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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 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.

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).

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, ...

The three-dimensional distribution of oxygen atoms segregated at Σ9{114} grain boundaries (GBs) in Czochralski-grown silicon ingots is analyzed within a high spatial resolution of less than 0.5 nm by atom probe tomography combined with a focused ion beam (FIB) operated at −150 °C. The analysis reveals a segregation of oxygen atoms within a range of 2.5 nm across the GB plane, which is much narrower in comparison with the previous reports obtained using a conventional FIB. The oxygen concentration profile accurately reflects the distribution of the segregation sites, which exist at bond-centered sites under tensile stresses above 2 GPa, as calculated by ab initio local stress calculations.

Ge/Si and Si/Ge core-shell nanowires (NWs) have substantial potential for application in many kinds of devices. Because impurity distributions in Ge/Si and Si/Ge core-shell NWs strongly affect their electrical properties, which in turn affect device performance, this issue needs urgent attention. Here we report an atom probe tomographic study of the distribution of boron (B), one of the most important impurities, in two kinds of NWs. B atoms were doped into the Si regions of Ge/Si and Si/Ge core-shell NWs. It was found that the B atoms were randomly distributed in the Si shell of the Ge/Si core-shell NWs. In the Si/Ge core-shell NWs, on the other hand, the B distributions depended on the growth temperature and the B2H6 flux. With a higher growth temperature and an increased B2H6 flux, the B atoms piled up in the outer region of the Si core. However, the B atoms were observed to be randomly distributed in the Si core after decreasing both the growth temperature and the B2H6 flux.

The three-dimensional (3D) distribution of nanosized silicon (Si) crystallites within a hydrogenated nanocrystalline Si (nc-Si:H) material is examined by laser-assisted atom probe tomography (APT). The amorphous and crystalline phases in nc-Si:H are distinguished by obtaining the 3D density distribution of H atoms, because the former contains a high H density. The H content in the amorphous phase is estimated to be approximately 15 at% by APT, which is consistent with that obtained by infrared spectroscopy. Thus, the 3D analysis of H distribution via APT is a powerful method to visualize the real shape of nanosized crystallites within nc-Si:H materials.

Non-coherent Σ3{111} grain boundaries (GBs) with a positive deviation in the tilt angle (θ 〈110〉 > 70.5°) exhibit a high recombination activity in high-performance multicrystalline silicon ingots. Most of the GB segments are composed of edge-type dislocations with the Burgers vector b of a/3〈111〉, unlike Lomer dislocations with b = a/2〈110〉 observed for negative deviations, arranged on coherent Σ3{111} GB segments. Stretched 〈110〉 reconstructed bonds along the tilt axis are introduced so as not to form dangling bonds, and large strains are generated around the dislocation cores. Oxygen and carbon atoms segregating due to the strains would induce the recombination activity.

Laser-assisted atom probe tomography was used to identify the impurity distribution in Si heterojunction (SHJ) solar cells composed of thin doped/intrinsic amorphous Si layers on the textured surface of a crystalline Si wafer. A site-specific lift-out technique involving a focused ion beam enabled the selection of a ∼2 × 2 μm2 area on an arbitrary pyramidal surface. The distributions of B, P and C in the amorphous Si layers introduced by p-type (trimethyl-borane or diborane) or n-type (phosphine) dopant gases were investigated. Standard guidelines for the assessment of the H content in amorphous Si of SHJ solar cells were provided.

Silicon (Si) self-diffusivity in a Si nanopillar under dry oxidation was quantitatively evaluated by atom probe tomography of Si isotope heterostructure interfaces. Dry oxidation of a nanopillar with 200 nm diameter at 920 °C for 4 h revealed that the Si self-diffusivity was the same as the one measured for the standard planar oxidation despite the fact that the diffusion region probed in the pillar was surrounded by approximately seven times more oxidation interface areas than the simple planar oxidation case. This finding can be understood by considering the large diffusion length of ∼300 μm of the interstitials for our thermal oxidation condition. The excess interstitials injected by the pillar oxidation as well as those injected by the oxidation of the base (100) plane can easily diffuse through the sample, including interiors of the pillars, making the concentration of the excess interstitials practically equal to those injected for the (100) planar oxidation case.

