Japanese Journal of Applied Physics

Power semiconductor devices are key components in power conversion systems. Silicon carbide (SiC) has received increasing attention as a wide-bandgap semiconductor suitable for high-voltage and low-loss power devices. Through recent progress in the crystal growth and process technology of SiC, the production of medium-voltage (600–1700 V) SiC Schottky barrier diodes (SBDs) and power metal–oxide–semiconductor field-effect transistors (MOSFETs) has started. However, basic understanding of the material properties, defect electronics, and the reliability of SiC devices is still poor. In this review paper, the features and present status of SiC power devices are briefly described. Then, several important aspects of the material science and device physics of SiC, such as impurity doping, extended and point defects, and the impact of such defects on device performance and reliability, are reviewed. Fundamental issues regarding SiC SBDs and power MOSFETs are also discussed.

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

We experimentally demonstrate the anti-ferroelectric (AFE) behavior of a Hf_1−xZr_xO₂ (HZO)/Si FET and its potential for high-endurance nonvolatile memory operation. The AFE-HZO FET with Zr content of 75% exhibits a double polarization switching and half-loop switching of its double hysteresis under bipolar and unipolar bias conditions, respectively. The counterclockwise hysteresis in the transfer I_d–V_g characteristics is demonstrated under unipolar V_g sweep through half-loop polarization in AFeFET. The steep subthreshold swing values were observed for both forward and backward V_g sweeps of I_d–V_g curves for AFeFET under unipolar bias condition. The nonvolatile feature of AFeFET is achieved by introducing the optimized hold voltage of 1.3 V during the retention period. The threshold voltage shift can be realized by utilizing the unipolar program/erase V_g pulses. Also, the high-endurance properties of HZO/Si AFeFET are demonstrated under unipolar V_g stress with observable memory window up to 10⁹ cycles without gate insulator breakdown.

Photocatalysis has recently become a common word and various products using photocatalytic functions have been commercialized. Among many candidates for photocatalysts, TiO₂ is almost the only material suitable for industrial use at present and also probably in the future. This is because TiO₂ has the most efficient photoactivity, the highest stability and the lowest cost. More significantly, it has been used as a white pigment from ancient times, and thus, its safety to humans and the environment is guaranteed by history. There are two types of photochemical reaction proceeding on a TiO₂ surface when irradiated with ultraviolet light. One includes the photo-induced redox reactions of adsorbed substances, and the other is the photo-induced hydrophilic conversion of TiO₂ itself. The former type has been known since the early part of the 20th century, but the latter was found only at the end of the century. The combination of these two functions has opened up various novel applications of TiO₂, particularly in the field of building materials. Here, we review the progress of the scientific research on TiO₂ photocatalysis as well as its industrial applications, and describe future prospects of this field mainly based on the present authors' work.

Ion channels regulate membrane potential by mediating the permeation of specific ion species via their transmembrane pore with gating. Understanding the structural dynamics of ion channels is important for elucidating their functional mechanisms. This review highlights the application of high-speed atomic force microscopy (HS-AFM) in investigating structural dynamics of ion channels and ligands. The use of oriented reconstitution techniques allowed for high-resolution, real-time visualization of ion channel dynamics such as pH-dependent clustering in KcsA potassium channels, induced-fit binding of agitoxin-2 (AgTx2), ligand-induced fluctuations in transient receptor potential vanilloid 1 (TRPV1), and voltage sensor dissociation in voltage-gated sodium channels (Na_v). These studies provide valuable insights into the molecular mechanisms that govern ion channel function and contribute to a deeper understanding of their physiological roles. Additionally, the findings underscore the potential of HS-AFM in exploring ion channel behavior under various conditions.

Breakdown voltage (BV) is arguably one of the most critical parameters for power devices. While avalanche breakdown is prevailing in silicon and silicon carbide devices, it is lacking in many wide bandgap (WBG) and ultra-wide bandgap (UWBG) devices, such as the gallium nitride high electron mobility transistor and existing UWBG devices, due to the deployment of junction-less device structures or the inherent material challenges of forming p-n junctions. This paper starts with a survey of avalanche and non-avalanche breakdown mechanisms in WBG and UWBG devices, followed by the distinction between the static and dynamic BV. Various BV characterization methods, including the static and pulse I–V sweep, unclamped and clamped inductive switching, as well as continuous overvoltage switching, are comparatively introduced. The device physics behind the time- and frequency-dependent BV as well as the enabling device structures for avalanche breakdown are also discussed. The paper concludes by identifying research gaps for understanding the breakdown of WBG and UWBG power devices.

