Structural, Optical and Chemical Properties of Zns and Cds Nanoparticles Obtained by an Improved Colloidal Chemistry Syn
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Structural, Optical and Chemical Properties of Zns and Cds Nanoparticles Obtained by an Improved Colloidal Chemistry Synthetic Route. M. Lucia Curri, Angela Agostiano, Mario Della Monica, Gabriella Leo1, Mauro Lomascolo1, Marco Alvisi1, Lorenzo Vasanelli1 C.S. CFILM - CNR, c/o Dipartimento di Chimica - Bari, Via Orabona 4 I-70126 Bari - Italy 1 IME – CNR, Via Arnesano I-73100 Lecce, Italy ABSTRACT In this work an improved synthetic route that exploits a quaternary water-in-oil microemulsion has been used to obtain nanocrystals of ZnS, CdS and their mixed compounds, - CdxZn1-xS - differing by their size and composition and having high crystalline quality, small dimensions and a quite good size distribution. The opportunity offered by the use of water-in-oil microemulsion to immobilize the nanocrystals onto solid substrate by selfassembling to obtain stable adherent layers has also been exploited. The physical and chemical properties of obtained nanocrystals and layers have been investigated by UV-vis spectroscopy, X-Ray Diffraction X-ray Photoelectron Spectroscopy and Scanning Tunneling Microscopy. The role played by the co-surfactant (pentanol) in controlling nanocrystal size and stability has been discussed. INTRODUCTION The study of physical and chemical properties of nanometer sized semiconductor clusters has been an active field of research because of their unique optical, electronic and photocatalytic properties due to the quantum size effects [1,2]. The increasing interest towards these materials has led to develop a wide range of chemical routes to prepare nanoparticles, aiming to the careful control of nanocrystallite size and, even more important, their size distribution. Moreover immobilization procedures are necessary to attach semiconductor nanocrystallites onto solid substrates in order to perform a more complete and exhaustive study of nanostructured materials and to develop novel devices, exploiting the mesoscopic physical and chemical characteristic of semiconductor nanoparticles. In this perspective the use of “water-in-oil” microemulsions represents an effective pathway to obtain both nanosized semiconductor particles and stable nanoparticle layers [3]. In particular an improved synthetic route which exploits a quaternary water-in-oil microemulsion (CTAB-cetyl-trimethyl ammonium bromide- / hexane / pentanol / water), has been proposed to obtain CdS nanocrystals of high crystalline quality, small dimensions and a high degree of monodispersity [4]. The presence of pentanol, the co-surfactant in the quaternary microemulsion, results to be a key factor in regulating the size, the size distribution and the stability of the crystallites. The role played by the pentanol can be summarized in two different actions: from one side the increased flexibility of the interfacial film influences the particle growth, and from the other side the absorption on the semiconductor surface determines the particle stabilization in solution, acting as a capping agent [4]. The possibility of exploiting the co-surfactant to
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