Table of contents

There is now a range of well-established experimental methods for quantitative determination of the structure of crystalline surfaces with sub-ångström precision, but increasingly in recent years structure "determinations" are being based only on a combination of scanning tunnelling microscopy images and density functional theory calculations. The dangers and limitations of this approach are described using a few specific examples that illustrate the complementarity, rather than competitive use, of these two different approaches.

Solution V, Nb K-edge XANES (X-ray absorption near edge structure) analysis of molecular catalysis, high oxidation state vanadium(V), niobium(V) complexes containing both imido ligands (possessing metal–nitrogen double bond, NR) and mono anionic ancillary donor ligands (L) of type, M(NR)(L)X₂ (X = Cl, Me), which catalyze ethylene dimerization/polymerization in the presence of Al cocatalysts, has been explored. The analysis method is highly useful to obtain the direct information of the active species (oxidation state, basic framework around the centered metal) in solution (in situ), and should thus become a powerful tool for better understanding the catalysis mechanism, basic coordination and organometallic chemistry.

Given the widespread use of density functional theory (DFT), there is an increasing need for the ability to model large systems (beyond 1000 atoms). We present a brief overview of the large-scale DFT code conquest, which is capable of modelling such large systems, and discuss approaches to the generation of consistent, well-converged pseudo-atomic basis sets which will allow such large-scale calculations. We present tests of these basis sets for a variety of materials, comparing to fully converged plane wave results using the same pseudopotentials and grids.

We performed X-ray fluorescence holography measurements on a Pb(Fe_1/2Nb_1/2)O₃ (PFN) multiferroic material in order to investigate the temperature dependence of three dimensional local structure around Fe atoms. It was found that the atomic image intensity of the nearest neighbor Pb atom abruptly decreases when the temperature becomes lower than the Néel temperature (T_N) of about 150 K, while the intensity of the atomic image at nearest Fe/Nb position remains almost unchanged. These observations show that the magnetic transition at T_N induces static positional shifts of Pb atoms but does not strongly influence the Fe/Nb atoms, which suggests the involvement of Pb ions into the superexchange interaction between Fe ions and its contribution to the spin-lattice coupling in PFN.

We have recently demonstrated an AC magnetic field sensing scheme using a simple continuous-wave optically detected magnetic resonance of nitrogen-vacancy centers in diamond. This scheme is based on electronic spin double-resonance excited by continuous microwave and radiofrequency (RF) fields. Here, we measure and analyze the double-resonance spectrum and magnetic field sensitivity for various microwave and RF frequencies. We observe a clear anticrossing of RF-dressed electronic spin states in the spectrum and estimate the bandwidth to be approximately 5 MHz at a center frequency of 9.9 MHz.

In this letter, the overlapping gate dopingless tunnel field-effect transistor (OGDL-TFET) is proposed and studied by TCAD simulation. To increase the tunneling efficiency and reduce the manufacture difficulty, a dopingless germanium tunneling junction based on charge plasma concept is induced in OGDL-TFET. A high efficiency line tunneling junction is formed by the gate/backgate overlap. The on-state current of 75.5 μA μm⁻¹ and subthreshold swing of 1.9 mV/dec can be obtained. With cut-off frequency of 16.53 GHz and gain bandwidth product of 2.44 GHz, OGDL-TFET obtains good analog and radio frequency performance. The considerable good performance makes OGDL-TFET very attractive for ultra-low power application.

We investigate the interaction between spin–orbit torque (SOT) and domain walls (DWs) created during magnetization reversal in perpendicularly magnetized ultrathin MnGa sandwiched between Ta and NiAl. We examine the out-of-plane hysteresis loops under various in-plane magnetic fields H_xs along the current I direction by using magnetotransport measurements. The applied I acts as an effective perpendicular magnetic field H_eff on magnetization under H_x. The slope of H_eff versus I varies proportionally to H_x and becomes saturated above ∼0.15 T, which is consistent with a model based on magnetization reversal through SOT-assisted chiral DW motion under H_x.

The dynamics of the inward-focusing ring Airy beam in the defocusing nonlinear media is investigated. It is found an interesting phenomenon that the propagation of the inward-focusing ring Airy beam exhibits a "funnel" when the beam intensity is sufficiently high. Additionally, the focus spot of such a funnel beam monotonously changes with the nonlocality of the media. The gradient force of the funnel beam is also studied in detail. The findings may pave the way to the optical tweezers in the nonlinear regime.

