V. Reboud

Lasing in nanoimprinted two-dimensional photonic crystal band-edge lasers

We demonstrate optically pumped polymer band-edge lasers based on a two-dimensional photonic crystal slab fabricated by nanoimprint lithography (NIL). Lasing was obtained at the photonic band-edge, where the light exhibits a low group velocity at the Γ point of the triangular lattice photonic crystal band structure. The active medium was composed of a dye chromophore-loaded polymer matrix directly patterned in a single step by nanoimprint lithography. Plane-wave and finite difference time domain algorithms were used to predict experimental lasing frequencies and the lasing thresholds obtained at different Γ points. A low laser threshold of 3u2009μJ/mm2 was achieved in a defect-free photonic crystal thus showing the suitability of nanoimprint lithography to produce cost-efficient optically pumped lasers.

Photoluminescence enhancement in metallic nanocomposite printable polymer

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.

Enhanced light extraction in ITO-free OLEDs using double-sided printed electrodes

We show how nanoimprint lithographic techniques are particularly suited for the realization of OLED device structures. We tested them to realize nanopatterned metallic electrodes containing photonic crystals to couple the light out and plasmonic crystals showing extraordinary transmission. At similar current densities, a two-fold electroluminescence is achieved with devices having double-sided structured metallic electrodes as compared to a control OLED with an ITO anode. The use of combined nanoimprint lithography processes has the potential to expand the performance range of various organic optoelectronic devices.

Au Based Nanocomposites Towards Plasmonic Applications

Incorporation of nano‐sized metals in polymers can transfer their unique features to the host matrix, providing nanocomposite materials with improved optical, electric, magnetic and mechanical properties. In this work, colloidal Au nanorods have been incorporated into PMMA based random co‐polymer, properly functionalized with amino groups and the optical and morphological properties of the resulting nanocomposite have been investigated by spectroscopic and AFM measurements. Au nanorods have demonstrated to preserve the plasmon absorption and to retain morphological features upon the incorporation, thus making the final metal modified polymer composite exploitable for the fabrication of plasmonic devices. The prepared nanocomposites have been then patterned by Nano Imprint Lithography technique in order to demonstrate the viability of the materials towards optical applications.

Nano-scale effects on Young's modulus of nanoimprint polymers measured by photoacoustic metrology

The ultrashort laser pulse photoacoustic method has been used to characterise the physical properties of spin-coated PMMA layers onto Si wafers with thicknesses from 586 to 13 nm, . Acoustic speeds of polymer films were derived from the measured time of flight of acoustic waves in polymers and from their calculated visco-elastic properties. A 12% increase, in comparison to the PMMA bulk value, of the acoustic speeds was measured for polymer films with thicknesses below 80 nm, which corresponds to an increase in Youngs modulus of 26%. In addition, we found that adding a hexamethyldisilazane primer monolayer between the polymer film and the Si substrate lessen the increase in Youngs modulus, suggesting that the nanoscale changes are due to interface effects.

Enhanced photoluminescence from metals and nanoimprinted photonic crystals

Strong enhancements in the spontaneous emission intensity of dye chromophores-loaded in a printable polymer have been achieved by coupling the dye emission to surface plasmons of metallic thin films and metallic nanoparticles. The nanocomposite materials embossed by nanoimprint lithography process show good imprint properties.

Enhancement of extraction efficiency in nanoimprinted optical device structures

We demonstrate strong enhancements in the spontaneous emission intensity of emitters embedded in a printable polymer by coupling excitons to surface plasmon polaritons of metallic thin films or to localized surface plasmons of metallic nanoparticles. The nanocomposite materials are patterned by nanoimprint lithography with photonic crystal to enhance the light extraction of the polymer films. We finally show how NIL can be used to pattern metallic electrodes containing photonic crystals to couple the light-out of the plane and to pattern metallic electrodes containing plasmonic crystals showing extraordinary transmission to realize ITO-free OLEDs.

Enhanced extraction efficiency in nanoimprinted light emitting structures mediated by plasmon-exciton interaction

The interaction between plasmons and excitons in photonic crystal structures is demonstrated to benefit the light extraction capabilities of polymer-based light emitting components. An enhancement of up to a factor of 40 is reported in structures fabricated by nanoimprint lithography.

Physical properties of thin nanoimprint polymer films measured by photo-acoustic metrology

The implementation of nanoimprint lithography as a nanoscale manufacturing technique for features below 50 nm requires accurate values for the physical properties of the polymers, such as Youngs modulus, used in this fabrication process. These affect the flow of polymer during imprinting, and determine the strength and stability of the polymer structures that are produced. Most physical parameter values used for nanoimprinting are taken from bulk measurements. However below 100 nm, physical properties can change significantly due to the increased importance of surface and interface effects, and the confinement of polymer molecules. It order to measure directly the physical properties of samples with very small dimensions the ultrashort laser pulse photoacoustic method has been applied to layers of poly(methyl methacrylate) of thicknesses from 586 to 11 nm, spin-coated onto silicon wafers. Acoustic speeds, calculated from time of flight and film thicknesses as measured by ellipsometry, were found to increase below approximately 80 nm, with an increase of 20% for a 13 nm sample, compared to the bulk value. This corresponds to an increase in Youngs modulus of 44%. It was found that when a layer of Hexamethyldisilazane (HMDS) adhesion promoter was spin-coated onto the silicon wafer, before the polymer, there was a much smaller increase in Youngs modulus, of approximately 21%, at 16 nm thickness, which indicates that the increase is due to chemical effects at the interface. The photoacoustic process is numerically modelled to ensure a full analysis of the recorded signal.