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In the present study, the diffusion coefficient of Cu in Fe was experimentally estimated from the precipitation kinetics down to 390°C. At this temperature, diffusion couples, which is a typical method to obtain diffusion coefficients, cannot be applied. The matrix Cu concentration and the number density of Cu precipitates in Fe–Cu alloy, which were the main parameters used to estimate the diffusion coefficient, were directly obtained using atom probe tomography. The temperature dependency of the diffusion coefficient of Cu in Fe estimated in the present study was more reliable than that obtained in a previous study, which also reported the diffusion coefficient of Cu in Fe from precipitation kinetics. This indicated that our estimation of the diffusion coefficient of Cu in Fe with atom probe tomography measurements yielded greater accuracy. In addition, the estimated diffusion coefficient of Cu in Fe tended to deviate to higher values from the extrapolated diffusion coefficient of Cu in Fe, which was obtained by diffusion couples, with decreasing temperature. This deviation is discussed by employing a kinetic Monte Carlo simulation.

Atom probe tomography (APT) and selected area electron diffraction (SAED) by transmission electron microscopy (TEM) were applied to nano-scale precipitates formed in a neutron-irradiated iron (99.9...

Atom probe tomography (APT) and transmission electron microscopy (TEM)/scanning transmission electron microscopy (STEM) have been used correlatively to explore atomic-scale local structure and chemistry of the exactly same area in the vicinity of growth front of a long-period stacking ordered (LPSO) phase in a ternary Mg–Al–Gd alloy. It is proved for the first time that enrichment of Gd atoms in four consecutive (0001) atomic layers precedes enrichment of Al atoms so that the formation of Al6Gd8 clusters occurs only after sufficient Al atoms to form Al6Gd8 clusters diffuse into the relevant portions. Lateral growth of the LPSO phase is found to occur by ‘ledge’ mechanism with the growth habit plane either {1$$\overline{1}$$ 1 ¯ 00} or {11$$\overline{2}$$ 2 ¯ 0} planes. The motion of ledges that give rise to lateral growth of the LPSO phase is considered to be controlled by diffusion of Al atoms.

A new technique of diamond and InGaP room temperature bonding in atmospheric air is reported. Diamond substrate cleaned with H2SO4/H2O2 mixture solution is bonded to InGaP exposed after removing th...

Three-dimensional distribution of arsenic (As) dopants at Σ3{111}, Σ9{221}, Σ9{114}, and Σ9{111}/{115} grain boundaries (GBs) in silicon (Si) is examined by correlative analytical methods using ato...

The microstructures of Cu/diamond interfaces prepared by surface-activated bonding at room temperature are examined by cross-sectional scanning transmission electron microscopy (STEM). A crystalline defect layer composed of Cu and diamond with a thickness of approximately 4.5 nm is formed at the as-bonded interface, which is introduced by irradiation with an Ar beam during the bonding process....

5-μm Al films are bonded to β-Ga 2 O 3 (−201) substrates using surface activated bonding. The nanostructural properties of as-bonded interfaces are examined using transmission electron microscopy and energy dispersive X-ray spectroscopy. 5-nm intermediate layers, which are likely to be due to the surface activation process, are observed.

The fabrication of Ga 2 O 3 (010)/Si(100) and Ga 2 O 3 (001)/Si(100) interfaces is achieved by the surface-activated bonding (SAB) of Ga 2 O 3 and Si substrates. The structure of the bonding interfaces is characterized by transmission electron microscope (TEM).

In diamond/silicon heterointerfaces fabricated by surface activated bonding at room temperature, an amorphous layer with carbon and silicon is formed in the bonding process, via atomic intermixing across the interfaces. The layer is crystallized by 1000°C annealing, forming a SiC compound.

Direct bonding of diamond and GaN is successfully fabricated by surface activated bonding method. An 80% contact area of diamond and GaN is obtained. The effect of annealing temperature on the structure properties of the bonding interface is investigated under in-situ annealing in a transmission electron microscope (TEM).

The self-heating of GaN-HEMTs is a serious issue in terms of the device performance and reliability. Therefore, diamond is the most promising candidate as a heat spreader material for HEMTs application because of its extremely high thermal conductivity. Therefore, we fabricate GaN-HEMTs on diamond substrate by using surface activated bonding method.

