| Co-Investigator(Kenkyū-buntansha) |
EMA Kazuhiro Faculty of Science & Engineering, Sophia University, Associate Professor, 理工学部, 助教授 (40194021)
ASAI Keisuke Graduate School, Faculty of Engineering, The University of Tokyo Associate Professor, 大学院・工学系研究科, 助教授 (60231859)
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| Research Abstract |
* "RBS analysis of Langmuir-Blodgett films bearing quantum-sized CdS particles"
Rutherford backscattering spectrometry is applied to an analysis of the structure of Langmuir-Blodgett (LB) films bearing quantum-sized cadmium sulfide particles (Q-CdS). Cadmium arachidate LB films before and after exposure to hydrogen sulfide are analyzed using a beam of 2 MeV ィイD14ィエD1HeィイD12+ィエD1. The change in the Cd-edge is ascribed to the Cd migration toward the substrate, which suggests that a well-ordered layer structure of the original film is disordered during Q-CdS formation. This finding indicates that the Q-CdS produced in hydrophilic interlayers cannot be two-dimensional platelets but are spherical particles.
* "Changes in the surface electronic states of quantum-sized semiconductor particles induced by high energy proton irradiation"
We performed steady-state and time-resolved measurements of the ion-induced emissions and photoluminescence (PL) measurement on quantum-sized semiconductor particl
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es prepared in Langmuir-Blodgett films. The proton irradiation caused a decrease in intensity of the emission via trapping sites, removing almost all the traps in the band gap. The low energy emissions, which showed a multiexponential decay, are considered to originate from a recombination of donor-acceptor pairs localizing in the surface region. Furthermore, PL spectra obtained after the irradiation changed drastically in the course of photo-oxidation of the particles.
* "DFWM study of thin films containing surface-modified CdS nanoparticles"
Degenerate four-wave mixing (DFWM) was used as a technique to estimate the third-order optical susceptibility, χィイD1(3)ィエD1(-ω ; ω, -ω, ω), of thin films prepared from cadmium sulfide (CdS) colloidal solutions. The formation of CdS films on a substrate, without any change in the particle size, enhanced the quantum yield of an excitonic band by removing a large number of surface traps. This film showed a large χィイD1(3)ィエD1 value near 〜 10ィイD1-7ィエD1 esu around the exciton resonance at room temperature. This was possibly brought about by an effective surface passivation as well as a high CdS microcrystallite concentration.
* "Resonant third-order optical nonlinearity in the layered perovskite-type material (CィイD26ィエD2HィイD213ィエD2NHィイD23ィエD2)ィイD22ィエD2PbIィイD24ィエD2"
The third-order nonlinear optical susceptibility, χィイD1(3)ィエD1(-ω ; ω, -ω, ω), of the layered perovskite-type material (CィイD26ィエD2HィイD213ィエD2NHィイD23ィエD2)ィイD22ィエD2PbIィイD24ィエD2 is measured by a transient four-wave mixing (FWM) technique using a 200-fs-pulse laser source. The maximum |χィイD1(3)ィエD1| value is 1.6 × 10ィイD1-6ィエD1 esu at the lowest-exciton resonance at 8 K. Longitudinal and transverse relaxation times of the excitons are 7 ps and 0.2 ps ; respectively. For excitation below the exciton resonance, biexciton contribution to the FWM signals was observed. The dephasing energy of the biexcitons was estimated to be larger than 10 meV. Less
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