Novel Structured Metallic and Inorganic Materials

The development of amorphous alloys and metallic glasses is briefly overviewed, and their structure, glass-forming ability (GFA), and physical, chemical, mechanical and magnetic properties are introduced. In particular, the history of the development of amorphous alloys and metallic glasses and the difference between amorphous alloys and metallic glasses are summarized in this chapter.

In this chapter, metallic glasses and amorphous alloys especially developed for environmental and energy engineering, electronic engineering, and biomedical engineering by the authors’ research group are overviewed. As for the achievements related to the environmental and energy engineering field, the development of the following four types of materials are presented: (1) Ni–Cr–P–B glassy alloys for bipolar plates of PEM fuel cell, (2) Au–Cu–Si–Ag glassy alloy with an extremely low glass transition temperature Tg for nanoimprinting in an energy- and cost-efficient manner, (3) Ni–Nb–Zr amorphous alloys for hydrogen separation, and (4) porous metals prepared by dealloying glassy/amorphous alloys for environmental catalysts. Furthermore, bonding and joining methods for metallic glasses are also evaluated and summarized. Electronic transport properties of Ni–Nb–Zr amorphous alloys are shown. Besides, effects of hydrogen absorption on the electrical resistivity and their possibilities to the applications are discussed in the viewpoint of the electronic engineering. As for the biomedical engineering field, recent progress in the developments of these biomedical BMGs, which include bioinert materials such as Ti-based BMGs, Zr-based BMGs, Fe-based BMGs and biodegradable materials such as Mg-based BMGs, Ca-based BMGs, Zn-based BMGs, and Sr-based BMGs, is described. Moreover, several metallic glasses with low magnetic susceptibility, which are promised materials for development of high-performance MRI, are described in detail.

Titanium (Ti) and its alloys are currently getting much attention for structural biomaterials, because they are much advantageous as compared with other metallic biomaterials such as biomedical stainless steels and Co-based alloys, and their practical uses in implant devices are widely spreading. In this paper, types of Ti alloys for biomedical applications are first described. Pure Ti, (α + β)-type, and β-type Ti alloys for biomedical applications including general β-type Ti alloys, superelastic and shape-memory β-type Ti alloys, Young’s modulus self-adjustable β-type Ti alloys, and β-type Ti alloys for reconstructive implants are then described.

Magnetic properties of Mn-based alloys and compounds are rich in the variety of their magnetism because the magnetic moment of Mn varies from almost zero to 5 μB depending on its environment and its sign of exchange interaction changes with the distance between Mn atoms. Mn-based alloys and compounds with large magnetic anisotropy are recently being focused on with regard to their applications to perpendicular magnetic films and alternate materials of permanent magnets. Although it is generally thought that magnetic anisotropy originates from large spin–orbit interaction due to heavy elements, such as Pt, Pd, and rare earth elements, some Mn-based alloys and compounds indicate comparatively large magnetic anisotropy without such heavy elements. MnAlGe pseudo-two-dimensional compound with a Cu2Sb-type structure is thought to be a candidate for perpendicular magnetic films. Clarification of the mechanism of magnetic properties is needed to improve the characteristics desired for applications. MnBi has been considered to be an alternate material for permanent magnet; however, a problem exists in which a single phase of MnBi is difficult to obtain. Among some ingenious fabrication processes, it has been found that solid-state reaction in a magnetic field is effective to improve the reaction. The application of a magnetic field during the reaction enhances not only the fabrication of a single phase of MnBi but also the assembly of the crystal orientation.

In this chapter, three functional materials developed in IMR are introduced. The first one is nanoporous metals produced by dealloying Ti-based amorphous alloys. Its process and surface analyses are briefly described. Moreover, Zr-based Zr–Ti gradient material as a biocompatible material is introduced and its microstructure and mechanical properties are summarized. Finally, the Fe–Co alloy thin films were prepared to apply for energy harvesters and their magnetostriction is briefly summarized.

