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170 results on '"Kawayama, I."'

1. Collective Antenna Effects in the Terahertz and Infrared Response of Highly Aligned Carbon Nanotube Arrays

Author

Ren, L., Zhang, Q., Pint, C. L., Wojcik, A. K., Bunney, M., Arikawa, T., Kawayama, I., Tonouchi, M., Hauge, R. H., Belyanin, A. A., and Kono, J.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We study macroscopically-aligned single-wall carbon nanotube arrays with uniform lengths via polarization-dependent terahertz and infrared transmission spectroscopy. Polarization anisotropy is extreme at frequencies less than $\sim$3 THz with no sign of attenuation when the polarization is perpendicular to the alignment direction. The attenuation for both parallel and perpendicular polarizations increases with increasing frequency, exhibiting a pronounced and broad peak around 10 THz in the parallel case. We model the electromagnetic response of the sample by taking into account both radiative scattering and absorption losses. We show that our sample acts as an effective antenna due to the high degree of alignment, exhibiting much larger radiative scattering than absorption in the mid/far-infrared range. Our calculated attenuation spectrum clearly shows a non-Drude peak at $\sim$10 THz in agreement with the experiment., Comment: 5 pages, 5 figures

Published
2013
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2. Terahertz Dynamics of Quantum-Confined Electrons in Carbon Nanomaterials

Author

Ren, L., Zhang, Q., Nanot, S., Kawayama, I., Tonouchi, M., and Kono, J.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Low-dimensional carbon nanostructures, such as single-wall carbon nanotubes (SWCNTs) and graphene, offer new opportunities for terahertz science and technology. Being zero-gap systems with a linear, photon-like energy dispersion, metallic SWCNTs and graphene exhibit a variety of extraordinary properties. Their DC and linear electrical properties have been extensively studied in the last decade, but their unusual finite-frequency, nonlinear, and/or non-equilibrium properties are largely unexplored, although they are predicted to be useful for new terahertz device applications. Terahertz dynamic conductivity measurements allow us to probe the dynamics of such photon-like electrons, or massless Dirac fermions. Here, we use terahertz time-domain spectroscopy and Fourier transform infrared spectroscopy to investigate terahertz conductivities of one-dimensional and two-dimensional electrons, respectively, in films of highly aligned SWCNTs and gated large-area graphene. In SWCNTs, we observe extremely anisotropic terahertz conductivities, promising for terahertz polarizer applications. In graphene, we demonstrate that terahertz and infrared properties sensitively change with the Fermi energy, which can be controlled by electrical gating and thermal annealing., Comment: 16 pages, 9 figures

Published
2012
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3. Carbon Nanotube Terahertz Polarizer

Author

Ren, L., Pint, C. L., Booshehri, L. G., Rice, W. D., Wang, X., Hilton, D. J., Takeya, K., Kawayama, I., Tonouchi, M., Hauge, R. H., and Kono, J.

Subjects
Condensed Matter - Materials Science
Abstract

We describe a film of highly-aligned single-walled carbon nanotubes that acts as an excellent terahertz linear polarizer. There is virtually no attenuation (strong absorption) when the terahertz polarization is perpendicular (parallel) to the nanotube axis. From the data we calculated the reduced linear dichrosim to be 3, corresponding to a nematic order parameter of 1, which demonstrates nearly perfect alignment as well as intrinsically anisotropic terahertz response of single-walled carbon nanotubes in the film., Comment: 13 pages, 3 figures

Published
2009
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5. Noncontact evaluation of electrical passivation of oxidized silicon using laser terahertz emission microscope and corona charging.

Author

Mochizuki, T., Ito, A., Nakanishi, H., Tanahashi, K., Kawayama, I., Tonouchi, M., Shirasawa, K., and Takato, H.