We successfully fabricate a Ga 2 O 3 /3C-SiC direct bonding by the surface-activated bonding (SAB) of 3C-SiC epitaxial layer grown on Si substrate to Ga 2 O 3 substrate. The structure of bonding interface will be investigated by transmission electron microscope (TEM).

Two kinds of 9Cr 2W steels with and without the addition of 0.1 wt% Si were irradiated with neutrons up to a fluence of 4.8 × 1023 n/m2 at 563 K. Precipitates, dislocation loops, radiation-enhanced nano-clusters and radiation-hardening were studied using advanced electron microscopy and micro-hardness test. Si reduced the number density of dislocation loops, and therefore the extent of radiation-hardening decreased. It also favored the formation of silicide-like nano-clusters. In this study, the role of Si in neutron irradiated 9Cr 2W steels is discussed, and then extended to nano-clusters and irradiation-hardening.

The in situ annealing observation in transmission electron microscope (TEM) is one of the effective methods for imaging thermally induced microstructural changes. For applying this dynamical characterization to bulk samples fabricated by ion-milling, electro-polishing or focused ion beam (FIB) mill, it is generally needed to use a heating-pot type system. We here report an initial trial to improve the spatial and temporal resolution during the in-situ annealing observation of bulk samples using a spherical aberration corrected (AC) TEM with a new thermal control unit. The information limit of 1.5 Å and the point resolution of 2.0 Å are achieved under isothermal annealing at 350°C, which is the same resolution at room temperature, and it is affected strongly of sample drift by the temperature variation. The sample is heated at a heating rate of +1.0°C/s, the drift distance observed by a TV readout speed CCD camera is less than 2.0 Å/s.

A FeCoNiCrTi0.2 high-entropy alloy strengthened by two types of coherent nano-precipitates but with the same composition was fabricated, and its tensile properties at room (293 K) and cryogenic temperatures (77 K) and the corresponding defect-structure evolution were investigated. Compared with the single-phase FeCoNiCr parent alloy, the precipitation-strengthened FeCoNiCrTi0.2 high-entropy alloy exhibits a significant increase in yield strength and ultimate tensile strength but with little sacrifice in ductility. Similar to the single-phase FeCoNiCr high-entropy alloy, the deformation behavior of this precipitation-strengthened FeCoNiCrTi0.2 high-entropy alloy shows strong temperature dependence. When the temperature decreases from 293 K to 77 K, its yield strength and ultimate tensile strength are increased from 700 MPa to 860 MPa and from 1.24 GPa to 1.58 GPa, respectively, associated with a ductility improvement from 36% to 46%. However, different from the single-phase FeCoNiCr high-entropy alloy with a twinning-dominant deformation mode at 77 K, multiple-layered stacking faults with a hierarchical substructure prevail in the precipitation-strengthened FeCoNiCrTi0.2 high-entropy alloy when deformed at 77 K. The mechanism of twinning inhibition in this precipitation-strengthened high-entropy alloy is the high energy barrier for twin nucleation in the ordered γ′ nano-particles. Our results may provide a guide for the design of tough high-entropy alloys for applications at cryogenic temperatures through combining precipitation strengthening and twinning/stacking faults.

We have investigated post-annealing induced microscopic structural change of kink boundaries (KBs), which have been initially introduced by a hot-extrusion of an Mg-Zn-Y alloy containing long period stacking/order (LPSO) phase, based on scanning transmission electron microscopy (STEM) and atom-probe tomography (APT). STEM observations show that the KBs appear to be segmented into several submicron-scale, each of which is composed of arrays of extended basal (a-) dislocations that are geometrically necessary to account for the LPSO crystal rotations. Atomic-scale STEM/APT observations reveal significant reconstructions of these extended dislocation-core structures, which occur at the solute-enriched face-centered cubic (fcc) layers in the LPSO structures and forms local hexagonal close-packed (hcp) Mg region with distinct solute depletions. These recovery features indeed enhance the thermal stability of the KBs, and the corresponding driving force can be reasonably described according to disclinations, whose elastic energy is defined by crystal rotations and the relevant dipole distances.