Ionic materials like oxides have a variety of crystal/atomic structures owing to the coexistence of long-range Coulomb interaction and short-range covalent bonds, which often produce natural nanostructures embedded in their crystal structures. Such structures and materials can be sources of unusual electronic structures and nonconventional materials properties and functions. This chapter reviews such exotic crystal structures in relation to their electronic structures and properties. It will be discussed for what applications such oxides can have advantages over the conventional functional materials such as Si.

Magnetic properties of materials relevant to the interface or surface provide a promising artificial material basis for the strategic design of spintronic devices. Giant magnetoresistance (GMR), spin accumulation, and spin transfer torque (STT), etc. are typical examples of such interface-related magnetic phenomena. Recent enormous and rapid growth of technology also allows to control magnetization orientation, magnetic phases, and spin polarization by manipulating the interface with an electric field without using either a magnetic field or an electric current. This leads to a drastic reduction in the power consumption. A full understanding of the interface-related magnetic phenomena is thus of crucial importance for the development of a major new direction of less energy dissipative spintronics. In this chapter, selected topics of interface-related magnetic phenomena and the fundamental physics underlying are described, placing a special emphasis on electric-field-induced strain transfer effect on the magnetic properties in multiferroic heterostructures.

Mechanical properties of ceramics, such as hardness, strength, and fracture toughness depend not only on electronic/crystal structures but also on their microstructures. The processing–property–microstructure relations and the principles of microstructural design will be critically reviewed in this section. The mechanical reliability of brittle ceramics is improved by decreasing the flaw size during the sintering process. The continuum theory of sintering is useful to find a way to suppress defects formation. The improvement of toughness is an alternative way to improve reliability. A novel nano/microstructure design was proposed to develop the strong and tough nanocrystalline ceramics recently.

Gas tungsten arc welding (GTAW) utilises an intense electric arc formed between a non-consumable tungsten electrode and the workpiece to generate controlled melting within the weld joint. Essentially, the arc can be used as if it was an extraordinarily hot flame. The use of a tungsten electrode and inert gas mixtures makes the process very clean. It is also a process with the potential to deliver relatively high-power densities to the workpiece, and so can be used on even the most refractory metals and alloys. In this chapter, principles of GTAW including energy transport, momentum transport and weld pool behaviour which are required to understand and control heat source properties of GTAW are reviewed in detail. Furthermore, future trends of applications of GTAW are also described.

This chapter describes characteristics of laser welding, features of main lasers used for welding, factors affecting weld penetration, laser welding phenomena including behavior of laser-induced plume, keyhole behavior, and melt flows in a molten pool during laser welding. It also refers to elucidation of formation of welding defects, preventive procedures of such defects, and examples of laser joining results of dissimilar metals and metal to plastic or CFRP, monitoring and adaptive control results during welding, and industrial applications as a recent trend for laser welding.

Several material designs using friction stir welding (FSW) are demonstrated. The FSW is solid-state processing techniques, which can be used for many processes such as welding and surface modification. In particular, this method is very useful for the material design of transformable materials such as steel and Ti alloys. When the FSW of steel is performed below the A1 point, the optimal microstructure consisting of very fine ferrite and globular cementite is obtained, regardless of the carbon content. When the FSW of Ti alloys is performed below the β transus, equiaxed grains of approximately 1–2 μm are obtained, and thus the mechanical properties, such as fatigue and toughness, are expected to improve.

Soldering is the major micro-joining process for assembling printed circuit boards of electronic products and is an important method of joining two metals without melting of base metals. In light of the remarkable progress in recent years in electronic products, the micro-joining process represented in soldering to incorporate devices and components into such products has become an essential technology. It can be truly said that soldering and electronics assembly technology have progressed with electronic products. In this chapter, the status of development and research of soldering and cutting edge joining process substituting for soldering are explained. In particular, in the first half, we will discuss development in Japan concerning lead-free solder, and the second half will look into research on materials with the potential to replace high-lead-containing solder for high-temperature applications.