It has been reported that erbium (Er) is a source of optical emission at λ=1.54 pm due to 4I 13/2 →4I 15/2 transition of Er3+. A method of oxygen (O) codoping with Er has attracted attention as a candidate for obtaining more efficient optical gain by forming Er:O complex. Although several simulations predict the equilibrium structure of Er:O complex, it is difficult to understand experimentally how related between these implanted ions followed by annealing for optical activation. In this workshop, we reported the preliminary results on three-dimensional distributions of Er and O co-implanted into Si investigated by atom probe tomography.

Luminescence of erbium in silicon has been intensively explored in the past in the high power emission regime, but its employment for manufacturability of active components for silicon photonics proved unfeasible. We explore the room-temperature photoluminescence (PL) at the telecomm wavelength of very low implantation doses of ErO x in Si for accessing few photon regime towards single photon emission. We achieve countable photon regime and we assess the lower-bound number of detectable emission centers by micron scale implanted dots, whose emission is collected by an inverted confocal microscope.

The diffusion coefficient and the solubility limit of copper in ferromagnetic iron were directly measured using atom probe tomography at lower temperatures than in previous studies. Cu–Fe diffusion couples were annealed at temperatures from 550 to 750 °C. The diffusion coefficient was determined to be D = 0.48 exp(−Q/kBT) m s−1 (Q = 3.22 eV), which, below 650 °C, is about 1.3 times higher than the extrapolation from a previous study considering the magnetic effect. The measured Cu solubility limit is in good agreement with literature.

The relationship between the laser power and the three-dimensional distribution of boron (B) in silicon (Si) measured by laser-assisted atom probe tomography (APT) is investigated. The ultraviolet laser employed in this study has a fixed wavelength of 355 nm. The measured distributions are almost uniform and homogeneous when using low laser power, while clear B accumulation at the low-index pole of single-crystalline Si and segregation along the grain boundaries in polycrystalline Si are observed when using high laser power (100 pJ). These effects are thought to be caused by the surface migration of atoms, which is promoted by high laser power. Therefore, for ensuring a high-fidelity APT measurement of the B distribution in Si, high laser power is not recommended.

cited By 4; International audience; Single planes of Si nanocrystals (NCs) embedded in a SiO2 matrix were synthesized by annealing SiO2/SiO/SiO2 multilayer structures deposited on Si (100) substrates by e-beam evaporation. The dependence of the shape, size, and areal density of Si NCs on the thickness of the initial SiO layer was investigated using atom probe tomography and validated by energy filtered transmission electron microscopy. Three kinds of samples were prepared with SiO layer thicknesses of 4, 6, and 10 nm. The size of Si NCs enlarged with increasing SiO layer thickness. The shape of Si NCs was mainly extended spheroid in all three kinds of samples. In the sample with the 4 nm-thick SiO layer, the Si NCs were more prolate than those in the other two samples. Moreover, many rod-shaped Si NCs appeared in the sample with the 10 nm-thick SiO layer. These rod-shaped Si NCs were found to be connected by small Si NCs. The areal densities of Si NCs were in the order of 1012 NCs per cm2 in all samples. © 2016 The Royal Society of Chemistry.

Atom probe tomography and secondary ion mass spectrometry were used to investigate the effects of carbon (C) co-implantation and subsequent annealing at 600 to 1200 °C on the behavior of implanted boron (B) atoms in silicon. When B alone was implanted, annealing at 600 to 800 °C caused it to form clusters in the peak region (1020 cm−3) of the concentration profile, and diffusion only occurred in the low-concentration tail region (

Hydrogen (H) plays an important role in determining the reliability and performance of HfO2- and Al2O3-based high-k dielectric electronic devices. In order to understand H behavior, deuterium (D), an isotope of H, was introduced into the poly-Si cap of Al2O3/HfxSi1−xO2/SiO2 high-k stacks by ion implantation. Atom probe tomography was used to image the D distribution in samples annealed under different conditions. The results clearly demonstrated that the D atoms were trapped at the interface of poly-Si and Al2O3 after annealing at 900 K for 10 min. Thus, it is possible that Al2O3 blocks the H atoms at the surface, preventing them from diffusing into the high-k dielectrics during the H2 annealing process in current fabrication technology. The current work also exhibits an example of investigating H behavior in semiconductors by atom probe tomography.

