Irradiated SiO2 Research Articles

UV Irradiated SiO2 Nanoparticles as Insulin and Immunoglobulin Molecule Carriers

Abstract Insulin and immunoglobulin therapy is commonly administered through injections that are invasive and painful. They cannot be taken orally because digestive enzymes break them down. To protect against enzymes, drug molecules may be “packed”, which decreases interaction of the active surface of the molecule with the environment. Silica nanoparticles (SiO2) may be used to attach proteins like insulin or immunoglobulin for use in drug delivery. They are stable and biocompatible. Exposing SiO2 nanoparticles to UV radiation may control molecule–nanoparticle attachment because of their electrostatic interactions. This study demonstrates the influence of UV radiation of SiO2 nanoparticles on insulin and immunoglobulin molecule attachment. Alteration of the surface electric potential of SiO2 nanoparticles by UV radiation was determined using electron work function measurements. Influence of radiation on formation of molecule-nanoparticle complexes was assessed by spectrophotometry of their sedimentation rate in solution. Increasing UV exposure time negatively charges the surfaces of SiO2 nanoparticles. Insulin exhibits better adsorption with SiO2 nanoparticles compared to immunoglobulin, likely due to favourable conditions promoting attractive electrostatic interactions. Longer UV exposure weakens insulin adsorption but does not significantly affect immunoglobulin adsorption.

Investigation of Low Energy Electron Irradiated SiO2 Based MOS Devices by Capacitance-Voltage and Thermally Stimulated Current Techniques

Investigation of Low Energy Electron Irradiated SiO2 Based MOS Devices by Capacitance-Voltage and Thermally Stimulated Current Techniques

Modulation sidebands spectra within inhomogeneous CW-EPR line detected by double modulation EPR spectroscopy.

Conventional modulation spectrum, MS, in continuous wave electron paramagnetic resonance, CW-EPR, is produced by applying longitudinal radiofrequency (RF) fields with the frequencies, ωrf, which exceeds the linewidth, 2πδ, of a single spectral line given in frequency units. The second longitudinal RF field with frequency, ωrf2, is employed to produce double modulation spectrum, DMS. In this work DMS are presented as a specific type of MS which can be produced from an ordinary homogenous line. The numerical simulations of DMS in the limit of low power saturation relied on the recently introduced multi-photon transitions formalism which includes one microwave photon in combination with an arbitrary number of radiofrequency photons. It is shown that DMS of an inhomogeneous line exhibits similar basic structure as MS and exhibits sideband peaks at multiples of basic radiofrequencies. Linewidths of these peaks are significantly narrower (cca. two - three orders of magnitude) than the inhomogeneous linewidth and can be correlated with the underlying homogeneous linewidth components on the basis of characteristic spin-lattice, T1, and spin-spin, T2, relaxation times. The capability to extract T1 and T2 from DMS was tested on the well-known E' defect in irradiated vitreous SiO2. The obtained results revealed the impact of "rapid passage" effect on DMS in improving the detection sensitivity of DMS in the study of paramagnetic centers with long relaxation times. Therefore, double modulation method can be considered as a complementary method for studying inhomegeneous broadening in the EPR spectra.

Spectral dependence of femtosecond laser induced circular optical properties in silica

Transmission Mueller-matrix spectroscopic ellipsometry is applied to study femtosecond laser induced nanogratings in silica glass in a wide spectral range 250–1800 nm. By using differential decomposition of the Mueller matrix, the circular birefringence and dichroism of femtosecond laser irradiated SiO2 are quantified for the first time in the UV and near-IR range. A maximum value of the effective specific rotation of α ∼ −860°/mm at 290 nm is found. In the near-IR range, we found a linear and circular dichroism band peaking around 1240 nm, which might be attributed to the formation of anisotropic species like the formation of oriented OH species and Si-O-Si bond.

