Multiple disciplines converge in this insightful exploration of complex metal oxides and their functions and properties
Oxide Electronics delivers a broad and comprehensive exploration of complex metal oxides designed to meet the multidisciplinary needs of electrical and electronic engineers, physicists, and material scientists. The distinguished author eschews complex mathematics whenever possible and focuses on the physical and functional properties of metal oxides in each chapter.
Each of the sixteen chapters featured within the book begins with an abstract and an introduction to the topic, clear explanations are presented with graphical illustrations and relevant equations throughout the book. Numerous supporting references are included, and each chapter is self-contained, making them perfect for use both as a reference and as study material.
Readers will learn how and why the field of oxide electronics is a key area of research and exploitation in materials science, electrical engineering, and semiconductor physics. The book encompasses every application area where the functional and electronic properties of various genres of oxides are exploited. Readers will also learn from topics like:
* Thorough discussions of High-k gate oxide for silicon heterostructure MOSFET devices and semiconductor-dielectric interfaces
* An exploration of printable high-mobility transparent amorphous oxide semiconductors
* Treatments of graphene oxide electronics, magnetic oxides, ferroelectric oxides, and materials for spin electronics
* Examinations of the calcium aluminate binary compound, perovoksites for photovoltaics, and oxide 2Degs
* Analyses of various applications for oxide electronics, including data storage, microprocessors, biomedical devices, LCDs, photovoltaic cells, TFTs, and sensors
Perfect for researchers in semiconductor technology or working in materials science, electrical engineering, and physics, Oxide Electronics will also earn a place in the libraries of private industry researchers like device engineers working on electronic applications of oxide electronics. Engineers working on photovoltaics, sensors, or consumer electronics will also benefit from this book.
Graphene Oxide for Electronics
Fenghua Liu1, Lifeng Zhang2, Lijian Wang3, Binyuan Zhao3 and Weiping Wu1
1Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai, China
2School of Materials Science and Engineering, Shaanxi University of Science and Technology, Xi'an, Shaanxi, China
3School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, China
Graphene, a single layer or a few layers of sp2-hybridized graphitic carbon, has generated much attention both in scientific and technological fields due to its unique physical and chemical properties. As a conducting semimetal, graphene has attracted lots of interests for the research and applications of electronics. Mass preparation of graphene with controllable size and economic cost is still a key challenge in its application to electronic devices. Different synthesis methods of graphene leaded to its various properties. Since the first successful preparation of graphene using the 'scotch tape' method, a series of methods have been developed for the synthesis of graphene . A significant proportion of the graphene research has been realized by the graphene oxide (GO) and its reduced form, the reduced graphene oxide (rGO) as the raw materials.
Graphite oxide is a compound of carbon (C), oxygen (O), and hydrogen (H), and has been synthesized by Hummers' method in 1958 , using the chemical reaction between graphite, potassium permanganate (KMnO4), sodium nitrate (Na2NO3), and sulfuric acid (H2SO4). The one-molecule-thick or few-layer version of the substance graphite oxide is known as graphene oxide (GO). The GO is not conductive but can be reduced by chemical reactions, thermal treatment, or many other methods, forming conductive rGO (Figure 1.1) . So far, many methods have been well developed to synthesis GO and rGO, including the chemical reduction, the microwave method, the plasma method, the laser method, and the hydrothermal method. Other synthesis methods, such as chemical vapour deposition (CVD) method, arc discharge method, ball milling approach, solvent-assisted exfoliation, etc., were also devoted to develop high-quality graphene, although these synthesis methods all have some trade-offs in terms of high quality, high yield, and environmental friendliness.
Figure 1.1 The chemical structures of graphene, graphene oxide (GO), the reduced graphene oxide (rGO) and the conversion of graphene into GO and rGO via oxidation/reduction reactions.
Source: Reprinted with permission from ref.  Copyright 2018, Springer Nature.
1.2 Synthesis and Characterizations of Graphene Oxide
1.2.1 Chemical Reduction of Graphene Oxide (GO)
Chemical reduction of graphene oxide (GO) is a common method to low-cost synthesize graphene . Exfoliation of GO to individual GO sheets (Figure 1.2) could be chemically reduced to rGO, using, for instance, NaBH4 or hydrazine . However, the product has problems, such as aggregation and defects. Moreover, the generally used reducing agents, such as hydrazine or NaBH4, are toxic. However, it still remained a great challenge to readily and efficiently synthesis of high-quality graphene with higher conductivity and less defects. Recently, some emerging methods of producing graphene, such as microwave method, plasma method, and laser method, have attracted a lot of interest, which will be presented in the following sections.