In order to probe the fundamental behaviors of point defects in silicon and germanium, we studied the self-diffusion using isotope superlattices. In ion-implanted germanium, vacancies are in thermal equilibrium and transient enhanced diffusion is not present under the experimental conditions employed in this study. In contrast, silicon self-interstitials are supersaturated in ion-implanted silicon and the self-interstitial concentration is going down to the thermal equilibrium value toward the surface.

In an effort to realize the long-term stability of the magnetostrictive property of electrodeposited Ni-Fe alloy films, heat treatments needed for eliminating the possible effect of hydrogen and hydrogen-induced vacancies have been investigated, mainly by use of thermal desorption spectroscopy. While metal-atom vacancies begin to move only above ∼500 K, hydrogen atoms can undergo slow motion and concomitant changes of state at room temperature, and are therefore believed to be a major cause of the long-term drift of the magnetism. Hydrogen atoms dissolved on regular interstitial sites can be completely removed by high-frequency pulse heating to 668 K, and those trapped by vacancies with relatively low binding energies by additional heat treatments to 453 K for over 1 h. This combination of heat treatments was found to reduce substantially the change of state of hydrogen during subsequent aging tests (383 K for 400 h), and proved to be effective for ensuring the long-term stability of magnetostrictive Ni-Fe film sensors.

Fabrication of the next generation silicon devices requires fundamental understanding of defect interactions that are characteristic of nano-scale device processing. Because a variety of intrinsic and extrinsic defects generated at surfaces and interfaces can easily diffuse and reach the active regions in the nano-scale devices, it becomes crucial to understand the transient and non-equilibrium behaviors of defect interactions related to nano-scale fabrications. In order to identify what types of kinetics and reactions are relevant to nano-processing, diffusion in silicon and silicon oxide is studied using isotopically controlled silicon heterostructures. Our experiments probing the effect of interfaces on impurity and silicon self-diffusion in silicon dioxide, silicon self-diffusion in silicon, and implanted-impurity and silicon interactions are reviewed. Then quantitative models based on such experimental studies are presented and how they will be utilized in the construction of diffusion simulators is discussed.

A new wire mesh metallic catalyst support has been studied by using a stainless heat resistant steel of including aluminum. This catalyst support was improved for the metal honeycomb catalyst support that had been put to practical use. The wire mesh catalyst support was made in the following procedures. First, it was made from flat plate made by the stainless steel from the machining. Second, the low oxygen atmosphere in the heat treatment furnace did the aluminum extraction processing. Third, the aluminum oxide layer was made on the surface of catalyst support by furnace in air. Metal honeycomb catalyst has been made for several years by this method. The aim of this study was to evaluate the aluminum oxide layer on the surface of wire mesh catalyst support. The aluminum oxide surface was measured using scanning electron microscopy (SEM) and X-ray reflection diffraction (XRD). This catalyst support has the performance similar to the conventional metal honeycomb catalyst support.

In an effort to realize the long-term stability of the magnetism of electrodeposited Ni-Fe alloy films, heat treatments needed for eliminating the possible effect of hydrogen and metal-atom vacancies have been investigated, mainly by use of thermal desorption spectroscopy. While metal-atom vacancies begin to move only above 480 K, hydrogen atoms can undergo slow motion and concomitant changes of states at room temperature, and are therefore believed to be a major cause of the long-term drift of the magnetism. Hydrogen atoms dissolved on regular interstitial sites can be completely removed by high-frequency pulse heating to 668 K, and those trapped by vacancies with relatively low binding energies can be removed by additional heat treatments at 453 K for over 1 h. The effectiveness of using this set of heat treatments to stabilize the performance of magnetostrictive Ni-Fe film sensors has been verified.

