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We investigate the stability of the polar surface of ZnO films grown homoepitaxially on atomically flat ZnO (000 1 ¯) O-face substrates by neodymium yttrium aluminum garnet (Nd:YAG) pulsed laser deposition (PLD). For films grown in the temperature range from 500 to 700 °C, ion scattering spectroscopy showed that the film surface termination was the same as the ZnO substrate. Even for a Mg0.2Zn0.8O/ZnO superlattice, no polarity reversal occurred, indicating that the ZnO (000 1 ¯) O-face is highly stable, despite the film surface sputtering caused by the high kinetic energy of the PLD plume generated by the Nd:YAG laser. [ABSTRACT FROM AUTHOR]

The effects of hydrogen absorption on the local lattice structure in palladium (Pd) were investigated by means of positron annihilation lifetime spectroscopy (PALS) and time-differential perturbed angular correlation (TDPAC) spectroscopy. The PALS measurements demonstrated that dislocations and vacancies formed in the preparation process of a pristine Pd plate can be clearly removed by vacuum annealing at 1073 K and the subsequent absorption of a large quantity of hydrogen, resulting in the production of the β-phase hydride PdH0.62, induces the formation of the open-volume defects again. It was also found that the absorbed hydrogen atoms remain in the Pd sample at 323 K but they are completely evacuated during 5 h heating at 383 K. In addition to the overall thermal behavior, an atomic scale observation of the hydrogen dynamics was carried out by means of TDPAC spectroscopy, indicating the nuclear quadrupole relaxation of the present (111m,111Pd → 111Ag→)111Cd probe, which evidently suggests that the hydrogen atoms show fast dynamic motion around the probe. From the temperature-dependent nuclear quadrupole relaxation rate, we obtained an activation energy of 41(4) meV for the motion. [ABSTRACT FROM AUTHOR]

Ultra-thin solar cells display high intrinsic radiation tolerance, making them interesting for space applications. This study investigates the dependence of the open-circuit voltage degradation and overall current–voltage behavior of devices with 80 nm thick GaAs absorber layers, on their absorber layer doping concentration and the radiation type used to introduce damage. The radiation types used were 1 MeV electrons and 20 keV, 100 keV, and 1 MeV protons. It is shown that the open-circuit voltage degradation rate increases with absorber layer doping concentration. This is linked to the increase in trap-assisted tunneling enhancement of the recombination rate, facilitated by the increase in electric field strength in the absorber layer with doping concentration. Trap-assisted tunneling is also found to contribute to the high local ideality factors observed in these devices, exceeding values of 2, and to be responsible for the trend of an increasing ideality factor with doping concentration. The significant role of trap-assisted tunneling in the devices is established through fitting of dark current–voltage data using a custom recombination–generation model. An open-circuit voltage degradation rate and local ideality factor curves are also shown to vary with radiation type, despite accounting for their differences in non-ionizing energy loss. This is corroborated by corresponding trends in carrier lifetime damage constants, extracted from the fitting of the dark current–voltage curves. This suggests that the introduction or behavior of radiation damage differs between ultra-thin and conventional, thicker solar cells, where non-ionizing energy loss theory tends to be reliable, especially over the studied proton energy range. [ABSTRACT FROM AUTHOR]

Illumination stress (IS) and negative bias under illumination stress (NBIS) cause considerable device instability in thin-film transistors based on amorphous In–Ga–Zn–O (a-IGZO). Models using in-gap states are suggested to explain device instability. Therefore, to provide reliably their density of states (DOS), this study investigated the valence band, conduction band, and in-gap states of an a-IGZO thin film. The DOS of in-gap states was directly determined in a dynamic range of six orders of magnitude through constant final state yield spectroscopy (CFS-YS) using low-energy and low-flux photons. Furthermore, light irradiation irreversibly induced extra in-gap states near the Fermi level and shifted the Fermi level to the vacuum level side, which should be related to the device instability due to IS and NBIS. Hard x-ray photoemission spectroscopy and ultraviolet photoemission spectroscopy using synchrotron radiation observed the large DOS of in-gap states near the Fermi level as in previous works. Here, we reveal that they are not intrinsic electronic states of undamaged a-IGZO, but induced by the intense measurement light of synchrotron radiation. This study demonstrates that CFS-YS is useful for determining the reliable DOS of the in-gap states for samples that are sensitive to light irradiation. The absorption spectrum measured through photothermal deflection spectroscopy is interpreted based on DOS directly determined via photoemission spectroscopies. This indicates that the line shape in the energy region below the region assigned to the Urbach tail in previous works actually roughly reflects the DOS of occupied in-gap states. [ABSTRACT FROM AUTHOR]

Measurement of high-temperature physical properties at microwave frequency is important to interpret the heating behavior of NiO observed in the author's previous studies. In this study, the impedance (4 Hz–5 MHz) and permittivity [at the microwave frequency (2.45 GHz)] of NiO powder particles were measured from room temperature (RT) to 800 °C. At high frequency above 100 kHz, the conductivity is almost independent of temperature up to a certain temperature (Ti). Above Ti, the conductivity showed a strong positive dependence on the temperature. In this region, the apparent activation energy is determined to be 0.51 eV, which is close to that of the previously reported large polaron transport mechanism (band-like conduction). It was also shown that the conductivity increased linearly with frequency and that a dielectric conductivity relation (σ = ωε″) holds, which is different from the hopping mechanism of the small polaron. Considering these results, it was understood that the temperature increase occurred preferentially in the microwave E-field. The slow increase from the room temperature is due to a small but finite dielectric loss at room temperature, and because of the low conductivity, induction current is not effectively generated in the H-field. On the other hand, after a certain time, the temperature rises to reach the large temperature-dependent conductivity, and then, a significant temperature rise occurs. [ABSTRACT FROM AUTHOR]

