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Superconducting technologies are reviewed as the integration of various technologies by considering its research history, present status, future prospects, and the application to energy, transportation, and communications. Superconductivity involves a persistent current, perfect diamagnetism, and the Josephson effect, and is a unique phenomenon that cannot be imitated. After the discovery of superconductivity 100 years ago, as long as half a century was required to clarify its difficult mechanism. To date, the applications of superconductivity have been limited to specific purposes that require ultimate performance. The reason for this undoubtedly lies in the cooling penalty. In addition, to exploit the advantages of superconductivity, it has been necessary to wait until elaborated composite materials, whose fabrication requires nanotechnologies, reached the desired level. Spurred on by the discovery of high-temperature superconductivity, this year, we celebrate the 100th anniversary of the discovery of superconductivity, which is predicted to play a key role in realizing a sustainable global environment and in human society in the future.

The mechanism underlying the high-temperature (T_c) superconductivity of copper oxides has remained unelucidated and is one of the most difficult challenges of physics remaining in the 21st century. Various types of advanced spectroscopy have been employed to clarify the mechanism, resulting in the advancement of these techniques. Although the mechanism has not yet been completely clarified, the pseudogap phase, which always accompanies a superconducting phase, is now being considered as an electron state that plays a key role in the clarification of superconductivity.

Superconducting wires are important from the viewpoints of energy saving and the realization of a low-carbon society, because their applications in various types of electric power applications enable not only improved efficiency but also the reduction of size and weight owing to the fact that they can allow a large electric current density without resistance. Wires of Nb–Ti and Nb₃Sn metallic superconductors have conventionally been used in various magnets. The research and development of high-temperature Cu-oxide superconducting wires has been intensively carried out focusing on Bi- and Y-based oxides; recently, the development of long wires of these oxides has also been in progress, and their applications to a variety of power systems are being eagerly discussed. MgB₂, whose superconductivity was discovered in Japan in 2001, is also being studied with the aim of fabricating MgB₂ wires, and promising performance has been obtained. The research and development of superconducting wires using these materials is expected to achieve further progress and lead to their practical applications in the future.

One hundred years after the discovery of superconductivity, we are now facing a new era that demands an increase in the superconducting transition temperature T_c. In addition to copper-based superconductors, iron-based superconductors that have been discovered recently have been considered high-temperature superconductors. The similarity and difference between the two high-T_c systems are discussed on the basis of our recent theoretical and experimental understandings. While the pairing mechanism and non-Fermi liquid behaviors in transport properties may have a common origin between the two systems, the strengths of electron correlation are different: Cuprate is a doped Mott insulator, while iron pnictide is an itinerant system with a weak correlation. Pseudogap phenomena in hole-doped cuprates and their absence in electron-doped cuprate are regarded as a consequence of a strong correlation. Recent topics in cuprates about electron–hole asymmetry and pseudogap phenomenon are reviewed from a theoretical viewpoint. For iron pnictides, anisotropic behaviors in antiferromagnetic phases and new iron-selenide superconductors are discussed.

The recent discovery of iron-based superconductors has evoked enthusiasm for extensive research on these materials because they form the second high-temperature superconductor family after the copper oxide superconductors and impart an expectation for materials with a higher transition temperature (T_c). It has also been clarified that they have peculiar physical properties including an unconventional pairing mechanism and superconducting properties preferable for application such as a high upper critical field and small anisotropy. This paper reviews the research on thin films, Josephson junctions, and superconducting wires and tapes made from iron-based superconductors, which has been performed toward the realization of future applications. Though there are many technical hurdles toward the practical application of these materials, some promising features such as a high critical current density in thin films under high magnetic fields and advantageous grain boundary properties over copper oxides have been clarified.

Among a series of high-temperature superconducting materials that have been discovered to date, (Bi,Pb)₂Sr₂Ca₂Cu₃O_10-x is the best candidate for superconducting wires that are long with commercial productivity, and critical current performance. In particular, the controlled overpressure (CT-OP) sintering technique gave us a 100% density of (Bi,Pb)₂Sr₂Ca₂Cu₃O_10-x portion, which leads to robustness, increase in critical current, and mechanical tolerance. Many application prototypes are already verified and are being evaluated worldwide. Current leads for large magnets and magnetic billet heaters are already commercial products. Commercial applications for power cables, motors for ship propulsion and electric vehicles, and many kinds of magnets are promising in the near future.

There are high expectations for coated conductors in electric power applications such as superconducting magnetic energy storage (SMES) systems, power cables, and transformers owing to their ability to contribute to stabilizing and increasing the capacity of the electric power supply grid as well as to reducing CO₂ emission as a result of their high critical-current characteristics. Research and development has been performed on wires/tapes and electric power devices worldwide. The Materials and Power Applications of Coated Conductors (M-PACC) Project is a five-year national project in Japan started in 2008, supported by the Ministry of Economy, Trade and Industry (METI) and the New Energy and Industrial Technology Development Organization (NEDO), to develop both coated conductors that meet market requirements and basic technologies for the above-mentioned power applications using coated conductors. In this article, research and development results are reviewed and compared with the interim/final targets of the project, and future prospects are discussed.

We fabricated superconducting FeSe wires by the chemical-transformation powder-in-tube (PIT) process. The obvious correlation between annealing temperature and phase transformation was observed. Annealing above 500 °C produced wire-core transformation from hexagonal to tetragonal phase. Furthermore the hexagonal phase completely transformed into the tetragonal phase by annealing at 1000 °C. With increasing annealing temperature, the superconducting property was dramatically improved, associated with the evolution of the tetragonal phase.

The effect of Co doping on the supercoductivity of FeSe_0.4Te_0.6 single crystals is investigated. The superconducting transition temperature decreases linearly for Co doping at a rate of -0.75 K/(Co %). On the other hand, the increase in residual resistivity is less than 50 µΩ cm for 4% Co doping. These data are consistent with the interband scattering mechanism of superconductivity with the sign change (s_± symmetry).

We report the molecular beam epitaxy (MBE) growth of the iron-based superconductors, Ba_1-xK_xFe₂As₂ and SmFeAs(O,F). In the growth of Ba_1-xK_xFe₂As₂ films, the key to incorporating volatile K in films is low-temperature (≤350 °C) growth in reduced As flux. The highest T_c thus far obtained is T_c^on (T_c^end) = 38.0 K (35.8 K). In the growth of superconducting SmFeAs(O,F), we adopted two methods. In the first method, we first grew pristine SmFeAsO films, and subsequently introduced F into the films by diffusion from an overlayer of SmF₃. In the second method, we grew as-grown superconducting SmFeAs(O,F) films by coevaporating Sm, SmF₃, Fe, and As. Thus far, better results have been obtained by the first F diffusion method. The films prepared by F diffusion showed T_c^on (T_c^end) = 56.5 K (55.3 K), whereas the as-grown films showed T_c^on (T_c^end) = 51.5 K (48.0 K).