Nozzle geometry influences gas dynamics, such as gas density, velocity and temperature, making sprayed particle behavior one of the most important parameters in cold spray process. Gas flow at the entrance convergent section of the nozzle takes place at relatively high temperature and are subsonic. Thus, this region is a very suitable environment for heating spray particle. In this study, numerical simulation and experiments were conducted to investigate the effect of nozzle contour (convergent -divergent and convergent-divergent-barrel), entrance geometry of convergent-divergent nozzle and powder injection position at nozzle on the cold spray process. The process changes inside the nozzle were observed through numerical simulation studies and the results were used to find a correlation with coating properties. A titanium powder was usedin the experiments. Working gas (is nitrogen) pressure and temperature at nozzle-intake were 3MPa and 626K, respectively. In addition, the change in the nozzle contour and the change in the convergent section length of the gun nozzle were found to have a slight effect on the coating microstructure. Powder injection position was also found to influence deposition efficiency and coating porosity with titanium powder. Deposition efficiency using axial injection was found to be higher than that using radial injection.

The structure and formation of superabundant vacancies in electroplated Ni64Fe36 alloy films have been studied by XRD and thermal desorption spectroscopy. The films, as deposited, consist of fine grains of ca. 10 nm in size, which, upon heating, start to undergo a gradual grain growth at ~600 K, and a rapid growth above ~670 K. The desorption of hydrogen occurred in seven stages; P0(385 K), P1(440 K), P2(560 K), P3(670 K), P4(960 K), P5(1170 K), and P6(>1270 K). P0 is attributed to desorption of H atoms on regular interstitial sites, P1~P2 and P4~P5 to H atoms trapped by vacancies, and P6 to hydrogen bubbles precipitated in the matrix. P3 and a desorption peak of CO+ (1100 K) are attributed to the decomposition of occluded C, H compounds. Binding energies of H in these trapped states are estimated, and possible configurations of these vacancy-H clusters are discussed.

P-type and n-type β-FeSi2 was produced by utilizing the process of mechanical alloying(MA)and spark plasma sintering(SPS)technique. Raw powders of pure iron, silicon, manganese and cobalt were mixed and mechanically alloyed for 72ks using planetary ball mill. The mixing fractions of the powders were in accordance with the mole fractions of the Fe0.92Mn0.08Si2 (p-type) and Fe0.98Co0.02Si2 (n-type), respectively. The SPS temperature for producing p-type β-FeSi2 was 1073-1153 K and n-type β-FeSi2 was 1073-1173 K, and the holding time was 0.3ks. When the sintering temperature was over these temperatures, α-FeSi2 was produced and thermoelectric properties were reduced. The density of p-type β-FeSi2 sintered at 1153 K was 4.64g/cm3(the relative density was 94.1%), and the maximum power factor was 0.30mW/mK2 at 850 K. The density of n-type β-FeSi2 sintered at 1173K was 4.71 g/cm3(the relative density was 95.5%), and the maximum power factor was 0.058 mW/mK2 at 650K.

Ion implantation through nanometer-scale apertures (nano-apertures) is a promising method to precisely position ions in silicon matrices, which is a requirement for next generation electronic and quantum computing devices. This paper reports the application of atom probe tomography (APT) to investigate the three-dimensional distribution of germanium atoms in silicon after implantation through nano-aperture of 10 nm in diameter, for evaluation of the amount and spatial distribution of implanted dopants. The experimental results obtained by APT are consistent with a simple simulation with consideration of several effects during lithography and ion implantation, such as channeling and resist flow.

The demand for single photon sources at $\lambda~=~1.54~\mu$m, which follows from the consistent development of quantum networks based on commercial optical fibers, makes Er:O$_x$ centers in Si still a viable resource thanks to the optical transition of $Er^{3+}~:~^4I_{13/2}~\rightarrow~^4I_{15/2}$. Yet, to date, the implementation of such system remains hindered by its extremely low emission rate. In this Letter, we explore the room-temperature photoluminescence (PL) at the telecomm wavelength of very low implantation doses of $Er:O_x$ in $Si$. The emitted photons, excited by a $\lambda~=~792~nm$ laser in both large areas and confined dots of diameter down to $5~\mu$m, are collected by an inverted confocal microscope. The lower-bound number of detectable emission centers within our diffraction-limited illumination spot is estimated to be down to about 10$^4$, corresponding to an emission rate per individual ion of about $4~\times~10^{3}$ photons/s.