The characteristic x-ray emission direction of a material indicates the direction of the bonding orbitals and spatial symmetry of the electron orbitals. Accordingly, the intensity of x-ray emission, which varies with the direction of emission and crystal orientation, provides crucial information regarding anisotropic electronic structures. This study utilized angle-resolved soft x-ray emission spectroscopy (SXES) on a layered material, NaAlSi, to ascertain the spatial distribution of the valence electrons. Distinct alterations in the spectral intensity distributions were observed in the Al–L2,3 and Si–L2,3 spectra with respect to the emission angle. To interpret the anisotropic SXES spectra, the spatial distribution of each valence electronic state was simulated using first-principle calculations. Although the anisotropic emission intensity could not explain the symmetry of the spatial distributions of the isolated s and d atomic orbitals, the anisotropy of the SXES spectra could be interpreted as the spatial distribution of these orbitals when hybridized with p orbitals. Furthermore, the spectral structure corresponding to the electronic states near the Fermi level reflected the characteristics of the d orbitals. Therefore, angle-resolved SXES measurements can effectively discern the spatial distribution of hybridized electron orbitals with specific energy levels, which could enhance techniques related to electron distribution analysis, with potential applications in material science and electronic structure characterization. [ABSTRACT FROM AUTHOR]

Additive incorporation into polymers can enhance properties, such as the dielectric constant and thermal conductivity. The improved properties of polymer composites have largely been attributed to aggregate and network formation, but the influence of material texture requires clarification. Herein, the relationship between the texture of composite materials and thermal conductivity was investigated based on the fractal nature of composites consisting of polyvinylidene fluoride (PVDF) with β-Si3N4 (SN) as a high-thermal-conductivity filler. The SN particle groups were found to contribute to the formation of thermal conduction paths in the composite material and, thus, improve the thermal conductivity. The characteristics of the particle group clusters involved in SN particle percolation were elucidated by analyzing the interactions between multiple particles as a function of the amount of each fractal dimension. In addition, based on the statistical relationships obtained from the multifractal analysis, the strengths of the interactions between particles during thermal conduction path formation were estimated. Overall, the texture of the SN/PVDF material was characterized by local particle group formation (self-assembly) and subsequent global particle group network construction (self-organization), depending on the amount of SN added. These results suggest that multifractal dimensions can be used as material design indices for the texture of polymer composites. [ABSTRACT FROM AUTHOR]

The effects of the dispersion state of BaTiO3 ceramic fillers, which significantly improve the dielectric constant of BaTiO3/polyvinylidene fluoride composites, were investigated. To understand the microscopic and macroscopic features of the obtained composite textures, we have attempted a multifractal analysis of the microstructure of composite materials. The fractal nature of the composite material texture was investigated using multifractal parameters (the qth-moment dimension D(q) and scaling exponent τq) in the formation of fractal aggregates of BaTiO3 (BT) particles in polyvinylidene fluoride (PVDF) composites. In the plots of D(q) and τ(q) vs q, the obtained results confirmed that q > 0 could be quantitatively evaluated as local characteristics (morphology, arrangement, and dispersion), whereas q < 0 could be quantitatively evaluated as global characteristics (aggregate network structure formation). As a result of evaluating the internal energies and entropies of the micro- and macro-regions from the plot of τq vs q, the aggregate formation energy (E1), aggregate network formation energy (E2), and interaction energy between the aggregates (Eint) had a relationship of E2 = E1 + Eint. The configuration entropy for the aggregate network formation (S2), particle arrangement entropy (S1), and aggregate configuration entropy (Sint) had a relationship of S2 = S1 + Sint. At q > 0, the increase in the aggregate formation energy with the amount of additive indicates the formation of particle groups. At q < 0, the generation of the interaction energy between the aggregates (Eint) suggests that the particle groups interact to form an aggregate network. Similarly, at q > 0, the increase in the arrangement entropy with the amount of additive is related to the arrangement of particles, while at q < 0, the generation of the configuration entropy (Sint) is related to the formation of the particle group network. It was clarified from the multifractal analysis that the formation of particle groups and their network structure are strongly related to the piezoelectric characteristics in this BT/PVDF system. It was revealed that the Eint and Sint obtained from the plots of D(q) and τ(q) vs q of the multifractal analysis could be related to the formation of particle groups (local interaction) and occurrence of network structure (global interaction). Therefore, the plots of D(q) and τ(q) vs q are effective means of characterizing self-organization from the fractal nature and are expected to be applied in more general research fields other than material and condensed matter. [ABSTRACT FROM AUTHOR]

Negatively charged silicon vacancy (VSi−) defects in silicon carbide are expected to be used for magnetic sensors under harsh environments, such as space and underground due to their structural stability and potential for high-fidelity spin manipulation at high temperatures. To realize VSi− based magnetic sensors operating at high temperatures, the temperature dependence of optically detected magnetic resonance (ODMR) in the ground states of VSi− defects, which is the basic principle of magnetic sensing, should be systematically understood. In this work, we demonstrate the potential of VSi− magnetic sensors up to at least 591 K by showing the ODMR spectra with different temperatures. Furthermore, the resonance frequency of the ground level was independent of temperature, indicating the potential for calibration-free magnetic sensors in temperature-varying environments. We also characterize the concentration of VSi− defects formed by electron irradiation and clarify the relationship of magnetic sensing sensitivity to VSi− concentration and find that the sensing sensitivity increases linearly with VSi− concentration up to at least 6.0 × 1016 cm−3. The magnetic sensitivity at a temperature above 549 K was reduced by half as compared to that at 300 K. The results pave the way for the use of a highly sensitive VSi−-based magnetic sensor under harsh environments. [ABSTRACT FROM AUTHOR]

