Fluorinated organic-inorganic hybrid mold as a new stamp for nanoimprint and soft lithography

In this paper, we fabricated a fluorinated organic-inorganic hybrid mold using a nonhydrolytic sol-gel process which can produce a crack-free mold without leaving any trace of solvent. No special chemical treatment of a release layer is needed because the fluorinated hybrid mold has fluorine molecules in the backbone. The other advantages of the hybrid mold are thermal stability over 300 degrees C. The hybrid mold produced from UV nanoimprint lithography (UV-NIL) was used as a mold for the next UV-NIL and soft lithography without requiring use of an antisticking layer. Various nanometer scale patterns including sub-100 nm patterns could be obtained from the hybrid mold. Nanopatterning processes using this low-cost mold are useful because they preserve the expensive original master.     

High-refractive index acrylate polymers for applications in nanoimprint lithography

The development of polymeric optical materials with a higher refractive index,transparency in the visible spectrum region and easier processability is increasingly desirable for advanced optical applications such as microlenses,image sensors,and organic light-emitting diodes.Most acrylates have a low refractive index(around 1.50)which does not meet the high perfo rmance requirements of advanced optical materials.In this research,three novel acrylates were synthesized via a facile one-step approach and used to fabricate optical transparent polymers.All of the polymers reveal good optical properties including high transparency(≥90%)in the visible spectrum region and high refractive index values(1.6363)at 550 nm.Moreover,nanostructures of these acrylate polymers with various feature sizes including nanogratings and photonic crystals were successfully fabricated using nanoimprint lithography.These results indicate that these acrylates can be used in a wide range of optical and optoelectronic devices where nanopatterned films with high refractive index and transparency are required.     

Polybenzoxazine as a mold-release agent for nanoimprint lithography

One of the most important tasks remaining to be resolved in nanoimprint lithography is the elimination of the resist sticking to the mold during demolding. Previously, the main approach was to apply a thin layer of fluorinated alkyl silane mold-release agent on the surface on the mold; however, this involves complicated steps and high costs. The low surface free energy material polybenzoxazine provides an efficient mold-release agent for silicon molds that is easier to process, costs less, and has no side reactions.     

Patterning of DNA nanostructures on silicon surface by electron beam lithography of self-assembled monolayer

Nanoscale patterns of modified oligonucleotides are produced on octadecyltrimethoxysilane self-assembled monolayers at a silicon surface by electron beam lithography. DNA structures with feature sizes of the order of 250 nm were detected by epi-fluorescence microscopy.     

Interface segregating fluoralkyl-modified polymers for high-fidelity block copolymer nanoimprint lithography

Block copolymer (BCP) lithography is a powerful technique to write periodic arrays of nanoscale features into substrates at exceptionally high densities. In order to place these features at will on substrates, nanoimprint offers a deceptively clear path toward high throughput production: nanoimprint molds are reusable, promote graphoepitaxial alignment of BCP microdomains within their topography, and are efficiently aligned with respect to the substrate using interferometry. Unfortunately, when thin films of BCPs are subjected to thermal nanoimprint, there is an overwhelming degree of adhesion at the mold-polymer interface, which compromises the entire process. Here we report the synthesis of additives to mitigate adhesion based on either PS or PDMS with short, interface-active fluoroalkyl chains. When blended with PS-b-PDMS BCPs and subjected to a thermal nanoimprint, fluoroalkyl-modified PS in particular is observed to substantially reduce film adhesion to the mold, resulting in a nearly defect-free nanoimprint. Subsequent lithographic procedures revealed excellent graphoepitaxial alignment of sub-10 nm BCP microdomains, a critical step toward lower-cost, high-throughput nanofabrication.     

