Search

Research is done on optical properties of a straight 50-row-long photonic crystal waveguide (PCW), which are examined. In conclusion, a coupling factor is revealed which is higher than 60% between a monomode ridge waveguide and the PCW.

With the rise of microfluidics for the past decade, there has come an ever more pressing need for a low-cost and rapid prototyping technology, especially for research and education purposes. In this article, we report a rapid prototyping process of chromed masks for various microfluidic applications. The process takes place out of a clean room, uses a commercially available video-projector, and can be completed in less than half an hour. We quantify the ranges of fields of view and of resolutions accessible through this video-projection system and report the fabrication of critical microfluidic components (junctions, straight channels, and curved channels). To exemplify the process, three common devices are produced using this method: a droplet generation device, a gradient generation device, and a neuro-engineering oriented device. The neuro-engineering oriented device is a compartmentalized microfluidic chip, and therefore, required the production and the precise alignment of two different masks. [ABSTRACT FROM AUTHOR]

In this work, the authors evaluate a new type of perfluoropolyether molecule (FLUOROLINK® S10) to be used as an antisticking mold treatment in UV nanoimprint lithography. Unlike currently used ones, this molecule has two anchoring ends groups allowing two covalent grafting sites of the molecule to the mold surface. Obtained results on this molecule are compared to Optool DSX’s ones. Using contact angle measurement, x-ray photoelectron spectroscopy, and electron spin resonance, the authors carried out chemical analysis of the evolution of antisticking treatments as a function of the number of imprints. It is found that both molecules have a roughly equivalent behavior. FLUOROLINK® S10 has shown less chemical resistance, attributed to its larger number of C–O bonds in the molecule, but an improved mechanical resistance, attributed to the double grafting mechanism. [ABSTRACT FROM AUTHOR]

Photopolymerizable epoxy polyhedral oligomeric silsesquioxane monomers with variable aliphatic spacer have been prepared and cured under UV radiation. Due to their organic/inorganic composition, these materials are promising candidates for microelectronic applications which requires high thermal and mechanical stabilities as well as a low dielectric constant, for example, for the fabrication of electrical interconnects. The authors pointed out by ellipsometric measurements that the use of a sensitizer in addition to the photoinitiator enhances the kinetic of the cationic polymerization of epoxy groups. The polymerization performed either in an EVG770® nanoimprint lithography stepper or under normal atmospheric conditions has been investigated by infrared spectroscopy, delivering information concerning polymerization mechanisms and allowing the optimization of the resin composition. Thermogravimetric analyses have shown that an annealing step is necessary after the UV curing of the resin to eliminate inert residues of the photoinitiator dissociation and thus improving the thermal resistance of the polymer. Finally they have demonstrated that the obtained polymers form interpenetrated networks and that their mechanical properties are retained up to a temperature of 375 °C. [ABSTRACT FROM AUTHOR]

In this article, the authors compare a polymer resist to a thermally curable monomer resist in a full 8 in. wafer thermal nanoimprint lithography process. Using exactly the same imprinting conditions, the authors compare the printing quality and investigate the resist distribution through large area gratings (6×6 mm2) with various densities. It is shown that a liquid monomer solution greatly enhance the printing uniformity because of a much wider resist redistribution and flow during the process. Redistribution of the monomer resist is observed over an entire grating, while it is observed only over a few periods of a grating for the polymer in the same conditions. Furthermore, a low molecular weight resist allows reducing the imprinting force as well as the total cycle time. [ABSTRACT FROM AUTHOR]

This article reports on the properties of ultraviolet nanoimprint lithography dedicated imprinting materials. Studied solutions are composed of a diacrylate-based monomer and a variable amount (1%, 2%, and 4% in weight) of three different photoinitiators from Ciba Specialty Chemicals (Irgacure 819, Irgacure OXE02, and Irgacure 379). Photopolymerization kinetic studies were conducted on these solutions. Quantity and type of photoinitiator could be optimized in order to obtain a polymerization rate higher than 95% with an exposure dose as low as 20 mJ/cm2. The etch resistance of this home-developed imprinting resist was characterized under standard plasma etching conditions. We observed that the polymerization rate has a large influence on the plasma etch resistance, and we show that the etch rates of our best material is comparable to the one measured for 193 nm photolithography resists and makes it a very good candidate as a masking layer for direct pattern transfer. [ABSTRACT FROM AUTHOR]

We present optical characterization of silicon-on-insulator (SOI)-based photonic crystal (PC) microcavities doped with erbium and oxygen. Photoluminescence (PL) is recorded up to the room temperature. A large PL intensity enhancement is obtained compared to the case of identically implanted SOI wafer at 1.54 mum. Moreover, no temperature-quenching effect is observed. [ABSTRACT FROM PUBLISHER]

The fabrication of a three-dimensional multilayered nanostructure is demonstrated with a newly developed nanofabrication technique, namely, reverse contact ultraviolet nanoimprint lithography. This technique is a combination of reverse nanoimprint lithography and contact ultraviolet lithography. In this process, a UV cross-linkable polymer and a thermoplastic polymer are spin coated onto a patterned hybrid metal-quartz stamp. These thin polymer films are then transferred from the stamp to the substrate by contact at a suitable temperature and pressure. The whole assembly is then exposed to UV light. After separation of the stamp and the substrate, the unexposed polymer areas are rinsed away with acetone leaving behind the negative features of the original stamp with no residual layer. [ABSTRACT FROM AUTHOR]

