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Terahertz band, which corresponds to the energy of inter-molecular binding, is expected to enable us a non-labeling detection such as antigen-antibody binding. We aim to enhance the sensitivity by surface plasmon resonance (SPR) combined with the signal enhancement effect due to the selective resonant excitation of the specific binding. In this study, we have focused on the topological insulators. They enhance SPR in THz band and confirm the occurrence of localized surface plasmon resonance by using periodic microstructures of well crystallized and prefer oriented Bi 2 Se 3 thin films fabricated by a pulsed laser deposition. We also observed the avidin-biotin coupling by THz-SPR, which is the first experimental observation of biological material interactions through THz-SPR using topological insulator.

(Ga,Fe)Sb is a promising ferromagnetic semiconductor for practical spintronic device applications because its Curie temperature $({T}_{\mathrm{C}})$ is above room temperature. However, the origin of ferromagnetism with high ${T}_{\mathrm{C}}$ remains to be elucidated. Here, we use soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) to investigate the valence-band (VB) structure of $(\mathrm{G}{\mathrm{a}}_{0.95},\mathrm{F}{\mathrm{e}}_{0.05})\mathrm{Sb}$ including the $\mathrm{Fe}\text{\ensuremath{-}}3d$ impurity band (IB), to unveil the mechanism of ferromagnetism in (Ga,Fe)Sb. We find that the VB dispersion in $(\mathrm{G}{\mathrm{a}}_{0.95},\mathrm{F}{\mathrm{e}}_{0.05})\mathrm{Sb}$ observed by SX-ARPES is similar to that of GaSb, indicating that the doped Fe atoms hardly affect the band dispersion. The $\mathrm{Fe}\text{\ensuremath{-}}3d$ resonant ARPES spectra demonstrate that the $\mathrm{Fe}\text{\ensuremath{-}}3d$ IB crosses the Fermi level $({E}_{\mathrm{F}})$ and hybridizes with the VB of GaSb. These observations indicate that the VB structure of $(\mathrm{G}{\mathrm{a}}_{0.95},\mathrm{F}{\mathrm{e}}_{0.05})\mathrm{Sb}$ is consistent with that of the IB model which is based on double-exchange interaction between the localized $3d$ electrons of the magnetic impurities.

This paper demonstrates intrinsic spin-to-charge current conversion in a two-dimensional electron gas using an all-epitaxial single-crystal heterostructure of LaSrMnO${}_{3}$/ LaAlO${}_{3}$ (LAO)/ SrTiO${}_{3}$ (STO), known to suppress spin scattering. As temperature decreases to 20 K, the spin-to-charge conversion efficiency is enhanced. The authors complement their experiments with band-structure calculation that agree with the observations and predict further enhancement by controlling the density and relaxation time of the carriers.

The authors investigate the optically induced metallization of NbO2. The optically induced modulation is found to be a result of a combination of photo-carrier induced refractive index changes and photothermally induced changes in NbO2, providing a better understanding of the optically induced metallization of NbO2 needed to develop all-optical modulator devices.

We present in this work advanced results concerning heat shielding based on assembled sheets of In2O3:Sn nanoparticles (ITO-NP sheets) in terms of particle size and interparticle gap. We demonstrate that the oxide semiconductor nanoparticles are crucial to achieve required optical properties relevant to energy-saving applications. In the infrared (IR) range, strong electric-field (E-field) interactions between NPs are formed locally at narrow interparticle gaps. Changes in thickness and particle size greatly increase the magnitude and peak separation of the resonant reflectance, which widely covers the IR range. As a consequence, the size-dependent plasmonic properties contribute to high heat-shielding efficiency. As confirmed by electrodynamic simulations, plasmonic coupling results in these spectral changes due to three-dimensional E-field interactions along the in-plane and out-of-plane directions. Moreover, the resonant reflectance is tuned by mechanical stretchable strains, indicating one of the impo...