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.

This study presents an efficient testing process for characterizing silicon photonic ICs. This process utilizes a coupling structure that integrates grating couplers and spot-size converters for efficient testing both at the chip and wafer levels, respectively. By leveraging wafer-level testing to estimate the characteristics of final chip-level devices, we anticipate a reduction in testing costs. To demonstrate the validity of the proposed testing process, we fabricated and measured silicon-on-insulator ring resonator devices on both wafer and chip levels. The results showed good agreement between the two levels of measurement, validating the effectiveness of our proposed testing process.

This paper describes the concepts for achieving n-type and p-type WSe₂ field-effect transistors (FETs) and their complementary metal-oxide-semiconductor (CMOS) inverter operation. First, n-type and p-type WSe₂ FETs were demonstrated using molecular chemistry approaches that offer the manipulation of WSe₂ properties through low-temperature, low-energy processes. Next, the advancement in device technology was explained to achieve symmetric characteristics in n-type and p-type WSe₂ FETs. WSe₂ single-channel CMOS offers a promising pathway for simplifying device integration to suppress variability and fluctuations in FET characteristics, although many challenges remain to be addressed. Further fundamental research holds the potential to advance the development of WSe₂ single-channel CMOS devices.

The diffraction limit of light fundamentally limits the spatial resolution of conventional optical microscopy. However, tip-enhanced Raman spectroscopy (TERS) which combines scanning probe microscopy with Raman spectroscopy overcomes this limitation by utilizing near-field technique with a plasmonic tip. This enables the simultaneous acquisition of morphology and optical response of materials present on the surface. As a result, the nanoscale features of surfaces and their optical signals, which are not accessible through far-field signals, can be measured at sub-nanometer resolution. In this review, we first provide a brief introduction followed by an overview of the essential components of TERS, including the working principle of TERS and fabrication methods of plasmonic tips. Subsequently, we will look into the advances in the instrumentation of TERS, such as the operation of TERS in various environments, dynamic control using a tip, and the implementation of adaptive optics in TERS. Finally, we will review very recent TERS studies in selected research areas, including biomaterials, 2D materials, catalytic processes, and single-molecule chemistry.

Electromagnetic acoustic resonance (EMAR) has been applied to fatigue-damage assessment because of its ability to accurately measure ultrasonic velocity and attenuation contactlessly, which are sensitive to microstructural changes. We applied EMAR using axial-shear-wave resonance, which can sense different depth information, to non-contacting in-situ evaluation of torsional fatigue damage of a carbon-steel rod. While previous studies have shown that ultrasonic velocity decreases monotonically as fatigue damage progresses and attenuation peaks before failure, we found an unusual increase in the velocity, which has never been reported. For the mechanism analysis, we observed the microstructures and measured the residual stress near the specimen surface. As a result, we found that it is difficult to explain the velocity change only by the dislocation-structure changes, by which ultrasonic behavior has been explained in previous studies, and that residual stress and solid-soluble precipitation are likely to contribute to the initial increase in the velocity.

This article reports an ionization by Ar⁺ impact (i.e. β process) found in simulations of capacitively coupled Ar plasmas in a gaseous electronics conference reference cell. The simulation, which was performed using a combination of our in-house GPU-parallelized particle-in-cell, Monte Carlo collision model, and a comprehensive ion-neutral collision model, has revealed for the first time that ionization by Ar⁺ occurs in the vicinity of the powered electrode surface. Although its impact on the plasma density is so small that the ionization rate can be negligible in comparison to other ion reaction rates for e.g. short- and long-range charge exchanges, its effect becomes significant by raising the voltage applied to the powered electrode due to an increase in energetic Ar⁺ flux.

In this study, we examine the impact of various seed layer materials that facilitate the growth of highly textured or epitaxial topological insulator Bi_0.9Sb_0.1(012) on Si/SiOx substrates. We found that cubic-textured (100) or tetragonal (001) seed layers facilitate the epitaxial growth of undoped Bi_1−xSb_x(012) with more square surface, while seed layers composed of (111) polycrystalline or, alternatively, nanocrystalline or amorphous materials are suitable for growth of highly textured Bi_1−xSb_x(012):X with more rectangular surface (012), where X is a dopant. By post annealing, we obtained a maximum spin Hall angle of 24 for epitaxial Bi_0.9Sb_0.1(012). Furthermore, we found a clear correlation between the spin Hall angle and the column height in Bi_0.9Sb_0.1(012) subjected to post annealing up to 215 °C and 3 h. Our findings establish a foundation for effective methodologies aimed at producing high-performance Bi_1−xSb_x in the (012) orientation on practical Si/SiO_x substrates using physical vapor deposition.

