Fumitaka Nishiyama

Lattice location of N atoms in heavily N-doped ZnSe studied with ion beam analysis and its implication on deep level defects

Abstract Molecular beam epitaxially grown ZnSe doped with 15 N as high as 1.5 × 10 20 cm -3 is characterized by means of ion beam analysis technique. Resonant nuclear reaction of 15 N(p, αγ) 12 C is utilized to detect 15 N, while particle induced X-ray emission (PIXE) is detected to get insight into the effect of N-doping on the lattice location of Zn and Se atoms. It is demonstrated that the incorporated N atoms are located at the substitutional sites and that both Zn and Se atoms are located at the substitutional sites. The results suggest that the carrier compensation in heavily N-doped ZnSe is not caused by such donors as N int or N Se -Zn int , but by complex defects which include donor-type complexes such as N Se -Zn-V Se and/or N Zn -N Se . It is also suggested that a cluster of N Se such as (N Se ) n -Zn may play a role as a deep acceptor.

Crystalline Qualities and Critical Current Densities of As-Grown Ba2YCu3Ox Thin Films on Silicon with Buffer Layers

As-grown Ba2YCu3Ox thin films (\lesssim100 nm) have been prepared by rf magnetron sputtering deposited on Si(100) with buffer layers of YSZ and Y2O3/YSZ. Epitaxial growth of Ba2YCu3Ox thin films is confirmed by ion channeling measurements along the (100) directions of the Si substrate showing a χmin of 60% on YSZ/Si, and 6% on Y2O3/YSZ/Si using 2.0 MeV He+. The as-grown films have critical current densities of 104 A/cm2 on YSZ/Si and 106 A/cm2 on Y2O3/YSZ/Si at 77 K. Our results indicate that the superconducting properties of the films are limited primarily by the value of lattice mismatch between the Ba2YCu3Ox and buffer layers.

Nitrogen doping and carrier compensation in p-ZnSe

Abstract The doping of nitrogen and compensating centers in N-doped ZnSe are investigated. Ion beam analysis is performed on N-implanted and N 2 -implanted ZnSe to get insight into the lattice location of N 2 in the ZnSe lattice. It is likely that a N 2 molecule is situated at a random site in the ZnSe lattice. Plausible compensation mechanisms are discussed in the light of experimental results so far. It is suggested that a few kinds of compensating centers are responsible for the compensation processes.

Preparative isotachophoretic analyser equipped with a dropwise fractionating device

Abstract A preparative isotachophoretic analyser with a series of four separation tubes of I.D. 0.5–5 mm was constructed and its fundamental efficiency was evaluated. The maximum injectable sample volume was 2.5 ml. The heat convection in the separation tube (I.D. = 5 mm) was suppressed by adding hydroxypropylcellulose to the leading electrolyte (1%) and sucrose to the terminating electrolyte (20%). The entire separated zones were fractionated dropwise (5.4 μl each) through a narrow-bore nozzle by a counter flow of the leading electrolyte. Variations in the course of dropping due to electrostatic forces were suppressed by a simple electrostatic device. The recoveries of several micrograms of separands were determined by photometric and PIXE analysis and were almost 100%. The separability and apparent sensitivity were very good; e.g., 150 ppb (109) Sm3+ (10−6M, 2 ml) was separated from a mixture with Dy3+, Tm3+ and Lu3+.

NO decomposition by ultrafine noble metals dispersed on the rare earth phosphate hollow particles

Novel fine polymer particles containing ultrafine Pd, Pt or Rh metal dispersed on the core-shell [core, poly(styrene-co-acrylamide) or poly(styrene-co-acrylic acid); shell, LnPO4(Ln = Ce, Nd, Pr, Sm, La)] type microsphere were prepared by the emulsifier-free emulsion polymerization of styrene with acrylamide or acrylic acid followed by the addition of PdCl2, HPtCl6, or RhCl3 and finally by the addition of a mixture of Ln(NO3)3 and NaH2PO4. Pyrolysis of the resulting polymer particles at 700–900°C provides polymer-free hollow particles (diameter 450–550 nm) composed of noble metals and LnPO4. The excellent catalytic reduction of NO gas into N2 and O2 was observed at 500–700°C using the rersulting particles as catalyst.

Study of isotachophoretic separation behaviour of metal cations by means of particle-induced X-ray emission : I. Separation of twenty metal cations using an acetic acid buffer system and α-hydroxyisobutyric acid complex-forming

Abstract Twenty metal ions were separated isotachophoretically and the zones were fractionated and analysed off-line by particle X-ray emission (PIXE). The recovery, migration order and separation efficiency were studied in relation to the use of a complexing agent, α-hydroxyisobutyric acid (HIB). The migration order using the WNH 4 Ac system [aqueous solution (W) of NH 4 + as the leading ion and acetate (Ac) ion as the pH-buffering counter ion, pH = 4.8] was Ba, Sr, Ca, Na, Mg, (Mn, Fe II , Co), Ni, Zn, La, Ce, Cd, Y, Li, Lu, Gd, (Cu, Pb) and (Zr IV O, Fe III ). The order using the WNH 4 Ac—HIB system was Ba, Sr, Ca, Na, Mg, Mn, Fe II , Cd, Co, Li, Ni, Zn, La, Pb, Ce, Gd, Cu, Y, Zr IV O, Lu. The recovery of the metal cations was 100% with both electrolyte systems, except for Fe II and Zr IV O. The low recoveryu of Zr IV O was due to hydroxyl complex formation and that of Fe II to hydroxyl complex formation of Fe III , the oxidation product of Fe II . For these ions, the recovery with the WNH 4 Ac—HIB system was lower than that with the WNH 4 Ac system.

