Self-assembled Polystyrene Microsphere Research Articles

Raman enhancement of large-area silver grating arrays based on self-assembled polystyrene microspheres

Two types of Ag grating arrays as surface-enhanced Raman scattering (SERS) were fabricated using the monolayer self-assembled polystyrene (PS) as a template, using the silver film and monocrystalline silicon wafer as the substrates, imprinting different thicknesses of silver (50 nm, 75 nm, 100 nm, 125 nm and 150 nm) on the template, then removing PS. Rhodamine 6G (R6G) was used as a probe to characterize the performance of Raman enhancement. Experimental results showed that two structures can obtain a Raman enhancement factor of more than 107 at arbitrary deposition thicknesses. The insensitivity of two arrays induced by incident polarization and the difference in near-field and far-field simulation were also compared. These novel SERS substrates can achieve considerable uniformity, and the relative standard deviation (RSD) of the characteristic peak calculated at 1650 cm−1 were about 9.2% and 9.5%, respectively.

A Hierarchical Anodic Aluminum Oxide Template.

Anodic aluminum oxide (AAO) templates are widely used for the development of various functional nanomaterials due to their highly ordered and tunable porous structures. Here, we report a new hierarchical AAO (hAAO) template with the hexagonally ordered unit cells and the radially distributed nanochannels. It is formed by integrating the self-assembled polystyrene microsphere template into the AAO fabrication process and rationalized in terms of mechanical stress and electric-field-induced oxide dissolution. The back side of the hAAO template resembles a moth-eye-like nanoarray, which shows good hydrophobicity. A variety of radial nanopillar arrays and moth-eye-like nanoarrays are fabricated by a series of materials and synthesis techniques employing the hAAO template. These unique nanoarrays demonstrate many physicochemical properties that are distinct from those obtained from the conventional AAO template.

Extraordinary optical transmission through titanium nitride-coated microsphere lattice

Titanium nitride (TiN), one candidate as an alternative plasmonic material, is deposited by the sputtering method on top of a self-assembled polystyrene microsphere lattice. The optical transmission spectra of the TiN-coated microsphere lattice reveal a transmission pass-band attributed to the extraordinary optical transmission phenomenon, known from subwavelength hole arrays in metal films. Simulations by finite element method show the presence of a hybrid mode resulting from coupling of surface plasmons on the TiN film to photonic guided resonance modes in the dielectric microsphere lattice. The crucial role of the microspheres in the transmission process is also evidenced by dedicated simulations. Such hybrid colloidal photonic-plasmonic crystals based on TiN are promising for future plasmonic applications requiring the thermo-mechanical stability of refractory ceramics complemented by a plasmonic efficiency similar to that of gold, but also for extending the range of current applications beyond the use of the classical noble metals gold and silver.

Flexible Pressure Sensors with a Wide Detection Range Based on Self-Assembled Polystyrene Microspheres.

Flexible pressure sensors are important components of electronic skin and flexible wearable devices. Most existing piezoresistive flexible pressure sensors have obtained high sensitivities, however, they have relatively small pressure detection ranges. Here, we report flexible pressure sensors with a wide detection range using polydimethylsiloxane (PDMS) as the substrate, carbon nanotube films as the electrode material, and self-assembled polystyrene microsphere film as the microstructure layer. The obtained pressure sensor had a sandwich structure, and had a wide pressure detection range (from 4 kPa to 270 kPa), a sensitivity of 2.49 kPa−1, and a response time of tens of milliseconds. Two hundred load–unload cycles indicated that the device had good stability. In addition, the sensor was obtained by large-area fabrication with a low power consumption. This pressure sensor is expected to be widely used in applications such as electronic skin and flexible wearable devices.

Enhanced electrochemical CO2 reduction selectivity by application of self-assembled polymer microparticles to a silver electrode.

The electrocatalytic reduction of CO2 to CO using an Ag electrode in an aqueous solution was enhanced following modification of the cathode surface with high-density self-assembled polystyrene microspheres. The modified electrode exhibited improved water repellency, which is believed to have increased its selectivity for the reduction of gaseous CO2.

