Submicrometer Spheres Research Articles

Fabrication of Iron Oxide Core/Gold Shell Submicrometer Spheres with Nanoscale Surface Roughness for Efficient Surface-Enhanced Raman Scattering

A method to synthesize Fe3O4 core/Au shell submicrometer structures with very rough surfaces on the nanoscale is reported. The Fe3O4 particles were first modified with uniform polymers through the layer-by-layer technique and then adsorbed a lot of gold nanoseeds for further Au shell formation. The shell was composed of a large number of irregular nanoscale Au particles arranged randomly, and there were well-defined boundaries between these Au nanoparticles. The Fe3O4 core/Au shell particles showed strong plasmon resonance absorption in the near-infrared range, and can be separated quickly from solution by an external magnet. This kind of very rough Fe3O4 core/Au shell multicomponent was used in the adsorption of 4-aminothiophenol and as a substrate for detection by surface-enhanced Raman spectroscopy.

Facile Synthesis, Characterization, and Microwave Absorbability of CoO Nanobelts and Submicrometer Spheres

Single crystal CoO nanobelts with thicknesses of several nanometers and widths of 30−100 nm and polycrystalline CoO submicrometer spheres self-assembled by nanoparticles with diameters ranging from 20 to 40 nm were synthesized via a microemulsion method under solvothermal conditions. The shape and size of CoO nanostuctures can be well controlled by H2O/surfactant molar ratio and other solvothermal parameters. Apart from structural and morpholoical characterizations of the submicrometer spheres and the nanobelts, powder X-ray diffraction, electron microscopy techniques, and microwave absorption properties of typical samples have also been investigated. The results indicate that the microwave absorption of nanobelts is stronger than that of submicrometer spheres.

Photoluminescence and Microstructure Investigation of SiO2@Y:Eu Photonic Bandgap Crystals

A photonic bandgap (PBG) crystal was established by self-assembly of monodispersed SiO2 submicrometer spheres. SiO2@Y2O5/or Y2SiO5:Eu3+ phosphors were then prepared by coating of Y3+ and Eu3+ at various concentrations on SiO2 PBG crystal templates. After calcination, red emission was obtained. In this study, the photoluminescent properties varied with different SiO2 sizes (periodicity of the PBG crystal), structure (ordered or random arrangement), and different calcination temperatures. Apparent enhancement of emission can be obtained in the phosphor with an ordered PBG crystal character because of the band-edge effect. Transmission electron microscopy cross-sectional images showed a core–shell structure of SiO2@Y2O3/or Y2SiO5:Eu3+ with a uniform 4–10 nm thickness of the crystalline shell layer.

BiVO 4/Bi 2O 3 submicrometer sphere composite: Microstructure and photocatalytic activity under visible-light irradiation

Bismuth vanadate (BiVO 4) powders were synthesized by homogeneous precipitation method with different surface dispersants. Bi(NO 3) 3·5H 2O and NH 4VO 3 were utilized as starting materials to synthesize BiVO 4 particles with the edge length of about 100–150 nm. Bismuth oxide (Bi 2O 3) was prepared by decomposing Bi(NO 3) 3·5H 2O at 600 °C. Techniques of X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and ultraviolet–visible diffuse reflectance spectra (UV–vis DRS) have been employed to characterize the as-synthesized materials. The results showed that the structure and morphology of BiVO 4 were various using different surface dispersant. We have also investigated the photocatalytic degradation of rhodamin B which showed that BiVO 4/Bi 2O 3 possessed a high photocatalytic activity under visible-light irradiation. The photocatalytic activity is in close relation with the surface dispersant about BiVO 4 synthesis. The result was better using N,N-dimethylacetamide (DMA) than using N-methyl-2-pyrrolidone. The inverse proportion between BiVO 4 and Bi 2O 3 was also important for the photocatalysis.

