Size Of Polystyrene Spheres Research Articles

Patterned Nanoparticle Arrays Fabricated Using Liquid Film Rupture Self-Assembly.

Self-assembly is an important bottom-up fabrication approach based on accurate manipulation of solid-air-liquid interfaces to construct microscale structures using nanoscale materials. This approach plays a substantial role in the fabrication of microsensors, nanosensors, and actuators. Improving the controllability of self-assembly to realize large-scale regular micro/nano patterns is crucial for this approach's further development and wider applications. Herein, we propose a novel strategy for patterning nanoparticle arrays on soft substrates. This strategy is based on a unique process of liquid film rupture self-assembly that is convenient, precise, and cost-efficient for mass manufacturing. This approach involves two key steps. First, suspended liquid films comprising monolayer polystyrene (PS) spheres are realized via liquid-air interface self-assembly over prepatterned microstructures. Second, these suspended liquid films are ruptured in a controlled manner to induce the self-assembly of internal PS spheres around the morphological edges of the underlying microstructures. This nanoparticle array patterning method is comprehensively investigated in terms of the effect of the PS sphere size, morphological effect of the microstructured substrate, key factors influencing liquid film-rupture self-assembly, and optical transmittance of the fabricated samples. A maximum rupture rate of 95.4% was achieved with an optimized geometric and dimensional design. Compared with other nanoparticle-based self-assembly methods used to form patterned arrays, the proposed approach reduces the waste of nanoparticles substantially because all nanoparticles self-assemble around the prepatterned microstructures. More nanoparticles assemble to form prepatterned arrays, which could strengthen the nanoparticle array network without affecting the initial features of prepatterned microstructures.

Releasing the Bubbles: Nanotopographical Electrocatalyst Design for Efficient Photoelectrochemical Hydrogen Production in Microgravity Environment.

Photoelectrochemical devices integrate the processes of light absorption, charge separation, and catalysis for chemical synthesis. The monolithic design is interesting for space applications, where weight and volume constraints predominate. Hindered gas bubble desorption and the lack of macroconvection processes in reduced gravitation, however, limit its application in space. Physico‐chemical modifications of the electrode surface are required to induce gas bubble desorption and ensure continuous device operation. A detailed investigation of the electrocatalyst nanostructure design for light‐assisted hydrogen production in microgravity environment is described. p‐InP coated with a rhodium (Rh) electrocatalyst layer fabricated by shadow nanosphere lithography is used as a model device. Rh is deposited via physical vapor deposition (PVD) or photoelectrodeposition through a mask of polystyrene (PS) particles. It is observed that the PS sphere size and electrocatalyst deposition technique alter the electrode surface wettability significantly, controlling hydrogen gas bubble detachment and photocurrent–voltage characteristics. The highest, most stable current density of 37.8 mA cm−2 is achieved by depositing Rh via PVD through 784 nm sized PS particles. The increased hydrophilicity of the photoelectrode results in small gas bubble contact angles and weak frictional forces at the solid–gas interface which cause enhanced gas bubble detachment and enhanced device efficiency.