This chapter describes the two typical examples of joining performance of structural and functional materials from the point of view of metallurgical characterization. At first, friction stir processing (FSP) is an effective grain refinement technique. FSP was conducted in the topmost 1-mm-thick layer of the steel welds, achieving increase of its fatigue strength and toughness. The FSP provided, for example, ultrafine equiaxial ferrite grains covered with thin layer cementite in a certain condition, based on characterization using transmission electron microscope. Second, a thin Ti-based self-formed barrier (SFB) formed by annealing a Cu(Ti) alloy film deposited on dielectrics at elevated temperature is one of the solutions to achieve low resistance and high reliability of Cu interconnects in ultra-large-scale integration devices. Identification of SFB was conducted using the electron diffraction, X-ray photoelectron spectroscopy, and Rutherford backscattering spectrometry techniques. That identification indicates that SFB consists of mainly amorphous Ti oxides, and its growth is concluded to be controlled by a thermally activated process.

Low-temperature and low-damage processing of materials is required for formation of advanced devices with inorganic/organic hybrid structure, including flexible electronics, photovoltaic cells, and biomaterials. For formation of high-quality organic/inorganic hybrid devices, low-temperature, and low-damage formation of high-quality inorganic functional layers (semiconductor and/or transparent conductive oxide) on organic materials is required and ultra-fine control of interface structure is significant for avoiding considerable degradation of the organic materials. In this chapter, low-temperature and low-damage processes with plasma process technology have been described on the basis of low-damage plasma production with low-inductance antenna (LIA) modules for sustaining inductively coupled radio-frequency discharges, which can provide high-density and low-damage plasmas.

Femtosecond laser-induced process, periodic nanostructures formation, for the creation of new functions on a titanium dioxide (TiO2) film is reviewed in this chapter. It has recently been reported that coating a TiO2 film on Ti plates may improve the biocompatibility of Ti. The periodic nanostructures have useful effects on the control of cell spreading. The scanning of femtosecond laser at wavelengths of 388 and 775 nm successfully produces periodic nanostructures on TiO2 film through the laser ablation process. The periodicity of nanostructures formed with those wavelengths are calculated using the surface plasmon polariton (SPP) model. The experimental results with those wavelengths were in the ranges of the calculated period, respectively. This suggests that the mechanism for the formation of periodic nanostructures on TiO2 film by femtosecond laser irradiation is due to the excitation of SPPs.

Uniform dispersion of unbundled carbon nanotubes (CNTs) was the bottleneck to convert their attractive properties to CNTs-reinforced composites. In this study, a solution ball milling (SBM) approach was developed to homogeneously disperse CNTs in Al matrix composites (AMCs). The process integrated strategies of solution coating, mechanical ball milling, and Al flake producing into a simple organic unity. The dispersion quality, crystal structure, and strengthening effect of CNTs in AMCs processed by SBM were investigated through scanning electron microscopy, transmission electron microscopy, Raman analysis, and tensile tests. Compared with previous methods, the SBM process was simple and effective to obtain a homogeneous CNT dispersion with a large aspect ratio and small CNT damages. The tensile strength of Al matrix was noticeably enhanced by CNT additions agreeing with the potential strengthening effect predicted by the load transfer mechanism. Shortened carbon nanotubes (CNT) were completely transformed to in situ Al4C3 nanorods by template reaction of CNT with Al matrix via powder metallurgy. Strong Al–Al4C3 interface, good distribution and complete single-crystal structure of Al4C3 nanorods, resulted in a remarkably improved strengthening effect in Al matrix composites. It concluded that in situ formed Al4C3 nanorod was a novel promising reinforcement for designing high-performance Al nanocomposites.

Powder processing technique supports the development of next-generation materials and products and thus plays an important role on numerous industries such as life science, energy, environment, and information. Drugs, cosmetics, electronic and magnetic materials, and phosphors as the application materials are widely used in our lives. Powder processing is located in the center of such advanced technologies. Here, we introduce the fabrication of functional materials by dry nanoparticle processing. The mechanically assisted particle bonding becomes a fundamental technique on the design and fabrication of functional materials. The particle bonding is achieved through the enhanced surface reactivity induced by mechanical energy, in addition to the intrinsic high surface reactivity of nanoparticles. Since this process does not require additional heat treatments, it is an environmentally friendly technique. Its applications for high-performance thermal insulation materials and electrodes of lithium-ion batteries and solid oxide fuel cells will be explained.