Stibnite inverse opal

A 3D photonic crystal (PhC), synthetic opal, has been constructed by self-assembly of sub-micrometre silica spheres and designed for operation in the visible spectral range. Because of its low refractive index contrast (RIC), this PhC does not exhibit a full photonic band gap (PBG), but this property could be achieved by increasing sufficiently the RIC. It is not easy to find a high refractive index material that is transparent in the visible spectral range, but we report here on a method for producing 3D PhC structures with increased RIC, using incorporation of stibnite (Sb 2 S 3 ) into a silica opal PhC. The template is infiltrated with the precursor (Sb[CS(NH 2 ) 2 ] 3 Cl 3 ), with subsequent thermal decomposition at 600degC to form Sb 2 S 3 in the voids of the opal PhC. Formation of Sb 2 S 3 and removal of silica spheres by a chemical etching process can produce a structure that exhibits a full PBG in the visible spectral range. The optical properties of the inverse Sb 2 S 3 opal have been measured and compared with theoretical calculations.

The Effect of Silica Coating on the Optical Response of Sub-micrometer Gold Spheres

The effects derived from the growth of silica shells on the optical properties of sub-micrometer gold spheres have been investigated as a function of shell thickness. The dipole plasmon resonance mode of these large spheres has been found to be significantly more sensitive to changes in the medium refractive index than the quadrupolar mode, in agreement with theoretical modeling based on the boundary element method (BEM) for concentric spheres. Near-field maps of both resonance modes in such coated nanoparticles show that the areas with significant near-field enhancement get progressively located within the silica shell as its thickness increases, with basically no enhancement outside of the shell when this is thicker than the sphere radius.

Permanent tuning of the opal stop-band with the application of uniaxial pressure

Three-dimensional photonic crystals have been prepared by self-assembly from sub-micrometre polystyrene spheres. Such crystals are known as a synthetic opal and possess a partial stop-band in the direction. The stop-band is tuned towards the shorter wavelengths by applying uniaxial pressure along the direction of the face-centred cubic opal structure. The tuning is found to be irreversible and it was also observed that the normalized stop-bandwidth increased after applying uniaxial pressure. The experimental results are compared with the simulation results and found to be in very close agreement.

Novel one-step route for synthesizing sub-micrometer PSt hollow spheres via redox interfacial-initiated method in inversed emulsion

Interfacial-initiated polymerization of styrene (St) was carried out in inversed emulsion with cumene hydroperoxide (CHPO) and ferrous sulfate (FeSO 4)/disodium ethylenediaminetetraacetate (NaEDTA)/sodium formaldehyde sulfoxylate (SFS) as the redox initiation system. The water-soluble Fe 2+–NaEDTA–SFS acted as the reducing component and the oil-soluble CHPO as the oxidant component of the redox initiation system. Therefore, the primary radicals were produced mainly at the oil/water interface to initiate the polymerization of St. Thus, sub-micrometer hollow polystyrene (PSt) spheres were obtained by one-stage polymerization, which was supported by the techniques of transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM).

Preparation of ordered porous NaCl and KCl crystals

Solids of NaCl (or KCl) containing macropores (∼380 nm in diameter) ordered in the face centered cubic manner were prepared by co-deposition of NaCl (or KCl) and organic colloids in water, followed by the removal of the polymer by calcination at 550 °C. These pore crystals showed the characteristics of an optically gapped material. The pores worked as a template to prepare submicrometer spheres of a liquid crystal, 5 OCB, and also a wax which are difficult to form spheres in usual conditions.

Functionalized magnetic micro‐ and nanoparticles: Optimization and application to μ‐chip tryptic digestion

The preparation of an easily replaceable protease microreactor for micro-chip application is described. Magnetic particles coated with poly(N-isopropylacrylamide), polystyrene, poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate), poly(glycidyl methacrylate), [(2-amino-ethyl)hydroxymethylen]biphosphonic acid, or alginic acid with immobilized trypsin were utilized for heterogeneous digestion. The properties were optimized, with the constraint of allowing immobilization in a microchannel by a magnetic field gradient. To obtain the highest digestion efficiency, sub-micrometer spheres were organized by an inhomogeneous external magnetic field perpendicularly to the direction of the channel. Kinetic parameters of the enzyme reactor immobilized in micro-chip capillary (micro-chip immobilized magnetic enzyme reactor (IMER)) were determined. The capability of the proteolytic reactor was demonstrated by five model (glyco)proteins ranging in molecular mass from 4.3 to 150 kDa. Digestion efficiency of proteins in various conformations was investigated using SDS-PAGE, HPCE, RP-HPLC, and MS. The compatibility of the micro-chip IMER system with total and limited proteolysis of high-molecular-weight (glyco)proteins was confirmed. It opens the route to automated, high-throughput proteomic micro-chip devices.

