Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/pssb.20220048

Authorship：Lead author,　Corresponding author   Language：Japanese  

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Language：Japanese   Publisher：Proceedings of SPIE - The International Society for Optical Engineering  

Large size and low dislocation density bulk gallium nitride (GaN) crystals were successfully grown by original acidic ammonothermal method SCAAT™ (Super Critical Acidic Ammonia Technology). It enabled us to obtain extremely high crystallinity true bulk GaN. In this article, 2-inch size non-polar m-plane GaN and nearly 4-inch size polar c-plane GaN were demonstrated. The dislocation and stacking fault density of m-plane GaN were in the range of 102 to 103 cm-2 and 0 to 5 cm-1, respectively. The full width at half maximum (FWHM) of X-ray rocking curve (XRC) on (10-12) plane was 6.4 arcsec. The dislocation density of c-plane GaN was in the range of 103 to 104 cm-2. The off-angle distribution of nearly 4-inch size c-plane GaN was ±0.006° in the span of 80 mm. The types of dislocations in the c-plane GaN were identified by transmission electron microscope (TEM) observation. Hydride vapor phase epitaxy (HVPE) growth on the SCAA™ c-plane seed was carried out and obtained 2-inch wafer. The crystallinity was comparable to SCAAT™ seed; FWHM of XRC was less than 10 arcsec and off-angle distribution was ±0.017°.

DOI： 10.1117/12.2540737

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publisher：Proceedings of SPIE - The International Society for Optical Engineering  

The dependence of growth temperature for the epitaxial films grown by tri-halide vapor phase epitaxy (THVPE) on the crystal characteristics, such as the surface morphology, the full width at half maximum (FWHM), the threading dislocation density (TDD), the impurity concentration, and the photoluminescence (PL) was investigated. The epitaxial films grown at relatively high growth temperature of 1300-1350 °C showed that the crystal quality, such as FWHM and TDD retained that for the used substrate. The near-band-edge emission for PL for 1300-1350 °C growth showed lager intensities due to low nonradiative recombination center (NRC). Moreover, the epitaxial growth on the supercritical acidic ammonia technology (SCAAT™) substrate was demonstrated. The TDD was as low as 2 × 104 cm-2, which indicated that the epilayer grown by THVPE retained the superior crystal quality of SCAAT™.

DOI： 10.1117/12.2543661

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publisher：Applied Physics Express  

The effect of the thermal annealing on an acidic ammonothermal gallium nitride (GaN) crystal grown toward the c- and m-directions was investigated. The specific annihilation of hydrogenated Ga vacancies was confirmed for the GaN crystal grown toward the m-direction but not for that grown toward the c-direction. A transparent and yellow luminescence-free ammonothermal GaN substrate was realized. The annihilation of the hydrogenated Ga vacancies was explained by the difference in the diffusion of F incorporated as a mineralizer between the c- and m-directions.

DOI： 10.7567/1882-0786/ab5459

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publisher：Japanese Journal of Applied Physics  

GaN with a film thickness of 200-600 μm was grown on the as-grown three-dimensional supercritical acidic ammonia technology (SCAATTM) bulk seed that comprised only semipolar planes at a temperature as high as 1390 °C by tri-halide vapor phase epitaxy; further, the GaN film was also characterized. The FWHM value of the X-ray rocking curves was ∼40″, which was almost similar to the value of the used seed. The curvature radii were as large as 40-64 m. Further, the carrier concentrations were observed to be as small as 5.1 × 1017-9.1 × 1017 cm-3. However, the basal plane stacking fault densities were observed to be 3.4 × 101-5.4 × 101 cm-1 and were observed to increase during the growth process because of the as-grown SCAATTM seed surface condition.

DOI： 10.7567/1347-4065/ab1479

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publisher：Japanese Journal of Applied Physics  

An evident issue in performing GaN growth along the c-direction is the generation of V-shaped pits on its surface. Here, we investigated the transition of the angle of facets forming a V-shaped pit via three-photon excitation photoluminescence (3PPL). The intermittent doping of Ge was introduced to GaN growth to observe the growth front. The size of the V-shaped pit composed of {} facets decreased along the growth direction, whereas that composed of {} facets, increased. Furthermore, planar growths of c-GaN and semipolar GaN having various surface orientations revealed that the V-shaped pit composed of {} was likely to annihilate rather than that of {} under the growth condition of N2 carrier gas, which coincides with the result of 3PPL.

