Monolayer Polystyrene Research Articles

SiN membranes with submicrometer hole arrays patterned by wafer-scale nanosphere lithography

In this work, nanosphere lithography was integrated with standard microfabrication for the wafer-scale fabrication of silicon nitride (SiN) membranes with arrays of submicrometer holes. A monolayer of polystyrene (PS) beads with a mean diameter of 428 or 535 nm was spin coated onto the front side of a (100)-silicon wafer double-side coated with 100 nm of low-stress SiN. The size of the deposited PS beads was reduced by oxygen plasma reactive ion etching. This allowed to tune the hole size in the released SiN membrane while maintaining the hole array periodicity. Using the size-reduced PS beads as a lift-off template in a standard nanosphere lithography lift-off procedure, a 20 nm thick chromium hole etch mask was realized. This hole mask was patterned by UV photolithography, thus allowing for the local dry-etching of holes into the SiN layer. The holey areas were released from the backside in a combined Si dry- and wet-etch process. During the final wet etch, the wafer front side was protected with a KOH-resistant polymeric coating (ProTEK®). In this way, holey SiN membranes with side lengths ranging from 400 μm up to 2.4 mm were fabricated. Preliminary application specific experiments show the membranes’ suitability for microfiltration and stencil applications.

Enhancing light extraction in organic light-emitting devices via hemispherical microlens arrays fabricated by soft lithography

We demonstrate enhanced light extraction in organic light-emitting devices (OLEDs) by using microlens arrays fabricated by a soft lithography technique. A large-area and close-packed polystyrene (PS) monolayer was formed on the SiO2 substrate using a convective-capillary assembly method, and a polydimethylsiloxane polymer was used to obtain a concave template, from which microlens arrays were fabricated from a photopolymerizable transparent optical adhesive. The microlens contact angle and array fill factor both depend on the size of PS microspheres, and nearly close-packed, hemispherical microlens arrays with microlens contact angle of (85 ± 5 deg) and array fill factor of (85 ± 3)% were obtained with 100-μm PS microspheres. The enhancement in the light-extraction efficiency in OLEDs when such fabricated microlens arrays were attached to the light-emitting surface depends on the contact angle of microlens, device size, and detailed multilayer structure of the OLED. For a large-area (12 × 12 mm) fluorescent OLED with a near close-packed hemispherical microlens array, a maximum enhancement of (70 ± 7)% in the light-extraction efficiency was achieved.

Hierarchically porous NiO film grown by chemical bath depositionvia a colloidal crystal template as an electrochemical pseudocapacitor material

Hierarchically porous NiO film has been successfully prepared by chemical bath deposition through monolayer polystyrene sphere template. The film possesses an architecture with a substructure of NiO monolayer hollow-sphere array and a superstructure of porous net-like NiO nanoflakes. The pseudocapacitive behavior of the NiO film is investigated by cyclic voltammograms (CV) and galvanostatic charge-discharge tests in 1 M KOH. The hierarchically porous NiO film exhibits weaker polarization, better cycling performance and higher specific capacitance in comparison with the dense NiO film. The specific capacitance of the porous NiO film is 309 F g−1 at 1 A g−1 and 221 F g−1 at 40 A g−1, respectively, much higher than that of the dense NiO film (121 F g−1 at 1 A g−1 and 99 F g−1 at 40 A g−1). The hierarchically porous architecture is responsible for the enhancement of electrochemical properties.

Dependence of Surface Free Energy of Polystyrene Thin Films on Temperature for Grafting Treatment

End-grafted polymer monolayers play an important role in colloidal stabilization, adhesion, and biocompatibility of artificial organs in medicine. There are two main methods to form end-grafting polymer layer:grafting-to and grafting-from methods. Grafting-to method has merit that is easy to conduct and easy to set a homogeneous degree of polymerization. We formed end-grafted polystyrene monolayers by a grafting-to method;a vinyl terminated polystyrene reacted with a H-terminated Si wafer and the polystyrene grafted to it. To clarify surface properties of the grafted polystyrene layer on the grafting density, we controlled it by a reaction temperature;The density could be controlled from 0.09 to 0.20 chains/nm2. At a lower grafting density region, the layer has high surface energy, high layer density, thin thickness, and smooth surface morphology. While at a higher grafting density region, the layer has low surface energy, low layer density, thick thickness, and smooth surface morphology.

