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3D periodic arrays of nanoparticles inside mesoporous silica films Sophie Besson1,2, Thierry Gacoin1, Catherine Jacquiod2, Christian Ricolleau3, Jean-Pierre Boilot1 1 LPMC, UMR CNRS 7643, Ecole Polytechnique, 91128 Palaiseau France 2 LSVI CNRS/Saint-Gobain, UMR CNRS 125, 39 quai Lucien Lefranc, 93303 Aubervilliers France 3 LMCP, UMR CNRS 7590, Universités Paris 6 et 7, 4 place Jussieu, 75252 Paris France ABSTRACT CdS nanoparticles were grown inside a 3D hexagonal porous silica film. The film pore size and organization allowed the perfect control of particle repartition and size (3.5 nm), leading to a 3D nanocrystal array inside the silica matrix. The method was extended to another silica porous structure with larger pores, which allowed to obtain larger particles (5.8 nm). This process was then successfully generalized to other metal sulfides. INTRODUCTION Since the past decade, nanocrystals below 10 nm have attracted worldwide interest as they display optical, electronic or magnetic properties which differ significantly from those of bulk materials [1]. These specific effects depend strongly on their size, shape and surface state. To elaborate nanoparticulate materials for applications such as nonlinear optics, optoelectronics, biology or catalysis, it may be important to control not only these parameters, but also the repartition of the nanocrystals which can strongly modify the properties. In this context, 3D periodic arrays of nanoparticles seem to be the optimal systems to study collective effects. Nevertheless, the production of such materials at a large scale and with good mechanical stability remains a challenge. Periodic mesoporous materials are potentially excellent candidates to support nanocrystals. These materials, discovered by Mobil Oil Corporation researchers in 1992 [2], are synthesized via the polymerization of inorganic species, generally silica, around a surfactant micelle liquid crystal, which is then eliminated by thermal treatment. By varying the surfactant nature and the synthesis conditions, different periodic structures with pore sizes from 2 to 30 nm can be formed [3,4]. As they have pores which are perfectly controlled in size, shape and organization, these materials can act as templates for the synthesis of periodic arrays of nanoparticles. A lot of studies have been published about nanoparticle growth inside mesoporous powders, but only few have succeeded in controlling the size, shape and organization of the nanocrystals, and usually in small domains [5,6]. Besides, for most applications, coatings filled with nanoparticles are needed instead of powders. We report here a general method to synthesize 3D quantum dot lattices (CdS, ZnS, PbS, Ag2S) in mesoporous silica films. EXPERIMENT Porous matrices were synthesized using a procedure previously described [7]: TEOS (Si(OC2H5)4), ethanol and water (pH=1.25) were mixed in the molar ratio 1:3.8:5 and aged 1h at AA4.3.1/W4.3.1

60°C. The cationic surfactant CTAB (cetyltriethyammonium bromide) was then added to the sol with Si/surfactant mola