Creation of glass-characteristic point defects in crystalline SiO2 by 2.5 MeV electrons and by fast neutrons

Point defects in crystalline SiO2, created by 2.5 MeV electron irradiation at dose below the amorphization threshold or by fast neutrons, were compared by luminescence spectroscopy. Oxygen dangling bonds (“non-bridging oxygen hole centers”, NBOHCs), peculiar to amorphous state of SiO2, were detected for the first time in electron-irradiated non-amorphized α-quartz crystal. Their presence may signal the formation of nucleation centers in crystal structure as the first step to radiation-induced amorphization. Compared to crystal, irradiated by 1019 cm−2 fast neutrons, their concentration was over 100 times lower, and their inhomogeneous broadening was at least 2.5 times smaller. Divalent silicons (“silicon oxygen deficiency centers”, SiODC(II)), inherent to oxygen-deficient or irradiated SiO2 glass, were detected in neutron-irradiated (1019 n/cm2) α-quartz but were not found after the electron irradiation. Radiation-induced interstitial O2 molecules, characteristic to irradiated glassy SiO2 and other oxide glasses, are found in α-quartz only after neutron irradiation. The oxygen atoms, displaced by the 2.5 MeV e− irradiation of α-quartz for fluences up to 1019 e−/cm2 evidently stays entirely in the peroxy linkage (Si-O-O-Si bond) form.

Photoluminescence and enhanced chemical reactivity of amorphous SiO2 films irradiated with high fluencies of 133-MeV Xe ions

SiO2/Si structures have been irradiated with 133 MeV Xe+17 ions at fluencies of (1010–5 × 1014) cm−2. The structure transformation and light-emitting properties of irradiated SiO2 films were studied using RS, SEM, TEM and PL techniques as well as chemical etching in 4% solution of hydrofluoric acid (HF). An intensive photoluminescence in visible range was registered from the samples irradiated at a fluence of 1014 cm−2 and higher. Simultaneously, it was found a drastic increase of SiO2 etch velocity in HF solution for the irradiated samples. Annealing (1100 °C, 2 h) of irradiated samples resulted in PL quenching and etch velocity recovery practically to the value of non-irradiated SiO2. It was concluded that radiative oxygen deficient centers are responsible for the PL appearance. It was also shown that the etch velocity ratio of the irradiated and virgin SiO2 in 4%-HF (Virr/Vvirgin) can be used in order to estimate the radiation damage in SiO2 matrix irradiated with high fluencies of swift heavy ions.

Nanoreinforced Concrete: Effect Of Gamma-irradiated SiO2 Nanoparticles

The effect of gamma-irradiated SiO2 nanoparticles on microstructure and mechanical properties of concrete was studied. SiO2 nanoparticles were irradiated at different irradiation doses (10, 50, 100 and 150 kGy) and then analyzed by transmission electron microscopy, Fourier-transform infrared and Raman spectroscopies. Such ionizing treatment allowed improving the physical interactions between the nanoparticles and the cementitious matrix. Compressive strength and dynamical modulus of elasticity on concrete samples were determined. The results show significant improvements on these mechanical features when irradiated SiO2 nanoparticles were added; having up to 127 % of improvement for compressive strength and a 24 % for elasticity modulus when comparing to non-irradiated nanoparticles-reinforced concrete. Such improvements are related to the microstructural changes of concrete analyzed by Infrared spectroscopy and observed by scanning electron microscopy. Research shows important advances in the development and understanding of microstructure for nanoreinforced concrete with irradiated SiO2 nanoparticles.