Stochastic resonance (SR) is a phenomenon wherein an information-carrying signal is enhanced via noise in a nonlinear system. This phenomenon enables living beings to adapt to noisy environments and use environmental noise to obtain useful information. A novel activation function of the echo state network (ESN) based on bistable SR is proposed in this study. Instead of using the tanh activation function—which is representative of the traditional threshold activation function—the bistable SR activation function is used to improve the noise adaptability of the ESN. Further, the proposed activation function provides a short-term memory (STM) ability that is not provided by the widely used threshold activation function, and thus, a physical reservoir can be designed using the proposed function. An STM task and a parity check task are used to verify the short-term memory and nonlinear ability of the bistable SR activation function. Further, two different prediction benchmarks prove that the proposed activation function can improve the noise adaptability of ESN. Finally, a visual recognition task is performed to demonstrate the potential of the SR activation function for physical reservoir computing.

Superparamagnetic tunnel junctions (STJs) are nanostructures with very low turnover barriers. The barrier height of an STJ is generally equal to the heat energy at room temperature; thus, it can oscillate automatically without external driving. Previous studies have shown that the randomness of an STJ can be driven by a subthreshold voltage. This synchronization can be adjusted using electrical noise, which is often considered as zero-field Gaussian white noise. However, the actual circuit and environment are inevitably associated with colored noise, which has not been considered previously. In this work, numerical simulations were performed to study the phase-locking characteristics of a single STJ with the aid of several typical types of colored noise. The results show that the phase-locked behavior of an STJ can be effectively enhanced by colored noise whose power spectral density per unit of bandwidth is proportional to its frequency. Meanwhile, colored noise whose power spectral density per unit of bandwidth and frequency are inversely proportional can suppress the synchronization of STJs by suppressing the increase in junction frequency.

The realization of ultra-low energy consumption spin wave device applications requires a material that can efficiently propagate the spin waves. Spinel-type ferrite is a promising insulator from the perspective of application in magnonic devices owing to its good crystal compatibility. In this study, thin films of spinel γ-Fe2−xAlxO3 (0 ≤ x ≤0.5) are fabricated on single-crystal MgO substrates through pulsed laser deposition. High crystalline quality and room temperature ferrimagnetism are observed in all the films. Spin wave propagation is observed in γ-Fe2−xAlxO3 films, and it is found that the spin-wave transmission properties significantly correlate with the crystallinity and magnetization of the films. The γ-Fe1.85Al0.15O3 thin film represents an excellent compromise between a sufficiently high spin-wave amplitude and long propagation distance. These results indicate that the γ-Fe2−xAlxO3 thin film is a highly promising candidate for application in spin-wave-based computing devices in the future.

Superparamagnetic tunnel junctions (SMTJs) are spintronic nanodevices that can oscillate spontaneously under the influence of thermal noise. Studies have proposed that SMTJs can be modeled as magnetic neurons by subjecting them to electrical Gaussian white noise and can be subsequently synchronized under subthreshold driving. Considering the non-Gaussian background noise in industrial applications, this study investigated the influence of levy noise on SMTJ subthreshold synchronization. The results revealed that levy noise with weak pulse characteristics can be used to promote the subthreshold synchronization of the SMTJs, whereas levy noise with enhanced pulse characteristics cannot be used. Under the same conditions, enhanced levy noise asymmetry is advantageous for achieving SMTJ synchronization under subthreshold driving.

A series of epitaxial Fe2−xTi1+xO5 (0 ≤ x ≤ 0.7) solid solution thin films was fabricated on SrTiO3 (100) substrates by pulsed laser deposition. A (230)-oriented single phase with an orthorhombic structure was obtained within a narrow growth temperature window (850–900 °C). Both the semiconducting Fe1.5Ti1.5O5 and the insulating Fe1.3Ti1.7O5, as n-type oxides, showed promising thermoelectric properties with giant Seebeck coefficients up to the mV/K level. The electrical conduction in the Fe1.5Ti1.5O5 film obeyed the Arrhenius law at 200–300 K but transitioned to three-dimensional variable range hopping at 120–180 K. Furthermore, at and above room temperature (∼400 K), all the films (x = 0, 0.3, 0.5, and 0.7) exhibited significant ferromagnetic behavior, which was closely dependent on the different ratios of Fe2+, Fe3+, and Ti4+ ions. These results potentially lay a solid foundation for future cost-effective spintronics applications of Fe2−xTi1+xO5 films as tunable ferromagnetic semiconductors.