Separation of rare-earth ions by isotachophoresis and capillary zone electrophoresis

Abstract The simultaneous separations of 15 rare-earth (RE) ions including yttrium and lanthanide both by isotachophoresis (ITP) and by capillary zone electrophoresis (CZE) were achieved by using the developed electrolyte systems containing α-hydroxyisobutyric acid (HIBA) as main complexing agent and malonic acid as the assistant one. The successful separation of Y3+ from Dy3+ without loss of the separation of Eu3+ and Gd3+ was briefly summarized. Based on the assumed equilibria existed in steady state zone while using such an electrolyte system with binary complexing agents, the effective mobilities of the RE complex ions and the qualitative indicies (RE, the ratio of the specific conductivity of the sample zone to that of the leading zone) for the RE complex zone were theoretically simulated. The reason for the successful separation was clarified from the view of complex formation, and the simulated isotachopherogram for an optimum electrolyte system was then obtained. The validity of the simulation was checked by comparison of the simulated RE with the observed ones. Furthermore, the historic sample didym prepared from a RE ore by Brauner was analyzed by ITP–particle-induced X-ray emission as well as by CZE, where the supporting electrolyte for CZE analysis is 30 mM creatinine containing 4 mM HIBA and 0.4 mM malonic acid buffered by 2-ethylbutryric acid to pH 4.8.

Strain measurements in heteroepitaxial yttria‐stabilized zirconia on Si by ion beam channeling

Yttria‐stabilized zirconia (YSZ) films have been epitaxially grown on Si(100) substrates at 800 °C by vacuum evaporation. By post‐annealing in dry O2 at 800 °C, SiO2 layer was formed at the YSZ/Si interface. Strain in heteroepitaxial cubic YSZ films has been measured by ion beam channeling. The strain was found to be tensile. This tensile strain is caused as the sample is cooled down after growth due to the difference in thermal expansion coefficients between YSZ and Si. The tensile strain is increased by annealing in dry O2, due to the SiO2 layer formed at the YSZ/Si interface. The tensile strain is also introduced in the near‐interface region of Si substrate under SiO2.

Bidirectional isotachophoretic separation of metal cations using EDTA as a chelating agent

Abstract An operational electrolyte system using EDTA as a chelating agent was developed for the bidirectional isotachophoresis (ITP) of metal ions. The anolyte used was 20 m M HCl buffered by adding β-alanine at pH 3.6. The catholyte was 20 m M ammonia solution buffered by acetic acid at pH 4.8 and containing EDTA in the range 0–1 m M . In relation to the concentration of EDTA, the isotachophoretic separation behaviour of eighteen metal cations containing equimolar EDTA was studied by using with particle-induced X-ray emission (PIXE). They were Na + , Li + , Ba 2+ , Sr 2+ , Mg 2+ , Ca 2+ , Mn 2+ , La 3+ , Ce 3+ , Co 2+ , Zn 2+ , Gd 3+ , Pb 2+ , Y 3+ , Ni 2+ , Cu 2+ , Lu 3+ and Fe 3+ in increasing order of chelate stability constants. When a catholyte containing 0.1 m M EDTA was used, Na + , Li + , Ba 2+ , Sr 2+ , Mg 2+ , Ca 2+ and Mn 2+ were completely recovered as cations and La 3+ , Ce 3+ , Co 2+ , Zn 2+ , Gd 3+ Pb 2+ , Y 3+ , Ni 2+ , Cu 2+ and Lu 3+ were completely recovered as chelate anions. The recovery was incomplete for a test mixture without adding EDTA, even when the EDTA concentration in the catholyte was 1 m M . Absolute mobilities of several chelates were obtained and the concentration and pH of isotachophoretic zones were simulated to clarify the decomposition during migration.

Evaluation of crystalline quality of zirconium dioxide films on silicon by means of ion‐beam channeling

Zirconium dioxide (ZrO2) films have been grown on Si(100) and Si(111) substrates at 800 °C by vacuum evaporation. A channeling spectrum of the Rutherford backscattering on the ZrO2 films shows that ZrO2 films [tetragonal (200)] are epitaxially grown on Si(100) substrate at 800 °C, which is consistent with x‐ray diffraction and reflection high‐energy electron diffraction observations. The spread of crystallite orientation in the epitaxial film is estimated to be 0.32°, by analyzing the angular dependence of the total backscattering yield.