Stereolithographic additive manufacturing was developed to create metal and ceramic components with functionally modulated geometry using a computer-aided design, manufacturing, and evaluation. Micrometer-scale ceramic lattices are propagated spatially in the computer graphic space. Photosensitive liquid resins with ceramic nanoparticles are spread on a glass substrate using a mechanical knife edge, and two-dimensional (2D) images are drawn by fine pattern exposure or fast laser scanning to create a cross-sectional solid layer. After these layers are stacked, the obtained three-dimensional (3D) structures of the composite precursors are dewaxed and sintered. Ceramic and metallic glass photonic crystals with dendritic and magnetic micro-lattices can be fabricated to control electromagnetic waves over the terahertz frequency range. Subsequently, solid electrolyte dendrites of yttria-stabilized zirconia with spatially ordered porous structures could be processed for fuel cell miniaturization. Moreover, artificial bones of calcium phosphate with dendritic scaffold structures can be modeled to achieve excellent biological compatibilities.

Nanoporous metals (NPMs) consist of an interconnected backbone and nanosized pores. NPMs were prepared from parent alloys by chemical and electrochemical etching. The interconnected ligaments and nanostructured pores of NPMs are the origins of their novel properties. NP Au and NP Pd exhibited remarkable catalytic reactions compared with nanoparticle-based and supported catalysts. NP Au showed prominent optical properties in plasmonics and surface-enhanced Raman scattering (SERS).

Studies on hydrogen permeation of Ni–Nb–Zr amorphous alloys conducted by the author’s research group are overviewed. In the early stage of these studies, it was found that the hydrogen permeation coefficients of Pd-coated (Ni0.6Nb0.4)70Zr30 amorphous alloys were 1.3 × 10−8 mol m−1 s−1 Pa−1/2 at 673 K and that its crystallization temperature was 794 K. Furthermore, the mechanism of hydrogen permeation was discussed based on radial distribution function analysis. Hydrogen extraction and purification from methanol steam reformed gas were successfully conducted by using a Ni–Nb–Zr-based amorphous alloy membrane. The Nb content was then increased to increase the crystallization temperature of the Ni–Nb–Zr-based amorphous alloys. The crystallization temperatures of the Nb42Ni40Co18 and Nb42Ni32Co6Zr20 amorphous alloys were 913 K and 859 K, respectively. The hydrogen permeation coefficient of the Pd-coated Nb42Ni32Co6Zr20 amorphous alloy was found to be 1.14 × 10−8 mol m−1 s−1 Pa−1/2. This value is as high as that of the traditionally used Pd-based alloys. The possibility and challenges for applying amorphous alloys for hydrogen permeable membranes are discussed in this chapter.

This section focuses on the syntheses and characterization of composite porous materials for solid oxide fuel cell (SOFC) electrodes. Considerable efforts have been made to enlarge the triple phase boundary (TPB) where electrode, electrolyte, and pore phases meet, for reducing polarization loss in SOFC. Composite particles, which consist of electrode and electrolyte materials, have been prepared for this purpose, because their utilization is to improve the homogeneity of electrode and electrolyte particle distribution in SOFC electrodes. Among several wet-chemical routes for syntheses of the composite particles, coprecipitation method has been found a particular interest because of its simplicity, cost-effective, and easy scale-up capability. The emphasis will be therefore placed on the development of coprecipitation methods for enlarged TPB in SOFC electrodes.

This chapter describes the syntheses and characterization of proton-conductive hybrid membranes for the use at intermediate temperatures from 100 to 150 °C. The inorganic–organic hybrid membranes were synthesized from an unsaturated organoalkoxysilane and a vinylphosphonic acid derivative via copolymerization and acidic hydrolysis. The hybrid membranes were characterized by infrared spectroscopy, thermogravimetry, and indentation test. The proton conductivity was measured for various compositions of the membranes. The current–voltage curves for the membrane electrode assembly consisting of the hybrid membrane were evaluated.