The crystallographic lattice constants and superconducting critical temperatures of FeSe_0.5Te_0.5 thin films grown on oxide substrates have been found to have no dependence on the in-plane lattice constants of the substrates. However, a correlation between various structural and transport properties of the films and the presence of oxygen penetration from the substrate into the film has been observed; i.e., oxygen penetration is suppressed in films with relatively high critical temperatures. Thus it is needed to identify appropriate substrates for the growth of iron chalcogenide superconducting thin films by considering the effects of the chemical properties of the substrate on the resulting structural and superconducting properties of the thin film. Upon characterization of the substrate materials used in our growth studies, the results strongly indicate that a "good" substrate has the following features: 1) its crystal structure does not have a vacancy that would permit electronegative elements to migrate, and 2) it is composed only of typical elements, in contrast to popularly used substrates that contain transition-metal elements.

The two most common types of MgB₂ conductor fabrication technique – in-situ and ex-situ – show increasing conflicts concerning the connectivity, an effective current-carrying cross-sectional area. An in-situ reaction yields a strong intergrain coupling with a low packing factor, while an ex-situ process using pre-reacted MgB₂ yields tightly packed grains, however, their coupling is much weaker. We studied the normal-state resistivity and microstructure of ex-situ MgB₂ bulks synthesized with varied heating conditions under ambient pressure. The samples heated at moderately high temperatures of ∼900 °C for a long period showed an increased packing factor, a larger intergrain contact area and a significantly decreased resistivity, all of which indicate the solid-state self-sintering of MgB₂. Consequently the connectivity of the sintered ex-situ samples exceeded the typical connectivity range 5–15% of the in-situ samples. Our results show self-sintering develops the superior connectivity potential of ex-situ MgB₂, though its intergrain coupling is not yet fulfilled, to provide a strong possibility of twice or even much higher connectivity in optimally sintered ex-situ MgB₂ than in in-situ MgB₂.

Superconducting Nd_1.85Ce_0.15CuO₄ (T_c^zero = 24 K) and Nd₂CuO₄ (T_c^zero = 25 K) thin films have been grown by molecular beam epitaxy and their magneto-transport and structural properties have been investigated. The as-grown films are insulators irrespective of the substitution level, and superconductivity is induced after the samples are treated by an annealing process under reducing atmospheres. Though the metallic conductivity is higher in the Ce⁴⁺ substituted sample, the superconducting properties are quite similar between Ce⁴⁺ substituted and substitution-free samples. A similar upper critical magnetic field as well as a similar superconducting transition temperature of Nd_1.85Ce_0.15CuO₄ and Nd₂CuO₄ shows that the addition of electrons merely influences the superconducting state. Consequently, the appearance of an antiferromagnetic Mott insulating state solely depends on the annealing process, not on the electron doping or cerium substitution level.

Tri-axial orientation under modulated rotation magnetic fields (MRFs) and the growth of single crystals in ambient pressure were demonstrated in various REBa₂Cu₄O₈ (RE124; RE, rare earth elements) compounds. RE124 crystals have been successfully grown for RE = Y, Sm, Eu, Gd, Dy, Ho, and Er. Optimal growth temperature regions for RE124 largely depended on the type of RE and became narrower in the case of lighter RE ions. By applying an MRF of 10 T, powders of all the grown RE124 were tri-axially oriented in epoxy resin at room temperature, and their orientation axes were clearly dependent on the type of RE ions in RE124. Furthermore, it was found from the changes in the degree of orientation under three different MRF conditions that tri-axial single-ion magnetic anisotropies of heavy RE³⁺ ions were highest among magnetic anisotropies generated by Cu–O networks and RE³⁺ ions. The appropriate choice of RE ions in RE-based cuprate superconductors enables the reduction of the magnetic field required for the production of bulk and thick films based on the magnetic orientation technique.

We study the proximity effect and charge transport in ferromagnet (F)/superconductor (S) and S/F/I/F/S junctions (where I is insulator) by taking into account simultaneously exchange field in F and spin-dependent interfacial phase shifts (SDIPS) at the F/S interface. We solve the Usadel equations using extended Kupriyanov–Lukichev boundary conditions which include SDIPS, where spin-independent part of tunneling conductance G_T and spin-dependent one G_φ coexist. The resulting local density of states (LDOS) in a ferromagnet depends both on the exchange energy E_ex and G_φ/G_T. We show that the magnitude of zero-temperature gap and the height of zero-energy LDOS have a non-monotonic dependence on G_φ/G_T. We also calculate Josephson current in S/F/I/F/S junctions and show that crossover from 0-state to π.

It is well known that the phenomenological balance equation between the Lorentz force and pinning force determines the electric current flow in superconductors in the mixed state. This equation is derived by using the variation principle for isolated or non-isolated flux line system. It might be questionable if this equation is applicable to practical cases, since it is in principle valid only for reversible states with respect to the flux motion. The statistical summation theory that derives the pinning force density from individual pinning potentials solves this problem. It describes the linear relationship between the pinning force density and the displacement of the flux line system in the reversible state and shows that the irreversible pinning force density is reached at the limit of reversible regime. As a result, the present theoretical treatment with existing theories generalizes the phenomenological critical state model to the critical state theory.

Spin Hall effect in a superconductor is theoretically studied. The spin injection from a ferromagnet into a superconductor creates quasiparticle spin and charge currents in SC, which generate charge and spin currents in the transverse direction to accumulate spin and charge imbalance near the side edges of a superconductor. A giant enhancement of spin and charge accumulation signals in the side jump and skew scattering mechanisms of the spin Hall effect is predicted to occur at low temperatures in the superconducting state.

Characteristic electromagnetic phenomena called longitudinal magnetic field effect are observed for a current-carrying superconductor in a parallel magnetic field. These phenomena and the mechanism of the longitudinal magnetic field effect are generally discussed from the viewpoint of flux motion in this article. This effect includes a significant enhancement of the critical current density from that in the transverse magnetic field, a deviation from Josephson's relation E= B×v for the induced electric field (B and v are the magnetic flux density and the velocity of flux lines), negative electric field in the resistive state, etc. These are attributed to the force-free torque to reduce the rotational shear in flux lines that appears in the force-free configuration and the resultant rotational flux motion. This is analogous to the electromagnetic phenomena in the transverse magnetic field in which the Lorentz force causes the flux motion. The similarity and difference of electromagnetic phenomena are discussed between the transverse and longitudinal magnetic field configurations.

Short-pulse tunneling spectroscopy on a time scale of 300 ns has been conducted using intrinsic Josephson junctions naturally built in the crystal structure of a slightly underdoped Bi₂Sr₂CaCu₂O_8+δ (Bi2212) by fabricating a very small and thin mesa of 6 nm in thickness and less than 5 µm in square width. The results are characterized by a pronounced superconducting peak at 79 meV accompanied by a broad pseudgap at a much higher energy of 125 meV, indicating discrete nature of both energy structures. The temperature rise due to self-heating in a small mesa is numerically calculated based on temperature-dependent thermal conductivity and specific heat for each constituent material. It is found that the temperature rise is less than 2 K for the present experiment, which reinforces that the tunneling spectra obtained represent the genuine superconducting properties of Bi2212.

Coherent and continuous radiation sources of the electromagnetic (EM) waves at terahertz (1 THz = 10¹² c/s) frequencies using a mesa structure fabricated from high temperature superconducting Bi₂Sr₂CaCu₂O_8+δ single crystals are described with a special emphasis on the physics of the radiation mechanism and the applications. After the intensive studies of many mesas fabricated with different conditions, it is revealed that the ac-Josephson effect works as a primary driving mechanism of the radiation and the cavity resonance needed for stronger radiation plays an additional role to the mechanism, although both are working together while radiating. A prototype of the imaging machine for multipurpose uses has successfully been developed.