Subjects
INTEGRATED circuit passivation, PASSIVATION, SILICON wafers, SUBMILLIMETER waves, CORONA discharge
Abstract

We evaluated electrical passivation of crystalline silicon wafers possessing oxidized layers using a laser terahertz (THz) emission microscope, measuring waveforms of laser-excited THz emission from those surfaces with a corona charging setup to tune surface potential without electrical contact. The THz waveform strongly correlated to the surface potential, evaluated by measuring surface photovoltage using a Kelvin probe when the surface was depleted or inverted. The waveform also correlated to the potential of the surface in the accumulation mode and inverted near the flatband condition. The minority carrier lifetime agreed with the theoretically determined dependence on the charge density. These results indicate that the surface potential of a semiconductor covered by an insulator which can be charged by the corona charging setup can be evaluated by assessing the THz emission. Further, such a sample can also be used as a reference to quantitatively relate the waveform of the THz emission and the internal field of surface band bending in semiconductors. [ABSTRACT FROM AUTHOR]

Published
2019
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6. Detection of magnetic signal in high-Tc superconductor devices by scanning laser magneto-optical microscope

Author

Kitamura, R., Murakami, H., Kawayama, I., and Tonouchi, M.

Subjects
Barium compounds -- Electric properties, Barium compounds -- Magnetic properties, Scanning microscopy -- Usage, Superconducting quantum interference devices -- Magnetic properties, Superconducting quantum interference devices -- Evaluation, Yttrium -- Magnetic properties, Yttrium -- Electric properties, Business, Electronics, Electronics and electrical industries
Published
2009

14. Evaluations of Oxidized Silicon Surfaces with Laser Terahertz Emission Microscope (LTEM) and Corona Charging

Author

Mochizuki, T., Ito, A., Nakanishi, H., Tanahashi, K., Kawayama, I., Tonouchi, M., Shirasawa, K., and Takato, H.

Subjects
Silicon Cells, Characterisation & Simulation Methods for Si Cells
Abstract

35th European Photovoltaic Solar Energy Conference and Exhibition; 270-272, Surface band bending evaluation by assessing Terahertz (THz) emission from silicon wafers using a laser terahertz emission microscope (LTEM) is systematically and quantitatively compared with the non-contact voltagecharge (V-Q) method which utilize a Kelvin probe. The amplitude of THz emission consistently changed with the surface barrier voltage Vsb of non-contact V-Q when the surface was depleted or weakly inverted. The deposited charge density required to zero THz amplitude was close to Qtot of noncontact C-V, the charge needed to move the surface from initial condition to the flatband. When the surface had accumulation layer, the THz emission showed sensitivity to the surface charging, while Vsb = 0 and was insensitive to the surface charging. The amplitude of THz emission saturated when the surface was strongly inverted or accumulated. The results show that the LTEM can be a tool similar to the non-contact V-Q in combination with a corona charging. Furthermore, the sensitivity of THz emission to the both of depleted and accumulated surface suggests that the LTEM can be a tool to evaluate surface field of silicon surfaces to which corona charging is not applicable.

Published
2018
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21. Dielectric and ferroelectric properties of c-axis oriented strontium bismuth tantalate thin films applied transverse electric fields.

Author

Kotani, K., Kawayama, I., Tonouchi, M., Hotta, Y., and Tabata, H.

Subjects
*DIELECTRICS, *FERROELECTRICITY, *PULSED laser deposition, *LOW temperatures, *POLARIZATION (Nuclear physics), *THIN films
Abstract

The in-plane dielectric and ferroelectric properties of c-axis oriented epitaxial strontium bismuth tantalate (SBT) thin films were investigated by interdigital surface electrode measurement. The four types of SBT thin films, which have various Sr/Bi atomic ratios, were prepared on MgO substrates by pulsed laser deposition. The dielectric properties at kilohertz and megahertz frequencies were studied from 20 to 870 K. Above room temperature, all the films show the phase transition. Sr0.99Bi1.61Ta2O9, Sr0.97Bi2.10Ta2O9, and Sr0.88Bi1.79Ta2O9 thin films show frequency dispersions near phase transition temperature. At low temperatures, dielectric and ferroelectric properties of Sr0.97Bi2.10Ta2O9 and Sr0.83Bi2.08Ta2O9 thin films were investigated. Both dielectric constant and remanent polarization show a tendency to decrease as temperature decreases, and the rapid change, which may indicate a phase transition, was observed in Sr0.97Bi2.10Ta2O9 near 80 K. [ABSTRACT FROM AUTHOR]

Published
2006
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23. Evaluation of Passivated Surface of Silicon with Laser Terahertz Emission Microscope (LTEM)

Author

Mochizuki, T., Ito, A., Nakanishi, H., Mitchell, J., Tanahashi, K., Kawayama, I., Tonouchi, M., Shirasawa, K., and Takato, H.

