Colloidal Monolayer Template Research Articles

Highly Selective and Sensitive Detection of Hydrogen Sulfide by the Diffraction Peak of Periodic Au Nanoparticle Array with Silver Coating

The two-dimensional (2D) periodic Au nanosphere array with silver coating was prepared by using a colloidal monolayer template to obtain a Au nanosphere array and subsequently depositing silver thin coating on it, which could be used as an optical sensor to effectively detect H2S. Such periodic Au nanosphere array with silver coating displayed a surface plasmonic resonance (SPR) peak and an optical diffraction peak. Compared with the SPR peak, the diffraction peak, originated from the periodic arrangements of the obtained array, demonstrated a more sensitive optical change to detect H2S with a significant redshift as the H2S concentration increased. It was attributed to the increase of the refractive index of the environment around the Au nanosphere arrays with silver coating due to the partial formation of Ag2S after detecting H2S. Furthermore, the H2S sensor based on the change of the optical diffraction peak, showed an excellent selectivity and it was very sensitive to detect H2S from 2 to 30 μM. This method was investigated by the analysis in H2S-spiked blood samples, which indicates that the method has the potential to detect H2S in blood samples. The presented work provides a new strategy of utilizing the optical diffraction peak of the periodic array to develop promising sensors.

Fabrication and optical properties of the Si honeycomb structure via colloidal monolayer template

We use solution immersion method to prepare the SiO2 network structure. A single-layer PS sphere template was immersed in SiO2 precursor solution for a certain period of time. Filter paper was used to absorb the residual liquid, and then the PS nanospheres were removed by high temperature-annealing to form SiO2 network structure. The Si honeycomb structure was formed on the SiO2 network structure by chemical vapor deposition method. The longer growth time caused the smaller sizes of the Si apertures and produced various quantum size effects. When the growth time is 15 min, the thermal conductivity of the sample is the lowest. The heat conduction behavior of the 15 min sample is similar to that of a phonon crystal due to the aperture size of the sample is almost the same as the mean free path of phonons. Scattering at the interface of the isolated honeycomb microstructures also contributed to the low thermal conductivity. The position and number of the reflection peak of the sample can be controlled by the deposition time. The luminescence properties of the samples are greatly influenced by the surface topography.

Spherical Nanoparticle Arrays with Tunable Nanogaps and Their Hydrophobicity Enhanced Rapid SERS Detection by Localized Concentration of Droplet Evaporation

Periodic hexagonal spherical nanoparticle arrays are fabricated by a sacrificial colloidal monolayer template route by chemical deposition and further physical deposition. The regular network‐structured arrays are first templated by colloidal monolayers and then they are changed to novel periodic spherical nanoparticle arrays by further sputtering deposition due to multiple direction deposition and shadow effect between adjacent nanoparticles. The nanogaps between two adjacent spherical nanoparticles can be well tuned by controlling deposition time. Such periodic nanoparticle arrays with gold coatings demonstrate a very stable and high sensitive surface‐enhanced Raman scattering spectroscopy (SERS) performance. The periodic nanoparticle arrays with 10 nm gaps display much stronger SERS enhancement due to electromagnetic coupling. The chemically modified nanoparticle arrays show good hydrophobicity, which shorten process of detecting probe molecules using them as SERS‐active substrates by localized concentration of droplet evaporation and a low detection limit of 10−12 m R6G can be achieved without solution wasting in a short time. The hydrophobic substrate offers a simple, convenient, and economical method to examine SERS performance by rapid concentration of solution on it and it is highly helpful to improve its practical applications in portable Raman detecting devices to detect organic molecules.

Physical deposition improved SERS stability of morphology controlled periodic micro/nanostructured arrays based on colloidal templates.