Potentiometric Hydrogen Sensing of Ordered SnO2 Porous Thin Films

Introduction The sensing performance of mixed-potential gas sensors is highly dependent on the electrode microstructure. Recently, much effort has been made to improve the sensor performance by engineering of the electrode microstructure [1, 2]. Nevertheless, the different microstructure parameters, such as thickness, porosity, and three phase boundary (TPB), contribute jointly to the sensing response, and their respective contributions are usually difficult to identify. Thus, deviation of the apparent sensor behavior from the reality is usually unable to judge due to the uncertain effect of electrode catalytic reaction. In order to unravel the true response behavior, it would be necessary to reduce or minimize impact of the electrode diffusion-reaction process and control the microstructure, which could be achieved by using a very thin electrode with well-defined and controllable morphology. Herein, we fabricated thin ordered SnO2 sensing electrodes on YSZ substrate by employing a Polystyrene (PS) sphere-template method [3]. By varying the PS sphere diameter, three sensors of different electrode thickness and electrode/electrolyte interface were obtained. The gas sensing characteristics of the sensors were systematically studied. The sensing behavior was discussed in relation to variation of the electrode process and TPB density. Sensor fabrication and characterization As depicted in Figure 1, highly-ordered porous thin film sensors were prepared by using PS sphere templates in 200 nm, 500 nm and 1000 nm diameters. SEM, TEM and AFM images of SnO2 porous film electrodes were presented in Figure 2. Periodically ordered films of inverse opal structure were observed, with uniform circular pore openings and interconnected walls as the skeleton. Each film was porous and a homogenous assembly of 10-20 nm sized particles. The wall height was roughly half of the PS sphere size, which increased from 121 nm to 248 nm and 448 nm for the three PF films. Sensing performance Figure 3a and b show the response values and response time of the three PF sensors as a function of hydrogen concentration at 500 °C. Obviously, the response significantly increased, i.e., became more negative, with decreasing template diameters, while the response time of the three sensors was short and generally rather close to each other, with a value of 4.5 s-6 s for 500 ppm H2 at 500 °C. Figure 3c displays the cross-sensitivities of the PF sensors to 100 ppm various gases at 450 °C. The PF sensors exhibited much poorer H2 selectivity than regular thick film sensors [4].The small film thickness and porous nature of the PF SE are highly favorable for the gas transport from the gas phase to the TPB, which are beneficial to the response kinetics. That the three PF sensors exhibited very close response time despite their minor difference in the film thickness, suggesting absence of significant electrode process and large H2 concentration reduction. This may allow us to study the effect of the TPB density on the sensing response. The TPB length was thus estimated for the PF sensors (Figure 4a). Clearly, the TPB density increased from 56.8 μm-1 to 89.7 μm-1 with the decreasing template diameters. It can also be seen that for each H2 concentration, the response increased (became more negative) monotonically with increasing TPB density (Figure 4b-c). It should be noted that thin film favors fast response kinetics and large response but may be disadvantageous to the selectivity. To achieve good overall sensing performance, e.g., fast response kinetics, large response, and high selectivity, careful tuning of the film thickness and TPB density would be demanded.

Potentiometric Hydrogen Sensing of Ultrathin Highly-Ordered SnO2 Films

Introduction The sensing performance of mixed-potential gas sensors is highly dependent on the electrode microstructure. Recently, much effort has been made to improve the sensor performance by engineering of the electrode microstructure [1, 2]. Nevertheless, the different microstructure parameters, such as thickness, porosity, and three phase boundary (TPB), contribute jointly to the sensing response, and their respective contributions are usually difficult to identify. In order to shed light on the role of TPB, it is crucial to minimize the influence of the diffusion-reaction process occurring inside the electrode, which could be achieved by using a very thin electrode. Moreover, a highly-ordered electrode morphology may help obtain well-defined TPB. Herein, we fabricated sub-micron thick ordered SnO2 sensing electrodes on YSZ substrate by employing a Polystyrene (PS) sphere-template method [3]. Three sensors were obtained by using PS spheres of different diameters in order to vary the TPB density. The gas sensing characteristics of the sensors were systematically studied. The sensing behavior was discussed in relation to the electrode microstructure. Sensor fabrication and characterization As depicted in Figure 1, ultrathin highly-ordered porous film sensors were prepared by using PS sphere templates in 200 nm, 500 nm and 1000 nm diameters. SEM, TEM and AFM images of SnO2 porous film electrodes were presented in Figure 2. Periodically ordered films of inverse opal structure were observed, with uniform circular pore openings and interconnected walls as the skeleton. Each film was porous and a homogenous assembly of 10-20 nm sized particles. The wall height was roughly half of the PS sphere size, which increased from 121 nm to 248 nm and 448 nm for the three PF film electrodes. Sensing performance Figure 3a and b show the response values and response time of the three PF sensors as a function of hydrogen concentration at 500°C. Obviously, the response significantly increased, i.e., became more negative, with decreasing template diameters, while the response time of the three sensors was generally rather close to each other, with a value of 4.5 s-6 s for 500 ppm H2 at 500°C. Figure 3c displays the cross-sensitivities of the PF sensors to 100 ppm various gases at 450°C. The PF sensors exhibited much poorer H2 selectivity than regular thick film sensors [4].The ultra-small film thickness and porous nature of the PF SE are highly favorable for the gas transport from the gas phase to the TPB. The three PF sensors exhibited very close response time despite their minor difference in the film thickness (in the order of hundreds of nanometer), suggesting absence of significant electrode process and of large H2 concentration reduction. This may allow us to study the effect of the TPB density on the sensing response. The TPB length was thus estimated for the PF sensors. Clearly, the TPB density values increased with the decrease of the PS template diameter. It can also be seen that for each H2 concentration, the response indeed increased (became more negative) monotonically with increasing TPB density (Figure 4). It should be noted, however, that the ultra-thin film electrode was disadvantageous to the selectivity. To achieve good overall sensing performance, e.g., fast response kinetics, large response, and high selectivity, careful tuning of the film thickness and TPB density would be demanded.

