**1. Introduction**

As the Internet of Things (IoT) continues to grow, networks are being built in which various devices share information with each other. At present, data from various devices is scattered and siloed, but it is predicted that in the latter half of the 2020s, hundreds of billions of devices will be connected to the Internet. In the second half of the 2020s, hundreds of billions of devices are expected to be connected to the Internet. A vast amount of data and information will be constantly being formed, but if the data is siloed, it will be impossible to share it. Therefore, it is necessary to create a wearable device that can constantly hold and share data. In order to achieve this, electronic devices with ubiquitous functions are expected to be realized as wearable devices, and flexible shapes, light weight, large area, and optically transparent functions are expected to be necessary.

Conductive oxide thin films such as indium-tin-oxide (ITO) and zinc oxide (ZnO) are expected to be the key semiconductor elements for wearable devices, but the manufacturing method to obtain conductive thin films with high electrical properties has not been established. ZnO thin films, which are introduced in this chapter, show great promise as photomechanical materials for photography [1, 2] and electrochemical and biosensor materials for various devices [3–7], and the applications of these thin films are diverse, including transparent electrodes, solar cells, and memory storage devices. When metal oxide thin films are used as optical films for liquid crystal displays and touch panels, both high transparency and low resistivity are required. At present, the aforementioned indium-tin oxide (ITO) and tin oxide are used in combination with other transparent materials. However, due to the low reserves of indium, it is expected to be depleted as a resource, and there is a need to search for alternative conductive materials, and research and development of alternative material technology has been conducted for many years. Research on ZnO has a history as long as that of ITO, and has produced many interesting results in recent years. ZnO has been grown by a number of methods, including sputtering [8–12], chemical vapor deposition [13], pulsed laser deposition [14], and wet coating [15]. each of these methods for growing ZnO introduces high conductance and high transparency properties into the film but high-performance ZnO films have yet to be fabricated using low-cost, simple processes. The low-cost process is characterized by a fast growth rate at low temperatures. However, ZnO fabrication techniques are sensitive to growth temperature, atmospheric pressure, and oxygen concentration, making it difficult to synthesize uniform ZnO films. In addition, the high dependence on the performance of the synthesis equipment has made it impossible to achieve a uniform crystal structure at low temperatures as well as a high growth rate. Therefore, we aimed to establish a simple, low-cost and stable fabrication process based on the wet coating method for growing ZnO films.

In this chapter, the author explains the need for a technological breakthrough to form oxide conductive thin films with stable conductivity on plastic films in order to utilize ZnO thin films as highly functional films for processing large amounts of data while maintaining their flexibility. The conductivity mechanism of oxide conductive materials has been inferred from indirect data such as the dependence of conductivity on oxygen partial pressure [1, 2]. In particular, ZnO, along with ITO, was first discovered as a semiconductor in the 1930s. Since then, its optical transparency in the visible range has been exploited, and research and development on its optical and electrical properties have been conducted for use as a transparent conductive film in memory devices, photovoltaics, transistors, and other applications. Furthermore, ZnO has a high carrier electron concentration, which is due to the potential presence of crystal defects caused by dopants and contaminants intervening in the crystal during ZnO synthesis. The problem of the electron mobility limit of ZnO has been clarified to some extent by a great deal of research and development into methods of ZnO synthesis and optimal selection of dopants. Although some progress has been made with ZnO thin films, they still do not have the high-performance characteristics to withstand the mega-data processing that will be required in IoT devices. The decrease in mobility is attributed to grain boundary scattering and ionized impurity scattering depending on the grain size, and the control mechanism of electrical properties differs depending on the synthesis form, such as thin film or nanowire.

**5**

**Figure 1.** *ZnO nanoparticles.*

*Nonthermal Crystalline Forming of Ceramic Nanoparticles by Non-Equilibrium Excitation…*

Therefore, the author focused on the "non-equilibrium reaction field" as a bottom-up architecture. Although many studies have been reported on the control of one-dimensional nanowire growth and the physical properties of the composites by moving the atomic and molecular groups constituting the oxide particles without heating, no technology has been found to create thin-film nanocomposite structures in a simple two-dimensional process. In this study, the author succeeded in discovering the basis of this technology by using an electron source that emits electrons uniformly in a plane. In addition, we will elucidate the interfacial phenomena and crosslinking mechanisms that occur during the bonding of metal oxide particles, and clarify the effects on the physical properties of the interface, mechanical properties, optical properties, and electronic structure. In addition, the author aims to create low-dimensional nanomaterials based on heterogeneous oxide-metal bonding with various dimensions, construct hybrid structures, control nanostructures, surfaces and interfaces, and control higher-order functional properties in metal-ceramics-semiconductor composites, and provide next-generation

Zinc nitrate (Zn(NO3)2) (high purity chemistry), ammonium carbonate ((NH4)2 CO3) (high purity chemistry), ethanol, and deionized water are used. Deionized water is purified to high purity water using a distillation vessel, and 1.0 M zinc nitrate and ammonium carbonate are dissolved in high purity water respectively. The zinc nitrate solution is dropped into the strongly stirred ammonium carbonate solution and reacts in a molar ratio of 1:1.5 (= Zn(NO3)2: (NH4)2CO3) to synthesize a white precipitate. The precipitate was filtered and cleaned several times with highpurity water and ethanol, and then dried at 100 °C in air for 6 hours to form the precursor of zinc oxide. The ZnO particles were then sintered at 400 °C for 4 hours in an electric furnace to obtain ZnO particles [16–18]. The obtained ZnO particles had a median diameter of 0.18 μmϕ, with 89% of the synthesized particles distrib-

uted between 0.12 and 0.25 μmϕ. The powder is represented in **Figure 1**.