The injection of Cooper pairs into a normal medium such as a semiconductor is known as the proximity effect at the superconductor/normal interface. We confirm this injection as well as the contribution of Cooper pairs to a drastic enhancement of inter-band optical transitions in semiconductor heterostructures. In this paper we investigate and clarify the relation of internal quantum efficiencies and radiative lifetimes in Cooper-pair light emitting diodes (CP-LEDs). A quantitative description of the dynamic photon generation processes is given, and the contribution of the Cooper-pair recombination relative to normal-electron recombination in CP-LEDs is discussed in detail.

Superconducting tunnel junction (STJ) array detectors with an asymmetric tunnel junction layer structure have been fabricated for the soft X-ray region between 100 eV and 1 keV. The asymmetric layer design was effective in solving the problem of double peak response to monochromatic X-rays, which is commonly observed in STJ detectors. The sensitive area was patterned by a lift-off technique that ensured no contamination on the top Nb electrode surface. The performance of a 100-pixel STJ array detector was investigated through fluorescent X-ray analysis of oxides and nitrides for the energy region of the K-lines of oxygen, nitrogen, and boron. The STJ array detector exhibited a high energy resolution of <15 eV, which cannot be achieved by semiconductor detectors, and an energy nonlinearity of <1%. It was demonstrated that the performance is suitable for fluorescence-yield X-ray absorption fine structure (XAFS) spectroscopy for light trace elements.

A method of AC waveform synthesis with quantum–mechanical accuracy has been developed on the basis of the Josephson effect in national metrology institutes, not only for its scientific interest but its potential benefit to industries. In this paper, we review the development of Josephson arbitrary waveform synthesizers based on the two types of Josephson junction array and their distinctive driving methods. We also discuss a new operation technique with multibit delta–sigma modulation and a thermometer code, which possibly enables the generation of glitch-free waveforms with high voltage levels. A Josephson junction array for this method has equally weighted branches that are operated by thermometer-coded bias current sources with multibit delta–sigma conversion.

We investigated the influence of ion-beam irradiation of the SiC(000) surface on the growth of carbon nanotubes (CNTs) by the SiC surface decomposition method. After an SiC(000) surface was irradiated by Ar⁺ ions at 1 keV with a dose of 4.5×10¹⁵ cm^-2 in an ultrahigh vacuum chamber, and then annealed at 1700 °C for 2 h at a pressure of 2×10^-2 Pa, CNTs formed on the surface that were longer than CNTs grown without ion-beam irradiation. When 5 keV Ar⁺ ions were used, no CNTs formed, but instead an amorphous carbon layer formed on the surface.

Towards a signal readout circuit for a highly sensitive stack-type image sensor, an entire transparent thin-film transistor (TFT) array using an amorphous In–Ga–Zn–O channel and indium–tin oxide electrodes was fabricated. The pixel pitch and number of pixels were 50 µm and 128×96, respectively. The transmittance of the TFT array for visible light reached up to 85%. The array also showed good switching characteristics. A monochromatic image sensor with a zinc phthalocyanine organic photoconductive film was fabricated using this array, and it produced clear images at 30 frames per second with a resolution corresponding to the pixel number.

An efficient pump beam combining technique using single-mode fibers was introduced. Well-defined modes formed from a single-mode fiber bundle were efficiently coupled into an output multimode fiber. The coupling rate can be maintained up to an input fiber number of 331. The total power of a multimode output fiber combined with single-mode fibers can greatly exceed the output power of a multimode laser diode pigtailed with the same multimode fiber.

L1₀-FeNi films were grown by alternate monatomic layer deposition on Au–Cu–Ni buffer layers at several substrate temperatures (T_s), and the relation between the uniaxial magnetic anisotropy energy (K_u) and the long-range chemical order parameter (S) was investigated. A large K_u of (7.0 ±0.2) ×10⁶ erg/cm³ and S of 0.48 ±0.05 were obtained. The value of K_u was larger than those reported previously for artificially synthesized FeNi films. It was first found that both K_u and S increased with T_s, and K_u was roughly proportional to S.

An iron density profile is accurately determined in Large Helical Device (LHD) using a space-resolved extreme ultraviolet (EUV) spectrometer, the absolute intensity calibration of which is carried out by bremsstrahlung continuum measurement. The effective intensity coefficients R (eV cm³ s^-1) of FeXV to FeXXIV are precisely calculated on the basis of a collisional-radiative model for iron density determination. The total iron density at the plasma center is found to be almost 4 or 5 orders of magnitude smaller than the electron density. The application of the present result to the study of impurity transport demonstrates a new way of examining the radial structure of transport coefficients and of determining the total impurity density.

Attractive polarization effects are investigated in binary atomic Si–Si collisions. The eikonal method and effective potentials are used to obtain the phase shifts and cross sections for the atomic collisions as functions of the impact parameter and collision energy. The results show that the attractive polarization effect suppresses the phase shift and cross section. It is found that the maximum positions of the differential cross section approach the collision center owing to the attractive polarization effects. It is also found that the attractive polarization effects on the total eikonal cross section decrease with increasing collision energy.

In this work, we investigated the influence of incorporating zirconia (ZrO₂) in HfO₂ gate dielectric on the electrical properties and reliability of n-channel metal oxide semiconductor field effect transistors (nMOSFETs). Detailed film physical, chemical and optical properties of Hf_1-xZr_xO₂ as a function of Zr content were studied using high resolution transmission electron microscopy (HR-TEM), angle resolved X-ray photoelectron spectroscopy (AR-XPS), and spectroscopic ellipsometer (SE). Compared to HfO₂, Hf_1-xZr_xO₂ provides not only higher k values for further equivalent oxide thickness (EOT) scaling but also lower capacitance–voltage (C–V) hysteresis, lower threshold voltage (V_t) shift (ΔV_t), and higher time-to-failure (TTF) lifetimes. Improved TTF lifetime of as high as three orders of magnitude and 35% lower V_t shift were achieved from the Hf_1-xZr_xO₂ gate stack with x=0.8. The improved reliability of the Hf_1-xZr_xO₂ gate dielectric is attributed to the reduced charge trapping in the Hf_1-xZr_xO₂ gate dielectric caused by the ZrO₂ incorporation.

Complex conductivity wideband spectra from 10^-1 to 10¹⁴ Hz (100 THz) were determined for 8 mol % yttria-stabilized zirconia (8YSZ) and 8 mol % ytterbia-stabilized zirconia (8YbSZ) ceramics. The contributions of electrolyte–electrode interfaces, grain boundaries, intragrain ion-hopping, and optical phonons were quantified to relate the microscopic conduction behavior to the overall conductivity. Intrinsic conductivity was mostly governed by ion-hopping. For both 8YSZ and 8YbSZ, ion-hopping followed the universal dielectric response (UDR) for broadband frequencies except for the phonon dispersion frequencies. The higher overall conductivities of the 8YbSZ ceramics compared to the 8YSZ ones were attributed to differences in the UDR contributions. The dominant factor determining the difference in the intrinsic conductivity in broadband frequencies from direct current (DC) to microwave between the 8YSZ and 8YbSZ ceramics was the DC conductivity due to UDR, σ_dc, where σ_dc(8YbSZ)>σ_dc(8YSZ). Other parameters in the UDR and the optical parameters did not greatly influence the intrinsic conductivities.