This chapter introduces the synthesis of nanomaterials by solution plasma process (SPP). The SPP was used as a simple method for metal nanoparticles (NPs) synthesis, bimetallic NPs, and NPs incorporated in mesoporous silica. The SPP, which is a non-equilibrium plasma, can provide an extremely rapid reduction of a metal ion to the neutral form without using a reducing agent. Preferential oxidation (PROX) of CO is an important practical process to purify H2 for use in polymer electrolyte fuel cells. Pt NPs in mesoporous silica synthesized by the SPP give a high conversion rate at a lower temperature. Recently, we focused on developing the SPP for producing carbon materials containing heteroatom as oxygen reduction reaction (ORR) catalyst. The SPP method can produce low-cost carbon materials, in one-step process, with controllable structure.

Nanostructured metals and metal oxides are combined to produce advanced automobile catalysts for exhaust pollutant control. Catalytic emissions control was introduced in the form of noble metal-based three catalysts for the removal of exhaust gas pollutants of hydrocarbons (HC), carbon monoxide, and nitrogen oxides (NOx). Alumina as wash coat components provides a high and stable surface area for dispersion of the precious metals. Cerium oxides (ceria, CeO2) and ceria-zirconia (CeO2–ZrO2) as oxygen storage capacity components are typical non-metallic functional materials in the automotive catalysts. The catalysts component layer is some hundreds of micrometers thick and loaded on the substrate, usually made from cordierite ceramic and metallic alloys, which is called coat layer with alumina-based and precious metal and ceria-based ceramic composite. This section deals with developed metal oxide materials controlled with nanometer scale, their structures, and some current advances including the author’s achievement.

Many materials are used in the field of medicine and dentistry. In this section, current metallic, ceramic, and polymer materials in medicine and problems of them are explained and future materials to solve the problems are prospected. A hard biomaterial is defined first against soft biomaterial and the necessity of biosis–abiosis intelligent interface between hard materials and living tissue is demonstrated. Tissue compatibility of titanium and surface treatment for hard tissue compatibility including its current problems, basis of materials research sometimes left behind, and hard materials for regenerative medicine, are discussed. In addition, medical use of metals, ceramics, and polymers are finally explained.

Metallic materials are mainly employed for the orthopaedic and dental implants because of high strength and appropriate ductility. Further, the implants are used for long term so that high fatigue strength is one of the most important properties in practical use. In addition, these implants are exposed to human body fluid, which is composed of corrosive liquid for metallic materials. In the case of metallic materials, corrosion sometimes accelerates the fatigue failure, that is, corrosion fatigue. Therefore, the effect of testing environment on fatigue strength should be also considered. In this chapter, the mechanical properties such as tensile properties and fatigue properties of the representative metallic materials for biomedical applications such as stainless steels, cobalt–chromium alloys, and titanium alloys in air and simulated body fluid are reviewed.

In biomedical materials, chemical properties are as important as mechanical properties. None of these materials can avoid deterioration by chemical reaction in a living body owing to various physiological factors. In this chapter, corrosion reaction, which is a primary process of deterioration in metallic biomaterials, is discussed. First, several important factors that influence the corrosion reactions of metallic biomaterials in actual environments are introduced. In the latter part of this chapter, representative methods for evaluating corrosion reactions of metallic biomaterials that are frequently used in the biomedical material research field are introduced. The principles, procedures, and examples of experimental results of these testing methods based on both electrochemical and non-electrochemical systems are explained.

Biocompatibility and cytocompatibility are explained in the beginning of this section. This section provides a clear presentation of practical methods for in vitro biological evaluations of medical devices. Also, this section takes into consideration the mechanisms of cell behaviors including cell adhesion, proliferation, and differentiation on biomaterial surfaces.

Bulk metallic glasses (BMGs) are promising materials for biomedical applications due to their high corrosion resistance, excellent mechanical properties, and good biocompatibility. In this chapter, recent progress in the biocompatibility evaluations of the biomedical BMGs, in particular to biomedical Ti-based BMGs and Mg-based BMGs, are summarized. Some examples about the BMGs for applications to biomedical fields such as biomedical tools, biomedical devices, and biomedical implants are described in detail.