Solvent-assisted soft nanoimprint lithography for structured bilayer heterojunction organic solar cells

We introduce a novel method to easily fabricate nanopatterns at ambient conditions using solvent-assisted soft nanolithography. For this purpose, a P3HT/PCBM bilayer, one of well-known standard models of solar cell systems, was chosen to optimize bilayer solar cells using the new lithographic technique. The nanopatterns of P3HT made using this method have improved device efficiency compared to planar bilayer heterojunction of the solar cell. The new patterning process creates solar cell devices with a greater than 2-fold increase in power conversion efficiency (PCE) compared to an otherwise equivalent, flat device. This improvement in efficiency is due to the increased interfacial area created by the patterning process. This result demonstrates the feasibility of extensive applications toward nanolithography, relevant to device fabrication, such as electronic devices.     

An ultraviolet-curable mold for sub-100-nm lithography

We describe a novel UV-curable mold that is stiff enough for replicating dense sub-100-nm features even with a high aspect ratio. It also allows for flexibility when the mold is prepared on a flexible support such that large area replication can be accomplished. The composite material of the mold is inert to chemicals and solvents. The surface energy is made low with a small amount of releasing agent such that the mold can be removed easily and cleanly after patterning. In addition, the material allows self-replication of the mold. These unique features of the mold material should make the mold quite useful for various patterning purposes.     

Hydrophilic composite elastomeric mold for high-resolution soft lithography

Here, we introduce a nanopatternable hydrophilic composite elastomer highly desirable for both nanostructure patterning via solvent-assisted micromolding (SAMIM) and microcontact printing of polar inks. This composite precursor is prepared by blending two UV-curable materials, Norland Optical Adhesives (NOA) 63 and poly(ethylene glycol) diacrylate (PEGDA), in an appropriate ratio; upon UV polymerization, a nanopatternable elastomer with preferential permeability both to aqueous and organic solvent is fabricated. Using this composite mold, nanoscale SAMIM of poly(4-vinylpyridine) (P4VP) and microcontact printing of a polar biomolecule, bovine serum albumin (BSA), was successfully demonstrated, paving the way for facile and efficient reproduction of various nanopatterns and a biomolecule-printed array platform.     

Adsorption and release behavior of bare and DNA-wrapped-carbon nanotubes on self-assembled monolayer surface

The adsorption and release behavior of single-stranded DNA-wrapped single-walled carbon nanotubes (ssDNA-w-SWCNTs) on alkylthiol self-assembled monolayer (SAM) surface was systematically characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Fast electron transfer between bare Au electrode and redox species blocked by the alkylthiol SAM can be restored by SWCNTs or ssDNA-w-SWCNTs. The release of ssDNA-w-SWCNTs is carried out by positive or negative desorption potential. SWCNTs/SAM or ssDNA-w-SWCNTs/SAM is completely removed from Au surface at +0.90 V or -1.40 V (vs. 3.0 M KCl|Ag|AgCl). The controlled release of SWCNTs/SAM and ssDNA-w-SWCNTs/SAM holds great promise for gene delivering.     

Gold film surface preparation for self-assembled monolayer studies

Evaporated gold films are frequently used as substrates for the study of biomolecular adsorbates, nanoparticle systems, amd partial and full monolayer films. These studies often benefit from a predeposition cleaning of the surface that removes adventitiously adsorbed material from laboratory contaminants. Scanning tunneling microscopy (STM) is used in this study to explore the microscopic consequences of two pretreatment protocols used in literature reports of self-assembled monolayers, based on sulfochromic and piranha acid solutions. These measurements show that treatment of the Au/mica surface with piranha acid can lead to extensive and uncontrolled etching of the surface and severe disruption of the surface topography; extended exposure causes the precipitation of crystallites on the surface that are highly mobile during STM imaging processes. Exposure of Au/mica surfaces to sulfochromic acid leads to the formation of permanent etch pits of the surface that are exclusively one Au layer deep; extended exposure leads to progressive etching and oxidation of the surface, ultimately leading to the formation of 0.33-0.36 nm high islands on the otherwise flat Au/mica surface. The piranha acid solutions are significantly more likely to cause the Au film to delaminate from the mica support than are the sulfochromic acid solutions. These results show that sulfochromic surface preparation is a direct and reliable method for the elimination of organic residues from Au(111)-textured surfaces, while causing a minimum of structural and chemical surface damage.     

