Published Papers - AKIMOTO Ikuko

Fast passage effect in cw-ODMR of an ensemble of NV− centers

Yusuke Maki, Hideto Matsuoka, Ikuko Akimoto

Journal of Chemical Physics   162   054202 - (1-7)   2025.02  [Refereed]

DOI

Cyclotron resonance imaging at cryogenic temperatures enabled by electric field modification in a microwave cavity

Ikuko Akimoto, Takayuki Suzuki, Nobuko Naka, Hideto Matsuoka （Part： Lead author )

Journal of Physics D: Applied Physics   58   025309   2024.10  [Refereed]

DOI

Photogenerate electron- and hole-trap distributions in Al-doped anatase TiO₂ crystals measured by cryogenic EPR imaging

Yamato Kitao, Hideto Matsuoka, Ayane Murano, Takao Sekiya, Ikuko Akimoto （Part： Last author,　Corresponding author )

Physica Scripta ( IOP Publishing )  99   025514   2024.01  [Refereed]

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Abstract

Electron paramagnetic resonance (EPR) imaging was performed on aluminium-doped anatase titanium dioxide (TiO₂) crystals to demonstrate the distributions of photoinduced trapped electrons and holes at cryogenic temperatures. Complementary distributions of trapped electrons and holes were observed at 25 K; trapped electrons were predominant on the {101} planes, whereas trapped holes were predominant on the (001) and {110} planes in the tetragonal crystal structure. These separate distributions are consistent with the reported facet-dependent photocatalytic efficiency of photoreduction and photooxidation in anatase crystals, resulting from crystal plane-dependent carrier transfer. By this extrinsic trap system, the carrier transport properties were derivatively extracted through electron and hole traps This report provides insight into the fundamental physics governing the facet dependence of photocatalytic effects.

DOI

Intrinsic Mobility of Low-Density Electrons in Photoexcited Diamond

K. Konishi, I. Akimoto, H. Matsuoka, J. Isberg, N. Naka

Physical Review Applied ( American Physical Society (APS) )  17 ( 3 )   2022.03  [Refereed]

DOI

Transient coexistence of excitons and charge carriers in high-purity diamond

Sayaka Hamabata, Junichi H. Kaneko, Nobuko Naka, Ikuko Akimoto

Diamond and Related Materials ( Elsevier BV )  120   108678 - 108678   2021.12  [Refereed]

DOI

Time-Resolved EPR and Theoretical Investigations of Naphthalene Diimide Spin Dynamics in the Excited State

Hideto Matsuoka, Yuki Shibano, Ikuko Akimoto, Yuki Kanzaki

Bulletin of the Chemical Society of Japan ( The Chemical Society of Japan )    2021.10  [Refereed]

DOI

Diffusion-related lifetime and quantum efficiency of excitons in diamond

K. Konishi, I. Akimoto, J. Isberg, N. Naka

Physical Review B     2020.12  [Refereed]

Low-temperature mobility-lifetime product in synthetic diamond

K. Konishi, I. Akimoto, H. Matsuoka, V. Djurberg, S. Majdi, J. Isberg, N. Naka

Applied Physics Letters     2020.12  [Refereed]

Time-resolved measurement of photocarrier generation in CH3NH3PbI3 single crystals

Y. Tanaka, I. Akimoto

Journal of Physics: Conf. Series   1220   012019   2019.08  [Refereed]

Temperature-dependent carrier injection routes under optical excitation in high-purity diamond crystals

S. Hamabata, I. Akimoto, N. Naka

Journal of Physics: Conf. Series   1220   012023   2019.08  [Refereed]

Photocarrier injection by two-photon excitation in rubrene single crystal

K. Goto, T. Takayama, K. Ohata, K. Matsushita, I. Akimoto

Journal of Physics: Conf. Series   1220   012010   2019.08  [Refereed]

Intrinsic carrier parameters and optical carrier injection method in high-purity diamonds

I. Akimoto, N. Naka

IntechOpen Diamonds in Scientific Research and High Technology     2019.04  [Refereed]

DOI

Evidence of exciton dissociation into carriers induced by electric field in rubrene crystals

K. Goto, T. Takayama, K. Ohata, K. Matsushita, I. Akimoto

Journal of Luminescence   205   46 - 51   2019  [Refereed]

Double Electron–Electron Resonance Between Trapped Electron and Hole in a Semiconductor

Ikuko Akimoto, Takao Sekiya

Applied Magnetic Resonance ( Springer-Verlag Wien )  49 ( 8 ) 1 - 10   2018.04  [Refereed]

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We demonstrate the spin interactions between dispersedly trapped electrons and holes in a semiconductor using the double electron–electron resonance (DEER) method of the pulsed electron paramagnetic resonance (EPR) techniques. An aluminum-doped titanium dioxide crystal is adopted as a spin system, in which optically generated electrons and holes are trapped, to reveal EPR signals that appear close to each other at a selected crystal orientation under an external magnetic field. We used the four-pulse DEER method by applying two microwave frequencies to a microwave cavity for pumping electrons and probing holes at the optimum temperature of 32 K. The dipolar modulation in the probed signal by pumping interacting spins was successfully detected. The observed non-oscillating decay shape indicates that the detected interaction is caused by widely distributed trapped electron and hole spins over long distances. We were able to extract a spin-pair distribution function by the first derivative of a background-corrected curve, referring to a previously reported method.

