Browsing by Author "Hashimoto, Shuichi"

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Fabrication of gold nanoparticle-doped zeolite L crystals and characterization by optical microscopy: Laser ablation- and crystallization inclusion-based approach
(2008-10-02)
Hashimoto, Shuichi
;
Uwada, Takayuki
;
Masuhara, Hiroshi
;
Asahi, Tsuyoshi
;
應用化學系
This letter reports the optical microscopy characterization of gold nanoparticle-doped zeolite L crystals prepared by applying two key techniques: laser ablation and crystallization inclusion. The former allowed the stable formation of Au NPs in the synthesis gel, while the latter permitted the encapsulation of Au NPs exceeding the pore openings of the zeolite crystals, still maintaining the crystal structure as a whole. The microscopy characterization was performed by exploiting single particle light scattering spectroscopy and imaging techniques which offered the Rayleigh scattering images of individual An particles within the crystals and the scattering spectra ascribable to the surface plasmon resonance band of Au NPs embedded. This is a unique demonstration for the application of laser ablation-induced NPs in solution to practical use for fabricating a nanocomposite material. Furthermore, the present results revealed that the dark field microscopy is capable of visualizing metal nanoparticles as small as 40 nm diameter confined in the light scattering crystalline medium.
Gold Nanoparticle-Assisted Laser Surface Modification of Borosilicate Glass Substrates
(2009-12-03)
Hashimoto, Shuichi
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Uwada, Takayuki
;
Hagiri, Masahide
;
Takai, Hiroaki
;
Ueki, Tomoyuki
This paper describes the photomodification of borosilicate glass substrates assembled with 40 nm diameter gold nanoparticles (Au NPs) with surface coverages ranging from 17 to 23% on excitation of the localized surface plasmon band of the NPs with a 532 nm nanosecond pulsed-laser beam. The laser irradiation allowed the splitting and fusion of NPs on the substrate surface and, at the same time, the formation of craters of less than 10 nm diameter at various places following one laser shot with a relatively high intensity of 460 or 370 mJ.cm(-2).pulse(-1) but well below the breakdown threshold of 25-40 J.cm(-2).pulse(-1). The formation of the craters was more and more distinctly observed by continuous irradiations. The number density, average diameter, and the surface coverage of the craters were not linearly dependent on the laser shot number but exhibited the saturation behavior due to the consumption of Au NPs. The threshold laser energy for the crater formation was dependent on the accumulated number of laser shots: a greater number of laser shots were necessary to form craters as the laser fluence decreases. Most interestingly, the laser-irradiated areas of the substrate exhibited a greater susceptibility to the wet chemical etching with aqueous hydrogen fluoride. The mechanism of the laser modification and a possible application to nanofabrication on glass surfaces by utilizing Au NPs were discussed on the basis of the scanning electron microscopy (SEM) observation as well as the extinction and light scattering spectroscopic measurements.
Laser microfabrication and rotation of ship-in-a-bottle optical rotators
(2008-08-04)
Matsuo, Shigeki
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Kiyama, Satoshi
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Shichijo, Yoshinori
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Tomita, Takuro
;
Hashimoto, Shuichi
We have fabricated optical rotators inside a silica substrate and rotated them by a laser trapping technique. The fabrication method used was femtosecond laser-assisted etching, i.e., modification of the host material by irradiation with femtosecond laser pulses along a predesigned pattern, followed by selective chemical etching. The rotators, which consist of the same material as the substrate, can move inside the microcavity but cannot get out. The rotation speed was proportional to the trapping laser power, and the maximum achieved was about 100 rpm. Such rotators will be applicable to micro-total-analysis systems and microfluidics. (c) 2008 American Institute of Physics.