An effective and inexpensive method is developed to fabricate periodic arrays by sacrificial colloidal monolayer template route by chemical deposition and further physical deposition. By a colloidal template induced precursor solution dipping strategy, different periodic arrays of semi-hollow sphere array, inverse opal with monolayer pore arrays and hole arrays are obtained under different conditions. After magnetron sputtering deposition, their morphologies are changed to novel micro/nanostructured arrays of honeycomb-shaped arrays, hollow cavity arrays, and regular network arrays due to multiple direction deposition of sputtering deposition and shadow effect. After coating a gold thin layer, these periodic micro/nanostructured arrays are used as SERS active substrates and demonstrate a very stable SERS performance compared with periodic arrays achieved by direct colloidal template-induced chemical deposition. Additionally, a honeycomb-shaped array displays better SERS enhancement than that of a hollow cavity array or a regular network array. After optimization of honeycomb-shaped arrays with different periodicities, an array with periodicity of 350 nm demonstrates much stronger SERS enhancement and possesses a low detection limit of 10(-11) M R6G. Such stable SERS performance is useful for practical application in portable Raman detecting devices to detect organic molecules.

Preparation and catalytic performance of the Co3O4/AAO composite

The Co3O4/AAO composite with novel morphology was successfully prepared by the solution-dipping method and the calcination of cobalt acetate precursor at 400°C for 2h in air. Porous anodic alumina (AAO) thin film was selected as new substrate to support colloidal monolayer template. Scanning electron microscopy (SEM) analysis indicated that the morphology of the as-prepared product could be controlled by changing the concentration of precursor. Catalytic test shows that the obtained Co3O4/AAO composite has a high decolorization ratio in the degradation of methylene blue (MB), which reaches 97.79% in 140min in the presence of sodium borohydride (NaBH4). Comparative experiments show that this nanomaterial has enhanced catalytic performance.

Fabrication of volcano-shaped nano-patterned sapphire substrates using colloidal self-assembly and wet chemical etching

Patterned sapphire substrates (PSS) have been widely used to enhance the light output power in GaN-based light emitting diodes. The shape and feature size of the pattern in a PSS affect its enhancement efficiency to a great degree. In this work we demonstrate the nanoscale fabrication of volcano-shaped PSS using a wet chemical etching approach in combination with a colloidal monolayer templating strategy. Detailed analysis by scanning electron microscopy reveals that the unique pattern shape is a result of the different corrosion-resistant abilities of silica masks of different effective heights during wet chemical etching. The formation of silica etching masks of different effective heights has been ascribed to the silica precursor solution in the interstice of the colloidal monolayer template being distributed unevenly after infiltration. In the subsequent wet chemical etching process, the active reaction sites altered as etching duration was prolonged, resulting in the formation of volcano-shaped nano-patterned sapphire substrates.

Hierarchical ZnO films with microplate/nanohole structures induced by precursor concentration and colloidal templates, their superhydrophobicity, and enhanced photocatalytic performance

Abstract

ChemInform Abstract: Physical Processes‐Aided Periodic Micro/Nanostructured Arrays by Colloidal Template Technique: Fabrication and Applications

AbstractReview: 96 refs.

Physical processes-aided periodic micro/nanostructured arrays by colloidal template technique: fabrication and applications

It has been proven that the use of colloidal templates is a facile, flexible strategy to create the periodic micro/nanostructured arrays in comparison with photolithography, electron beam lithography etc. Utilizing colloidal monolayers as templates or masks, different periodic micro/nanostructured arrays including nanoparticle arrays, pore arrays, nanoring arrays and nanorod/nanotube arrays can be fabricated by chemical and physical processes. Chemical routes, including direct solution/sol dipping strategy, wet chemical etching, electrodeposition, electrophoretic deposition etc. have advantages of simple operation and low costs. However, they have some disadvantages of impurities on surface of arrays due to incomplete decomposition of precursors, residue of surfactants in self-assembling or electrochemical deposition. More importantly, it is quite difficult to achieve very uniform morphology of micro/nanostructure arrays on a large-area by the above routes. Whereas another method, a physical route (for instance: reactive ion etching, pulsed laser deposition, thermal evaporation deposition, atomic layer deposition, sputtering deposition), combining with colloidal monolayer template can well resolve these problems. In this review, we focus on introducing the recent progress in creating micro/nanostructured arrays based on colloidal templates with physical routes. The parameters of the microstructure or nanostructure can be tuned by colloidal templates with different periodicity and experimental conditions of the physical processes. The applications of micro/nanostructured arrays with controllable morphology and arrangement parameters in self-cleaning surfaces, enhanced catalytic properties, field emitters etc. are also presented in the following sections.