The fabrication of highly-ordered nanostructures by self-organization is one of the greatest challenges in nano science. Herein, we report the formation of a self-organized nanostructure in the CoGa0.8Mn1.2O4 thin film through a thermal annealing treatment. The thin film as-deposited by pulsed laser deposition exhibits a single crystalline phase epitaxially oriented along the [0 0 1] direction the SrTiO3 [0 0 1] substrate. Post-annealing in air was found to promote crystalline phase separation into tetragonal and cubic phases driven by the Jahn–Teller effect resulting in the formation of the nano-zigzag pattern. The structural and magnetic properties of the nanostructured films strongly depend on the annealing time, which can be attributed to the inter-diffusion of Ga and Mn ions.

The measurement and control of hydroxide ion (OH−) concentration in solution are essential in industrial processes. However, no portable sensing method directly targeting OH− ion with low-cost has been reported till date. Herein, we demonstrate an electrical detection method for OH− concentration in solution based on impedance spectroscopy of hydroxyl ions (OH−) attached to amorphous InGaZnO4 (aIGZO) film surfaces. The systematic examination of impedance response reveals that the resistance component of impedance is sensitive to the OH− ions interaction with the film surface. Results of X-ray photoemission spectroscopy confirm that the change of the impedance property is directly attributed to the amount of hydroxyl radical on the film surface originated from OH− ions in the solution. The impedance behavior of the film upon interaction with OH− was reasonably described by the theoretical analysis of optical measurements based on a vacancy-dependent model. Developed by applying this mechanism as a reference application, an easy-to-use aIGZO thin film based resistance OH− sensor at room temperature shows superior sensitivity, reproducibility, and linearity in the alkali range. This study extends the understanding and usage of aIGZO thin film regarding surface-sensing for the detection of surface interaction and process involving chemical ions and species.

Strontium titanate (SrTiO

A major challenge in spin-based electronics is reducing power consumption for magnetization switching of ferromagnets, which is being implemented by injecting a large spin-polarized current. The alternative approach is to control the magnetic anisotropy (MA) of the ferromagnet by an electric field. However, the voltage-induced MA is too weak to deterministically switch the magnetization without an assisting magnetic field, and the strategy towards this goal remains elusive. Here, we demonstrate a new scheme of orbital-controlled magnetization switching (OCMS): A sharp change in the MA is induced when the Fermi level is moved between energy bands with different orbital symmetries. Using a ferromagnetic oxide interface, we show that OCMS can be used to achieve a deterministic and magnetic-field-free 90 degree-magnetization switching solely by applying an extremely small electric field of 0.05 V/nm with a negligibly small current density of 10^-2 A/cm^2. Our results highlight the huge potential of band engineering in ferromagnetic materials for efficient magnetization control.

The epidemiology of patients with traumatic brain injury (TBI) has changed dramatically over recent decades as a result of rapid advances in aging societies. We assessed the influence of age on outcomes of patients with TBI and sought to identify prognostic factors for in-hospital mortality of TBI among elderly patients.Using a nationwide database, we analyzed data from 5651 patients with TBI. Univariate analysis was conducted to compare patient demographics, neurologic status on admission, radiologic findings, systemic complication rates, length of hospital stay, in-hospital mortality, and home discharge rates between elderly and nonelderly groups. Multivariable analysis was conducted to determine prognostic factors for in-hospital mortality among elderly patients.Overall in-hospital mortality was significantly higher in elderly patients (12.8% vs. 19.3%; P0.001). In-hospital mortality of elderly patients with mild TBI increased significantly at7 days after admission, whereas that of elderly patients with moderate or severe TBI was significantly higher immediately after admission. Age (odds ratio [OR], 1.62; P = 0.024), male sex (OR, 1.30; P = 0.004), Japan Coma Scale score on admission (OR, 5.95, P0.001), and incidence of acute subdural hematoma (OR, 1.89; P0.001) were associated with in-hospital mortality in elderly patients with TBI.Elderly patients with TBI showed significantly higher in-hospital mortality. Delayed increases in in-hospital mortality were observed among elderly patients with mild TBI. Level of consciousness on admission was the strongest predictor of in-hospital mortality among elderly patients.