1.2.2 Microwave Method
Microwave absorbs heat energy through the medium and conducts micro-gradient heating from inside the material, which is considered as a unique method for material synthesis. The strong microwave absorption capability of graphene oxide (GO) can quickly remove oxygen-containing functional groups and further exfoliates GO. This feature has a fatal temptation for the preparation of high-quality and pollution-free graphene. As early as in 2011, microwave method was employed by Zhu et al. to exfoliate GO . Through the subsequent activation of KOH, they prepared graphene with a high specific surface area (SSA) value of 3100?m2 g-1 and a high conductivity of 500?S m-1. Another example of utilization of microwaves is the exfoliation of graphite in molecularly engineered ionic liquids . It is supposed that the cation-p interactions can improve the affinity of graphene surfaces. The as-exfoliated graphene exhibited a high single-layer proportion. Besides, ID/IG value of 0.14 and C/O ratio of 30 are close to the values of the graphite precursor, indicating the excellent structural integrity.
Figure 1.2 AFM image of exfoliated graphene oxide (GO) sheets with three height profiles acquired in different locations.
Source: Reprinted with permission from ref.  Copyright 2007 Elsevier Ltd.
One of the challenges on producing GO and rGO is the use of the toxic chemicals, such as sulfuric acid and hydrazine hydrate. Lots of methods have been developed to synthesize rGO by green reduction methods, using hydroiodic acid (HI), citric acid, plant extracts, phytochemicals, or alternatively by thermal heating in the inert atmosphere. In 2016, Voiry et al. reported on the fabrication of high-quality graphene through the microwave reduction of GO . This result attracted much interest because they used a conventional microwave oven operated at 1000?W to rapidly and efficiently reduce GO nanosheets with ~50 µm size (Figure 1.3a). The higher-power microwave pulses locally and ultra-fast-heated GO up to several thousand degrees to thoroughly eliminate the oxygen functional groups and reorder the graphene basal plane. The XPS results (Figure 1.3b) suggest that microwave-reduced GO (MW-rGO) shows a negligible in-plane oxygen concentrations of ~4 at. %. This oxygen content is much lower than the theoretical value of rGO annealed at 1500 K . The Raman spectra of MW-rGO and other compared samples are shown in Figure 1.3c. The as-prepared MW-rGO exhibited highly ordered graphene-like Raman features with sharp and symmetrical 2D and G peaks and a very low ID/IG ratio (<0.1). It is also found that MW-rGO shows higher I2D/IG ratios and larger graphene domain sizes as compared with rGO and solution-exfoliated flakes (Figure 1.3d). Although microwave method has potential advantages in the efficient preparation of high-quality graphene, it should be noted that the yield is so low that scale-up fabrication of high-quality graphene remains a great challenge.
1.2.3 Plasma Method
Plasma etching may not be able to precisely control the microstructure of the product at the atomic level, and even may entail undefined structural disorders or defects of the products. However, as a simple and efficient method, plasma etching still was widely used for etching of carbon materials . Graphene was once prepared by unzipping of carbon nanotubes (CNTs) through plasma etching with poly(methyl methacrylate) (PMMA) films . Herein, PMMA protects CNTs as an etching mask during the etching process. The top side walls of CNTs were etched faster and removed by the plasma. For 10?seconds of Agron (Ar) plasma etching, 20% of the starting CNTs were converted into single- or few-layer graphene nanoribbons (GNRs) with ~10-20?nm width and 2?nm height. Pang et al. reported on the patterned GN synthesized by means of an oxygen-plasma etching approach from solution-processed GO films . They used low-cost aluminium as sacrificial metal and protective masks to remove the graphene regions not covered by the aluminium when the sample was exposed to oxygen plasma. They argued that oxygen-plasma etching of graphene film with sacrificial aluminium contact patterns is an effective method for accurately controlling the size of graphene electrodes. Wang and coworkers reported the preparation of graphene from the GO using a radio frequency (RF) dielectric barrier discharge plasma system with different plasma gas, such as O2, N2, and CH4 .
Figure 1.3 (a) SEM of GO nanosheets. (b) High-resolution XPS C1s spectra and (c) Raman spectra of MW-rGO and other compared samples. (d) Evolution of the I2D/IG ratio versus the crystal size (La).
Source: Reprinted with permission from ref.  Copyright 2016 The American Association for the Advancement of Science (AAAS).
1.2.4 Laser Method
The laser method for the fabrication of graphene has advantages over the conventional methods requiring high synthesis temperature or tedious post-treatments. Laser technologies enabled the process to be simpler and more compatible. Although this technology still faces the problem of large-scale production, it has been demonstrated to produce high-quality graphene. El-Kady et al. used a standard LightScribe DVD optical drive to carry out the direct laser reduction of GO films to GN with high electrical conductivity (1738?S m-1) and SSA (1520?m2 g-1), which can be used directly as supercapacitor electrodes without...