Calcium plays an important role for the phase relations and elasticity of the Earth's mantle because of its high abundance in the Earth. Diopside (CaMgSi20~) is a major host mineral of calcium in the upper mantle. Recent experimental studies clarified that diopside decomposes into an assemblage of CaSiO3 plus MgSiO3 at about 17 GPa.1>,2) CaSiO3 crystallizes in a cubic perovskite structure and a solubility of Mg into CaSiO3 is very limited. These experimental results imply that perovskite-type CaSi0 ,3 may be an important constituent mineral in the lower mantle. Its physical and chemical properties are, however, not well known yet. The purpose of the present study is to clarify the stability and equation of state of perovskite-type CaSi0 ,3 under the conditions of the lower mantle through high pressure in situ X-ray diffraction study.The starting material was prepared from a mixture of CaC03 and Si02 which was melted at 1580°C in air and then annealed at 1400°C for 47 hours. The product was examined by X-ray diffraction and was confirmed to be CaSiO3 with the pseudo-wollastonite structure. It was then ground into a fine powder and a small amount (a few percent by weight) of platinum black, which works as an absorber of the YAG laser for heating, was mixed with it. A lever and spring type diamond anvil apparatus3> was used throughout the high pressure experiments. The anvils were beveled, one-quater carat, brilliant-cut diamonds. The culet and central flat size were 0.5 mm and 0.25 mm, respectively, and the bevel angle was 7°. Molybdenum Kc radiation from a high power X-ray source (operated at 55 kV and 160 mA) was collimated by a 60 µm pin-hole collimator and the diffracted X-ray pattern was recorded on a film with a radius of approximately 57.3 mm. Accurate sample to film distance was determined by measuring diffractions from a standard material (e.g. silver) which was stuck on the surface of the diamond anvil. The typical exposure time was 60 to 80 hours. In order to accelerate a possible phase transformation or a decomposition reaction, the sample was heated above 1000°C by a YAG laser after each pressure increment. A thin laser beam (approximately 15 µm in diameter) from the 12 W single mode YAG laser was scanned to heat the whole area of the sample and the total heating duration was about 30 min. After the heating, X-ray measurements were made at room temperature. The pressure was measured using ruby fluorescence scale.4~ The powdered sample was compressed directly, and therefore a large pressure gradient was observed in the sample chamber. Many fine grains of ruby powder were spread over the entire region of the sample and the measured values in the area exposed to the X-ray (70 µm in diameter) were averaged to :k ) Tokyo
We have investigated the lattice site location of B in Si using ion channeling in combination with nuclear reaction analysis (NRA). Silicon samples implanted with Boron at an energy of 10 keV and a dose of 5 × 1014 cm−2 (low dose samples) or 5 × 1015 cm−2 (high dose samples) were annealed at 1000 °C for 10 seconds (RTA) or at 800 °C for 10 minutes (FA). The activation efficiencies of these samples were estimated from the B atomic concentration and the hole concentration obtained by secondary ion mass spectrometry (SIMS) and spreading resistance profiling (SRP), respectively. We also studied the ion implantation damage of Si crystals using ion channeling combined with Rutherford backscattering spectrometry (RBS). We found that the activation efficiency is proportional to the substitutionality, meaning that substitutional B is fully activated without any carrier compensation. We also found that B atoms go to the substitutional sites and are activated up to the solubility limit in the high dose samples. However, the ion implantation damage of the crystalline Si in the high dose samples increases somewhat after annealing.
Well-defined hexagonal-shaped dislocation loops were introduced into an n-type silicon crystal grown by the floating-zone technique. The electron beam induced current (EBIC) contrasts of screw parts and 60° parts of the loops showed different dependencies on the temperature of observation. Such difference is interpreted with the idea that the physical parameters controlling carrier recombination at the dislocation core are different between screw and 60° dislocations.
A new computer-aided electron beam induced current system was developed which makes it possible to obtain two-dimensional mapping of the absolute magnitudes of electron beam induced current signals over the temperature range 15 K-400 K. Electronic states of defects in cast silicon and deformation-induced dislocations in float-zone silicon were investigated from the analyses of temperature dependencies of electron beam induced current contrasts of the defects measured with the system. Electron beam induced current active defects in cast Si were identified to be Fe impurity atoms or Fe-B pairs incorporated at the dislocation core depending on the cooling rate of a crystal. Dislocations in float-zone silicon were shown to have an energy leve1 for carrier recombination in the lower half of the band gap.
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