Cathodic Electrografting of Alkyl Nanopatterns on Silicon (100)

Nanoscale patterns are created on silicon (100) surfaces via cathodic electrografting of alkyls. Self-assembled polystyrene microspheres on silicon surfaces can serve as dielectric masks. Cathodic potentials are applied to masked substrates in liquid hexynoic acid or phenylacetylene leading to the formation of nanoscale islands with monolayers of covalently bound functional groups on silicon. Silicon surfaces functionalized with islands of hexynoic acid are demonstrated using a biotin reaction. Cyclic voltammetry, scanning electron microscopy, and atomic force microscopy are used to characterize the patterned surfaces. The method provides a facile and high throughput process for spatially defining the local reactions on silicon with nanometer-scale resolution.

Protein Micropatterning Using Surfaces Modified by Self-Assembled Polystyrene Microspheres

A technique for micropatterning of proteins on a nonplanar surface to improve the coverage and functionality of biomolecules is demonstrated. A nonplanar microstructure is created by the self-assembly of polystyrene microspheres into an array of microwells on a silicon wafer to allow the integration of a nonplanar spot on a planar chip. After the microspheres were deposited into the microwells, they were conjugated with proteins. The curve surfaces of the microspheres present more surface area for attaching biomolecules which will increase the density of biomolecules and, hence, the sensitivity for detection. Moreover, proteins immobilized on a curved surface can retain their native structures and function better than on a planar surface because of a smaller area of interaction between the protein and the substrate. Patterning of biomolecules was tested with two model fluorescent proteins. The results show that precise patterning of biomolecules on a nonplanar spot can be achieved with this technique.

Self-assembled systems obtained by chemical and electrochemical techniques for photonic crystal fabrication

The present work reports the formation of self-assembled systems by chemical and electrochemical techniques for photonic crystal structures fabrication. The chemical technique was used to the fabrication of self-assembled polystyrene micro-spheres structures. The influence of temperature setup and monodispersion concentration in the chemical self-assemble mechanism was studied. The electrochemical technique also was used to fabricate the self-assembled porous alumina structures. The influence of electrolyte type and anodic voltage in the electrochemical self-assemble process was studied. The self-assembled structures were analyzed to the possibility of application as photonic crystal structures

Nanosphere lithography: fabrication of large-area Ag nanoparticle arrays by convective self-assembly and their characterization by scanning UV-visible extinction spectroscopy.

This work employs UV-visible extinction spectroscopy as a new spectral mapping technique to characterize self-assembled polystyrene microsphere samples produced by convective self-assembly (CSA). This spectroscopic technique was successfully used to analyze the periodic particle arrays produced by the polystyrene template, yielding a detailed characterization of each sample. The CSA-prepared samples proved to be more uniform across a sample as well as more reproducible than previous sample preparation techniques. For the first time, a detailed characterization and quantitative evaluation of the entire sample has been performed by spectroscopic mapping.

Optical coupling between a self-assembled microsphere grating and a rib waveguide

We report the fabrication of a linear array of self-assembled polystyrene microspheres side coupled to a rib waveguide. The optical coupling between the lateral evanescent field and the periodically perturbed effective refractive index alongside the waveguide results in a transmission stopband at the Bragg wavelength. The observed transmission spectrum shows a notch centered at λ≈1590 nm, which is in close agreement with theory. The coupling coefficient, κ, and the spectral response are derived for variable cladding medium index using perturbation theory. Structures of this type are expected to find application in wavelength selection, optical sensing, and optical delays.

Changes in the Morphology of Self-Assembled Polystyrene Microsphere Monolayers Produced by Annealing

Ordered monolayers of polystyrene (PS) microspheres were prepared on both hydrophilic and hydrophobic substrates by convective self-assembly. Changes in the degree of ordering in the microsphere monolayers during annealing at temperatures below and above the glass transition temperature Tg of PS was quantitatively assessed using a customized image analysis method. This method overcomes the shortcomings of traditional Fourier transform methods for the analysis of images containing a small number of objects. In general, large ordered domains in the monolayers break up into smaller regions separated by cracks, due to thermal expansion of the polymer and the attractive dispersion force between microspheres. The substrate influences this phenomenon: the evolution was much slower for instance for monolayers on glass than for monolayers on PMMA substrates. In annealing experiments above Tg of PS, measurements of the widths of cracks in the monolayers showed differences between substrates: At later stages the width of the cracks in monolayers on PS substrates were observed to decrease more quickly than for monolayers on PMMA substrates. After very long times at relatively high temperatures, the monolayers on both substrates became essentially smooth films.