Chemical composition around diamond/silicon heterointerfaces fabricated by surface activated bonding (SAB) at room temperature is examined by energy-dispersive X-ray spectroscopy under scanning transmission electron microscopy. Iron impurities segregate just on the bonding interfaces, while oxygen impurities segregate off the bonding interfaces in the silicon side by 3–4 nm. Oxygen atoms would segregate so as to avoid the amorphous compound with silicon and carbon atoms, self-organized at the bonding interfaces in the SAB process. When the bonding interfaces are annealed at 1000 °C, the amorphous compound converts into cubic silicon carbide (c-SiC), and nano-voids 5–15 nm in size are formed at the region between silicon and c-SiC, at which the oxygen density is high before annealing. The nano-voids can act as the gettering sites in which metal impurities are preferentially agglomerated, and the impurity gettering would help to improve the electronic properties of the bonding interfaces by annealing.

研究グループは、ダイヤモンドに接合された窒化ガリウムを熱加工し、トランジスタの作製に成功するとともに放熱性の向上を実証しました。窒化ガリウムを利用したトランジスタは、シリコンに代わる次世代半導体として、携帯電話の基地局などで幅広く使用されているものの、動作時の発熱により性能が大きく制限されており、大型の放熱部材も必要とされていました。研究グループは、2021年9月に世界で初めてGaNとダイヤモンドの直接接合に成功し、1,000 ℃の熱処理にも耐えることを実証しました。今回の研究では、ダイヤモンドとの直接接合に成功した窒化ガリウムに約800℃の熱処理を行うことで、放熱性に優れたトランジスタの作製に成功しました。地球上で最も熱伝導率が高く、最も効率的に熱を逃すことができるダイヤモンドを使用しているため、シリコン上でのトランジスタと比べて放熱性が向上していること、また、窒化ガリウム層の品質が劣化しないことも明らかとなりました。本研究成果により、接合後にトランジスタを作製することでダイヤモンド上窒化ガリウムの大面積化が進展し、レーダーやインバータなどの大電力用途にも使用範囲が拡大することが期待されます。, We fabricate AlGaN/GaN high electron mobility transistors (HEMTs) on diamond substrates by transferring 8 μm heterostructures grown on 3C-SiC/Si templates and subsequently applying the conventional device process steps. No exfoliation of 3C-SiC/diamond bonding interfaces is observed during 800 °C annealing, the essential step for forming ohmic contacts on nitrides. The thermal resistance of HEMTs on diamond is 35% of that of HEMTs on Si, which is assumed to be the origin of smaller negative drain conductance in on-diamond HEMTs. The results imply that the bonding-first process is applicable for fabricating low-thermal-resistance HEMTs with thick nitride layers.

In this work, we fabricated Ga2O3(001)/Si(100) and Ga2O3(010)/Si(100) heterointerfaces by surface activated bonding at room temperature and investigated the effect of Si thickness on the thermal stability of the heterointerfaces by heating the bonding samples at different temperatures. The heterointerface with a thin Si exhibited a good thermal stability at 1000 °C. A 4 nm thick intermediate layer with a uniform thickness was formed at the as-bonded Ga2O3(001)/Si(100) heterointerface, but for the as-bonded Ga2O3(010)/Si(100) heterointerface, an intermediate layer with a non-uniform thickness was formed. The thickness of both intermediate layers ranged from 3.6 to 5.4 nm and decreased after annealing at 500 °C, followed by an increase after annealing at 1000 °C. The component of the intermediate layer includes Ga, O, and Si atoms.

We investigated the fluence dependence of irradiation-induced solute cluster, dislocation loop, and very small defect to reveal the hardening mechanism in surveillance test specimens from a reactor pressure vessel steel with low-Cu content (0.04 wt%) using atom probe tomography (APT), weak-beam scanning transmission electron microscopy (WB-STEM), and positron annihilation spectroscopy. A high number density (>1023 m−3) of solute clusters mainly composed of Ni, Mn, and Si atoms were found in highly neutron irradiated specimens (∼1024 neutrons m−2 (E > 1 MeV)) by APT. These solute clusters were one of the main sources of hardening as reported previously. On the other hand, it was also revealed that dislocation loops were formed with a number density of ∼1022 m−3 in the high-fluence specimens by WB-STEM. The estimated hardening due to dislocation loops was more than half of the actual hardening, showing that dislocation loops are also main source of irradiation hardening at high neutron fluence with the solid experimental evidences. Regarding specimens subjected to a low neutron fluence (∼1023 neutrons m−2), very small defects, not detected by either WB-STEM or APT, were formed by positron annihilation spectroscopy. This result suggested that, at a low neutron fluence, the defects were the initial hardening source and they may grow the dislocation loops observed by WB-STEM at high fluence range.

