Microscopic structure of nanometer-sized silica particles

Uchino, Takashi; Aboshi, Atsuko; Kohara, Shinji; Ohishi, Yasuo; Sakashita, Mami; Aoki, Katsutoshi

doi:10.1103/physrevb.69.155409

Cited by 93 publications

(102 citation statements)

References 45 publications

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“…It had a nominal surface area of 380±30 m 2 /g and a average primary particle size of 7 nm (product specification). We have recently shown that the structural and optical characteristics of fumed silica are interesting in its own right [16], but we here use it as a silica substrate with a large specific surface area. OTS SAMs were prepared according to the literature method [17].…”

Section: Methodsmentioning

confidence: 99%

Visible luminescence from octadecylsilane monolayers on silica surfaces: Time-resolved photoluminescence characterization

Sagawa

Uchino

2005

Applied Physics Letters

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We have found that the adsorption of octadecyltrichlorosilane (OTS) monolayers on nanometer-sized silica particles yields a stable blue photoluminescence (PL) with a time scale of nanoseconds. The observed PL intensity increases after curing at temperatures from ∼100 to ∼300 °C, suggesting that condensations between adjacent OTS molecules on the silica surface are related to the PL. The PL decay curve of the cured samples remains unchanged from 77 to 450 K, whereas the time-integrated PL intensity shows a monotonous decrease with increasing temperature. From these experimental results, a model of radiative and nonradiative process associated with the PL is presented.

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Section: Methodsmentioning

confidence: 99%

Visible luminescence from octadecylsilane monolayers on silica surfaces: Time-resolved photoluminescence characterization

Sagawa

Uchino

2005

Applied Physics Letters

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“…After drying, the specimen was mounted on a brass specimen holder and Table 1. Classification of amorphous silica by thermodynamic characteristic and its origin * (1) Beall (1994), (2) Newton and Manning (2008), (3) Pratsinis (1998), (4) Uchino et al (2004), (5) Stöber et al (1968).…”

Section: Sample Treatmentmentioning

confidence: 99%

Pressure–induced crystallization of biogenic hydrous amorphous silica

Kyono

Yokooji

Chiba

et al. 2017

Journal of Mineralogical and Petrological Sciences

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Samples of the diatom Nitzschia cf. frustulum, collected from Lake Yogo, Siga Prefecture, Japan, were cultured in the laboratory. Organic components of the diatom cell were removed by washing with acetone and sodium hypochlorite. The remaining frustules were studied by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX), Fourier-transform infrared (FTIR) spectroscopy, and synchrotron X-ray diffraction. The results showed that the spindle-shaped diatom frustule was composed of hydrous amorphous silica. Pressure-induced phase transformation of the diatom frustule was investigated by in situ Raman spectroscopic analysis. With exposure to 0.3 GPa at 100°C, the Raman band corresponding to quartz occurred at ν = 465 cm −1 . In addition, a characteristic Raman band for moganite was observed at 501 cm −1 . From the integral ratio of Raman bands, the moganite content in the probed area was estimated to be approximately 50 wt%. With increased pressure and temperature, the initial morphology of diatom frustules was totally changed to a characteristic spherical particle with a diameter of about 2 µm. Increasing pressure to 5.7 GPa at 100°C resulted in the appearance of a Raman band assignable to coesite at 538 cm −1 . That is, with compression and heating, hydrous amorphous silica can be readily crystallized into quartz, moganite, and coesite. First-principles calculations revealed that a disiloxane molecule with a trans configuration is twisted 60°with a close approach of a water molecule, which leads to a trans to cis configuration change. It is therefore reasonable to assume that during crystallization of hydrous amorphous silica, an Si-O-Si bridging unit with the cis configuration would survive as a structural defect, and could subsequently crystallize into moganite by maintaining that geometry. This hypothesis is adaptable to the phase transformation from hydrous amorphous silica to coesite as well, because coesite has four-membered rings and is easily formed from hydrous amorphous silica under high pressure and temperature conditions.

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“…Tan et al (1999) measured XRD profiles of compressed SiO 2 glass and showed that the FSDP positions shift to a high angle with an increase in the pressure. Uchino et al (2004) reported structural changes induced by heat treatment of fumed silica (nanometer -size SiO 2 particles). Matsuoka et al (2004) discussed fracture -induced permanent strain in crushed SiO 2 glass.…”

Section: Introductionmentioning

confidence: 99%