The 50 most-cited articles in Japanese Journal of Applied Physics, 2020

Abstract Understanding the fundamental relationships between physics and its information-processing capability has been an active research topic for many years. Physical reservoir computing is a recently introduced framework that allows one to exploit the complex dynamics of physical systems as information-processing devices. This framework is particularly suited for edge computing devices, in which information processing is incorporated at the edge (e.g. into sensors) in a decentralized manner to reduce the adaptation delay caused by data transmission overhead. This paper aims to illustrate the potentials of the framework using examples from soft robotics and to provide a concise overview focusing on the basic motivations for introducing it, which stem from a number of fields, including machine learning, nonlinear dynamical systems, biological science, materials science, and physics.

Abstract Energy harvesting technology is attracting attention as “enabling technology” that expands the use and opportunities of IoT utilization, enriches lives and enhances social resilience. This technology harvests energy that dissipates around us, in the form of electromagnetic waves, heat, vibration, etc. and converts it into easy-to-use electric energy. This paper describes the features of these technologies, recent topics and major challenges, and boldly predicts the future prospects of the development.

Abstract The possibility of reconciliation between seemingly mutually exclusive properties in one system can not only lead to theoretical breakthroughs but also potential novel applications. The research on the coexistence of two purportedly contra-indicated properties, ferroelectricity/polarity and conductivity, proposed by Anderson and Blount over 50 years ago was recently revitalized by the discovery of the first unambiguous polar metal LiOsO 3 and further fueled by the demonstration of the first switchable ferroelectric metal WTe 2 . In this review, we first discuss the reasons why the coexistence of ferroelectricity/polarity and conductivity have been deemed incompatible, followed by a review on the history of ferroelectric/polar metals. Secondly, we review the important milestones along with the corresponding mechanisms for the ferroelectric/polar metallic phases in these materials. Thirdly, we summarize the design approaches for ferroelectric/polar metals. Finally, we discuss the prospects and potential applications of ferroelectric/polar metals.

Abstract The establishment of economical and eco-friendly technologies for water treatment is a crucial issue for the realization of a sustainable society. Plasma-based treatments are promising methods for the decomposition of persistent organic compounds. This progress report summarizes recent improvements to plasma-based water treatment technologies by focusing on two types of contaminated solutions: solutions containing high concentrations of acetic acid and solutions containing surfactants, such as perfluorooctane sulfonic acid. Decomposition processes were analyzed based on chemical and physical characteristics, such as chemical reactions, the transportation of reactive species, and characteristics of target compounds. When treating solutions containing acetic acid, the optimization of bulk reactions involving ozone, which regenerates OH radicals from hydrogen peroxide, is a key factor for achieving high decomposition rates and energy efficiency. In contrast, the treatment of surfactants involves interfacial reactions at the plasma–liquid interface, where the accumulation of…

Abstract Twenty five years after the first theoretical prediction of two-dimensional (2D) honeycomb-like silicon and germanium, now coined silicene and germanene, the last Group 14 artificial cousin of graphene has been synthesized, thus terminating the lineage from silicene (2012) to germanene (2014), stanene (2015), and finally plumbene (2019). Here, we describe the realizations and review the tantalizing properties of these outstanding novel 2D materials.

Abstract By actively using not only charge transport of electrons and holes but also their spins, we can create a variety of new phenomena and functional materials. It is highly expected that these new materials and phenomena are applied to the development of next-generation electronics and information technology. This field, called spintronics, is emerging and rapidly making progress in many subfields. This article focuses on one of the most important materials, ferromagnetic semiconductors (FMSs) which have the properties of both ferromagnets and semiconductors, and their applications. We review the recent progress in the studies of FMSs and their applications, particularly, spin transistors.

Abstract Vapor phase growth of c -plane κ -Ga 2 O 3 films has been reported on various substrates such as sapphire, GaN, and AlN. However, these films are not single crystalline, but rather a mixture of nanometer-sized in-plane 120° rotational domains. We demonstrate a technique that solves the in-plane rotational domain problem. κ -Ga 2 O 3 was grown by epitaxial lateral overgrowth. A SiO x mask with a striped or dotted-striped pattern was aligned on a c -plane sapphire substrate with a TiO x buffer layer so that the stripe was parallel to the [ 11 2 ¯ 0 ] direction of the sapphire. κ -Ga 2 O 3 was then grown on the substrate by halide vapor phase epitaxy. Electron backscatter diffraction, X-ray diffraction, transmission electron microscopy, and selective area electron diffraction revealed that the three in-plane orientations of the κ -Ga 2 O 3 domains converged into one whose [010] direction was perpendicular to the stripe. The convergence occurred through a geometrical natural selection mechanism.