To clarify the irradiation hardening behavior of neutron-irradiated tungsten(W), the formation behavior of rhenium(Re)-enriched cluster and W-Re precipitation with displacement damage in fission reactors environment was investigated by the atom probe tomography (APT) technique, and the results obtained by APT and microstructural observation by transmission electron microscopy (TEM) were compared. Neutron-irradiated pure W and W-10Re alloys were used for the analysis. These samples were irradiated to 0.96 dpa at 538 °C in a fast experimental reactor Joyo, and irradiated to 0.90 dpa at 500 °C in a mixed spectrum reactor HFIR. The chemical compositions of the matrix, Re clusters, and precipitates were determined by the AP analysis. The Joyo-irradiated samples contained lower levels of transmuted Re and Os, while the HFIR-irradiated samples contained higher levels of Re and Os. The Re-enriched clusters demonstrated characteristic spatial distribution related to defect cluster distribution in each irradiated specimen.

The composition evolution of γ′ nanoparticles as a function of aging duration in the Ti-doped CoFeCrNi high entropy alloy was studied by atom probe tomography (APT) and first-principle calculations. The APT results indicate that the evolution behaviors of Co, Fe, and Cr in the Ni3Ti-type γ′ nanoparticles are significantly different. Co saturates to a stable concentration in the γ′ nanoparticles rapidly in the initial stage of the precipitation, whereas Fe and Cr atoms are incorporated into the γ′ nanoparticles during the coarsening. The APT results are supported by the first-principle calculations from the perspective of the electronic state.

Deuterium trapping at irradiation-induced defects in tungsten, a candidate material for plasma facing components in fusion reactors, was revealed by positron annihilation spectroscopy. Pure tungsten was electron-irradiated (8.5 MeV at ∼373 K and to a dose of ∼1 × 10−3 dpa) or neutron-irradiated (at 573 K to a dose of ∼0.3 dpa), followed by post-irradiation annealing at 573 K for 100 h in deuterium gas of ∼0.1 MPa. In both cases of electron- or neutron-irradiation, vacancy clusters were found by positron lifetime measurements. In addition, positron annihilation with deuterium electrons was demonstrated by coincidence Doppler broadening measurements, directly indicating deuterium trapping at vacancy-type defects. This is expected to cause significant increase in deuterium retention in irradiated-tungsten.

Solute clusters (SCs) formed in pressurized water reactor surveillance test specimens neutron-irradiated to a fluence of 1 × 1020 n/cm2 were analyzed via atom probe tomography to understand the effect of silicon on solute clustering and irradiation embrittlement of reactor pressure vessel steels. In high-Cu bearing materials, Cu atoms were aggregated at the center of cluster surrounded by the Mn, Ni, and Si atoms like a core-shell structure. In low-Cu bearing materials, Mn, Ni, and Si atoms formed cluster and these solutes were not comprised core-shell structure in SCs. While the number of Cu atoms in clusters was decreased with decreasing nominal Cu content, the number of Si atoms had clearly increased. The cluster radius ( r ) and number density ( N d ) decreased and increased with increasing nominal Si content, respectively. The shift in the reference temperature for nil-ductility transition (ΔRTNDT) showed a good correlation with the square root of volume fraction ( V f ) multiplied by ( V f × r ) . The negative relation between the nominal Si content and ΔRTNDT indicated that increasing of nominal Si content reduces the degree of embrittlement.