High performance microwave absorption through multi-scale metacomposite by intergrating Ni@C nanocapsules with millimetric polystyrene sphere

We demonstrated the desirable microwave absorption properties in a 3D Ni@C/polystyrene (PS) sphere metacomposite, originated from the electromagnetic transform between the permittivity and the permeability. The metacomposite is composed of an array of millimetric PS spheres coated by high-performance Ni@C nanocapsule microwave absorbents. Such a phenomenon is caused by the near-field electromagnetic interaction, modeled by a theoretical simulation, resulting in the reciprocal resonances for the dielectric and magnetic loss factors. The resonance frequencies are proportional to the PS sphere size. This study provides a bottom-up strategy to fabricate the metacomposite and meanwhile has important implications in understanding the electromagnetic transformation.

Synthesis of three-dimensionally ordered macroporous LaFe0.7Co0.3O3 perovskites and their performance for chemical-looping steam reforming of methane

Three-dimensionally ordered macroporous (3DOM) LaFe0.7Co0.3O3 perovskite-type oxides were synthesized using a polystyrene (PS) colloidal crystal templating method. The obtained 3DOM LaFe0.7Co0.3O3 perovskites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Brunauere-Emmette-Teller (BET) surface area. Its performance as oxygen carriers in chemical looping steam methane reforming (CL-SMR) to produce syngas (H2 + CO) and hydrogen were investigated in a fixed-bed reactor. The size of PS spheres obviously increases as the styrene addition increases. The calcination temperature is the major factor to affect the prepared 3DOM perovskite. SEM and TEM analysis show that the samples calcined at 500, 800 and 850°C exhibit good 3DOM structures which collapse when the sample is calcined at 900°C. XRD results suggest that the obtained 3DOM LaFe0.7Co0.3O3 perovskites are pure crystalline. Two kinds of oxygen species, bulk lattice oxygen and surface adsorbed oxygen, are found to exist on the 3DOM LaFe0.7Co0.3O3 perovskites. The surface oxygen contributes to the complete oxidization of methane to CO2 and H2O in beginning of the reaction, while the bulk lattice oxygen tends towards partial methane oxidation to H2 and CO. In the methane conversion step, methane is partially oxidized into syngas at a H2/CO molar ratio close to 2:1 by the 3DOM-LaFe0.7Co0.3O3 in a wide range of the reactions, suggesting that the sample exhibits a good resistance to carbon deposition. In the steam oxidation step, the reduced perovskites are oxidized by steam to generate hydrogen with hydrogen productivity about 4 mmol/g oxygen carriers.

Scalable Fabrication of Quasi-Three-Dimensional Chiral Plasmonic Oligomers Based on Stepwise Colloid Sphere Lithography Technology.