Performance improvement of a bi-layer tunneling field effect transistor (TFET) with a hetero tunneling junction composed of an oxide-semiconductor (OS) and a group-IV semiconductor is demonstrated. Improvement of the channel thickness uniformity by introducing an amorphous ZnSnO layer is effective for increasing ON current and high ON/OFF current ratio, and decreasing averaged sub-threshold swing. A guideline for material design in the bilayer TFETs is addressed, based on electrical characteristics including the temperature dependence.

We present a dynamic spin wave (SW) modulation technique using direct current (DC) to manipulate the magnetic properties of an ultralow-damping Y3Fe5O12 thin film. The microwave excitation and detection technique with two coplanar waveguide antenna arrangements on the Y3Fe5O12 (YIG) surface is used to characterize the SW. An additional platinum (Pt) stripe connected to a current source is integrated between the coplanar waveguide pair to demonstrate the SW resonant frequency and amplitude modulation by current induction. We selected a Pt stripe due to its significantly lower spin wave absorption property. The application of current through the Pt stripe generates local joule heating that modifies the magnetic properties of the YIG film. Temperature variation through local heating modifies the saturation magnetization of the YIG film, which, in turn, modulates the SW frequency. Moreover, the amplitude of the SW spectra is found to be tuned by the current amplitude. This phenomenon is mainly described by magnon–magnon scattering induced by the spin Seebeck effect in the case of local heating. Furthermore, the group velocity of the proposed device is also found to be responsive to the current, which has been explained by both magnon–magnon and magnon-phonon scattering.

In this study, lutetium iron garnet (Lu3Fe5O12; LuIG) thin films have been grown on Y3Al5O12 (1 1 1) substrates by a pulsed laser deposition and are co-substituted with strong magnetically anisotropic ions of Co2+ and nonmagnetic ones of Si4+. LuIG is a garnet-structured ferrimagnet with an exceptionally low Gilbert damping constant as 10−5. The substitution of Co2+ and Si4+ induces a chemical disorder and competing antiferromagnetic and ferromagnetic interactions, which induce a spin glass behavior. When the Co–Si substitution ratio is increased, a spin-freezing behavior is observed below the spin-freezing temperature TG = 190–220 K of the Lu3Fe4Co0.5Si0.5O12 film; this indicates the presence of a cluster glass phase. The film demonstrates a characteristic memory effects in the temperature range 120–180 K, which are below TG; this reveals the presence of a metastable magnetic state in the multi-valley energy landscape with shallow activation energy barriers. Ferromagnetic resonance measurements confirm increased perpendicular anisotropy energy induced by Co substitution and spin-wave characteristics including the inverse spin Hall effect voltage (VISHE). Lu3Fe5-2xCoxSixO12 films show an increase in damping and a decrease in VISHE at the cryogenic temperature, which are attributed to the impurity relaxation mechanism. Therefore, the Co- and Si-substituted films exhibit strong spin-wave damping at a low temperature, which reflects the spin-freezing dynamics of cluster glass behaviors.

Strontium titanate (SrTiO3 or STO) is important for oxide-based electronics as it serves as a standard substrate for a wide range of high-temperature superconducting cuprates, colossal magnetoresistive manganites, and multiferroics. Moreover, in its heterostructures with different materials, STO exhibits a broad spectrum of important physics such as superconductivity, magnetism, the quantum Hall effect, giant thermoelectric effect, and colossal ionic conductivity, most of which emerge in a two-dimensional (2D) electron gas (2DEG) formed at an STO interface. However, little is known about its counterpart system, a 2D hole gas (2DHG) at the STO interface. Here, a simple way of realizing a 2DHG with an ultrahigh mobility of 24 000 cm2 V-1 s-1 is demonstrated using an interface between STO and a thin amorphous FeOy layer, made by depositing a sub-nanometer-thick Fe layer on an STO substrate at room temperature. This mobility is the highest among those reported for holes in oxides. The carrier type can be switched from p-type (2DHG) to n-type (2DEG) by controlling the Fe thickness. This unprecedented method of forming a 2DHG at an STO interface provides a pathway to unexplored hole-related physics in this system and enables extremely low-cost and high-speed oxide electronics.