Abstract We report on the mass production of plasma activated water (PAW) by a non-thermal atmospheric pressure plasma. As a non-thermal plasma source, we used planar dielectric barrier discharge (DBD) and two types cylindrical DBDs. The manufacturing characteristics of PAW were investigated for each DBD type. The results show that the radical transfer characteristics from plasma to water have a dominant effect on the PAW properties. Of the two cylindrical DBD reactors, the “direct” type in which the mesh electrode was replaced with the conductor (Al) showed superior characteristics over “indirect” type. DBD reactor with an Al electrode with the length of 1 m long achieved a PAW production capacity of 520 liters per hour and production efficiency of 65 l kWh −1 . Such a large-capacity PAW manufacturing device can be applied to various industries including agriculture, sterilization, and water treatment.

Abstract The development of a full-color micro-display at the Industrial Technology Research Institute (ITRI) was reviewed in this study. The blue micro-display with 960 × 540 pixel arrays and 1984 PPI resolution is demonstrated on a CMOS active matrix addressing circuit. Different methods of fabricating such a micro-panel are developed to overcome the limitation in mass transfer. For the device size ranging from 5–100 micrometers, low-current external quantum efficiency of 10%–14% can be obtained. To achieve a full-color scheme, we adapt color-conversion layer design and use colloidal quantum dots as the illuminating material. A full-color array on a transparent substrate of 170 PPI resolution was demonstrated with a large-area blue LED backlight. The red and green pixels were fabricated by a photolithography process and had a size of 30 μ m. The FWHM of 21 and 28 nm and the quantum yield of 28% and 41% for the green and red pixels, respectively, were measured by a 2D spectroradiometer. With superior color provided by quantum dots, it shows a wide color gamut that can fill 87% of…

Abstract We present an optical modeling and characterization study of prototype ultraviolet laser diode (LD) structures grown on single-crystal AlN substrates, with focus on the reduction of modal loss caused by optical mode coupling to the absorptive layers on the p-side (i.e. p-contact and p-metal layers). The transparent AlN substrates enabled optical pumping for measuring modal loss without requiring functioning LDs. The modal loss measured in this way was in good agreement with electrically evaluated results of processed LDs, and both results were consistent with optical modeling predictions. By using 0.32 μ m thick p-side cladding, we were able to suppress the modal loss of the designed LD structure to 8.4 cm −1 , where the contribution from the absorptive p-contact layers was less than 3 cm −1 .

Abstract Photoelectron spectroscopy resolved in three-dimensional momentum space with a microscopic field of view is realized by combining a so-called Momentum Microscope with a soft X-ray synchrotron radiation source. A new experimental station for momentum-resolved photoelectron micro-spectroscopy and spectro-microscopy has been built at BL6U, an undulator-based soft X-ray beamline of the UVSOR synchrotron facility. This experimental station specializes in characterizing the electronic structure of surface atomic sites, thin films, molecular adsorbates, and bulk crystals. The instrument details are described along with possible measurement techniques.

Abstract The surface roughness of silicon wafer is one of the most important issues that degrade characteristics of semiconductor devices. The importance of spatial roughness frequency as an influential parameter has been pointed. In this research, the effect of roughness frequency on MOSFET characteristics was studied using samples with different roughness for frequency. From the obtained results, it was found that roughness with a low spatial wavelength affects electron mobility and gate insulating film reliability such as E bd, Q bd and SILC.

Abstract We demonstrated high free dielectric permittivity ( ε 33 T / ε 0 ) > 8000 and piezoelectric coefficient d 33 > 1950 pC/N of 72Pb(Mg 1/3 Nb 2/3 )O 3 -28PbTiO 3 (PMN–28PT) single crystals (SCs) obtained by low-voltage AC poling (LV ACP) of 1.5 to 3.5 kV RMS cm −1 at a high temperature (HT) of 80 °C in an air atmosphere. The minimum standard deviation ( σ ) of 170 was similar to conventional DC poling (DCP) and a high average ε 33 T / ε 0 of 8800 was confirmed with a 2.0 k V RMS cm −1 of ACP for five samples. The ACP voltages were less than 50% compared with previous studies of 2.9 to 8.5 k V RMS cm −1 . We assume ACP at 80 °C with a frequency of 0.1 Hz decreased coercive field E C the most which led to easy poling reversal. The LVHT air ACP process is very effective in obtaining enhanced dielectric and piezoelectric properties for PMN–PT SC transducers for medical echo ultrasound equipment application with less risk of breakdown and organic solvent-free for poling.

Abstract We report on the growth and characterization of BiSb thin films deposited on sapphire substrates by sputtering deposition with Ar and Kr plasma. By optimizing the growth conditions, we are able to obtain quasi-single-crystal BiSb(001) thin films with equivalent twin crystals. The conductivity of BiSb at the studied thicknesses exceeds 10 5 Ω −1 m −1 , reaching 1.8 × 10 5 Ω −1 m −1 at 10 nm. From the temperature dependence of the electrical resistivity, we confirm the existence of metallic surface states. Our results demonstrate that it is possible to obtain sputtered BiSb thin films with quality approaching that of epitaxial BiSb grown by molecular beam epitaxy.

