Strong Tensile Stress Research Articles

48‐4: Analysis of Fracture Mechanism in Sand Paper Drop Test for Cover Glass

Fracture mechanism of cover glasses on mobile devices in a drop event was investigated through high speed camera observation and conventional fracture surface analysis. Drop tests were performed for various chemically strengthened glasses with different mechanical properties and stress profiles. These were dropped on sandpapers with grit size of 180. Based on the observations, we confirmed that the fracture of cover glasses in the drop tests is caused by two consecutive steps. The first one is nucleation of a crack due to the contact with the protrusions of the sandpaper, which causes a strong tensile stress localized around the protrusions. The second one is the propagation of the crack due to a stress caused by bending of the smart phone during the rebound process after the first contact with the sandpaper. According to these investigations, we established a prediction formula for the “fracture drop height” for the sandpaper drop tests. It enables us to understand key parameters to improve the fracture drop height. For example, in addition to the stress induced by chemical strengthening, the mechanical properties of the cover glass and the body of the smartphone are key factors to improve the fracture drop height. We believe the knowledge in this study is important for improving the strength of the cover glasses in the future.

Examining the seismic stress evolution in the face slab of concrete-faced rock-fill dams using dynamic centrifuge tests

This paper aims to characterize the seismic behavior of concrete-faced rock-fill dams. A series of dynamic centrifuge tests were carried out. The experimental results demonstrate that the stress evolution in the face slab is related to the pattern of energy buildup and that the overall stress evolution pattern is highly affected by pre-shaking. For the dams which have not experienced a relatively strong earthquake, compressive and tensile stress increments due to shaking are developed on the outer and inner faces, respectively. However, for the dams which have experienced a relatively strong earthquake, the inner face exhibits an overall tensile stress increment with time while the stress on the outer face only fluctuate around zero with minor overall variation. As for the failure mode under an extremely strong earthquake, slight surface sliding initially occurs, and then rock-fill particles move towards downstream direction, leading to deep sliding and significant dam deformation.

Microscopic deformation compatibility during biaxial tension in AZ31 Mg alloy rolled sheet at room temperature

In this paper, in situ electron back scattered diffraction combined with scanning electron microscopy and digital image processing techniques were used to study the microscopic deformation compatibility of AZ31 Mg alloy rolled sheets with strong basal texture during biaxial tension at room temperature. The results firstly quantitatively showed that the distribution of microscopic strain in AZ31 rolled sheet was inhomogeneous during formation. Strain concentrations happened in some regions even at early stage of deformation. Short distorted bands also appeared in these regions and extended to connect each other with increasing macroscopic strain. The appearance of distorted bands play an important role in strain compatibility since the materials lack easy deformation modes at room temperature. Besides slips and twins, the grain distortion should also be an indispensable mechanism in accommodating plastic deformation in some parts in distorted bands. According to the analysis from the Schmid factor, the geometric compatibility factors and slip trace identification, the comprehensive effect of strong basal texture and biaxial tensile stress state not only led to the quite low SFs for prismatic <a>, pyramidal <a> slips and tensile twinning, but limited the compatibility between slip systems and tensile twins. This mechanism was the main reason for the lack of easy deformation modes and the appearance of distorted bands, which further led to the inhomogeneous strain distribution at room temperature. Therefore, the formability of Mg alloys rolled sheets with strong basal texture was weakened at room temperature.

Laboratory investigation on cryogenic fracturing of hot dry rock under triaxial-confining stresses

Hot dry rock (HDR) has substantial potential as a thermal energy source. It can be exploited by hydraulic fracturing to extract heat and generate electricity. Because of its great depth (2–6 km) and consequent high temperature (150–650°C) and high pressure, the stimulation of HDR is difficult. The purpose of this study is to study the feasibility of cryogenic fracturing on HDR. We conducted a series of laboratory experiments on rock samples under triaxial-confining stresses. Two schemes were utilized: gas fracturing with and without liquid nitrogen (LN) (−196°C) treatment. For the LN treatment, high-temperature granitic specimens were immersed in LN for several hours before the fracturing tests. Three critical factors were considered, namely, rock specimen temperature (100–600°C), axial stress (5–20 MPa), and lateral stress (5–20 MPa). Subsequently, the fracture patterns were identified and correlations for both LN rapid-cryogenic and natural-cryogenic stimulations were developed to predict the breakdown pressure based on the experimental data. Finally, the field applications for LN cryogenic stimulation in HDR reservoir were discussed and a thermal-hydraulic coupled transient numerical model was established to provide suggestions of LN injection schedule for an effective cryogenic stimulation. The results show that the LN cryogenic stimulation could reduce the breakdown pressure level by 9–51% more than that of the untreated specimens. Particularly, LN provides superior fracturing efficiency on rock specimens above 200°C. This could be attributed to a sharp thermal gradient induced by LN, which can cause the strong local tensile stress to expand the micro-pore structures inside the high-temperature rock samples. Furthermore, with the assistance of LN, larger fracture apertures and better-connected fracture networks inside the rocks can be generated. Additionally, LN treatment, or rapid cryogenic fracturing, plays an increasingly important role when high-temperature rocks are subjected to higher anisotropic stresses. The key findings of this study could provide an efficient approach to explore HDR resources for geothermal development.

