Submicron Silica Spheres Research Articles

Highly Dispersed RuOOH Nanoparticles on Silica Spheres: An Efficient Photothermal Catalyst for Selective Aerobic Oxidation of Benzyl Alcohol

HighlightsUltrasmall RuOOH nanoparticles of 2–3 nm are loaded on submicron silica spheres and capable of activating molecular oxygen.Photothermal conversion efficiency of the supported RuOOH nanoparticles is nearly unity.Photothermal effect promotes selective oxidation of benzyl alcohol under the illumination of visible light.

High Reflectance of Artificial Opals and Engineering Applications

The artificial opals are three-dimensional photonic crystals (PCs) whose microspheres are arranged periodically in a face-centered-cubic (FCC) lattice. In this work, we investigated the reflective properties of artificial opals composed of submicron silica spheres. The finite-difference time-domain (FDTD) method for electromagnetics was used to calculate the directional–hemispherical reflectance spectra of artificial opals. Factors including structural parameters, filling dielectrics, and incident light were considered to study their effect on the reflectance. It is found that the shape, value, and position of peak of the reflectance spectra can be affected by these factors. Furthermore, by analyzing the distribution and propagation of the Poynting vectors at normal incidence of P-polarization, the high reflectance of artificial opals can be attributed to the fact that reflected light from parallel crystal face generates constructive interference to strengthen the total reflected beam. As to the engineering applications, we performed a detailed analysis of the detection sensitivity of artificial opals acting as a chemical sensor. It is found that the diameter of the spheres of artificial opals has a prominent influence on the detection sensitivity which is improved with the increase in the diameter of the spheres. This work will facilitate the design, manufacture, and application of artificial opals.

Ultrasonic cleaning optimization research for ultrasmooth optical substrate with artificial micron/submicron silica spheres

Micron and submicron scale artificial silica spheres were used to quantitatively detect the ultrasonic cleaning procedure for an ultrasmooth optical substrate. Silica spheres with sizes from 1 to 3 μm were explored to efficiently reduce the ultrasonic power for ultrasonic frequencies of 40, 80, and 120 kHz. On account of submicron silica spheres with sizes from 0.3 to 1.0 μm, the cleaning efficiencies for the ultrasonic frequencies of 170, 220, and 270 kHz were quantity evaluated, and the removal efficiency was effectively increased by employing a solution of NH4OH, H2O2, and deionized water with an optimized configuration. Furthermore, for the range from 40 to 270 kHz, according to investigations of the ultrasonic time, the particles’ removal process was explored during the ultrasonic treatments, and the damages of ultrasound on the ultrasmooth substrate within the ultrasonic time were also detected. The quantitative results give us many clues for realizing the optimization of an ultrasonic cleaning procedure for ultrasmooth optical substrates.

Stability in Air of Silver and Silver Oxide Nanoparticle Shells Deposited Over Silica Spheres Without Using Coupling Agents

The deposition of silver nanoparticles on the surface of silica was carried out using our simple, robust and rapid chemical method without surface modification of silica or added coupling agents. The process was carried out at room temperature using water/methanol mixtures, tetraethyl orthosilicate as Si source and silver nanoparticles (NPs) in a single-pot reaction. Using EDS, XRD, HRTEM and High Angle Annular Dark Field (HAADF) STEM characterization techniques, we have found the coexistence of silver NPs and silver oxides NPs anchored to the surface of sub-micron silica spheres, with Ag NPs predominating sizes around 2-3 nm approximately, and Ag2O NPs sizes over 10 nm.

Designing photonic band gaps in SiO<sub>2</sub>-based face-centered cubic-structured crystals

We designed face-centered cubic-structured (fcc) photonic crystals whose lattice parameters were tuned by varying the size of the constituent spherical silica particles in the range 100 to 520 nm. From wide-angle optical transmission investigations and Gaussian fitting of the absorbance spectra over UV-Vis-Near IR range, we found that in these crystals the Bragg wavelengths of the photonic band gaps (PBGs) corresponding to the reflected crystal planes linearly increase with the size of the spheres as expected. From this data, the average refractive index along the different crystal planes of the fcc structure was found to be in the 1.24 to 1.32 range. The Bragg wavelengths were tuned between 400 and 1100 nm. Thus, photonic crystals of the same structure can be designed to tune the Bragg wavelengths of PBGs by selecting the sphere size. These studies open up possibilities to design a new class of "smart" photonic crystals consisting of dielectric entities of sub-micron silica spheres with added functionality from magnetic or piezoelectric nanoparticles embedded in them.