We report a simple and scalable method for the fabrication of spiral-type chiral plasmonic oligomers based on the stepwise colloid sphere lithography technology. Through carefully adjusting the azimuthal angle Φ of polystyrene (PS) sphere array monolayer and the deposition thickness kn, the chiral plasmonic oligomers composed of four achiral particles can be successfully fabricated on a desired substrate. And their chiral sign, i.e., left-hand or right-hand, is dependent on the anticlockwise or clockwise deposition sequence of the achiral particles. The measured results show a large chiroptical resonance in the visible region, and this resonance can be easily adjusted by using different sizes of PS spheres. Our in-depth theoretical and experimental researches further reveal that the obtained chiral plasmonic oligomers are indeed a kind of quasi-three-dimensional chiral nanostructures, which own a three-dimensional geometrical morphology, but with nonreciprocity chiroptical effect. The ease and scalability (>1 cm2) of the fabrication method make chiral plasmonic oligomers promising candidates for many applications, such as chiral biosensor and catalysis.

폴리스티렌 구형입자를 주형으로 이용한 할로우 메조포러스 질화탄소 구형입자의 합성

주형으로 구형의 폴리스티렌을 사용하고 질소와 탄소원으로 시안아미드를 사용하여 열처리 과정을 거친 후 구형의 할로우 메조포러스 질화탄소 물질을 합성하였다. 이때 할로우 메조포러스 질화탄소 물질을 합성하는 과정에서 실리카와 같은 무기물 주형을 사용하지 않기 때문에 이차적인 실리카 제거 공정이 필요 없고 용매를 전혀 사용하지 않는다. 구형의 폴리스티렌 입자는 약 170 nm 크기였고 그리고 할로우 메조포러스 질화탄소 구형입자의 할로우 직경은 약 82 nm, 벽 두께는 약 13 nm이었다. 또한 할로우 메조포러스 질화탄소 물질의 표면적, 나노세공 크기, 세공부피는 각각 <TEX>$188m^2g^{-1}$</TEX>, 3.8 nm, <TEX>$0.35cm^3g^{-1}$</TEX>이었다. 한편, 할로우 벽은 흑연구조와 유사한 박막층의 쌓임 구조를 가졌으며 이러한 할로우 메조포러스 질화탄소 물질은 연료전지, 촉매, 광촉매, 전자방출 소자 등과 같은 분야에 매우 높은 응용 가능성을 가질 것으로 기대된다. Hollow mesoporous carbon nitride material with sphere shape was synthesized using polystyrene sphere as template and cyanamide as nitrogen and carbon atom sources via thermal treatment process. The process of the silica removal is not necessary because silica as template is not in use for the synthesis of hollow mesoporous carbon nitride material and any solvents are also not in use. The size of polystyrene spheres was about 170 nm. Hollow diameter and wall thickness were 82 nm and 13 nm, respectively, in hollow mesoporous carbon nitride sphere. Surface area, mesopore size and pore volume of hollow mesoporous carbon nitride material was <TEX>$188m^2g^{-1}$</TEX>, 3.8 nm and <TEX>$0.35cm^3g^{-1}$</TEX>, respectively. The wall in hollow sphere has graphitic structure. Hollow mesoporous carbon nitride material has potential applications in the area of fuel cell, catalysis, photocatalysis, electroemmision device, etc.

Cathodoluminescence of ZnO Nanostructure Arrays Hydrothermally Grown on the Patterned Seed Layers Using a Polystyrene-Sphere-Based Lithographic Method