Synthesis of Inorganic-Organic 2D CdSe Slab-Diamine Quantum Nets.

Porous semiconductors attract great interest due to their unique structural characteristics of high surface area as well as their intrinsic optical and electronic properties. In this study, synthesis of inorganic-organic 2D CdSe slabs-diaminooctane (DAO) porous quantum net structures is demonstrated. It is found that the hybrid 2D CdSe-DAO lamellar structures are disintegrated into porous net structures, maintaining an ultrathin thickness of ≈1 nm in CdSe slabs. Furthermore, the CdSe slabs in quantum nets show the highly shifted excitonic transition in the absorption spectrum, demonstrating their strongly confined electronic structures. The possible formation mechanism of this porous structure is investigated with the control experiments of the synthesis using n-alkyldiamines with various hydrocarbon chain lengths and ligand exchange of DAO with oleylamine. It is suggested that a strong van der Waals interaction among long chain DAO may exert strong tensile stress on the CdSe slabs, eventually disintegrating slabs. The thermal decomposition of CdSe-DAO quantum nets is further studied to form well-defined CdSe nanorods. It is believed that the current CdSe-DAO quantum nets will offer a new type of porous semiconductors nanostructures under a strong quantum-confinement regime, which can be applied to various technological areas of catalysts, electronics, and optoelectronics.

Expansion and Fragmentation of a Liquid-Metal Droplet by a Short Laser Pulse

We report an experimental and numerical investigation of the fragmentation mechanisms of micrometer-sized metal droplet irradiated by ultrashort laser pulses. The results of the experiment show that the fast one-side heating of such a droplet may lead to either symmetric or asymmetric expansion followed by different fragmentation scenarios. To unveil the underlying processes leading to fragmentation we perform simulation of liquid-tin droplet expansion produced by the initial conditions similar to those in experiment using the smoothed particle hydrodynamics (SPH) method. Simulation demonstrates that a thin heated surface layer generates a ultrashort shock wave propagating from the frontal side to rear side of the droplet. Convergence of such shock wave followed by a rarefaction tale to the droplet center results in the cavitation of material inside the central region by the strong tensile stress. Reflection of the shock wave from the rear side of droplet produces another region of highly stretched material where the spallation may occur producing a thin spallation layer moving with a velocity higher than expansion of the central shell after cavitation. It is shown both experimentally and numerically that the threshold laser intensity necessary for the spallation is higher than the threshold required to induce cavitation in the central region of droplet. Thus, the regime of asymmetrical expansion is realized if the laser intensity exceeds the spallation threshold. The transverse and longitudinal expansion velocities obtained in SPH simulations of different regimes of expansion are agreed well with our experimental data.

Wearable, robust, non-enzymatic continuous glucose monitoring system and its in vivo investigation

Electroplating of nanoporous Pt (nPt) induces an extremely strong tensile stress, which results in the exfoliation of nPt on flexible polymer substrate despite plasma treatment to improve adhesion. Here, we overcame this challenge by modifying flexible stainless-steel, and developed wearable, robust, flexible, and non-enzymatic continuous glucose monitoring system. The flexible stainless-steel was highly effective in improving the adhesion between the metal layer and substrate. The developed wireless system included electrochemical analysis circuits, a microcontroller unit, and a wireless communication module. Finally, we evaluated the continuous glucose monitoring system through two animal testing, by implanting into subcutaneous tissue and measuring interstitial fluid (ISF) glucose values at 5–15-min intervals. Comparison of the measured ISF glucose with blood glucose determined by the Clarke error grid analysis showed that 82.76% of the measured glucose was within zone A. Furthermore, the wearable glucose sensor exhibited bio-compatible to implant through various bio-compatibility tests.