Abstract All-solid-state Li-ion batteries (ASSB) are one of the most attractive next generation batteries for large scale application due to improved safety and higher energy density. However, the high temperature process required for densification of the solid-state electrolytes and for co-sintering of the multilayered ASSB is still a major challenge for large scale fabrication. In this study, a low temperature process, named cold sintering process, is applied to co-sinter all the layers in the ASSB at a low temperature. The cold sintered ASSB, a full-cell of Li4Ti5O12/Li7La3Zr2O12/LiFePO4, has densified microstructures and exhibits impressive electrochemical performance. The ASSB delivers high capacity of 140 mAh g−1 at 0.1 C, rate capability of up to 2 C with 85 mAh g−1, and 90% capacity retention over 100 cycles at room temperature under a current density of 0.2 C.

Abstract The electron temperature T e and density N e of atmospheric-pressure non-equilibrium dielectric barrier discharge argon (Ar) plasma are measured with optical emission spectroscopy. Continuum emission due to bremsstrahlung is applied to the analysis of the electron temperature and density with the spectrometric system in the visible wavelength range calibrated absolutely. The assumption of the Maxwellian electron energy distribution function (EEDF) results in T e ≃ 0.29 eV and N e ≃ 1.1 × 10 16 cm −3 , whereas the Druyvesteyn EEDF leads to the result T e ≃ 0.79 eV and N e ≃ 1.4 × 10 14 cm −3 . To confirm the validity of these values, several line intensities of the excited states of the Ar atom are observed experimentally and compared with the theoretical population densities calculated by the Ar collisional–radiative (CR) model that includes atomic collisional processes. It is confirmed that the order of the observed excited-state number densities agrees well with that calculated numerically by the CR model with the Druyvesteyn EEDF, while the Maxwellian EEDF gives poor…

Abstract Dislocations and their arrays in a {010}-oriented β -Ga 2 O 3 substrate were observed using synchrotron X-ray diffraction (XRD) and X-ray topography (XRT). The XRD measurements used spatially-resolved ω -rocking curves to show that dislocation arrays have a linear contrast with a lower diffraction intensity and a broader full-width at half maximum. Further XRT observations at three different g ⃗ vectors resolved these lines as dot contrasts aligned along the four different directions 100 , 102 , 201 , and 001 , which correspond to the outcrops of threading dislocations that lay in four different slip planes. The Burgers vectors for these dislocation arrays were determined using the g ⃗ ∙ b ⃗ invisibility criterion. The results indicate there are four slip systems of (1) 010 {001}, (2) 010 { 2 ¯ 01}, (3) 201 {10 2 ¯ }, and (4) 001 {100}. The slip system 201 {10 2 ¯ } ha

Abstract To produce high-quality GaN (0001) substrates with a low threading dislocation density (TDD) and a small off-angle variation, we have developed a technique named the “maskless-3D method.” This method, which is applied during GaN boule growth by hydride vapor phase epitaxy (HVPE), induces three-dimensional (3D) growth on a normal GaN (0001) seed substrate. We showed that by an appropriate choice of HVPE conditions, and without using a mask, the 3D growth shape was controlled to eliminate the c-plane and thereby suppress the propagation of dislocations from the seed. Subsequently, two-dimensional (2D) growth was carried out on the 3D structure. This 2D growth area was machined to produce a 2 inch GaN substrate with a TDD of about 4 × 105 cm−2 and an off-angle variation of 0.05°. We also confirmed that it was possible to insert the 3D growth area twice, thereby further reducing the TDD to 104 cm−2.

Abstract The thickness- and orientation- dependences of Curie temperature were investigated for (111)-oriented, (100)-oriented and randomly-oriented 0.07YO 1.5 -0.93HfO 2 films using high-temperature X-ray diffraction to study temperature stability of ferroelectric HfO 2 based films. These (111)-, (100)- and randomly-oriented films with various film thickness were prepared at room temperature on (111)YSZ, (100)YSZ and Pt/TiO x /SiO 2 /Si substrates by pulsed laser deposition, respectively, and subsequent 1000 °C annealing to obtain ferroelectric orthorhombic phase. Although (111)-oriented films show that Curie temperature decreases with the decrease in thickness, the temperature was higher than 350 °C in 4.6–110 nm thickness range. (100)-oriented films show no thickness dependence of Curie temperature of 550 °C in 15–86 nm thickness range. Moreover, the Curie temperature of 10 nm thick randomly-oriented films was also 550 °C. These results revealed that the Curie temperature was above 350 °C, which is significantly high for the stable operation of memory application, regardless of…

Abstract We formulate scattering mechanisms in quasi-two-dimensional systems with a large density of interface states such as 4H-SiC MOS interfaces, and calculate the electron Hall mobility in 4H-SiC MOS inversion layers by Monte Carlo simulation. In addition to phonon, ionized impurity, and surface roughness scattering, we take account of Coulomb scattering by the electrons trapped at the interface states and the interface fixed charges and scattering by electrically neutral defects. Considering that the number of trapped electrons can be comparable to or larger than that of mobile electrons, the trapped electrons are assumed to contribute to screening as well as scattering. Using the developed model, we analyze the dependence of Hall mobility in 4H-SiC MOS inversion layers on the body acceptor density, temperature, and interface state density. Our calculation reasonably reproduces the experimental behaviors of Hall mobility. We also discuss the physical mechanisms underlying the obtained results.