We report on the fabrication of planar and channel single mode waveguide operating at infrared-fiber band in ZnSe single crystal by using 6.0 MeV C and O ion implantation and standard lithography technique. The effective refractive indices of the planar waveguide mode at 1539 nm is recorded using the prism-coupling method at the dark environment. Near field intensity distributions of the single mode in ZnSe single crystal waveguide at 1539 nm are measured by an end-face coupling system and reconstructed by the finite difference beam propagation method, respectively. Micro-Raman spectrometry is used to analyze microstructural changes of the substrate and waveguide structure.

This paper demonstrates the formation and control of jet atomization by inserting a steel plate into distilled water on an ultrasonic transducer. The direction of jet atomization was perpendicular to the vibration direction of the transducer, and inserting a steel plate succeeded in generating jet atomization in a direction different from the vibration direction of the transducer. This study also revealed that the amount of atomization can be adjusted; atomization was generated evenly from both sides of the plate at a rate of 1.77 mg s⁻¹ when the plate was set at the center of the transducer, and it was generated from only one side of the plate at a rate of 1.5 mg s⁻¹ when the plate was shifted 2 mm from the center of the transducer. The techniques developed in this study will greatly contribute to the fields of engineering, medicine, and sonochemistry, wherein various atomization controls are desired.

In this paper, we demonstrate excellent ultrafast optical performance of ternary transition metal dichalcogenide ReS_1.02Se_0.98 saturable absorber with high power tolerance and large modulation depth in thulium-doped fiber laser. Q-switching with tunable repetition frequency and pulse duration, and mode-locking with high pulse energy were generated in our experiment. The average output power/pulse energy/pulse duration of the mode-locked pulse train were 313 mW/13.6 nJ/1.43 ps, respectively.

This study demonstrates two approaches to the growth of GaN-based LEDs on (−2 0 1)-oriented β-Ga₂O₃ single crystal substrates using metal-organic CVD under atmospheric pressure. One approach induces non-continuous growth between low-temperature undoped-GaN (u-GaN) and high-temperature u-GaN, whereas the other approach induces continuous growth. We observed the following reduction in the FWHM of X-ray diffraction rocking curves: GaN (0 0 2) on (−2 0 1) β-Ga₂O₃ substrate (from 464 to 342 arcsec) and GaN (1 0 2) (from 886 to 493 arcsec). An LED with six pairs of InGaN/GaN multiple quantum wells was successfully fabricated on the (−2 0 1) β-Ga₂O₃ single crystal substrate.

Ultrafast unidirectional reversal of magnetic vortex core confined in a cylindrical nanocavity is numerically investigated using micromagnetic simulations for the permalloy nanodisk. The excited modes (convergence/divergence) of the core motion are modulated differently by the cavity, depending on the dimension of the cavity, which is the main reason for the unidirectional vortex polarization switching. Assisted with the cavity, the core can be reversed well below 200 ps with less than 10 mT external magnetic field and over a wide range of field frequency. In particular, the core can be selectively switched by varying the dimension of the cylindrical cavity.

We carried out in situ transmission electron microscopy (TEM) on the microstructural change of a sintered Ag die-attach layer heated to 600 °C. It was found that the addition of 2 wt% tungsten carbide (WC) particles to the sintered Ag layer significantly suppressed the microporous structure growth at elevated temperature. In the case of a pure Ag layer without anything added, microporous structure growth started from 450 °C. However, microporous structure growth was hardly observed in the sintered Ag layer with WC added up to 600 °C.

We investigated the electric field effect on the magnetic properties of the Pt or Ru/Cr₂O₃/Co/Pt structures fabricated by molecular beam epitaxy (MBE). The Cr₂O₃ layer fabricated using radical assisted MBE exhibits a high breakdown voltage (∼1.5 MV cm⁻¹) comparable to the thicker films. Owing to interfacial perpendicular magnetic anisotropy, the Co layer exhibits a sufficiently large magnetic anisotropy energy (K_eff > 1 × 10⁶ J m⁻³). Further, a voltage-induced coercivity change is observed for the structure, with an efficiency of −0.5 mT V⁻¹. The Cr₂O₃/Co multilayer is a promising structure for further investigation of the electric field effect of Co-based materials.

