Search

Abstract: In this work, a novel nanofabrication technique is presented, namely “Reverse contact Ultraviolet Nanoimprint Lithography” (RUVNIL). It is based on reverse nanoimprint lithography and ultraviolet contact lithography. It provides flexibility in building complex three-dimensional structures allowing selective imprint over pre-patterned surfaces with or without residual layer in opposition to what is often encountered in the normal NIL process. We have investigated and optimized the imprinting parameters that are required for three-dimensional nanofabrication and applied it to the fabrication of nano-fluidic channels. This lithography technique is a very promising process for three-dimensional nanofabrication. [Copyright &y& Elsevier]

Abstract: Template-directed synthesis is a promising route to realize vanadate-based 1-D nanostructures, an example of which is the formation of vanadium pentoxide nanotubes and associated nanostructures. In this work, we report the interchange of long-chained alkyl amines with alkyl thiols. This reaction was followed using gold nanoparticles prepared by the Chemical Liquid Deposition (CLD) method with an average diameter of 0.9 nm and a stability of 85 days. nanotubes (VOx-NTs) with lengths of 2 m and internal hollow diameters of 20–100 nm were synthesized and functionalized in a Au-acetone colloid with a nominal concentration of  mol dm−3. The interchange reaction with dodecylamine is found only to occur in polar solvents and incorporation of the gold nanoparticles is not observed in the presence of n-decane. [Copyright &y& Elsevier]

Abstract: In the context of Si-based photonics, we report on a strategy to integrate two optical components, a 3D photonic crystal light emitter and a waveguide, in a silicon-on-insulator patterned substrate. Self-assembled colloidal photonic crystals are produced with high crystalline quality and spatial selectivity. Plane wave expansion and finite-difference time-domain have been used to find suitable configurations for positioning emitters and waveguides. The first steps toward the realisation of these configurations are presented. [Copyright &y& Elsevier]

Abstract: Anisotropic specimens of MoS2 are obtained by pressing the microcrystalline powder into special die. This inelastic compression results in a rearrangement of the disulfide micro platelets observed by atomic force microscopy and reflected in the macroscopic anisotropy in electrical conductivity in these samples. The conductivity measured parallel and perpendicular to the direction of applied pressure exhibits an anisotropy factor of 10 at 1 GPa. This behaviour of the conductivity as a function of applied pressure is explained as the result of the simultaneous influence of a rearrangement of the micro platelets in the solid and the change of the inter-grain distances. [Copyright &y& Elsevier]

In this work we address key fabrication issues, specific to fabricating an embedded single mode waveguide system for the telecommunication window. These are the control of adhesion between polymer layers and filling in cavities on pre-patterned polymer substrates. We report the fabrication of two embedded polymer single-mode waveguides, namely, polystyrene/Teflon® AF and mr-L 6000/Teflon® AF, fabricated by means of electron beam lithography and/or nanoimprint lithography. For both waveguides, it is possible to realize a low confinement of the guided mode in the core due to the low refractive index contrast between the core material and the cladding layer (around 0.05–0.2). This gives the flexibility to reduce waveguides optical losses if the losses of the core polymer are too high, which is usually the case in near infrared for most polymers. [Copyright &y& Elsevier]

The deterministic fabrication of microscopic structures in self-assembled three-dimensional (3D) photonic crystals is reported. Microscopic 1 μm deep controlled structures, cavities with width as small as 5 μm and trenches as narrow as 2 μm, been fabricated using direct electron-beam writing on a poly(methyl methacrylate) (PMMA) opal film. The technique is highly accurate, versatile and is probably suitable to fabricate buried defects. [Copyright &y& Elsevier]

Different methods of functionalisation of thin opal films are discussed, including synthesis of opals on pre-patterned substrates, post-synthesis electron beam lithography, preparation of opals with heterogeneous photonic band gap structure and integrating opals with light sources. These approaches have been tested experimentally and key technological problems have been identified. [Copyright &y& Elsevier]

Transmission, scattering and reflectance of bulk opals and thin opal films have been studied using a micro-optical set-up. Spectra of transmitted and scattered light are similar and complementary to reflectance spectrum. Long- and short-range attenuation mechanisms have been identified and related to the scattering on lattice defects. [Copyright &y& Elsevier]

Fluorescence microscopy is introduced as a low cost quality control process for nanoimprint lithography. To depict imprinted structures down to 1 μm lateral size and to detect residues down to 100 nm lateral size, the standard printable polymer mr-I8000 is labelled with less than 0.1 wt.% fluorescent dye. Three different types of stamps are used to determine the dependence of the shape and size of stamp features in a series of imprints. The quality of a stamp is given by the sticking polymer residues per unit area. Fluorescence light images as well as visible light images are analysed. Changes in the area of the stamp covered with polymer as a function of the number of imprints is summarised in a statistical process chart. Adhesion was artificially induced in order to observe self cleaning of virgin stamps. They were detected and monitored, suggesting that this method is a suitable technique for quality control and that it could be easily adapted to the nanoimprint process. [Copyright &y& Elsevier]