The behavior of excitons excited in anatase crystalline materials affects the photocatalytic performance of the materials. Thus, investigating the properties of such excitons is essential for understanding the origin of their influence on photocatalytic performance. Here, angle-resolved electron energy-loss spectroscopy was applied to evaluate the size of the spatial spread of excitons in anatase TiO2. Three kinds of excitons (I–III), which were reported by polarized light absorption experiments, were experimentally identified in the electron energy-loss spectroscopy (EELS) spectra. Exciton size was evaluated from absorption intensity, which was derived by the Kramers–Kronig analysis of the EELS spectra, depending on the momentum transfer (q). The sizes of excitons I, II, and III were evaluated to be 8, 5, and 6 nm, respectively. The larger size of exciton I than that of III was with the same tendency as in the theoretical results. Exciton II, which was evaluated as a delocalized one, was evaluated to have a finite size in this experiment. The largest size of exciton I, approximately 8 nm, is the same order of the exciton diffusion lengths of the material. Therefore, exciton I should significantly influence the photocatalytic activity of anatase. [ABSTRACT FROM AUTHOR]

Freeze- and spray-dried inclusion complexes (ICs) of chlorhexidine (CHX) in β-cyclodextrin were characterized by Fourier transform (FT)-Raman, 1H nuclear magnetic resonance (NMR), and photoacoustic spectroscopy. The active Raman modes of CHX were simulated using the density functional theory. By considering semiempirical calculations, it was observed that the guest penetrates on the wider rim of the host in a proportion of 1:2. We observe from the FT-Raman analysis that the drying method influences the CHX:β-cyclodextrin conformational adjustment by the rearrangement of hydrophilic biguanides of the guest. The photoacoustic spectroscopy results inferred that the freeze-drying method provided a better inclusion due to a lower interaction between phenyl groups and hexamethylene of CHX. The freeze-dried IC achieved a faster dissolution pattern. These ICs provided immediate drug dissolution profiles in an aqueous medium better than a pure drug. The release profiles of freeze- and spray-dried ICs were explained by Fickian diffusion. These data support further planning and development projects of novel immediate release systems based on CHX. [ABSTRACT FROM AUTHOR]

Anisotropic magnetoresistance (AMR) effect on a Weyl semimetal Co2MnAl Heusler alloy was experimentally and theoretically investigated by changing the Co content, the direction of electric current against the crystal axis, and the measurement temperature. The experimentally fabricated Co2MnAl thin films epitaxially grown on a MgO single-crystal substrate showed the positive AMR ratios independent of the Co content, the direction of electric current, and the measurement temperature. The AMR ratios for the direction of electric current along Co2MnAl[100] were larger than those along Co2MnAl[110]. The maximum AMR ratios for Co2MnAl[100] were 0.576% at 5 K and 0.349% at 300 K for a Co content of 47 at. %, which is close to the stoichiometric composition. Furthermore, the theoretical calculations of AMR ratios based on the s-d scattering process of the electrons at the Fermi energy, including the information on the density of states (DOS) obtained from first-principles calculations, exhibited trends similar to the experimental results. Compared with the AMR results of Co2MnGa[110], we found that the magnitude relation between the partial DOS of the ε and γ orbitals of the d state of Co atoms determined the sign of the AMR ratios. These results suggest that the AMR effect of Weyl semimetal Co2MnAl can be elucidated by the s-d scattering process of the electrons. [ABSTRACT FROM AUTHOR]

Defect levels in the vicinity of the Al2O3/p-type GaN interface were characterized using a sub-bandgap-light-assisted capacitance–voltage (C–V) method. For metal–oxide–semiconductor (MOS) diodes prepared using p-type GaN (p-GaN) and Al2O3 formed by atomic layer deposition, the C–V curves measured in the dark showed capacitance saturation at a negative bias and a large negative voltage shift compared with ideal curves, which implied the effects of donor-like gap states in the vicinity of the Al2O3/p-GaN interface. Upon illumination with monochromated sub-bandgap light with photon energies higher than 2.0 eV under a large positive bias, the subsequently measured C–V curves showed three plateaus. The plateau under the positive bias voltage due to the surface inversion appeared despite the sub-bandgap illumination, which did not appear at 1.8 eV light illumination, indicating the existence of midgap defect levels. Moreover, the other plateaus were attributed to defect levels at 0.60 and 0.7–0.8 eV above the valence band maximum. For a sample whose surface was prepared by photo-electrochemical (PEC) etching to a depth of 16.5 nm, the C–V curve measured in the dark showed a reduced voltage shift compared with the unetched sample. Furthermore, sub-bandgap-light-assisted C–V curves of the sample with PEC etching showed no plateau at a positive bias, which indicated the reduction in the density of the midgap defect states. Possible origins of the detected defect levels are discussed. The obtained results showed that the interface control can improve the properties of p-GaN MOS structures. [ABSTRACT FROM AUTHOR]

A novel dielectric barrier discharge (DBD) plasma-actuator module with an exposed electrode and two covered electrodes was developed to enhance electrohydrodynamic force generation based on the concept that it separates the ionization and acceleration processes. The conventional three-electrode configuration of the DBD plasma actuator suffers from unexpected spark discharge between the exposed electrodes, thereby failing to strengthen the electric field intensity for accelerating charged particles or generating a stable ionic wind. In this study, a third electrode was embedded in the dielectric layer to prevent spark discharge. Furthermore, an alternating current (AC) waveform was employed as the bias voltage, which was applied to the third electrode, instead of the direct current (DC) voltage used in a conventional DBD plasma actuator. Induced flow visualization using particle image velocimetry technique revealed that the DC bias voltage forms a weak ionic wind in the proposed DBD plasma actuator owing to the electric field screening effect, and the ionic wind periodically appears when the polarity of the voltage is reversed by applying an AC-bias voltage. The velocity of the ionic wind increases with increasing frequency and the AC bias voltage amplitude. Also, decreasing the distance between the second and third electrodes results in ionic wind enhancement. The results obtained in this study provide insights into the drastic improvement in the performance of DBD plasma actuators with the enhancement of the electric field intensity for charged particle acceleration. [ABSTRACT FROM AUTHOR]