Abstract A poly(4-hydroxystyrene) (PHS) backbone polymer and a tetramethylammoniumhydroxide (TMAH) aqueous developer are typically combined to form a positive chemically amplified resist. We investigated the dissolution kinetics of PHS with different molecular weights and molecular weight dispersions and different concentrations of TMAH by quartz crystal microbalance (QCM) measurement. QCM graphs showed different dissolution rates and forms for different concentrations. We attempted to explain the dissolution kinetics by introducing a dissolution index calculated from swelling and dissolving factors. These factors were calculated using a penetrating factor (water or TMAH molecules) and a disentanglement factor. It is considered that the dissolution index depends on the molecular weight distribution because polymers with different molecular weight distributions have different voids in their bulk and different tendencies of disentanglement. Our results suggest that dissolution can be controlled by adjusting the molecular weight distribution, which will lead to reduced defect…

Abstract We have designed and fabricated a compact, 250 cm 3 electric field cooling alternate current poling (FC ACP) system and obtained an enhanced dielectric permittivity ( ε T 33 / ε 0 ) of 7920 which was 10 to 33% larger than that of high temperature (HT) ACP of 0.70Pb(Mg 1/3 Nb 2/3 )O 3 -0.30PbTiO 3 (PMNT) single crystal (SC) with phase change temperature ( T pc ) of 93 °C. However, when the FC ACP temperature from 200 to 35 °C was applied for 0.31Pb(In 1/2 Nb 1/2 )O 3 -0.43Pb(Mg 1/3 Nb 2/3 )O 3 -0.26PbTiO 3 (PIMNT) SC with a T pc of 136 °C, the ε T 33 / ε 0 decreased by 55% compared with that of HT ACP. Temperature dependence of the ε T 33 / ε 0 and phase analysis by X-ray diffraction of these SCs produced by a continuous-feeding Bridgman process showed clear different properties. We conclude the effects of FC ACP on the electrical and physical properties are different from the compositions, T pc , Curie temperature, etc., and it is required to find the best FC ACP condition according to each SC.

Abstract We have made a three-dimensional (3D) map of the band-gap energy of the Cu(In 1– x Ga x )(S y Se 1– y ) 2 (CIGSSe) quinary system. The band-gap energy of the CIGSSe system monotonically increased from CuInSe 2 ( x = 0.0 and y = 0.0) with simultaneously increasing Ga/(Ga+In) (GGI, x ) and S/(S + Se) (SSSe, y ) ratios. We also made a 3D map of the energy levels of the valence band maxima (VBMs) and conduction band minima (CBMs) of the CIGSSe system from the ionization energies measured by photoemission yield spectroscopy and the band-gap energies. The substitution effect of S for Se in CuInSe 2 was different from that of Ga for In. The VBM level of the CIGSSe system did not change significantly and the CBM level increased with an increasing GGI ratio, x . On the other hand, the VBM level decreased and the CBM level increased with an increasing SSSe ratio, y .

Abstract To reveal dislocations in β -Ga 2 O 3 and categorize them by their Burgers vectors, we have carried out a comprehensive dislocation characterization by synchrotron X-ray topography (XRT), chemical etching, and transmission electron microscopy (TEM). An important type of dislocation confirmed by XRT is the screw-type dislocations extending in the 〈010〉 direction at a density of about 4.2 × 10 4 cm −2 . These dislocations had length in millimeters and seldom bent to other directions. Chemical etching using molten KOH + NaOH at 200 °C formed hillocks with multiple crystallographic facets on the (010) surface. These hillocks showed various geometrical features that indicated the direction of the dislocation lines. TEM observation confirmed that the hillocks were related to dislocations. Finally, the feasibility of using TEM weak-beam dark-field images and large-angle convergent-beam electron diffraction to identify dislocation Burgers vectors was examined, which seemed to be problematic due to the low-symmetry of the monoclinic crystal structure of β -Ga 2 O 3 .

Abstract In this report, a thickness expansion mode film bulk acoustic resonator (FBAR) was fabricated using 4 μ m thick 36°Y-LiNbO 3 (LN) single crystal thin plate. The LN thin plate was made by polishing after bonded to a Si bare wafer. The LN FBAR showed a bandwidth of 10.3% and an impedance ratio of 45 dB at 800 MHz. The spurious response due to a thickness shear (TS) mode was much smaller than the main mode, because the optimal cut angle was chosen. The quality factor of anti-resonance is poor probably due to acoustic loss caused by a misalignment of the upper and lower electrodes, the series connection of two resonators etc. By minimizing the acoustic loss, the impedance ratio can be improved up to 60 dB.