Ni-metal-induced crystallization (MIC) of amorphous Si (α-Si) has been employed to fabricate low-temperature polycrystalline silicon (poly-Si) thin-film transistors (TFTs). Although the high leakage current is a major issue in the performance of conventional MIC-TFTs since Ni contamination induces deep-level state traps, it can be greatly improved by using well-known technologies to reduce Ni contamination. However, for active-matrix organic light-emitting diode (AMOLED) display applications, the bias reliability and thermal stability are major concerns especially when devices are operated under a hot carrier condition and in a high-temperature environment. It will be interesting to determine how the bias reliability and thermal stability are affected by the reduction of Ni concentration. In the study, the effect of Ni concentration on bias reliability and thermal stability was investigated. We found that a device exhibited high immunity against hot-carrier stress and elevated temperatures. These findings demonstrated that reducing the Ni concentration in MIC films was also beneficial for bias reliability and thermal stability.

Effects of metal electrode on the electrical performance of amorphous In–Ga–Zn–O (a-IGZO) thin film transistor (TFT) have been studied. Electrical performances and interface stability between Mo, Al, and Cu electrode and a-IGZO semiconductor have been investigated before and after air-annealing. No inter-diffusion and interfacial reaction has been observed between Mo and a-IGZO and the turn-on voltage of the Mo electrode TFT was 0 V after annealing. As for Al, Al oxide was formed at the interface, and the number of conduction electrons in a-IGZO increased. Thus, a negative turn-on voltage was observed after air-annealing. As for Cu, Cu diffused into a-IGZO during air-annealing and acted as an acceptor. Therefore the a-IGZO TFT with a Cu electrode had a positive turn-on voltage and sub-threshold slope increased after air-annealing. These results indicate that the transistor performance can be affected by the metal types due to inter-diffusion or interfacial reaction between metal and a-IGZO.

Pb(Zr,Ti)O₃ (PZT) ceramics were prepared by the conventional mixed oxide method, and the strength of the resultant PZT ceramics was evaluated using modified small punch (MSP) tests. Load–displacement curve test results showed that the crack-initiation and fracture strengths of PZT ceramics decreased after polarization. The effect of the polarization accelerated the fatigue properties of PZT ceramics. Scanning electron microscopy (SEM) results showed that microcracks were formed before the maximum load in the MSP test, and the first load drop corresponded to crack initiation.

0.85(0.94Bi_0.5Na_0.5TiO₃–0.06BaTiO₃)–0.15K_0.5Na_0.5NbO₃ thin films have been prepared on indium–tin-oxide-coated glass substrates by pulsed laser deposition. Both X-ray diffraction and transmission electron microscopy reveal that the films have tetragonal crystal structure with columnar-like grains. The films show excellent optical transmittance of 90% and the band gap is calculated to be 3.61 eV. The slim polarization-electron filed hysteresis loop indicates the weak ferroelectricity, which is consistent with the capacitor-electric field curves. These results may be helpful for searching transparent ferroelectric materials.

Lead-free 0.94(K_0.5Na_0.5NbO₃)–0.06(LiSbO₃) (KNN–LS) ceramics were prepared by conventional solid-state reaction route (CSSR). For single perovskite phase formation the calcination was done at 850 °C for 6 h. Whereas for obtaining dense morphology the sintering of KNN–LS ceramics was carried out at 1060, 1080, 1100, and 1120 °C temperatures for 4 h, respectively. The structural study revealed that with the increase in sintering temperature the structure of the ceramic transformed from pure tetragonal to pseudocubic phase. Scanning electron microscopy (SEM) micrographs indicated that the optimum sintering temperature of the ceramic was found to be 1080 °C. The Curie temperature (T_c) of the KNN–LS ceramic was found to decrease at higher sintering temperature. The development of typical hysteresis loop confirmed the ferroelectric and piezoelectric nature of the KNN–LS ceramics sintered at different temperatures. The KNN–LS ceramics sintered at 1080 °C showed better ferroelectric and piezoelectric properties i.e., remnant polarization (P_r)∼17.2 µC/cm², coercive field (E_c)∼13.5 kV/cm, piezoelectric coefficient (d₃₃)∼161 pC/N, coupling coefficient (k_p)∼0.36 and remnant strain ∼0.06% were obtained.

Using first-principles density functional theory and nonequilibrium Green's function formalism, we investigate the effect of chemical modifications on the electronic transport properties of the dihydroazulene optical molecular switch. The molecule that comprises the switch can convert between the closed and the open forms upon photoexcitation. Theoretical results show that the chemical modifications play an important role in determining the switching behavior of such molecular device. This result reflects that the current ratio can be manipulated with the careful selection of the substituents and can provide fundamental guidelines for the design of functional molecular devices.

We have investigated the charge injection into a host–guest type of molecularly doped liquid crystalline thin film in liquid crystal cells. A 2-phenylnaphthalene smectic liquid crystal of 2-(4'-octylphenyl)-6-dodecyloxynaphthalene was used as a host material and a diketopyrrolopyrrole derivative of 1,4-diketo-N,N '-dimethyl-3,6-bis(4-dodecyloxyphenyl) pyrrolo[3,4-c]pyrrole was used as a dopant material: the current–voltage characteristics of the thin films with Pt, indium–tin oxide (ITO), MgAg, and Al electrodes were measured and analyzed on the basis of the Schottky mechanism. By comparing the current–voltage characteristics, we determined the majority carriers dominating the current and estimated the barrier height for electrons and holes. We found that the barrier height was smaller than the energy difference between energy levels of the host liquid crystalline material and the work functions of electrode materials. We concluded that the current in the host–guest thin film was dominated by the guest material that has a narrow energy gap and is responsible for the charge injection into the host material.

In this paper, we present a novel ohmic back metal for n-type Si devices. Using an AuSn adjusting layer, a simple and low-cost process is provided, as well as assuring strong adhesion between the metal and the Si substrate. The thickness of the Au layer under the AuSn layer for adjusting the Sn concentration at the interface between the metal and the Si substrate, and the deposition temperature are optimized. A novel back metal is deployed as a good substitute for the conventional AuSb back metal. The eutectic melting ratio (Au 80 wt %, Sn 20 wt %) of the AuSn alloy is confirmed by focused ion beam (FIB) and energy dispersive X-ray spectrometry (EDX). A good ohmic characteristic is obtained upon Sn diffusion to the Au layer. This method is useful for the metallization of various devices owing to its simple and low cost process and its high performance.

It was found that the structural properties with gadolinium (Gd) and europium (Eu) incorporation into nickel (Ni) fully silicided (FUSI) gate electrodes are markedly different and resulted in different degrees of effective work function modulation. It was found that Ni–Gd alloys tend to form stable compounds during silicidation and produced a Si-rich layer with amorphous/nanocystalline structure near the FUSI gate electrode/high-k dielectric interface. This compositional and structural change is the main mechanism responsible for effective work function modulation with Gd incorporation. However, in the case of Europium, Eu atoms tend to segregate outside the Ni-FUSI layer during silicidation and resulted in a uniform Ni_xSi_y layer with Eu pile-up layer at the FUSI gate electrode/high-k dielectric interface. This pile-up is believed to be the main cause of effective work function modulation with Eu incorporation. It was also found that the incorporation of Gd and Eu metals into Ni-FUSI gate can remotely scavenge the interfacial oxide layer resulting in lower equivalent oxide thickness (EOT) of the device.