Effect of laser irradiation on the early-stage seed formation of laser-induced submicrometer-scale silica spheres

We describe the effect of irradiation on the early-stage seed formation of submicrometer-scale (SS) SiO2 spheres by a laser-induced process. A quartz cell containing chemical reagents was exposed to a pulsed laser (Nd:YAG, 532 nm) tuned to various energy densities, while SiO2 SS spheres are synthesized in the quartz cell by the Stöber, Fink, and Bohn method. Higher laser energy densities typically produce wider size distributions. In particular, bidisperse SiO2 spheres were obtained when the laser energy density was 1.15 J/cm2. The size distributions were widest with 1.15 J/cm2 and narrowest with 0.33 J/cm2 laser energy density. However, the compositions of the SiO2 SS spheres were not affected by laser irradiation, and we observed by the energy-dispersive X-ray spectroscopy that the compositions of the irradiated and nonirradiated SiO2 SS spheres were the same.

Electron Kinetics in Femtosecond X‐Ray Irradiated SiO2

AbstractA theoretical study of the ultrafast electron kinetics in solid SiO2, irradiated with a femtosecond X‐ray laser pulse, is presented. A Monte Carlo code for event‐by‐event simulations of individual particles is applied to model the electron kinetics within the irradiated SiO2 bulk. The simulation includes photoionization, elastic and inelastic scatterings of electrons, Auger decays of core holes, and electron‐hole recombination via exciton self‐trapping mechanism. Transient electron density is followed, at different photon energies and pulse durations. The change of the optical properties (reflectance, transmittance) of the material is estimated with the help of the Drude model. The analysis of the results allows us to conclude that within the X‐ray excited dielectric, the holes in the valence band give the predominant contribution to the transient changes of optical properties within the material. The increase rate of the free electron density is limited by the duration of secondary electron cascading. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Review of doped silica glass optical fibre: Their TL properties and potential applications in radiation therapy dosimetry

Review is made of dosimetric studies of Ge-doped SiO2 telecommunication fibre as a 1-D thermoluminescence (TL) system for therapeutic applications. To-date, the response of these fibres has been investigated for UV sources, superficial X-ray beam therapy facilities, a synchrotron microbeam facility, electron linear accelerators, protons, neutrons and alpha particles, covering the energy range from a few eV to several MeV. Dosimetric characteristics include, reproducibility, fading, dose response, reciprocity between TL yield and dose-rate and energy dependence. The fibres produce a flat response to fixed photon and electron doses to within better than 3% of the mean TL distribution. Irradiated Ge-doped SiO2 optical fibres show limited signal fading, with an average loss of TL signal of ∼0.4% per day. In terms of dose response, Ge-doped SiO2 optical fibres have been shown to provide linearity to x and electron doses, from a fraction of 1Gy up to 2kGy. The dosimeters have also been used in measuring photoelectron generation from iodinated contrast media; TL yields being some 60% greater in the presence of iodine than in its absence. The review is accompanied by previously unpublished data.

Nanoscale density fluctuations in swift heavy ion irradiated amorphous SiO2

We report on the observation of nanoscale density fluctuations in 2 μm thick amorphous SiO2 layers irradiated with 185 MeV Au ions. At high fluences, in excess of approximately 5 × 1012 ions/cm2, where the surface is completely covered by ion tracks, synchrotron small angle x-ray scattering measurements reveal the existence of a steady state of density fluctuations. In agreement with molecular dynamics simulations, this steady state is consistent with an ion track “annihilation” process, where high-density regions generated in the periphery of new tracks fill in low-density regions located at the center of existing tracks.

Raman scattering investigation of C-doped a-SiO2 after high energy heavy ion irradiations

Thermally grown amorphous SiO2 films were implanted at room temperature with 100 keV C-ions to 5.0×1017 or 1.2×1018 ions/cm2. These samples were irradiated at room temperature with 853 MeV Pb-ions to 5.0×1011, 1.0×1012, 5.0×1012 ions/cm2, or with 308 MeV Xe-ions to 1.0×1012, 1.0×1013, 1.0×1014 ions/cm2, respectively. Then the samples were investigated using micro-Raman spectroscopy. From the obtained Raman spectra, we deduced that Si—C bonds and sp2 carbon sites were created and nano-inclusions may also be produced in the heavy ion irradiated C-doped SiO2. Furthermore, some results show that Pb ion irradiations could produce larger size inclusions than Xe ions and the inclusion size decreased with increasing the irradiation fluence. The possible modification process of C-doped a-SiO2 under swift heavy ion irradiations was briefly discussed.

