LIBS allows fast optical spectra recording and line identification with an excellent spatial resolution (the laser beam is focused at a spot of ≈100 μm diameter), in addition to minimal damage to the film [70, 71]. The quantitative LIBS measurement method, based on the calculation of the spectral radiance of plasma in local thermal equilibrium, was used to measure the Zn/ (In+Zn) ratio and its variation over the length of samples synthesized by CPLD.

based on nanostructured tungsten oxide [38, 39], CNx/Si thin heterostructures [40]; complex (As2S3)(100‐x)(AgI)x chalcogenide glass [41]; vanadium oxide thin films with various crystal structures [42]; tin oxide for detecting NO2 [43]; protective coatings and barriers (e.g., DLC [44], BN [45], TiN [46], ZrC [47], ZrN [48, 49], ZrC/TiN and ZrC/ZrN thin multi‐layers [50]; TiN biocompatible coatings (prostheses coatings [51–53]); particles for drug delivery [54]; antimicrobial coatings [55]; tissue engineering [56]; organic thin films, i.e., polymethylmeta‐ crylate (PMMA) [57–59]. For biosensor applications: CuO thin film for uric acid biosensor [60],

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

One simple approach to study a binary or ternary system is to map all the possible composi‐ tions of the phase diagram. Of course, one can synthesize and test one composition at a time, but the disadvantages are the large number of experiments and lots of wasted time. By using a multi‐target carousel holder and rhythmically changing the deposition targets during a PLD experiment or two laser beams that irradiate two targets at the same time, one can obtain alternating layers with different periodicities both vertically and horizontally, along the substrate surface (**Figure 12**) [62]. In a single CPLD experiment, thousands of different compositions can be synthesized on a substrate of a few square centimetres [10]. Different stoichiometries can give rise to a variety of different structures and properties. The feasibility and utility of this concept has been demonstrated in the discovery of a number of new materials with much improved physico‐chemical properties than the precursors [63–65]. **Figure 12** shows a schematic of a CPLD deposition experiment. The experimental set‐up can include two independent laser beams or a split laser beam that hits two targets alternatively or one target at a time, the targets being interchanged with the desired frequency via a mobile carousel.

**1.** Thin film libraries can be synthesized in relatively short time (minutes).

**2.** A large number of new binary or ternary compounds with different properties to study

**3.** By monitoring the number of laser pulses, one can control the deposition of materials at an atomic layer level. If targets of different nature are used, composite materials will be

We give a practical example of IZO (indium‐zinc‐oxide) compositional libraries synthesized by CPLD [66–69]. Due to the reduced availability of indium, in order to minimize costs, Zn is used for partial replacement of this element. Normally, individual thin films should be synthesized by PLD for measuring their conductivity. By CPLD, we synthesise a library with hundreds of IZO compositions, identify the areas with high conductivity and then we assess the IZO composition using a punctual spectroscopic technique (laser induced breakdown spectroscopy‐LIBS). Thus, a significant reduction of time devoted to film deposition and individual analyses could be achieved. LIBS allows fast optical spectra recording and line identification with an excellent spatial resolution (the laser beam is focused at a spot of ≈100

gold‐coating of silicon microcantilever for DNA biosensors [61].

**2.2. Combinational pulsed laser deposition (CPLD)**

*2.2.1. Advantages of CPLD*

can be obtained.

synthesized.

**Figure 12.** Schematic presentation of a CPLD experiment, along the line the plasmas overlap producing a composition‐ al library.

From the study of the obtained compositional libraries, optimum values of the optical transmittance higher than 85%, resistivity around (5–7) × 10−4 Ohm cm and mobility in the (45– 53) cm2 /(V s) range, were inferred.

**Figure 13.** Evolution of (a) In and Zn concentrations and (b) Zn/In ratio on the transversal axis. Twelve measurements were performed on a distance of 6 cm from border towards the centre of the sample (Reproduced with permission from Ref. [72]).

The LIBS measurements started from the border of the glass plate where Zn has the largest concentration, towards the centre of the sample, along the transversal axis [72]. At the border A (close to the ZnO target) the In/(In+Zn) ratio was of 0.40. The trend for this ratio is to increase continuously. Up to measurement 6 (corresponding to 3 cm towards the centre of the sample), it increases by 8%, that is, to a value of 0.44. The Zn decrease and the In increase are almost linear (**Figure 13a**), the overall In/(In + Zn) ratio increases when shifted towards the centre of the sample. From 3 to 6 cm (in respect with the centre of the sample), the ratio continues its ascendant trend to reach a value of 0.50 at the centre of the film.

In **Figure 13b**, the evolution of the In/(In+Zn) ratio is presented. Starting from the glass border towards the centre, an ascendant trend from 0.40 to 0.54 is observed. Along a distance of 6.5 cm, the In/(In + Zn) ratio increased by 26%. The results are very similar to the values obtained by EDS investigations on the same CPLD samples [73].