Periodically distributed ZnO nanostructure arrays were hydrothermally grown on silicon substrates. For the preferential, site-selective growth of the ZnO nanostructures, a seed layer was patterned using self-assembled monolayers of polystyrene spheres (PSs) lithography technique. The size of the seed layer was controlled by the size of PSs, which was determined by oxygen plasma etching time. Due to the existence of numerous nucleation sites, flower-like (FL) ZnO nanostructures grew on the large seed layer over 800 nm in diameter. By reducing the size of the seed layer, we could make a couple of ZnO nanowires grow on a single seed layer island. We examined the cathodoluminescence (CL) spectra of FL ZnO nanostructure arrays and coupled (CO) ZnO nanowire arrays. Since the dimension of the nanostructures is smaller than or comparable to the penetration depth of the incident electron, CL signal would be generated in the whole body of the nanostructures. So, the CL intensity might be proportional to the surface area through which the photons could escape. As a result, it is natural that the CL intensity from the FL ZnO nanostructure arrays should be stronger than that from the CO ZnO nanowire arrays. However, in spite of the smaller surface area, the CL intensity was strikingly enhanced in the CO ZnO nanowire arrays compared with the closely-packed ZnO nanowire arrays. It could be attributed to the suppression of the near-band-edge ultraviolet emission in the [0001] direction, which was observed in the monochromatic CL measurement.

Influencing Factors of Macrosporous Ordering in TiO&lt;sub&gt;2&lt;/sub&gt; and ZrO&lt;sub&gt;2&lt;/sub&gt; Inverse Opals

TiO2 inverse opals, as well as used as photonic crystals, can be applied to the dye sensitized solar cells (DSSC), photocatalysis, and so on. In above applications, ordering of pore arrangement in TiO2 inverse opal is crucial as it determines the application effect of TiO2 inverse opal. In this paper, TiO2 inverse opals were prepared by infiltrating and removing of polystyrene (PS) colloidal crystal templates. Using scanning electron microscope (SEM), it is found that the pore structure of inverse opals can be tuned by using different heating temperature and different size of PS spheres, and ordering of pore arrangement is strongly affected by ordering of PS spheres alignment, heating temperature, and size of PS spheres.

Hydrothermal fabrication of hierarchically macroporous Zn2SnO4 for highly efficient dye-sensitized solar cells

Hierarchical macroporous Zn(2)SnO(4) consisting of nanoparticles has been synthesized for the first time through an in situ hydrothermal and a following annealing process in the presence of a polystyrene (PS) template. Zn(2)SnO(4) macropore sizes are tuned in the range of 180-650 nm by selecting the appropriate size of PS spheres, and the building unit size of the Zn(2)SnO(4)macropore is 4.2 nm regardless of the PS sizes. The photovoltaic performances of the dye-sensitized solar cell based on hierarchical macroporous Zn(2)SnO(4) with 200, 400, 600 and 750 nm PS spheres are 5.01, 4.76, 4.39 and 3.92%, respectively. The smaller pore size of Zn(2)SnO(4) exhibits higher photovoltaic performance, which is ascribed to the higher dye loading, faster electron transport rate and slower electron recombination rate. These are confirmed by UV-vis absorption spectroscopy, intensity-modulated photocurrent spectroscopy, intensity-modulated photovoltage spectroscopy and electrochemical impedance spectroscopy. The double layered photoelectrode based on a Zn(2)SnO(4) nanoparticles dye adsorption layer (4.2 nm in particle size, 15 μm in film thickness) and a macroporous light scattering layer (180 nm in macropore size, 4.0 μm in thickness) shows a remarkable enhancement in power conversion efficiency (6.10%) compared to that of Zn(2)SnO(4) nanoparticles photoelectrode (5.36%) because of its superior light scattering ability.

Development of Adaptive SEM Technology for Genome/Proteome Expression Analysis in Single Cell Level