Observation of unconventional optical diffraction in α-Fe2O3/Si two-dimensional photonic crystal slab fabricated by sol-gel method

The α-Fe2O3/Si two-dimensional (2D) photonic crystal (PC) with hexagonal honeycomb structure was fabricated by self-assembly and solution-dipping method based on colloidal monolayer template with 780 and 470 nm diameter polystyrene (PS) spheres. Optical diffraction measurement was carried out under wavelengths of 800, 532 and 400 nm. An interesting dispersion phenomenon with a hexagonal diffraction pattern composed of six elliptical spots is observed under specific wavelengths. Both theoretical and experimental calculations reveal that the diffraction can only occur when the incident wavelength is smaller than \(\sqrt{3}/2\) of lattice constant, and both the shape and distribution of these spots can be modified by the PC lattice constant and the incident wavelength. All these results reveal that optical properties of these 2D PC slabs are different from conventional diffractive devices.

Fabrication of tunable pore size of nickel membranes by electrodeposition on colloidal monolayer template

Large-area nickel patterned membranes with tunable pore size are prepared by the combination of self-assembly nanosphere lithography and electrodeposition. The morphology of the nickel membranes exhibits a honeycomb or egg-shell-roofed structure depending on the deposition time and the electrostatic-induced absorption effect. With an increase of electrodeposition time, the movement of polystyrene spheres caused by metal-filling gradually changes the contact evolution between the spheres and the substrate from facet contact to quasi-point contact, until complete lift from the substrate. Hence, the pore size can be controlled by varying the deposition time; i.e., by controlling the contact area between the polystyrene spheres and the substrate. Such membranes can be useful as templates for nanofabrication. The site and density control of one-dimensional nanostructures, depending on the distance and the size of the pore, is a critical issue in many potential applications, such as optical antennas, biosensors and bioprobes, and field emission devices.

Fabrication of size-controllable Fe2O3 nanoring array via colloidal lithography

Tailed-Fe(2)O(3) ring arrays are fabricated by solution-dipping on a colloidal monolayer template. The influence of synthesis parameters on the quality of nanostructures has been investigated. The ring size can be controlled by changing the precursor concentration and varying the annealing time of the polystyrene sphere colloidal monolayer. In addition, the edge of the rings is sensitive to the surface tension of precursor solution, and high quality ordered ring arrays can be obtained by tuning the surface tension. This strategy allows the fabrication of specific metal oxides ring arrays with high quality and uniform morphology.

Metal ion-doped SnO2 ordered porous films and their strong gas sensing selectivity

Based on a sol-gel technique and the colloidal monolayer template, ion-doped SnO2 ordered porous films were fabricated, and the corresponding gas-sensing properties were studied. The sensitivity to the given test gases strongly depends on the doping species and doping amount. Importantly, when the doping amount is 1% M, the Cr+3 and Pd+2 doped porous films demonstrate a greatly enhanced sensitivity and strong selectivity to ethanol and ammonia, respectively. The improved sensing properties are attributed to the doping-induced surface modification of the films. Such ion-doped porous films are expected to bring new opportunities for application of future porous film-based gas sensors.