Spatially controlled dissolution of Ag nanoparticles in irradiated SiO 2 sol–gel film

In this paper, we report the spatially controlled dissolution of silver nanoparticles in irradiated SiO 2 sol–gel films. The Ag nanoparticles have been formed in the sol–gel solution before the film deposition by adding Triton and ascorbic acid and also after the film deposition using a heat treatment at 700 °C for few minutes or at 550 °C for 6 h in reducing atmosphere. Using a spectrometer, a new view white light interferometer and a micro-thermal analyzer, we demonstrate that the silver nanoparticles can be dissolved using a continuous black ray UV lamp or with a near-infrared (NIR) femtosecond laser, due to a significantly increase in the local temperature. We confirm that the micro-thermal analyzer can be used as a new tool to study the dissolution of metallic nanoparticles in thin film if located at the surface of the films.

S 29 i attribution of the 1.3 mT hyperfine structure of the E′γ centers in amorphous SiO2

We report an experimental investigation by electron paramagnetic resonance of the doublet of lines split by ∼1.3 mT and centered on the E′γ center resonance line in the spectrum of irradiated amorphous SiO2. Commercial and sol-gel materials, some of which subjected to hydrogen-deuterium exchange, were investigated. Exposure to γ or β rays at room temperature of the samples and subsequent thermal treatments were carried out to induce the defects and to study their thermal stability. In all the materials used the ratio between the signal of the E′γ centers and that of the 1.3 mT doublet is constant and independent of the OH and OD contents. Furthermore, the 1.3 mT doublet and the E′γ center feature similar thermal stability. These results support the attribution of the 1.3 mT doublet to the hyperfine interaction between the unpaired electron magnetic moment of the E′γ center and the nuclear magnetic moment of a second near neighboring S29i atom. Our results also suggest that the E′γ site needs an appropriate surrounding of S29i in back-bond configuration to experience this hyperfine interaction.

Energy dependent saturation width of swift heavy ion shaped embedded Au nanoparticles

The transformation of Au nanoparticles (NPs) embedded in SiO2 from spherical to rod-like shapes induced by swift heavy ion irradiation has been studied. Irradiation was performed with A197u ions at energies between 54 and 185 MeV. Transmission electron microscopy and small angle x-ray scattering measurements reveal an energy dependent saturation width of the NP rods as well as a minimum size required for the NPs to elongate. The NP saturation width is correlated with the ion track diameter in the SiO2. NP melting and in-plane strain in the irradiated SiO2 are discussed as potential mechanisms for the observed deformation.

High-Energy Heavy Ion Irradiation-Induced Structural Modifications: A Potential Physical Understanding of Latent Defects

From annealing experiments performed on both irradiated SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -Si structures and MOS devices, swift heavy ions-induced morphological oxide defects are proposed to possibly act as latent defects.

Measurement of latent tracks in amorphous SiO2 using small angle X-ray scattering

In this paper we present preliminary yet promising results on the measurement of latent ion tracks in amorphous, 2μm thick SiO2 layers using small angle X-ray scattering (SAXS). The tracks were generated by ion irradiation with 89MeV Au ions to fluences between 3×1010 and 3×1012ions/cm2. Transmission SAXS measurements show distinct scattering from the irradiated SiO2 as compared to the unirradiated material. Analysis of the SAXS spectra using a cylindrical model suggests a core–shell like density distribution in the ion tracks with a lower density core and a higher density shell as compared to unirradiated material. The total track radius of ∼48Å is in very good agreement with previous experiments and calculations based on an inelastic thermal spike model.