In this paper, we propose the use of a semi-circular array to achieve two-dimensional positioning in shallow water. We fabricated a semi-circular array and conducted experiments in a coastal area to evaluate an appropriate array signal processing technique. The obtained results suggest that the use of the delay-and-sum beamforming method is suitable for applications allowing some error, while multiple signal classification method provides more precise positioning when additional computational resources are available.

This study demonstrates the critical role of integrating energy band engineering with asymmetric composite passivation structures in enhancing silicon heterojunction (SHJ) solar cell performance. By investigating the effect of deposition pressure on the optical bandgap of pure silane passivation layers, tunable bandgap values ranging from 1.65 to 1.89 eV were achieved. This pressure-induced bandgap modulation enabled the implementation of asymmetric energy band engineering at the c-Si/a-Si:H interface, reducing the band offset from 0.50 to 0.30 eV and increasing the effective minority carrier lifetime by 29%. The optimized SHJ solar cells exhibited an open-circuit voltage (V_oc) of 734.8 mV and a fill factor of 85.08%, reflecting respective improvements of 3.0% and 3.5%, and a power conversion efficiency of 24.2% on G12 half-area wafers. These results confirm that energy band engineering of asymmetric composite passivation layers effectively balances passivation quality and carrier transport, significantly enhancing device performance.

Fe₃GeTe₂ is a van der Waals ferromagnet that has attracted significant attention due to its tuneable magnetic properties and potential applications in spintronic devices. In this work, we present a comprehensive study on high-quality Fe_3−xGeTe₂ (FGT) crystals using techniques including scanning tunneling microscopy (STM), atomic force microscopy (AFM), Kelvin probe force microscopy (KPFM), superconducting quantum interference device (SQUID) magnetometry, and X-ray magnetic circular dichroism (XMCD). STM and AFM reveal the atomic-scale surface morphology and layer-dependent structural features, highlighting the high crystallinity and terrace structures typical of van der Waals materials. KPFM measurements provide insights into the surface potential distribution and work function variations, indicating electronic structure modifications across different domains. Using the element-specific XMCD technique, we probe the local electronic characteristics of the magnetic ground state of FGT. From sum rule analysis, a significant difference between the orbital and spin moments is observed, leading to a notable spectroscopic splitting factor (g-factor). Our findings confirm notable contribution of both the Fe 3d and Ge–Te hybridized orbitals to the overall magnetic properties, shedding light on the microscopic mechanisms governing ferromagnetism in this material. This multi-technique approach provides a detailed understanding of the interplay between structure, electronic properties, and magnetism in FGT, paving the way for future applications in nanoscale magnetic devices.

This article showcases how optical pickup units, a type of optical data storage technology, can be sustainably hacked for advanced applications in atomic force microscopy (AFM) and medical diagnostics. The evolution of these technologies from compact discs to Blu-ray is discussed, and their creative applications in high-precision, cost-effective scientific tools are detailed. The transition from data storage to nanoscale imaging has implications for skin nanotexture biometrics, as demonstrated by the example of high-speed dermal AFM for dermatological analysis. Although several technical challenges arise, this approach can have considerable economic and educational benefits and future possibilities, including integration with internet of things and artificial intelligence for stronger functionality. Innovation grounded in hacking can democratize scientific exploration, promote sustainable research, and advance precision medicine, thereby creating a new paradigm for the development of scientific instrumentation.

For frequency filter applications in next-generation mobile communications, bulk acoustic wave (BAW) resonators are required to have high frequency operation, high k_eff², high Q, and high power durability. High-overtone mode BAW resonators with multilayer polarization-inverted films can operate at higher frequencies than standard single-layer BAW resonators, while maintaining the device volume and power durability. In this paper, the frequency characteristics and BAW behavior of polarization-inverted AlN film SMRs were investigated using the finite element method and Mason's equivalent circuit models. Polarization-inverted ScAlN film bulk acoustic wave resonators and SiAlN/AlN solidly mounted resonators (SMRs) operating in the GHz range were experimentally fabricated and evaluated. We theoretically demonstrated that the k_eff² of the AlN film SMRs improves with increasing the number of polarization-inverted layers due to the improvement of the BAW energy trapping into the AlN films. We also experimentally found that the polarization-inverted SiAlN/AlN SMRs operating in high-overtone mode had higher Q and k_eff² than the single-layer AlN SMR.

