DOI: 10.1002/adfm.200800244 Soft Nanopatterning on Light-Emitting Inorganic–Organic Composites** By Luana Persano, Sandra Molle, Salvatore Girardo, Antonio A. R. Neves, Andrea Camposeo, Ripalta Stabile, Roberto Cingolani, and Dario Pisignano* 1. Introduction Nanocomposite systems [1] consisting of a polymer matrix filled by inorganic nanoparticles exhibit tailored or improved mechanical, [2] thermal, [3] catalytic [4] or optical [5] properties. In particular, the incorporation of micro- or nanocrystals in conjugated polymers [5a,c,e,g,i] allows one to exploit the wide tunability, ease of processing and structural flexibility of organics, together with the optical and thermal stability of inorganic light-emitting fillers for the specific design of broadly tunable optically active materials. In our previous work, [5i] we studied how the organic–inorganic interaction can be often described through a dipole-surface scheme, determining the characteristic activation energies of the exciton recombina- tion routes in the nanocomposite. However, a crucial issue for the realization of nanocomposite-based optoelectronic devices still is the development of suitable lithographic technologies for wavelength-scale (sub-micrometer) pattern- ing. To date, patterning of hybrid nanocomposites embedding luminescent nanocrystals has been accomplished by electron- beam, [6] optical [7] and imprint lithographies, [8] by exploiting optically inert matrices such as methacrylate polymers and copolymers, [6,7b,8b] epoxy-based photoresists [7a] and titania pre-polymers. [8a] Instead, notwithstanding the great impor- tance of these materials for both fundamental studies and applications, [5a,c,e,g,i] nanopatterning of composites with nano- crystals incorporated in light-emitting organics is basically unexplored, likely due to the more difficult processability induced by the limited solubility and relatively poor thermo- plastic behaviour of many conjugated polymers. Here we demonstrate the nanopatterning of such an important class of composites by soft moulding (SM) lithography, achieving resolutions up to a few hundreds of nanometres on several light-emitting polymers embedding zinc oxide particles [molecular structures (1–4) and crystalline structure of ZnO displayed in Fig. 1]. 2. Results and Discussion The SM, or capillary force lithography, [9] combines proce- dures and advantages of soft [10] and nanoimprint [11] methods. A scheme of our process is shown in Figure 2a–d. Once an elastomeric mould is put in contact with the surface of the nanocomposite film (Fig. 2a), the overall system is driven above the softening temperature of the polymer matrix (Fig. 2b). Widely employed in soft lithographies, [10] low Young modulus elastomeric stamps are particularly advisable for texturing nanocomposites, whose surface roughness can be substantially increased by the incorporated nanocrystals and their possible aggregates, hence requiring remarkable short- scale (<10 mm) [12] conformability of the moulds to obtain effective pattern transfer. The composite starts to wet the lateral walls of the recessed features in the mould up a filled height depending on the heating time (Fig. 2b, c). Afterwards, the system is driven below the matrix glass transition temperature (T g ), and the mould is detached from the surface (Fig. 2d), which turns out to be textured with the same pattern FULL PAPER [*] Dr. D. Pisignano, þ Dr. L. Persano, S. Molle, S. Girardo, Dr. A. A. R. Neves, Dr. A. Camposeo, R. Stabile, Prof. R. Cingolani NNL, National Nanotechnology Laboratory of Instituto Nazionale di Fisica della Materia-Consiglio Nazionale delle Ricerche, c/o Distretto Tecnologico ISUFI via Arnesano, I-73100 Lecce (Italy) E-mail: luana.persano@unile.it [þ] Present address: Istituto Superiore di Formazione Interdisciplinare (ISUFI), Universita ` del Salento, Lecce (Italy) [**] We gratefully acknowledge the financial support from the Regional Strategic Project ‘Ponamat’, from the Italian Institute of Technology, and from the Italian Ministry of University and Research through the FIRB project RBIP06SH3W. In this work we demonstrate the nanopatterning of nanocomposites made by luminescent zinc oxide nanoparticles and light- emitting conjugated polymers by means of soft molding lithography. Vertical nanofluidics is exploited to overcome the polymer transport difficulties intrinsic in materials incorporating nanocrystals, and the rheology, fluorescence, absolute quantum yield, and emission directionality of the nanostructured composites are investigated. We study the effect of patterned gratings on the directionality of light emitted from the nanocomposites, finding evidence of the enhancement of forward emitted light, due to the printed wavelength-scale periodicity. These results open new possibilities for the realization of nanopatterned devices based on hybrid organic-inorganic systems. 2692 ß 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Funct. Mater. 2008, 18, 2692–2698