Using the atom probe tomography, transmission electron microscopy, and ab initio calculations, we investigate the three-dimensional distributions of oxygen atoms segregating at the typical large-angle grain boundaries (GBs) ( Σ 3 { 111 } , Σ 9 { 221 } , Σ 9 { 114 } , Σ 9 { 111 } / { 115 }, and Σ 27 { 552 }) in Czochralski-grown silicon ingots. Oxygen atoms with a covalent radius that is larger than half of the silicon's radius would segregate at bond-centered positions under tensile stresses above about 2 GPa, so as to attain a more stable bonding network by reducing the local stresses. The number of oxygen atoms segregating in a unit GB area N GB (in atoms/nm2) is hypothesized to be proportional to both the number of the tensilely-stressed positions in a unit boundary area n bc and the average concentration of oxygen atoms around the boundary [ O i] (in at. %) with N GB ∼ 50 n bc [ O i ]. This indicates that the probability of oxygen atoms at the segregation positions would be, on average, fifty ti...

The effects of the argon gas flow rate and furnace pressure on the oxygen concentration in a transverse magnetic field applied Czochralski (TMCZ) silicon single crystals were examined through experimental crystal growth. A gas controller which had been proposed by Zulehner was used for this series of experiments. In the TMCZ gas-controlled crystals, a decrease in the oxygen concentration with a decrease in furnace pressure was found. A clear relationship between the oxygen concentration and the argon gas flow rate was not obtained due to the limited experimental conditions. The relationships between the oxygen concentration and the furnace pressure and the argon gas flow rate previously observed for Czochralski (CZ) crystals by a similar gas controller were confirmed by the present gas controller. The oxygen concentration changes in the TMCZ and the CZ crystals were analyzed in terms of the calculated flow velocity of the argon gas between the gas controller and the silicon melt surface. In contrast with the CZ gas-controlled crystals, the oxygen concentration was decreased with an increase in the flow velocity of argon gas in the TMCZ gas-controlled crystals. The surface temperature model and the melt flow pattern model which had been proposed in the previous report are discussed again in light of the present experimental results.

The displacement of germanium (Ge) atoms induced by arsenic (As) ion implantation at room temperature was investigated using Ge isotope superlattices grown by molecular beam epitaxy. The depth profiles of 74Ge isotopes in the 70Ge/natGe isotope superlattices before and after ion implantation were obtained by secondary ion mass spectrometry. By representing the experimental data using a conventional integral model, Ge atomic displacement as a function of depth was obtained, from which we determined that 0.75 nm is the critical displacement necessary to make the structure appear amorphous under examination by cross-sectional transmission electron microscopy. However, we found that the amorphous Ge layers were recrystallized due to a local elevation of temperature caused by the implantation, which indicates that the samples should be cooled down during implantation to avoid the regrowth of amorphous Ge layers for this analysis.

It is becoming important to evaluate silicon self-diffusion with progress of a silicon semiconductor industry. In order to evaluate the self-diffusion of silicon, silicon isotope superlattices (SLs) is the only marker. For this reason, it is important to correctly evaluate a film thickness and a depth distribution of isotope SLs by secondary ion mass spectrometry (SIMS). As for film thickness, it is difficult to estimate the thicknesses correctly if the cycles of SLs are short. In this work, first, we report the determination of the film thickness for short-period SLs using mixing roughness-information (MRI) analysis to SIMS profile. Next, the uncertainty of the conventional method to determine the film thicknesses of SLs is determined. It was found that the conventional methods cannot correctly determine film thickness of short-period-isotope SLs where film thickness differs for every layer.

