Colloids and Surfaces A: Physicochemical and Engineering Aspects 177 (2001) 3 – 12 Size tailoring of CdS nanoparticles by different colloidal chemical techniques Sabrina Foglia a , Lorenza Suber a, *, Marcofabio Righini b a ICMAT-CNR, CP 10, Via Salara km 29.300, 00016 Monterotondo Stoz, Rome, Italy b ISM-CNR, Via del Fosso del Caaliere 100, 00133 Rome, Italy Received 15 November 1999; accepted 16 March 2000 Abstract Three different synthetic routes were used for the preparation of CdS nanoparticles and the samples were characterized structurally and optically. Sample composition, dimension and quantum confinement excitations are discussed and compared. Sharp edges present in the absorbance spectra indicated that these systems are promising for optoelectronic and photonic device applications. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Cadmium sulfide nanoparticles; Sol-gel synthesis; Nanoparticles www.elsevier.nl/locate/colsurfa 1. Introduction The synthesis and characterization of semicon- ductor clusters with dimensions from micro crys- tals to macro atoms (or quantum dots) represent areas of intense basic and applied research. The sol-gel process is now well known as a synthetic route for preparation of semiconductor and oxide materials starting from molecular precursors in solution [1 – 5]. Many synthesis procedures have been developed, which all use an organic com- plexing agent to stabilize the nanoparticles and to passivate their surface. It is well known that as the diameter of the cluster approaches the Bohr radius of the Wannier exciton, quantization of the energy bands becomes apparent and a blue shift in the valence-conduction transition energy can be observed in optical spectroscopy. Moreover, the influence of surface organic molecules on optical response is three-fold: (a) as surface passivation for avoiding surface traps; (b) for taking under control electron, hole and ambivalent exciton tun- nel between adjacent dots; and (c) it influences the dielectric confinement of the Wannier exciton. In the present paper we report the sol-gel syn- thesis of CdS semiconductor nanoparticles with different passivating organic surface molecules. The CdS particles are either nanoparticles, result- ing from controlled growth in inverted micelles with subsequent addition of organic capping molecules, or small clusters prepared in the pres - ence of organic capping molecules; the CdS clus- ter size in the particles range from 8 to 20 nm in * Corresponding author. Tel.: +39-06-90672338; fax: +39- 06-90672316. E-mail address: suber@mlib.cnr.it (L. Suber). 0927-7757/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0927-7757(00)00673-7