Identification of each cellular phenotype in a tissue is essential for understanding community effect in living system. One useful way is in situ measurement of expressed biomarkers in single cell level using a lot labels; however, production and identification of such labels are still challenging. We propose a new sensing technology, which is a comprehensive development of production and identification of nano-particle (NP) labels for simultaneous in situ measurements of expressed biomarkers in single cell.For the fabrication of NPs, various sizes of polystyrene spheres were used as casts, and metals were deposited on the spheres by thermal evaporation. When polystyrene casts were interfering with measurements, degradation of organic substances was performed, and cup-shaped metal NP shells can be also obtained. For the identification of fabricated NPs, field emission scanning electron microscopy (FE-SEM) was used. Both diameters and elements of NPs were identified with observations of secondary electron (SE) and backscattered electron (BE) in the FE-SEM.By using our method, more than 500 types of NPs were fabricated. Metal shell layers were formed by thermal evaporation; therefore, multi-layered NPs can be easily fabricated with sequential evaporation. We used double-layered NPs; outer is Au for easy immobilization of biomolecules to use these NPs as labels of biomarkers, and inner layer is various to apply label varieties. Spatial distributions and diameters of NP labels were identified by SE observation, and NP elements were identified by BE observation as the difference of intensities in the image caused by the difference of atomic number of inner metal. We call it “adaptive SEM” technology (i.e., NP identification is adaptive for various samples). These results indicate a possibility for quantitative in situ detection of expressed biomarkers in a cell by the suggested technology.

Particle size effects of carbon sources on electrochemical properties of LiFePO4/C composites

Carbon-coated LiFePO4 cathode materials were prepared by a solid-state method incorporating different sizes of polystyrene (PS) spheres as carbon sources. In scanning electron microscope images, small PS spheres appear more effective at preventing aggregation of LiFePO4 particles. From transmission electron microscopy images, it was found that the LiFePO4 particles were completely uniformly coated with 5-nm carbon layer when the carbon source was 0.22 μm PS spheres. When the size of PS sphere was increased to 2.75 μm, a network of carbon was formed and wrapped around the LiFePO4 to create a conductive web. Raman spectroscopy and four-point probe conductivity measurement showed that using larger sizes of PS spheres as carbon sources leads to greater conductivity of LiFePO4/C. The LiFePO4 precursor sintered with 0.22 μm PS spheres delivered an initial discharge capacity of 145 mAh g−1 at a 0.2 C rate, but it only sustained 289 cycles at 80% capacity. When the diameter of PS spheres was increased to 2.75 μm, the discharge capacity of LiFePO4/C decreased, but the cycle life reached 755 cycles, the highest number in this work probably due to the network formation of carbon wrapping around LiFePO4 particles.

Annealing study of two-dimensional patterned Ge nanostructures via nanosphere lithography

Abstract Experimental studies on patterning hexagonal Ge nanostructures have been conducted on Si substrates through deposition of Ge with colloidal particles as a mask. The deposited Ge thin film possesses, according to the X-ray diffraction measurements, in plane texture, being epitaxial and aligned with the (111) Si substrate. The size distribution of the patterned Ge nanostructures is narrow, as indicated by the atomic force microscopy and scanning electron microscopy measurements. We have obtained Ge nanostructures with lateral dimension of 490 nm (height 12 nm), 200 nm (height 6 nm) and 82 nm (height 6 nm) by using different sizes of polystyrene spheres. We have performed in depth studies of the Ge nanostructures’ behavior due to thermal and rapid thermal post-annealing processes. FT micro-Raman spectroscopy shows that there is no Si intermixing during the annealing process. In order to quantify the changes in the height and lateral dimension, we have performed atomic force microscopy and white light interferometry analysis. The changes in shape and the decrease in the area of a cross-section of Ge nanostructure will be discussed in respect to similar results shown in the literature for Ge thin films during the annealing process.

One-step synthesis of hierarchical porous γ-alumina with high surface area

Hierarchical porous γ-alumina is successfully fabricated from a precursor solution consisting of surfactants, polystyrene (PS) spheres, inorganic salts and solvents. After calcinations, uniform macropores are closely packed. The macropore size coincides with the original PS sphere size. These macropores are connected by small windows. In addition, the macropore walls have mesoporous structures, as confirmed by SAXS measurement and TEM observation. After calcination at 900 °C, the amorphous alumina frameworks are converted to the crystallized γ-alumina phase. Even after crystallization, the existence of uniform mesopores and high surface are well retained, though the mesoporous ordering is lower.