We have evaluated the hydration properties of bio related materials by a terahertz spectroscopy. In particular, we have focused on ions and water-soluble polymers which have potential use for a basic understanding and practical applications in bio-medical fields. The dielectric loss of samples obtained by the terahertz spectroscopy is found to strongly depend on the molecular weight of the polymers and the density of the solution. We have revealed that the hydration number per monomer depends on the molecular weight of the polymer. Experimental results are evaluated by a machine learning analysis to discussed details of hydration.

Recently, biogas detection has been received much attention in order to identify the specific disease such as lung cancer. In this work, we focus on a molecular sieve effect of a zeolite to detect biogases in real time. Zeolite nanoparticles of a ZSM-5 type were chosen as a molecular screening of an acetone gas. We propose a new gas sensing method based on a surface plasmon resonance using a metal-zeolite hybrid structure.

Plasmon resonances on 2D nanosquare arrays and their temperature-dependent modulations are demonstrated using the insulator-to-metal transition (IMT) of VO2. A comparison between observed experimental trends and electromagnetic simulations reveals that the plasmon coupling is effective in the periodic 2D alignment of metallic VO2 nanosquares and results in a collective plasmon excitation. This plasmon excitation affects the optical responses of VO2 nanosquares in the mid-infrared (IR) range through reduction of plasmon damping in relation to the specific band structure of VO2. This preliminary understanding is important for the elucidation of temperature-dependent plasmon resonances. The IMT of VO2 produces temperature-dependent plasmon resonances with respect to spectral features. The electrodynamic simulations reveal that these phenomena are based on plasmon coupling in the nanosquare array when each nanosquare acts as a single metallic domain. The hysteretic plasmon resonances are derived from resonant coupling between metallic VO2 nanosquares via the IMT nature of VO2, which results in temperature-dependent changes in collective plasmon excitations in the nanosquare array.

Analysis of gases emitted from human skin and contained in human breath has received increasing attention in recent years for noninvasive clinical diagnoses and health checkups. Acetone emitted from human skin (skin acetone) should be a good indicator of fat metabolism, which is associated with diet and exercise. However, skin acetone is an analytically challenging target because it is emitted in very low concentrations. In the present study, zeolite was investigated for concentrating skin acetone for subsequent semiconductor-based analysis. The adsorption and desorption characteristics of five zeolites with different structures and those hydrophobicities were compared. A hydrophobic zeolite with relatively large pores (approximately 1.6 times larger than the acetone molecule diameter) was the best concentrator of skin acetone among the zeolites tested. The concentrator developed using zeolite was applied in a semiconductor-based gas sensor in a simulated mobile environment where the closed space was frequently collapsed to reflect the twisting and elastic movement of skin that would be encountered in a wearable device. These results could be used to develop a wearable analyzer for skin acetone, which would be a powerful tool for preventing and alleviating lifestyle-related diseases.

Amorphous InGaZnO4 (aIGZO) has been widely used as a transparent semiconductor. However, no research has been found yet applying aIGZO to biosensing. This paper examined the single strand DNA (ssDNA) immobilization on aIGZO by absorption with a comparison to ITO, which is the first step for many biosensing schemas. The DNA quantification by florescence intensity shows that the absorption capacity of aIGZO film to ssDNA is 6.7 times greater than that of ITO. XPS and contact angle analysis proved the high DNA absorption affinity on aIGZO film is related to its high effectiveness to OH− attachment. A feasible method to immobilized ssDNA on aIGZO thin film is evaluated in this paper, and consequently, enables a possible approach to apply aIGZO in biosensing.