Enhanced electrochromic properties of ordered porous nickel oxide thin film prepared by self-assembled colloidal crystal template-assisted electrodeposition

Highly ordered porous NiO film is prepared by self-assembled monolayer polystyrene sphere template-assisted electrodeposition. The as-prepared NiO film shows an ordered hexagonal close-packed bowel-like array that is made up of macrobowls with about 500 nm in diameter. The electrochromic properties of NiO film are investigated in an aqueous alkaline electrolyte (0.1 M KOH) by means of transmittance, cyclic voltammetry and chronoamperometry measurements. The ordered porous NiO film prepared with PS sphere template exhibits a noticeable electrochromism with reversible color changes from transparent to dark brown, and presents quite good transmittance modulation with a variation of transmittance up to 76% at 550 nm. The ordered porous NiO film also shows high coloration efficiency (41 cm 2 C −1), fast switching speed (3 s and 6 s) and good cycling performance, compared with the dense NiO film prepared without PS sphere template. The improvements of electrochromic performances are attributed to the highly porous morphology, which shortens the ion diffusion paths and provides bigger surface area.

Ordered magnetic multilayer nanobowl array by nanosphere template method

Ordered magnetic multilayer [Co/Pt] n nanobowls have been fabricated over a silicon substrate based on a polystyrene (PS) monolayer film. The ordered PS monolayer was first prepared by the self-assembly technique, which was used as the template for the multilayer film [Co/Pt] n deposition. The ordered magnetic multilayer [Co/Pt] n nanobowl array was obtained after the transferring and the selective etching process. The nanobowls show a uniform size and smooth surfaces. The nanobowls stuck to the neighbors and notches were observed in the bowl brims because of the contact points between the closed-packed PS beads. The nanobowls could be separated from their neighbors by thinning the PS beads before the film deposition and no notches were observed anymore. Compared to the chemical method, this method showed more flexible choices of the material to fabricate the nanobowls, which extended the application scope of the nanobowls greatly.

Size Tunable Nano Patterns Using Nanosphere Lithography with Ashing and Annealing Effect

This work presents a fabrication procedure to make large-area, size-tunable, periodically different shape metal arrays using nanosphere lithography (NSL) combined with ashing and annealing. A polystyrene (PS, 580 mu m) monolayer, which was used as a mask, was obtained with a mixed solution of PS in methanol by multi-step spin coating. The mask morphology was changed by oxygen RIE (Reactive Ion Etching) ashing and temperature processing by microwave heating. The Au or Pt deposition resulted in size tunable nano patterns with different morphologies such as hole and dots. These processes allow outstanding control of the size and morphology of the particles. Various sizes of hole patterns were obtained by reducing the size of the PS sphere through the ashing process, and by increasing the size of the PS sphere through annealing treatment, which resulted in tcontrolling the size of the metallic nanoparticles from 30 nm to 230 nm.

FORMATION, STRUCTURE AND PROPERTIES OF HIGHLY ORDERED SUB-30-nm PHASE CHANGE MATERIALS (GST) NANOPARTICLE ARRAYS

Chalcogenide phase change material Ge1Sb2Te4 (GST) nanoparticle arrays with long-range-order were fabricated by using a monolayer of self-assembled polystyrene (PS) spheres as mask. The morphology of nanoparticle arrays can be controlled via changing RIE processing conditions. Images of atomic force microscopy (AFM) and scanning electron microscopy (SEM) show that highly uniform GST nanoparticle arrays with particle density around 109 cm-2 were formed. The sizes of nanoparticles can be reduced to a tiny diameter in the range of 30–40 nm (top diameter). The GST nanoparticle arrays exhibit a prominent peak near 580 nm in reflectance spectra, which indicates that they possess a photonic band gap. These results confirm that GST nanoparticle arrays have a 2D periodicity and long-range order. The method of nanosphere lithograph may apply to manufacturing of high density memory devices based on phase change-based memory materials.

