fulltext32 - Size Distributions of Cadmium Sulde...

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Size Distributions of Cadmium Sulfide Nanoparticles Obtained from Templating Methods P AULO J. G. C OUTINHO , C ANDIDO A. G. M ENDES , AND T ERESA S. V. R EIS Departamento de F´ ısica, Universidade do Minho, Campus de Gualtar, Braga, Portugal Cadmium sulfide (CdS) nanoparticles were obtained by soft templating methods using either an already established revered micelle route or a new procedure based on gel electrophoresis. The UV- Vis absorption or the photoluminescence excitation spectra were fitted using the CdS electronic structure available in the literature together with a size distribution. The obtained results indicate that the amount of sodium dodecyl sulphate as a component of the agarose gel formulation has a profound effect on the resulting nanoparticle population. Key words: CdS nanoparticles; templating; size distribution; photoluminescence Introduction Nanotechnology is a field of very active investiga- tion. There is a wide scope of technological applica- tions ranging from photocatalysis and sensors to fluo- rescence imaging. In this work, cadmium sulfide (CdS) nanoparticles have been prepared by templating methods using sur- factants and gel electrophoresis. The surfactant tem- plating protocol was based on that of Pileni, 1 using AOT [sodium bis(2-ethylhexyl) sulfosuccinate] water- in-oil microemulsions. In the gel electrophoresis pro- cedure, cadmium and sulfide ions migrate under an electric field in opposite directions until they meet and react within the gel pores. This reaction is thus con- trolled by diffusion through the gel pores. The applica- tion of reaction–diffusion processes in nanofabrication involving gels has recently been reviewed. 2 The size dependence of CdS electronic states was obtained by a tight binding approximation. 3 Using these theoreti- cal results, in conjunction with a size distribution and a Mie formalism for the scatter/absorption of nanoparti- cles of a given size, we were able to fit the experimental absorption and excitation spectra of CdS nanoparti- cles, either in AOT reversed micelles or in dried gels. In the case of AOT templating, the resulting particles should be spherical and the calculated average sizes can be compared to those obtained using empirical re- lations between first absorption peak and nanoparticle Address for correspondence: Paulo J.G. Coutinho, Departamento de ısica, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal. Voice: + 351 253 604321; fax: + 351 253 604061. [email protected] size proposed by Yu and colleagues. 4 In the gel elec- trophoresis templating experiments, excess concentra- tion of one of the ions and the presence of sodium dodecyl sulphate (SDS) surfactant was found to influ- ence the size distribution of the nanoparticles and the corresponding photoluminescence spectra.
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