Understanding and controlling the interfacial magnetic properties of ferromagnetic thin films are crucial for spintronic device applications. However, using conventional magnetometry, it is difficult to detect them separately from the bulk properties. Here, by utilizing tunneling anisotropic magnetoresistance in a single-barrier heterostructure composed of La0.6Sr0.4MnO3 (LSMO)/LaAlO3 (LAO)/Nb-doped SrTiO3 (001), we reveal the presence of a peculiar strong two-fold magnetic anisotropy (MA) along the [110]c direction at the LSMO/LAO interface, which is not observed in bulk LSMO. This MA shows unknown behavior that the easy magnetization axis rotates by 90° at an energy of 0.2 eV below the Fermi level in LSMO. We attribute this phenomenon to the transition between the eg and t2g bands at the LSMO interface. Our finding and approach to understanding the energy dependence of the MA demonstrate a new possibility of efficient control of the interfacial magnetic properties by controlling the band structures of oxide heterostructures.

A great deal of attention has been given to reducing the levels of infrared (IR) light entering automobiles and buildings in relation to energy-saving technology. The present use of thermal-shielding methods cuts IR radiation not by absorption, but through reflection in an effort to decrease re-radiation of heat indoors. Recent demands for thermal-shielding materials require visible and microwave transmissions with high heat-ray reflections. However, these films are unable to fully transmit electromagnetic waves in the microwave range, which are currently difficult to employ in window applications. Recently, IR plasmonic excitations on film surfaces have been observed on transparent oxide semiconductors. The sub-wavelength nanostructures are capable of supporting local surface plasmon resonances, which provide a novel concept of thermal-shielding. In this presentation, we employ experimental and theoretical approaches to report on the plasmonic properties of assembled films of ITO NPs. We show that the selective light reflections in the IR range are based on plasmon hybridizations due to field interactions induced at inter-nanoparticle gaps, and which are demonstrated by changes in the structural size of the NPs. We also focus our attention on the field interactions of .E-fields along the in-plane and out-of-plane directions in an effort to account for the matter by which the assembled films facilitate high IR reflectance. This study provides new insights for the enhancement of heat-insulating capability.

We demonstrated bandgap engineering of iron oxide (α-Fe2O3), which is one of the most promising photocatalysts for solar water splitting. It was found that V substitution and thermal annealing in air following film deposition efficiently narrow the bandgap of α-Fe2O3. The experimental results suggested that the observed decrease in the bandgap energy is due to the effective hybridization of the 3d t 2g orbitals of V5+ and Fe3+ at the conduction band minimum of V-substituted α-Fe2O3. Consequently, a significant enhancement in the photocurrent is observed using the Fe1.67V0.33O3-based photoelectrochemical cell over the wavelength range of 500–800 nm.

In this study, we experimentally characterize the electrical properties of a bilayer tunneling field effect transistor (TFET) with a heterotunneling junction composed of an oxide-semiconductor source and a group-IV-semiconductor channel in detail. Bilayer TFETs with a n-ZnO/p-Si or n-ZnO/p-Ge heterotunneling junction with type-II energy band alignment are fabricated by pulsed-laser deposition of a zinc oxide (ZnO) layer on Si or Ge with various impurity concentrations. The evidence of the TFET operation are examined through a comparison of the electrical characteristics with ZnO thin film transistors as well as the tunneling junction area dependence, which is important for clarifying the operating mechanism. The source material and its impurity concentration significantly affect the Id-Vg and Id-Vd characteristics of the bilayer TFETs, with reducing tunneling barrier height and tunneling distance. The influence of the source materials and doping concentrations is also studied by simulation. As a result, the minimum subthreshold swing (SS) of 71 mV/dec and the Ion/Ioff ratio of ∼6 × 108 have been achieved for n-ZnO/p-Si and n-ZnO/p-Ge TFETs, respectively, at room temperature. It is also found that the fabricated TFET shows weak measurement temperature dependencies of Ion and SS, which are expected for TFETs, with the extremely low off-state current in a fA/μm range. These characterizations of the electrical characteristics of the bilayer TFETs are important not only for a physical understanding of the operating mechanism but also for further improvement of the TFET performance.