Abstract Barium disilicide (BaSi 2 ) has attracted significant attention as a promising next-generation thin-film solar cell material. However, there are still significant barriers to bringing BaSi 2 to the device level. This is mainly because the fundamental physical properties of BaSi 2 are not well understood. In this article, we review the recent progress in understanding the fundamental properties of semiconducting BaSi 2 using various advanced computational methods. We summarize the status of first-principles calculations on electronic structures, optical properties, and defect properties of BaSi 2 . Recent development and immediate challenges are also outlined. In addition, we present our recent studies on a comprehensive band diagram and the physics of defects in BaSi 2 .

Abstract Thermoplastic elastomers (TPEs) may generate a residual strain after being stretched, which hinders their potential for use in high-performance materials. However, the mechanism of the residual strain formation has not been sufficiently elucidated thus far. Here, we used atomic force microscopy-based nanomechanical mapping to investigate a stretched TPE specimen consisting of poly(styrene- b -ethylene- co -butylene- b -styrene) with a content of 15 wt% styrene (SEBS-15). In the SEBS-15 polymer structure that maintained a strain of 0.5, hard-segmental (HS) amorphous domains aggregated by poly(styrene) segments deformed and became oriented parallel to the stretching direction, whereas soft-segmental rubbery domains aggregated by poly(ethylene- co -butylene) segments elongated, formed a stress network using the HS domains as junction points. Moreover, an in situ observation adopted for the stretched SEBS-15 revealed that HS domains therein underwent a relative displacement and partial separation that was influenced by the formed stress network, which was strongly related to…

Abstract We have developed prototype parallel and series types of band rejection filters at 0.9 GHz using a heteroacoustic layer (HAL) surface acoustic wave (SAW) resonator. The HAL SAW resonator is made on 0.63 μ m thick 25° YX LiTaO 3 supported with a 42°45′ Y 90° X quartz substrate. Steep attenuation was obtained due to the large impedance ratio of the HAL SAW resonator. There is no obvious spurious response up to 6 GHz thanks to the spurious-free characteristic of the HAL SAW resonator, and temperature frequency stability is good. In addition, the attenuation at frequencies other than the rejection frequency is small. This HAL SAW band rejection filter may be useful for carrier aggregation and Internet of Things systems.

Abstract The failure of photovoltaic modules in high-temperature and high-humidity tests is generally caused by the loss of electrical contact between the cell emitter and finger metallization, due to the corrosion of the glass layer by the acetic acid which is generated by the hydrolysis of the ethylene vinyl-acetate copolymer that is used as the encapsulant. In this study, a high-temperature high-humidity test was conducted on a photovoltaic module—namely, a solar cell with reduced output—to examine the metallization–Si wafer interface. The results confirmed that Pb was eluted from the glass layer to form an alteration layer that inhibits electron movement from the emitter layer to the metallization, thereby decreasing the output of the module. The corrosion products generated from the eluted Pb indicated that the front-side metallization was statically exposed to the same environment inside the PV module as that in an aqueous solution of acetic acid.

Abstract The circular polarization of light scattered by biological tissues provides valuable information and has been considered as a powerful tool for the diagnosis of tumor tissue. We propose a non-staining, non-invasive and in vivo cancer diagnosis technique using an endoscope equipped with circularly polarized LEDs (spin-LEDs). We studied the scattering process of the circularly polarized light against cell nuclei in pseudo-healthy and cancerous tissues using the existing Monte Carlo method. The calculation results indicate that the resultant circular polarizations of light scattered in pseudo tissues shows a clear difference in a wide range of detection angles, and the sampling depth depends on those detection angles. The structure of the endoscope probe comprising spin-LEDs is designed based on the calculation results, providing structural and depth information regarding biological tissues simultaneously.

Abstract A novel electro-active shape memory polymer (SMP) was fabricated with fully soluble self-doped poly(3,4-ethylenedioxythiophene) (S-PEDOT) and SMP using a solution mixing method at various S-PEDOT weight ratios ( W S-PEDOT ). The percolation analysis showed an extreme low percolation threshold of 0.38 vol% and critical exponent of 1.15, which was associated with the S-PEDOT conductive networks formed by phase separation in the S-PEDOT:SMP composite. The shape memory characteristics were observed at W S-PEDOT ≤ 30 wt%, while the glass transition temperature ( T g ) was almost constant ca. 50 °C. The S-PEDOT:SMP composite film at W S-PEDOT = 10 wt% showed electrical conductivity ( σ ), shape fixing ratio ( R f ), and shape recovery ratio ( R r ) of 29 S cm −1 , 95.4%, and 90.1%, respectively. Furthermore, an electro-active SMP soft actuator, fabricated using the S-PEDOT:SMP composite film at W S-PEDOT = 10 wt%, quickly recovered from a temporary bent shape to its original open shape within 5 s upon application of 6 V.

