Low temperature fabrication of 5-10 nm SiO2/Si structure using advanced nitric acid oxidation of silicon (NAOS) method

We have developed the advanced nitric acid oxidation of Si (NAOS) method to form relatively thick (5-10 nm) SiO₂/Si structure with good electrical characteristics. This method simply involves immersion of Si in 68 wt% nitric acid aqueous solutions at 120 °C with polysilazane films. Fourier transform infrared absorption (FT-IR) measurements show that the atomic density of the NAOS SiO₂ layer is considerably high even without post-oxidation anneal (POA), i.e., 2.28 × 10²² atoms/cm², and it increases by POA at 400 °C in wet-oxygen (2.32 × 10²² atoms/cm²) or dry-oxygen (2.30 × 10²² atoms/cm²). The leakage current density is considerably low (e.g., 10⁻⁵ A/cm² at 8 MV/cm) and it is greatly decreased (10⁻⁸ A/cm² at 8 MV/cm) by POA at 400 °C in wet-oxygen. POA in wet-oxygen increases the atomic density of the SiO₂ layer, and decreases the density of oxide fixed positive charges.     

Effect of particle size and shape on nonresonant random laser action of dye-doped polymer random media

We present an experimental study of the light emission from dye-doped polymer random media dispersed with TiO₂ particles of various sizes, shapes, and structures. Random lasing with nonresonant feedback, similar to that for spherically shaped particles that are used for conventional random lasers, is observed for almost all types of particles and aggregates. The efficiency of random lasing for each medium is analyzed using the relationship between the emission spectrum and the transport mean free path (TMFP), which is measured by enhanced backscattering experiments. Results show that the peak emission intensity depends strongly on the particle shape and structure, whereas the spectral linewidth is governed by the TMFP.     

A role of solvent in vibrational energy relaxation of metalloporphyrins

The formation of a vibrationally excited photoproduct of metalloporphyrins upon (π, π*) excitation and its subsequent vibrational energy relaxation were monitored by picosecond time-resolved resonance Raman spectroscopy. Stokes Raman bands due to a photoproduct of nickel octaethylporphyrin (NiOEP) instantaneously appeared upon the photoexcitation. Their intensities decayed with a time constant of 300 ps, which indicates electronic relaxation from the (d, d) excited state (B_1g) to the ground state (A_1g), being consistent with the results of transient absorption measurements by Holten and coworkers. Anti-Stokes ν₄ and ν₇ bands for vibrationally excited (d, d) state of NiOEP decayed with time constants of 10 and 300 ps. The former is ascribed to vibrational relaxation, while the latter corresponds to the electronic relaxation from the (d, d) excited state to the electronic ground state. While the rise of anti-Stokes ν₄ intensity was instrument-limited, the rise of anti-Stokes ν₇ intensity was delayed by 2.6±0.5 ps, which indicates that intramolecular vibrational energy redistribution has not been completed in subpicosecond time regime. To study a mechanism of intermolecular energy transfer, solvent dependence of the time constants of anti-Stokes kinetics was investigated using various solvents. No significant solvent dependence of the rise and decay constants was observed for NiOEP. For an iron porphyrin, we observed two phases in intermolecular energy transfer. The fast phase was insensitive to solvent and the slow phase depended on solvents. A model of classical thermal diffusion qualitatively reproduced this behavior. For solute-solvent energy transfer process, low-frequency modes of proteins seem to be less important.     

Color Conversion Method for Multiprimary Display Using Matrix Switching

The range of reproducible color, i.e., color gamut, of conventional three-primary display devices is sometimes insufficient for reproducing the natural color of an object through color imaging systems. A multiprimary display is being developed for the purpose of reproducing an expanded color gamut using more than three primary colors. In this paper, a color conversion method is proposed to reproduce the natural color by additive mixture of multiprimary colors. The multiprimary color signal in this conversion method is calculated from the three-dimensional color coordinates CIE-XYZ, considering the dynamic range of each primary color. Divided into some linear elements from the polyhedral color solid of the multiprimary display, the conversion considering the constraint of the dynamic range can be performed by simple calculation without iterative calculation or a huge three-dimensional look up table. A fast computation method with a two-dimensional look-up-table is also presented. Using the proposed method, the result of the color reproduction is experimentally demonstrated by a six-primary projection display.     

Helicity suppression mechanism of decay amplitudes in relativistic quark model

Structures of the matrix elements of two-and four-quark operators are investigated in connection with the argument of “helicity suppression” in the decay amplitudes. The analysis is made by expanding the quark operators in terms of the constituentquark modes in a relativistic way. It is shown that the naive consideration of helicity suppression can be applied to the case of two-quark operators. The situation is quite different in the case of four-quark operators; sometimes we find maximum value of the decay amplitude, which is suppressed according to the naive helicity suppression. It is made clear which aspects of the constituent-quark picture are essential to cause the difference between our results and those from the free quark picture. Remarks are given on nonleptonic decays ofK-andD-mesons.     

Mössbauer studies of mixed-valence spin-crossover iron complexes with a hexadentate tripod ligand

The spin-crossover behaviors of mixed-valence iron compounds [Fe^IIH₃L][Fe^IIIL](NO₃)₂ (1) and [Fe^IIH₃L^Me][Fe^IIIL^Me](NO₃)₂ (2) have been investigated by ⁵⁷Fe Mössbauer spectroscopy, where H₃L is a hexadentate N₆ tripod ligand containing three imidazole groups and H₃L^Me is its 2-methylimidazole derivative. Deconvolution analyses of the Mössbauer spectra revealed that a two-step SCO (LS Fe^II–LS Fe^III→HS Fe^II–LS Fe^III→HS Fe^II–HS Fe^III) proceeds in each compound on elevating the temperature. Compound 2 exhibited lower spin-transition temperatures than 1. “Frozen-in effect” was observed below 120 and 50 K for 1 and 2, respectively.     

Effect of temporal resolution on the estimation of left ventricular function by cardiac MR imaging

The aim of this study was to investigate the effect of temporal resolution on the estimation of left ventricular (LV) function by cardiac magnetic resonance (MR) imaging using a steady-state free precession (SSFP) sequence. Left ventricular function was assessed by cine MR imaging using a segmented SSFP sequence in 10 healthy volunteers. Views per segment (VPS) were set at 8 and 20, resulting in high and low true temporal resolution, respectively. Irrespective of VPS, images were reconstructed at 40 cardiac phases, providing high apparent temporal resolution. Data were analyzed using 40, 20 and 10 phases to simulate different apparent temporal resolutions. Increasing the cardiac phases used for analysis slightly decreased mean end-systolic volume (ESV) and slightly increased mean ejection fraction (EF). No substantial difference in estimates of end-diastolic volume (EDV) was found between VPSs of 8 and 20. Imaging with a VPS of 20 yielded a larger ESV and smaller EF than imaging with a VPS of 8 when 40 phases were used. In conclusion, low true temporal resolution causes overestimation of ESV and underestimation of EF. Improvement of apparent temporal resolution mildly reduces but does not eliminate the errors caused by low true temporal resolution.