Operation mechanisms and electrical characteristics of tunneling field-effect transistors (TFETs) employing a hetero tunneling junction by utilizing an n-type oxide-semiconductor (OS) and a p-type group-IV-semiconductor are comprehensibly analyzed. Gate-normal band-to-band tunneling (BTBT) has high potential for the superior TFET performance such as high on-state current and small sub-threshold swing (S.S.). Additionally, a hetero tunneling junction with type-II energy band alignment is promising to exponentially increase tunneling probability with keeping small off-state current. Therefore, in this study, we investigate the impact of key material and device parameters such as energy band alignment of source/channel regions and thickness of the OS channel layer or gate insulator based on technology computer aided design (TCAD) simulation. The gate-controlled uniform band bending along the source-drain direction realizes uniform BTBT in the entire region of the hetero tunneling junction. Also, the reduction of the tunneling barrier height, which is continuously controlled by the conduction band minimum of the OS-channel and the valence band maximum of the IV-source, is effective to increases on-state current and decrease S.S. value. On the other hand, the thicknesses of OS channel layer and gate insulator have strong influences on tunneling probability and threshold voltage. Therefore, the sub-threshold characteristics of TFETs are sensitive to non-uniformities in the tunneling junction such as channel thickness fluctuation and surface potential fluctuation at the metal-oxide-semiconductor (MOS) interfaces. These numerical analyses of the device operation are essentially important to understand the effects of key device parameters on the TFET performance and to realize the superior electrical performance.

A new sensor platform is realized by surface plasmon resonance on doped oxide semiconductors of In2O3:Sn layers (oxide-based SPR) in the near-infrared range. The detection sensitivity of oxide-based SPR is initially demonstrated by enhancement of the absorption band ascribed to molecular-vibrational modes in the NIR range, which indicates that the enhancing effects occur only when coupling is achieved between excitations of surface plasmons and molecular vibrations. These results are supported by theoretical analyses of electromagnetic field amplitudes on the layer surfaces. Further studies with SPR measurements of glucose-water solutions reveal that the precise detection sensitivity (S) of oxide-based SPR is 7576 nm RIU−1, which is consistent with the theoretically estimated sensitivity (S = 7447 nm RIU−1). The experimentally and theoretically obtained resolution in the refractive index is on the order of 10−5, which also supports the appearance of molecular-vibrational modes in the SPR spectra. Finally, it is found that the detection sensitivity of oxide-based SPR is close to that of Au metal-based SPR working in the visible range, a result that is discussed in relation to the spatial coherence and major characteristics of SP waves at the metal–water interfaces of In2O3:Sn and Au layers.

Iron oxides, which are also called ferrites, have been known to humans since ancient times and have been the subject of intensive research activity from fundamental as well as practical perspectives for a long time. One of the most advantageous properties of iron oxides is that they are chemically stable and nontoxic. In addition, Fe and O are earth-abundant elements [high Clarke numbers for Fe (4.7) and O (49.5)]. These features mean that the ferrites are suitable for applications in low cost, environmentally-friendly electronics. In this chapter, we examine some of the functional iron oxides and their heterostructures. First, we focus on the growth of FeO (wustite) epitaxial thin films, and their properties as p-type transparent semiconductors will be discussed. Next, we will consider α-Fe2O3 (hematite), which is well known as the main component of red rust. It is demonstrated that band engineering and control of the crystal growth direction of α-Fe2O3 are useful to enhance its photoelectrochemical properties for high efficiency water splitting using sunlight. The third topic is Fe3O4 (magnetite), which is known to be a ferromagnetic oxide semiconductor. The control of the carrier type in Fe3O4 and its possible application to spintronic devices will be discussed. Finally, we will focus on the spin-fluctuation system in iron oxides. The long-term potentiation with the photomemory effect is observed in a Si-substituted garnet ferrite with high temperature spin-glass-like properties, which mimics the pre- and post-synaptic potentials of biological systems.