We investigated the radiation damage to carrier lifetimes in the neutral and depletion regions of the InGaP and GaAs subcells of an InGaP/GaAs/Ge triple-junction solar cell. It is difficult to clarify the degradation characteristics of the carrier lifetime in each region using the conventional analysis method (e.g., the dark current–voltage characteristic analysis), so we propose a novel method using the internal luminescence efficiency. The radiation damage coefficients for the carrier lifetimes in the neutral region of InGaP and GaAs subcells were two or three orders of magnitude larger than those in the depletion region. This result suggests that the effective radiation-induced defects in the regions, which significantly impact a solar cell's electrical characteristics, differ. This paper discusses the effective radiation-induced defects that contribute to the output degradation in each region. We compare the radiation damage coefficients for the carrier lifetimes obtained in our analysis, the product of the capture cross section, and the defect introduction coefficient of each defect reported in previous studies. [ABSTRACT FROM AUTHOR]

Minute examination of local lattice structures in matter affected by impurity doping is of special importance for the development of functional materials. In order to obtain microscopic information on spinel ferrites, in the present work, we introduced nonmagnetic In3+ ions in Fe3O4 and probed their site selectivity and the doping effect on the local lattice structures and bulk magnetism by means of 57Fe Mössbauer spectroscopy and positron annihilation spectroscopies. The Mössbauer parameters of the area intensity and isomer shift (IS) show that In3+ ions predominantly reside in the tetrahedral A site, especially at low doping level. With increasing concentration of In ions, however, they gradually occupy the octahedral B site replacing Fe3+ ions. Along with the site information, the IS values confirmed that the introduced In ions squeeze the B-site Fe ions at their nearest neighbors. Supporting results were obtained from positron annihilation lifetime spectroscopy; positron lifetimes become shorter with increasing In concentration, signifying that the oxygen ions are pressed by the introduced In ions resulting in lowering the volume of the adjacent lattice vacancies. The results of Doppler broadening spectroscopy also support the squeezing effect; the positrons in the vacancies adjacent to In ions are more likely to annihilate with the inner shell electrons of the surrounding oxygen ions as a result of a reduction in the vacancy volume. [ABSTRACT FROM AUTHOR]

Minute examination of local lattice structures in matter affected by impurity doping is of special importance for the development of functional materials. In order to obtain microscopic information on spinel ferrites, in the present work, we introduced nonmagnetic In3+ ions in Fe3O4 and probed their site selectivity and the doping effect on the local lattice structures and bulk magnetism by means of 57Fe Mössbauer spectroscopy and positron annihilation spectroscopies. The Mössbauer parameters of the area intensity and isomer shift (IS) show that In3+ ions predominantly reside in the tetrahedral A site, especially at low doping level. With increasing concentration of In ions, however, they gradually occupy the octahedral B site replacing Fe3+ ions. Along with the site information, the IS values confirmed that the introduced In ions squeeze the B-site Fe ions at their nearest neighbors. Supporting results were obtained from positron annihilation lifetime spectroscopy; positron lifetimes become shorter with increasing In concentration, signifying that the oxygen ions are pressed by the introduced In ions resulting in lowering the volume of the adjacent lattice vacancies. The results of Doppler broadening spectroscopy also support the squeezing effect; the positrons in the vacancies adjacent to In ions are more likely to annihilate with the inner shell electrons of the surrounding oxygen ions as a result of a reduction in the vacancy volume. [ABSTRACT FROM AUTHOR]

We have investigated the electronic structure of silver chalcogenides Ag2X (X = S, Se, Te) and their solid solutions using hard x-ray photoemission spectroscopy in combination with density functional theory calculations using generalized gradient approximation (GGA). By including the corrections for on-site Coulomb interactions (GGA + U), we successfully reproduced the valence band photoemission spectra, which consist mainly of the Ag 4d band, by calculation. The estimated values for U = 4–6 eV are slightly high for Ag 4d electrons but are consistent with those used in previously reported structural studies. On the other hand, the magnitude of the energy gap is virtually independent of U. These results suggest the strong correlation between Ag 4d electrons in Ag2X compounds to have surprisingly little impact on their electron transport properties. [ABSTRACT FROM AUTHOR]

4H-SiC epitaxial layers with ultrahigh resistivity of over 1010 Ω cm were successfully grown by using a hot wall chemical vapor deposition system with vanadium doping. The resistivity of the vanadium doped epilayer was found to be strongly dependent on the types of dopant impurities. The resistivity of n-type-based vanadium doped semi-insulating 4H-SiC epilayers showed stronger dependence on vanadium incorporation than that of p-type-based epilayers. This means that the carrier trap characteristics of vanadium atoms may differ with respect to electrons and holes. As the result, an ultrahigh resistivity of over 1010 Ω cm was realized on an n-type-based 4H-SiC epilayer with vanadium doping. [ABSTRACT FROM AUTHOR]

This article was originally published online on 13 June 2024 with errors throughout. All online versions of this article were corrected on 27 June 2024; the article is correct as it appears in the printed version of the journal.By A. Barthel; S.-I. Sato; L. Sayre; J. Li; T. Nakamura; T. Ohshima; M. Imaizumi and L. C. HirstReported by Author; Author; Author; Author; Author; Author; Author; Author [Extracted from the article]

The typical experimental conditions inside a transmission electron microscope (TEM), such as ultra-high vacuum, high-energy electron irradiation, and surface effects of ultrathin TEM specimens, can be the origin of unexpected microstructural changes compared with that of bulk material during in situ thermal-annealing experiments. In this paper, we report on the microstructural changes of a Fe–15%Si alloy during in situ TEM annealing, where, in its bulk form, it exhibits an ordering transformation from D03 to B2 at 650 °C. Using a heating-pot type double tilt holder with a proportional–integral–differential control system, we observed the precipitation of α-Fe both at the sample surface and inside the sample. Surface precipitates formed via surface diffusion are markedly large, several tens of nm, whereas precipitates inside the specimen, which are surrounded by Fe-poor regions, reach a maximum size of 20 nm. This unexpected microstructural evolution could be attributed to vacancies on Si sites, which are induced due to high-energy electron irradiation before heating, as well as enhanced thermal diffusion of Fe atoms. [ABSTRACT FROM AUTHOR]

