**4.2 Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX)**

The EDX analysis (**Figure 13**) was used to determine the elemental composition of the TiO2 films. The results show that as the power used during the reactive magnetron sputtering process increases, there is a corresponding increase in the intensity of the Ti peak. This finding supports the expected result that an increase in the number of Ti-O bonds contributes to the growth of the TiO2 film. In other words, the higher the power used during the sputtering process, the greater the amount of titanium present in the film.

As the power and oxygen percentage during the reactive magnetron sputtering process are increased, the resulting TiO2 films exhibit a nanostructured morphology in certain areas, similar to that seen in Zone 1 of Thornton et al.'s model [46]. This morphology is primarily due to the adatoms on the surface of the growing film having low mobility and the "shadow" effect. A nanostructured thin film exhibits nano-scale surface features, typically ranging in size from a few nanometers to several hundred nanometers. These features can include nanopores, nanocrystals, nanotubes, or other nano-items that are engineered into the film's surface by adjusting the deposition

### **Figure 12.**

*Sequence of the ginger lily fiber preparation process for deposition of TiO2 films by reactive magnetron sputtering. (a) Plant harvest; (b) stem preparation; (c) extraction of long fibers; (d) film deposition apparatus.*

parameters, such as temperature, pressure, and substrate morphology. The structural and physical properties of the thin film can be controlled at the nanoscale. The nanostructured surface greatly increases the surface area of the coating and is well suited to photocatalytic applications due to its large surface area-to-volume ratio. The presence of pores, for example, increases the density of active sites with high accessibility of photons, but also facilitates diffusion and increases the adsorption capacity of pollutants. The size, shape, and distribution of the pores can be precisely controlled, allowing for the customization of the film's properties for specific applications.

In sputtering, the bombardment of the substrate surface with high-energy ions causes atoms to be ejected from the target and deposited onto the substrate surface. If the bombardment intensity is insufficient for film densification, the presence of pores can dominate the film's structure. When the deposited atoms do not have enough kinetic energy to overcome the surface diffusion and adhesion forces, they can accumulate on the substrate surface and form islands. These islands can coalesce and form a continuous film, but the presence of voids and pores between the islands can significantly affect the film's properties.

*TiO2 Nanocoatings on Natural Fibers by DC Reactive Magnetron Sputtering DOI: http://dx.doi.org/10.5772/intechopen.110673*

**Figure 13.**

*SEM/EDX of the TiO2 films deposited by DC reactive magnetron sputtering: (a) 50% O2–500 W, (b)75% O2–500 W, (c)50% O2–1000 W, (d)75% O2–1000 W.*

The presence of pores in sputtered films can have both positive and negative effects on their properties. For example, in some applications, such as sensing or photocatalysis, the large surface area-to-volume ratio provided by the pores can enhance the film's activity. On the other hand, in other applications, such as barrier coatings or electronic devices, the presence of pores can reduce the film's performance and durability.

The greater availability of oxygen (75%) in the chamber during sputtering causes more ions to be generated, leading to an increase in the number of atoms bombarding the surface of the growing film. This results in a denser film which can lead to the formation of ridges and depressions on the film's surface.

Overall, the effect of the increased oxygen concentration in the chamber during sputtering is to create films with a high roughness topography, which can be advantageous or disadvantageous depending on the intended application. The ability to control the oxygen concentration and other process parameters during sputtering is therefore important for achieving the desired film properties.

### **4.3 X-ray photoelectron spectroscopy (XPS)**

**Figure 14a** is shown the XPS survey spectra of the film 75% O2–1000 W. Carbon and oxygen lines dominate as expected because of the organic nature of the fiber. Intense Ti lines are also observed due to the TiO2 film on the fiber surface. Typically, the fiber surface area can be divided into two kinds of regions: those covered with TiO2 and those covered with organic material. These two regions are on different potentials, so that their reference binding energies are different. Nevertheless, the analysis can be performed by using the charge reference Ti 2p3/2 assumed to be at 458.5 eV, which is characteristic for TiO2 phase [47] and the C 1 s line, with the smallest binding energy corresponding to adventitious carbon at 284.8 eV. It is believed that Ti at the surface of a "TiOx material" is generally present as TiO2. Since in this case of study, the measured Ti 2p lines clearly show only a single phase, as can be seen from **Figure 14b**, which confirms that only TiO2 phase is present.