Selection rules for Brillouin light scattering from eigenvibrations of a sphere

Selection rules governing Brillouin light scattering from the vibrational eigenmodes of a homogeneous, free-surface submicron sphere have been derived using group theory. The derivation is for the condition where the sphere diameter is of the order of the excitation light wavelength. Well-resolved spectral data obtained from Brillouin light scattering from submicron silica spheres provide experimental verification of the selection rules.

Influence of shape, adhension and simulated lung mechanics on amorphous silica nanoparticle toxicity

Prevailing theories suggest that acicular, or fiber-like, particles induce enhanced toxicity over isotropic material through hindrance of phagocyte-mediated clearance mechanisms and through the aggravation of proximal cells via mechanical interactions. Currently, the degree to which either of these mechanisms operates is not well understood. To gain a more fundamental understanding of acicular particle toxicity, we have synthesized submicron and nanoscale amorphous silica spheres and rods as model materials for shape-driven toxicological experimentation. To accentuate contributions from mechanical damage in vitro, exposure studies were performed in the presence and absence of simulated lung mechanics. To promote and mitigate cell–particle contact-mediated mechanical interactions, the adhesion of the particles to the cell membrane was respectively modified by the physisorption of fibronectin and chemisorption of the polyethylene glycol to the silica particle surface. Lactic acid dehydrogense (LDH) and interleukin (IL)-8 release were used as endpoints for cytotoxicity and inflammation, respectively. The results indicate that particle exposures in the presence of physiological stretch induce increased LDH release and IL-8 expression regardless of shape. Moreover, it is evident that shape-induced aggregation may play a significant role in mitigating particle clearance pathways.

Fabrication and photoluminescence properties of core-shell structured spherical SiO2@Gd2Ti2O7:Eu3+ phosphors

A sol-gel technique was used to prepare Gd2Ti2O7:Eu3+-coated submicron silica spheres (SiO2@Gd2Ti2O7:Eu3+). The resulted SiO2@Gd2Ti2O7:Eu3+ core-shell particles were characterized by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive x-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, as well as kinetic decays. The XRD results demonstrate that the Gd2Ti2O7:Eu3+ layers begin to crystallize on the SiO2 spheres after annealing at 800 °C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have perfect spherical shape with narrow size distribution (average size ∼620 nm), non-agglomeration, and smooth surface. The thickness of the Gd2Ti2O7:Eu3+ shells on the SiO2 cores could be easily tailored by varying the number of deposition cycles (60 nm for four deposition cycles). Under the irradiation of 310 nm ultraviolet, the SiO2@Gd2Ti2O7:Eu3+ samples show strong emission of Eu3+. For the samples annealed from 600 to 800 °C, the emission is dominated by 613 nm red emission ascribed to 5D0–7F2 transition of Eu3+, while for those annealed from 900 to 1000 °C, the emission is dominated by 588 nm orange emission due to 5D0–7F1 transition of Eu3+. The PL intensity of Eu3+ increases with increasing the annealing temperature and the number of coating cycles.

Two-dimensional nonclose-packed colloidal crystals formed by spincoating

We report a simple spin-coating technique for the production of monolayer nonclose-packed colloidal crystals. Dispersions of submicron silica spheres in triacrylate monomers are spincoated and polymerized to form two-dimensional colloidal crystal-polymer nanocomposites. By removing the polymer matrix, wafer-scale nonclose-packed colloidal crystals with high crystalline quality can be made. The technique is compatible with standard microfabrication and allows for the production of microstructures for potential devices. Normal-incidence reflectivity spectra in the visible and near-infrared regions show sharp peaks due to Bragg diffraction from the colloidal monolayers. The peak position matches with the theoretical prediction using scalar wave approximation.