We present a silicon isotope superlattice structure that we believe to be the most ideal secondary ion mass spectrometry standard sample for the dopant concentration depth profiling required for characterization of the shallow junction formed by ion implantation. The precisely stacked alternating layers of silicon isotopes function as a depth ruler. Therefore, it enables us to calibrate the depth scale of dopant based on the positions of silicon isotopes. We show the depth profiles of silicon isotopes and arsenic in the arsenic ion-implanted silicon isotope superlattice as a representing example.

Accurate determination of the intrinsic diffusivities of boron (B), phosphorus (P), and arsenic (As) in silicon (Si) is reported. We show that the differences in the B, P, and As diffusivities reported in the previous works arise from whether SiO2 films existed on the Si sample surfaces. Impurity diffusion near the Si surface without SiO2 is affected by oxidation of Si even in the nominally inert atmosphere, which has unavoidable residual oxygen background due to the open furnace. On the other hand, a surface SiO2 film of ~20 nm thickness prepared before the diffusion annealing is sufficient to block further oxidation of Si, i.e., truly intrinsic diffusivities of impurities have been obtained from samples having surface oxide layers.

The behavior of impurity (arsenic or boron) and silicon host atoms during ion implantation was investigated using silicon isotope superlattices. The depth profiles of silicon isotopes in the 28 Si/ 30 Si isotope superlattices before and after ion implantation were obtained by secondary ion mass spectrometry. The experimentally determined profiles were reproduced very well by a theoretical model to yield the average displacement of silicon atoms as a function of the depth. The critical displacement of silicon to induce the amorphous layer was determined together with cross-sectional transmission electron microscopy. r 2007 Elsevier B.V. All rights reserved.

The effects of argon gas flow rate and furnace pressure on oxygen concentration in Czochralski (CZ) grown silicon crystals were examined through experimental crystal growth. A newly designed gas controller was used for this study. Increase in the oxygen concentration with an increase in argon gas flow rate or with a decrease in furnace pressure was demonstrated for the first time. The results of oxygen concentration changes were analyzed in terms of calculated velocity of argon gas flow along the gas controller over the silicon melt surface. The flow velocity of argon gas was affected both by the argon gas flow rate and the furnace pressure. The flow velocity of argon gas was found to increase with an increase in argon gas flow rate under a fixed furnace pressure or with a decrease in furnace pressure under a fixed argon gas flow rate. The oxygen concentration in the CZ silicon crystals was found to be proportional to the flow velocity of argon gas. Two possible mechanisms which could explain this relationship were discussed.

Three-dimensional distribution of impurity atoms was determined at functional Σ5{013} and small-angle grain boundaries (GBs) in as-grown mono-like silicon crystals by atom probe tomography combined with transmission electron microscopy, and it was correlated with the recombination activity of those GBs, CGB, revealed by photoluminescence imaging. Nickel (Ni), copper (Cu), and oxygen atoms preferentially segregated at the GBs on which arrays of dislocations existed, while those atoms scarcely segregated at Σ5{013} GBs free from dislocations. Silicides containing Ni and Cu about 5 nm in size and oxides about 1 nm in size were formed along the dislocation arrays on those GBs. The number of segregating impurity atoms per unit GB area for Ni and that for Cu, NNi and NCu, were in a trade-off correlation with that for oxygen, NO, as a function of CGB, while the sum of those numbers was almost constant irrespective of the GB character, CGB, and the dislocation density on GBs. CGB would be explained as a linear co...

The effect of P or B predoping on As diffusion in polycrystalline Si was investigated by atom probe tomography. In all samples, a high concentration of As was found at grain boundaries, indicating that such boundaries are the main diffusion path. However, As grain-boundary diffusion was suppressed in the B-doped sample and enhanced in the P-doped sample. In a sample codoped with both P and B, As diffusion was somewhat enhanced, indicating competition between the effects of the two dopants. The results suggest that As grain-boundary diffusion can be controlled by varying the local concentration of P or B.