A comprehensive strategy of crystal quality control for AlN grown on a nano-patterned sapphire substrate has been explored based on the period size effect. It is found that the crystalline perfection of AlN can be greatly improved by enlarging the period size from 1.0 to 1.4 μm, and the X-ray diffraction ω-scan FWHM values for (0002) and (10-12) planes reach 162 and 181 arcsec, respectively, owning to the significantly reduced area ratio of the coalescence zone. Our results indicate the pattern design requires a critical balance between reducing the area ratio of the coalescence zone and decreasing the coalescence thickness.

An n-type charge layer was introduced into the 4H-SiC separated absorption and multiplication avalanche photodiode. The effect of the charge layer on the optoelectronic characteristics of the photodiode was modeled and studied to optimize the performance of the photodiode. According to the modeling results, 4H-SiC photodiodes were fabricated. A low breakdown voltage of 77.6 V and a significant gain of more than 10⁵ were obtained. The peak responsivity for 270 nm illumination of the photodiode biased at −40 V was 83 mA W⁻¹, corresponding to an external quantum efficiency over 38.2%. Both the simulated and experimental spectral responses are almost identical.

We report the development of an ultrahigh-Q aluminum superconducting microwave resonator on diamond. Our lumped-element LC resonator consists of a central inductive wire, interdigitated comb fingers and signal coupling pads. The resonance frequency of the ground-state mode is measured to be 2.80 GHz with a maximum internal quality factor of 1.0 × 10⁶ at 20 mK. Replacing the micron-scale inductive wire with a nanometric one, our resonator will make it possible to detect and manipulate single solid-state qubits, e.g. nitrogen-vacancy centers, using single microwave photons.

The effect of hydrogen on Pt/Al₂O₃/GaN metal-oxide-semiconductor capacitors was investigated by capacitance–voltage (C–V) measurements. The results showed that hydrogen exposure shifted the C–V curves towards the negative bias direction, indicating that hydrogen was incorporated into Al₂O₃ as a positive charge. Dry air exposure shifted the C–V curves back towards the positive bias direction more quickly than nitrogen did, which suggests that Pt has a catalytic function. Moreover, applying a negative bias to Pt resulted in faster shifts of the C–V curves back towards the positive bias direction. These results may suggest that hydrogen plays a critical role in post-metallization annealing.

The influence of the change in cation distribution on the magnetic and catalytic properties by the thermal annealing process of CoFe₂O₄ spinel was investigated. CoFe₂O₄ was synthesized by solid-state reaction and annealed at 500 °C for 100 h. Samples of single-phase cubic spinel structure with and without annealing were characterized using X-ray diffraction. The thermal annealing caused a change in the cation distribution in the CoFe₂O₄ structure, as confirmed by the X-ray absorption fine structure technique and least-squares fitting method. This result in the Co²⁺cation in the octahedral site increased with the Fe³⁺ cation decreasing, which effected the change in cation distribution. This was responsible for decreasing the saturation magnetization after annealing for the magnetic property, and increasing the degradation percentages of the solution after annealing for the catalytic property. This confirmed that thermal annealing on CoFe₂O₄ was effective for cation distribution change and affected the magnetic and catalytic properties.

Cs₈Ba₁₆Ga₄₀Sn₉₆ was expected to have good thermoelectric properties; we prepared almost single-phase sintered samples of the clathrate. They exhibited a maximum dimensionless figure-of-merit, 0.87, room-temperature (RT) mobility, ∼50 cm² V⁻¹ s⁻¹, and RT lattice thermal conductivity, 12 mW cm⁻¹ K⁻¹. However, these values were inferior to those, 1.19, 170 cm² V⁻¹ s⁻¹, and 5 mW cm⁻¹ K⁻¹, of (K, Ba)₂₄(Ga, Sn)₁₃₆, respectively. Band structure calculation suggests that Cs₈Ba₁₆(Ga, Sn)₁₃₆ would have high carrier mobility like (K, Ba)₂₄(Ga, Sn)₁₃₆. However, the former sintered samples strongly suffered from potential barrier scattering and impurity band conduction; the impurity band conduction may be associated with localized states due to Sn vacancies. Also, the clathrate had relatively large atomic displacement parameters (ADP) of ∼0.1 Å², but the rattling effect to suppress thermal conduction was not so strong because the ADP were in "on center" mode.