Spatially-separated and photo-enhanced semiconductor corrosion processes for high-efficient and contamination-free electrochemical nanoimprint lithography

Free of any thermoplastic or photocuring resists, electrochemical nanoimprint lithography(ECNL) has emerged as an alternative nanoimprint way to fabricate three-dimensional micro/nano-structures(3D-MNSs) directly on a semiconductor wafer by a spatially-confined corrosion reaction induced by the metal/semiconductor contact potential. However, the consumption of electron acceptors in the ultrathin electrolyte between imprint mold and semiconductor wafer will slow down or even cease the corrosion r...     

Thin self-assembled monolayer for voltammetrically monitoring nicotinic acid in food

A novel and sensitive method for the determination of nicotinic acid was proposed and based on voltammetric behavior of nicotinic acid on a self-assembled monolayer of mercaptoacetic acid coated gold electrode. The adsorption-controlled anodic peak current for the oxidation of nicotinic acid on mercaptoacetic acid covered gold electrode was affected by the type and pH value of supporting electrolyte and by accumulation potential as well as by accumulation time, and enhanced linearly with the concentration of nicotinic acid in the range of 0.8 mM–0.45 μM with a detection limit of 0.14 μM. The proposed method was utilized successfully for the monitoring of nicotinic acid in food. The possible interaction of nicotinic acid with mercaptoacetic acid, which is responsible for the enhanced response of nicotinic acid on modified electrode, was also suggested.     

Improved pattern transfer in nanoimprint lithography at 30 nm half-pitch by substrate-surface functionalization

Resist detachment from the substrate during mold-substrate separation is one of the key challenges for nanoimprint lithography as the pitch of features decreases. We analyzed the problem by considering the surface and interfacial free energies of the initial state and the possible final states of the mold-polymer-substrate system and designed the chemistry of the system to provide the desired final state. We dramatically improved the resist adhesion to the substrate by assembling a monolayer of surface linker molecules on the substrate surface. A 37 nanowire pattern at 30 nm half-pitch was imprinted onto the surface-modified substrate.     

Electroanalytical performance of self-assembled monolayer gold electrode for chloramphenicol determination

Monolayers of 2-mercapto-5-methylbenzimidazole (MMB) were prepared on a polycrystalline gold electrode via a self-assembly process to produce a self-assembled monolayer. The resulting electrode was investigated by cyclic voltammetry and electrochemical impedance spectroscopy, and applied to the determination of chloramphenicol (CAP) in a pharmaceutical formulation using flow injection analysis along with amperometric detection. The amperometric cell was operated at ?0.75 V (vs Ag/AgCl) at a flow rate of 3 mL min^?1. The method was applied to the determination of CAP in ophthalmic solutions, and its performance was compared to a previously validated HPLC method. The response to CAP is linear in the range from 0.050 to 1.000 µmol L^?1 (r?=?0.9990), and the limit of detection is 44 µmol L^?1.     

Photodegradable polyurethane self-assembled nanoparticles for photocontrollable release

Light-responsive drug delivery systems are particularly appealing that are capable of releasing active molecules at the appropriate site and rate. We synthesized a series of photodegradable polymers that can form nanoparticles for drug encapsulation. These particles in aqueous solutions are stable in buffers with different pHs or at evaluated temperatures, while light can trigger the crash of particles and the release of encapsulated substances. The release efficiency can reach up to 90% based on Nile red fluorescence intensity upon 15 min light irradiation. Nanoparticle uptake by phagocytic cells and light-triggered release in cells were observed by fluorescence emission of the hydrolyzed fluorescein diacetate upon photoinduced degradation of these nanoparticles. No significant toxicity of these nanoparticles was found at the concentrations up to 1000 μg/mL before or after light irradiation. Further encapsulation and triggered release of a bioactive model drug (Tagalsin G) was evaluated for RAW 264.7 cells. Tagalsin G encapsulated in nanoparticles did not show cytotoxity to cells, while light triggered the release of Tagalsin G increasing cell death dramatically from 9% to 67%. Our model studies show a new promising strategy to trigger drug release in cells.     