Cryogenic Fracturing of Wellbores Under True Triaxial-Confining Stresses: Experimental Investigation

Summary A laboratory study of cryogenic fracturing was performed to test its ability to improve oil/gas recovery from low-permeability reservoirs. Our objective is to develop well-stimulation technologies using cryogenic fluids [e.g., liquid nitrogen (LN)] to increase permeability in a large reservoir volume surrounding wells. The new technology has the potential to reduce formation damage caused by current stimulation methods and minimize or eliminate water usage. The concept of cryogenic fracturing is that a sharp thermal gradient (thermal shock) created at the surfaces of formation rocks by applying cryogenic fluid can cause strong local tensile stress and start fractures. We developed a laboratory system for cryogenic fracturing under true-triaxial loading, with LN-delivery/control and -measurement systems. The loading system simulates confining stresses by independently loading each axis up to approximately 5,000 psi on 8×8×8-in. cubes. Temperature in boreholes and at block surfaces and fluid pressure in boreholes were continuously monitored. Acoustic and pressure-decay measurements were obtained before and at various stages of stimulations. Cubic blocks (8 × 8×8-in.) of Niobrara shale, concrete, and sandstones were tested, and stress levels and anisotropies varied. Three schemes were considered: gas fracturing without cryo-stimulation, gas fracturing after low-pressure cryogen flow-through, and gas fracturing after high-pressure cryogen flow-through. Results from pressure-decay tests show that LN stimulation clearly increases permeability, and repeated stimulations further increase the permeability. Acoustic velocities and amplitudes decreased significantly after cryo-stimulation, indicating fracture creation. In the gas fracturing without the stimulation, breakdown (complete fracturing) occurs suddenly without any initial leaking, and major fracture planes form along the plane containing principal-stress and intermediate-stress directions, as expected theoretically. However, in the gas fracturing after cryogenic stimulations, breakdown occurred gradually and with massive leaking because of thermal fractures created during stimulation. In addition, the major fracture direction does not necessarily follow the plane containing the principal-stress direction, especially at low confining-stress levels. In tests, we observed that cryogenic stimulation seems to disrupt the internal stress field. The increase in borehole temperature after stimulation affects the permeability of the specimen. When a stimulated specimen is still cold, it maintains high permeability because fractures remain open and local thermal tension is maintained near the borehole. When the rock warms back, fractures close and permeability decreases. In these tests, we have not used proppants. Overall, fractures are clearly generated by low- and high-pressure thermal shocks. The added pressure of the high-pressure thermal shocks helps to further propagate cryogenic fractures generated by thermal shock. Breakdown pressure is significantly lowered by LN stimulation, with observed breakdown-pressure reductions up to approximately 40%.

Effects of Mechanical Stress on Flexible Dual‐Gate a‐InGaZnO Thin‐Film Transistors

The effects of mechanical tensile and compressive stress on dual‐gate amorphous InGaZnO thin‐film transistors (a‐IGZO TFTs) on a flexible substrate were investigated. Both the tensile and compressive stresses led to increases in free electrons and deep states in a‐IGZO. Strong tensile stress tends to form more deep defects than compressive stress, resulting in severe deterioration in performance. Small compressive stress seems to repair defects in the relatively poor quality etch‐stop layer (ESL), resulting in increased mobility in the top‐gate‐controlled performance.

Laboratory system for studying cryogenic thermal rock fracturing for well stimulation

The concept of cryogenic fracturing is that a sharp thermal gradient developed by applying a cryogenic fluid on a rock surface causes a strong local tensile stress that initiates fractures. Prior field tests suggest that field application with special equipment rated for cryogenic temperatures may deliver potential benefits. The tests did not, however, identify the fracture mechanisms at work in downhole conditions. In this study, we present our laboratory designs and procedures developed for studying cryogenic fracturing mechanisms in a well environment, and examine typical data indicative of the performance of the system. The experimental apparatus and procedures were specifically designed to conduct cryogenic fracturing tests in specimens under confining stress, with integrated cryogen transport, measurements, and fracture characterization. A true-triaxial loading system was built to simulate reservoir stress levels and anisotropic stress application, and was designed to avoid thermal stresses in tests involving cryogen by arranging discrete components in an open chamber. To maximize thermal shock on the wellbore surface, tubing and wellhead are configured so that liquid nitrogen enters the borehole and flow out after contributing to thermal shock. The temperature at boreholes and along flow lines, borehole pressure, and liquid nitrogen consumption are monitored throughout treatments. Acoustic transmission and pressure-decay measurements are used to characterize fractures before and after the experiments. Breakdown tests performed on un-stimulated specimens and stimulated specimens compare breakdown pressures of the two groups and thus evaluate the performance of thermal fracturing. The laboratory design was able to effectively apply cryogenic stimulations to laboratory rock specimens. The characterization methods were able to capture fracture creation and rock property changes due to cryogenic fracturing.