We have demonstrated that it is possible to reproducibly quantify hydrogen concentration in the SiN layer of a SiO2/SiN/SiO2 (ONO) stack structure using ultraviolet laser-assisted atom probe tomography (APT). The concentration of hydrogen atoms detected using APT increased gradually during the analysis, which could be explained by the effect of hydrogen adsorption from residual gas in the vacuum chamber onto the specimen surface. The amount of adsorbed hydrogen in the SiN layer was estimated by analyzing another SiN layer with an extremely low hydrogen concentration (

The cutting mechanism in ultraprecision-machining of aluminum single crystals having various orientations using a trial ultraprecision machine was investigated. The (111) plane cutting requires the lowest cutting force and provides the best finished surface roughness among those for (001), (110) and (111) planes. The cutting in the direction of [011] on (111) plane gives the best finished surface roughness .The cutting forces and shear angles were affected by the crystal orientation when the depth of cut was 3 and 4μm. The crystal orientation dependency was not observed at a cutting depth of 1 and 2μm. This is reasonably explained by an affected layer, and this characteristic phenomena is shown in the micro cutting. The cutting force varies when shear strain is less than 3 according to the result on the relation between shear stress and shear strain. The finished surface roughness is affected by the cutting direction, suggesting that the control of the workpiece orientation is effective for improving the working accuracy. Width of lamella on the free surface of chips is affected by the cutting direction and depth of cut.

The successful formation of abrupt phosphorus (P) δ-doping profiles in germanium (Ge) is reported. When the P δ-doping layers were grown by molecular beam epitaxy (MBE) directly on Ge wafers whose surfaces had residual carbon impurities, more than a half the phosphorus atoms were confined successfully within a few nm of the initial doping position even after the growth of Ge capping layers on the top. On the other hand, the same P layers grown on Ge buffer layers that had much less carbon showed significantly broadened P concentration profiles. Current–voltage characteristics of Au/Ti/Ge capping/P δ-doping/n-Ge structures having the abrupt P δ-doping layers with carbon assistance showed excellent ohmic behaviors when P doses were higher than 1 × 1014 cm−2 and the capping layer thickness was as thin as 5 nm. Therefore, the insertion of carbon around the P doping layer is a useful way of realizing ultrashallow junctions in Ge.

The impact of carbon (C) co-implantation on boron (B) activation in crystalline silicon was investigated. The detailed distribution of B and C atoms and B activation ratios dependent on the C ion-implantation energies were examined based on three-dimensional spatial mappings of B and C obtained by atom probe tomography and from depth profiles of their concentrations from secondary ion mass spectrometry and depth profiles of carrier concentrations with spreading resistance measurements. At all C implantation energies (8, 15, and 30 keV), B out-diffusion during activation annealing was reduced, so that more B atoms were observed in the C co-implanted samples. The carrier concentration was decreased throughout the entire implanted region for C implantation energies of 15 and 30 keV, although it was only increased at greater depths for C co-implantation at 8 keV. Two different effects of C co-implantation, (I) reduction of B out-diffusion and (II) influence of B activation, were confirmed.

It has been increasingly important to develop lightweight and high-strength materials for improving energy-efficiency through the weight reduction of transportation carriers. Magnesium alloys have attracted lots of attentions[1-3], since the density of magnesium is approximately two thirds of that of aluminum and one fifth of steel. As a result, magnesium alloys offer a very high specific strength among conventional engineering alloys. In addition, magnesium alloys posses good damping capacity, excellent castability, and superior machinability. However, compared to other structural metals, magnesium alloys have a relatively low mechanical strength, especially at elevated temperature. The need for high-performance and lightweight materials for some demanding applications has led to extensive efforts in the development of magnesium matrix composites and cost-effective fabrication technologies. They are proved to have good mechanical properties through an incorporation of structural filler (e.g., ceramic whiskers such as silicon carbide whisker and others, aluminum oxide, graphite and other particles, carbon fibers and carbon nanotubes: CNTs) [4-7]. Within this context, the dimensionally nano-sized, mechanically strong CNTs [8-11], considered as the ideal reinforcing filler in various composite systems [12-15], have been incorporated into magnesium matrix [16-19]. This chapter put the spotlight into the very attractive new magnesium alloy matrix composites reinforced with CNTs.