InGaN/GaN multi-quantum-well (MQW) solar cells are investigated with temperature-dependent DC and AC analysis, and the effects of differing QW number and thickness are determined. The carrier transport is shown to be dominated by thermionic emission rather than tunneling at elevated temperature but limited by recombination outside the depletion region. Temperature-dependent AC parameters of the III-N MQW devices in high-level injection are determined through a refined AC circuit model of the device. It is shown that the use of AC small-signal analysis and its ability to extract stored charge in the QWs, the comparison of built-in potential to V_OC, and other solar cell critical values allows a device designer insight not possible via DC analysis alone. This critical data suggests that the number of QWs and total depletion volume needs to be matched to the operational temperature of a given high temperature solar cell.

In this paper, we investigate the floating body effect (FBE) in fully depleted polysilicon-body ultrathin-body MOSFETs. Generally, the FBE cannot occur in a fully depleted body. However, we demonstrate that an FBE-like phenomenon can be observed in fully depleted polysilicon-body MOSFETs due to the grain boundaries of the polysilicon. To analyze this, devices with various conditions were fabricated and measured. As a result, we may argue that generated holes can be trapped at grain boundaries, which causes an FBE-like phenomenon. Based on this, we expect that thin-polysilicon devices can be utilized for various applications such as 1T-DRAM or synaptic devices.

In this paper, the temperature dependence of the characteristic parameters for a p-type mono-crystalline silicon photovoltaic cell before and after a potential-induced degradation (PID) stress, is measured and compared. It is demonstrated that a 9 h PID stress causes both a drastic decrease in the value of shunt resistance by ∼35 times and a decrease in the open-circuit voltage, V_oc by ∼34%. Consequently the maximum power density, P_max is decreased by ∼62%. The temperature coefficient (TC) of P_max increases from −0.459 to −0.330 caused by a 0 to 3 h PID stress and then decreases to −0.471%/°C caused by a 3 to 9 h PID stress. Before PID stress, the TC of P_max was determined mainly by the TC of V_oc. However, after PID stress, the TC of P_max was determined both by the TCs of V_oc as well as by the fill factor.

Molecular-dynamics simulations of the pressure-induced structural changes of amorphous Si have been performed using the Tersoff interatomic potential to examine the validity of this potential. Amorphous Si with a tetrahedral network was prepared by melt-quenching methods, and it was then compressed under isothermal–isobaric conditions. The changes of the atomic pair-distribution functions and static structure factors with increasing pressure were in agreement with those observed experimentally. The pressure-induced amorphous structures contained a short-range order similar to the β-tin and Imma structures. These results suggest that the Tersoff potential is suitable for describing the structural changes of amorphous Si under high pressure.

Water and organic-based amorphous InGaZnO thin-film transistors (a-IGZO TFT) were fabricated and their electrical performances were analyzed. By comparing the threshold voltage, subthreshold slope, and field-effect mobility with scaling characteristics, we found that the a-IGZO TFT performances were mainly dependent on the solvent types and stirring times of the precursor solution. In addition, it is shown that the field-effect mobility values follow the Poole–Frenkel mobility model for water-based TFTs when the stirring time is under 24 h indicating that there are large defect density of states that degrade the field-effect mobility. When the stirring time is sufficiently long for the water-based sample, the sample shows superior field-effect mobility compared to the organic-based one, which is attributed to the high annealing efficiency of the water-based IGZO active layer compared to the organic-based one.

Realistic quantum key distribution (QKD) systems suffer from side-channel attacks, which manipulate single-photon detectors. Although measurement-device-independent QKD schemes were proposed to free QKD parties (Alice and Bob) from such measurement devices, these schemes are not easy to be implemented in practice because they require precise synchronization between signals from distant parties. On the other hand, differential phase shift (DPS) QKD is a simple system for practical implementation with current optical equipment. In this study, we propose a simple modification in DPS QKD to prevent side-channel attacks (control blinding and controlling attacks) such that Bob randomly attenuates the incoming signal. This modification allows Bob to utilize photon statistics during attenuated time slots in DPS-QKD systems, using which the side-channel attacks are revealed.