Fabrication and optical properties of core–shell structured spherical SiO 2@GdVO 4:Eu 3+ phosphors via sol–gel process

Europium-doped nanocrystalline GdVO 4 phosphor layers were coated on the surface of preformed submicron silica spheres by sol–gel method. The resulted SiO 2@Gd 0.95Eu 0.05VO 4 core–shell particles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, low voltage cathodoluminescence (CL), time resolved PL spectra and kinetic decays. The XRD results demonstrate that the Gd 0.95Eu 0.05VO 4 layers begin to crystallize on the SiO 2 spheres after annealing at 600 °C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have spherical shape, narrow size distribution (average size ca. 600 nm), non-agglomeration. The thickness of the Gd 0.95Eu 0.05VO 4 shells on the SiO 2 cores could be easily tailored by varying the number of deposition cycles (50 nm for four deposition cycles). PL and CL show that the emissions are dominated by 5D 0– 7F 2 transition of Eu 3+ (618 nm, red). The PL and CL intensities of Eu 3+ increase with increasing the annealing temperature and the number of coating cycles. The optimum concentration for Eu 3+ was determined to be 5 mol% of Gd 3+ in GdVO 4 host.

Sol–Gel Fabrication and Photoluminescence Properties of SiO<SUB>2</SUB> @ Gd<SUB>2</SUB>O<SUB>3</SUB>: Eu<SUP>3+</SUP> Core–Shell Particles

A uniform nanolayer of europium-doped Gd2O3 was coated on the surface of preformed submicron silica spheres by a Pechini sol-gel process. The resulted SiO2 @ Gd2O3:Eu3+ core-shell structured phosphors were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), photoluminescence (PL) spectra as well as kinetic decays. The XRD results show that the Gd2O3:Eu3+ layers start to crystallize on the SiO2 spheres after annealing at 400 degrees C and the crystallinity increases with raising the annealing temperature. The core-shell phosphors possess perfect spherical shape with narrow size distribution (average size: 640 nm) and non-agglomeration. The thickness of the Gd2O3:Eu3+ shells on the SiO2 cores can be adjusted by changing the deposition cycles (70 nm for three deposition cycles). Under short UV excitation, the obtained SiO2@Gd2O3:Eu3+ particles show a strong red emission with 5D0-7F2 (610 nm) of Eu3+ as the most prominent group. The PL intensity of Eu3+ increases with increasing the annealing temperature and the number of coating cycles.

Plasma resonance of silver nanoparticles deposited on the surface of submicron silica spheres

Silver nanoparticles of 20 and 70 nm, respectively, were deposited on the surfaces of submicron silica spheres. Plasma resonances of the submicron silica spheres with dense and uniform silver layer were investigated using UV/vis absorption spectra. It was found that the silver plasma resonance band of the silica–silver core-shell spheres was broadened and shifted to longer wavelength several hundreds nanometers. The dipole–dipole interactions of neighboring silver particles and Mie scattering of silver shell as a whole may serve as the mechanism of such shift and broadening.

Surface-enhanced Raman spectra of substances adsorbed on Ag0 clusters deposited on SiO2 submicron spheres prepared by the sol–gel method

Submicron silica spheres containing silver nanoparticles on their surfaces have been obtained by the sol–gel technology. The silver-doped matrices were immersed in solutions of various substances enabling the solute molecules to interact with surfaces of the Ag 0 -doped silica spheres. Raman spectra of the Ag 0 -doped matrices after impregnation in solutions of the solute molecules have been measured. The impregnated silica matrices which did not contain silver nanoparticles were used as a reference. These experiments have been performed in order to establish whether Raman signal enhancement could be obtained by adsorption of various solute molecules on the surface of Ag 0 inclusions in the sol–gel matrices analogously to the standard surface-enhanced Raman spectroscopy (SERS) method.