Mechanical testing of directionally solidified eutectic ceramics (DSECs): specific problems and limitations

The specific problems of DSECs mechanical testing result from the particularities of these 3-D interconnected eutectic ceramics. First of all, 4-point bending tests ensure pure bending loading, whereas 3 PB tests only lead to a tensile and shear stress combination. Consequently, due to the 3-D microstructure of DSECs, interfaces between the various phases are subjected to a mixed (tensile and shear) loading which makes the interpretation of the results (strength) and of the fracture surfaces, rather difficult. For usual ceramics, biaxial flexure testing offers many advantages over 3- or 4-point beam-bending testing. The coaxial-ring test is free of edge influences (flaws): cracks initiate in the central area and propagate outwardly. However, in the case of DSECs, due to the presence of high internal thermal stresses (especially for ternary eutectics), interfaces can be subjected to a strong radial tensile and shear (near the free surface) stress combination. In the presence of the radial tensile stress resulting from biaxial loading, this internal thermal stress combination can lead to premature crack initiation leading to failure. Specimen machining through grinding leads to the formation of a strongly damaged layer. Annealing of this layer leads to the formation of a rough surface: slightly protruding phases and stress concentrations at the interfaces. The measured strength is ≈20% lower after annealing than that directly after grinding. Concerning the effect of the microstructure size, four representative sizes have been selected in the ≈10 µm to submicrometre range. A classical crack propagation criterion has allowed explaining the corresponding strength values.

Investigation on Crack Suppression by Thermal-Plasma-Jet Crystallization of Amorphous Silicon Films on Flexible Glass Substrate

Introduction.Ultra-thin glass substrate is attracting much attention as flexible substrates for curved display applications. In fabrication of thin-film transistors (TFTs) on flexible glass, crystallization of amorphous Si (a-Si) is one of the key process technologies [1-3]. Rapid-thermal-annealing (RTA) in microsecond regime is necessary to form high crystallinity Si without thermal damage to glass. We have proposed the application of atmospheric pressure DC ark discharge thermal-plasma-jet (TPJ) to the crystallization of a-Si films [4]. Because of its simple structure and atmospheric pressure process, TPJ enables low cost crystallization compared with excimer laser annealing (ELA) technique. High speed lateral crystallization (HSLC) is induced by sweeping a molten region at a speed as high as 4000 mm/s. However, residual tensile stress is generated because of the densification of glass surface after RTA process. As a result, significant number of cracks are generated on the surface of glass substrate in cases of sever annealing conditions. In this study, we applied µ-TPJ crystallization of a-Si films on ultra-thin glass substrate and investigated the effect of glass thickness on residual stress and crack generation. Experimental.After RCA cleaning and HF treatment of 100-µm-thick flexible glass and 500-µm-thick conventional glass substrates, 100-nm-thick a-Si films were deposited by plasma-enhanced chemical vapor deposition (PECVD) at a substrate temperature of 250 °C. Dehydrogenation was carried at 450 °C in N2 ambient for 1 h. TPJ irradiation set up is shown in Fig. 1. µ-TPJ was generated by DC arc discharge under atmospheric pressure with supplying power (P) of 1.7 kW between electrodes. The Ar gas flow rate (f) was 1.0 L/min. µ-TPJ was generated by blowing out the thermal plasma through an orifice with its diameter (ϕ) of 600 µm. The distances between the plasma source and glass substrates (d) were fixed at 1.0 mm and the substrates were linearly moved by a motion stage in front of the µ-TPJ with scanning speed (v) of 2200 mm/s. For the measurement of temperature profile in the glass substrate, transient reflectivity during TPJ annealing was measured by irradiating bare conventional glass substrate with a He-Ne laser (632.8nm) from the back surface. Details of the non-contact temperature measurement are described in Ref [5]. Results and discussion.The microscope images of crystallized Si films on each substrate are shown in Fig. 2. Many cracks were observed in conventional glass substrate. On the other hand, no crack was observed in flexible glass substrate, although both glass substrates were annealed at the same time. Crystallization was conducted under various µ-TPJ irradiation conditions, and almost no cracks were found in flexible glass and it showed significant resistance against RTA. This result suggests that the tensile stress at glass surface is significantly reduced in the case of ultra-thin flexible glass. Previous study calculated residual stress profile in glass substrate on the basis of multilayered beam theory [6]. To obtain stress profile, we measured transient temperature profile during TPJ irradiation by optical probe (Fig .3). We assumed surface densification of glass when the temperature exceeded softening point (1258 K). We conducted residual stress analysis of glass substrate as the residual stress is shown in Fig. 4 [6]. Strong tensile stress is introduced in glass surface due to the shrinkage by RTA. At the same time, compressive stress is introduced inside of glass to compensate the tensile stress at the surface. It should be noted that the depth of stress compensation is in the range of ~400 µm as shown in Fig. 4, which is larger than the thickness of flexible glass. It is expected that the back side of thin glass substrate is free to relax the stress and plays a roll in suppression of residual stress in the surface of glass. Conclusions.We have crystallized a-Si films on flexible glass substrate by µ-TPJ without crack generation. Flexible glass substrate is useful to relieve surface tensile stress and as the result, crack generation is significantly suppressed. Acknowledgments. A part of this work was supported by Research Institute for Nanodevice and Bio Systems (RNBS) Hiroshima University, and JSPS KAKENHI Grant Number (B)(16H0433400).