The characteristics and benefits of two types of cross-linking prepolymers with low glass transition temperature (Tg) for nanoimprinting are reported. They are soluble in organic solvents and their solutions can be processed like those of common thermoplastics. The imprinted patterns receive high thermal and mechanical stability through cross-linking polymerization. The course of the polymerization was investigated to determine the appropriate conditions for the imprint process. In thermally cross-linked polymers mr-I 9000, the cross-linking occurs during imprinting. Process time and temperature depend on the polymerization rate. Volume shrinkage during the polymerization does not adversely affect imprinting. Photochemically cross-linked polymers mr-L 6000 make possible imprint temperatures below 100 °C and short imprint times. The Tg of the prepolymer determines the imprint temperature. The cross-linking reaction and structural stabilization is performed after imprinting. 50-nm trenches and sub-50-nm dots confirm the successful application of the polymers. [Copyright &y& Elsevier]

A study of optical and transport properties of semiconductor quantum well structures subjected to nanoimprint lithography (NIL), with its pressure and temperature cycles, has been undertaken to ascertain if this lithography technique induces detrimental changes in these properties of the active layers over a range of pressures and temperatures, typically used in this printing process. Ga0.47In0.53As–InP and GaAs–Al0.3Ga0.7As multiple quantum well samples were investigated. Luminescence and the photoluminescence excitation were recorded before and after printing. No impact upon the luminescence energy and intensity were detected. From the photoluminescence spectrum no evidence of induced strain was found. The magneto transport experiments yielded no evidence of deterioration of neither the mobility nor carrier concentration of a two-dimensional electron gas in a modulation-doped Ga0.25In0.75As/InP heterostructure. Results on samples subjected to the NIL process over a wide range of applied pressure and temperature are presented and discussed. [Copyright &y& Elsevier]

Stamp fabrication for nanoimprinting can be significantly simplified, when specialized crosslinking polymers are applied to pattern definition. The polymer patterns can be used as stamps themselves. Two possibilities are reported: (1) An e-beam sensitive resist was developed, which enables the fabrication of polymer-on-silicon stamps. Patterns with a feature size of 70 nm could be created. (2) Full plastic stamps were obtained by a casting-moulding technique, which enable pattern transfer from any conventional mould. The quality of the two stamp variants were proved by imprinting experiments. [Copyright &y& Elsevier]

Thin films made of organic semiconductors (α-sexithiophene, PDAS and PBAS) have been printed and the impact on morphology studied by optical, atomic force and electron microscopy. Surfaces in contact with the stamp during printing undergo a change towards smoother and more ordered material at the macromolecular scale. Interdigitated nanoelectrodes to be used as source and drain in TFTs have been made and printed down to 100 nm. PDAS and PBAS can be printed at room temperature and preserve their printed feature provided they are cross-linked afterwards. [Copyright &y& Elsevier]

Abstract: In this work artificial crystal structures designed to exhibit large and simultaneous photonic and phononic bandgaps, known as phoXonic crystals, are fabricated in silicon. Simulations have shown that honeycomb and square symmetry phoXonic crystals with high filling-fractions can produce large bandgaps in the photonic and phononic dispersion relations. To achieve this at hypersonic phononic frequencies and infrared (telecommunications) photonic frequencies, critical dimensions smaller than 100nm are typically required. In this paper, dose variation for Electron Beam Lithography (EBL) combined with Reactive Ion Etching (RIE) and Thermal Oxidation (TO) are shown to be effective methods to carefully control these parameters. [Copyright &y& Elsevier]

Abstract: Photoluminescence of dye chromophores-loaded in printable polymer has been strongly enhanced thanks to two-dimensional nanoimprinted photonic crystals. Comparing the out of plane emission of the spin-coated dye-doped polymer on metallic corrugated and flat surfaces, the PL emission intensity increased by a factor 26 from the area with the nanostructure. This enhancement is explained by a coupling plasmon–exciton in the vicinity of the metal layer and an efficient diffraction of the surface plasmon modes by the metallic structures. [Copyright &y& Elsevier]

Abstract: The mask fabrication is a critical issue for the development of nanoimprint lithography (NIL) as an effective low-cost mass production technique. In this paper, we present results on the synthesis and the use of low-viscosity hybrid organic/inorganic resists based on polyhedral silsesquioxane cages functionalized with photo-polymerizable aliphatic epoxy groups. These materials are very attractive because they present a high thermal and mechanical resistance (as well as a reduced dielectric constant) and they can be processed by ultraviolet (UV)-assisted NIL. For these reasons, they are good candidates for the fabrication of 2nd generation stamps for both thermal and UV-NIL. [Copyright &y& Elsevier]