DOI： 10.7567/1347-4065/ab0402

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publisher：Journal of Crystal Growth  

The initial growth of CdTe having a thickness of 20–500 nm on (2 1 1) Si substrates was investigated to observe the growth of CdTe at the interface for hetero-epitaxial growth. The dependence of surface morphologies at the initial growth on the II/VI and the growth time was evaluated. The (1 3 3) surface orientation at the interface was shown in CdTe films grown on (2 1 1) Si substrates, which was irrespective of the II/VI. For a relatively high II/VI of 36, hillocks having a (2 1 1) orientation were observed on the underlayer having a (1 3 3) orientation. CdTe having a (2 1 1) orientation was dominant during the growth, due to its lateral coalescence on the underlayer. The dependence of the orientation between (1 3 3) and (2 1 1) CdTe films on (2 1 1) Si substrates on the II/VI was explained by the difference between the step-flow growth on the step and the spontaneous nucleation on the terrace.

DOI： 10.1016/j.jcrysgro.2018.10.038

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publisher：Journal of Electronic Materials  

Single-crystalline CdTe films were grown in both (133) and (211) surface orientations on (211) Si substrates by vapor-phase epitaxy using metallic Cd source as a group-II precursor. The orientation of epitaxial films depended on the ratio of group-II and -VI precursors, i.e., II/VI. The orientation of epitaxial films was changed from (133) to (211) by increasing the II/VI under the CdTe growth condition. The surface morphology for (133) CdTe was smooth, whereas the surface for (211) CdTe was composed of hillocks with (111), (110), (101), and (100) facets. The full width at half maximum (FWHM) of the epitaxial films with the same thickness showed that the crystalline quality of (133) CdTe was better than that of (211) CdTe. The dependence of the orientation between (133) and (211) CdTe films on (211) Si substrates on the II/VI was explained by the difference between the step-flow growth on the step and the spontaneous nucleation on the terrace.

DOI： 10.1007/s11664-018-6728-1

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publisher：Journal of Electronic Materials  

We successfully performed epitaxial CdTe growth on a Si (211) substrate with vapor-phase epitaxy using a cost-effective metallic cadmium source as a group-II precursor. The thermodynamic data demonstrate that the combination of metallic Cd and diisopropyl-telluride (DiPTe) with a H2 carrier gas enables the growth of CdTe crystals. A CdTe single crystal with a (422) surface orientation was obtained when a growth temperature between 600°C and 650°C was employed. The surface morphology and crystalline quality were improved with increasing film thickness. The full-width at half-maximum of the x-ray rocking curves with a film thickness of 15.7 μm for the skew-symmetrical (422) and asymmetrical (111) reflection were 528 arcsec and 615 arcsec, respectively.

DOI： 10.1007/s11664-017-5584-8

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publisher：Physica Status Solidi (B) Basic Research  

We demonstrated the selective-area growth (SAG) of the nonpolar m-plane (Formula presented.) and the polar −c-plane (Formula presented.) substrates to determine the quasiequilibrium crystal shape (quasi-ECS) by trihalide vapor phase epitaxy (THVPE). The results were compared with those by hydride vapor phase epitaxy (HVPE). The polar N-face (Formula presented.) and the nonpolar m-planes (Formula presented.) were consistently stable with the semipolar planes (Formula presented.) emerging only at high temperature for the quasi-ECS grown by THVPE. The clear facets of the polar Ga-face (0001) and Ga-face sense semipolar planes such as (Formula presented.) did not appear. The kinetic Wulff plots for THVPE were constructed using the growth velocities for each emerging facet of the SAG. Bird's-eye view SEM images of the selective-area GaN crystals grown on the m-plane and –c-plane for THVPE.

DOI： 10.1002/pssb.201600679

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publisher：Journal of Crystal Growth  

Thermodynamic analysis of CdTe growth using cost-effective metallic Cd and dialkyl telluride was performed. The major vapor species at source zone in equilibrium were gaseous Cd for the group-II precursor, and Te2 and H2Te for the group-VI precursors. The driving force for the CdTe deposition was still positive even at 650 °C. This indicates that CdTe formation from gaseous Cd can proceed thermodynamically. Furthermore, the calculations showed that CdTe decomposes at higher temperature and increasing the II/VI ratio increases the limit of the growth temperature, which coincides with the experimental results.

DOI： 10.1016/j.jcrysgro.2017.04.027

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publisher：Journal of Crystal Growth  

GaN layers of thickness 0.5–1.3 mm were grown at 1280 °C at a growth rate of 95–275 µm/h by tri-halide vapor-phase epitaxy on nonpolar m-plane (101̅0) and semipolar (101̅1̅) ammonothermal GaN substrates. For nonpolar m-plane (101̅0) with a −5° off-angle, the full widths at half maximum (FWHMs) of X-ray rocking curves (XRCs) and the basal plane stacking fault (BSF) density increased from 50 to 178″ and from 4.8×101 to 1.0×103 cm−1, respectively, upon increasing the growth rate from 115 to 245 µm/h. On the other hand, the XRC-FWHM and the BSF density for semipolar (101̅1̅) grown at 275 µm/h were as small as 28″ and 8.3×101 cm−1, respectively.