Subjects
Wafer-Based Silicon Solar Cells and Materials Technology, Silicon Solar Cell Characterisation and Modelling
Abstract

32nd European Photovoltaic Solar Energy Conference and Exhibition; 510-513, Terahertz emission from silicon wafers with silicon-oxide passivation lasers were measured using a laser terahertz emission microscope (LTEM) with strong correlation between THz waveform and the surface potential being observed. The surface potential were electrically tuned by an indium-tin oxide transparent electrode disk on the top and evaluated by capacitance-voltage (C-V) characteristics. The sample were excited by Ti-Sapphire laser pulses and the waveform of THz emission were measured by the THz time-domain spectroscopy techniques using LTEM. The observed waveform changed with the external bias and inverted near the flatband voltage, and changes similar to the C-V characteristics were shown in the peak amplitude. These results indicate that the LTEM can measure and map the surface band bending of Si by analysing the waveform of THz emission. We expect that the LTEM can be applied as an optical inspection tools of passivation layers of solar cells.

Published
2016
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26. Demonstration of a Novel Inspection System for a Solar Cell Using Terahertz Emission Imaging

Author

Nakanishi, H., Ito, A., Mizubata, M., Kawayama, I., Murakami, H., and Tonouchi, M.

Subjects
WAFER-BASED SILICON SOLAR CELLS AND MATERIALS TECHNOLOGY, Silicon Solar Cell Characterisation and Modelling
Abstract

31st European Photovoltaic Solar Energy Conference and Exhibition; 511-513, A laser terahertz emission microscope (LTEM) is a non-contact inspection technique based on a THz emission spectroscopy and imaging that can visualize intensity of pulsed terahertz radiation from the materials and devices excited by femtosecond laser pulses. We have applied LTEM to characterize local properties of a solar cell and have demonstrated the potential of LTEM as imaging technique of photoexcited current in a solar cell. In this study, we experimentally compared LTEM with conventional analysis methods, e. g. electroluminescence (EL), and laser beam induced current (LBIC) images, in order to examine its feasibility as a solar cell inspection technique. It was found that LTEM image was clearly different from EL and LBIC images and LTEM was more sensitive to the surface morphology and crystallographic grains of solar cells than EL and LBIC. We could clearly distinguish grain boundaries, steps and cracks in a polycrystalline silicon solar cell, which could not be seen with EL and LBIC. Finally, we have succeeded in the development of the prototype of solar cell inspection system based on LTEM for commercial application. The prototype system will be installed in the Fukushima Renewable Energy Institute, AIST (FREA) in Japan.

Published
2015
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50. Ferroelectric Soft Mode in a SrTiO3 Thin Film Impulsively Driven to the Anharmonic Regime Using Intense Picosecond Terahertz Pulses

Author

Katayama, I., Aoki, H., Takeda, J., Shimosato, H., Ashida, M., Kinjo, R., Kawayama, I., Tonouchi, M., Nagai, M., and Tanaka, K.

Subjects
Condensed Matter::Materials Science
Abstract

The ferroelectric soft mode in a SrTiO3 thin film was impulsively driven to a large amplitude using intense picosecond terahertz pulses. As the terahertz electric field increased, the soft-mode absorption peak exhibited blueshifting and spectral narrowing. A classical anharmonic oscillator model suggests that the induced displacement is comparable to that of the ferroelectric phase transition. The spectral narrowing indicates that the displacement exceeds that induced by any inhomogeneities in the film, demonstrating that the method can be used to explore intrinsic quartic anharmonicity.

Published
2012

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