In this paper, a dual-metal gate In_0.53Ga_0.47As dopingless TFET with a platinum metal strip insertion (Pt-MSDG-TFET) is proposed and systematically investigated by using the numerical simulation. Different from that the hafnium metal strip directly reduces the lateral tunneling distance, the platinum metal strip shifts the tunneling junction toward the gate electrode, which obtains a smaller lateral tunneling distance through the applied gate voltage so as to more benefit the electron tunneling. Meanwhile, it makes the performance for Pt-MSDG-TFET more sensitive to the variation of tunneling gate workfunction (Φ_M4), so that better DC and RF performances can be obtained with the decrease of Φ_M4. Moreover, the investigation on the misalignment of the metal strip contributes to give a direction for the practical feasibility of manufacturing. Research indicates that the proposed Pt-MSDG-TFET is a promising TFET for ultra-low power consumption RF application.

The multifunctional biocompatible Janus shaped plasmonic-magnetic silver-magnetite nanoparticles have been developed via a single phase microemulsion technique and investigated for different physical properties. The noble metal integration with magnetite nanoparticles introduces superior optical properties into the nanostructures. The dynamic light scattering technique has been used to measure the hydrodynamic size, monodispersity and zeta potential to check their suitability as multimodal agents. The synthesized silver-magnetite nanoparticles are monodispersed and possess colloidal stability. The UV–visible spectra for Janus silver-magnetite nanoparticles shows a surface plasmon resonance peak at 372 and 474 nm which lies in the visible region of electromagnetic spectrum. The photoluminescence spectrum confirms the obtained nanoparticles to be optically active. The measurements of response for bare magnetite as well as silver-magnetite nanoparticles in an alternating magnetic field reveal their suitability in hyperthermia applications. These synthesized integrated magnetite-silver nanostructures show its potential as an excellent candidate for multimodal applications.

We have found that methyl-terminated layered germanane (GeCH₃) is well dispersed in halogenated solvents by liquid exfoliation, which stands stably for more than half a year. GeCH₃ dispersions and their cast films were characterized using electron microscopy and optical spectroscopies, which revealed the exfoliation of GeCH₃ into a few tens of layers with lateral dimensions of a few hundred nanometers and a thickness of a few tens of nanometers. The resulting dispersion of GeCH₃ by liquid exfoliation opens up a potential route to fabricate thin-film devices by a solution process.

The scaling effect on the thermoelectric heating process in phase-change memory (PCM) cells is computationally investigated through a three-dimensional finite-element simulation of the reset operation on Ge₂Sb₂Te₅ (GST) mushroom cells. Both isotropic and non-isotropic scaling are considered. Thomson heat within GST and Peltier heat at the electrode-GST interface are separately analyzed through the captured thermal profiles within PCM cells. The results of this study indicated that the influence of Peltier heat became weaker with the cell size decreasing mainly due to a larger heat loss via the electrodes, and the steeper thermal gradients within the GST layer sustained the contribution of Thomson heat. The thermoelectric heat can be enhanced by modifying the Seebeck coefficient and the thermal conductivity of materials. Our model provides useful insights of the impact of cell scaling on thermoelectric effects, which are critical parts of effective cell engineering.

This study discusses the fabrication and characterization of optically responsive microfibers with uniaxially ordered nematic liquid crystal molecules at their core. The liquid crystal microfibers were electrospun from a solution of polyvinylpyrrolidone (PVP) and N-(4-methoxybenzylidene)-4-butylaniline (MBBA). A study of phase transition and optical behavior was performed using optical observation by polarized optical microscope, and intermolecular interaction was investigated using Fourier transform infrared (FTIR). The diameter, orientational order of the fibers and light intensity that passed through the fibers depended on the MBBA concentration during the electrospinning process. The nematic–isotropic temperature (T_NI) of PVP–MBBA microfibers shifted lower from the T_NI of MBBA. Meanwhile a reverse correlation between MBBA concentrations and phase transition was found in the isotropic phase; a significant increase in temperature rate and response time was occurred with small weightage of MBBA. FTIR measurement confirmed that the liquid crystal molecules were self-phase separated from the PVP chains in the fibers.