Vertical InGaN multiple quantum wells light-emitting diodes (LEDs) with through-holes structure were transferred from Si(111) substrate onto the electroplating copper submount successfully. The additional series resistances induced by the AlN buffer layer and other interlayer were shorted by the metals filled through-holes. The LED with through-hole structure shows a low vertical conducting operating voltage and a small series resistance. Combining with substrate removal and copper electroplating technique, the operating voltage at 350 mA and series resistances of the LED were reduce from 5.6 to 5.1 V and 7 to 4 Ω, in comparison with through-hole LED before substrate removal. At the same time, the light output intensity was improved by 75%, which was mainly attributed to both the removal of light absorptive substrate and the substitution for highly thermal conductive copper submount with metal reflector.

A systematic study to understand the relationship between wavelength uniformity and substrate curvature during InGaN growth is described in relation to the initial bow of sapphire substrate. The initial bow of the substrate acted as the offset parameter for its curvature throughout the stages of the epitaxy process. Substrate flatness during InGaN growth was found to be important for achieving high wavelength homogeneity. The impact of n-GaN layer thickness and InGaN growth temperature on the substrate curvature shape was investigated to obtain a perfectly flat substrate shape at the InGaN growth stage. Temperature adjustment showed a strong impact on substrate curvature at the InGaN growth stage. The best initial bow was found as a function of InGaN growth temperature, and the importance of the initial bow of the sapphire substrate for obtaining high homogeneity in light emitting diode (LED) wavelength was experimentally verified.

We fabricated infrared wire-grid polarizers consisting of a 500-nm pitch Al grating on a low toxic chalcogenide glass (Sb–Ge–Sn–S system) using the direct imprinting of subwavelength grating followed by a deposition of Al metal by thermal evaporation. To fabricate the subwavelength grating on a chalcogenide glass more easily, the sharp grating was formed on the mold surface. The fabricated polarizer with Al thickness of 130 nm exhibited a polarization function with a transverse magnetic transmittance greater than 60% in the 5–9 µm wavelength range, and an extinction ratio greater than 20 dB in 3.5–11 µm wavelength range. The extinction ratio of the element with Al wires of 180-nm thickness reached 27 dB at 5.4-µm wavelength. The polarizer can be fabricated at lower costs and simpler fabrication processes compared to conventional infrared polarizers.

A surface sensor rendering an extended detection range was proposed and demonstrated, taking advantage of a Y-branch structure. The sensing and reference waveguides, comprising the Y-branch structure, were overlaid with TiO₂ films of different thicknesses; thus, they show unequal sensitivities. The phase change experienced by the two waveguides was in situ monitored through a birefringence analyzer. The interference number for the sensing waveguide was derived from the response of the reference waveguide. The implemented sensor was evaluated by varying the concentration of glucose solution, confirming that the proposed sensing scheme is useful for efficiently extending the detection range.

A loss-less wavelength converter based on a periodically poled MgO-doped congruent LiNbO₃ (PPMgCLN) waveguide was demonstrated. The waveguide was simply fabricated by applying annealed proton exchange (APE) to a ridge structure. To optimize the APE condition, the proton concentration profiles and the diffusion coefficients were evaluated by secondary ion mass spectroscopy. We also optimized the mode field profiles within the ridge waveguide to improve the overlapping among different wavelengths. The parametric gain of the cascaded difference frequency generation was 2.5 dB. Since the insertion loss of the wavelength conversion module was 2.2 dB, a loss-less PPMgCLN wavelength converter was successfully demonstrated.

To clarify whether the thermal diffusivity along the X-axis of a periodically poled Mg 1-mol %-doped near-stoichiometric LiTaO₃ (PPMgSLT) frequency-conversion device is the same as that of bulk-MgSLT crystal, we measured the thermal diffusivity along the X-axis (the direction perpendicular to the domain-wall) of a PPMgSLT device with a domain-inverted period of 8.0 µm by using a modified AC calorimetric method (laser-heating Ångström method) at room temperature. We found that the thermal diffusivity [(1.98±0.06)×10^-6 m²/s] was almost the same as that of bulk-MgSLT crystal [(2.09±0.04)×10^-6 m²/s]. This means that domain-walls are not phonon scattering centers with respect to thermal diffusivity and that domain-walls do not affect thermal diffusivity at room temperature. Consequently, the thermal diffusivity of bulk-MgSLT crystal is acceptable for PPMgSLT devices.

We examine the effect of junction sizes on the magnetization reversal process and spin-transfer torque switching of the MgO-based CoFeB magnetic tunnel junctions (MTJs) with perpendicular magnetic anisotropy (PMA). From the magnetic field transport measurements, it was found that the miniaturization of MTJs inherently enhances the switching asymmetry and the PMA of the soft layer. Our micromagnetic simulations confirmed that the dipolar field from the hard layer is responsible for the switching asymmetry and the increase in perpendicular shape anisotropy induces improvement of the PMA. It was further revealed that this additional anisotropy gained from the smaller MTJ sizes is not sufficient to sustain the thermal stability to meet the long-term information storage at the state-of-the-art complementary-metal–oxide semiconductor technology node. The pulsed spin-transfer torque measurements showed that a higher current density is needed to switch the magnetization of the soft layer in MTJ with smaller lateral dimensions, which is attributed to the increase in PMA.

Cu(In,Ga)Se₂ (CIGS) solar cells which have yielded high performance devices under 1-sun were experimentally evaluated under various concentrated lights. The open-circuit voltage, fill factor, and efficiency of the fabricated solar cell under 6.6-suns were 728 mV, 0.770, and 20.3%, respectively. It was found that the efficiency of low performance CIGS solar cells was increased by the irradiation of concentrated light and was comparable to the efficiency of high performance CIGS solar cells. Theoretical simulation revealed that the increment of the recombination velocity toward the defect density in CIGS thin films were reduced under concentrated light, due to the compensation of defects by the large amount of carriers generated by irradiating concentrated light.

A mechanism for the decay of charged voltage, which leads to the lowering of the voltage holding ratio of liquid crystal displays (LCDs), was proposed using a model for the behavior of ions in an LC layer. The proposed model was verified by experimental results using two LC cells of different LC materials. The decay of the charged voltage occurs with two decay components; one originates from the ions arriving at the surface of an alignment layer due to the application of pulsed voltage diffusing toward the LC layer, and the other originates from the ions in the LC layer moving toward the opposite surface and canceling the dielectric polarization of LC molecules during an open-circuit period. We found that the decay of the charged voltage increases with increasing density of ions arriving at the surface before the open-circuit period.

We report geometries and electronic structures of diamond nanoclusters with clean surfaces using first-principles total-energy calculations in the framework of the density functional theory. We find that the surface morphology strongly depends on the size of the diamond clusters. For clusters with diameters greater than 1 nm, the substantial surface reconstruction leads to a transformation of their outermost shell into a graphitic structure that wraps around the inner core. The surface reconstruction also results in both sp³ and sp² bonding features in their electronic structures. Furthermore, a detailed analysis of the electronic structure of the diamond nanoclusters reveals that the electronic property depends sensitively on the size and surface morphology of the clusters. This finding implies that the surface reactivity of the diamond nanoclusters could be controllable by proper tuning of cluster size and its surface shape.

