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Abstract: We report on the fabrication and characterization of photonic band-gaps structures by nanoimprint lithography in a dye-doped polymer. Photonic band calculations show that photonic crystal slabs composed of a triangular array of polymer pillars could exhibit photonic band-gaps for the magnetic-like modes. The resulting structures show that the nanoimprint lithography process is well-suited to fabricate in a single-step process, these challenging photonic structures opening perspectives to realize integrated photonic band-gap circuits. [Copyright &y& Elsevier]

A status report of nanoimprint lithography is given in the context of alternative nanofabrication methods. Since the ultimate resolution of nanoimprint appears to be determined by the stamp, this is discussed in detail, particularly the recent developments on polymer stamps. The scope of the technique is illustrated with applications in passive optical structures and organic devices. Throughout the report, critical dimensions are discussed, as well as other challenges facing nanoimprint lithography. [Copyright &y& Elsevier]

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]

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: 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]