Anatomical study of the inferior patellar pole and patellar tendon.

In this study, detailed investigations into the shape of the inferior patellar pole, the site of the patellar tendon attachment, and the length and course of the patellar tendon were performed with the aim of examining the anatomical factors involved in the developmental mechanism of patellar tendinitis. The investigation examined 100 legs from 50 cadavers. The inferior patellar pole was classified into three types: pointed, intermediate, and blunt. The attachment of the patellar tendon to the inferior patellar pole was classified into two types: an anterior and a posterior. The length of the patellar tendon was measured from the tibial tuberosity to the inferior patellar pole. The pointed type was seen in 57% of legs, the intermediate type in 21%, and the blunt type in 22%. Twenty-one legs were the pointed type, as well as the anterior type. The patellar tendon was significantly shorter with the posterior type than with the anterior type. The blunt type also had a significantly shorter patellar tendon than the pointed type. In legs that were both the pointed type and the anterior type, the inferior patellar pole and the proximal posterior surface of the patellar tendon impinged during knee flexion due to the posterior tilt of the patella, suggesting the possibility that this may induce damage. With the posterior type and blunt type, on the other hand, the possibility of strong tensile stress on the tendon fibers of the posterior facet of the inferior patellar pole was suggested.

Numerical modeling of cryogenic fracturing process on laboratory-scale Niobrara shale samples

Cryogenic fracturing is a new fracturing concept that uses cryogenic fluids as fracturing fluids. Its mechanism rests on the effect of a thermal shock (sharp thermal gradient) introduced by cryogen on the hot surface of reservoir rock. Fractures can then be initiated and propagated due to strong local tensile stress. The objective of this research is to simulate the cryogenic fracturing experiments on Niobrara shale samples. The experimental processes are simulated under different conditions and matched with the actual experiment results. The influences of different confining stress, injection pressure and failure criteria are identified by comparing results from modeling and experiments. The simulation tool developed can also predict the distribution of artificial fractured samples.

Restrained TGO growth in YSZ/NiCrAlY thermal barrier coatings by modified laser remelting

Abstract Thermal barrier coatings (TBCs) are widely applied in high temperature gas turbines and jet engines to protect the superalloy components. Due to oxygen transfer through topcoat and the oxidation of bond-coat alloy, a thin layer of thermally grown oxide (TGO) will generate between the ceramic topcoat and the metallic bondcoat of TBCs after long-term operation. Cracking and spalling are often observed at the topcoat-TGO and TGO-bondcoat interfaces since the thickening of TGO layer may lead to strong tensile stress. Previously, laser remelting process has been developed as an effective way in restraining the TGO growth. In the present research, preheating laser remelting and sol-gel repairing laser remelting were respectively employed to further decelerate the TGO growth by reducing the number density and average size of vertical cracks in the topcoat. After 100 h isothermal oxidation, the TGO growth rate of the modified laser remelted specimens are much lower than the conventional laser remelted specimens, which shows the potentiality of preheating and sol-gel repairing as effective promotions of laser remelting process in restraining the TGO growth.