The diffraction limit of light fundamentally limits the spatial resolution of conventional optical microscopy. However, tip-enhanced Raman spectroscopy (TERS) which combines scanning probe microscopy with Raman spectroscopy overcomes this limitation by utilizing near-field technique with a plasmonic tip. This enables the simultaneous acquisition of morphology and optical response of materials present on the surface. As a result, the nanoscale features of surfaces and their optical signals, which are not accessible through far-field signals, can be measured at sub-nanometer resolution. In this review, we first provide a brief introduction followed by an overview of the essential components of TERS, including the working principle of TERS and fabrication methods of plasmonic tips. Subsequently, we will look into the advances in the instrumentation of TERS, such as the operation of TERS in various environments, dynamic control using a tip, and the implementation of adaptive optics in TERS. Finally, we will review very recent TERS studies in selected research areas, including biomaterials, 2D materials, catalytic processes, and single-molecule chemistry.

Physical vapor deposition (PVD) methods for polymer thin films were reviewed with an emphasis on those techniques that use energy beams such as UV light, electron beam, and ion beam. One class of PVD is a direct evaporation of polymer materials, which can produce thin films consisting of small molecular weights. Molecularly oriented thin films can be obtained with this method for some types of polymers. The other class called vapor-deposition polymerization, involves a polymerization reaction in the process of film growth. The vapor-deposition polymerization can be achieved either by the stepwise reaction, such as polycondensation or polyaddition of co-evaporated monomers or by the chain reaction through radical polymerization of single monomer species activated by UV light, electron beam, ion beam, etc. Typical examples of film formation and applications are reviewed for each process. Also, mentioned is a strategy to covalently tether the interface between the polymer films and the substrates.

We directly bonded 17-μm thick Al foils to 2-μm SiO₂ films on Si substrates with a resistivity of 1-10 Ωcm by using the surface activated bonding and fabricated coplanar waveguides (CPWs) as a prototype of bonding-based interconnects on interlayer dielectrics on low-resistivity substrates. Their RF characteristics were compared with the characteristics of CPWs made of evaporated 0.8-μm thick Al layers on the SiO₂ films and those of CPWs directly fabricated on the exposed surfaces of underlying Si substrates. The Al-foil based CPWs on the SiO₂ films revealed the smallest attenuation constant, which implied that their conductor and/or substrate losses were lower than those of the other CPWs. This result indicates that the direct bonding of metal foils to dielectric films is promising for realizing low-loss interconnects monolithically integrated on low-resistivity substrates.

We fabricated encapsulant-less, curved, large-area crystalline silicon (c-Si) photovoltaic (PV) modules using a polycarbonate (PC) base and front cover. To investigate their mechanical strength against static loads and impact durability, we conducted sandbag load tests and hail impact tests. The PC front cover demonstrated excellent durability against loads and impacts due to its high elastic modulus and impact resistance. In the sandbag load test, the front cover did not undergo plastic deformation even under prolonged loading, and we observed no damage caused by contact between the front cover and the solar cells. Furthermore, in the hail impact test, there were no damage to the solar cells or scratches on the front cover due to the hail impact, suggesting that the PC front cover can serve as an alternative to conventional cover glass. These results confirm that encapsulant-less, curved, large-area c-Si PV modules possess sufficient mechanical strength comparable to conventional modules.

This study utilizes the ERA5 reanalysis dataset to simulate hourly DC power output using pvlib python (PVLIB) for three years (2018–2020), validated with high–resolution observational measurements from a rooftop PV system in Thailand. We have identified the optimal PVLIB configuration to predict the power output from five experiments conducted. Simulations performed better under clear–sky conditions, achieving a correlation exceeding 0.74, RMSE less than 0.94 kW, and nRMSE less than 18.80%. On the other hand, the performance tended to decline under cloudy–sky, exhibiting a correlation exceeding 0.75, RMSE exceeding 1.0 kW, and nRMSE of more than 94%. Although the performance indicates that ERA5 could be a good substitute data for predicting PV power output, the reliability of these simulations could be improved by assessing additional ERA5 variables and applying bias correction techniques.

Electromagnetic forces have been applied to control crystal growth in molten metals, typically via magnetic forces, because electrostatic energy is lower than magnetic energy. This study investigated the application of intense electrostatic energy to molten titanium (Ti), by heating the tip of a Ti wire utilizing a laser under an electrostatic field, resulting in the formation of convex-molten Ti with a concentrated electrostatic field. When 15 kV was applied across the molten Ti, electric stress exceeding surface tension pulled the melt upward, forming a sharp Ti tip whose apex was surrounded by facets. However, when 10 kV was applied, the surface tension of the melt was greater than the electrostatic stress; therefore, the melt could not grow upward, resulting in a rounded Ti tip. This study demonstrates that the electrostatic field applied during laser heating effectively controls melt growth, offering significant potential for precise material structuring.

