Search

A large relative surface area is crucial for high catalytic activity. Monolithic catalysts are important catalytic materials because of minimal self-degradation. Regarding large surface area catalysts, the glass–ceramics (GCs) with high formability, obtained by heat-treatment of the precursor glass, are plausible candidates. This study examines the photocatalytic behaviour of porous GCs obtained after acid leaching of MgO–TiO2–P2O5 GCs. After heat-treatment, anatase TiO2 was precipitated along with other phases. The diffraction intensity ratio between anatase and other phases was the maximum for a heat-treatment temperature of 900 °C. After acid leaching of the GCs, the relative surface area decreased with increasing TiO2 fraction; the surface area was also affected by the sample morphology. H2 generation was observed from porous GCs, while GCs without etching exhibited approximately zero activity. Thus, it was demonstrated that high surface area and prevention of the reduction reaction to Ti(III) are important for tailoring monolithic photocatalytic materials.

We performed terahertz time-domain spectroscopy and low-frequency Raman scattering on polymethyl methacrylate to investigate the boson peak (BP) which is a universal excitation in glass, and the fracton which is expected to be expressed in polymer glass. In the infrared spectrum, the BP was observed in the plot of α(ν)/ν2, where α(ν) is the absorption coefficient. In addition, the infrared light-vibration coupling constant C IR (ν) and the Raman coupling constant C Raman (ν) were determined, and the fracton was observed as a linear region in the log-log plots of C IR (ν) and C Raman (ν).

We performed terahertz time-domain spectroscopy, low-frequency Raman scattering and low-temperature specific heat measurements to investigate different compositions of sodium silicate glasses. The boson peak (BP) behavior was successfully detected in all measurements. The BP frequency was found to be insensitive to Na2O composition. Additionally, comparing the Raman spectrum and terahertz absorption spectrum confirmed that the BP vibration mode is a combination of different fundamental vibration modes.

The complex dielectric constant of 17.3 mol% lithium chloride aqueous solution, which is a typical hydrogen-bonded glass system, was determined from 291 K to 14 K using terahertz time-domain spectroscopy. The boson peak appeared at 1.3 THz at 14 K, suggesting that the determinant of boson peak frequency is hydrogen bonds between water molecules.

Amorphous materials with non-periodic structures are commonly evaluated based on their chemical composition, which is not always the best parameter to evaluate physical properties, and an alternative parameter more suitable for performance evaluation must be considered. Herein, we quantified various structural and physical properties of Ce-doped strontium borate glasses and studied their correlations by principal component analysis. We found that the density-driven molar volume is suitable for the evaluation of structural data, while chemical composition is better for the evaluation of optical and luminescent data. Furthermore, the borate-rich glasses exhibited a stronger luminescence due to Ce3+, indicating a higher fraction of BO3/2 ring and larger cavity. Moreover, the internal quantum efficiency was found to originate from the local coordination states of the Ce3+ centres, independent of composition or molar volume. The comparison of numerical data of the matrix is useful not only for ensuring the homogenous doping of amorphous materials by activators, but also for determining the origin of physical properties.

This study investigated the broadband terahertz and low-frequency Raman spectroscopy of liquid water (H2O, D2O, and H218O) over 2 decades of frequency to address long-standing challenges regarding ...

To investigate multi-boson peaks (multi-BP), terahertz time-domain spectroscopy was performed on amorphous silicon monoxide (a-SiO), which exhibits unusual disproportion in the nanoscale region where the SiO 2 and Si regions are separated. In the resulting THz spectrum, the BP was observed at 2.4 THz, as a broad asymmetric peak, and the BP frequency was evidently higher than that of silica glass. The results suggest that the higher BP frequency of a-SiO in the infrared spectrum originates from the a-Si cluster region.

For disordered systems, a universal excitation called the boson peak appears in the terahertz range. In this study, we performed terahertz time-domain spectroscopy on an oxide glass with entropic elasticity—mixed alkali metal metaphosphate glass with the chemical composition Li 0.25 Na 0.25 K 0.25 Cs 0.25 PO 3 (LiNaKCsPO 3 )–to detect the boson peak. The obtained spectra were compared with results of low-frequency Raman scattering and low-temperature specific heat measurements.