*DOI: http://dx.doi.org/10.5772/intechopen.97037*

nanodevice components in a broad sense.

**2.1 Nanoscale ZnO particle synthesis**

**2. Experiment**

*Nonthermal Crystalline Forming of Ceramic Nanoparticles by Non-Equilibrium Excitation… DOI: http://dx.doi.org/10.5772/intechopen.97037*

Therefore, the author focused on the "non-equilibrium reaction field" as a bottom-up architecture. Although many studies have been reported on the control of one-dimensional nanowire growth and the physical properties of the composites by moving the atomic and molecular groups constituting the oxide particles without heating, no technology has been found to create thin-film nanocomposite structures in a simple two-dimensional process. In this study, the author succeeded in discovering the basis of this technology by using an electron source that emits electrons uniformly in a plane. In addition, we will elucidate the interfacial phenomena and crosslinking mechanisms that occur during the bonding of metal oxide particles, and clarify the effects on the physical properties of the interface, mechanical properties, optical properties, and electronic structure. In addition, the author aims to create low-dimensional nanomaterials based on heterogeneous oxide-metal bonding with various dimensions, construct hybrid structures, control nanostructures, surfaces and interfaces, and control higher-order functional properties in metal-ceramics-semiconductor composites, and provide next-generation nanodevice components in a broad sense.

#### **2. Experiment**

*Materials at the Nanoscale*

Therefore, it is necessary to create a wearable device that can constantly hold and share data. In order to achieve this, electronic devices with ubiquitous functions are expected to be realized as wearable devices, and flexible shapes, light weight, large area, and optically transparent functions are expected to be necessary. Conductive oxide thin films such as indium-tin-oxide (ITO) and zinc oxide (ZnO) are expected to be the key semiconductor elements for wearable devices, but the manufacturing method to obtain conductive thin films with high electrical properties has not been established. ZnO thin films, which are introduced in this chapter, show great promise as photomechanical materials for photography [1, 2] and electrochemical and biosensor materials for various devices [3–7], and the applications of these thin films are diverse, including transparent electrodes, solar cells, and memory storage devices. When metal oxide thin films are used as optical films for liquid crystal displays and touch panels, both high transparency and low resistivity are required. At present, the aforementioned indium-tin oxide (ITO) and tin oxide are used in combination with other transparent materials. However, due to the low reserves of indium, it is expected to be depleted as a resource, and there is a need to search for alternative conductive materials, and research and development of alternative material technology has been conducted for many years. Research on ZnO has a history as long as that of ITO, and has produced many interesting results in recent years. ZnO has been grown by a number of methods, including sputtering [8–12], chemical vapor deposition [13], pulsed laser deposition [14], and wet coating [15]. each of these methods for growing ZnO introduces high conductance and high transparency properties into the film but high-performance ZnO films have yet to be fabricated using low-cost, simple processes. The low-cost process is characterized by a fast growth rate at low temperatures. However, ZnO fabrication techniques are sensitive to growth temperature, atmospheric pressure, and oxygen concentration, making it difficult to synthesize uniform ZnO films. In addition, the high dependence on the performance of the synthesis equipment has made it impossible to achieve a uniform crystal structure at low temperatures as well as a high growth rate. Therefore, we aimed to establish a simple, low-cost and stable fabrication process based on the wet coating method for growing ZnO films.

In this chapter, the author explains the need for a technological breakthrough to form oxide conductive thin films with stable conductivity on plastic films in order to utilize ZnO thin films as highly functional films for processing large amounts of data while maintaining their flexibility. The conductivity mechanism of oxide conductive materials has been inferred from indirect data such as the dependence of conductivity on oxygen partial pressure [1, 2]. In particular, ZnO, along with ITO, was first discovered as a semiconductor in the 1930s. Since then, its optical transparency in the visible range has been exploited, and research and development on its optical and electrical properties have been conducted for use as a transparent conductive film in memory devices, photovoltaics, transistors, and other applications. Furthermore, ZnO has a high carrier electron concentration, which is due to the potential presence of crystal defects caused by dopants and contaminants intervening in the crystal during ZnO synthesis. The problem of the electron mobility limit of ZnO has been clarified to some extent by a great deal of research and development into methods of ZnO synthesis and optimal selection of dopants. Although some progress has been made with ZnO thin films, they still do not have the high-performance characteristics to withstand the mega-data processing that will be required in IoT devices. The decrease in mobility is attributed to grain boundary scattering and ionized impurity scattering depending on the grain size, and the control mechanism of electrical properties differs depending on the

**4**

synthesis form, such as thin film or nanowire.

#### **2.1 Nanoscale ZnO particle synthesis**

Zinc nitrate (Zn(NO3)2) (high purity chemistry), ammonium carbonate ((NH4)2 CO3) (high purity chemistry), ethanol, and deionized water are used. Deionized water is purified to high purity water using a distillation vessel, and 1.0 M zinc nitrate and ammonium carbonate are dissolved in high purity water respectively. The zinc nitrate solution is dropped into the strongly stirred ammonium carbonate solution and reacts in a molar ratio of 1:1.5 (= Zn(NO3)2: (NH4)2CO3) to synthesize a white precipitate. The precipitate was filtered and cleaned several times with highpurity water and ethanol, and then dried at 100 °C in air for 6 hours to form the precursor of zinc oxide. The ZnO particles were then sintered at 400 °C for 4 hours in an electric furnace to obtain ZnO particles [16–18]. The obtained ZnO particles had a median diameter of 0.18 μmϕ, with 89% of the synthesized particles distributed between 0.12 and 0.25 μmϕ. The powder is represented in **Figure 1**.

**Figure 1.** *ZnO nanoparticles.*