Oxide dispersion strengthened Cu alloys (ODS-Cu) having dispersed yttria (Y2O3) fabricated using hot isostatic pressing (HIP) of mechanically alloyed (MA) Cu-Y powders. They exhibited a heterogeneous mixed grain structure, which were composed of a large and small Cu grain area. In the small Cu grain regions, Y₂O₃ particles were segregated along the grain boundaries, and acted as a crack propagation path, leading to brittle fracture. Therefore, we investigated the microstructural changes by the MA and heat treatment processes for the microstructure optimization. The powders of 4 to 32 MA hours formed a nested crust-like layered structure with large and small Cu grains. The layers were destroyed by heat treatment at 500°C, because recrystallization and grain growth of Cu occurred in the temperature range of 310 - 330°C. It was considered that Y2O3 was moved out to the circumferential area of the powders. Based on these results, it was suggested that the structural changes inside MA powders during HIP are the essential factor of the Y2O3 distribution within the Y2O3-added ODS-Cu alloys.

Radiation-enhanced diffusion (RED) of copper (Cu) in iron (Fe) is essential for understanding solute/impurity diffusion in nuclear materials, especially reactor pressure vessel steel, but has been rarely reported experimentally. In this study, we performed a high-precision investigation of RED using well-controlled electron irradiation and three-dimensional atom probe (3D-AP). Cu-Fe diffusion pairs were created using high-purity Fe and Cu as base materials, and irradiated by 2 MeV electron at a temperature of 773 – 893 K controlled to within ±3 K. Cu diffusion into the Fe matrix was observed at the atomic level using 3D-AP, and the diffusion coefficient was obtained directly using Fick's law. RED was clearly observed, and the ratio of diffusion under irradiation to thermal diffusion was increased as the irradiation temperature decreased. RED was quantitatively evaluated using the reaction kinetics model, and the model which consider only vacancies gave a good agreement. This gave experimental clarification that RED was dominated by irradiation-induced vacancies. In addition, the direct experimental results on the effect of irradiation on the solubility limits of Cu in Fe was obtained; solubility limits under irradiation were found to be lower than those under thermal aging.

研究グループは、窒化ガリウムとダイヤモンドの直接接合に成功しました。窒化ガリウムを利用したトランジスタは、シリコンに代わる次世代半導体として、携帯電話の基地局などで幅広く使用されているものの、動作時に極度に温度上昇するため性能が大きく制限されています。加えて大型の放熱部材も必要です。研究グループは、地球上で最も熱伝導率が高く、最も効率的に熱を逃すことができるダイヤモンドと窒化ガリウムとの常温での直接接合に成功し、直接接合が1,000℃の熱処理にも耐えることを実証しました。更に、接合に際してダイヤモンドの結晶構造が壊れるものの、熱処理することで再結晶化することを明らかにしました。これは界面で高い熱伝導率が保持することを示します。今回の成果により窒化ガリウムトランジスタで発生する温度上昇をこれまでの1/4倍程度まで抑制でき、大幅な省エネにつながると予測されます。今後、窒化ガリウムトランジスタの使用範囲が拡大し、レーダーやインバータなどの大電力用途にも使用できるとともに、持続可能な社会の実現にも貢献すると期待されます。, The direct integration of gallium nitride (GaN) and diamond holds much promise for high-power devices. However, it is a big challenge to grow GaN on diamond due to the large lattice and thermal-expansion coefficient mismatch between GaN and diamond. In this work, ...

Bimetallic plates of CuCrZr/316LN are important heat sink components in the ITER first wall. Their in-reactor performance was investigated with 6.4 MeV Fe3+ ion irradiation (500 °C/10.5 dpa), as an analogue for neutron damage. Detailed characterizations showed that the CuCrZr/316LN joints have maintained good structural integrity after irradiation. The as-irradiated interface consisted of a nanocrystalline interlayer, typically of

Explosion-welded CuCrZr/316LN joints, which serve as key joining components in enhanced-heat-flux type first wall panels of ITER, have been neutron irradiated in the BR2 reactor (Belgium) at

We have investigated a post-annealing effect on microscopic structural changes of kink boundaries (KBs), which have been initially introduced by a hot-extrusion of an Mg-Zn-Y alloy containing long period stacking/order (LPSO) phase, based on scanning transmission electron microscopy (STEM) and atom-probe tomography (APT). STEM observations show that most of the KBs appear to be segmented into several submicron-scale, each of which is composed of arrays of extended basal (a-) dislocations that are geometrically necessary to account for the LPSO crystalline rotations. Atomic-scale STEM/APT observations reveal significant reconstructions of these extended dislocation-core structures, which occur at the solute-enriched face-centered cubic layers in the LPSO structures and forms local hexagonal close-packed Mg region with distinct solute depletions. These recovery-like features indeed enhance the thermal stability of the KBs, and the corresponding driving force can be reasonably described according to disclinations, whose elastic energy is defined by crystal rotations and the relevant dipole distances.