Terahertz time-domain spectroscopy and low-frequency Raman scattering were performed on polymethyl methacrylate to detect the boson peak (BP) and fracton, which are universal excitations of glass. In infrared spectrum, BP is observed in the $\alpha(v)/v^{2}$ plot, where $\alpha(v)$ is absorption coefficient. Log-log plot of $\alpha(v),\ v\chi^{\prime\prime}(v)$ and the vibrational density of states show linear frequency dependence above the BP frequency, where $\chi^{\prime\prime}(v)$ is the imaginary part of Raman susceptibility. We determined the infrared light vibration coupling constant $C_{\text{IR}}(v)$ and Raman coupling constant $C_{\text{Raman}}(v)$ to investigate how the fractal dimension and the fracton dimension appear in $C_{\mathrm{R}}(v)$ and $C_{\text{Raman}}(v)$ .

Backscattering Raman spectroscopic investigations were performed on an yttrium-iron garnet single crystal using linearly and circularly polarized light. A terahertz (THz) magnon of the Kaplan-Kittel (KK) exchange resonance was discovered, which had been regarded as unobservable via optical methods. The KK exchange resonance had a 7.8-THz frequency at 80 K, and the polarization selection rule led to an antisymmetric Raman tensor of the ${A}_{2}$ mode. Moreover, the assignment of all the Raman-active phonon modes, $3{A}_{1\mathrm{g}}, 8{E}_{\mathrm{g}}$, and $14{T}_{2\mathrm{g}}$, was proposed. This study will stimulate further investigation of the coupling of THz magnons and phonons and pave the way toward THz optomagnonics.

Disordered systems exhibit universal excitation, referred to as the boson peak, in the terahertz region. Meanwhile, the so-called fracton is expected to appear in the nanoscale region owing to the self-similar structure of monomers in polymeric glasses. We demonstrate that such excitations can be detected using terahertz spectroscopy. For the interaction between terahertz light and the vibrational density of states of the fractal structure, we formulate an infrared light-vibration coupling coefficient for the fracton region. Accordingly, we show that information concerning fractal and fracton dimensions appears in the exponent of the absorption coefficient. Finally, using terahertz time-domain spectroscopy and low-frequency Raman scattering, we experimentally observe these universal excitations in a protein lysozyme system that has an intrinsically disordered and self-similar nature in a single supramolecule. These findings are applicable to disordered and polymeric glasses in general and will be key to understanding universal dynamics of disordered systems by terahertz light.

Terahertz time-domain spectroscopy and low-frequency Raman scattering were performed on the natural polymer starch to investigate the boson peak (BP) dynamics. In the infrared spectrum, the BP was observed at 0.99 THz at the lowest temperature. Compared to the result from a previous study for vitreous glucose, both the frequency of the BP and absorption coefficient show lower values than those of the vitreous glucose. These behaviors originate from the longer correlation length of the medium-range order and lower concentration of hydroxyl groups in the starch. In the Raman spectrum, the BP was observed at 1.1 THz at room temperature, although the BP was not observed around room temperature due to the excess wing of the fast relaxation modes in the infrared spectrum. The temperature dependence of ε″(ν) during the heating process and cooling process shows a hysteresis below 230 K. During the heating process, kinks were observed at 140 K and 230 K. These kinks are attributed to the β-relaxation and the βwet-relaxation, respectively.

Ultrafast control of magnets using femtosecond light pulses attracts interest regarding applications and fundamental physics of magnetism. Antiferromagnets are promising materials with magnon frequencies extending into the terahertz range. Visible or near-infrared light interacts mainly with the electronic orbital angular momentum. In many magnets, however, in particular with iron-group ions, the orbital momentum is almost quenched by the crystal field. Thus, the interaction of magnons with light is hampered, because it is only mediated by weak unquenching of the orbital momentum by spin–orbit interactions. Here we report all-optical excitation of magnons with frequencies up to 9 THz in antiferromagnetic CoO with an unquenched orbital momentum. In CoO, magnon modes are coupled oscillations of spin and orbital momenta with comparable amplitudes. We demonstrate excitations of magnon modes by directly coupling light with electronic orbital angular momentum, providing possibilities to develop magneto-optical devices operating at several terahertz with high output-to-input ratio., 超短光パルスで磁性体中に大振幅テラヘルツ・スピン波を励起 --超高速・高効率磁気光学デバイスへ期待--. 京都大学プレスリリース. 2017-09-29.

