Motoyuki Yamagami

Chloride-ion hydration in supercritical water by neutron diffraction

Abstract Pulsed neutron diffraction measurements by using chlorine-isotopic substitution have been made on 3.0 molar aqueous lithium chloride solutions in supercritical D 2 O at T = 648 K and P = 169 MPa as well as under ambient condition ( T c = 643.9 K and P c = 21.7 MPa for D 2 O). The first-order difference data have revealed that the hydrogen bonding between the chloride ion and water is substantially weakened, accompanied by a much less correlated orientation between the water molecules and the chloride ion. The number of nearest water D atoms around Cl − decreases from 5.8 at 298 K to 2.5 at 648 K, suggesting that dehydration of the chloride ion proceeds at 648 K. The present findings are compared with the results obtained from computer simulations.

An X-ray diffraction study on concentrated aqueous calcium nitrate solutions at subzero temperatures

Abstract X-ray scattering measurements on aqueous solutions of Ca(N03)2 · R H 2 O with R = 6 and 12 have been performed over a temperature range of 258 – 298 K. The analysis of the X-ray data gave the coordination number of Ca 2+ nearly seven with a Ca 2+ -0 distance = 247 pm. It has been found that with decreasing temperature the hydration shells of Ca 2+ and N0 3 are significantly perturbed in the saturated solution (R= 6), accompanied by evolving of hydrogen bonded network in the water structure. Contact ion-pairs between Ca 2+ and N0 3 are present in both solutions, as also evidenced by Raman spectroscopy, the nitrate ion coordinating to Ca 2+ in a monodentate fashion with a Ca 2+ - N(N0 3 ) distance 300 – 310 pm.

Pulsed neutron diffraction study on lithium (I) hydration in supercooled aqueous chloride solutions

Pulsed neutron diffraction measurements have been performed on aqueous LiCl solutions (mole ratio D2O:LiCl=5) in the supercooled state (258, 213, and 173 K) and at room temperature (295 K). An isotopic substitution method with respect to Li has been used to derive the Li+‐related radial distribution function. The neutron diffraction data at all the temperatures have shown the Li–O and Li–D distances to be 2.02±0.05 and 2.61±0.05 A, respectively, and the most likely orientation of the coordinated water molecules has been found to be such that the four atoms in a Li+–D2O unit is pyramidal. It has also been found that at temperatures from 295 K down to 213 K the Li+ hydration is represented mostly by the primary hydration shell of about four coordinated water molecules, whereas at 173 K, about 40 K above the glass transition temperature, the definite second hydration shell of Li+ is formed. The obtained structural characteristics of the supercooled solutions are discussed in connection with nucleation of ice...

NEUTRON DIFFRACTION STUDY ON CHLORIDE ION SOLVATION IN WATER, METHANOL, AND N,N-DIMETHYLFORMAMIDE

Pulsed neutron diffraction measurements have been carried out on 8.6, 5.8, and 1.7 molar lithium chloride (LiCl) solutions in deuterated water (D2O), methanol‐d4 (MeOD), and N,N‐dimethylformamide‐d7 (DMF), respectively. A first‐order difference method with chlorine isotopes substitution was used to derive the Cl−‐dependent partial structure factors and radial distribution functions. The oscillation patterns of all Cl−‐related structure factors normalized by the concentration persist up to the high momentum transfer region (∼10 A−1), suggesting the presence of the short‐range ordering around chloride ion in the three solvent systems. The normalized radial distribution functions have revealed that methanol molecules are hydrogen bonded to a chloride ion with almost linear orientation of Cl⋅⋅⋅D–O, as in the case of chloride hydration. The nearest‐neighbor Cl–D distance and the solvation number for Cl− in the methanol solutions were determined as 2.21±0.03 A and 3.6±0.5, respectively, compared with 2.29±0.01 ...

VPD/TXRF analysis of trace elements on a silicon wafer

A combination of vapor-phase decomposition (VPD) and total reflection x-ray fluorescence (TXRF) was used for the trace analysis of light elements (Na and Al) and transition metals (Fe, Ni, Cu, and Zn). TXRF measurement using the W Mα line was conducted for the high-sensitivity analysis of Na and Al. Through the use of VPD/TXRF, the lower limits of detection (LLDs) were improved by two orders of magnitude compared with those of TXRF without use of the VPD technique. For 150 mm Si wafers, the LLD was 3 × 1010 atoms cm−2 for Na and 2 × 109 atoms cm−2 for Al. The LLDs for Fe, Ni, Cu, and Zn were 4 × 107, 5 × 107, 6 × 107 and 9 × 107 atoms cm−2, respectively. The analytical results obtained by VPD/TXRF were cross-checked with results obtained by atomic absorption spectrometry. The two sets of values were in good agreement. The glancing angle dependence of TXRF intensity was investigated on samples before and after undergoing VPD treatment. The angle dependence proved that the sample after VPD treatment became a particle type on the wafer. Copyright