Optical losses are the major drawback to overcome in the solar energy industry and development. Conversion of solar radiation into heat accounts for over 80% of the incident solar energy, which is driven by several aspects like the chosen design and encapsulation of the devices, built-in materials, and the mismatch between the solar spectrum and the active cell's bandgap energy. Photoacoustic (PA) and photothermal (PT) methods are characterization techniques based on the heat generation after the illumination of a material and respective detection. Since the beginning of the solar panel industrial development, these methods have been successfully applied to evaluate the photovoltaic efficiency of devices and the thermophysical parameters of related materials. Here, we present the state-of-art of application of these PA and PT methods to characterize solar cell devices and their built-in materials. Historical aspects, conceptual mechanisms of the basic phenomena, and perspectives on their application for energy-conversion measurements in the new frontier of solar cell research will be discussed. [ABSTRACT FROM AUTHOR]

Exchange-correlation (XC) effects in carrier electrons have a significant influence on the dielectric properties and electric characteristics of a material. In this study, momentum-transfer (q) resolved electron energy-loss spectroscopy was conducted to experimentally evaluate the XC effects of carrier electrons in LaB6 bulk crystals, whose nanoparticles have been used for near-infrared-light shielding filters. By measuring q dependence of plasmon energy due to carrier electrons and evaluating the deviation from the free electron gas model in random phase approximation, the dielectric correction factor due to the XC effects, i.e., the local field correction G(q), for the carrier electrons in LaB6 were experimentally derived. This experimental result confirmed that the XC effects are non-negligible for the carrier electrons in LaB6. Because the XC effects influence dipole surface plasmon energy of LaB6 nanoparticles, the evaluation of the XC effects is important for a precise understanding of the optical properties of LaB6 nanoparticles. [ABSTRACT FROM AUTHOR]

The fabrication of epitaxial ferroelectric materials on Si substrates is key to the design of superior ferroelectric devices for applications involving microelectromechanical systems (MEMS). The domain structures of epitaxial PbTiO3 films grown on Si substrates with an epitaxial SrTiO3 buffer layer were investigated, especially in terms of film thickness dependence. The low thermal expansion coefficient of Si was found to affect the volume fraction of (001)-oriented domains not only in relatively thick film regions but also in the thinner ones. Compared with the PbTiO3 films deposited on SrTiO3 substrates, (100)-oriented domains were observed in films as thin as 18 nm, notwithstanding the strong misfit strain induced by the substrate. Moreover, the saturated volume fraction of the (001)-oriented domain was smaller than that of PbTiO3 on SrTiO3. Thermal strain plays a critical role in determining domain structures and is, therefore, expected to govern the electric properties of films useful in MEMS devices. [ABSTRACT FROM AUTHOR]

Co content (x) dependences of cationic distribution and local fields at the tetrahedral A-site and octahedral B-site nuclei in Co ferrites, CoxFe3−xO4 (x = 0–1.0), were investigated by means of hyperfine interaction techniques. A combined investigation by 57Fe transmission and 57Co emission Mössbauer spectroscopies revealed that about 6% of Co2+ ions occupy the A sites for the sample with Co contents of x = 0 and 1.0. This observation evidently suggests that the site selectivity of Co2+ ions is independent of x for samples prepared on the same heat treatment condition. For hyperfine interaction parameters, obvious x dependence was observed for the B-site Fe nuclei, reflecting variation of the atomic ratio of Fe3+/Fe2+ changing with x, whereas for the A-site Fe nuclei, the parameters hardly change along with x. Contrary to the x-independence for the A-site Fe nuclei, however, it was demonstrated by perturbed angular correlation spectroscopy with the nonmagnetic probe 111Cd(←111In) that the hyperfine field at the A site significantly changes along with x. These contradictory results on the A-site fields verify that the nonmagnetic probe can distinguish a subtle change in the local fields with higher sensitivity. [ABSTRACT FROM AUTHOR]

Ferroelectric domain dynamics in Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 single crystals have been studied by in situ biasing high-voltage transmission electron microscopy with a direct electron detection camera. We have achieved time-resolved recording of polarization switching in real space on a 2.5 ms time scale. The reversible response of micrometer-scale domains was observed by applying an electric field of 1 kV/mm. Detailed analyses on smaller sized domains 100–500 nm in size revealed that the domain switching initiated at a corner of a rectangular domain and propagated inward rapidly. The switching proceeded within 60 ms and the maximum switching rate, as fast as 6–8 μm/s, was observed. The domain switching kinetics was classified as two-dimensional nucleation and growth mode based on the Kolmogolov–Avrami–Ishibashi model. [ABSTRACT FROM AUTHOR]

Color centers that emit light at telecommunication wavelengths are promising candidates for future quantum technologies. A pressing challenge for the broad use of these color centers is the typically low collection efficiency from bulk samples. Here, we demonstrate enhancements of the emission collection efficiency for Er 3 + incorporated into 4H-SiC surface nano-pillars fabricated using a scalable top-down approach. Optimal Er ion implantation and annealing strategies are investigated in detail. The substitutional fraction of Er atoms in the SiC lattice is closely correlated with the peak photoluminescence intensity. This intensity is further enhanced via spatial wave-guiding once the surface is patterned with nano-pillars. These results have broad applicability for use with other color centers in SiC and also demonstrate a step toward a scalable protocol for fabricating photonic quantum devices with enhanced emission characteristics. [ABSTRACT FROM AUTHOR]

