LxRay Co.

Nishinomiya, Japan

LxRay Co.

Nishinomiya, Japan
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Katayama I.,Yokohama National University | Maekawa K.,Yokohama National University | Minami Y.,Yokohama National University | Kitajima M.,Yokohama National University | And 4 more authors.
Optics InfoBase Conference Papers | Year: 2016

We have investigated bias-voltage dependence of carrier dynamics in metallic single-walled carbon nanotubes. By tuning the Fermi energy with the bias-voltage, the carrier relaxation time becomes minimum near the Dirac point, indicating the carrier-carrier interaction.

Katayama I.,Yokohama National University | Xu R.,Yokohama National University | Minami Y.,Yokohama National University | Yanagi K.,Tokyo Metroplitan University | And 4 more authors.
Optics InfoBase Conference Papers | Year: 2017

Using probe-wavelength-resolved coherent phonon spectroscopy, we investigated coherent phonon dynamics in chirality-mixed carbon nanotube solutions. The chirality dependent electron-phonon coupling is clearly visualized in phonon-frequency vs. probe-wavelength twodimensional mapping. © OSA 2017.

Yoshioka K.,Yokohama National University | Katayama I.,Yokohama National University | Arashida Y.,Yokohama National University | Minami Y.,Tokushima University | And 5 more authors.
Optics InfoBase Conference Papers | Year: 2017

We demonstrate that single-cycle terahertz electric fields manipulate the motion of electrons in a single tunnel junction. The direction of the electron tunneling through the junction strongly depends on the carrier-envelope phase of terahertz pulses. © OSA 2017.

Kitajima M.,Japan National Defense Academy | Kitajima M.,LxRay Co. | Narushima T.,Japan Institute for Molecular Science | Kurashina T.,University of Tsukuba | And 5 more authors.
Journal of Physics Condensed Matter | Year: 2013

We report the real-time observation of the stress change during sub-nanometer oxide growth on the Si(100) surface. Oxidation initially induced a rapid buildup of tensile stress up to -1.9 × 108 N m -2 with an oxide thickness of 0.25 nm, followed by gradual compensation by a compressive stress. The compressive stress saturated at 5 × 107 N m-2 for an oxide thickness of 1.2 nm. The analysis, assisted by theoretical study, indicates that the observed initial tensile stress is caused by oxygen bridge-bonding between the Si dimers. Atomistic model calculations considering mutually orthogonal orientations of the Si(100) surface structure reproduce the stress inversion from the tensile to the compressive side. © 2013 IOP Publishing Ltd.

Maekawa K.,Yokohama National University | Sato K.,Yokohama National University | Minami Y.,Yokohama National University | Katayama I.,Yokohama National University | And 5 more authors.
Springer Proceedings in Physics | Year: 2015

Coherent phonons in single-walled metallic carbon nanotubes were measured under the application of a gate voltage through ionic liquid. We found that the frequencies, amplitudes and phases of the phonons strongly depend on the voltage. © Springer International Publishing Switzerland 2015.

Sato K.,Yokohama National University | Tahara K.,Yokohama National University | Minami Y.,Yokohama National University | Katayama I.,Yokohama National University | And 6 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

High-frequency coherent phonons resonantly excited in metallic single-walled carbon nanotubes (M-SWCNTs) were investigated via spectrally resolved pump-probe spectroscopy using 7.5-fs laser pulses. In addition to first-order coherent phonons such as radial breathing mode (RBM) and M and G modes, we clearly observed second-order high-frequency coherent phonons of 2D and 2G modes, which can be regarded as squeezed phonons. We found that the amplitudes of the RBM, G and 2D modes were resonantly enhanced at specific wavelengths: the maximum resides at a wavelength whose energy is smaller than that of the van Hove singularities in M-SWCNTs by an amount corresponding to the phonon energy. Furthermore, the 2D mode has stronger enhancement than the other first-order Raman modes. These results indicate that the enhancement originates from a Stokes-stimulated Raman-scattering process at van Hove singularities and that efficient resonance enhancement occurs for the 2D mode, possibly through double resonance due to the trigonal warping effect and strong electron-phonon coupling due to the Kohn anomaly. © 2014 American Physical Society.