We report a detailed small angle neutron scattering study on relaxor ferroelectric (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (x = 0.30). Anisotropic diffuse scattering elongating along the directions is observed in a wide temperature range 300–500 K. At T = 500 K, the q-dependence of the scattering intensity, I(q), shows Porod's law. For T ≤ 450 K, an additional scattering appears in the Q-range below 0.1 A−1 and shows a power-law behavior. The power law behavior is discussed in terms of a fractal correlation of polar-nano-regions.

Sodium metavanadate has pyroxene-type one dimensional VO4-tetrahedral chains, which is analogous to the SiO4-chains in Bi2SiO5. Although it is known to undergo ferroelectric phase transition, its m...

Terahertz time-domain spectroscopy has been applied to protein myoglobin dried sample. The boson peak (BP) which is a universal excitation of disordered system has been detected around 0.5 THz. While, fracton will be a universal excitation in the self-similar structure, and it has been observed above the BP frequency. How the fracton appear in the infrared spectrum is explained using the fracton model and the linear response theory for amorphous materials.

We performed terahertz time-domain spectroscopy on protein myoglobin to detect the universal boson peak (BP) behavior in glassy materials and fracton expected to universally appear in polymer glasses. The obtained spectral shape of log $\varepsilon$ ” vs $\log$ frequency $[\varepsilon$ ”: the imaginary part of complex dielectric constants] indicates that the fracton region appears above the BP frequency. The fractal and fracton dimensions were evaluated from the obtained spectra.

We performed terahertz time-domain spectroscopy and low-frequency Raman scattering on lithium borate glasses to detect the universal boson peak behavior in glassy materials. In addition, the vibrational density of states spectrum was extracted from the low-temperature specific heat measurement data. The light-vibration coupling coefficients of the infrared and Raman were determined and a quantitative analysis was performed.

We performed terahertz time-domain spectroscopy (THz-TDS) on two different soda-lime glass plates. One of the glasses is transparent and the other is black. In addition, terahertz imaging was performed on the two-color integrated glass plate. It was found that the metallic element added to the black glass almost does not affect the absorption coefficient around the terahertz region. Based on the obtained results of the glass samples by THz-TDS, we found a clear boson peak structure in the $\alpha(v)/v^{2}$ spectrum, where $\alpha$ is the absorption coefficient. This result shows that the boson peak imaging is possible by THz-TDS without being affected by the color in the visible light region which causes a problem in the low-frequency Raman scattering.

We performed terahertz time-domain spectroscopy and low-frequency Raman scattering on microwave-treated carboxymethyl starch (CMS-Na), to detect universal boson peak (BP) behavior in glassy materials and fracton which is expected to universally appear in polymer glass. The obtained spectral shape of BP plot a(v)/v2of the CMS-Na-slu, where a(v) is the absorption coefficient, is different from either starch or vitreous glucose of the previous study. It suggests that existence of the fracton in the CMS-Na-slu.

Sillén–Aurivillius perovskite Bi4NbO8X (X = Cl, Br) is a promising photocatalyst for water splitting under visible light, as well as a potential ferroelectric material. In this work, we investigate the crystal growth conditions by mainly varying soak temperature, soak time and cooling rate. Under the optimal conditions, we successfully obtained yellow platelet single crystals with an in-plane distance of several hundred microns. As opposed to conventional crystal growth, a moderate cooling is essential to suppress an evaporation of the Bi–O–Cl species from a melt zone. The single crystals of Bi4NbO8Br were also grown using a similar condition. We suggest that the knowledge obtained in this study can be generally applied to other Sillén–Aurivillius phases and related oxyhalides.

Terahertz time-domain spectroscopy and low-frequency Raman scattering have been performed on the protein hen egg white lysozyme. The boson peak (BP), which is the universal dynamics of disordered materials, has been detected around 0.5 THz. On the other hand, fracton behavior, which is universal in the self-similar structure, has appeared above the BP frequency. How the fracton appeared in the infrared spectrum is explained using the fracton model and the universal infrared coupling coefficient model for disordered materials.