Detection of a small amount of oxygen vacancies is often difficult. In this study, using near-ambient pressure hard X-ray photoelectron spectroscopy, oxygen vacancies were formed in situ in SnO2-x and WO3-y under a reducing gas atmosphere. The number of oxygen vacancies was so small that they could not be detected in the core-level photoelectron spectra. However, the effects of the vacancies were observed in the valence band spectra. This is because under the measurement conditions, the relative sensitivity of the metal outer orbitals (Sn 5s and W 5d) occupied when the oxygen vacancies are formed is significantly higher than that of the O 2p orbital predominantly forming the valence band. The x and y values were estimated to be ∼0.007 to 0.01 and ∼0.008 to 0.02, respectively, which correspond to vacancy ratios of sub-percent.

This study demonstrates the critical role of integrating energy band engineering with asymmetric composite passivation structures in enhancing silicon heterojunction (SHJ) solar cell performance. By investigating the effect of deposition pressure on the optical bandgap of pure silane passivation layers, tunable bandgap values ranging from 1.65 to 1.89 eV were achieved. This pressure-induced bandgap modulation enabled the implementation of asymmetric energy band engineering at the c-Si/a-Si:H interface, reducing the band offset from 0.50 to 0.30 eV and increasing the effective minority carrier lifetime by 29%. The optimized SHJ solar cells exhibited an open-circuit voltage (V_oc) of 734.8 mV and a fill factor of 85.08%, reflecting respective improvements of 3.0% and 3.5%, and a power conversion efficiency of 24.2% on G12 half-area wafers. These results confirm that energy band engineering of asymmetric composite passivation layers effectively balances passivation quality and carrier transport, significantly enhancing device performance.

Selective-area growth of InGaAs nanowires (NWs) and vertical gate-all-around (VGAA) transistors using the vertical InGaAs NWs on Silicon-on-insulator (SOI) substrates were characterized toward future three-dimensional integrated circuit applications using III-V NW-based VGAA transistors. On an n-type SOI, the VGAA transistor acts as a field-effect transistor (FET), involving carrier transport and the electrostatic modulation inside the InGaAs NW channels. While on a p-type SOI, the transistor exhibited tunnel FET properties, involving tunnel transport at the InGaAs NW/SOI interface. Characterization of the VGAA transistors with the variation of NW diameter revealed that device properties, including off-leakage current and subthreshold slope, were degraded with large NW diameter due to misfit dislocation at the NW/Si interface.

〈100〉 oriented single-crystalline ZrC nanoneedles were successfully fabricated using a dual-beam FIB-SEM system. Atomic characterization of the pristine ZrC crystal confirmed the consistency and uniformity of nanoneedles' crystallographic orientation, ensuring tip stability and precision. Nanoneedles with 10–100 nm tip radii were evaluated as field emitters, yielding field enhancement factors of 1.78 × 10⁷–4.85 × 10⁶ m⁻¹ and tip emission areas of 0.93–97.3 nm². This work underscores the importance of geometric optimization in improving field emission performance and demonstrates a scalable and efficient method for developing high-performance electron sources for advanced electron-beam applications.

In this study, we present a novel elevated-laser-liquid-phase-epitaxy (ELLPE) technique that has been developed for the fabrication of single-crystal germanium (Ge) films with (100) orientation, which is ideal for monolithic three-dimensional integrated circuits (3D ICs). The crystalline quality and orientation of the ELLPE Ge films were validated using scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. Additionally, heat transfer dynamics during the laser crystallization process were analyzed through COMSOL Multiphysics simulations. More significantly, the ELLPE technique maintains the temperature of the underlying silicon (Si) substrate below the critical 400 °C thermal budget, ensuring full compatibility with monolithic 3D integration processes. The combination of low thermal budget and high-quality single-crystal Ge film states ELLPE technique as a promising method for enhancing the performance of future monolithic 3D ICs.

