The Experts below are selected from a list of 153 Experts worldwide ranked by ideXlab platform
Tetsuya Yamamoto - One of the best experts on this subject based on the ideXlab platform.
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Defect centers and optical absorption edge of degenerated semiconductor ZnO thin films grown by a reactive plasma deposition by means of piezoelectric photothermal spectroscopy
Journal of Applied Physics, 2006Co-Authors: Kentaro Sakai, T. Kakeno, Tetsuo Ikari, Sho Shirakata, Toshiyuki Sakemi, Kiyoshi Awai, Tetsuya YamamotoAbstract:Undoped and Ga-doped (3 wt %) n-type ZnO thin films were grown by a reactive plasma deposition method on glass substrates at 200 °C under an oxygen flow rate from 0 to 50 SCCM. In this paper, we report on the defect and band edge related signals in the optical absorption spectra for ZnO thin film by using a piezoelectric photothermal (PPT) spectroscopy, which is effective in observing a Nonradiative Transition process. The PPT peak around 2.5 eV was observed only for the undoped ZnO samples grown under a low oxygen flow rate. This signal is considered to be related to the oxygen vacancies, because it disappears with the increase of the oxygen flow rates. No corresponding peak was found for the Ga-doped samples. This result indicates that Ga doping inhibits the generation of the oxygen vacancies, and it agrees with that from the first-principle electronic band structure calculations. We have also carried out the theoretical calculation for the optical absorption edge of degenerated ZnO as a function of the...
Yuichi Fujimura - One of the best experts on this subject based on the ideXlab platform.
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ultrafast Nonradiative Transition pathways in photo excited pyrazine ab initio analysis of time resolved vacuum ultraviolet photoelectron spectrum
Chemical Physics, 2018Co-Authors: Benoit Mignolet, Yuichi Fujimura, Manabu Kanno, N Shimakura, Shiro Koseki, Francoise Remacle, Hirohiko KonoAbstract:Abstract The internal conversion of photo-excited pyrazine, which occurs rapidly on a time scale of about 20 fs, has long been considered to proceed via a conical intersection between the optically bright S2 (1B2u, ππ∗) and dark S1 (1B3u, nπ∗) states. Since 2008, several theoretical studies have raised the possibility that other dark states S3 (1Au, nπ∗) and S4 (1B2g, nπ∗) may participate dominantly in the early stage of the Nonradiative decay of S2. To clarify this issue, being motivated by the recent pump–probe experiment by Horio et al. [J. Chem. Phys. 145 (2016) 044306], we calculated vacuum ultraviolet photoelectron spectra for ionization from each of the four excited states. Comparison was made with the measured time-resolved photoelectron spectrum exhibiting a temporally varying multi-band structure. We confirmed no contribution of S3 or S4 and thus the validity of the conventional two-state (S2 → S1) picture for ultrafast Nonradiative Transition in pyrazine.
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ab initio quantum dynamical study on ultrafast Nonradiative Transition pathways of pyrazine
19th International Conference on Ultrafast Phenomena (2014) paper 07.Mon.P1.25, 2014Co-Authors: Manabu Kanno, Noriyuki Shimakura, Yuichi Fujimura, Shiro Koseki, Hirohiko Kono, Yuta ItoAbstract:We theoretically verified the participation of optically dark nπ* states other than S1 in ultrafast internal conversion of pyrazine. Contrary to a recent semiclassical study, our quantum dynamical calculations demonstrated that their contributions are negligible.
I Broser - One of the best experts on this subject based on the ideXlab platform.
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Nonradiative Transition rates of fe2 in iii v and ii vi semiconductors
Journal of Luminescence, 1994Co-Authors: L Podlowski, R Heitz, P Thurian, A Hoffmann, I BroserAbstract:Calorimetric absorption and transmission spectroscopy at mIK temperatures has been performed to determine the quantum efficiency of the internal Fe 2+ ( 5 T 2 → 5 E) Transition in different semiconductors. Experimental results are presented for III-V (GaAs, GaP, InP) and II-VI (ZnS, ZnO, CdS) semiconductors. The Transition rates of the competing radiative and Nonradiative processes in different host lattices are discussed
Tetsuo Ikari - One of the best experts on this subject based on the ideXlab platform.