DOI

Quantitative relevance of substitutional impurities to carrier dynamics in diamond

Takaaki Shimomura, Yoshiki Kubo, Julien Barjon, Norio Tokuda, Ikuko Akimoto, Nobuko Naka

Physical Review Materials   2   094601   2018  [Refereed]

Two optical routes of cold carrier injection in silicon revealed by time-resolved excitation spectroscopy

Ikuko Akimoto, Nobuko Naka

APPLIED PHYSICS EXPRESS ( IOP PUBLISHING LTD )  10 ( 6 )   2017.06  [Refereed]

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We reveal two routes of optical carrier injection in pure silicon by means of high-resolution excitation spectroscopy on nanosecond cyclotron resonances. Free carriers are generated either by the band-to-band transition assisted by phonon emission, or via two-body collisions of excitons. The first route was previously masked by a strong excitonic response in steady-state optical spectra at low temperatures. Furthermore, valley polarization is achieved for the cold carriers created by the second route with optimized excess energy. These optical carrier injection routes are crucial to initialize the momentum and valley degrees of freedom of carriers in order to enable versatile applications of indirect-bandgap semiconductors. (C) 2017 The Japan Society of Applied Physics

DOI

Excitons and fundamental transport properties of diamond under photo-injection

Nobuko Naka, Hikaru Morimoto, Ikuko Akimoto

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE ( WILEY-V C H VERLAG GMBH )  213 ( 10 ) 2551 - 2563   2016.10  [Refereed]

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Exciton diffusivity and carrier mobility are key features in determining transport properties of a material. The optimum values required for high-performance devices are expected to be realized in undoped intrinsic materials. Diamond, one of the emergent high-mobility materials, has a wide band gap suited for use in power electronics and optoelectronics. For many years, however, mobility measurement for diamond has been limited by carrier freezing at deep impurity levels. Recently, attempts at utilizing photoexcited carriers in undoped diamond have been made in a wide temperature range and various excitation schemes. A series of investigations demonstrated a wealth of intriguing observations such as dominant role of excitons and emergence of low-temperature anomaly in momentum relaxation. This article highlights recent experimental advances and progresses in understanding transport properties of photoexcited intrinsic diamond. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI

White-light emission from solid carbon in aqueous solution during hydrogen generation induced by nanosecond laser pulse irradiation

Ikuko Akimoto, Shota Yamamoto, Kosuke Maeda

APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING ( SPRINGER )  122 ( 7 )   2016.07  [Refereed]

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We previously discovered a novel method of hydrogen generation from high-grade charcoal in an aqueous solution using nanosecond laser pulse irradiation. In this paper, white-light emission during this reaction is reported: A broad spectrum over the visible range is observed above a threshold excitation energy density. The white-light emission is a simultaneous product of the hydrogen generation reaction and is attributed to blackbody radiation in accordance with Planck's Law at a temperature above 3800 K. Consequently, we propose that hydrogen generation induced by laser irradiation proceeds similarly to classical coal gasification, which features reactions at high pressure and high temperature.

DOI

Time-resolved cyclotron resonance on dislocation-free HPHT diamond

I. Akimoto, N. Naka, N. Tokuda

Diamond and Related Materials ( Elsevier Ltd )  63   38 - 42   2016.03  [Refereed]

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Intrinsic transport properties in diamond are remained frontiers in material research of semiconductors. Here, we apply the time-resolved cyclotron resonance (TRCR) method to dislocation-free HPHT diamonds in order to elucidate the momentum relaxation mechanisms of photoexcited carriers. Two specimens of single sector crystals oriented along [001] and [111] directions are examined. The both specimens show clear TRCR signals below 40 K, where the signals in the (111)-oriented diamond decay faster than those in the (001)-oriented one. From the temperature dependence of the CR spectrum in the (111)-oriented diamond, carrier momentum relaxation rates at the low temperature limit are extracted. The rates are two/four times larger for heavy/light holes in the HPHT diamond than the previous results obtained in a high-purity CVD diamond, and include temperature-independent scattering by neutral impurities. We also deduce that the TRCR detection is rather insensitive to crystalline dislocations by considering the cyclotron radii of carriers.

DOI

21pPSA-19 Infrared spectroscopy on high-purity CVD and HPHT diamond crystals

Shimomura T., Naka N., Tokuda N., Akimoto I.

Meeting Abstracts of the Physical Society of Japan ( The Physical Society of Japan (JPS) )  71   1579 - 1579   2016

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