Minami Y.,Yokohama National University | Takeda J.,Yokohama National University | Dao T.D.,Japan International Center for Materials Nanoarchitectonics | Dao T.D.,Japan Science and Technology Agency | And 8 more authors.
Applied Physics Letters | Year: 2014

Linear and nonlinear electron dynamics of polycrystalline gold (Au) ultrathin films with thicknesses ranging from 1.4 to 5.8 nm were investigated via transmittance terahertz (THz) spectroscopy with intense electric field transients. We prepared ultrathin films with low surface roughness formed on a Si-(7 ×7) reconstructed surface, leading to the observation of monotonic decrease in THz transmittance with respect to film thickness. Furthermore, at all tested thicknesses, the transmittance decreased nonlinearly by 10%-30% with the application if high-intensity THz electric fields. Based on a Drude-model analysis, we found a significant decrease in the damping constant induced by the THz electric field, indicating that electrons are driven beyond the polycrystalline grain boundaries in Au thin films, and consequently leading to the suppression of the electron-boundary scattering rate. © 2014 AIP Publishing LLC.

Yoshioka K.,Yokohama National University | Minami Y.,Yokohama National University | Shudo K.-I.,Yokohama National University | Dao T.D.,Japan International Center for Materials Nanoarchitectonics | And 10 more authors.
Nano Letters | Year: 2015

Improved control over the electromagnetic properties of metal nanostructures is indispensable for the development of next-generation integrated nanocircuits and plasmonic devices. The use of terahertz (THz)-field-induced nonlinearity is a promising approach to controlling local electromagnetic properties. Here, we demonstrate how intense THz electric fields can be used to modulate electron delocalization in percolated gold (Au) nanostructures on a picosecond time scale. We prepared both isolated and percolated Au nanostructures deposited on high resistivity Si(100) substrates. With increasing the applied THz electric fields, large opacity in the THz transmission spectra takes place in the percolated nanostructures; the maximum THz-field-induced transmittance difference, 50% more, is reached just above the percolation threshold thickness. Fitting the experimental data to a Drude-Smith model, we found furthermore that the localization parameter and the damping constant strongly depend on the applied THz-field strength. These results show that ultrafast nonlinear electron delocalization proceeds via strong electric field of THz pulses; the intense THz electric field modulates the backscattering rate of localized electrons and induces electron tunneling between Au nanostructures across the narrow insulating bridges without any material breakdown. © 2015 American Chemical Society.

Katayama I.,Yokohama National University | Sato K.,Yokohama National University | Koga S.,Yokohama National University | Takeda J.,Yokohama National University | And 6 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

Coherent large-wave-vector phonons in graphene layers were excited by using a 7.5-fs ultrashort laser, and observed by wavelength-resolved pump-probe transient reflectivity spectroscopy. Inter-Dirac-cone electron scattering mediated by edges and defects in graphene layers drives large-wave-vector coherent D-mode phonons near the Dirac point (K point) of the Brillouin zone. In contrast to the normal coherent phonons generated with first-order Raman process, phonon chirp is observed, and amplitude and frequency strongly change depending on the probed wavelength. The results are discussed on the basis of doubly resonant Raman scattering process, demonstrating that generated D-mode coherent phonons can propagate as nanoscale optical-phonon wave packets. © 2013 American Physical Society.

Hase M.,University of Tsukuba | Hase M.,Japan National Institute of Materials Science | Ushida K.,Kitasato University | Kitajima M.,University of Tsukuba | And 2 more authors.
Journal of the Physical Society of Japan | Year: 2015

The anharmonic decay of coherent optical phonons in the semimetal Sb has been investigated by a femtosecond pump-probe technique. The coherent A1g mode is observed in the time domain in a wide temperature range of 7-290 K. The decay rate (the inverse of the dephasing time) systematically increases as the lattice temperature increases, which is well explained by anharmonic phonon-phonon coupling, causing the decay of the optical phonon into two acoustic phonon modes. The frequency of the A1g mode decreases with increasing temperature, which is interpreted as the results of both thermal expansion and anharmonic phonon-phonon coupling. The temperature dependence of the amplitude of the coherent A1g mode exhibits a decrease with increasing lattice temperature, which is well reproduced by considering the peak intensity of spontaneous Raman scattering assuming a Lorentzian line shape with the linewidth controlled by the anharmonic decay, and this model is applicable to other metallic systems, such as Zn. © 2015 The Physical Society of Japan.

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