Abstract The trends in AI chip development since 2013 can be divided into two categories of applications: server and edge. As for the server, recently, ASIC chips designed for learning functionalities have become mainstream, with competitively computational performance. However, the limitations of Moore’s Law have started to impose themselves on this emerging type of AI chips, creating the need for new technological innovation. Meanwhile, regarding edge AI chips, research on data compression technology is advancing to lower power consumption while maintaining high performance. Further improvements have been made since 2017 in recognition accuracy in binary/ternary; moreover, there has been research on in-memory processing to configure 1 bit by combining memory and arithmetic element, where non-volatile memory can achieve higher performance and lower power consumption. With these backdrops, this paper summarizes the progress made to date in the field of AI chip technology while also identifying the future direction of next-generation technologies.

Abstract We investigated the imaging capability of fixed-voltage fundamental wave amplitude difference (fixed-voltage FAD), which is one of the nonlinear ultrasonic phased array imaging techniques, for three-dimensional crack open/closed distribution. We fabricated two fatigue crack specimens with different thicknesses, which were selected to create different open/closed distributions in them. As a result of applying fixed-voltage FAD with mechanical scans to the thick and thin specimens, the difference in the crack open/closed distribution was successfully visualized. The results are in good agreement with fracture mechanics. Thus, it was demonstrated that fixed-voltage FAD is useful not only for nondestructive testing for aging infrastructures but also for the progress in fracture mechanics.

Abstract Fast scintillation materials based on the ternary halide crystals of Cs 2 ZnCl 4 and Cs 3 ZnCl 5 were synthesized. Under X-ray irradiation, an emission band at 310 nm with shoulders at 260 and 410 nm was observed for Cs 2 ZnCl 4 , and emission bands at 240, 290, and 390 nm were observed for Cs 3 ZnCl 5 . The observed bands were primarily attributable to Auger-free luminescence (AFL). In the temporal scintillation profiles, scintillation decay time constants of 1.7 and 1.1 ns were found for Cs 2 ZnCl 4 and Cs 3 ZnCl 5 , respectively. These fast components are attributed to AFL and constituted greater than 88% of the total scintillation amount. On the basis of the pulse height spectra, the light yields of Cs 2 ZnCl 4 and Cs 3 ZnCl 5 were estimated to be 1280 and 440 photons MeV −1 , respectively. The light yield of the fast component of Cs 2 ZnCl 4 was slightly lower than that of BaF 2 , which is a commercially available fast scintillator exhibiting AFL.

Abstract The Coulomb-limited mobility ( μ Coulomb ) of Si-face 4H-SiC MOSFETs with nitrided gate oxide is experimentally evaluated. μ Coulomb is experimentally determined using samples with various acceptor concentrations by varying the body bias. It is found that the depletion-charge and surface-carrier densities in the inversion layer can be utilized to well formulate μ Coulomb . In addition, μ Coulomb is investigated as a function of the inversion-carrier average distance from the MOS interface ( Z AV ), and it is established that Z AV can universally describe μ Coulomb in the inversion layer of Si-face 4H-SiC MOSFETs with nitrided gate oxide.

Abstract Heterogeneous wafer bonding of InP/Si at room temperature is studied using surface-activated bonding (SAB) technology. To minimize the degradation of optical property while maintaining enough bonding strength, various bonding conditions including gas species of fast atom beam (FAB) were examined. The results show that a bonding strength of over 0.5 MPa can be obtained with less degradation of photoluminescence (PL) property of InP/Si hybrid wafer by combining Xe and Ar gases for FAB. Using this condition, hybrid wafer including quantum wells were fabricated, which showed sufficient PL property for the fabrication of hybrid photonic devices. The bonding conditions described in this study enabled realization of continuous wave (CW) operation of InP-based layers/SOI hybrid laser.

Abstract Recently, many studies on bio-mimic soft robots have been reported. Among living organisms, the locomotion of soft-bodied creatures, such as snails, worms and nematodes, have been actively studied. These soft creatures locomote by deforming the muscles of the whole body into waveforms and propagating the waves of the deformation. This locomotion of soft creatures could be applicable to develop a worm-type soft robot, which can move in drain pipes and even in a human body. In this study, we developed worm-like robots that could generate wavy motion under a rotating magnetic field using silicone and magnetic rubber, and investigated their movement characteristics. In addition, based on a deformation experiment of a silicone cantilever with a single magnetic element inside made of the same material as a worm-like robot, we investigated the effect of the size of the worm robot for further miniaturization.