Fe₃GeTe₂ is a van der Waals ferromagnet that has attracted significant attention due to its tuneable magnetic properties and potential applications in spintronic devices. In this work, we present a comprehensive study on high-quality Fe_3−xGeTe₂ (FGT) crystals using techniques including scanning tunneling microscopy (STM), atomic force microscopy (AFM), Kelvin probe force microscopy (KPFM), superconducting quantum interference device (SQUID) magnetometry, and X-ray magnetic circular dichroism (XMCD). STM and AFM reveal the atomic-scale surface morphology and layer-dependent structural features, highlighting the high crystallinity and terrace structures typical of van der Waals materials. KPFM measurements provide insights into the surface potential distribution and work function variations, indicating electronic structure modifications across different domains. Using the element-specific XMCD technique, we probe the local electronic characteristics of the magnetic ground state of FGT. From sum rule analysis, a significant difference between the orbital and spin moments is observed, leading to a notable spectroscopic splitting factor (g-factor). Our findings confirm notable contribution of both the Fe 3d and Ge–Te hybridized orbitals to the overall magnetic properties, shedding light on the microscopic mechanisms governing ferromagnetism in this material. This multi-technique approach provides a detailed understanding of the interplay between structure, electronic properties, and magnetism in FGT, paving the way for future applications in nanoscale magnetic devices.

GeO2 prepared via thermal oxidation at ambient pressure is known to be of poor-quality owing to numerous defects and high interface states. Several methods for fabricating high-quality GeO2 films been reported, such as applying pressure, but all of them present challenges. Therefore, a simpler fabrication method is required. In this study, we attempted to reduce defects and interface states in GeO2/Ge prepared via atmospheric-pressure thermal oxidation using ultraviolet–ozone (UVO) treatment. Measurement results indicated that UVO treatment can reduce defects and interface states to the same level as that of high-quality GeO2/Ge reported thus far.

This article showcases how optical pickup units, a type of optical data storage technology, can be sustainably hacked for advanced applications in atomic force microscopy (AFM) and medical diagnostics. The evolution of these technologies from compact discs to Blu-ray is discussed, and their creative applications in high-precision, cost-effective scientific tools are detailed. The transition from data storage to nanoscale imaging has implications for skin nanotexture biometrics, as demonstrated by the example of high-speed dermal AFM for dermatological analysis. Although several technical challenges arise, this approach can have considerable economic and educational benefits and future possibilities, including integration with internet of things and artificial intelligence for stronger functionality. Innovation grounded in hacking can democratize scientific exploration, promote sustainable research, and advance precision medicine, thereby creating a new paradigm for the development of scientific instrumentation.

This study aims to develop surface modification pretreatment for ultrasonic bonding to optimize aluminum-to-aluminum metal direct bonding for multilayer packaging applications. Vacuum ultraviolet (VUV) irradiations in air or formic acid atmosphere were adopted. Experimental results indicate that VUV pre-treatment could alter the functional group bonding on the aluminum surface, especially the increase in the content of Al–OH bonds. The atmosphere of formic acid vapor gave rise to the formation of formate ligands via monodentate coordination mode. An appropriate amount of Al–OH and formate ligands enhance the strength of aluminum/aluminum joints. However, excessive organic acid treatment resulted in incomplete reaction residues, leading to a deterioration in bonding.

We review our studies to assess charge carrier dynamics inside a perovskite film and interfacial charge transfer dynamics for a perovskite layer sandwiched by an electron transporting layer (ETL) such as TiO2 compact or mesoporous layer and a hole transporting layer (HTL) such as spiro-OMeTAD. Both electron and hole injection occurs faster than electron-hole recombination inside a perovskite film, however both change injection yields decrease with increase in excitation intensity. Since the electron mobility inside methylammonium lead iodide (MAPbI3) perovskite is smaller than the hole mobility, employing a mesoporous ETL structure is suitable to maximise an electron injection yield. Interfacial charge recombination lifetime increases with increase in perovskite film thickness and separated charge carrier density. We therefore conclude that for p-type MAPbI3 solar cells, the perovskite film thickness should be increased to the hole diffusion length while the mesoporous ETL structure should be employed to maximise the electron injection yield.

Ultraviolet-induced degradation (UV-ID) of various PV cell types was analyzed under optical UV filters with different cutoff wavelengths. Cell types studied included interdigitated back contact (IBC), passivated emitter and rear totally diffused (PERT), and heterojunction technology (HJT) based on crystalline Si (c-Si), and metal halide perovskite (MHP) cells. Analyzing degradation rates in two distinct regimes proved beneficial for all cell types. We used empirical linearizing functions ln(t) for c-Si technologies and ²√t for MHP samples where t is time. These were applied to extrapolate UV-induced degradation over the lifetime of PV modules under various levels of optical UV filtering and used to predict the relative economic benefits for PV power plants. Degradation rates for all technologies were generally faster under the long pass optical filters having shorter cutoff wavelengths transmitting more UV irradiation and at elevated temperatures when testing MHP samples in the range between 60 °C and 90 °C.

