Yong Wan

Binary colloidal crystals fabricated with a horizontal deposition method

We describe the use of a horizontal deposition method to prepare large-area binary colloidal crystals (bCCs). Two different sets of binary polystyrene spheres were employed to demonstrate the validity of this method. By varying the number ratios of small spheres with respect to large spheres, the stoichiometric configuration of the bCCs can be altered. Stable corresponding replica structures of the bCCs were also prepared, and the cross-sectional images of the binary inverse opals were obtained. Optical characterization demonstrated the presence of pseudostop bands, which were in agreement with the compositions of the material. The formation of the bCC by such a simple self-assembly method was attributed to the cooperative effect of interparticle electrostatic interactions and geometrical constrictions. This facile fabrication method further enhances the application potential of the bCCs and their inverse porous replicas with a binary pore system in the fields of photonics, solar cells, separations, catalysis, and biosensing.

Effect of the agglomeration of TiO2 nanoparticles on their photocatalytic performance in the aqueous phase

TiO(2) nanoparticles have been widely explored as photocatalysts in the degradation of organic matters present in water. However, spontaneous agglomeration of TiO(2) nanoparticles in a suspension is a crucial issue that must be addressed before the photocatalyst can be used for water treatment. In the present work, the nature of the agglomeration of TiO(2) nanoparticles in aqueous suspension was investigated. Two approaches to minimize the agglomeration of colloidal TiO(2) particles were investigated. A careful control over the pH of the system was found to be an effective method for stabilizing colloidal TiO(2) particles and to significantly enhance the adsorption of orange II. As a result, the overall photocatalytic degradation rate was greatly accelerated. In addition to pH control, modification of TiO(2) particles using polyelectrolyte poly allylamine hydrochloride (PAH) was observed to be an effective approach for preventing colloidal TiO(2) particles from agglomeration.

An improved convective self-assembly method for the fabrication of binary colloidal crystals and inverse structures

We report an improved convective self-assembly method for the fabrication of highly ordered, crack-free binary colloidal crystals (BCCs) and the associated inverse structures in large domains at length scales of several centimeters. With this method, BCCs can be fabricated in a non-close packed pattern and binary inverse opal films can be obtained over a centimeter scale. The presence of tetraethyl orthosilicate (TEOS) sol in the self-assembly system was found to play a significant role in the resultant structures. The pseudostop band positions are adjustable via varying the number ratio of small to large polystyrene (PS) spheres. At a given TEOS-to-PS ratio, the binary inverse opal film thickness was controllable by varying the colloidal volume fraction with an upper thickness threshold (>16 layers).

Vapor-phase silanization of oxidized porous silicon for stabilizing composition and photoluminescence

A vapor-phase deposition approach to the silanization modification of the oxidized porous silicon (PSi) surface using (CH3O)3Si(CH2)3NH2 has been exploited. Standard clean (SC)-1 (NH3H2O/H2O2/H2O, 1:1:5,v/v) and SC-2 [HCl/H2O2/H2O (1:1:6,v/v)] solutions are utilized for the first time to obtain oxidized PSi and have been proved to be a very efficient combination for creating Si–OH species on the PSi surface. After the modification, an amine group terminated surface was successfully created as demonstrated by the contact angle with water, the x-ray photoelectron spectroscopy, and the Fourier transform infrared (FTIR) spectra. The influences of the surface derivatives on the composition stability of the PSi layer and on its photoluminescence properties were investigated by means of FTIR spectra, photoluminescence spectra, and time-resolved photoluminescence measurements.

Spontaneous decoration of Au nanoparticles on micro-patterned reduced graphene oxide shaped by focused laser beam

We report a facile, two-step method for the micro-landscaping of Au nanoparticles(NPs) on reduced graphene oxide (rGO) film en route to micro-patterned Au(NPs)-rGO hybrid functional materials. This method employs a focused laser beam to first locally convert GO to rGO before immersing the micro-patterned GO-rGO film into HAuCl4 solution. The rGO micro-pattern, shaped by the focused laser beam, serves as nucleation sites for the reduction of Au ions. The reduction mechanism that governs the decoration of Au NPs on rGO films is akin to electroless deposition process. In this instance, surface charges that are formed during laser reduction of GO to rGO provide active nucleation sites for Au3+ ions to form Au NPs when HAuCl4 solution is introduced. The number density, the size, and size distribution of the Au NPs can thus be directly tuned and preferentially anchored onto the rGO micro-pattern by varying the incident laser power, the scanning speed of the laser, or the concentration of HAuCl4. The resulting h...