Lead-free piezoelectric (1 − x)(Bi, Na)TiO3–xBaTiO3 (x = 0.06–1.0) thin films were deposited, and their crystal structures, ferroelectricity, and piezoelectric properties were studied. These films were epitaxially grown on SrRuO3 covered (100) SrTiO3 substrates by pulsed laser deposition using ceramic targets. For all the compositions, the tetragonal films were found to be grown with (001), polar-axis orientation, mainly due to the thermal strain caused by the different thermal expansion coefficients between the substrate and films. Tetragonal films with x = 0.3 and 0.5 showed higher tetragonality, c/a ratio, than the reported values for the bulk ceramics due to the clamp of the in-plane a-axis by underlying SrRuO3 lattice. Here, a and c are the lattice parameters along in-plane and out-of-plane directions, respectively. This larger c/a ratio results in higher Curie temperature. It was revealed that remanent polarization and coercive electric field correlate with the increase in the c/a ratio of the films. The film with x = 0.06 exhibits the maximum piezoelectric property. [ABSTRACT FROM AUTHOR]

The origin of low conductivity and high near-infrared absorption observed in sputtered Cs-polytungstate (CPT) thin films was studied using x-ray photoelectron spectroscopy (XPS), thermal desorption spectroscopy (TDS), and first-principles calculations. The film's resistivity was directly correlated with the intensity of XPS W5+4f peaks, and the mobility of the conduction band (CB) electrons was evaluated as 1.27 × 10−7 cm2 V−1 s−1, both implying the dominance of W5+-trapped electrons in the CB. The presence of H2O residue in the films was detected from XPS O 1s and TDS spectra, suggesting that the incorporation of water upon film deposition induced numerous W/Cs defects reported in Part I. The two representative types of optical profiles were reproduced by first-principles calculations with W-deficient CPT and H2O-incorporated pyrochlore, respectively. We conclude that water-induced W/Cs defects annihilated free electrons in the films, causing loss of conductance and plasma reflection, whereas W5+-trapped electrons generated by O and W vacancies underwent polaronic excitations that generated large near-infrared absorption. [ABSTRACT FROM AUTHOR]

Sputtered thin films with strong near-infrared absorption and high visible transmission and electrical resistivity (≥102 Ω cm) have been obtained using highly conductive cesium tungsten bronze targets. The origin of the low electrical conductivity and high near-infrared absorption of the films has been investigated by focusing on internal defects and reported in two parts. In Paper I, the optical and electrical properties of the films and their microstructural characterization using x-ray diffraction and high-resolution transmission electron microscopy are presented. Abundant planar W and Cs defects were found on hexagonal prismatic planes that locally expanded the defect plane and triggered the hexagonal-to-orthorhombic crystallographic transition. These cationic defects diminished conduction electrons and suppressed electrical conduction, whereas oxygen vacancies generated W5+-trapped electrons to activate polaronic excitations for strong near-infrared absorption. [ABSTRACT FROM AUTHOR]

We investigate the electrical transport characteristics of graphene channel field-effect transistors (FETs) gated via ionic solid (IS), where the conventional gate insulator, such as SiO 2 , has been replaced by solid electrolytes, such as LiP 3 O 4. In this study, we focus on (i) the gate controllability of the current in comparison to conventional graphene FETs with SiO 2 as an insulating material and (ii) the transient characteristics of the drain current and time required to switch on the current. We employ the tight-binding formalism and Boltzmann equation to calculate the electronic band structure and the electronic transport in graphene, while the Nernst–Planck–Poisson equations have been employed to calculate the time-dependent charge distribution in solid electrolytes and the resulting electric double layer formation at the graphene/IS and IS/gate interfaces. Our simulations have shown that graphene FET gated via IS shows superior gate controllability more than SiO 2 -gated graphene FET with the insulator thickness of 1 nm, and the saturated drain current is insensitive to the IS thickness. Moreover, the time required to switch on the drain current is proportional to the thickness of IS, and the limited number of Li + ion vacancies in IS is preferable in obtaining faster switching than the case of unlimited vacancy cases while keeping the superior gate controllability. [ABSTRACT FROM AUTHOR]

Contactless photo-electrochemical (CL-PEC) etching was used to fabricate recessed-gate AlGaN/GaN high-electron-mobility transistors (HEMTs). Self-termination of etching was observed during CL-PEC etching on an AlGaN barrier layer whose residual thickness had a uniform value of 6 nm overall on the same chip. After tetramethylammonium hydroxide post-treatment, the root-mean-square roughness of the etched surface was around 0.4 nm, which had smoothness comparable to that of the unetched surface. Recessed-Schottky HEMTs showed a positive shift in Vth, the suppression of drain leakage currents, and an improvement in the subthreshold-slope value as compared with planar-gate HEMTs. By applying a metal–insulator–semiconductor (MIS)-gate structure, the gate and drain leakage currents were significantly reduced, leading to an increased input dynamic range. Furthermore, the standard deviations (σ) of the Vth of CL-PEC-etched recessed-Schottky HEMTs and recessed-MIS HEMTs were very small, 5.5 and 16.7 mV, respectively. These results showed that the CL-PEC etching process is promising for the fabrication of recessed-gate AlGaN/GaN HEMTs having excellent uniformity for normally-off device operations. [ABSTRACT FROM AUTHOR]

The band structures of Sn nanowires with various cross-sectional shapes and orientations were calculated by a tight-binding method. The wave functions of bulk Sn and Sn nanowires were also analyzed. The calculation revealed that the conduction band minimum of some Sn nanowires originates from the electronic states in the valence band of bulk Sn. This behavior was discussed in terms of the dependence on the orientation and cross-sectional shape of Sn nanowires. In addition, we clarified that the [110]-oriented nanowires with a narrow (001) sidewall and [111]-oriented nanowires have the lightest effective mass among the considered nanowires. [ABSTRACT FROM AUTHOR]

This document is an erratum for a paper titled "Dielectric conductivity and microwave heating behavior of NiO at high temperature" published in the Journal of Applied Physics. The erratum corrects Equation (8) in the original paper and provides the correct version. It also includes additional sentences that clarify the frequency dependence of the conductivity and the validity of the conclusion. Finally, Equation (9) is replaced with the correct version. The erratum is authored by Noboru Yoshikawa and Haruto Sato. [Extracted from the article]

