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RISS 인기검색어
- 검색키워드
- 저자 : Masuhara, Hiroshi (검색결과 4 건)
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Tada, Takuji,Asahi, Tsuyoshi,Masuhara, Hiroshi,Tsuchimori, Masaaki,Watanabe, Osamu Korean Society of Photoscience 2003 Journal of Photosciences Vol.10 No.1
The excitation wavelength dependence of laser ablation dynamics of an azobenzene-containing urethane-urea copolymer film was investigated by measuring the laser fluence dependence of etch depth, transient absorbance change at each excitation wavelength, and transient absorption spectra. Moreover expansion/contraction dynamics was studied by applying nanosecond time-resolved interferometry. The threshold was determined at several excitation wavelengths from etch depth measurement, while time-integrated absorbance was obtained under excitation conditions. The photon energy required to remove the topmost of surface layer of the film did not .depend on excitation wavelength, and the penetration depth of excitation pulse dominated the etch depth. When the excitation wavelength was longer than 500 nm, permanent swelling was clearly observed but not for shorter wavelength excitation. In the latter case, photoisomerization occurred during excitation and the following photoreduction may play an important role. On the basis of the observations made in this study, a photochemical and photothermal mechanisms can explain mostly the short and long wavelength excitation results, respectively.
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Mito, Takashi,Masubuchi, Tomokazu,Tada, Takuji,Fukumura, Hiroshi,Masuhara, Hiroshi Korean Society of Photoscience 1999 Journal of Photosciences Vol.6 No.3
Intense excimer laser irradiation of polymer films results in expansion and the following contraction , recovering ithe initial flat surface. The morphological dynamics is meausred directly by nanosecond time-resolved interferometry for polystyrene(PS), polyurethane, and polyimide films. The expansion proceeds with a speed of a few nm/ns , while the contraction depends upon the polymer ; very low contraction for PS, rapid 2 component shrinking for polyurethane, and rapid monotonous decay for polymide. These characteristic behavior are considered from viewpoints of interpenetrating structures of polymers, glass-rubber phase transitioni, thermal diffusion, and photothermal mechanism.
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Jeon, Ki-Seok,Oh, Seung-Do,Suh, Yung Doug,Yoshikawa, Hiroyuki,Masuhara, Hiroshi,Yoon, Minjoong Royal Society of Chemistry 2009 Physical chemistry chemical physics Vol.11 No.3
<P>Blinking photoluminescence was observed in single TiO<SUB>2</SUB> nanodiscs (NDs) by using a laser scanning confocal microscope (LSCM)-coupled steady-state and ps-time-resolved photoluminescence (PL) spectroscopic system, while it was not significantly observed for TiO<SUB>2</SUB> quantum dots (QDs). Analysis of the PL blinking time trajectories revealed single-exponential kinetics with the average lifetimes of on-state (∼286 ms) and off-state (∼58 ms), implying the existence of inherent surface-trap sites which can be filled by photogenerated electron or hole. The PL spectra of single TiO<SUB>2</SUB> NDs exhibited broad surface emissions with four decay times, which may be due to diffusion of the energies of electron or hole trap states related to surface structural changes by modification of TiO<SUB>2</SUB> QDs. These results and the surface structural analysis (IR and XPS) suggests a simple model for the PL blinking of single TiO<SUB>2</SUB> NDs that is based on repetitive interfacial electron transfer to the inherent surface trap sites (<SUB>4</SUB>Ti<SUP>4+</SUP>–OH) with Auger-assisted hole trapping in the multiple surface states as modified by the diffusive coordinate model and the surface-trap-filling model. Based on this blinking mechanism and kinetics, the rates of the interfacial electron transfer and the back electron transfer in TiO<SUB>2</SUB> NDs were determined to be 18 ns and 58 ms, respectively, which are slow enough to keep the polarization of e–h pairs at the surface for efficient photocatalysis and photovoltaic activities. The present methodology and results may be applicable to obtain surface exciton dynamics of various photoelectronic semiconductor nanostructures.</P> <P>Graphic Abstract</P><P>Blinking photoluminescence was observed in single TiO<SUB>2</SUB> nanodiscs, which is due to repetitive interfacial electron transfer to the inherent surface trap sites. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b812361f'> </P>
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Ryu, Su-Young,Yoon, Min-Joong,Choy, Jin-Ho,Hwang, Sung-Ho,Frube, Akihiro,Asahi, Tsuyoshi,Hiroshi, Masuhara Korean Chemical Society 2003 Bulletin of the Korean Chemical Society Vol.24 No.4
Some new nanohybrid materials have been synthesized by intercalating the oxotitanium(IV) meso-tetrakis(4- sulfonatophenyl) porphyrin$(O=Ti^{(IV)} TSPP)$ into the Zn/Al layered double hydroxides (LDHs), and their structures and photophysical properties have been investigated by various laser spectroscopic techniques. According to the XRD pattern of the synthesized nanohybrid materials, the macrocycle plane of $O=Ti^{(IV)}$ TSPP are grafted perpendicular to the LDH layers. The $O=Ti^{(IV)}$ TSPP-intercalated LDH exhibits band broadening of the absorption spectrum and a blue shift of Q-band as compared to that observed in solution. Resonance Raman spectral measurements demonstrate that the positively charged LDHs give rise to a slight decrease of the electronic density of the porphyrin ring accompanying a small change of the electronic distribution of the $O=Ti^{(IV)}$ TSPP. Consequently the LDH environment affects the energies of the two highest occupied molecular orbitals (HOMOs) of the $O=Ti^{(IV)}$) TSPP, $a_{1u}$ and $a_{2u}$, producing a mixed orbital character. Being consistent with these electronic structural changes of $O=Ti^{(IV)}$ TSPP in LDH, both the fluorescence spectral change and the fsdiffuse reflectance transient measurements imply that the photoexcitation of the $O=Ti^{(IV)}$ TSPP intercalated into LDH undergoes fast relaxation to the O=Ti(IV) $TSPP^+-LDH^- $charge transfer (CT) state within a few picoseconds, followed by a photoinduced electron transfer between the O=Ti(IV) TSPP and LDHs with a rate constant greater than %1×10^{10}S^{-1}$. No evidence is found for back electron transfer. In conclusion, the $O=Ti^{(IV)}$ TSPP intercalated LDH seems to be a possible candidate for an artificial reaction center for an efficient solar energy conversion system.
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