Hierarchically ordered porous nickel oxide array film with enhanced electrochemical properties for lithium ion batteries

Hierarchically ordered porous nickel oxide array film was prepared by electrodeposition through monolayer polystyrene spheres template. The as-prepared film had a highly porous structure of interconnected macrobowls array possessing nanopores. As anode material for lithium ion batteries, the porous array NiO film exhibited weaker polarization, higher coulombic efficiency and better cycling performance in comparison with the dense NiO film. After 50 cycles, the discharge capacity of porous array NiO film was 518 mAh g − 1 at 1 C rate, higher than that of the dense NiO film (287 mAh g − 1 ). The enhancement of the electrochemical properties was due to the unique hierarchical porous architecture, which provided fast ion/electron transfer and alleviated the structure degradation during the cycling process.

Preparation of Nanoscale Ag Semishell Array with Tunable Interparticle Distance and Its Application in Surface-Enhanced Raman Scattering

Nanoscale Ag semishell arrays with controlled size and tunable interparticle distance were prepared by combining nanosphere lithography with reactive ion etching. First, a large-area ordered monolayer of polystyrene (PS) nanospheres was deposited on glass substrates using the Langmuir−Blodgett (LB) technique. The PS spheres with different diameters were employed in LB procedures. Second, the monolayers of PS spheres were etched to control the diameter and tune the interparticle distance. Finally, a Ag layer was evaporated on the etched PS templates. Ag films with periodical nanostructures were obtained and can be used as surface-enhanced Raman scattering (SERS) substrates. These substrates exhibited homogeneity and good enhancement ability. SERS enhancement factor (EF) was represented on the order of 104−105. The correlation between nanoscale morphology and SERS activity of the substrates was investigated. When the size of Ag-semishell was fixed, the EF value decreased with the increase of interparitcle d...

Cobalt Oxide Ordered Bowl-Like Array Films Prepared by Electrodeposition through Monolayer Polystyrene Sphere Template and Electrochromic Properties

In this paper, we report a facile method to produce large-area periodical bowl-like cobalt oxide (Co3O4) array films based on a self-assembled monolayer polystyrene sphere template and electrodeposition. After the template is removed, the resulting Co3O4 films consist of periodic, interconnected networks of monodisperse submicrometer pores with a diameter of 1 μm. Moreover, the individual bowl contains a large number of pores with a diameter of 50 ± 20 nm and the interstices between bowls are filled with Co3O4 nanoflakes. As a preliminary test, the electrochromic properties of the Co3O4 macrobowl arrays have been investigated and it is found that the film annealed at lower temperature exhibits better electrochromic performance. The Co3O4 array film annealed at 200 °C exhibits good electrochromism with color changes from dark gray to pale yellow and fast response times. The coloration efficiency is calculated to be 29 cm2 C−1 at 633 nm, with a variation of transmittance up to 33%.

Improved electrochromic performance of hierarchically porous Co3O4 array film through self-assembled colloidal crystal template

Abstract A hierarchically porous cobalt oxide (Co3O4) array film, in which the skeleton is composed of ordered non-close-packed bowl array possessing nanoporous walls, is successfully prepared by electrodeposition through self-assembled monolayer polystyrene sphere template. As an anodic coloring material for electrochromic application, the hierarchically porous Co3O4 array film exhibits enhanced electrochromic properties with higher optical modulation, faster switching speed and better cycling performance, compared to dense Co3O4 film. The porous Co3O4 array film presents a quite good transmittance modulation with 42% in the visible range and also shows good reaction kinetics with fast response time of about 2 s, much higher than those of the dense film (25% and 4.5 s). The better electrochromic performances of the porous film are attributed to its highly porous morphology, which shortens the ion diffusion paths and provides bigger surface area.