Microscopic structural changes on Ti surfaces under low-energy (≤30 eV) and perpendicular hydrogen ion (H⁺, H₂⁺) irradiation were investigated using molecular dynamics simulations and topological data analysis. Under H₂⁺ irradiation, H retention peaked at 5–7 eV, while H⁺ irradiation decreased monotonically with increasing energy. Detailed analysis for H₂⁺ irradiation revealed that the retention ratio of two hydrogen atoms composing the H₂ molecule followed a similar trend. Persistence diagrams showed additional ring structures formed by H incorporation, leaving the original Ti ring framework intact. Most new rings comprised one H atom and two Ti atoms, with H-Ti distances contracting at lower irradiation energies. The centers of these rings shifted to shallower regions of the Ti surface with decreasing irradiation energy. These findings underscore the potential of low-energy hydrogen ion irradiation for controlled H incorporation into Ti surfaces, suggesting the atomic-level control of plasma-assisted surface engineering.

Ultraviolet-induced degradation (UV-ID) of various PV cell types was analyzed under optical UV filters with different cutoff wavelengths. Cell types studied included interdigitated back contact (IBC), passivated emitter and rear totally diffused (PERT), and heterojunction technology (HJT) based on crystalline Si (c-Si), and metal halide perovskite (MHP) cells. Analyzing degradation rates in two distinct regimes proved beneficial for all cell types. We used empirical linearizing functions ln(t) for c-Si technologies and ²√t for MHP samples where t is time. These were applied to extrapolate UV-induced degradation over the lifetime of PV modules under various levels of optical UV filtering and used to predict the relative economic benefits for PV power plants. Degradation rates for all technologies were generally faster under the long pass optical filters having shorter cutoff wavelengths transmitting more UV irradiation and at elevated temperatures when testing MHP samples in the range between 60 °C and 90 °C.

We conducted a fundamental study to elucidate the relationship between acoustic and electrical properties in the context of liver steatosis. The speed of sound, attenuation coefficient, conductivity and relative permittivity were measured in rat livers with varying degrees of fat deposition. Fat deposition results in a decrease in the speed of sound, an increase in the attenuation coefficient and a reduction in conductivity and relative permittivity. However, no linear correlation was observed between these properties and fat content or droplet size individually. However, a notable correlation between changes in acoustic and electrical properties was identified when the structural and organizational effects of fat were considered in combination. In particular, attenuation changes were found to correlate with corresponding changes in electrical properties. These findings underscore the importance of comprehensively considering structural factors, such as fat droplet size and distribution, to better understand the physical mechanisms underlying the relationship between acoustic and electrical properties.

Ga/In alloy, known for its low melting point and liquid state at room temperature, is a promising material for producing fine metal particles. Conventional methods often face challenges in efficiency or particle uniformity, particularly for particle sizes below 10 μm. Ultrasonic processing offers a potential solution, enabling efficient production of microscale and sub-microscale particles. This study examined the effects of ultrasonic frequency and power on the particle size distribution of Ga/In alloy. The effect on particle refinement of adding a second ultrasonic irradiation step was also evaluated. High-speed video imaging was used to capture the dispersion process in real time. The results indicate that particle size depended strongly on ultrasonic frequency and power, with higher frequencies yielding finer particles. The secondary irradiation effectively improved size distribution and dispersion. These findings provide insights into the controlled formation of metal microparticles using ultrasonic techniques.

We evaluated surface activated bonding (SAB), a room temperature bonding, for hybrid surfaces bonding. At first, SAB process was evaluated on copper and silicon oxide full sheet surfaces, in order to separately study the impact of the SAB activation on both types of materials embedded in a hybrid surface layer. Then, 200 mm wafers with 2.5 μm copper pads 2.5 μm apart in a silicon oxide matrix were used to probe the impact of activation with atomic force microscopy. Two test vehicles were then manufactured in order to morphologically and electrically study the bonding interface. Thus, hybrid wafers were aligned and bonded in an EVG^®COMBOND^® equipment. Cross-sectional scanning and transmission electron microscopy characterizations were performed on both test vehicles in order to observe the bonding interface. Electrical tests were also performed at the end of full 3D integration on daisy chain structures to demonstrate a high connectivity through the bonding interface.