In this paper, we report an efficient process to grow well-aligned carbon nanotube (CNT) arrays with a good area distribution density (about 5.6 ×10⁷ CNT/mm²). Vertically aligned carbon nanotubes (VA-CNTs) have been produced by controlling flow rate, temperature and catalyst nanoparticles using a floating catalyst chemical vapor deposition (FC-CVD) technique. They were synthesized on quartz substrates at 800 °C from toluene as a carbon source. VA-CNT samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and their surface area and pore size were determined by nitrogen adsorption analysis. The synthesized CNTs have a length of 500 µm and diameters ranging from 120±40 nm. The CNT filaments form a strength structure and exhibit a good vertical alignment. The remarkable properties of CNTs make them attractive for separation applications, especially for water and wastewater treatment.

Knowledge of thermal conductance of carbon nanotubes under mechanical deformation is important to characterize the robustness of carbon nanotube heat conduction. In this study, using molecular dynamics simulations, we have calculated thermal conductance of an elastically buckled single-walled carbon nanotube. A local buckle was formed by mechanically bending a carbon nanotube at an angle of 60°, and thermal conductance through the buckle was calculated by a nonequilibrium molecular dynamics approach. The thermal conductance exhibits strong diameter dependence, correlated with the strain energy generated in the buckle. Despite the highly strained deformation, the thermal resistance across a buckle is similar to that of a point defect and heterotube junction, revealing a robust nature of carbon nanotube heat conduction to buckling deformation.

Surface morphologies of GaInP films grown on germanium (Ge) by metal–organic vapor-phase epitaxy (MOVPE) have been investigated for different pre-growth treatments. A high temperature pre-annealing to the Ge substrate results in a smooth surface of GaInP, while a surface degradation in the case of a low temperature annealing is obtained, which might come from an incomplete carbon and/or oxide desorption. An improved surface morphology of GaInP with silicon doping and with increasing Ge substrate misoriented angle was also observed, which indicates that the highly disordered GaInP film and the neat interface between Ge and GaInP were formed with the assistance of a high temperature pre-growth treatment.

A KrF excimer laser (λ= 248 nm) has been adopted for annealing cost-effective Nb-doped TiO₂ (NTO) films. Sputtered NTO layers were annealed on SiO₂-coated flexible poly(ethylene terephthalate) (PET) substrates. This local laser annealing technique is very useful for the formation of anatase NTO electrodes used in flexible organic solar cells (OSCs). An amorphous NTO film with a high resistivity and a low transparency was transformed significantly into a conductive and transparent anatase NTO electrode by laser irradiation. The 210 nm anatase NTO film shows a sheet resistance of 50 Ω and an average optical transmittance of 83.5% in the wavelength range from 450 to 600 nm after annealing at 0.25 J/cm². The activation of Nb dopants and the formation of the anatase phase contribute to the high conductivity of the laser-annealed NTO electrode. Nb activation causes an increase in the optical band gap due to the Burstein–Moss effect. The electrical properties are in agreement with the material characteristics determined by X-ray diffraction (XRD) analysis and secondary ion mass spectrometry (SIMS). The irradiation energy for the NTO electrode also affects the performance of the organic solar cell. The laser annealing technique provides good properties of the anatase NTO film used as a transparent electrode for flexible organic solar cells (OSCs) without damage to the PET substrate or layer delamination from the substrate.

The (h00) textured Ba(Zr_0.085Ti_0.915)O₃ (BZT) ceramics were fabricated by templated grain growth using anisotropically shaped BaTiO₃ (BT) templates. A high orientation degree (Lotgering's factor) of 85% calculated from X-ray diffraction (XRD) patterns was obtained. The dielectric, ferroelectric, piezoelectric properties of the random and textured BZT ceramics have been studied. The Curie temperature of the textured BZT ceramics was 94 °C, which was higher than that of the random BZT ceramics. The textured BZT ceramics exhibited excellent piezoelectric performance with the piezoelectric coefficient d₃₃ = 234 pC/N, strain levels of 0.22% at 40 kV/cm, normalized strain (S_max/E_max) level of 550 pm/V calculated from the unipolar strain–electric field (S–E) hysteresis loops and remnant polarization P_r = 11.46 µC/cm² sintered at 1450 °C for 4 h with 85% of Lotgering's factor.

This paper reports the crystallization of amorphous InGaZnO (a-IGZO) films using solid-phase crystallization and discusses the mechanisms responsible for degradation of device performance after crystallization. The field-effect mobility (µ_FE) and subthreshold gate swing (S) value of the nanocrystallite embedded-IGZO thin-film transistors (TFTs) were significantly degraded to 3.12 cm² V^-1 s^-1 and 1.26 V/decade, respectively, compared to those (13.72 cm² V^-1 s^-1 and 0.38 V/decade) for the a-IGZO TFTs. The decreased µ_FE is explained based on indium deficiency by diffusion of its atoms in the channel layer and grain-boundary trapping of mobile carriers. The predominant mechanism of increasing S value has been attributed to increased interface and grain-boundary trapping.

The nitridation mechanism of the GaAs(001) surface using an RF-radical source at a low temperature of 350 °C was systematically studied by changing the As supply and nitridation time to obtain a smooth nitrided layer without the formation of Ga droplets. Atomic force microscopy (AFM) measurements indicated that supplying As is useful in suppressing the re-evaporation of As atoms and in maintaining a smooth surface. However, the degree of nitridation was decreased with increasing As pressure in the samples nitrided for 30 min. In contrast, the time dependence of nitridation indicated that the degree of nitridation increases with nitridation time. After optimizing the conditions, a two-monolayer-thick GaN layer was successfully obtained by nitridation for 120 min, regardless of the supply of the As molecular beam. The structure of the nitrided layers was also investigated using angle-resolved X-ray photoemission spectroscopy, and a thin layer that contains As and N atoms was found to cover the nitrided GaN layer.

We have deposited silicon/nitrogen-incorporated diamond-like carbon (Si–N-DLC) films by radio-frequency plasma-enhanced chemical vapor deposition (PECVD) using methane (CH₄), argon (Ar), and hexamethyldisilazane [(CH₃)₃Si]₂NH as the Si and N source, and investigated the structure and the mechanical and tribological properties of the films. We compared the properties of the Si–N-DLC films with those of the Si-incorporated DLC (Si-DLC) films prepared by PECVD using monomethylsilane (CH₃SiH₃) as the Si source. It was found that the N incorporation together with Si into DLC was effective in further decreasing the internal stress and increasing the adhesion strength. The friction coefficients of the Si–N-DLC films containing 4.0% N or less were as low as those of the Si-DLC films. We also found that the Si–N-DLC film containing 10.0% Si and 4.0% N had a higher wear resistance than the Si-DLC film containing 10.8% Si. The wear rate was comparable to that of the undoped DLC film.

