Developing defect-tolerant demolding process in nanoimprint lithography

A simple method was developed to obtain the polymerization shrinkage stress exerted on the sidewalls of resist/stamp interface in ultraviolet nanoimprint lithography. This method is based on the measurements of demolding force which is the sum of adhesion and friction forces. The mean polymerization shrinkage stress on the sidewalls can readily be decoupled from overall demolding force by independently measuring the friction coefficient, adhesion force and geometries of stamp structures. The polymerization shrinkage stress on the sidewalls is overall larger than adhesion and increases by adding more cross-linking agent to the resist composition. This indicates that in addition to lowering the adhesion at the resist/stamp interface, development of resists with low degrees of shrinkage during UV curing is critical to reducing demolding force. It was also found that the shrinkage stress depends not only on the resist composition but also the stamp structure. A pillar structured stamp leads to a larger stress than a stamp with gratings with identical depth and width.

Two-Step curing method for demoulding in UV nanoimprint lithography

Effect of cross-linking agent and heteropolyacid (HPA) contents on physicochemical characteristics of covalently cross-linked sulfonated poly(ether ether ketone)/HPAs composite membranes for water electrolysis

The use of 2-hydroxyethyl methacrylate (HEMA)-based polymer as a biocompatible material has been well-established. HEMA-based resins containing cross-linking agents have several potential clinical applications. It is hypothesized that the incorporation of cross-linking agent will improve the mechanical properties of HEMA-based polymers while reducing water absorption and solubility. The purpose of the work reported here was to test this hypothesis and to determine the most effective cross-linking agent. A relationship among flexural strength, modulus, water absorption and solubility, and concentration of cross-linking agent was demonstrated. Strength and modulus tend to increase as the cross-linking agent concentration is increased, up to about 50%, after which the values level out or begin to fall. Water absorption drops with increasing cross-linking agent over the whole range of concentrations. Solubility tends to show a small decrease initially (up to 40%), followed by a noticeable increase as cross-linking agent concentration is increased. The trends were similar for all cross-linking agents, although there were differences in the absolute values in all properties depending upon the type of cross-linking agent used.

Antireflection (AR) structure is the most promising nano-scale application for AR film such as flat panel display, mobile phone display and so on. Ultraviolet nanoimprint lithography (UV-NIL) is a potentially powerful tool for such a nanofabrication, thus, we have been established the fabrication method of AR structure film using photo-curable polymer and UV-NIL. The AR structure mold was fabricated by oxygen ion beam irradiation to glassy carbon (GC) surface. This process can obtain large area and uniform AR structure surface easily. The AR structured surface has strong adhesive force, thus, release layer is important. The developed release method is chromium deposition and succeeding fluorinate silnane coupling agent. This release layer enables to transfer during UV-NIL. First, AR structures were replicated on PET film and reflection property was measured. However, interface between AR structured polymer and PET generates interface reflection. To reduce the interface reflection, we have been developed the fabrication method of self-support photo-curable polymer with AR structures. The method is utilizing polyvinyl alcohol (PVA) instead of PET film. PVA is water-soluble material, thus, after the AR structure replication by UV-NIL, PVA was removed by dipping water. The fabricated self-support film is 0.5 % reflectivity at visible light wavelength.

This work presents an improvement in the chemical and mechanical stability of a nanofluidic device formed in poly(ethylene glycol) diacrylate (PEGDA), a PEGbased UV resin for UV-NIL, by adding a cross-linking agent.

Exchange of adsorbed serum proteins during adhesion of Staphylococcus aureus to an abiotic surface and Candida albicans hyphae—An AFM study

Reflection loss can cause harmful effects on the performance of optoelectronic devices, such as cell phones, notebooks, displays, solar cells, and light-emitting diode (LED) devices. In order to obtain broadband antireflection (AR) properties, many researchers have utilized surface texture techniques to produce AR subwavelength structures on the interfaces. Among the AR subwavelength structures, the moth-eye nanostructure is one of the most promising structures, with the potential for commercialization in the near future. In this research, to obtain broadband AR performance, the optimization of moth-eye nanostructures was first carried out using the finite difference time domain method within the spectral ranges of 400-800nm, including the optimization of shape, height, pitch, and residual layer thickness. In addition, the continuous production of moth-eye nanostructure array upon a flexible polyethylene terephthalate substrate was demonstrated by using the roll-to-roll ultraviolet nanoimprint lithography (R2R UV-NIL) process and anodic aluminum oxide mold, which provided a solution for the cost-effective fabrication of moth-eye nanostructure array. The AR performance of moth-eye nanostructure array obtained by the R2R UV-NIL process was also investigated experimentally, and good consistence was shown with the simulated results. This research can provide a beneficial direction for the optimization and cost-effective production of the moth-eye nanostructure array.