Young’s moduli of metallic biomaterials for implant devices such as artificial hip joints, bone plates, intramedullary rods, and rods for spinal fixation devices should be similar to that of cortical bone to prevent stress shielding [1].

An electret is a dielectric material that has quasi-permanently stable polarization and surface charges, and forms electric fields in its neighborhood. In this chapter, the basics of electrets are briefly introduced, and a representative electret for biomedical use is presented. The most important ceramics for biomedical applications, hydroxyapatite, can be polarized and become an electret. The properties of hydroxyapatite electrets and the application, i.e, an ability to promote bone regeneration, are reviewed.

Surface modification of metallic and inorganic materials with femtosecond laser irradiation for biomedical applications is reviewed in this chapter. Titanium (Ti) and titania (TiO2) were selected as the models for metallic and inorganic substrates, respectively. Femtosecond laser scanning successfully creates unique periodic surface topography on various materials through a one-step process. Present data showed that surface modification with a femtosecond laser had scale-independent effects on the surface chemical properties and biocompatibility. By controlling the unique periodic surface topography, surface wettability could be changed, and cell adhesion, proliferation, differentiation, calcification, and hemocompatibility could be regulated in vitro. A relative in vivo study also showed that this unique hierarchical periodic topography by femtosecond laser surface modification could also be effective regulating the biocompatibility of the metallic and inorganic material with bone tissues. It was revealed that surface modification with a femtosecond laser can be an effective technology to create unique hierarchical periodic surface topography on metallic and inorganic materials. Moreover, the scale of surface topography can be controlled with a one-step modification and has positive effects in controlling the biocompatibility, which is predicted to be very useful for further medical applications.

A sodium-contained amorphous titanium oxide layer having nano size mesh-like structure was fabricated on TiCuZrPd and TNTZ substrates by three different processes using alkaline solution. XPS result suggested that TiCuZrPd samples surface-modified by hydrothermal–electrochemical (HE) process exhibited the much less toxic Cu content than the original substrate composition, which is favorable for implant material. HE-processed TiCuZrPd sample had intermediated layer in which the structure was gradually changed to thickness direction with a widely diffused interface and it caused strong adhesion of hydroxyapatite layer. The nanomesh structure formed on TiCuZrPd substrate by HE process exhibited enough bioactivity in vitro test to form hydroxyapatite on their whole surface after immersing in SBF for 12 days. The surface chemical composition affects the apatite induction ability of TNTZ samples. The surface incorporation of fewer niobium species exhibited hydrophilic condition. The HE treated TNTZ sample at 90 °C for 2 h had a rough surface with fewer Nb content and it exhibited enough high bioactivity without forming any cracks or peeling.

Corrosion-resistant valve metals, such as Ti, Nb, Ta, and Zr, and their alloys have attracted much interest as bone substitutes in dental and orthopedic fields. However, in their pure form, these metals and alloys do not always encourage hard-tissue growth on their surface in living bodies. Surface characteristics always influence the biological response at the interface between the implants and body tissues. Titanium dioxide (TiO2) is known as an osteoconductive material and it has been shown to exhibit strong physicochemical fixation with living bone. In this paper, our experimental results using anodized TiO2 coatings are briefly outlined, including their in vivo evaluation. Based on these results, a comprehensive description of the factors that influence osteoconductivity with respect to the surface characteristics of the implants is presented, and a new approach to controlling the osteoconductivity of Ti and other valve metals and their alloys by using hydrothermal treatment is proposed. Furthermore, the hydrophilization of ceramics such as alumina and zirconia, and polymers such as polyetheretherketone (PEEK) and polyethersulfone (PES) is discussed. The protein adsorbability of the surface-treated samples and the osteoconductivity of the protein-adsorbed samples are also discussed.

