Growth kinetics of tin oxide nanocrystals in colloidal suspensions under hydrothermal conditions Eduardo J.H. Lee a , Caue Ribeiro c, * , Elson Longo b , Edson R. Leite a a Centro Multidisciplinar para o Desenvolvimento de Materiais Cera ˆmicos (CMDMC-LIEC), Universidade Federal de Sao Carlos, Caixa Postal 676, Sao Carlos, SP 13565-905, Brazil b Centro Multidisciplinar para o Desenvolvimento de Materiais Cera ˆmicos (CMDMC-LIEC), Universidade Estadual Paulista, Insituto de Quı ´mica, Rua Prof. Francisco Degni s/n, Araraquara, SP, Brazil c Universidade Federal de Ouro Preto, ICEB-DQ, Campus Morro do Cruzeiro, Ouro Preto, MG, Brazil Received 24 February 2006; accepted 29 June 2006 Available online 4 July 2006 Abstract Colloidal suspensions of tin oxide nanocrystals were synthesized at room temperature by the hydrolysis reaction of tin chloride (II), in an ethanolic solution. The coarsening kinetics of such nanocrystals was studied by submitting the as-prepared suspensions to hydrother- mal treatments at temperatures of 100, 150 and 200 °C for periods between 60 and 12,000 min. Transmission electron microscopy (TEM) was used to characterize the samples (i.e. distribution of nanocrystal size, average particle radius and morphology). The results show that the usual Ostwald ripening coarsening mechanism does not fit well the experimental data, which is an indicative that this process is not significant for SnO 2 nanocrystals, in the studied experimental conditions. The morphology evolution of the nanocrystals upon hydro- thermal treatment indicates that growth by oriented attachment (OA) should be significant. A kinetic model that describes OA growth is successfully applied to fit the data. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Crystal growth; Oriented attachment; Hydrothermal treatment; Tin dioxide 1. Introduction In the past decades a lot of interest has been devoted to the investigation of nanostructured materials. New effects and properties observed in the nanoscale are very promis- ing for a number of improved or novel applications [1–3]. These new properties arise mainly from surface or spatial confinement effects. Hence, characteristics such as particle size and morphology play a crucial role in determining the final properties of nanostructures. For instance, it has been demonstrated that the band gap energy of semicon- ducting nanocrystals is a function of particle size, when the Bohr exciton radius is comparable to the nanocrystal size [4]. This effect of quantum confinement may be used to improve the absorption yield of solar cells or for lasing devices, for example. Therefore, the abilities to synthesize different nanomaterials and to control their size and mor- phology are strongly motivated. Synthesis techniques of nanomaterials are very numer- ous in the literature. In particular, several methods have been reported for the preparation of nanoparticles, nano- wires and quantum wells, especially for semiconductors and metals [5,6]. To some lower extent, research on the fab- rication of nanocrystalline functional oxides is also an active field [7,8]. Lately, bottom-up methods based in chemical processes have gained considerable interest, due to their ability to process nanomaterials inexpensively and with good quality. However, several processes are involved in the preparation of nanocrystals by bottom-up approaches, such as nucleation, growth and coarsening. A thorough knowledge of these processes is of great impor- tance, to enable the tailor making of nanostructures with controlled properties. Several studies have demonstrated 0301-0104/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.chemphys.2006.06.032 * Corresponding author. Tel.: +55 16 3361 5215; fax: +55 16 3351 8214. E-mail address: caue@liec.ufscar.br (C. Ribeiro). www.elsevier.com/locate/chemphys Chemical Physics 328 (2006) 229–235