**4.1 Investigation of ZnO nanostructures with the effects of laser repetition rate and deposition temperatures**

The structure and properties of the transparent ZnO films deposited on glass substrates were then analyzed using X-ray Diffraction (XRD) as shown in **Figure 4** and confirmed the presence of hexagonal wurzite ZnO for the samples deposited at 300 °C, 450 °C and 600 °C [8].

#### **Figure 4.**

*XRD spectra of ZnO thin films (a) 10 Hz samples and (b) 5 Hz samples - (i) as deposited, (ii) at 150 °C, (iii) at 300 °C, (iv) at 450 °C and (v) at 600 °C.*

It is also confirmed by the card no. 80–0074 of the Joint Committee on Powder Diffraction Standards (JCPDS) [9]. The XRD results provide the wurzite hexagonal crystal structure for the sample deposited at the temperature from 300-450 °C. The high intensity (002) plane preferentially grows in thin films above 300 °C. The (002) peaks become intense if the substrate temperature is increased from 300 to 600 °C. The grain size of the polycrystalline film increased with increasing the substrate temperature while deposition. **Table 2** provides the details of the bandgap energy calculated from the UV transmission spectra of the sample at various temperatures such as 25 °C (as deposited), 150 °C, 300 °C, 450 °C and 600 °C samples.

The transmission spectra for 10 Hz and 5 Hz samples are shown in **Figure 5**. The ZnO thin films deposited at 10 Hz and 5 Hz shows an excellent transmittance and high transparency rate along with a decreasing energy bandgap as the temperature increases from as deposited sample at room temperature to 450 °C. The value of bandgap is estimated from fundamental absorption edge of the films. For

the direct transitions, the absorption coefficient is expressed by

$$\left(\alpha h\nu\right)^{2} = k\left(h\nu - E\_{\sharp}\right) \tag{1}$$

**51**

**Table 3.**

**Figure 5.**

*Binary Metal Oxides Thin Films Prepared from Pulsed Laser Deposition*

assigned to be the free exciton. It is also observed that at 600 °C the energy bandgap started to increase slightly. The bandgap energies obtained from Tauc-plot of opti-

*UV-Transmittance (T%) spectra at various deposition temperatures (a) Wavelength Vs T% of 10 Hz samples, (b) Tauc-plot of 10 Hz samples (c) Wavelength Vs T% of 5 Hz samples and (d) Tauc-plot of 5 Hz samples.*

**Figure 6** shows the FESEM images of the pulsed laser deposited with various thin film of molybdenum oxide. The sample deposited at 450 °C and using the O2 gas atmosphere, near the edges and unfilled region, hexagonal (100) nanotubes, along with neatly arranged orthorhombic (040) molybdenum trioxide (MoO3) structures is shown in **Figure 6a**. Followed with **Figure 6b** shows the sample

deposited at 450 °C using the O2 gas atmosphere, uniformly arranged orthorhombic (040) structures of the MoO3 seen. Then, **Figure 6c** shows the sample stored at

**Samples Eg at 10 Hz (eV) Eg at 5 Hz (eV)** As deposited 3.189 3.239 150 °C 3.165 3.198 300 °C 3.106 3.143 450 °C 3.073 3.083 600 °C 3.118 3.170

*DOI: http://dx.doi.org/10.5772/intechopen.96161*

cal transmittance are tabulated in **Table 3**.

**4.2 Investigation of MoO3 and MoO2 nanostructures**

*Bandgap energy obtained from Tauc plot of optical transmittance.*

where k is constant, Eg is the energy bandgap, ν is the frequency of the incident radiation and h is Planck's constant. Because ZnO has a large exciton binding energy of 60 meV, an obvious exciton effect will always appear in the absorption spectra of high-quality ZnO films. As the ZnO thin film quality improves, a pronounced exciton absorption peak located at 3.1–3.3 eV was observed. The UV band was


**Table 2.**

*Bandgap energy of the samples deposited at various temperatures obtained from UV transmission spectra.*

*Binary Metal Oxides Thin Films Prepared from Pulsed Laser Deposition DOI: http://dx.doi.org/10.5772/intechopen.96161*

**Figure 5.**

*Practical Applications of Laser Ablation*

*at 300 °C, (iv) at 450 °C and (v) at 600 °C.*

It is also confirmed by the card no. 80–0074 of the Joint Committee on Powder Diffraction Standards (JCPDS) [9]. The XRD results provide the wurzite hexagonal crystal structure for the sample deposited at the temperature from 300-450 °C. The high intensity (002) plane preferentially grows in thin films above 300 °C. The (002) peaks become intense if the substrate temperature is increased from 300 to 600 °C. The grain size of the polycrystalline film increased with increasing the substrate temperature while deposition. **Table 2** provides the details of the bandgap energy calculated from the UV transmission spectra of the sample at various temperatures such as 25 °C (as deposited), 150 °C, 300 °C, 450 °C and 600 °C samples. The transmission spectra for 10 Hz and 5 Hz samples are shown in **Figure 5**. The ZnO thin films deposited at 10 Hz and 5 Hz shows an excellent transmittance and high transparency rate along with a decreasing energy bandgap as the temperature increases from as deposited sample at room temperature to 450 °C. The value of bandgap is estimated from fundamental absorption edge of the films. For

*XRD spectra of ZnO thin films (a) 10 Hz samples and (b) 5 Hz samples - (i) as deposited, (ii) at 150 °C, (iii)* 

( ) ( ) <sup>2</sup>

where k is constant, Eg is the energy bandgap, ν is the frequency of the incident radiation and h is Planck's constant. Because ZnO has a large exciton binding energy of 60 meV, an obvious exciton effect will always appear in the absorption spectra of high-quality ZnO films. As the ZnO thin film quality improves, a pronounced exciton absorption peak located at 3.1–3.3 eV was observed. The UV band was

> **Bandgap energy (eV)**

As deposited 399 nm 3.209 400 nm 3.218 150 °C 395 nm 3.177 395 nm 3.177 300 °C 393 nm 3.161 394.8 nm 3.176 450 °C 393 nm 3.161 393.5 nm 3.165 600 °C 409 nm 3.290 394.3 nm 3.172

*Bandgap energy of the samples deposited at various temperatures obtained from UV transmission spectra.*

 ν

*h kh E* = − *<sup>g</sup>* (1)

**UV emission center at 5 Hz (nm)**

**Bandgap energy (eV)**

the direct transitions, the absorption coefficient is expressed by

**Samples UV emission center** 

**at 10 Hz (nm)**

αν

**50**

**Table 2.**

**Figure 4.**

*UV-Transmittance (T%) spectra at various deposition temperatures (a) Wavelength Vs T% of 10 Hz samples, (b) Tauc-plot of 10 Hz samples (c) Wavelength Vs T% of 5 Hz samples and (d) Tauc-plot of 5 Hz samples.*

assigned to be the free exciton. It is also observed that at 600 °C the energy bandgap started to increase slightly. The bandgap energies obtained from Tauc-plot of optical transmittance are tabulated in **Table 3**.