The thermal oxidation of titanium (Ti) thin films has been investigated, focusing on the depth profile of oxygen and crystallinity. Ti thin films were epitaxially grown on Si(001) substrates, even at room temperature, by electron bombardment. The thermal oxidations of the Ti films were carried out in an oxygen environment of 0.1 Torr at temperatures ranging from 200 to 1000 °C for a fixed oxidation time of 30 min. It was found that the Ti film was insufficiently oxidized at a temperature lower than 600 °C, and crystalline TiO and Ti₂O₃ were formed. Above 600 °C, the Ti film was sufficiently oxidized and its crystal structure became completely rutile-type TiO₂. No anatase crystal structure appeared at any oxidation temperature. A thermal diffusion model of oxygen in a Ti film is presented for each oxidation temperature. The volume expansion of the Ti film due to oxidation was also examined and obtained to be 1.77.

The changes in the electrical properties, such as work function and resistance, of Pt thin films in the presence of hydrogen gas were studied. They were simultaneously measured with a flow-through cell at different concentrations of hydrogen gas in atmosphere containing gaseous nitrogen and that containing air. The resistance was measured by a four-terminal sensing method and the relative work function changes were measured using a field effect transistor. In both atmospheres, the resistance decreased as the concentration of hydrogen gas increased. This result was repeatable only in air because of the differences in the dynamic mechanism of increased density of electrical carriers inside the Pt film as a result of diffused H atoms. In the nitrogen atmosphere, the diffused H atoms were not easily released because of the surface barrier. On the other hand, oxygen gas reacted with H atoms at the surface and this reaction accelerated atom release into air. The work function showed repeatable responses in both atmospheres, but the response characteristics were different. The equilibrium reaction between the adsorption and desorption of hydrogen occurred at the surface in the nitrogen atmosphere, whereas the equilibrium reaction of hydrogen and oxygen to form water molecules occurred in air. The changes in work function and resistance in the presence of hydrogen were due to changes in dissociated hydrogen intensity in the bulk, as well as to the surface reactions.

We use scanning tunneling spectroscopy (STS) to investigate the electronic structures of dense Pb overlayers of three phases grown on the Si(111) surface: the 1 ×1, √7 ×√3, and stripe incommensurate (SIC) phases. Although their atomic structures are all very different, the STS spectra of all three phases show nearly identical oscillatory features with two resonance peaks. These resonances are not common quantum-well states; they are energy bands originating from the dominant 1 ×1 potential in these phases. However, the local electronic states found by STS show that the resonance peaks are modulated with the superstructure of the √7 ×√3 phase, and that the resonance energy varies with the domains and the domain walls in the SIC phase.

Improvement of the electromagnetic wave absorption ability was examined from the electromagnetic point of view. The oscillation behavior in relation to incident impedance derived from a hyperbolic tangent function can be reduced by increasing the imaginary part, i.e., loss value, of permeability and/or permittivity owing to its mathematical characteristics. It was demonstrated that the electromagnetic wave absorption ability was obviously enhanced by inserting the lossy magnetic layer between the electromagnetic wave absorber and a reflector. The absorption ability was improved further by pilling the polyurethane foam plate having lower permittivity to provide -9.6 dB (ca. 89% absorption) for the frequency range above 0.75 GHz with a total absorber thickness of 15.15 mm.

Polycrystalline thin films of CuGaSe₂-related Cu-deficient materials were prepared by vacuum co-evaporation. The composition was adjusted in order to prepare copper gallium selenide, abbreviated as CGSe, with an optimal band gap and valence band maximum position for photoelectrochemical water splitting. The effect of the Ga/Cu ratio on the photoelectrochemical properties of CGSe was also studied. With increasing Ga/Cu ratio, the band gap of CGSe became larger, and the valence band maximum position became deeper against the vacuum level. However, an analysis of the photocurrent and onset potential indicated that the Ga/Cu ratio should be less than 3.5 for optimal performance. A Pt-deposited CGSe electrode with a Ga/Cu ratio of 3 showed an onset potential of about 1.1 V vs RHE and an energy conversion efficiency of 0.35% under AM 1.5G light illumination in a 0.1 M Na₂SO₄ solution with pH 9.5.

We investigated the structural and transparent conductive properties of oxygen-deficient TiO_x films that were deposited by metal-mode reactive electron cyclotron resonance plasma sputtering from a Ti target at 400 °C. Crystallites in a strongly reduced state (x≈1) had face centered cubic (fcc) structures with the resistivities ranging from 10^-4 to 10^-3 Ω cm, and the optical transmittance in the visible wavelength was between 25 and 55%. In a sufficiently oxidized state (x≈2), rutiles nucleated with resistivites higher than 10^-2 Ω cm, and the optical transmittance was between 60 and 80%. The intermediate composition (1< x < 2) corresponded to fcc structures although the crystallinity approached an amorphous state with increasing x. Crystallization into magneli phases (Ti_nO_2n-1) was observed only for thick films at deposition temperatures higher than 500 °C. Carriers were n-type for rutile, but p-type for the fcc and magneli phases. Nb-doped TiO_x films were produced by metal-mode sputtering of TiO_x with co-sputtering Nb and O from an Nb₂O₅ target. The donor role of Nb⁵⁺ could be identified only in the oxidized rutile state, but the resistivity increased at higher Nb₂O₅ sputtering powers due to oxidation of Nb atoms that substituted Ti sites.

To realize precise and high-throughput multiprocesses in a single plasma process chamber with a rapid alternative of multiple gases, gas flow characteristics in a plasma process chamber are investigated and a pulse-controlled gas injection method is developed. It is found that gas replacement characteristics greatly depend on the gas supply method used. An upper shower plate has a great advantage in realizing a rapid gas replacement over the case without using the upper shower plate, resulting from the realization of the down flow pattern of feed gas in the chamber. The pulse-controlled gas injection method employs the intentional overshoot pulse at the beginning of gas supply to rapidly stabilize gas pressure. Interference matrix operation is newly introduced to determine the pulse size for the arbitrary gas flow pattern in the chamber. The optimum pulse size can be successfully obtained in the case of HBr addition to a pure Ar plasma.

A quantum chemical investigation of the chemical dry etching of SiO₂ using H₂ downflow plasma with flowing NF₃ was carried out using the B3LYP/6-31+G(d,p) method. The results provide a reasonable interpretation of how the chemical dry etching of SiO₂ takes place in a down flow area. Experimentally, it was found that the etch rates of thermal silicon oxide film range from 1 to 10 nm/min depending on the etching conditions, and white powder was produced on the etched surface. It was deduced that the etchants were HF and NH₃ produced by the reaction of H+ NF₃, and that the white powder on the etched surface was produced by the decomposition of (NH₄)₂SiF₆ formed on the etched surface. The calculated results support the HF and NH₃ production mechanism and clarify the molecular structures of (NH₄)₂SiF₆ and the white powder. Another important point in the chemical dry etching of SiO₂ was the realization of a high etching selectivity to Si. As the F atom was deduced to be the main etchant of Si, its generation mechanism in H₂ down flow plasma with the addition of NF₃ was also studied and a method of suppressing F atom production was proposed in this research.

The precise etching of organic films with a low dielectric constant (low-k) in a dual-frequency capacitively coupled plasma etching reactor with a plasma generation of 100 MHz and an applied bias of 2 MHz employing a gas mixture of hydrogen and nitrogen was performed by real-time control of the densities of hydrogen (H) and nitrogen (N) radicals based on real-time measurement of the Si substrate temperature. H and N radical densities were monitored near the sidewall of the reactor by vacuum ultraviolet absorption spectroscopy, and temperature was monitored by an optical fiber-type low-coherence interferometer. On the basis of the results of surface analysis by X-ray photoelectron spectroscopy, etched profiles were effectively determined from the chemical component of protection layers on the sidewall of the etched pattern affected by the ratio of H/(H+N) and substrate temperature. As the etching feature evolves, the ratio of radical density should be controlled temporally to maintain vertical profiles according to the change in substrate temperature. As a result, we have successfully realized an organic film with a vertical feature. These results indicate the need for autonomous control of the etch process based on real-time information on the plasma process for the next-generation ultrafine etching.