D4(H)/D4(V) silicone: a replica material with several advantages for nanoimprint lithography and capillary force lithography

Reported are demonstrations that D(4)(H)/D(4)(V) silicone (the product of the platinum-catalyzed hydrosilylation reaction between tetramethylcyclotetrasiloxane and tetramethyltetravinylcyclotetrasiloxane) is useful and practical as a replica material for both nanoimprint lithography (NIL) and capillary force lithography (CFL). The multiple advantageous properties of this extremely cross-linked material include UV transparency (for photo NIL and photo CFL), thermal stability (for high printing temperatures), high modulus (for high printing pressures), low surface energy (for easy demolding), and low viscosity precursors (for replicating small scale features). The replication performance of this material was tested using Blu-ray discs with sub-25 nm features and anodized aluminum foil with sub-10 nm features. Structures of ～5 nm length scale on the surface of the anodized Al were replicated using D(4)(H)/D(4)(V) silicone as a mold material for CFL with a photocurable epoxy resin and for NIL with poly(methyl methacrylate) (PMMA). Features (holes in the anodized aluminum) with aspect ratios of greater than 9 were replicated.     

A tetrafluorophenyl activated ester self-assembled monolayer for the immobilization of amine-modified oligonucleotides

A tetrafluorophenyl (TFP) ester-terminated self-assembled monolayer (SAM) for the fabrication of DNA arrays on gold surfaces is described. Activated ester SAMs are desirable for biomolecule array fabrication because they readily react with amine-containing molecules to form a stable amide linkage. N-Hydroxysuccinimide (NHS) ester SAMs are commonly used for this purpose but are subject to a competing hydrolysis side reaction, limiting their effectiveness under basic conditions. TFP was evaluated here as an alternative activated ester leaving group with a potentially greater stability under basic conditions. It is shown that TFP SAMs are much more stable to basic pH than their NHS analogs and are also more hydrophobic, which is an advantage in the fabrication of high-density spotted arrays. DNA arrays prepared on TFP SAMs at pH 10 have a 5-fold greater surface density of DNA molecules, reduced fluorescence background, and smaller spot radii than those prepared on NHS SAM analogs.     

Preferential adsorption of amino-terminated silane in a binary mixed self-assembled monolayer

The composition and structure of a binary mixed self-assembled monolayer (SAM) of 3-aminopropyltriethoxysilane (APS, NH(2)(CH(2))(3)Si(OCH(2)CH(3))(3)) and octadecyltrimethoxysilane (ODS, CH(3)(CH(2))(17)Si(OCH(3))(3)) on a silicon oxide surface have been characterized by water contact-angle measurements, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and sum frequency generation (SFG) vibrational spectroscopy. XPS demonstrated that APS in the mixed SAM is significantly enriched in comparison to that in solution, indicating the preferential adsorption of APS during the SAM formation. AFM observations showed that the mixed SAM becomes rougher. SFG revealed that the coadsorption of APS induced a conformation disordering in the ODS molecules present in the mixed SAM. The surface enrichment of APS has been explained in terms of differences in the surface adsorption rates of the two components as well as in the self-congregation states of APS molecules in the bulk solution. Furthermore, the structure of the water molecules on the mixed SAM surface in contact with the aqueous solutions at different pH's has also been studied. The results indicate that the mixed-SAM modified surface is positively charged at pH < 5 and negatively charged at pH > 7.