Structure and dynamics of supercooled and glassy aqueous ionic solutions

Abstract X-ray diffraction, neutron diffraction isotopic substitution(NDIS), and quasi-elastic neutron scattering(QENS) measurements have been made on concentrated aqueous solutions of lithium halides LiX (X=C1, Br, and I) in a temperature range covering the room-temperature liquid, the supercooled liquid, and the glassy state. X-ray radial distribution functions have revealed that the hydration shell of the halide ions is gradually structured with lowering temperature. Another interesting feature is the evolution of water-water interactions centered at 4.3 and 6.9 A independent of the halide ions, due probably to reinforced hydrogen bonds at low temperatures. The NDIS radial distribution functions related to Li + and Cl - have demonstrated that the orientational correlation of bound water molecules for Cl - is more strongly temperature-dependent than that for Li +. At low temperature the formation of a second hydration shell of Li + and Cl - has been established. The QENS data have shown that the translational motion of water molecules in the LiCl solution is more hindered with lowering temperature. The structural and dynamic characteristics of the supercooled and glassy solutions are discussed in connection with nucleation of ice, isotropic reorientational motion of water, and the partial recovery of hydrogen bonds in these solutions.

The local structure around hydrogen atoms in a hydrogenated amorphous LaNi5.0 film studied by neutron diffraction

Abstract The local environments around hydrogen atoms in a hydrogenated amorphous LaNi 5.0 film have been investigated by neutron diffraction and were compared with those in a hydrogenated crystalline bulk. From the pair correlation functions for amorphous LaNi 5.0 D x ( x = 0, 2.5), the interatomic distances of DNi pairs were found to be longer for the amorphous LaNi 5 than for the crystalline bulk, indicating that hydrogen atoms in the amorphous LaNi 5 occupy the distorted hydrogen sites suggested from an extended X-ray absorption fine structure analysis. Furthermore, the hydrogen atoms absorbed in the amorphous LaNi 5 prefer to occupy the La 2 Ni 2 tetrahedral site rather than the La 2 Ni 4 octahedral site in comparison with the case of the crystalline LaNi 5 .

Structure of ionic hydration in non-ambient conditions

Abstract Neutron diffraction measurements have been performed on highly concentrated LiCI solutions in D 2 O over a wide temperature range covering their glassy and supercooled states and the supercritical temperature of water. The 6 Li/ 7 Li and 35 Cl/ 37 Cl isotopic substitution method was used to derive the Li- and Cl-related radial distribution functions. Both neutron data sets have revealed temperature-dependent microscopic structures of ionic hydration in terms of ion-water distances, hydration number, orientation of coordinated water molecules, and hydrogen bonding.

Development of vapor phase decomposition-total-reflection X-ray fluorescence spectrometer ☆

A total reflection X-ray fluorescence spectrometer integrated with vapor phase decomposition, VPD-TXRF, was newly developed. This instrument was designed to achieve a minimum footprint, to avoid cross contamination during operation, and to protect people and instruments from HF gas. Comparisons between analysis by VPD-TXRF and by atomic absorption spectrometry (AAS) indicated very good agreement in a wide range, from 108 to 1012 atoms/cm2. The lower limits of detection (LLDs) were improved by two orders of magnitude compared with straight TXRF. For 300-mm Si wafers, the LLDs were 5×108 atoms/cm2 and 1×107 atoms/cm2 for Al and Ni, respectively. VPD-TXRF was able to perform ultra-trace analysis at the level of 108 atoms/cm2.

A method of locating dried residue on a semiconductor wafer in vapor phase decomposition-total-reflection X-ray fluorescence spectrometry by monitoring scattered X-rays

Abstract Vapor phase decomposition-total-reflection X-ray fluorescence spectrometry (VPD-TXRF) is used in the analysis of whole-surface trace metal contamination on silicon wafers at a very high sensitivity. In VPD-TXRF, locating the exact position of dried residue is critical for obtaining a reliable analysis. To locate the residue, the fluorescence from the internal element added as standard reference for quantification is most commonly used as a search marker. However, the added internal standard reference sometimes interferes with the determination of analytes. To avoid such interference, we introduce a new method of locating the residue that utilizes the scattered X-rays from it. Basic experiments have shown that scattered X-rays can be used as markers of residue position instead of the fluorescence from an internal standard reference. An x – y –θ-controlled stage has been proven to be preferable in the application of this locating method than an r –θ-controlled stage. The repeatability of our method is the same as that of the conventional internal standard reference method. There are many advantages in our new method: no interference with analytes of interest, speed, and ease of application. In addition, the method is compatible with the conventional internal standard reference method.