Abstract High-voltage and plasma applications to keep the freshness and quality of agricultural produce are described focusing on functions of plasma in each application of a post-harvest stage. The high voltage and the plasma are used for decontamination of airborne bacteria in a storage house and a transport container of agricultural produce. The working mechanisms of the decontamination are mainly caused by inactivation through the oxidization process with reactive oxygen species and the collection of airborne bacteria as an electric precipitating process. The plasma is also used to maintain a freshness by decomposition of the agricultural produce exhausting gases such as ethylene, which works as a plant hormone and accelerates ripening of some kind produces in a mix-loading container. The decomposition of the ethylene is mainly an oxidization process by the atomic oxygen in dry gas condition. The ethylene is also decomposed by hydroxyl radical under the humid air condition.

Abstract We investigate A-site cation ordering in the ferroelectric perovskite Bi 0.5 Na 0.5 TiO 3 (BNT) by synchrotron X-ray total scattering. Although BNT has a problem of low depolarization temperature, it is a promising lead-free piezoelectric material. Since the depolarization temperature is presumed to correspond to a relaxor-like gradual order–disorder phase transition, local structural analysis is necessary to understand the structure of the disorder phase. Using this approach, we reveal the elusive connection between chemical and structural heterogeneity. The short-range order structure largely deviates from the rhombohedral average structure due to the off-center shift of Ti with large randomness. Consequently, the Ti off-center shift is averaged out beyond the unit cell and the structure becomes identical to the average structure beyond the unit cell. We further locate nanoscale regions of monoclinic distortion due to the heterogeneity of the A-site ion composition. The change in the short-range-order structure with distance can determine the BNT depolarization…

Abstract Quantitative ultrasound (QUS) methods have been widely used for soft tissue characterization. Spatial resolution (i.e. ultrasound frequency) is an important factor for QUS methods. In a previous study, a double Nakagami (DN) distribution model to echo signals from fatty livers using a 15 MHz transducer was used to permit fine-resolution QUS. This study used a filtering approach to quantify steatosis progression using three QUS parameters obtained by fitting a DN distribution model to experimental envelope data. The filter was designed using QUS parameters obtained from three healthy liver. A strong correlation ( r = 0.96, p < 0.001) was found between histologically quantified steatosis percentage and the percentage of the liver having non-healthy liver features. This approach was able to successfully diagnose fatty livers (>20% steatosis percentage) in a dataset of 12 livers ranging from 0% to 90% steatosis.

Abstract A resonant-tunneling diode (RTD) terahertz oscillator composed of a long narrow RTD and a rectangular cavity resonator is proposed, and its oscillation characteristics are simulated and analyzed. The rectangular cavity resonator reduces both the oscillator inductance and resistance, while the large-area RTD enables high output power with a high oscillation frequency. To estimate the radiation power accurately, a detailed equivalent circuit model was extracted from 3D electromagnetic simulation. From the analysis, the proposed device is expected to produce a high output power of approximately 2–3 mW at around 1 THz.

Abstract We propose Si microring resonator (MRR) crossbar arrays as a programmable nanophotonoic processor (PNP) for a deep learning accelerator. The proposed MRR crossbar array can perform multiply-accumulate (MAC) operation in an optical domain. We numerically reveal that an optical neural network (ONN) based on the proposed MRR crossbar arrays can be used for the pattern recognition task with a similar performance to that of an ONN based on cascaded Mach–Zehnder interferometers. We predict that the power consumption can be reduced by approximately tenfold. The small area of the MRR also contributes to the reduction in its chip size by a factor of 36. The fabricated test devices consisting of Si MRRs with phase shifters exhibited no significant crosstalk between neighboring MRRs and showed the feasibility of MAC operation. Photonic integrated circuit using the proposed MRR crossbar arrays is promising for large-scale and low-power PNP for deep learning.

Abstract Recently, cold atmospheric plasma (CAP) treatment on seed germination has emerged as a useful technique to increase agriculture production, although, the mechanism of the cold plasma in seed germination is still under investigation. In this work, we studied the role of pigments in the seed coat of radish sprouts on the electron spin resonance (ESR) signals before and after CAP treatment. Radish sprouts seeds having gray color show enhanced ESR signals after the CAP treatment, whereas, no increased ESR signals were observed for brown color seeds of radish sprouts as compared to their respective control seeds. These results reveal that seeds from the same harvest year having different seed coat colors show different responses to the plasma treatment. Although ESR signal intensity can vary with the harvest year, the change in ESR signal intensity after plasma treatment depends on the seed coat color. Independently on the harvest year (2017 and 2018), CAP increased ESR signals stronger in the grey seeds in comparison to the brown ones. The results indicated that seed coat color…

Abstract A thermocell with use of the electrochemical Seebeck coefficient ( α ≡ d E d T ; E and T are the redox potential and temperature, respectively). is a promising energy-harvesting device. α is the key parameter that governs the thermal efficiency ( η ) of the thermocell. Here, we systematically investigated the variation (Δ α ) in α of a redox couple of [Fe(CN) 6 ] 4− /[Fe(CN) 6 ] 3− in water, by adding 9% organic solvent in molar ratio. We found that Δ α for 11 organic solvents well scale to the molar volume ( V ). The empirical volume effect is understood in terms of the replacement of water molecules with organic molecules depending on V .