New Colloidal Lithographic Nanopatterns Fabricated by Combining Pre-Heating and Reactive Ion Etching

We report a low-cost and simple method for fabrication of nonspherical colloidal lithographic nanopatterns with a long-range order by preheating and oxygen reactive ion etching of monolayer and double-layer polystyrene spheres. This strategy allows excellent control of size and morphology of the colloidal particles and expands the applications of the colloidal patterns as templates for preparing ordered functional nanostructure arrays. For the first time, various unique nanostructures with long-range order, including network structures with tunable neck length and width, hexagonal-shaped, and rectangular-shaped arrays as well as size tunable nanohole arrays, were fabricated by this route. Promising potentials of such unique periodic nanostructures in various fields, such as photonic crystals, catalysts, templates for deposition, and masks for etching, are naturally expected.

Synthesis of Polymer Grafted Magnetite Nanoparticle with the Highest Grafting Density via Controlled Radical Polymerization.

The surface-initiated ATRP of benzyl methacrylate, methyl methacrylate, and styrene from magnetite nanoparticle is investigated, without the use of sacrificial (free) initiator in solution. It is observed that the grafting density obtained is related to the polymerization kinetics, being higher for faster polymerizing monomer. The grafting density was found to be nearly 2 chains/nm2for the rapidly polymerizing benzyl methacrylate. In contrast, for the less rapidly polymerizing styrene, the grafting density was found to be nearly 0.7 chain/nm2. It is hypothesized that this could be due to the relative rates of surface-initiated polymerization versus conformational mobility of polymer chains anchored by one end to the surface. An amphiphilic diblock polymer based on 2-hydroxylethyl methacrylate is synthesized from the polystyrene monolayer. The homopolymer and block copolymer grafted MNs form stable dispersions in various solvents. In order to evaluate molecular weight of the polymer that was grafted on to the surface of the nanoparticles, it was degrafted suitably and subjected to gel permeation chromatography analysis. Thermogravimetric analysis, transmission electron microscopy, and Fourier transform infrared spectroscopy were used to confirm the grafting reaction.

The fabrication and application of patterned Si(001) substrates with ordered pits viananosphere lithography

A new scalable approach has been developed for fabricating large-scale pitpatterns with controllable periodicity on Si(001) substrates. The fabricationprocesses start with self-assembling a monolayer of polystyrene (PS) spheres onhydrogenated Si(001) substrates. A novel net-like mask in combination of the Aupattern thermally evaporated in between the PS spheres and the Au-catalyzedSiO2 around them is naturally formed. After selective etching of Si by KOH solution,two-dimensionally ordered pits with a periodicity equal to the diameter of the PS spheresin the range from micrometers to less than 100 nm can be obtained. The shape of the pitscan be modulated by controlling the chemical etching time. Such pit-patterned Sisubstrates facilitate the formation of ordered Si-based nanostructures, such as orderedself-assembled GeSi quantum dots, by deposition of Ge using molecular beamepitaxy.

Fabrication of large-area nickel nanobump arrays

Nanostructures have found wide applications in biochemical sensors and optical devices. Therefore, fabrication techniques are required to be suitable for preparing large-area nanopatterns at high throughput and low cost. This paper presents such an approach for fabricating hexagonally close-packed nickel nanobump arrays by a combination of monolayer self-assembly (MSA), poly (dimethylsiloxane) (PDMS) moulding and electroforming. A monolayer of polystyrene (PS) nanospheres on a substrate was used as a template for replicating the PDMS nanobowl mould. Good uniformity and smooth internal surface were observed in the nanobowl arrays. Highly ordered nickel nanobump arrays were fabricated by electroforming with the PDMS mould. The geometry of the nickel nanobumps can be tuned through changing the film thickness of the conductive layer and the electroforming material can also be extended to other metals and alloys. The simplicity and low cost of this approach may make widespread applications of these nickel nanopatterns possible.