Coherent synchrotron radiation (CSR) fields are generated when a bunched beam moves along a curved trajectory. A new code, named CSRZ, was developed using finite difference method to calculate the longitudinal CSR impedance for a beam moving along a curved chamber. The method adopted in the code was originated by Agoh and Yokoya [Phys. Rev. ST Accel. Beams 7 (2004) 054403]. It solves the parabolic equation in the frequency domain in a curvilinear coordinate system. The chamber considered has uniform rectangular cross-section along the beam trajectory. The code was used to investigate the properties of CSR impedance of a single or a series of bending magnets. The calculation results indicate that the shielding effect due to outer chamber wall can be well explained by a simple optical approximation model at high frequencies. The CSR fields reflected by the outer wall may interfere with each other along a series of bending magnets and lead to sharp narrow peaks in the CSR impedance. In a small storage ring, such interference effect can be significant and may cause microwave instability, according to a simple estimate of instability threshold.

MnO₂ slurry can polish SiO₂ film faster and planarize wide feature steps (2 ×2 mm²) to a lower height than conventional silica slurry. A comparison of Gibbs free energies indicates that the MnO₂ abrasive directly reacts on the SiO₂ film. In post-Chemical mechanical polishing (CMP), the MnO₂ abrasive can be completely removed by dipping it in mixed solutions of inorganic acids and H₂O₂ followed by scrubbing and dipping in HF solution. A comparison of Gibbs free energies clarifies that the MnO₂ abrasive on the wafer is easily dissolved in a mixed solution of an inorganic acid and H₂O₂.

Reducing proximity effects is a key factor for achieving a higher resolution in electron-beam lithography and realizing the mastering of patterned media. The effect of substrate materials on backscattering electrons was investigated by simulation and experiment, and resolution enhancement was demonstrated. In Monte Carlo simulations with 100 keV incident electrons, the intensity of backscattering electrons decreased with decreasing atomic number of substrates. On the other hand, both the density of substrates and the existence of 10 nm thin films had negligible effects on the intensity of backscattering electrons. The measured exposure distributions from line-scanned electron beams supported the results of simulations. The intensity of backscattering electrons was reduced by using a carbon substrate, and circumferentially aligned high-density patterns of 878 Gbit/in.² were resolved.

This study reports the effect of poly(tetrafluoroethylene) (Teflon) as a surface modification layer, which was deposited on the surface of gate insulator and source/drain (S/D) electrodes, on bottom-contact pentacene-based organic thin-film transistors (OTFTs). The inserted 1.5-nm-thick Teflon layer can enhance the device performance because of the improved molecular orientation in pentacene film and reduced contact resistance (R_C) between the pentacene film and the S/D electrodes. The improved molecular orientation of pentacene film is caused by the hydrophobic and smooth Teflon layer surface. The reduced R_C is a result of the tunneling process at the Au/pentacene interface. This study also found that the device performance decreased as the Teflon layer increased in thickness. This is because of the increased R_C and decreased carrier injection efficiency between the pentacene film and the S/D electrodes. Compared to devices without a Teflon layer, the drain current and field-effect mobility of devices with a 1.5-nm-thick Teflon layer increased by 93 and 105%, respectively.

Reduction of the bowing of GaN-on-sapphire and GaN-on-silicon substrates was demonstrated with an internally focused laser processing. Stress implantation was successfully achieved inside the sapphire and silicon substrates by the internally focused laser process to compensate for the strain generated by the GaN/sapphire and GaN/Si systems which resulted in substrate bow reduction. This new approach gives us a larger flexibility in the design engineering of epitaxial and device fabrication processes and thus accelerates the realization of a larger diameter device process with GaN-on-sapphire and GaN-on silicon.

We have developed a soft-X-ray laser interferometer based on a double Lloyd's mirror and obtained a single-shot interferogram using a 7-ps-duration pulse at a wavelength of 13.9 nm. Micrometer grooves with a depth of 5 nm were successfully reconstructed from the interferogram. The lateral and depth resolutions were estimated to be 1.5 µm and better than 1 nm, respectively. This interferometer will be an attractive diagnostic device for observing transiently changing nanometer-scale deviations on solid surfaces.

The spin-resolved electronic structure of buried magnetic layers is studied by hard X-ray photoelectron spectroscopy (HAXPES) using a spin polarimeter in combination with a high-energy hemispherical electron analyzer at the high-brilliance BL47XU beamline (SPring-8, Japan). Spin-resolved photoelectron spectra are analyzed in comparison with the results of magnetic linear and circular dichroism in photoelectron emission in the case of buried Co₂FeAl_0.5Si_0.5 layers. The relatively large inelastic mean free path (up to 20 nm) of fast photoelectrons enables us to extend the HAXPES technique with electron-spin polarimetry and to develop spin analysis techniques for buried magnetic multilayers and interfaces.

The mechanical stresses in Si metal–oxide–semiconductor field-effect transistors (MOSFETs) were evaluated by polarized UV Raman spectroscopy measurements and stress simulations. To calibrate stress parameters of the materials used in the Si MOSFETs, we compared measured and simulated Raman frequency shifts on the cleaved Si(110) surfaces of the MOSFETs. Consequently, we extracted intrinsic stress values of -400 MPa for a SiO₂, -200 MPa for polycrystalline Si (poly-Si), 700 MPa for Ni silicide, 1250 MPa for a SiN tensile stress liner, and -3500 MPa for a SiN compressive stress liner by finding good agreement between the measured and simulated Raman shift distributions. To verify our stress simulation, we investigated the source/drain width dependences of Raman frequency shifts near the channel regions of Si MOSFETs by top-view Raman measurements. The calculated Raman frequency shifts agreed well with the results of polarized Raman measurements in terms of not only relative tendencies but also absolute Raman shift values.

Structures and stability of AlN(0001) and (000) surfaces under hydrogen rich conditions are theoretically investigated by performing first-principles pseudopotential calculations. The calculated surface energies demonstrate that several hydrogen incorporated structures are stabilized depending on the chemical potentials of constituting elements. Using surface phase diagrams, which are obtained by comparing the calculated adsorption energy with vapor-phase chemical potentials, we find that H atoms tend to desorb from AlN(0001) surface even under high H₂ pressures. In contrast, N–H bonds on AlN(000) surface are found to be favorable over the wide range growth conditions. These results imply that the growth processes on AlN(0001) surface could be changed by growth conditions such as temperatures and pressures.

We have realized a phase noise standard of a signal with a -100 dBc/Hz flat phase noise at 10 MHz for Fourier frequencies of 1 Hz to 100 kHz, which ensures traceability to the International System of Units (SI). The flat phase noise signal is produced using a carrier combined with white noise. To ensure traceability, both the flat phase noise signal power and the power spectral density of white noise are determined with a calibrated power meter and the noise standard, respectively. The flatness of the phase noise standard is within ±0.7 dB.

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