Papers by Keyword: Impurity

Abstract: In solution growth of 4H-SiC, we have investigated changes in macrostep height with addition of the Group III (B, Al, Ga), Group IV (Ge, Sn), Group V (N) elements, and transition metals (Ti, V, Cr, Ni) to Si solvents, in order to find additives improving severe step bunching which often occurs during growth. The addition of Al, B, Sn, N, and V decreased the average macrostep height compared with the crystal grown with Si solvents. The addition of Al, B, Sn, N, and V suppressed the generation of trench-shaped surface defects in long-term growth of 10 hours. This result demonstrated that the addition of Al, B, Sn, N, and V has an advantage to achieve high quality bulk crystal growth from solution.

Abstract: Iron (Fe) impurity concentrations in a SiC bulk crystal and source powders used for the bulk crystal growth are analyzed by means of secondary ion mass spectrometry and the validity of the obtained data are discussed. The secondary ion signal of ⁵⁶Fe is found to be affected significantly by the mass interference of ²⁸Si₂, and therefore measurements of ⁵⁴Fe instead of ⁵⁶Fe offer a better detection limit for the analysis. A high concentration of Fe is found at proximity of the SiC bulk crystal surface. Possible sources of the Fe contamination are discussed based on the depth profile data of Fe in both the bulk crystal and the source powders.

Abstract: One of the main aims of our work is to obtain general equations for the diffusion fluxes under strain that give the possibility for using these equations at low temperatures, as in this case the strain influence on the diffusion fluxes is manifested in maximal degree. Our approach takes into consideration that the strains can alter the surrounding atom configuration near the jumping atom and consequently the local magnitude of the activation barrier and a rate of atom jumps. The approach is derived under assumptions that the total energy depends on the pair distances only and the attempt frequencies are the same for all jumps. The rates of atom jumps in different directions define the flux density of the defects. Now we take into account that the strain tensor is different at the saddle point and at the rest atom position, that differentiates our approach from previous ones. As a result, general equations for the vacancy fluxes and impurity fluxes are obtained for fcc and bcc metals. These equations differ significantly from those obtained earlier.

Abstract: Ab initio calculations of electronic structures of Zr–H and Zr–He systems have been done. The influence of hydrogen or helium impurities on the electron density distribution of the host metal has been considered. Extremely inhomogeneous redistribution of the metal valence charge density within the first coordination sphere of the impurity was found. The character of the observed anisotropy depends on the impurity type.

Abstract: Within the next ten years, advanced semiconductor manufacturing will move into the sub-10 nm regime [1]. At these dimensions, there is concern that molecular scale impurities (≤ 1 nm diameter) within cleaning chemistries will have an increasing impact on wafer cleanliness, device yield, and performance. Considering that these impurities may be on the same size scale as some of the active ingredients, this will raise significant challenges for solution developers in terms of impurity identification and prevention. Herein, we will describe our efforts to better understand the impurities within a semi-aqueous residue remover (RR). This work has primarily focused on identifying trace water-insoluble impurities not readily detectable by standard impurity characterization techniques, such as gas and liquid chromatography. The first part of this project involves a proof of concept study of isolating known impurities from a corrosion inhibitor (CI), and the second part of this study is the identification of unknown impurities within RR and the identification of the source of these impurities.

Abstract: SnO₂ nanowires with a tetragonal structure were synthesized by thermal evaporation of tin grains at 900 °C. The obtained SnO₂ nanowires were doped with Pt and Pd. The morphology, crystal structure, and H₂ sensing properties of undoped, Pt-doped, and Pd-doped SnO₂ nanowires were investigated. SnO₂ nanowires were approximately 30–200 nm in diameter and several tens of micrometers in length. Gas sensors based on undoped, Pt-doped, and Pd-doped SnO₂ nanowires showed a reversible response to H₂ at an operating temperature of RT–300 °C. The response was improved in the order undoped < Pt-doped < Pd-doped SnO₂ nanowire sensors under the same conditions. The highest response upon exposure to 1000 ppm H₂ was 252.9 at 100 °C for Pd-doped SnO₂ nanowire sensor. The results demonstrated that impurity doping improved the sensor response and lowered the operating temperature at which the sensor response was maximized.

Abstract: The Co- and Ni-bearing pyrite (100) surfaces were studied using density functional theory (DFT). The calculated results show that the covalency of the bonds on surface is weakened due to the presence of Co or Ni impurity, especially for the Ni-bearing pyrite surface. Hybridization occurs between Co 3d and S 3p and between Ni 3d and S 3p. The electrical conductivity of surface is enhanced due to the presence of Co and Ni impurities. Surface Co atom is predicted as spin-polarized and surface Ni atom is calculated as low-spin state.

Abstract: Microstructures and mechanical properties of the D-SSF (Deformation Semisolid Forming) processed Al-Zn-Mg alloys with high Fe content up to 2 mass% were investigated. A high ductility alloy even containing 1 mass% Fe was successfully produced by applying the D-SSF process. Especially, the D-SSF processed alloy with 1 mass% Fe was superior to the conventionally processed alloy with Fe-free in the properties of the tensile strength and elongation. These results clearly indicate that the harmful influence by the addition of 1 mass% Fe is effectively modified into not harmful one by applying the D-SSF process. Furthermore, the former liquid phase regions (FLP regions) which are finally solidified during the D-SSF process are completely extinguished by the solution treatment and resultantly the mechanical properties are greatly improved. The extinction process of the FLP regions during the solution treatment was examined using an EBSD method in terms of the crystal orientations of the α-Al grains.

Abstract: Fundamental studies on durability and reliability of SOFC modules/stacks had started as one of the new NEDO project from FY2005 and the organization had been partly modified at FY2008 and FY2013[1]. The main target is to make sure the long term durability within 10 % of degradation rate in the range of 40,000 h (5 years), and reliability during 250 times of starting up and ending operations. In this project, the effect of impurities on degradation of SOFCs was examined for 5 different stacks/modules (Kyocera, Tokyo gas, TOTO, MMC-KEPCO and MHI) at AIST. During the operation of SOFC stacks and modules, several kinds of impurities are carried continuously with air and fuels and react with cell components. The concentration of impurity in cell components was carefully investigated before and after long term operation by using a secondary ion mass spectrometer (SIMS) as a main analytical tool with conventional analytical techniques such as a scanning electron microscopy (SEM) and an electron probe micro analyzer (EPMA). Many approaches were carried out to investigate the effect of gaseous impurities as listed below. (1)The concentration of impurity in cell components was carefully investigated before and after long term operation. (2)Chemical reactivity between impurities and cell components are examined from the view point of thermodynamics. (3)In order to understand the mechanism of the degradation due to impurities, the effect of impurities on degradation of laboratory scale button cell were examined. (4)Cation diffusion were carefully investigated in some diffusion couples to clear the mechanism on formation of secondary phases between the cathode and electrolyte. (5)Acceleration tests on degradation by impurities were also carried out by using a button cell to predict the degradation rate depending on the contamination of impurities in the cathode. The results of the project is partly introduced in this report.

Abstract: Small angle grain boundaries have been grown in a small Bridgman furnace, using seeded growth method, at three different pulling rates i.e. 3 μm/s, 13 μm/s and 40 μm/s. In order to assess segregation mechanisms of impurities towards the central grain boundary, melt has been polluted by 50ppma of either copper or indium. Secondary ion mass spectrometry (SIMS) local analyses have been performed to investigate the impact of solid state diffusion and limited rejection of solute at the grain boundary for each growth rate. The results are discussed in connection with an atomistic model built on Vienna Ab-initio Simulation Package (VASP).