DOI： 10.1016/j.jcrysgro.2017.01.005

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Authorship：Lead author,　Corresponding author  

Authorship：Lead author,　Corresponding author   Language：Japanese   Publisher：Applied Physics Express  

Homoepitaxial tri-halide vapor-phase epitaxy (THVPE) growth on polar, semipolar, and nonpolar bulk GaN substrates was demonstrated using GaCl3 as the precursor. The influence of the surface orientation of the substrate on GaN growth by THVPE was compared with that observed for GaN grown by hydride vapor-phase epitaxy. The dependence of the GaN growth on the surface orientation of the substrate was confirmed; GaN could be grown on (1010), (3031), (2021), (1011), and (0001) but not on (0001), (1011), (2021), or (3031). This behavior was explained to be due to the changes in adsorption energy, the magnitudes of which were estimated by theoretical calculations.

DOI： 10.7567/APEX.9.105501

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publisher：Physica Status Solidi (A) Applications and Materials Science  

InGaN/GaN-based light emitting diodes (LEDs) can be grown by using metal organic chemical vapor deposition (MOCVD) to make eight, 3-inch diameter wafers with a thin, tapered reactor cell at atmospheric pressure. The reactor configuration was optimized for the purpose of improving the GaN growth rate and its in-plane distribution. The growth rate and the layer uniformity of GaN were improved when the reactor cell was narrowed down and tapered. The on-wafer deviation of the electroluminescence (EL) peak wavelength and power were 5 nm and within 4%, respectively, except at the edge. The full width at half maximum (FWHM) of EL spectrum for an LED grown at atmospheric pressure was consistently smaller than that of one grown at reduced pressure over the entire wavelength range. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssa.200983434

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Language：Japanese   Publisher：Japanese Journal of Applied Physics  

Modified optical filter elements were fabricated to access blue and violet spectral ranges of InGaN/GaN light-emitting diodes (LEDs) in characterizing luminescence via a fluorescence microscope. As band gap energies of GaN and InGaN layers were close, it was not trivial to separate excitation and luminescence light, which caused slight detection of excitation light. Nevertheless, the results obtained on c- and m-plane LEDs were compared with our previous work, leading consistent understanding of luminescence characteristics in terms of the quantum-confined Stark effect. © 2009 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.48.098003

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Language：Japanese   Publisher：Journal of Physics D: Applied Physics  

Optical and electrical characteristics of InGaN/GaN quantum-well (QW) light-emitting diodes (LEDs) are the subjects of this study. Samples were prepared on nonpolar (1 0 0) and semipolar (1 1 2) orientations of bulk GaN substrates. Electrical-bias-applied photoluminescence was employed as a characterization technique. It was confirmed that saturation of reverse photocurrent occurred around 0 V in nonpolar LEDs and at positive voltages in (1 1 2)-oriented LEDs, while our previous study found negative voltages in (0 0 0 1)-oriented LEDs (Masui et al 2008 J. Phys. D: Appl. Phys. 41 165105). These results indicated that (1 1 2)-oriented InGaN/GaN QWs experience piezoelectric fields being in the same direction as the built-in field. Piezoelectric field intensity was estimated to be -0.3 MV cm-1 in the (1 1 2)-oriented QW structure. Spectral comparison between photoluminescence and electroluminescence of the LED samples exhibited a tendency that spectral differences were insignificant in single-QW LEDs. © 2009 IOP Publishing Ltd.

DOI： 10.1088/0022-3727/42/13/135106

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Language：Japanese   Publisher：Applied Physics Letters  

GaN crystals grown by the basic ammonothermal method were investigated for their use as substrates for device regrowth. X-ray diffraction analysis indicated that the substrates contained multiple grains while secondary ion mass spectroscopy (SIMS) revealed a high concentration of hydrogen, oxygen, and sodium. Despite these drawbacks, the emission from the light emitting diode structures grown by metal organic chemical vapor deposition on both the c -plane and m -plane epitaxial wafers was demonstrated. The SIMS depth profiles showed that the diffusion of the alkali metal from the substrate into the epitaxial film was small, especially in the m -direction. © 2009 American Institute of Physics.