Fabrication and magnetic properties of hierarchical porous hollow nickel microspheres

Hierarchical porous hollow nickel microspheres with nickel nanoparticles as the in situ formed building units have been fabricated via a novel precursor hydrothermal redox method in alkaline solution of KBH4. The microspheres exhibit enhanced coercivity and remanent magnetization as compared with hollow nickel submicrometer spheres, hollow nickel nanospheres, bulk nickel, and free Ni nanoparticles. Investigations have demonstrated that the enhancement is attributed to the hierarchical porous hollow structure, while the hierarchical structure has little influence on saturation magnetization.

Synthesis and characterization of poly(methyl methacrylate) obtained by ultrasonic irradiation

AbstractWe have studied the influence of surfactant nature and concentration, and monomer concentration on the synthesis of poly(methyl methacrylate) (PMMA) using high-frequency ultrasound. Polymerization was carried out via free radicals from aqueous solutions with several concentrations of an anionic (sodium lauryl sulfate, SLS) or a cationic surfactant (cetyltrimethylammonium bromide, CTAB) and different concentrations of the insoluble monomer methyl methacrylate (MMA) as the dispersed phase. The polymer particles obtained were characterized by FTIR, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The IR spectra show the presence of the characteristic absorption bands for PMMA when SLS was used. When CTAB was employed, for all surfactant concentrations and high monomer concentration (14% v/v), PMMA was obtained. However, bands of the surfactant were present for lower monomer concentrations. The glass transition temperature measured by DSC was in the range 106 - 126°C characteristic of PMMA. Maximum conversion was obtained when the anionic surfactant was employed. SEM studies show the formation of sub-micrometric PMMA latex spheres with average particle size from 65 to 100 nm when the anionic surfactant was used and 65 nm - 0.3 μm for the cationic surfactant.

The spectrum of vibration modes in soft opals

Numerous vibrational modes of spherical submicrometer particles in fabricated soft opals are experimentally detected by Brillouin light scattering and theoretically identified by their spherical harmonics by means of single-phonon scattering-cross-section calculations. The particle size polydispersity is reflected in the line shape of the low-frequency modes, whereas lattice vibrations are probably responsible for the observed overdamped transverse mode.

Polymorphic tin dioxide synthesis via sol–gel mineralization of ethyl–cyanoethyl cellulose lyotropic liquid crystals

The polymorphic tin dioxide (SnO2) was synthesized by calcinating the sol–gel mineralized hybrid of the tin source solution (SnCl4/ethanol/H2O) and the lyotropic liquid crystal of ethyl–cyanoethyl cellulose((E-CE)C)/acrylic acid (AA). The sub-micrometer SnO2 spheres with bimodal distribution at 370 and 860 nm were obtained after calcinating the hybrid at 400°C for 5 h. When the hybrid was exposed to ultraviolet first and then calcinated the flying-saucer-like SnO2 was formed. The exposure time was found to influence the morphology of the as-prepared SnO2. Except for the spherical and the flying-saucer-like SnO2, a small amount of well-developed polyhedral SnO2 was also observed in the as-prepared samples. On this basis, the lyotropic liquid crystal of (E-CE)C/AA afforded a novel route to obtain polymorphic SnO2.

A facile colloidal templating method to monodisperse hollow Ag and Ag/Au submicrometer spheres

Monodisperse hollow Ag and Ag/Au submicrometer spheres have been synthesized by a facile colloidal templating method. In this method, the silver nanoparticle seeds are synthesized on the silica colloids surface through the electroless plating approach to avoid the complex surface functionalization, and the subsequent seeding growth and dissolving silica core are carried out simultaneously. The as-prepared hollow spheres remain mostly the fine monodispersity and spheric shape of the silica core, and can self-assemble directly into ordered structure, which is realized for the first time. The method is simple and versatile, and can be used to prepare other monodisperse hollow composite metallic or bimetallic spheres.