Significance of an in-situ generated boundary film on tribocorrosion behavior of polymer-metal sliding pair

Polymer composites have a high potential for applications as tribo-materials exposed to sea water owing to their self-lubrication characteristic and high chemical stability. In the present work, tribological behaviors of polyetheretherketone (PEEK) composites rubbing with stainless steel in sea water were explored using a pin-on-disc tribometer integrated with a potentiostat for electrochemical control. It was demonstrated that further adding 5 vol% hexagonal boron nitride (h-BN) nanoparticles into PEEK reinforced with short carbon fibers (SCF) significantly enhanced the wear resistance. Moreover, the stainless steel exhibited significantly enhanced tribocorrosion resistance when rubbing with the hybrid nanocomposite, in comparison to the sliding against PEEK filled only with SCF. Nanostructures of the boundary films formed on the steel surface were comprehensively investigated. It was manifested that tribo-chemistry products of h-BN, i.e. H3BO3 and B2O3, were arrayed in a closely packed boundary film. It seems that inclusion of layer-structured H3BO3 and B2O3 improved the resilience of the boundary film. The continuous boundary film covering the steel surface provided a lubrication effect and strengthened the passivation layer. A new route for enhancing simultaneously tribological and corrosion resistance of polymer-metal pairs by controlling in-situ tribo-chemistry was thus proposed.

Relation Between Crystal Structure and Electrochemical Performance of LiNi1/3ZnxCo1/3−xMn1/3O2 (0.000 ≤ x ≤ 0.133)

LiNi1/3ZnxCo1/3-xMn1/3O2 (0.000 ≤ x ≤ 0.133) hollow microspheres are synthesized using MnO2 hollow microspheres both as a self-template and Mn source. These hollow microspheres, ~4 μm in diameter, are composed of approximately 300 nm basic nanoparticles. The XRD patterns of LiNi1/3ZnxCo1/3-xMn1/3O2 were analyzed by the RIETAN-FP program, and the obtained samples have a layered α-NaFeO2 structure. Electrochemical performances of the samples were carried out between 2.5 V and 4.5 V. The behavior of the lattice parameters is consistent with Cycling performance and rate performance change with increase of x. Compared with the others, the sample of x = 0.133 exhibits a relatively superior electrochemical performance. The specific capacity of x = 0.133 was increased by 10.7% than no-doped. In addition, the cyclic voltammograms curves of the second cycle show no significant alteration compared with the first cycle and the electrochemical impedance of zinc doping sample showed smaller transfer resistance than the no-doping sample.

Structure Analysis and Fabrication of Binary Colloid Crystals

In this paper, the bandgap characteristics of binary colloidal crystals (BCCs) constructed with polystyrene (PS) particles are analyzed, and several binary colloidal crystals were fabricated, specifically the non-close packed structures with improved vertical deposit method. The SEM images and reflectance spectra of the structures exhibit fine orderly structures obtained.

Slow Light Effect of Photonic Crystal Waveguides by Adjusting Parameters of Crescent Scatterers

Crescent scatterers possess the properties of anisotropy and multiple degrees of freedom. With plane-wave expansion method (PWE), the slow light effect with high ngand low dispersion can be achieved by optimizing the structure parameters of photonic crystal waveguide with line defect, such as changing the radius of two circles and center distance. Slow light with low dispersion can be obtained by these methods, which implies that choosing suitable scatterers and adjusting their parameters can efficiently achieve slow light with high ng and low dispersion.

Fabrication of Colloidal Crystals on Different Patterned Silicon Substrates by Self-Assembly Method

Silica and polystyrene (PS) microspheres assembled on two quite different patterned silicon substrates, cross-like pillar pattern and eye-like pattern, respectively. The results indicated that the surface pattern imposes a predetermined lattice orientation in colloidal crystals (CCs). Other influent factors, such as microsphere size, the altitude of pattern and the concentration of colloidal suspension, may also play an important role on the self-assembly process.