A method for the analysis of sub parts per trillion levels of rare-earth elements (REEs) and yttrium (Y) In seawater after preconcentration with solvent extraction and back-extraction has been developed. Almost perfect extraction and backextraction of all REE and Y were achieved by single extraction, and most of the matrix elements were removed during the extraction procedure. Even after 200-fold preconcentration, matrix problems by ICP-MS measurement were negligible. Contamination from reagents and water used during the pretreatment was below 1 % of the concentration of REE and Y In seawater. The standard deviation obtained for triplicate separation of 100and 1000-mL samples of the same seawater was better than 5% for all REE. The average precision of the measurement for all REE and Y after preconcentration of 1000 mL of raw seawater to 5 mL of final measurement solution was calculated to be less than 2.5 %. Since there Is no standard seawater sample for REE and Y, in order to evaluate this novel technique, the analytical results obtained by this method were compared with those obtained by Isotope dilution mass spectrometry coupled with Fe coprecipitation. The comparison indicated the good accuracy of the present method. Sample preparation and measurement could be carried out within 30 min for every sample. Two internal standard elements, In and Cd were used to check sample loss during the extraction and back-extraction procedures and to control the possible matrix effect and Instrument fluctuation.
We investigated low temperature out‐diffusion of Cu impurity from the bulk of p‐ and n‐type silicon wafers after contamination followed by diffusion of Cu into silicon during annealing. We show that Cu impurity in the bulk after low‐temperature out‐diffusion can be measured at the surface by total x‐ray fluorescence and graphite furnace atomic absorption spectroscopy 1010 atom/cm3. In addition, a benefit of low‐temperature annealing is the removal of Cu contamination from the bulk by surface cleaning. We also find that Cu contamination in the bulk of p‐type Si wafers out‐diffuses at room temperature after removing the surface oxide, but this does not happen in the case of n‐type Si material.
The effectiveness of phosphorus diffusion gettering (PDG) and related segregation coefficients for different metal impurities were measured applying thermal treatments in the temperature range 800-950 °C for different times. We used multi-crystalline and mono-crystalline CZ p-type wafers with different boron concentrations and different levels of dislocations and bulk micro-defects (BMD). In all sample types, for Cu and Ni we found complete gettering in the temperature range investigated. In the case of Fe, the segregation coefficient increases with both increase in temperature and extension of time. The increase is qualitatively changing when going above 900 °C. At 950 °C the segregation coefficient increases faster at shorter diffusion time but at extended diffusion time it increases slower as compared to diffusion at 900 °C. At the same temperature and time of phosphorus diffusion the segregation coefficient is found to be independent of the metal impurity concentration in the range of 1012-1015 cm-3 investigated. We have shown that the presence of BMD and dislocations in bulk silicon does not impede the ability of PDG to completely remove Fe, Ni and Cu metal impurities from the bulk. Further analysis suggests that the PDG has the same gettering efficiency for mono-crystalline silicon and multi-crystalline silicon. We conclude that if any bulk precipitation of Fe, Ni and Cu impurities is present in multi-crystalline silicon it cannot seriously compete with PDG. However we found that increasing the boron concentration in the samples reduces the segregation coefficient of Fe, and this reduction is more severe at lower temperatures. Finally, by applying a post anneal ramp down from 900 °C to 700 °C after phosphorus diffusion, we found that the Fe segregation coefficient increases by a factor of 36 for lightly B doped samples, from 53 to 1919, leading to a significant reduction of Fe in the bulk after 2 hours ramp down anneal.
To analyze data, descriptive statistics and inferential statistics, i.e. independent sample t-test, were run. Descriptive analysis indicated that participants suffer from language anxiety and fear of negative evaluation. The result of independent sample t-test showed there was no significant difference between males and females in the levels of anxiety. The computation of means and standard deviations of statements in questionnaires revealed that the prime sources of language anxiety and fear of negative evaluation are fear of failing class and fear of leaving unfavorable impression on others, respectively. Furthermore, Pearson correlation analysis indicated there is a significant correlation between foreign language anxiety and fear of negative evaluation. The present study will examine the causes of anxiety of students through the various types of anxiety that the students encounter in relation to learning English in a foreign land. Specifically, the research will look into foreign language classroom anxiety and fear of negative evaluation, as well as to determine the relationship between the two. Index Terms-foreign language anxiety, fear of negative evaluation, sources and causes
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