Thickness impacts on permeation reduction factor of Er2O3 hydrogen isotopes permeation barriers prepared by magnetron sputtering

In hydrogen energy and thermal fusion energy, hydrogen isotopes permeation barriers (HIPB) are used to reduce hydrogen isotopes permeation, which may result in hydrogen isotopes leak and construction materials brittleness. Here, we made Er2O3 HIPB by magnetron sputtering and studied the relation between deuterium-permeation reduction factor (D-PRF) and coating thickness, micro-morphology. The 0.2 μm Er2O3 coatings can reduce deuterium permeation by 1/10 ∼ 1/20 at 600 °C ∼ 300 °C. However, the reduction ability decreases gradually with the increase in coating thickness when the coatings are thicker than 0.2 μm. The reason may be ascribed to the deuterium invasion in deuterium permeation test. After deuterium invasion into coatings, the coatings suffer intrinsic stress, thermal stress and expansion stress from deuterium invasion. As a result of grain size dependence on coating thickness in PVD-derived coatings, i.e. grains become coarse with increasing coating thickness, the sum of stresses in various type increases with increasing coating thickness. The coatings crack easily when they suffer more strong tensile stress. So, the damages of coatings become serious and D-PRF reduces with increasing coating thickness.

Quantitative evaluation of adhesion quality of surface coating by using pulse laser-induced ultrasonic waves

Abstract This study aims to evaluate delamination characteristics of surface coating by using strong ultrasonic wave induced by pulsed laser irradiation. Strong tensile stress wave is induced by pulse laser irradiation, and delamination of the coating layer/substrate interface (or spallation) is produced by confined silicone grease breakdown (i.e. ablation). Upon various levels of energy of irradiation laser, the coating delamination and displacement are measured in-situ. Parallel computation of elastic wave propagation using FDTD (finite difference time domain) yields the wave propagation in the specimen, and estimates the interfacial strength with stress wave distribution. The delamination area is visualized by laser ultrasonic wave scanning technique after the laser spallation test. The interaction between displacement waveform and delamination is explored. The present technique may shed some light on various coating depositions for assessing the coating adhesion quality.

Experimental research on creep behaviors of sandstone under uniaxial compressive and tensile stresses

The consideration of time dependence is essential for the study of deformation and fracturing processes of rock materials, especially for those subjected to strong compressive and tensile stresses. In this paper, the self-developed direct tension device and creep testing machine RLW-2000M are used to conduct the creep tests on red sandstone under uniaxial compressive and tensile stresses. The short-term and long-term creep behaviors of rocks under compressive and tensile stresses are investigated, as well as the long-term strength of rocks. It is shown that, under low-stress levels, the creep curve of sandstone consists of decay and steady creep stages; while under high-stress levels, it presents the accelerated creep stage and creep fracture presents characteristics of brittle materials. The relationship between tensile stress and time under uniaxial tension is also put forward. Finally, a nonlinear viscoelastoplastic creep model is used to describe the creep behaviors of rocks under uniaxial compressive and tensile stresses.

Calculation of Basic Domain Width Considering Lancet Domains in (110)[001]Fe3%Si

This paper presents the calculation method of basic domain width in demagnetized states of (110)[001]Fe3%Si under tensile stress in the range of lancet domain occurrence. Accurately calculating the 180 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> basic domain width in demagnetized states is one of the important estimations to evaluate the anomalous eddy-current losses. Previously, stripe domain models, under sufficient strong tensile stress to annihilate lancet domains, were used so that the discrepancy between the calculated and the observed widths under tensile stress in which lancet domains occur became large. Applying the decrease of the surface magnetic charge by lancet domains to calculations of the stray field energy of basic domains enables us to accurately evaluate the 180 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> basic domain width under tensile stress in demagnetized states. Furthermore, the eddy-current losses evaluated using the calculated basic domain width show good agreement with the measured values under the tensile stress in the range of lancet domain occurrence.

Performance of Fully Recessed AlGaN/GaN MOSFET Prepared on GaN Buffer Layer Grown With AlSiC Precoverage on Silicon Substrate

A crack-free AlGaN/GaN heterostrucure is grown on 4-in Si (111) substrate with AlSiC precoverage layer. Covering the Si surface with the AlSiC layer, until the growth of the AlN wetting buffer layer, is found to be effective in compensating the strong tensile stress in the GaN layer grown on Si substrate. The metal-oxide-semiconductor field-effect transistor, fabricated on this AlGaN/GaN heterostructure, exhibits excellent normally-off characteristics with threshold voltage of 7.2 V, maximum drain current of 120 mA/mm, ON/OFF current ratio of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\sim}10^{8}$</tex></formula> , and subthreshold slope of 80 mV/decade.