We experimentally demonstrate the anti-ferroelectric (AFE) behavior of a Hf_1−xZr_xO₂ (HZO)/Si FET and its potential for high-endurance nonvolatile memory operation. The AFE-HZO FET with Zr content of 75% exhibits a double polarization switching and half-loop switching of its double hysteresis under bipolar and unipolar bias conditions, respectively. The counterclockwise hysteresis in the transfer I_d–V_g characteristics is demonstrated under unipolar V_g sweep through half-loop polarization in AFeFET. The steep subthreshold swing values were observed for both forward and backward V_g sweeps of I_d–V_g curves for AFeFET under unipolar bias condition. The nonvolatile feature of AFeFET is achieved by introducing the optimized hold voltage of 1.3 V during the retention period. The threshold voltage shift can be realized by utilizing the unipolar program/erase V_g pulses. Also, the high-endurance properties of HZO/Si AFeFET are demonstrated under unipolar V_g stress with observable memory window up to 10⁹ cycles without gate insulator breakdown.

We elucidate the role of gallium (Ga) in the structural and electronic properties of amorphous indium gallium oxide (a-IGO) for different Ga concentrations with oxygen interstitial defects using hybrid density functional methods. Ab initio molecular dynamic simulations reveal that Ga substitution significantly affects the structural characteristics, and that Ga–O coordination is particularly sensitive to changes in oxygen stoichiometry. The electronic structure indicates the formation of an O–O dimer in the neutral state. The stability of this dimer upon capturing electrons is influenced by the local atomic structure around the dimer. When the bond breaks, the dimer's antibonding defect level is significantly lowered from the conduction band, approaching the valence band. This makes it more energetically advantageous for the dimer to capture two electrons. We statistically studied the Ga concentration dependence on the impact of O₂ dimer generation in a-IGO. Formation transition energy indicates that O–O bond is broken easily with more Ga, which acts as an electron trap identifying the origin of positive bias stress observed in the transistor behavior.

Dynamic ultrasound scattering methods are becoming established to allow measurements of the dynamics of microparticles in Brownian motion. Using a focused transducer, nanoparticles can be analyzed, but applying strong ultrasound to large submicron particles causes problems with excessive acoustic energy that interferes with the dynamics of the particles. Backscattering is an attractive setup that maximizes spatial resolution, but when the sample thickness is reduced to eliminate the acoustic flow effects, the reflected waves of two cell windows that sandwich the suspension and the weak particle scattering signal interfere with each other. Therefore, a new technique was attempted to remove the reflected waves and extract only the scattered waves. After showing that the acoustic energy does not interfere with the analysis of nanoparticles even in the presence of large particles, we showed that these sizes can be extracted simultaneously, using a mixture of particles with diameters of 50 and 500 nm.

This work presents a comprehensive study on the sensitivity optimization of electrical impedance flow cytometry devices for identifying analytes suspended in a flowing liquid. The optimization is achieved by investigating the influence of various parameters, including applied frequency, electrode geometry dimensions, bacterial properties, and buffer characteristics. The study utilizes COMSOL Multiphysics simulation to analyze the impedance variation based on differential Maxwell's equations solved using finite element methods. The frequency optimization reveals that the sensitivity peak is around 12.6 kHz when considering imaginary impedance due to medium conductivity. Geometry optimization involves electrode dimensions with a length of 30 µm and a gap of 15 μm, as well as a channel width and height of 20 μm. Furthermore, the paper explores the effect of buffer conductivity, showing that it plays a significant role in defining total impedance with or without cells/particles. Higher buffer conductivity leads to dominant changes in real impedance, while lower conductivity affects imaginary impedance more prominently. The study also investigates the impact of variations in bacterial parameters, such as cell membrane permittivity and cytoplasm conductivity. These parameters influence total impedance, with cell radius showing a notable effect on sensitivity. By optimizing these parameters, the sensitivity and performance of impedance-based flow cytometry devices can be enhanced, making them more effective for bacterial analysis and characterization in various applications.

We examined the stability of writing in a magnetic domain wall device from the Oersted field induced by electrical current flowing in an embedded metal line. We found that the Joule heating from the writing current raises the device temperature, leading to destabilization of its magnetization after the pulse ends abruptly. To address this issue, we suggested adding a falling trailing edge to the main writing pulse, providing a stabilizing Oersted magnetic field while the device temperature reduces. We found the adequate trailing edge length fits to the thermal transient obtained from the 3D thermal simulations. This approach improved the writing stability of the device and highlights the importance of writing pulse shape and thermal management for stable writing of domain wall devices.