Decreased lung carcinoma cell density on select polymer nanometer surface features for lung replacement therapies

AbstractPLGA (poly-lactic-co-glycolic acid) has been widely used as a biomaterial in regenerative medicine due to its biocompatibility and biodegradability properties. Previous studies have shown that cells (such as bladder smooth muscle cells, chondrocytes, osteoblasts, and vascular smooth muscle cells) respond differently to nano-structured PLGA surfaces (such as those with surface features less than 100 nm in at least one dimension) compared to nano-smooth surfaces. The purpose of the present in vitro research was to prepare PLGA films with various nanometer surface features and determine, for the first time, whether lung cancer epithelial cells respond differently to such topographies. Poly(dimethylsiloxane) (PDMS) molds prepared by placing PDMS onto various polystyrene monolayers and two solution evaporation methods were used to create nanometer surface features on PLGA. The intended spherical surface nano-topographies on PLGA with RMS values of 2.23, 5.03, 5.42 and 36.90 nm were formed, while PLGA surfaces with RMS values of 0.62 and 2.23 nm were obtained by different solution evaporation methods. Most importantly, lung cancer epithelial cells adhered less on the PLGA surfaces with an RMS value of 0.62, 2.23 and 5.42 nm after 4 hours of culture compared to any other PLGA surface created here. After three days, PLGA surfaces with an RMS value of 0.62 nm had much lower cell density than any other sample. In this manner, PLGA with specific nanometer surface features may inhibit lung cancer cell density which may provide for an important biomaterial for the treatment of lung cancer for a wide range of applications (from drug delivery to regenerative medicine).

Nanohole 3D-size tailoring through polystyrene bead combustion during thin film deposition

A novel approach is presented for nanohole 3D-size tailoring. The process starts with a monolayer of polystyrene (PS) beads spun coat on silicon wafer as a template. The holes can be directly prepared through combustion of PS beads by oxygen plasma during metal or oxide thin film deposition. The incoming particles are prevented from adhering on PS beads by H 2O and CO 2 generated from the combustion of the PS beads. The hole depth generally depends on the film thickness. The hole diameter can be tailored by the PS bead size, film deposition rate, and also the combustion speed of the PS beads. In this work, a series of holes with depth of 4–24 nm and diameter of 10–36 nm has been successfully prepared. The hole wall materials can be selected from metals such as Au or Pt and oxides such as SiO 2 or Al 2O 3. These templates could be suitable for the preparation and characterization of novel nanodevices based on single quantum dots or single molecules, and could be extended to the studies of a wide range of coating materials and substrates with controlled hole depth and diameters.

Fabrication and phase transition of long-range-ordered, high-density GST nanoparticlearrays

We use a monolayer of self-assembled polystyrene (PS) spheres (220 nm indiameter) as a reactive ion etching (RIE) mask to fabricate large-scale (more than1 cm2), long-range-ordered,high-density Ge1Sb2Te4 (GST) phase-change material nanoparticle arrays. Atomic force microscopy (AFM) andscanning electron microscopy (SEM) images show that periodic and isolated GST nanoparticlearrays 30–80 nm high and 150–200 nm bottom diameter were formed. Phase transitions ofthe GST films and nanoparticle arrays were studied by subjecting the samples tohigh-resolution transmission electron microscopy (HRTEM) electron-beam radiation.Nanocrystals between 2 and 5 nm in diameter were observed for GST nanoparticle arrays dueto the large surface-to-volume ratio. The density of the GST arrays can reach as high as109 cm−2, which can lead to the realization of future high-density phase-change random accessmemory (PCRAM).

Surface-Guided Self-Assembly of Silver Nanoparticles on Edges of Heterogeneous Surfaces

A general method for the generation of two-dimensional (2D) ordered silver nanoparticles (av 45 nm) ring array has been demonstrated via controllable self-assembly. The selective self-assembly is conducted on the edges of a gold coated polyelectrolyte film. This film is fabricated using the monolayer polystyrene (PS) spheres (av 600 nm) on a substrate as template, followed by depositing a positively charged polyelectrolyte and gold colloids (av 17 nm) via the layer-by-layer (LbL) self-assembly technique, and finally by eliminating the PS monolayer. This gold coated polyelectrolyte film has a regular pattern of sharp edges, and those edges are composed of abundant polyelectrolyte. This heterogeneous surface is easily prepared and universal for site-selective absorption of nanoparticles (silver nanoparticles in this paper, av 45 nm). This surface-guided self-assembly is powerful for fabricating micro/nanostructures on the edges of prepatterns. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the products.