DOI： 10.1063/1.3079813

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Language：Japanese   Publisher：Physica Status Solidi (A) Applications and Materials Science  

The present article provides an overview of developments in nonpolar-oriented GaN-based materials as polarized light emitters over the past 15 years. The strong interest in nonpolar materials emerged around 1996, but nonpolar-oriented light-emitting diodes were not demonstrated until 2004. The later technological key achievement was the commercialization of nonpolar-oriented bulk GaN substrates; it is now feasible to discuss the electronic band structure of such highquality nonpolar GaN as well as device applications of polarized light emitters. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA.

DOI： 10.1002/pssa.200880407

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Language：Japanese   Publisher：Journal of Physics D: Applied Physics  

Spontaneously polarized light emission from m-plane InGaN/GaN light-emitting diodes was studied as a function of In composition in the InGaN single quantum-well layer. Emission wavelength was varied between 394 and 472 nm. A strong correlation was confirmed between optical polarization and In composition; the higher the In composition, the stronger the optical polarization. The photon-energy difference between the emission spectra associated with the two polarizations, ΔM, was evaluated as a function of current. ΔM exhibited a negative monotonic current dependence for the 394 nm emitting sample and the dependence was changed to positive monotonic as the wavelength became longer towards 472 nm. This change was tentatively attributed to the valence band mixing and the crystal momentum conservation that became relevant with the band filling. ΔM and optical polarization exhibited only a moderate correlation; the Fermi-Dirac function has been used to explain the weakened optical polarization under increased current injection. © 2008 IOP Publishing Ltd.

DOI： 10.1088/0022-3727/41/22/225104

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Language：Japanese   Publisher：Journal of Crystal Growth  

Effects of off-axis substrates on m-plane InGaN/GaN light-emitting diodes (LEDs) grown by metal organic chemical vapor deposition were investigated. The surface morphology of n-GaN was improved by increasing an off-axis angle from the m-plane toward the c-plane. The InGaN/GaN quantum wells (QWs) grown on the off-axis substrates toward the c--direction (N-polar) emitted at a longer peak wavelength than the on-axis m-plane substrates, indicating that the off-axis substrates have impact on enhancement of the indium incorporation in the InGaN/GaN QWs. The LED on the c--5° off-axis substrate emitted at 457 nm under DC current of 20 mA and showed 0.7 nm red-shift from 1 to 20 mA. The c--5° off LED showed an optical polarization ratio of 0.91, which is comparable to the nonpolar material. © 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2008.06.079

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Language：Japanese   Publisher：Physica Status Solidi (A) Applications and Materials Science  

A confocal microscope was applied to characterize near-field optical polarization of light emission from InGaN-based light-emitting diodes prepared on a nonpolar orientation. Detection of stray light was significantly reduced as a result of the confocal technique compared to broad-area measurements. The confocal measurement required no special sample preparation and obtained data was directly interpretable. A polarization ratio of 0.83 was measured on long-wavelenght emitting devices and was sustained over two orders of magnitude of low current range. Energy shifts and separation of emission peaks for the two polarization components were evaluated to discuss the valence-band structure. Energy shifts indicated that the topmost band {norm of matrix}X〉 had a heavier effective mass than the lower band {norm of matrix}Z〉. Splitting energy of InGaN was estimated to be 30 meV. Results were consistent with the past reports, thus it was confirmed that the confocal microscope is a valid technique to characterize near-field optical polarization. An m-plane InGaN/GaN LED used in the study. ©2008 WILEY-VCH Verlag GmbH & Co. KGaA.

DOI： 10.1002/pssa.200824044

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Language：Japanese  

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Language：Japanese   Publisher：Applied Physics Express  

Characteristics of m-plane InGaN/GaN light emitting diodes (LEDs) with various indium compositions were investigated. X-ray diffraction revealed that indium compositions in the InGaN multi quantum wells (MQWs) on m-plane substrate were 2-3 times lower than those on c-plane substrate. The optical polarization ratio for m-plane LEDs increased from 0.27 to 0.89 with increasing emission wavelength from 383 to 476 nm due to compressively strained InGaN QWs. The output power of electroluminescence decreased above 400 nm although polarization-related internal electric fields were eliminated. © 2008 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.1.041101

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Language：Japanese   Publisher：Applied Physics Letters  

Optical polarization characteristics of InGaNGaN light-emitting diodes (LEDs) were studied. Light-emitting diode samples were fabricated on four types of GaN substrates near (10 1- 0) orientation with intentional off-axis cuts of 0°, 5°, 10°, and 27° towards [000 1-]. A confocal microscope was used to characterize the optical polarization of electroluminescence at various currents. The highest polarization ratio of 0.91 was measured on samples fabricated on a 5° off-cut substrate. First moments were calculated on emission spectra to assess emission peak shifts of two polarization components. We drew a conclusion that substrate off-axis cut is a technique to improve optical polarization characteristics of nonpolar-oriented InGaNGaN LEDs. © 2008 American Institute of Physics.