Vanadium dioxide (VO₂) is the core material for thermochromic smart windows, which can control near-infrared light while maintaining visible light transmittance in response to ambient temperature. This study is an experiment that can shorten the time to make a thermochromic thin-film using nanoink containing VO₂ powder. VO₂ (β) particles were synthesized via hydrothermal synthesis using V₂O₅ as the raw material and oxalic acid as the reductant. Thin-films were prepared by a solution-based process using nanoink, which contained VO₂ (β) powder with polyvinylpyrrolidone and ethyl cellulose in a solvent of water and ethanol. Only VO₂ (R/M) undergoes a fully reversible metal–insulator transition. Therefore, annealing conditions that can change VO₂ (β) to VO₂ (M) while removing the polymer on the thin-film surface are required. A VO₂ (β) thin-film was successfully converted to VO₂ (M) when annealed at 800 °C for 1 h, and the intrinsic properties of VO₂ (M) were found in optical results.

Cu(In,Ga)Se₂ (CIGS) is a promising material for thin-film photovoltaic devices. Elucidation of the crystal structure of CIGS thin-films is significant for understanding the properties of CIGS solar cells. This study demonstrates the structural evaluation of CIGS thin-films prepared by a three-stage process using Se K-edge depth-resolved X-ray absorption fine structure (XAFS). The CIGS films changed from a Cu-poor to Cu-rich composition during the second stage of the three-stage process. Notably, Cu_2−xSe is generated at the surface of the film at the end of the second stage. After the third stage process, CIGS films have a Cu-poor composition from the surface to a depth of 200 nm. Depth-resolved XAFS technique is sufficiently applicable for evaluation of electronic and crystal structure of CIGS thin-film. This study will provide useful information for the elucidation of the structure of CIGS thin films.

In this study, we developed a calibration method for a fast steering antenna for investigating the mode conversion window used in electron Bernstein wave heating in the large helical device. The calibration was carried out in under-dense plasma against a line-of-sight with an optical thickness which varied spatially. Although multi-reflected background radiation becomes dominant in optically thin lines-of-sight, we succeeded in calibrating the fast steering antenna by including the effect of multi-reflected background radiation in the solution of the radiation transfer equation as the constant by which the temperature of the center of the plasma is multiplied. In addition, we report the initial results of experiments investigating the mode conversion window in over-dense plasma using the calibrated antenna.

While plasma devices delivering combined stimuli such as electric current and reactive species to biological tissues are promising medical tools, improvements in invasiveness and controllability are required for practical use. We herein demonstrated stable discharge generation in phosphate-buffered saline using thin (φ2.2 mm) and bendable cable without working gas supply toward the combination use with endoscope proposed as less invasive surgery. The discharge generated H₂O₂, $\text{\unicode{x02022}}$OH, and ClO⁻/HClO in accordance with the discharge duration, whereas only electric current treatment without the discharge generated relatively low level of ClO⁻/HClO. In particular, the increase rate of the ClO⁻/HClO generation to the discharge duration was lower than that of H₂O₂ generation, showing the potential of the generation ratio control of ClO⁻/HClO as RCS (reactive chlorine species) to H₂O₂ as ROS (reactive oxygen species).

The damage growth characteristic determines the lifetime of optical components and the operating costs of high power laser systems. Knowledge of the lateral size and the depth of damage sites are crucial to evaluate the subsequent growth. An on-line detection method based on optimal modified lateral shearing interferometry is proposed to simultaneously measure the lateral size and the depth of damage sites. Thus, the damage growth characteristics can be estimated more comprehensively and efficiently. In the presented method, critical parameters of the common-path configuration are analyzed and optimized to meet the measurement requirements. Experimental results are presented to confirm the feasibility of the proposed method for on-line measurement. The damage growth characteristics of an optical film under different fluences are also analyzed and discussed simply.

The charge carrier balance and performance of CdSe/ZnS quantum-dot light-emitting diodes (QD-LEDs) with a vacuum-deposited electron-transport layer (ETL) and carrier-restricting layer (CRL) were successfully improved. Optimizing the fabrication process of the reactively sputtered zinc-tin-oxide (ZTO) ETL and adopting a thermally evaporated tungsten-oxide (WO_x) CRL improved the electron-hole balance, thus leading to QD-LEDs with improved performance. Impedance spectroscopy analysis was successfully exploited in investigating charge carrier injection into each layer of the QD-LED and electron-hole recombination behaviors. The QD-LED with optimized ZTO ETL and without WO_x CRL exhibited 2600 cd m⁻² luminance and 3.2 cd A⁻¹ current efficiency, and the QD-LED with both optimized ZTO ETL and a WO_x CRL exhibited 3900 cd m⁻² luminance and 5.1 cd A⁻¹ current efficiency. These results imply a practical method for improving the electron-hole balance and performance of QD-LEDs, and provide a reliable technique for analyzing the carrier behavior of QD-LEDs.