Geometric phase analysis based on the windowed Fourier transform for the deformation field measurement

Removal of UV-cured resin using a hybrid cleaning process for nanoimprint lithography

Previous clinical research has suggested that the consumption of cranberry products prevents the adhesion of Escherichia coli to uroepithelial cells by causing changes in bacterial fimbriae. Atomic force microscopy was used to probe the adhesion forces between E. coli (nonfimbriated strain HB101 and the P-fimbriated variant HB101pDC1) and a model surface (silicon nitride), to determine the effect of growth in cranberry products on bacterial adhesion. Bacteria were grown in tryptic soy broth supplemented with either light cranberry juice cocktail (L-CJC) or cranberry proanthocyanidins (PACs). Growth of E. coli HB101pDC1 and HB101 in L-CJC or PACs resulted in a decrease in adhesion forces with increasing number of cultures. In a macroscale bacteria-uroepithelial cell adhesion assay a decrease in bacterial attachment was observed for E. coli HB101pDC1 grown in L-CJC or PACs. This effect was reversible because bacteria that were regrown in cranberry-free medium regained their ability to attach to uroepithelial cells, and their adhesion forces reverted to the values observed in the control condition. Exposure to increasing concentrations of L-CJC resulted in a decrease of bacterial attachment to uroepithelial cells for the P-fimbriated strain after L-CJC treatment (27% by weight) and after PACs treatment (345.8 microg/mL). Cranberry products affect the surface properties, such as fimbriae and lipopolysaccharides, and adhesion of fimbriated and nonfimbriated E. coli. The concentration of cranberry products and the number of cultures the bacteria were exposed to cranberry determines how much the adhesion forces and attachment are altered.

Electron-beam-initiated grafting of trimethylolpropane triacrylate (TMPTA) onto the bulk ethylene propylene diene monomer (EPDM) was carried out with varying concentrations of TMPTA at a constant irradiation dose of 100 kGy and over a wide range of irradiation doses (0–500 kGy) at a fixed concentration (10%) of TMPTA. The rubber was also modified in the bulk by tripropylene glycol diacrylate (TPGDA, 10%) and tetramethylol methane tetraacrylate (TMMT, 10%) at an irradiation dose of 100 kGy. The modified rubbers were characterized by IR spectroscopy, crosslinking density measurements, and mechanical, dynamic mechanical, and electrical properties. The IR studies indicated increased peak absorbances at 1730, 1260, and 1019 cm−1 due to increased 〉CO and COC concentrations up to certain levels of TMPTA and irradiation dose. These are accompanied by an increase in the crosslinking density. The tensile strength of the samples increases gradually with increasing both the concentration of the monomer and radiation dose up to a certain level. The values of the modulus also increase at the expense of the elongation at break. An increase in the number of double bonds from two in the case of the diacrylate to four in the case of the tetraacrylate also brings about an increase in the tensile strength and moduli values. The elongation at break, however, decreases. The DMTA measurements indicate changes in the glass transition temperature, Tg, and tan δmax on modification. The Tg shifts to a higher temperature with a simultaneous lowering of the tan δmax values as the TMPTA level is increased. A similar trend is observed when the irradiation dose is increased and the nature of the monomer changes from di- to tetraacrylate. The dielectric loss tangent registers an increase on modification by irradiation of TMPTA while the permittivity is decreased. All the results could be explained on the basis of the structural modification and crosslinking density. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 323–337, 2000

The thermal degradation kinetics of high-performance polymer composite electrolyte membranes were investigated by thermal gravimetric analysis in this study. The novel porous polymer composite membranes were fabricated by crosslinking poly (ethylene-co-vinyl alcohol) (EVOH) with polybutylene terephthalate (PBT) nano fiber. The PBT nano-scale fiber non-woven cloth was first prepared by the electrospinning method to form a labyrinth-like structure, and the crosslinking was carried out by filtering it through a solution of EVOH and crosslinking agent triallylamine using the Porcelain Buchner funnel vacuum filtration method. The PBT–EVOH composite membranes with various crosslinking agent ratios and ethylene carbonate/dimethyl carbonate (EC/DMC) immersion times were investigated for their thermal stability and ionic conductivity. The results showed that the higher crosslinking agent content would lower the crystallinity and enhance thermal stability. The thermal degradation activation energy was dramatically increased from 125 kJ/mol to 340 kJ/mol for the 1.5% crosslinking agent content sample at 80% conversion. The triallylamine crosslinking agent was indeed effective in improving thermal degradation resistivity. The best ionic conductivity of the polymer composite membranes was exhibited at 5.04 × 10−3 S cm−1 using the optimal weight ratio of EVOH/PBT composite controlled at 1/2. On the other hand, the EC/DMC immersion time was more effective in controlling the Rb value, thus the ionic conductivity of the membranes. A higher immersion time, such as 48 h, not only gave higher conductivity data but also provided more stable results. The triallylamine crosslinking agent improved the membrane ionic conductivity by about 22%.

Accurate determination of dielectric properties and surface characteristics of two‐dimensional (2D) perovskite nanosheets, produced by chemical exfoliation of layered perovskites, is often hindered by exfoliation agent residues such as tetrabutylammonium (TBA). This study investigated the effect of ultraviolet (UV) light exposure duration on the removal of TBA residues from 2D Ca2NaNb4O13− nanosheets deposited on silicon substrates via Langmuir‐Blodgett method using atomic force microscopy (AFM). Nanoscale adhesion forces between silicon AFM tips and nanofilms exposed to UV light for 3, 12, 18, and 24 hours were measured. Nanofilms exposed to UV for 12 hours showed significant heterogeneity in adhesion forces compared to control nanofilms not exposed to UV. This heterogeneity improved after 18 hours and reached maximum homogeneity at 24 hours. A noticeable decrease in adhesion forces indicated a reduction in TBA residues after 18 hours, with further reduction observed at 24 hours. The most probable adhesion forces for control nanofilms and those exposed to UV for 3 and 12 hours were 1.6‐fold and 2.0‐fold higher, respectively, compared to nanofilms exposed to UV for 18 and 24 hours. Similarly, surface roughness peaked at 12 hours and then decreased with longer exposure, resulting in a smoother surface at 24 hours.

Photo-DSC and dynamic mechanical studies on UV curable compositions containing diacrylate of ricinoleic acid amide derived from castor oil