Nonlinear dispersion properties of subwavelength photonic crystals

Nonlinear pulse compression and pulse broadening have been analyzed and demonstrated with a coherent array of submicron silica spheres embedded with silicon and germanium nanoparticles (nano within a nano).

Linear and nonlinear optical properties of erbium-implanted coherent array of submicron silica spheres

A coherent array of silica spheres, which was implanted with erbium ions, showed nonlinear behavior at λ=0.532 μm. This was attributed to a large nonlinear refraction effect, which was enhanced by the structure of the opaline matrix. In addition, near infrared photoluminescence measurements showed an overall enhancement as a function of the sphere’s size. A large photoluminescence peak was found around λ=900 nm and attributed to the lensing effect of the opaline matrix.

Thickness Dependence of the Optical Properties of Ordered Silica-Air and Air-Polymer Photonic Crystals

We report observations of the optical stop band of periodic planar arrays of submicron silica spheres, and of macroporous polymers grown from these silica templates. The stop-band width and peak attenuation depend on the number of layers and on the dielectric contrast between the spheres and the interstitial regions, both of which are experimentally controlled. The results are compared to the predictions of the scalar wave approximation. This is the first systematic study of the thickness dependence of the stop band in colloidal photonic band gap structures.

Optical gain of CdS quantum dots embedded in 3D photonic crystals

Three-dimensional photonic crystals used in this study were synthetic opals, composed of submicron silica spheres, close-packed in a face-centered cubic lattice with a period of 200 nm, which exhibit a photonic gap around 600 nm. We report on the first observation of optical gain enhancement in semiconductor quantum dots embedded in a photonic crystal caused by modifications of light–matter interaction at the edges of the photonic gap.

Optical gain and lasing in a semiconductor embedded in a three-dimensional photonic crystal

Three-dimensional photonic crystals used in this study were synthetic opals, composed of submicron silica spheres, close-packed in a face-centered cubic structure with a period of 200 nm, which exhibit photonic stop-bands around 600 nm. We report on a substantial optical gain in CdS nanocrystals embedded inside the interstitials between the silica spheres. It is found that the optical gain is enhanced at the edges of the photonic gap due to multiple coherent Bragg scattering of light in the periodic photonic crystal. The latter provides an efficient feedback mechanism for lasing action.

Enhancement of optical gain of semiconductors embedded in three-dimensional photonic crystals

The three-dimensional photonic crystals used in this study were synthetic opals, composed of submicron silica spheres, close-packed in a face-centered cubic structure with a period of 200 nm, that exhibit photonic stopbands around 600 nm. We present measurements of the optical gain of CdS quantum dots (QDs) embedded inside the interstitials between the silica spheres. Unlike the usual gain spectra of CdS QDs in glass matrices, which display maximum gain at energies of the first quantum-confined transitions, for QDs embedded in photonic crystals the gain maximum is shifted toward the high-frequency edge of the photonic stopband (2.2 eV) far below the absorption edge of the semiconductor (2.5 eV). Studies of temperature, intensity, and orientation dependencies of the gain spectra allow one to ascribe the observed effect to gain enhancement caused by multiple coherent Bragg scattering of light in the periodic photonic crystal.

Viscoelastic behavior of concentrated spherical suspensions

Experimental results on the linear viscoelastic behavior of concentrated suspensions are presented. The materials studies were prepared by dispersing submicron silica spheres at volume fractions φ ranging from 0.3 to 0.6, in a highly viscous liquid. The response to oscillatory shearing was determined over a wide range of frequency, ω. The zero frequency viscosity η0 and the limiting high‐frequency viscosity η’∞ for all particle radii studied were essentially identical to results previously obtained for suspensions having hard sphere interactions. In this range of concentrations, the frequency dependence of the dynamic moduli, G’ and G‘−ωη’∞, appears to be described by universal functions of ωτw where τw is the mean longest relaxation time proportional to a characteristic (Peclet) time defined as τp=a2/6Ds(φ). Herein a denotes the particle radius and Ds(φ) is a φ dependent short‐time self‐diffusion constant. We also found that at sufficiently high frequencies, G’ has a plateau, G∞, that is given by kT/a3 t...