Synthesis of CdS nanocrystals in polymeric films studied by in-situ GID and GISAXS
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Synthesis of CdS nanocrystals in polymeric films studied by in-situ GID and GISAXS Tiziana Di Luccio1,2 , Dina Carbone3,ǂ, Silvia Masala4, Karthik Ramachandran2 and Julie Kornfield2 1 ENEA Agenzia Nazionale per le Nuove Tecnologie, l’Energia e lo Sviluppo Economico Sostenibile, UTTP NANO, P.le E. Fermi 1, 80055 Portici (Napoli), Italy 2 California Institute of Technology, Division of Chemistry and Chemical Engineering, 1200 E. California Blvd. Pasadena, CA 91125, U.S.A. 3 ESRF European Synchrotron Radiation Facility, 71, avenue des Martyrs, 38000 Grenoble, France 4 Solar and Photovoltaic Engineering Research Center, 4700 King Abdullah University of Science & Technology, Thuwal 23955-6900 Kingdom of Saudi Arabia ǂ
Present address: MAX IV Laboratory, Lund University, P.O. Box 118 SE-221 00 Lund Sweden
ABSTRACT In this work, we describe the synthesis of CdS nanocrystals in thin polymeric films by insitu Grazing Incidence Diffraction (GID) and Grazing Incidence Small Angle Scattering (GISAXS). The 2D GISAXS patterns indicate how the precursor structure is altered as the temperature is varied from 25°C to 300°C. At 150°C, the CdS nanocrystals start to arrange themselves in a hexagonal lattice with a lattice parameter of 27 Å. The diffraction intensity from the hexagonal lattice reaches a maximum at 170°C and decreases steadily upon further heating above 220oC indicating loss of symmetry. Correspondingly, the GID scans at 170°C show strong crystalline peaks from cubic CdS nanocrystals that are about 2 nm size. The results indicate that a temperature of 170°C is sufficient to synthesize CdS nanocrystals without degradation of the polymer matrix (Topas) in thin films (about 30nm). INTRODUCTION Hybrid organic-inorganic nanocomposites of polymeric materials and inorganic nanoparticles have a wide variety of applications [1] due to the difference in properties of the individual components and of the resulting composite material. In particular, nanocrystals (NCs) of II-VI semiconductors and their polymer nanocomposites can be used as an active layer in hybrid electronic devices such as solar cells [2], organic light emitting diodes [3] and organic thin film transistors [4]. Ex-situ methods of preparation usually blend colloidal nanocrystals after their synthesis with polymer solutions [5]. The blend procedures can be complicated by the use of incompatible solvents that may lead to undesired agglomeration and phase segregation. On the other hand, there are a number of in-situ methods that allow the synthesis of nanocrystals directly in the polymer matrix. One of these methods is the thermolysis of a metal-thiolate precursor that has been dispersed in a solution-cast polymer film [6]. This film is then heated to temperatures in the range of 200-300°C [7] that cause the precursor to decompose and form metal sulfide nanocrystals. In bulk polymer foils obtained by drop casting, the nanoparticle size and
aggregation depend upon annealing conditions such as the temperature and the duration of treatment [8]. Metal sulfide NCs such
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