Deposition of TiO2 increase the amount of oxygen at the fiber surface. This fact can be interpreted in three ways: (a) the reactive atmosphere during the deposition process contribute to significant surface oxidation of the surface; (b) the reactive atmosphere in the magnetron chamber etches (probably chemically) the surface and "opens" oxygen-rich phases laying below the carbon-rich surface layer; and (c) after the magnetron sputtering the samples are able to adsorb more water which is bound strongly so that it remains at the surface in vacuum [18].

During the deposition process, the increase in oxygen content mainly occurs for two reasons: (1) deposition of the TiO2 film and (2) oxidation of the organic material. The latter occurs due to the presence of O–C–O and COOH groups in the fiber [18]. The XPS analysis in this study is related to the fitting of the C 1 s line, which have four contributions related to (a) C-C and C-H bonds, (b) C-OH and C-O-C bonds, (c) O-C-O bonds, and (d) COOH group [18]. From **Figure 14c**, C1 is attributed to the saturated C-C and C-H bonds. C2 at 287.0 eV is attributed to oxygen bound to two neighboring carbon atoms, forming a triangle. C3 at 288.7 eV can be attributed to carboxyl group (C=O)-OH, and C4 can be only attributed to –O–(C=O)–O– group [18].

### **4.4 Fourier transform infrared (FTIR) spectroscopy**

The FTIR spectra observed in **Figure 15** show the presence of TiO2 on the surface of the fibers. The peak observed between 800 and 450 cm<sup>1</sup> , at 670 cm<sup>1</sup> , is quite intense in the 75% O2–1000 W sample, being attributed to the Ti–O elongation, which is one of the characteristic peaks of the FTIR spectrum of TiO2. Švagelj et al. [48] in a study of TiO2 deposition on Al2O3 substrates, they reported the presence of the Ti–O elongation band, in the range of 640–700 cm<sup>1</sup> . This peak is associated with the

*TiO2 Nanocoatings on Natural Fibers by DC Reactive Magnetron Sputtering DOI: http://dx.doi.org/10.5772/intechopen.110673*

### **Figure 14.**

*(a) XPS survey spectrum from coated fiber 75% O2–1000 W, (b) high-resolution XPS spectrum of the line Ti 2p, and (c) high-resolution XPS spectrum of the line C 1 s taken from the pristine fiber. Adapted from [18].*

**Figure 15.** *FTIR spectra of the TiO2 films deposited by DC reactive magnetron sputtering in the 900–500 cm<sup>1</sup> . Adapted from [18].*

presence of O–Ti bonds in the TiO2 film, which, in turn, bond to the surface of natural fibers, possibly by hydrogen bonding or van der Waals forces.

### **4.5 X-ray diffraction (XRD)**

The structure of the deposited films is influenced by various deposition parameters, such as sputtering power, pressure, target-substrate distance, and the amount of reactive gases present in the deposition chamber.

The formation of a solid film during the sputtering process is affected by two factors: the heat generated by the substrate and the energy of the sputtered particles hitting the substrate. In situations where the substrate is not intentionally heated, it can still reach temperatures between 60 and 100°C due to the energy transfer from the sputtered particles. Normally, amorphous TiO2 films require annealing at temperatures above 300°C to crystallize. However, Sério et al. [10] observed that crystallization occurred in as-sputtered TiO2 thin films not because of the thermal energy, but rather due to the energy of the sputtered particles.

The sputtered particles could be from the target, such as atomic Ti, molecular TiO, molecular TiO2, and TiO2 clusters, as well as energetic electrons, negative ions (O), and neutrals reflected from the target (e.g., atoms of argon and oxygen) [10]. The films prepared with a sputtering power of 1000 W were found to be crystalline, likely due to the enhancement of plasma density in front of the substrate and an increase in the cluster growth rate with an augment in the sputtering power (**Figure 16**) [10].

*TiO2 Nanocoatings on Natural Fibers by DC Reactive Magnetron Sputtering DOI: http://dx.doi.org/10.5772/intechopen.110673*

### **Figure 16.**

*XRD patterns of as-sputtered TiO2 thin films deposited at 5% O2–500 W, 20% O2–1000 W, and 50% O2– 1000 W [10].*