Abstract In this work, electron beam lithography proximity effect correction (PEC) was experimentally studied for patterning of Si photonic waveguides with a relatively thick resist mask. Beam’s energy density distribution (EDD) was experimentally extracted by the line exposure method; however, exposure lines in this work were developed after cleavage with a high-contrast process to reduce developer-related effects. The measured line spread function was fitted to a 4-Gaussian function to model mid-range energy densities accurately. The extracted EDD showed less proximity effects compared to conventional Monte-Carlo simulation performed by a commercial software. PEC processes with both techniques were experimentally compared for a Si photonic waveguide pattern with different side-cladding trench widths. Microscopic images confirmed that the presented calibration method could achieve better development conditions near the required clearance dosage. Single-mode propagation loss for a 500 × 220 nm Si wire waveguide was reduced from 3.2 to 2.4 dB cm −1 using the presented process.

Abstract The influence of compressive strain in high-quality AlN templates on the subsequent growth of AlGaN-based device layers was investigated. The AlN templates showed compressive strain of ∼−0.29% and threading dislocation densities (TDDs) below 6.5 × 10 8 cm −2 . By introducing high Si-doping in MOVPE-grown AlN, the compressive strain was relaxed while preserving the low TDD. By this method, the low TDD was transferred from the AlN template to the micron-thick n-Al 0.63 Ga 0.37 N. A 275 nm LED was demonstrated with a ∼2.5 times power enhancement than the same LED on conventional MOVPE-grown AlN template under low current injection. The maximum external quantum efficiency (EQE) was enhanced from 1.6% to 2.2% with an improved n-AlGaN.

Abstract This paper is focused on evaluation methods for materials at high amplitudes of ultrasonic vibrations. First, basic concepts on piezoelectric ultrasonic transducers utilized in power applications are introduced as well as horns and vibration converters. Second, an electrical equivalent circuit model of piezoelectric transducers is described. Then, a standard method to measure the output acoustic power of ultrasonic transducer is demonstrated. Third, the electromechanical coupling factor and quality factor are defined. The last half of this paper is dedicated to the transient method and quality factor measurement under high vibration strain. The quality factor and piezoelectric constant of piezoelectric ceramics are discussed as functions of vibration strain with the transient method. Next, an evaluation method for the quality factor of non-piezoelectric materials is proposed on the basis of the definition of quality factor. Ultrasonic characteristics of several metals and polymers are explored using the proposed method.

Abstract The story of information processing is a story of great success. Todays’ microprocessors are devices of unprecedented complexity and MOSFET transistors are considered as the most widely produced artifact in the history of mankind. The current miniaturization of electronic circuits is pushed almost to the physical limit and begins to suffer from various parasitic effects. These facts stimulate intense research on neuromimetic devices. This feature article is devoted to various in materio implementation of neuromimetic processes, including neuronal dynamics, synaptic plasticity, and higher-level signal and information processing, along with more sophisticated implementations, including signal processing, speech recognition and data security. Due to the vast number of papers in the field, only a subjective selection of topics is presented in this review.

Abstract We exploit the problem of ion migration in the halide perovskite CH 3 NH 3 PbI 3 (MAPbI 3 ) by developing a memtransistor (i.e. hybrid memristor and transistor) with the field-effect transistor geometry. Application of an electric field between the drain and the source results in resistive switching from a high resistance state (HRS) to a low resistance state (LRS) due to dynamic redistribution of ions in the MAPbI 3 layer. The gate enables continuous tuning of this LRS across several orders of magnitude. The LRS persists after removing the power supply and the memtransistor can be switched back to the HRS by reversing the bias polarity. Excellent state retention is demonstrated for 10 4 s and a switching ratio (HRS/LRS) of 10 2 is maintained for 1000 cycles, thus confirming good retention and cyclic endurance for the resistive switching behavior. Continuous tuning of the state conductance is essential for neuromorphic architectures and hard to achieve with two-terminal memristors.

Abstract We propose the use of compressed sensing for an underwater acoustic (UWA) communication system with orthogonal signal division multiplexing (OSDM) to achieve reliable communication in UWA channels with large delay and Doppler spreads. However, OSDM does not fully exploit the characteristics of UWA channels, which have long but sparse reverberation tails. Hence, we propose an OSDM channel estimator using compressed sensing and evaluate its performance in simulations and experiments. The simulations revealed that the optimal gain determining the performance of the channel estimator depends on standard deviation of noise σ , and OSDM using compressed sensing outperforms normal OSDM. We also evaluate OSDM performance using compressed sensing in field testing in the coastal area of Suruga Bay, Japan. The experimental results suggest that compressed sensing can boost OSDM performance; the number of OSDM error blocks using compressed sensing is half that in normal OSDM. Thus, OSDM using compressed sensing provides reliable communication.