We summarize the findings from an interlaboratory study conducted between ten international research groups and investigate the use of the commonly used maximum separation distance and local concentration thresholding methods for solute clustering quantification. The study objectives are: to bring clarity to the range of applicability of the methods; identify existing and/or needed modifications; and interpretation of past published data. Participants collected experimental data from a proton-irradiated 304 stainless steel and analyzed Cu-rich and Ni–Si rich clusters. The datasets were also analyzed by one researcher to clarify variability originating from different operators. The Cu distribution fulfills the ideal requirements of the maximum separation method (MSM), namely a dilute matrix Cu concentration and concentrated Cu clusters. This enabled a relatively tight distribution of the cluster number density among the participants. By contrast, the group analysis of the Ni–Si rich clusters by the MSM was complicated by a high Ni matrix concentration and by the presence of Si-decorated dislocations, leading to larger variability among researchers. While local concentration filtering could, in principle, tighten the results, the cluster identification step inevitably maintained a high scatter. Recommendations regarding reporting, selection of analysis method, and expected variability when interpreting published data are discussed.

Atomistic structure of interfaces fabricated by surface activated bonding (SAB) at room temperature can be modified under the irradiation of a focused ion beam for structural analysis, presumably due to the migration of atoms assisted by point defects that are introduced during the SAB process.

Elemental distribution around GaAs homointerfaces fabricated by surface-activated bonding (SAB) is examined by atom probe tomography (APT). Our APT detected small amount of contaminants accidentally introduced on the SAB interfaces. We confirmed that As-deficient intermediate layer at the as-bonded interfaces was recovered by post-bonding annealing.

Tane M., Nishiyama H., Umeda A., et al. Diffusionless isothermal omega transformation in titanium alloys driven by quenched-in compositional fluctuations. Physical Review Materials 3, 043604 (2019); https://doi.org/10.1103/PhysRevMaterials.3.043604., In titanium alloys, the ω(hexagonal)-phase transformation has been categorized as either a diffusion-mediated isothermal transformation or an athermal transformation that occurs spontaneously via a diffusionless mechanism. Here we report a diffusionless isothermal ω transformation that can occur even above the ω transformation temperature. In body-centered cubic β-titanium alloyed with β-stabilizing elements, there are locally unstable regions having fewer β-stabilizing elements owing to quenched-in compositional fluctuations that are inevitably present in thermal equilibrium. In these locally unstable regions, diffusionless isothermal ω transformation occurs even when the entire β region is stable on average so that athermal ω transformation cannot occur. This anomalous, localized transformation originates from the fluctuation-driven localized softening of 2/3[111]β longitudinal phonon, which cannot be suppressed by the stabilization of β phase on average. In the diffusionless isothermal and athermal ω transformations, the transformation rate is dominated by two activation processes: a dynamical collapse of {111}β pairs, caused by the phonon softening, and a nucleation process. In the diffusionless isothermal transformation, the ω-phase nucleation, resulting from the localized phonon softening, requires relatively high activation energy owing to the coherent β/ω interface. Thus, the transformation occurs at slower rates than the athermal transformation, which occurs by the widely spread phonon softening. Consequently, the nucleation probability reflecting the β/ω interface energy is the rate-determining process in the diffusionless ω transformations.

This paper presents a study of the production of a single W boson in association with one or more jets in proton-antiproton collisions at √ s = 1.96 TeV , using the entire data set collected in 2001–2011 by the Collider Detector at Fermilab at the Tevatron, which corresponds to an integrated luminosity of 9.0 fb − 1 . The W boson is identified through its leptonic decays into electron and muon. The production cross sections are measured for each leptonic decay mode and combined after testing that the ratio of the W ( → μ ν ) + jets cross section to the W ( → e ν ) + jets cross section agrees with the hypothesis of e - μ lepton universality. The combination of measured cross sections, differential in the inclusive jet multiplicity ( W + ≥ N jets with N = 1 , 2, 3, or 4) and in the transverse energy of the leading jet, are compared with theoretical predictions.