DOI： 10.1063/1.2890050

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Language：Japanese  

DOI： 10.1002/pssr.200701313

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Language：Japanese   Publisher：Japanese Journal of Applied Physics, Part 2: Letters  

Effect of m-plane GaN substrate miscut was investigated for InGaN/GaN multi quantum wells (MQWs) light emitting diodes (LEDs). The n-GaN and InGaN/GaN LEDs were grown by metal organic chemical vapor deposition on m-plane (1100)GaN substrates with miscut angles toward the [0001̄] direction of 0.01 (nominally on-axis m-plane), 0.45, 0.75, 5.4, and 9.6°. The surface morphology improved with increasing the miscut angles toward the [0001̄] direction. The peak emission wavelength of the electroluminescence grown on the on-axis m-plane and the miscut angle of 0.45° was 391-396 nm, while the miscut angle of 5.4 and 9.6° showed 440-454nm. These results demonstrate that the surface morphology of GaN and In incorporation in the MQWs are strongly impacted by the miscut angle of GaN substrate. © 2007 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.46.L1117

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publisher：Japanese Journal of Applied Physics, Part 2: Letters  

Improved nonpolar m-plane (11̄00) light emitting diode (LED) with a thick InGaN active layer of 8 nm and a thick GaN barrier layer of 37.5 nm for multi-quantum-well (MQW) structure have been fabricated on low extended defect bulk m-plane GaN substrates using metal organic chemical vapor deposition (MOCVD). The peak wavelength of the electroluminescence (EL) emission from the packaged LED was 468 nm. The output power and external quantum efficiency (EQE) were 8.9 mW and 16.8%, respectively, at a DC driving current of 20 mA. © 2007 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.46.L960

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Language：Japanese   Publisher：Japanese Journal of Applied Physics, Part 2: Letters  

We demonstrate continuous-wave (CW) operation of nonpolar m-plane InGaN/GaN laser diodes without Al-containing waveguide cladding layers. Thick InGaN quantum wells (QWs) are used to generate effective transverse optical mode confinement, eliminating the need for Al-containing waveguide cladding layers. Peak output powers of more than 25 mW are demonstrated with threshold current densities and voltages of 6.8 kA/cm2 and 5.6 V, respectively. The unpackaged and uncoated laser diodes operated under CW conditions for more than 1.5 h. © 2007 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.46.L761

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Authorship：Lead author   Language：Japanese  

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Authorship：Lead author   Language：Japanese   Publisher：Studies in Surface Science and Catalysis  

Capillary electrophoresis has been used to measure the ζ-potential of zwitterionic micelles in various electrolytes. Even for intrinsically neutral zwitterionic micelles, detectable ζ-potential is induced by the imbalance between anionic and cationic partition. Its magnitude and sign are determined by the natures of ions (dominantly anionic ones) and the polarity of surfactant molecules. However, the former is a principal factor governing the ζ-potential of zwitterionic micelles in aqueous solutions.

DOI： 10.1016/s0167-2991(01)82048-6

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Authorship：Lead author   Language：Japanese   Publisher：Langmuir  

The surface potentials of n-dodecyltrimethylammoniopropanesulfonic acid (DDAPS) micelles in various electrolytes have been evaluated by capillary electrophoresis.This zwitterionic micelle has an inner cationic surface and an outer anionic surface and accommodates anions better than cations, indicating that a negative surface potential is induced by anion-dominated partition. Selectivity terms, i.e., solvation changes of ions and ion association between ions and charged groups in the DDAPS micelles, are introduced into the Poisson-Boltzmann equation for the spherical geometry. This model allows the interpretation of differences in the ionic partition and surface potential between electrolytes. The selectivity parameters have been determined by assuming agreement between the zeta potential determined by capillary electrophoresis and the calculated outer surface potential of the micelle. The obtained selectivity parameters can also explain the potentiometrically evaluated partition of ClO4- and I-. It has been confirmed that capillary electrophoresis has wide applicability in surface potential measurements and can detect surface potentials of less than 1 mV. The selectivity origin in the partition into the DDAPS micelles is also discussed on the basis of evaluated parameters. The hydration changes mainly govern the uptake of well-hydrated anions, whereas poorly hydrated anions are partitioned into the micelle principally by ion-pair formation with the cationic groups in the micelles.

DOI： 10.1021/la0003544

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