We performed terahertz time-domain spectroscopy on glassy glucose, and successfully detected the boson peak, which is a universal feature of glassy materials. In addition, we have experimentally determined the infrared-vibration coupling coefficient (C IR (v)) using the vibrational density of states. The obtained C IR (v) shows linear frequency-dependence and the behavior deviates from the inorganic glass e.g. silica glass. In the temperature dependence, the complex dielectric spectra showed thermal hysteresis below about 240 K, which might be attributed to confined water molecules.

We experimentally investigated the hypersonic attenuation process of a longitudinal mode (L-mode) sound wave in ${\mathrm{TeO}}_{2}$ from room temperature to a lower temperature using Brillouin scattering and impulsive stimulated thermal scattering (ISTS) measurements. For precise measurement of the Brillouin linewidth at low temperatures, whereby the mean free path of the phonon becomes longer than the sample length, it is indispensable that the phonon should propagate along the phonon-resonance direction. To figure out the suitable direction, we defined two indices characterizing a degree of phonon divergence and a purity of propagation direction. The best direction that we found from these indices is [110] direction in ${\mathrm{TeO}}_{2}$, and it was used to discuss the temperature and frequency dependences of Brillouin spectra. We extracted the temperature dependence of the attenuation rate of ${T}^{4}$ from the modulated Brillouin spectra due to the phonon resonance below Debye temperature. The frequency dependence ${\ensuremath{\omega}}^{1}$ of the hypersonic attenuation was also estimated from the polarization dependence of the Brillouin linewidth. Theoretically, it predicted that the L-mode phonon attenuation at low temperatures in ${\mathrm{TeO}}_{2}$ is a result of Herring's process, which shows the attenuation behavior of ${\ensuremath{\omega}}^{2}{T}^{3}$. The ${\ensuremath{\omega}}^{1}{T}^{4}$ dependence is not allowed in Herring's process but is allowed by the $L+L\ensuremath{\rightarrow}L$ process, which has been considered to be forbidden so far. We evaluated the thermal phonon lifetime using ISTS and established that it was finite even at 20 K, thereby allowing the $L+L\ensuremath{\rightarrow}L$ process. Therefore, we conclude that the $L+L\ensuremath{\rightarrow}L$ process dominates the attenuation of an L-mode phonon in ${\mathrm{TeO}}_{2}$ in the low-temperature region.

Nagakubo A., Tsuboi S., Kabe Y., et al. Zero temperature coefficient of sound velocity in vitreous silicon oxynitride thin films. Applied Physics Letters, 114(25), 251905 (2019) https://doi.org/10.1063/1.5098354., Vitreous silicon oxide (v-SiO2) shows anomalous phonon properties such as the positive temperature coefficient of velocity (TCV). Variation of the Si-O-Si bond angle between SiO4 tetrahedrons has been recognized to be the key, but the origin of TCV still remains unclear. In this study, we controlled the bond angle by doping nitrogen and measured TCV of vitreous silicon oxynitride thin films with various nitrogen concentrations using picosecond ultrasonics. TCV significantly decreases by adding a small amount of nitrogen, and it shows positive to negative values as the nitrogen concentration increases. We evaluated the bond-angle change by Fourier-transform infrared spectroscopy, which decreases with the increase in the nitrogen content. We also find that the temperature rise in nondoped v-SiO2 decreases the bond angle, leading to an increase in the sound velocity. We then reveal theoretically that the bond-angle change dominates the origin of the positive TCV. This study indicates the existence of a zero-TCV single material, and we discover that the specific content of v-SiO1.71N0.19 achieves this.

We employed femtosecond pump probe technique to investigate the dynamics of coherent optical phonons in iron garnet. A phenomenological symmetry-based consideration reveals that oscillations of the terahertz T2g mode are excited. Selective excitation by a linearly polarized pump and detection by a circularly polarized probe confirm that impulsive stimulated Raman scattering (ISRS) is the driving force for the coherent phonons. Experimental results obtained from ISRS measurements reveal excellent agreement with spontaneous Raman spectroscopy data, analyzed by considering the symmetry of the phonon modes and corresponding excitation and detection selection rules., Comment: 20 pages, 6 figures, 3 tables

Understanding glass structure is still challenging due to the result of disorder, although novel materials design on the basis of atomistic structure has been strongly demanded. Here we report on the atomic structures of the zinc phosphate glass determined by reverse Monte Carlo modelling based on diffraction and spectroscopic data. The zinc-rich glass exhibits the network formed by ZnOx (averaged x, ガラスが熱で変形しやすいのはなぜか、原子レベルで一端を解明. 京都大学プレスリリース. 2017-06-01.