Electrochemical deposition of Te and electroless deposition of Se nanoparticles in etched tracks of Au + ions in SiO 2 layer on n-Si(1 0 0) wafers

The techniques for Te electrodeposition and Se electroless deposition into nanoporous SiO 2 layer on n-Si(1 0 0) substrate are developed. To produce a porous SiO 2 layer, scanned beams of 400 MeV Au + ions are employed for the bombardment of silicon oxide thermally grown on Si(1 0 0) substrate. Pores are formed by chemical etching of the irradiated SiO 2 layer in dilute HF. Etching results in the formation of the uniform pores randomly distributed over the surface and shaped like truncated cones with base diameters of 100 and 250 nm. Electrodeposition of Te into nanopores of SiO 2 layer takes place at potentials below the silicon flat band potential. Te electrodeposited selectively into the nanopores – deposition on insulating SiO 2 layer – is excluded. Electrodeposition of Se into nanopores takes no place due to Se reduction to H 2Se. Chemical interaction of H 2Se and H 2SeO 3 in the solution leads to the formation of roundish Se particles on SiO 2 surface near the pores. Precipitation of Se into nanopores is realized by electroless deposition from SeO 2 solution with addition of HF.

Electrochemical deposition of PbSe and CdTe nanoparticles onto p-Si(100) wafers and into nanopores in SiO 2/Si(100) structure

Electrochemical deposition of PbSe and CdTe nanoparticles onto p-Si(100) wafers and into nanopores in SiO 2 layer grown thermally on p-Si(100) substrates (SiO 2/Si(100) structure) under illumination was studied. To produce nanopores we used SiO 2 layer with tracks developed by irradiation of 350 MeV Au ions. Pores structure was formed by chemical etching of the irradiated SiO 2 layer in dilute HF. The pores were shaped like truncated cones with a base diameter of 200 and 250 nm and height of 200 nm. Photoelectrochemical deposition of PbSe and CdTe was carried out with constant cathodic potentials from the water solutions containing Pb 2+, Cd 2+ cations and H 2SeO 3, H 2TeO 3 acids. The potentials applied were more positive than the equilibrium E Me n+ /Me 0 redox potential. The underpotential deposition of Pb (or Cd) occurs only onto the co-deposited Se (or Te) atoms due to electrons photogenerated in Si substrate. The average sizes of PbSe and CdTe particles electrodeposited onto Si(100) wafers were dependent on the duration of electrodeposition, changing from 50 to 200 nm for PbSe and 30–80 nm for CdTe. According to XRD data, PbSe particles formed at ambient conditions had the crystalline structure. To deposit CdTe nanoparticles we used an electrolyte heated up to 80 °C. Variations in the electrodeposition time enabled one to form either separate chalcogenide particles or a polycrystalline film-like layer in case of electrodeposition onto p-Si(100) wafers and to control the degree of pore filling in case of electrodeposition into the nanopores of SiO 2/Si(100) structure.

Two mechanisms of crater formation in ultraviolet-pulsed-laser irradiated SiO2 thin films with artificial defects

Atomic force microscopy was employed to investigate the morphology of ultraviolet nanosecond-pulsed-laser damage in SiO2 thin films. Gold nanoparticles, 18.5-nm diameter, embedded in the film were used as calibrated absorbing defects. Damage-crater diameter, depth, and cross-sectional profiles were measured as a function of laser fluence and the lodging depth of gold nanoparticles. The results indicate that, at laser fluences close to the crater-formation threshold and for lodging depths of a few particle diameters, the dominating regime of the material removal is melting and evaporation. The morphology of craters initiated by deep absorbing defects, with a lodging depth larger than ∼10 particle diameters, clearly points to a two-stage material-removal mechanism. The process starts with the material melting within the narrow channel volume and, upon temperature and pressure buildup, film fracture takes place. Crater-diameter variation with lodging depth and laser fluence is compared with theoretical predictions.