Influence of etching depth on the interface properties in Al₂O₃/n-GaN MOS diodes has been investigated. The n-GaN surface was etched by inductively coupled reactive-ion-etching (RIE) with shallow (20 nm) and deep etching (1200 nm) depth. The resulting Al₂O₃/n-GaN interface properties were then evaluated by the capacitance/conductance–voltage (C/G–V) and current–voltage (I–V) characteristics measurements. It was found that: (i) the interface state density of the shallow-etched MOS diode is almost the same as that of the un-etched reference sample, (ii) the deep-etched MOS diode showed around five times higher interface state density than the shallow-etched MOS diode, (iii) the increased interface state density with deep etching was not recovered by Tetra-Methyl-Ammonium Hydroxide (TMAH) treatment nor by post annealing, and (iv) the deep-etched MOS diode indicated about five orders of magnitude higher leakage current, which could be attributed to the lowering of the effective barrier height in the Fowler–Nordheim type conduction. The results obtained in this study indicate that improved RIE process has to be developed for the fabrication of GaN MOS FETs that require deep etching such as vertical trench-type FETs.

Control of the plasma-CVD SiO₂/InAlN interface by N₂O plasma oxidation of the InAlN surface was studied. The interface was characterized by both X-ray photoelectron spectroscopy (XPS) and capacitance–voltage measurement of metal–insulator–semiconductor (MIS) diodes. An excessively long duration of oxidation led to the deterioration of the stoichiometry of the InAlN surface and plasma oxide, resulting in a high-density of interface states in the completed MIS diodes. Meanwhile, the surface-localized oxygen deficiency in the plasma oxide layer was observed by XPS. The intensity ratio of the oxygen-deficient component to the fully oxidized component in the O 1s spectrum decreased with increasing oxidation duration. Consequently, there was an optimum oxidation duration. The interface state density was reduced by almost one order in the case of plasma oxidation for an appropriate duration compared with the case of the direct deposition of SiO₂ onto InAlN.

This paper reports a plasma post-treatment technique to improve the performance of GaN ultraviolet avalanche photodiodes (APDs). A BCl₃-based plasma post-etching technique was developed to smooth the roughened GaN surface after inductively-coupled-plasma etching. Atomic-scale surface roughness around 0.278 nm rms and photoluminescence intensity more than doubled were achieved after the post-treatment. The surface smoothing technique was applied to the fabrication process of double-mesa structure GaN APDs grown on a sapphire substrate. Compared to the non-treated APDs, the post-treated GaN APDs show high field leakage current suppressed more than two orders and the average gain increased from 2 × 10⁴ to 1 × 10⁵, indicating the low surface damage after BCl₃ plasma post-treatment. For the GaN APDs fabricated into a 3 × 3 array, the devices show uniform distribution of the breakdown voltages after the plasma post-treatment.

An H-shaped piezoelectric vibration energy harvester (VEH) with two dimensional receiving direction is designed to provide power for engine fault monitoring in this work. The VEH consist of one main-beam which receives the vibrational excitation of horizontal direction, and two sub-beams which receive the vibrational excitation of vertical direction. The main-beam and the sub-beam of this H-shaped VEH are almost independent. So this H-shaped VEH could be modelled as a lumped-mass model. The models of the output voltage and the output power are given. The H-shaped VEH is fabricated using computer numerical control technology. The measured results show that the main-beam's output voltage is 1011 mV with the resonant frequency of 110 Hz, and the sub-beam's output voltage is 1021 mV with the resonant frequency of 118 Hz. The measured maximum output power of main-beam is 24.5 μW when the sliding rheostat is at 12.9 kΩ. And the measured maximum output power of sub-beam is 12.3 μW when the sliding rheostat is at 29.0 kΩ. The power density of the main-beam is about 0.286 μW mm⁻³, and the power density of the sub-beam is about 0.149 μW mm⁻³. Therefore, this H-shaped VEH can provide an effective solution of energy harvesting for engine fault monitoring system. In the future, the size of the structure will be reduced by MEMS technology and this H-shaped VEH can be integrated with other electronic devices.