Micro-arc oxidation (MAO) is one of the methods of surface modification of metal substrates and is a relatively simple procedure. The MAO surface is suitable for biomaterials because of its rough complex geometry and the ability to incorporate various ions. The conditions of MAO coatings can be optimized using some parameters, such as electrolytes and electrical factors. In this chapter, the principle of MAO is explained in the first section. The applications of MAO to biomedical fields are introduced in subsequent sections. The second section describes the efficacy on bioactivity of metallic biomaterials in vitro. The third section describes the methodology of in vivo evaluation of the osseointegration capability of titanium implants. Because direct integration of titanium implant to bone tissue is closely involved in bone formation around titanium surfaces without fibrous soft tissue, the evaluation of histological and three-dimensional morphology of bone tissue is absolutely imperative. Furthermore, the stability of titanium implants evaluated by mechanical test has an impact on the clinical situation.

Semiconductor electronics has utilized characteristics of electron charge: transportation of electrons and holes. Although an electron has a spin angular momentum, the electron spin had been ignored in electronic devices until the discovery of giant magnetoresistance (GMR) in 1988. The technology exploiting the characteristics of spin is called “Spin electronics” or “Spintronics”.

Field-effect transistor (FET)-based biosensors are used to detect charge density change as a result of biomolecular recognition on the gate of the transistor. To realize rapid detection and precise analysis of biomolecules using FET-based biosensors, design, and fabrication of chemical modifications at gate surface are important considerations. In this chapter, we showed fundamental working principles of a FET-based biosensor and described its application to the detection of DNA and electrically neutral biomolecules, and to the analysis of cell functions. Since the detection of electrically neutral molecules is one of challenges in electrical/electrochemical detection methods, we showed two possibilities employed stimuli-responsive polymer gel technique and aptamer-based chemistry for a FET-based biosensor. Furthermore, we indicated cell functional analysis results using ion-sensitive FET for a future alternative method of animal experiment. FET-based biosensors have potential advantages in miniaturization of the sensing device and parallel analysis. These advantages promote future medical care such as early diagnosis, telemedicine, and point-of-care test.

Amorphous oxide semiconductor (AOS) is now commercialized in many flat-panel displays. On the other hand, its electronic structures and defects are largely different from conventional covalent semiconductors such as Si. This chapter explains their origins and reviews the defects that have been known to date. Finally, we will discuss how to fabricate high-quality, stabile AOS.

This chapter describes a novel low-temperature Au–Au bonding method using nanoporous Au–Ag powder and vacuum ultraviolet irradiation in the presence of oxygen gas (VUV/O3) pretreatment. The nanoporous powder, which was fabricated by dealloying Ag–Au alloy sheet, was used to form the bump structure on the Au substrate by simple filling process, while an Au-coated Si substrate was used as the chip. The VUV/O3-treated bumps and chip were bonded under a bonding pressure of 20 MPa at 200 °C for 20 min in a vacuum atmosphere of 1 kPa. A ligament size of the nanoporous structure on powder surface was found to be grown dramatically during bonding process. The tensile strength reached 10.1 MPa which is 2.3 times higher than that without VUV/O3 treatment. This suggests that organic contaminants on each ligament surface were effectively removed by VUV/O3 treatment, and consequently, the diffusion of gold atoms in the nanoporous powder was significantly promoted to change into bulk structure. The proposed method will be highly a promising method for 3D-LSI and MEMS packaging. And, we investigated the composition, morphology, and dissolution behavior of an Au–Ag nanoporous structure formed by electrodeposition and dealloying. Formation of the films was carried out by changing the bath composition and the annealing temperature. The samples that were annealed at 50 °C before dealloying indicated a finer nanoporous structure. This finer nanoporous structure is connected to the highest bond strength of the evaluated samples.

Because carbon nanotube forest formed by surface decomposition of silicon carbide (CNT forest on SiC) is densely packed and vertically aligned with no entangle parts, it is useful to investigate the electrical properties of dense CNT forest. CNTs atomically bond to SiC substrates, causing good electrical contact for SiC power devices, where the Schottky barrier height is considerably low as ~0.4 eV. CNTs contact with each other in dense CNT forest and contact conductance of CNT/CNT interface can be evaluated as ~108 S cm−2. This value corresponds to the tunneling conductance between electron clouds of adjacent graphene sheets.