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Defect centers and optical absorption edge of degenerated semiconductor ZnO thin films grown by a reactive plasma deposition by means of piezoelectric photothermal spectroscopy
Journal of Applied Physics, 2006Co-Authors: Kentaro Sakai, T. Kakeno, Tetsuo Ikari, Sho Shirakata, Toshiyuki Sakemi, Kiyoshi Awai, Tetsuya YamamotoAbstract:Undoped and Ga-doped (3 wt %) n-type ZnO thin films were grown by a reactive plasma deposition method on glass substrates at 200 °C under an oxygen flow rate from 0 to 50 SCCM. In this paper, we report on the defect and band edge related signals in the optical absorption spectra for ZnO thin film by using a piezoelectric photothermal (PPT) spectroscopy, which is effective in observing a Nonradiative Transition process. The PPT peak around 2.5 eV was observed only for the undoped ZnO samples grown under a low oxygen flow rate. This signal is considered to be related to the oxygen vacancies, because it disappears with the increase of the oxygen flow rates. No corresponding peak was found for the Ga-doped samples. This result indicates that Ga doping inhibits the generation of the oxygen vacancies, and it agrees with that from the first-principle electronic band structure calculations. We have also carried out the theoretical calculation for the optical absorption edge of degenerated ZnO as a function of the...
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investigation of the electron Nonradiative Transition in extremely thin gainnas gaas single quantum well by using a piezoelectric photothermal spectroscopy
Japanese Journal of Applied Physics, 2004Co-Authors: Kenji Imai, Tetsuo Ikari, S Fukushima, Masahiko KondowAbstract:Room-temperature piezoelectric photothermal spectroscopy (PPTS) measurements were carried out for the single-quantum-well (SQW) structures of GaInNAs. Four as-grown samples with thicknesses of 10, 7, 5 and 3 nm were used to investigate the quantum confinement effect in the SQW. The exciton contribution was clearly distinguished from the two-dimensional step like band-to-band Transition. The thickness dependence of PPT signal peak energy were well understood by quantum mechanics. The decrease in well thickness results in increases in quantized energy level and exciton binding energy. The present results showed that the newly developed PPT methodology is a unique and powerful tool for investigating the optical absorption spectra of extremely thin quantum well structures.
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investigation of Nonradiative Transition processes in p and n type silicon single crystals by piezoelectric photothermal spectroscopy
Review of Scientific Instruments, 2003Co-Authors: Aftab Ahmed Memon, Atsuhiko Fukuyama, S Sato, Tetsuo IkariAbstract:The piezoelectric photothermal spectroscopy (PPTS) technique was used to study the Nonradiative excitation/deexcitation process in p- and n-type single crystal silicon. The effectiveness of PPTS to investigate surface states and bulk properties of single crystal silicon has been demonstrated. PPTS measurements were conducted on p- and n-type, 〈100〉 orientation, single crystal silicon samples. A broad peaked signal around 1.18±0.01 eV at room temperature showed the characteristics of slow surface states present on a silicon surface. One more signal bearing a peak around 1.07±0.005 eV was due to bulk effect. The PPTS measurements conducted at various temperatures revealed band-to-band and valence band-to-excitons states’ Transition with phonon assistance. The measurements at 4.2 and 110 K resolved four types of phonon participation. A good agreement between theoretical expressions and experimental data substantiates our findings that our proposed technique is useful to investigate phonon contribution in the...
Takeshi Ohno - One of the best experts on this subject based on the ideXlab platform.
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Nonradiative Transition of phosphorescent charge transfer states of ruthenium ii to 2 2 biquinoline and ruthenium ii to 2 2 6 2 terpyridine in the solid state
Inorganic Chemistry, 1998Co-Authors: Ashraful Islam, Noriaki Ikeda, And Akio Yoshimura, Takeshi OhnoAbstract:Temperature-dependent decays of the charge-transfer triplet excited states (3CT) of ruthenium(II) compounds have been investigated in a wide temperature range (77−480 K) for the crystals of Ru(biq)3(ClO4)2, Ru(bpy)2(biq)X2·2H2O, and Ru(tpy)2X2, (bpy = 2,2‘-bipyridine, tpy = 2,2‘:6‘,2‘‘-terpyridine, biq = 2,2‘-biquinoline, X = ClO4-, PF6-). The width of the 1CT absorption band and the peak of 3CT emission of the Ru(bpy)2(biq)X2·2H2O crystal at 298 K are unchanged from those of the ethanol/methanol solution sample. The 3CT of Ru(bpy)2(biq)X2·2H2O and Ru(biq)3(ClO4)2 in the solid state above 370 K are converted to a higher lying excited state, the d−d triplet lowest excited state (3(d−d)), with a frequency factor of >1013 s-1 and an activation energy of >3100 cm-1, followed by the rapid degradation of the higher excited state. A small frequency factor (<1012 s-1) and an activation energy (<2000 cm-1) of the Nonradiative decay of 3CT for [Ru(tpy)2]X2 in the solid state indicates that the exoergonic intersyste...