We have prepared a set of polycrystalline samples of PbPd 1 − x − y Fe y Li x O 2 (x = 0 , 0.01, 0.02, 0.03, and 0.04; y = 0 , 0.02, and 0.05) and have measured synchrotron x-ray diffraction and magnetization systematically. We have found high-temperature ferromagnetism in Fe- and Li-substituted samples and the largest magnetic moment of 0.023 μ B per formula unit in PbPd 0.93 Fe 0.05 Li 0.02 O 2. The ferromagnetism survives at 700 K, and the Curie temperature will be far above 800 K. Although similar but controversial high-temperature ferromagnets have been reported in many thin-film samples thus far, the discovered ferromagnetism is macroscopic in the sense that bulk samples stick to a permanent magnet at room temperature. The Fe and Li dependence of the ferromagnetism is complicated, implying that the ferromagnetism is truly unconventional. [ABSTRACT FROM AUTHOR]

A sensor using the photothermoelectric effect of graphene is anticipated as a candidate for infrared sensors that can operate at room temperature with fast response and high sensitivity. We investigate photothermoelectric detection and the signal-to-noise characteristics of a sensor with a simple metal–graphene–metal structure numerically and analytically and obtain an analytical expression giving the ideal value of specific detectivity D ∗ for a sensor having an ideal potential distribution. It is found that the optimal sensor length is approximately three times longer than the cooling length and that the value of D ∗ for such a sensor with typical cooling length is estimated to be as large as 106 cm Hz / W. The sensor performance can be greatly enhanced by employing light-confining structures such as cavities and plasmon antennas, achieving D ∗ above 108 cm Hz / W. [ABSTRACT FROM AUTHOR]

This study investigated the effects of atmospheric-pressure cold plasma-generated short-lived species, long-lived species, and electric fields on skin melanoma and basal cell carcinoma cells (A2058 cells, BCC cells) and normal cells (BJ cells, Detroit 551 cells). Previous studies showed that either plasma-generated species or electric fields can cause cell apoptosis, but the effects of plasma-generated short-lived species, long-lived species, and electric fields on skin cancer cells have not been fully investigated yet. In this research, we adjusted the distance between the cells and plasma–medium interface to treat the cells with different concentrations of short-lived species such as •OH. A phosphate-buffered saline (PBS)–agarose gel was used to cover the PBS solution surface to prevent the plasma-generated species entering the liquid, ensuring the cells were treated with the electric field only. We compared cell viability and apoptosis to determine which factor had a greater impact on the cells. The results showed that the penetration depth of •OH in PBS reached ∼0.6 mm. With our experimental setup, long-lived species and electric field generated by the plasma did not have significant effects on either the normal or cancer skin cells. By contrast, the short-lived species significantly inhibited the viability and induced apoptosis of skin cancer cells but not the normal skin cells. By comparing the effects of plasma-generated short-lived species, long-lived species, and electric field on skin cancer cells (A2058, BCC) and normal cells (BJ, Detroit 551), this study verified that short-lived species in plasma inhibit skin cancer cells more than normal skin cells. [ABSTRACT FROM AUTHOR]

The topological properties of graphene nanoribbons (GNRs) have received a significant amount of attention in emerging fields such as spintronics and quantum computing. This study is focused on the energetics and magnetism of symmetry-protected junction state arrays, which are realized in the alternating periodic structures of two topologically different armchair GNRs. We found that the antiferromagnetic states require at least eight unit cells for each segment of the periodic armchair GNRs, where the armchair GNRs whose numbers of carbon atoms in a row are seven and nine are connected with a junction structure. We also found the junction structure that provides more stable antiferromagnetic states. Furthermore, we propose an end (armchair GNRs/vacuum interface) structure to avoid disturbing the global topological properties of the junction state array. This means that if the topological end states (non-trivial phases of the Su, Schrieffer, and Heeger model or Majorana fermions) exist, they are properly formed at the endmost junctions without the requirement for extra effort such as long end extension. We believe that this study can add new guidelines and challenges for realizing graphene-based quantum computing. [ABSTRACT FROM AUTHOR]

Cs-doped hexagonal tungsten bronze (CsxWO3–y) nanoparticles (NPs) constitute an infrared-absorbing material with high visible transparency. In this study, anisotropic dielectric responses of individual NPs were evaluated by employing high-energy-resolution electron energy loss spectroscopy (EELS) operated in the aloof-beam mode. EELS data were obtained by setting an electron nanoprobe just aside NP edges either parallel or perpendicular to the c-axis to realize an anisotropic interaction condition with NPs. In the EELS spectra, peaks were observed at around 1.3 or 0.9 eV, respectively, depending on beam conditions parallel (∥c) or perpendicular (⊥c) to the c-axis. Those peaks dominantly reflected the dielectric tensor components of either ɛzz or ɛxx and evidenced the anisotropic responses of individual NPs. The peak energy in the ∥c condition was larger than that in the ⊥c condition; this finding qualitatively agrees with optical reflection measurements using polarized light. The experimental values of peak energies and widths were, respectively, smaller and larger than the theoretically evaluated values. These differences could be attributed to a damping of dipole oscillation by electronic excitations owing to oxygen vacancies. In addition, the peak energies of ⊥c and ∥c interaction conditions varied in ranges of 0.7–1.0 eV and 1.1–1.6 eV, respectively. Those variation ranges are larger than the measurement error of about 0.1 eV. Such variation in peak energies supports the presence of ensemble inhomogeneity in dielectric responses of NPs. Those results indicate that the anisotropy and inhomogeneity of dielectric response are important factors for understanding the optical properties of nanoparticulate dispersions. [ABSTRACT FROM AUTHOR]