Synthesis of ZnO nanotubes and nanotube-nanorod hybrid hexagonal networks using a hexagonally close-packed colloidal monolayer template

We present a new synthetic approach, via hydrothermal process with the use of polystyrene (PS) colloids, to fabricate vertically aligned, single crystalline ZnO nanotube arrays. Electron microscopy images revealed that single crystalline nanotubes with inner diameters of ∼15–20 nm and wall thicknesses of ∼10–15 nm were formed just below the PS colloids, whereas solid nanorods were grown in the absence of PS colloids. In addition, nanorods enclosing the PS colloids exhibited much faster growth rates than those on the area not covered with PS colloids. These results indicate that the introduction of PS colloids affected the formation and diffusion of adatoms. The growth behavior of ZnO crystals with regards to the PS colloids was exploited to convert the ZnO nanostructures from solid to nanotube-nanorod hybrid networks by introducing hexagonally close-packed PS colloidal monolayers. Moreover, we demonstrated further conversion to complete tubular forms by reducing the aperture size between adjacent PS colloids with thermal annealing.

Magnetic step regions in α-Fe 2O 3 nanostructured ring arrays

α-Fe 2O 3 nanostructured ring arrays with different ring sizes were fabricated by solution-dipping on a colloidal monolayer template. The magnetic properties of the arrays are investigated. An abnormal magnetic step region was observed in the hysteresis loop at room temperature, showing existence of a steady “Vortex” state in α-Fe 2O 3 ring arrays at room temperature. However, at a low temperature (50 K), the step region disappeared. Also, no step region is found from Fe ring array with the similar morphology to that of α-Fe 2O 3. This is attributed to the weak dependence of hysteresis loop on size and morphology of the single ring for α-Fe 2O 3 at room temperature.

Morphology-controlled 2D ordered arrays by heating-induced deformation of 2D colloidal monolayer

We develop a strategy to fabricate morphology-controlled two dimensional (2D) ordered arrays by solution-dipping sintered colloidal monolayer template. By heating colloid monolayer templates for different times, the morphology of ordered arrays can be controlled effectively, which is valuable to investigate the morphology-dependent optical, magnetic, electrochemical, catalytic properties of arrays. With increase of the heating time for templates, 2D ordered arrays with different morphologies can be fabricated in turn, such as, spherical pore array, honeycomb-shaped nanowall array, nanopillar array and regular network. Two kinds of morphology-controlled 2D periodic arrays, ferric oxide and silica, have been fabricated successfully by this way. This route is universal for synthesis of other compounds’ ordered arrays with controlled morphology. This strategy has expanded the applications of the colloidal monolayers as templates to prepare ordered nanostructured functional arrays.

Electrodeposition-Induced Highly Oriented Zinc Oxide Ordered Pore Arrays and Their Ultraviolet Emissions

Highly oriented ZnO ordered pore arrays (films) were electrochemically deposited on substrate based on colloidal monolayer template. Such oriented porous film has a preferential orientation along c-axis and shows strong and steady ultraviolet photoluminescence at room temperature, accompanied by a much weaker visible emission. This is in contrast to the randomly oriented film on ITO-glass substrate, which shows both weak ultraviolet and relatively strong visible luminescence. The growth of preferential orientation for such film on substrate was attributed to the oriented substrate which leads to formation of oriented ZnO nuclei.

Morphology Control and Transferability of Ordered Through‐Pore Arrays Based on the Electrodeposition of a Colloidal Monolayer

A colloidal-monolayer template- directed electrodeposition strategy for producing morphology-controlled ordered pore arrays with one pore thickness, is reported (see Figure). Film morphology is controlled by heating the colloidal monolayer before deposition, and electrodeposition time. Deposited films can be integrally transferred to any insulating substrate, even those with curved surfaces.

Fabrication of large-scale zinc oxide ordered pore arrays with controllable morphology.

The fabrication of large-scale ZnO ordered pore arrays by the potentiostatic electrochemical deposition method based on a two-dimensional ordered colloidal monolayer template is reported. The pore morphology evolves from hemispherical to a well-like structure by controlling the deposition potential.