Submicrometer Cavity Surface Plasmon Sensors

A miniaturized spherical surface plasmon sensor for measuring the binding kinetics of unlabeled molecules is introduced. The sensor has a submicrometer footprint with a sensitivity that rivals that of state-of-the-art commercial planar surface plasmon sensors, which makes it valuable for applications requiring integration of detection of molecular species in microfluidic channels. The basic principle of the sensor is exploiting the wavelength shifts of the cavity resonances of a metal-coated submicrometer sphere embedded in an opaque metal film due to molecular adsorption. The sensor has been found to be exquisitely responsive in air to water and ethanol vapor adsorption on the bare gold sensor surface. When immersed in a liquid, the sensor can detect the adsorption of less than one monolayer of dodecanethiol (approximately 1.5 nm) on the gold coating of the sphere.

Wetting of Regularly Structured Gold Surfaces

In this study we report results for a systematic study of the wetting of structured gold surfaces formed by electrodeposition through monolayer templates of close-packed uniform submicrometer spheres. Removal of the template after deposition leaves a regular hexagonal array of sphere segment pores where the depth of the pores and, thus, the topography of the surface are controlled by the thickness of gold deposited through the template. We find that, as the thickness of the porous film increases up to the radius of the pores, the apparent contact angle for water on the surface increases from 70 degrees on the flat surface to more that 130 degrees , and then with increasing thickness above the radius of the pores the apparent contact angle decreases back toward 70 degrees . We show that these changes in the apparent contact angle agree with the model of Cassie and Baxter for nonwetted surfaces even though the gold itself is hydrophilic. We also show that the apparent contact angle is independent of the diameter of the pores over the range 400-800 nm. This is the first reported example showing the change of a hydrophilic surface (theta; < 90 degrees ) into a hydrophobic surface (theta; > 90 degrees ) purely by control of the surface topography. The role of the pore shape and size in stabilizing the nonwetting (Cassie-Baxter) droplet on the surface is discussed.

Preparation and characterization of silica–silver core-shell structural submicrometer spheres

Dense, uniform and thickness controllable silver layers were successfully coated on the mono-dispersed submicrometer silica spheres to obtain silica–silver core-shell structural spheres. The growth process of nanoscaled silver layer on silica spheres mainly includes two steps, i.e. nanoscaled nuclei formation and controllable layer growth process. The nuclear-growth mechanism is responsible for the deposition processes. The reagent concentrations and reaction time were found to be the key factors for the formation of controllable silver layer. High quality silver layer with dense and uniform structure was verified by transmission electron microscopy, X-ray diffraction and Energy Dispersive X-ray microanalysis.

Direct sulfidization synthesis of high-quality binary sulfides (WS 2, MoS 2, and V 5S 8) from the respective oxides

High-quality binary sulfides WS 2, MoS 2, and V 5S 8 have been prepared via a direct sulfidization route from the respective oxides, using NH 3·H 2O and CS 2 as starting materials to produce H 2S acting as sulfur source. Characterizations by X-ray powder diffraction and X-ray photoelectron spectra suggest that all three sulfides have the pure phases and stoichiometric compositions as expected. Flaky WS 2 and V 5S 8 with irregular shapes are determined by transmission electron microscopy. In particular, MoS 2 submicrometer spheres with the yield of ca. 100% are observed by field-emission scanning electron microscopy. It is found that the reaction temperature plays an important role in the reaction system. A possible mechanism is proposed.

Formation of Hollow Submicrometer Spheres of Nickel Selenides

Abstract Hollow submicrometer spheres of nickel selenides have been successfully prepared via sodium dodecyl sulfate (SDS)-assisted hydrothermal reduction route in which aqueous hydrazine was used as a reducing agent and the surfactant SDS was used as a structure-directing agent.