Highly sensitive size discrimination of sub-micron objects using optical Fourier processing based on two-dimensional Gabor filters

We use optical Gabor-like filtering implemented with a digital micromirror device to achieve nanoscale sensitivity to changes in the size of finite and periodic objects imaged at low resolution. The method consists of applying an optical Fourier filter bank consisting of Gabor-like filters of varying periods and extracting the optimum filter period that maximizes the filtered object signal. Using this optimum filter period as a measure of object size, we show sensitivity to a 7.5 nm change in the period of a chirped phase mask with period around 1 microm. We also show 30 nm sensitivity to change in the size of polystyrene spheres with diameters around 500 nm. Unlike digital post-processing our optical processing method retains its sensitivity when implemented at low magnification in undersampled images. Furthermore, the optimum Gabor filter period found experimentally is linearly related to sphere diameter over the range 0.46 microm-1 microm and does not rely on a predictive scatter model such as Mie theory. The technique may have applications in high throughput optical analysis of subcellular morphology to study organelle function in living cells.

Formation of Si Nanowire Arrays by Metal-Assisted Chemical Etching

Formation of Si nanowire (SiNW) arrays using top-down methods based on metal-assisted chemical etching of Si is reported. Three different approaches were tested: i) a two-step process consisting in the electroless deposition of Ag nanoparticles followed by HF/H2O2 etching; ii) simultaneous electroless Ag deposition and etching in HF and highly concentrated AgNO3; iii) a multi-step process using an Au replica mask obtained by Au evaporation on Si samples covered with polystyrene spheres, followed by HF/H2O2 etching. The morphologies of the Si structures obtained in each case are discussed in terms of the influence of different parameters. The third approach led to well controlled etching. Depending on the polystyrene sphere size, Si pillars 1 µm or SiNWs 200 nm in diameter could be obtained.

Fabrication and optical properties of two-dimensional ZnO hollow half-shell arrays

Two-dimensional optically active ZnO shells on polystyrene (PS) templates have been fabricated using a sputtering technique. Periodic ZnO hollow half-shell structure has been obtained by removing PS templates. It exhibits several anomalous dips in transmission spectra that have not been reported. The dips can be tuned up by changing the shell thickness and PS sphere size. The PL spectra confirm that the structure has enhanced defect emission of ZnO.

Preparation of ordered porous SnO 2 films by dip-drawing method with PS colloid crystal templates

Ordered macroporous SnO 2 thin films were fabricated by using colloid crystal template of polystyrene (PS) spheres. Efficient dip-drawing method was used in both PS template assembly and the fabrication of porous structure. The PS templates were orderly assembled on clean glass substrates through colloid crystallization of monodisperse PS latex spheres, which were synthesized by an emulsion polymerization technique. The porous SnO 2 thin films were prepared through filling SnO 2 precursor sol into the spaces among the close-packed PS templates, and then annealing at 500 °C to remove the PS spheres and form SnO 2 crystal wall. The forming mechanism of PS templates through dip-drawing method was explained based on three driving forces existing in the assembly processes. The SnO 2 sol concentration and PS sphere size had important effects on formation of ordered porous structure The X-ray diffraction (XRD) spectra indicated the thin film was rutile structure and consisted of nanometer grains. The transmittance spectrum showed that optical transmittance kept above 80% beyond the wavelength of 440 nm. Optical band-gap of the porous SnO 2 film was 3.68 eV.

Hydrophobicity of Model Surfaces with Loosely Packed Polystyrene Spheres after Plasma Etching

Polystyrene (PS) sphere films with loosely packed arrays were prepared by plasma etching of closely packed PS sphere arrays. The size of PS spheres can be efficiently reduced with plasma etching, and surface topography can be manipulated by controlling the initial PS sphere size and the time of plasma exposure. These surfaces with loosely packed arrays provide a well-characterized model system for studying water repellency behavior. It was found that the surface hydrophobicity could be systematically tailored due to the well-defined and controlled surface topography. Sphere size and the interparticle distance between two adjacent spheres are critical factors in determining the water repellency behavior of the surface. A model based on the Cassie theory was proposed to elucidate the effect of surface topography on hydrophobicity, and the predicted contact angles agree well with the experimental results.