We derived a formula to describe the stimulated Brillouin spectral shape in crystals for various temperatures ranging from room temperature to liquid-helium temperature. We modeled a sample as a one-dimensional system with a finite thickness in which the optically induced phonon propagates, partly interacting with the pump and probe laser beams. When the sample length is shorter than the propagation distance (i.e., the mean free path) of phonons, the spectral shape becomes multipeaked due to the multiple phonon reflections in the sample. Such a situation can be realized in a thin film or a bulk sample at low temperatures. We experimentally measured the Brillouin gain spectra with a multipeak structure in ${\mathrm{TeO}}_{2}$ and ${\mathrm{PbMoO}}_{4}$ crystals at low temperatures. We found that these spectra were reproduced by our formula for both the coaxial and off-axis phonon propagations with respect to the laser beams. It was revealed that our formula is very useful in estimating the phonon attenuation coefficient from the observed spectra, which gradually change from Lorentzian shape to a multipeak spectrum with decreasing temperature.

We have developed a large, thin solid hydrogen target (SHT) that is 30 mm in diameter and 1 mm thick for elastic scattering of protons from unstable nuclei. By using para-H 2 that has a high thermal conductivity at low temperatures, we could prevent sublimation at the target center due to radiation from the higher temperature surroundings. The uniform SHT was used during long-term scattering experiments and it maintained its shape and thickness.

The low-frequency light-scattering spectrum in Pb(Mg1/3Nb2/3)O3 single crystal is investigated at 297 K. A quasielastic scattering is found, and its line shape is identified as a “power-law” type, instead of a single Lorentzian or superposition of two Lorentzian curves. The power-law spectrum implies the existence of a wide distribution of relaxation times in relaxors.

We study the light-scattering spectrum in SrTiO 3 in the low frequency range (< 1000 GHz). Two components of quasielastic peaks were observed at relatively high temperatures. We found that the collective phonon-excitation in a crystal accounts for both quasielastic components. The anomalous broad Brillouin component in SrTiO 3 , which was reported previously, can also be accounted for by our model, and it has been strongly indicated that the origin of the broad doublet is “second sound”. The broader quasielastic component arises from the interactions between two second sounds, and it can be understood as the “Mountain mode” in crystals.

Quasielastic light scattering by phonon-density fluctuations in dielectric crystals has been investigated both experimentally and theoretically. In particular, the collisionless phonon regime, which has not been explored previously, has been studied in detail. The analysis using extended thermodynamics for the quasielastically scattered spectra in some dielectric crystals has been found to be consistent with the observed anomalous wave-vector dependence of the quasielastic scattering by phonon-density fluctuations at low temperatures. In addition, it can reproduce a broad doublet spectrum, which resembles those previously observed in quantum paraelectrics SrTiO 3 and KTaO 3 when the normal (momentum-conserving) phonon collision is dominant.

We have improved the correlated-fields spectroscopy in order to extend the available offset frequency-range up to ± 40 MHz by compensating the frequency-dependent Bragg diffraction of acousto-optic frequency shifter. This jitter-free technique has been applied to the studies of two-beam coupling in Nd:glass and Ti:S, Rayleigh wing scattering in liquid crystal, and hole-burning spectroscopy in Tm 3+ :YAG. Spectral resolution of less than 10 kHz has been obtained in these first two subjects, and the hole-burning spectrum with line width less than 150 kHz has been clearly resolved despite the use of nonstabilized laser sources.

We present a model for vibron–phonon scattering in molecular crystals. A general kinetic equation for the vibrons is derived. We use this equation to calculate the frequency shift and dephasing rate of the vibrons as functions of temperature. We find good agreement between the calculated results and the experimental observations for the Raman shift and Raman width of the fundamental vibrational Raman transition of solid parahydrogen.