In general, fluorinated antisticking layers (F-ASL) are deposited on the imprint stamps to ease their separation from the imprinted resist in UV nanoimprint lithography. However, these layers are found to degrade with repeated imprint operations. A drastic decrease in fluorinated species is observed on the mold surface. Yet, there is still a debate on the nature of the exact mechanisms involved in this degradation. In this paper, electron spin resonance (ESR) is used to investigate the chemical reaction occurring between the fluorinated molecules and the UV curable resist. Free radicals of the resist, generated under UV illumination, have been observed by ESR. The decrease in their corresponding signal in the presence of fluorinated ASL species shows evidence of the chemical reactivity of the resist toward the F-ASL. [ABSTRACT FROM AUTHOR]

A 1.7-fold enhancement in the spontaneous emission intensity of dye chromophore loaded in a printable polymer is achieved by coupling the dye emission to surface plasmons of metallic nanoparticles. The nanocomposite material, embossed into arrays of wires by nanoimprint lithography process, shows good imprint properties. The results prove the potential of the prepared luminescent functional materials for micro- and nanofabrication and suggest the use of nanocomposite materials in prospective nanoplasmonic applications. [ABSTRACT FROM AUTHOR]

We report on the fabrication and characterization of two-dimensional polymer photonic crystal band-edge lasers operating in the visible range. The components have been fabricated in a dye chromophore-loaded polymer matrix by nanoimprint lithography. High-symmetry band-edge modes are used to generate laser emission. The experimental lasing frequencies are in good agreement with those calculated using a two-dimensional plane wave algorithm. These results demonstrate the potential of nanoimprint lithography for the fabrication of two-dimensional planar photonic crystal structures in an active medium in a one-step process. [ABSTRACT FROM AUTHOR]

The authors report on the fabrication and optical characterizations of two-dimensional photonic crystals fabricated by nanoimprint lithography in a nanocomposite polymer incorporating highly luminescent and red emitting (CdSe)ZnS core-shell colloidal nanocrystals. Photonic crystal structures enhance the light emitted from the quantum sized nanoparticles in the composite layer by slowing the propagation speed of the photons, thus increasing the coupling to the out-of-plane radiative modes. A 200% enhancement of the light collection is achieved compared to an unpatterned sample. [ABSTRACT FROM AUTHOR]

Very high photoluminescence extraction is observed from defectless two-dimensional photonic crystals etched in the upper 200-nm-thick silicon layer of a silicon-on-insulator (SOI) substrate. Predicted very low group velocity modes near the Γ point of the band structure lying above the light line are used to extract light from the photonic crystal slab into the free space. It is found that light is extracted on a 80-nm-wide band along directions near to the perpendicular to the slab, with an extraction enhancement up to 70 compared to an unpatterned SOI. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Optical properties of two-dimensional photonic crystals (PCs) integrated in a silicon-on-insulator stripe waveguide are reported. Transmission measurements are done on a wide wavelength range (1.1-1.7 µm) by coupling a white-light source in the cleaved edge of the sample and collecting light at the other cleaved side of the waveguide. PC mirrors and one-dimensional (1D) Fabry-Pérot cavities formed between two PC reflectors have been fabricated and characterized. The photonic band gap of the mirror is observed in the Γ-M direction for the transverse electric like guided modes. For the waveguide with the 1D Fabry-Pérot cavity, resonant modes appear within the gap. It is found that the experimental spectra are in very good agreement with both the theoretical photonic band structure and the theoretical transmission calculated by finite difference time domain. [ABSTRACT FROM AUTHOR]

In this work, the authors evaluate the impact of chemical and mechanical properties of UV nanoimprint lithography resists on the durability of antisticking treatments applied on the quartz mold surface. To do this, three acrylate-based resists were formulated and characterized. Fourier transform infrared spectroscopy was used to investigate the degree of conversion of each formulation as a function of the exposure dose and electron spin resonance was used to investigate the chemical reactivity of each formulation with respect to a fluorinated antisticking layer (Optool DSX from Daikin Chemicals). The impact of resist mechanical properties on the mold surface treatment degradation was also studied. Elastic modulus and hardness were measured by nanoindentation as a function of the polymerization degree. Then, these resists were imprinted with a dummy quartz template treated beforehand with the antisticking layer. The release properties of the molds were monitored by measuring their free surface energy as a function of the chemical and mechanical properties of the imprinted resists. A detailed comparative study has shown that release properties degradation is more governed by a mechanical than by a chemical interaction. [ABSTRACT FROM AUTHOR]

The fabrication of two-dimensional photonic crystals by nanoimprint lithography is established to realize lasing oscillations at three band edge frequencies. The optically pumped lasers are based on a dye-chromophore-loaded polymer matrix on a transparent substrate. A two-dimensional plane-wave algorithm was used to design the band-edge lasers showing a good agreement with the experimental lasing frequencies. These results show that nanoimprint lithography is well-suited to the one-step fabrication of two-dimensional active-polymer photonic crystals. [ABSTRACT FROM AUTHOR]

Abstract: Thanks to their low surface energy, fluorinated anti-sticking layers are widely used in UV nanoimprint lithography (UV–NIL) to treat the mold and facilitate its separation from the imprinted resist. However, it has been reported that release properties of the stamp deteriorate with repeated imprint operations. In this paper, X-ray photoelectron spectroscopy is used to study the mechanism of the fluorinated treatment degradation. A specific experimental protocol is used in order to avoid further degradation under X-ray exposure. It has been observed that a large amount of fluorinated molecules are removed in the first imprint steps and deposited on the surface of the imprinted resist. After this first stage, we observed that fluorinated molecules are progressively degraded along their chain during the NIL process. [Copyright &y& Elsevier]