Search results for "SIO2"

Twofold coordinated Ge defects induced by gamma-ray irradiation in Ge-doped SiO2

2008

We report an experimental study by photoluminescence, optical absorption and Electron Paramagnetic Resonance measurements on the effects of exposure of Ge-doped amorphous SiO2 to gamma ray radiation at room temperature. We have evidenced that irradiation at doses of the order of 1 MGy is able to generate Ge-related defects, recognizable from their optical properties as twofold coordinated Ge centers. Until now, such centers, responsible for photosensitivity of Ge-doped SiO2, have been induced only in synthesis procedures of materials. The found result evidences a role played by gamma radiation in generating photosensitive defects and could furnish a novel basis for photosensitive pattern wr…

Luminescence activity of surface and interior Ge-oxygen deficient centers in silica

2005

We report a comparative study on the optical activity of surface and interior Ge–oxygen deficient centers in pressed porous and sol–gel Ge-doped silica, respectively. The experimental approach is based on the temperature dependence of the two photoluminescence bands at 4.2 (singlet–singlet emission, S1! S0) and 3.1 eV (triplet–singlet emission, T1! S0), excited within the absorption band at about 5 eV. Our data show that the phonon assisted intersystem crossing process, linking the two excited electronic states, more effective for surface than for interior centers in the temperature range 5–300 K. For both centers, a distribution of the activation energies of the process is found. Based on th…

H(II) centers in natural silica under repeated UV laser irradiations

2004

We investigated the kinetics of H(II) centers (=Ge'-H) in natural silica under repeated 266nm UV irradiations performed by a Nd:YAG pulsed laser. UV photons temporarily destroy these paramagnetic defects, their reduction being complete within 250 pulses. After re-irradiation, H(II) centers grow again, and the observed recovery kinetics depends on the irradiation dose; multiple 2000 pulses re-irradiations induce the same post-irradiation kinetics of H(II) centers after each exposure cycle. The analysis of these effects allows us to achieve a deeper understanding of the dynamics of the centers during and after laser irradiation.

Photocatalytic CO2 Reduction in Gas-Solid Regime in the Presence of Bare, SiO2 Supported or Cu-Loaded TiO2 Samples

2013

Both commercial and home prepared (HP) TiO2 samples have been tested for the photocatalytic reduction of CO2. (HP) TiO2 powders were prepared by using TiCl4 or Ti(OC4H9)4 as the precursors to obtain HP1 and HP2 samples, respectively. Also HP Cu-loaded and SiO2 supported TiO2 powders were prepared. The HP samples were more active than the commercial ones for the photoreduction of CO2 with and without water vapour. HP1 produced mainly formaldehyde, HP2 principally methane. Acetaldehyde was found to be the primary product obtained when HP1 was supported on SiO2. The addition of Cu increased the photocatalytic reactivity either of bulk and SiO2-supported HP1. In particular, 1 wt % of Cu improve…

SiO2, Advanced Dielectrics and Related Devices - Proceedings of the 7th Symposium on SiO2, Advanced Dielectrics and Related Devices, Saint-Etienne, F…

2009

Quantum confinement effects observed by the photoluminescence of SiOx/SiO2 multilayers

2012

Spectral and decay features related to the red emission from Si nanocrystals were investigated by time-resolved photoluminescence spectra carried out on SiOx/SiO2 nanosized multilayers. On decreasing the SiOx thickness from 8.4 nm to 2.2 nm this luminescence band exhibits a blue-shift from 1.65 eV to 1.75 eV and its lifetime increases from 12μs to 17 μs. These results are discussed on the basis of previous models proposed in literature and agree with quantum confinement effects arising from differently sized Si nanocrystals in our samples.

The role of nanoparticles in decreased washout of underwater concrete

2019

Abstract The paper presents research results of the influence of SiO2 nanoparticles on the washout of underwater concrete and hardened concrete. Based on infrared spectroscopy (FTIR) and thermogravimetric (TGA) analyses of the applied anti-washout admixture (AWA), its chemical structure was determined. A beneficial effect of SiO2 nanoparticles on the reduction of the mix washout was demonstrated and the most probable reason for that phenomenon was given, taking into account the AWA chemical structure and its behaviour in the concrete mix environment. It was found that a dosing method of AWA and nanoparticles to the concrete influenced the washout.

Synthesis and Characterization of TiO2 Deposited on Silica

2008

Low-temperature atomic layer deposition of SiO2/Al2O3 multilayer structures constructed on self-standing films of cellulose nanofibrils

2018

In this paper, we have optimized a low-temperature atomic layer deposition (ALD) of SiO 2 using AP-LTO® 330 and ozone (O 3 ) as precursors, and demonstrated its suitability to surface-modify temperature-sensitive bio-based films of cellulose nanofibrils (CNFs). The lowest temperature for the thermal ALD process was 80°C when the silicon precursor residence time was increased by the stop-flow mode. The SiO 2 film deposition rate was dependent on the temperature varying within 1.5–2.2 Å cycle −1 in the temperature range of 80–350°C, respectively. The low-temperature SiO 2 process that resulted was combined with the conventional trimethyl aluminium + H 2 O process in order to prepare thin mul…

Assessment of protection treatments for carbonatic stone using nanocomposite coatings

2020

In this paper the effect of the application of four kinds of polymer dispersions containing nanoparticles, used as protectives, on two type of carbonatic lithotypes, White Noto and Comiso stone, is reported. The study was conducted by analysing the contribution of each component of the system. After the structural characterization of the coating itself, the performance of those colloidal systems has been studied upon application on the calcarenites, preferring non-invasive techniques and microdestructive techniques. Effect of the nanoparticles presence on hydrorepellency and roughness of the stone surface and on chromatic changes has also been considered. The tests conducted have proven tha…