We measured light scattering in a single crystal of ZrW2O8 (ZWO) in the frequency range between 0.1 and 1100 cm−1 and in the temperature range between 3.5 and 300 K. From the temperature dependence of the optical and acoustic phonon frequencies, we found that low-frequency phonon modes below 100 cm−1 have large relative temperature coefficients (total anharmonicity values). The longitudinal acoustic mode, whose Brillouin light scattering has not been reported thus far, was found to have the largest negative total anharmonicity in a wide temperature range, indicating the possibility that the acoustic modes, as well as the low-frequency optical modes that are associated with the motions of WO4 and ZrO6 polyhedra, should contribute to the negative thermal expansion of ZWO.

We performed terahertz time-domain spectroscopy, low-frequency Raman scattering, and Brillouin light scattering on vitreous glucose to investigate the boson peak (BP) dynamics. In the spectra of $\ensuremath{\alpha}(\ensuremath{\nu})/{\ensuremath{\nu}}^{2}$ $\mathrm{[}\ensuremath{\alpha}(\ensuremath{\nu})$ is the absorption coefficient], the BP is clearly observed around 1.1 THz. Correspondingly, the complex dielectric constant spectra show a universal resonancelike behavior only below the BP frequency. As an analytical scheme, we propose the relative light-vibration coupling coefficient (RCC), which is obtainable from the combination of the far-infrared and Raman spectra. The RCC reveals that the infrared light-vibration coupling coefficient ${C}_{\mathrm{IR}}(\ensuremath{\nu})$ of the vitreous glucose behaves linearly on frequency which deviates from Taraskin's model of ${C}_{\mathrm{IR}}(\ensuremath{\nu})=A+B{\ensuremath{\nu}}^{2}$ [S. N. Taraskin et al., Phys. Rev. Lett. 97, 055504 (2006)]. The linearity of ${C}_{\mathrm{IR}}(\ensuremath{\nu})$ might require modification of the second term of the model. The measured transverse sound velocity shows an apparent discontinuity with the flattened mode observed in the inelastic neutron scattering study [N. Violini et al., Phys. Rev. B 85, 134204 (2012)] and suggests a coupling between the transverse acoustic and flattened modes.

Fluorescence line narrowing spectroscopy has been performed in dye (Al-phthalocyanine tetrasulfonate) doped poly(acrylamide) (PAAm) gel in order to investigate the electron–phonon interaction of the dye dissolved in interstitial water. The peak frequency of the one-phonon profile in this sample was found to be large when compared with other polymers such as poly(styrene) and poly(vinyl alcohol), and furthermore found to shift from 33 to 38 cm −1 after hydrolysis. From Brillouin scattering measurements in several polymers, including the present polymer, we found that the Brillouin shift in PAAm gel is higher than that of other polymers and that the hydrolysis makes the Brillouin shift even higher. This means that the elastic constant in PAAm gels is relatively large. This is argued to be due to the fact that the interstitial water confined in the network of PAAm gel stiffens the polymer structure. It should be noted that the sideband peak frequency of 38 cm −1 is exactly the same as that in hyperquenched glassy water investigated by Small and coworkers. The temperature dependence of fluorescence line narrowed spectrum shows that the electron-phonon interaction in this sample is relatively weak and that the zero phonon line is still discernible above 110 K.

Quasielastic light scattering consisting of two components has been observed in single crystals of rutile (TiO{sub 2}). The broad component with a linewidth of 330 GHz at 297 K becomes narrower with decreasing temperature. In contrast, the narrow component, which has a linewidth of 1.1 GHz at 297 K, broadens as the temperature decreases. We present a unified explanation for both components, which is based on two-phonon difference Raman scattering. For the narrow component, it will be shown that two-phonon difference processes from a {ital single} acoustic phonon branch explain the temperature dependence of the intensity and the wave vector dependence of the linewidth at low temperatures. The conventional explanation in terms of entropy-fluctuation scattering is also attempted for temperatures above 200 K where phonon collisions occur more frequently than at lower temperatures and the phonon system may be considered hydrodynamically. For the broad component, two-phonon difference scattering from {ital different} phonon branches will be shown to provide a good explanation for the temperature dependent intensity. Furthermore, temperature dependence of the linewidth and its insensitivity to changes in scattering wave vector are also explained with this model. {copyright} {ital 1999} {ital The American Physical Society}