Semiconducting barium disilicide (BaSi2) is an emerging material for solar cell applications, and therefore, defect passivation is critical for improving its solar cell performance. Herein, the effect of atomic hydrogen (H) on the photoresponsivity of 500 nm-thick boron (B)-doped p-BaSi2 films was examined. The photoresponsivity reached ∼4 A/W (about twice the highest reported value for H-passivated undoped BaSi2 films) in B-doped p-BaSi2 films exposed to an atomic H supply for 5 − 10 min because of an increased minority-carrier lifetime, as measured by the microwave-detected photoconductivity decay. Furthermore, a ≥15 min atomic H supply was found to degrade photoresponsivity. Ab initio studies were used to interpret and understand experimental observations by analyzing states in the gap region, which can act as traps, in B-doped p-BaSi2 with H incorporation. The effect that atomic H had on the performance of B-doped p-BaSi2/n-Si heterojunction solar cells was also studied. The saturation current density was found to decrease by three orders of magnitude with the atomic H supply, and the conversion efficiency was increased up to 6.2%. Deep-level transient spectroscopy revealed a reduction of defect densities induced by the atomic H supply. Both experimental and theoretical viewpoints show that an atomic H supply is beneficial for BaSi2 solar cells. [ABSTRACT FROM AUTHOR]

Micromagnetic simulations have been performed to investigate the controllability of the skyrmion position in antiferromagnetic nanotracks with their magnetic properties modified spatially. In this study, we have modeled magnetic defects as local variations on the material parameters, such as the exchange stiffness, saturation magnetization, perpendicular magnetocrystalline anisotropy, and Dzyaloshinskii–Moriya constant. Thus, we have observed not only pinning (potential well) but also scattering (potential barrier) of antiferromagnetic skyrmions, when adjusting either a local increase or a local reduction for each material parameter. In order to control the skyrmion motion, it is very important to impose certain positions along the nanotrack where the skyrmion can stop. Magnetic defects incorporated intentionally in antiferromagnetic racetracks can be useful for such a purpose. In order to provide guidelines for experimental studies, we vary both material parameters and the size of the modified region. The results obtained show that the efficiency of skyrmion traps depends on a suitable combination of magnetic defect parameters. Furthermore, we discuss the reason why skyrmions are either attracted or repelled by a region magnetically modified. [ABSTRACT FROM AUTHOR]

Manganites exhibit various types of electronic phenomena, and these electronic characteristics can be controlled by carrier doping. Herein, we report the dielectric and magnetic properties of electron-doped manganite Ca 1 − x Sr x Mn 0.85 Sb 0.15 O 3 (x = 0 , 0.1, 0.2, and 0.3). The temperature dependence of the real part of the dielectric constant exhibits a broad and large peak just below the kink temperature of magnetization and a sharp decrease at lower temperatures, accompanied by an anomaly of the imaginary part. Furthermore, isovalent Sr substitution enhances the temperature of the dielectric peak by more than 50 K. Interestingly, the dielectric peak exhibits a negative magnetic-field effect. For all measured samples, the low-temperature variation of the dielectric constant can be qualitatively explained based on the Maxwell–Wagner (MW) model that describes a system composed of grain boundaries and semiconducting grains. However, the observed peak and its negative magneto-capacitance effect at high temperatures cannot be reproduced by a combination of the MW model and magnetoresistance effect. The dielectric peak strongly indicates polaronic relaxation in the present system. These results suggest that polarons form clusters with a dipole ordering and magneto-electric coupling, which might be consistently understood by the charge-ordering scenario. [ABSTRACT FROM AUTHOR]

La-doped ASnO3 (A = Ba and Sr) have great potential as advanced transparent oxide semiconductors due to their large optical bandgap and relatively high electron mobility. The bandgap of Ba1 − xSrxSnO3 solid solution increases from 3.2 eV (BaSnO3) to 4.6 eV (SrSnO3) with x. However, the increase in the bandgap is accompanied by reductions in the electrical conductivity. The versatility in the changes in the electrical properties is not trivial, and property optimization has been challenging. Here, we propose a simple metric for quantifying the transport properties of ASnO3. We investigated the electron/thermal transport properties of Ba1 − xSrxSnO3 solid solution films and their relationship with the lattice distortion. The results suggest that all the transport properties of Ba1 − xSrxSnO3 are dominated by the lattice distortion. This phenomenon is attributed to the distortions in the SnO6 octahedron, which consists of the conduction band. [ABSTRACT FROM AUTHOR]

The relationship between the valence states of Eu ions in Eu-doped GaN and their magnetic properties is investigated by experiments and simulations. X-ray measurements have verified that the valence states of Eu ions can be controlled through growth temperature and codopants and that the highest concentration of divalent Eu ions is found in samples grown at 700 ° C by codoping with Si and O. According to our phenomenological analysis, magnetoresistance measurement implies the presence of Zener's p–f exchange interaction. However, the magnetization dependence on an external magnetic field shows non-hysteretic sigmoidal curves in all the samples. Our simulations suggest that this is due to the formation of nanostructures of the magnetic impurities in the samples by spinodal decomposition. [ABSTRACT FROM AUTHOR]

The temperature dependence of interdot spin-transfer dynamics at laterally coupled excited states (ESs) in high-density InGaAs quantum dots (QDs) was studied using spin- and time-resolved photoluminescence spectroscopy. At low temperatures below 100 K, temporary suppression of electron-spin polarization decay due to selective relaxation of minority spins from emissive ESs to lower-energy states in neighboring QDs was observed. In the temperature range from 20 K to 140 K, thermal activation of electron spins from lower-energy QD states to higher-energy states via interdot transfer prevents the aforementioned selective relaxation of minority spins, leading to a faster decay of electron-spin polarization during light emission. At high temperatures above 140 K, reinjection of depolarized electron spins from barriers after thermal escape from QD ESs accelerates the further decay of the electron-spin polarization, wherein the electron spins can be activated via ladderlike interdot transfer. These findings indicate that the suppression of reinjection of electron spins from barriers in a high-density QD system is crucial for maintaining high electron-spin polarization during light emission at high temperatures. [ABSTRACT FROM AUTHOR]