In this paper, we report the effective minority carrier lifetime (τ_eff) in fresh and potential-induced degradation (PID) acceleration tested p-type single-crystalline Si modules. τ_eff in different regions of solar cells was measured using the microwave photoconductance decay (μPCD) method. Electroluminescence (EL), lock-in-thermography, and dark and light current–voltage (I–V) measurements were carried out as a complementary analysis of μPCD. In addition, τ_eff in every stage of Si solar cell fabrication (wafer to solar cell) was measured to investigate the change of carrier dynamics. From the obtained results, a great decrease in τ_eff was observed in the PID-affected regions, confirming the excess non-radiative recombination centers in that region, suggesting that τ_eff from the μ-PCD method can be an effective indicator to judge whether PID phenomenon has occurred.

Recent developments in the field of vibration-based power generators have highlighted the advantages of using Fe–Ga alloys; these are excellent-magnetostrictive materials having good mechanical properties, which makes them well suited for use as magnetostrictive elements. A rectangular Fe–Ga element oriented along the 〈100〉 direction in a U-shaped unimorph device produces a higher power generation efficiency than samples with other orientations such as 〈110〉 and 〈111〉. The crystal growth direction of the ingots and plane orientation of the elements have a minimal effect on the power-generation efficiency. The observations of the magnetic domain and elastic properties suggest that the anisotropy in power generation is attributable to the anisotropic magnetic and elastic properties of the Fe–Ga alloy. Thus, a high-performance, vibration-based power generator using the Fe–Ga alloy should be fabricated using elements with a 〈100〉 orientation, cut from a single-crystal Fe–Ga ingot.

We have developed a gamma-ray detector based on a single-crystal diamond in order to improve the heat and radiation resistances of gamma-ray monitors. We fabricated prototypes with two types of diamond grown by a chemical vapor deposition method. The count rates with temperature and accumulated dose were obtained using a ¹³⁷Cs gamma-ray source, then the errors at full scale (%FS) were evaluated using a method to reduce the dark count. The prototype-A worked to 643 K within 2.9%FS and to 3.1 MGy within 4.9%FS; on the other hand, the prototype-B worked to 545 K within 3.4%FS and to 5.0 MGy within 0.47%FS. This study demonstrates that the diamond semiconductor was promising for monitoring with enhanced heat and radiation resistances.

The conversion efficiency of passivated emitter and rear cell (PERC) photovoltaic (PV) modules decreases via light-induced degradation (LID). In this study, two models of commercial PERC PV modules were employed. These modules were exposed outdoors until the accumulated solar irradiation reached 687 kW m⁻² to investigate their power generation behavior during the early installation stage. The maximum output power (P_max) finally decreased by 1.52% in one model and by 4.29% in the other model. P_max of the latter model increased after LID owing to light-induced regeneration under open-circuit conditions. However, power generation in the array of the latter model connected to an electrical power grid was not changed after LID and no recovery was observed. It was found that the extent of degradation and the behavior differ depending on not only the difference in models but also the circuit conditions during exposure.

We developed a measurement system that enables the reconstruction of γ-ray time spectra in cascade decay schemes with 0.3 ns time resolution, which is sufficient for nuclear decay with more than nanoseconds half-life. As this system records all the time and energy information of γ-rays, the energy regions for the γ-ray identification can be optimized after the measurement. Moreover, this system has five timing inputs and thus we can record the timing data of external perturbations; we can investigate the responses to the perturbation afterward. This property fulfills the demands required for quantum information research with γ-rays.

The periodic variation of the average electron velocity vector under crossed ac electric and dc magnetic fields is formulated analytically on the basis of kinetic equations for single-electron motion assuming constant-collision-frequency models with and without ionization. The velocity vector draws elliptic loci with the alternation of the electric field, and this is verified by Monte Carlo simulations. The amplitude and the mean deflection angle of the velocity vector, which represent basic features of electron transport in magnetized plasmas, are explicitly described with the collision frequency, the ac angular frequency, and the intensities of the fields.