Mechanistic Aspect of Surface Modification on Glass Substrates Assisted by Single Shot Pulsed Laser-Induced Fragmentation of Gold Nanoparticles
(2011-03-31)
Hashimoto, Shuichi
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Uwada, Takayuki
;
Hagiri, Masahide
;
Shiraishi, Ryowya
;
應用化學系
This paper describes the mechanistic investigation on the photomodification of a borosilicate glass substrate assembled with 47 +/- 8 nm gold nanoparticles and exposed to a single shot of 532 nm nanosecond pulsed-laser light. The laser fluences ranging from 180 to 430 mJ cm(-2) pulse(-1), the values of which are 2 orders of magnitude lower than the breakdown threshold of quartz of 15-20 J cm(-2) pulse(-1) were used. Upon photomodification, the craters of similar to 20 nm diameter and similar to 10 tun depth were formed on the glass surface simultaneously with the laser-induced splitting of Au nanopartides to generate smaller particles of 15 nm diameter. The number density of the craters increased depending on the laser fluence with a sharp rise, the onset of which occurred at similar to 160-170 mJ cm(-2) pulse(-1), and reached a value of twice the number density of original Au particles (150 +/- 10 particles mu m(-2)) with a weak tendency to level off at high fluences. The onset of the crater formation coincides with splitting of gold nanopartides due to the temperature rise above the boiling point of gold resulting from the absorption of the laser energy. Thus, the explosive evaporation of gold nanoparticles is postulated to play a crucial role for the modification observed here. This assumption gained a solid support from the estimation of laser fluence-dependent thermoacoustic pressures due to the sudden evaporation of gold. This finding may represent a new application of the laser ablation/fragmentation of nanoparticles to material processing.
Remarkable Photothermal Effect of Interband Excitation on Nanosecond Laser-Induced Reshaping and Size Reduction of Pseudospherical Gold Nanoparticles in Aqueous Solution
(2010-06-15)
Werner, Daniel
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Hashimoto, Shuichi
;
Uwada, Takayuki
;
應用化學系
;
應用化學系分子科學碩博班
An in situ spectroscopic study of the nanosecond laser-induced melting and size reduction of pseudospherical gold nanoparticles with 54 +/- 7 nm diameter allowed the observation of a heating efficiency that was very dependent on the excitation wavelength. A remarkably greater efficiency was observed for the photothermal effect of interband excitation than that of intraband excitation. This noteworthy observation is ascribed to an altered electron heat capacity, c(e), during photoexcitation depending on the excitation energy, which is a phenomenon that has not been realized previously. As a result, a 60% reduction of the specific heat capacity, c(p), compared to that of bulk gold was obtained for interband excitation at 266 nm whereas the c(p) value for the excitation of the intraband transition at 532 nm was unaltered. A semiquantitative explanation was given for this striking phenomenon induced by interband excitation in which excitation relaxation cycles of electrons upon excitation of 5d electrons to the 6sp band lead to a reduced number of electrons contributing to the electron temperature rise in the vicinity of the Fermi level during the nanosecond laser pulse duration. By contrast, electronic-excitation within the 6sp band results in no net reduction in the number of electrons near the Fermi level, giving rise to a value of c(p) similar to that of bulk gold. Our finding that the heat capacity of gold nanoparticles can be changed upon UV laser excitation is important for understanding the fundamental nature of noble metal nanoparticles. Furthermore, this finding might be useful for preparing new metal alloy particles as well as for manipulating the thermodynamic properties of the nanoparticles.
Studies on the interaction of pulsed lasers with plasmonic gold nanoparticles toward light manipulation, heat management, and nanofabrication
(2012-03-01)
Hashimoto, Shuichi
;
Werner, Daniel
;
Uwada, Takayuki
;
應用化學系
;
應用化學系分子科學碩博班
This review describes the fundamental aspects of laser-gold nanoparticle (Au NP) interaction that leads to nanoscale energy deposition to the surroundings through light amplification and heat generation. Besides the importance of the primary process in physics and chemistry, application of the light-NP interaction has attracted significant interest from various areas ranging from analytical chemistry to material chemistry and biomedicine. Here we consider both mechanistic and application aspects. Our attention is focused on pulsed-laser-induced fast processes that revealed the heating-cooling dynamics of electrons, lattice (particle), and particle's environment. On the application side, we focus on material fabrication and processing that beat diffraction-limited resolution. Together, we will shed a light on the essence of research activities carried out in the past 10 years. In addition to an abundance of latest information obtained from currently available literature, this review includes figures obtained by our own calculations to provide readers with a better understanding of the basics of the optical properties and energy and heat-transfer processes of Au NPs, which are not familiar to photochemists. (C) 2012 Elsevier B.V. All rights reserved.