Preparation and isolation of gold nanoparticles coated with a stabilizer and sol-gel compatible agent
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P.J. Morais and R.M. Almeida Departamento de Engenharia de Materiais/INESC, Instituto Superior Te´cnico, Av. Rovisco Pais, 1000-049 Lisboa, Portugal (Received 6 August 2001; accepted 9 May 2002)
In this work an attractive technique is presented that brings together the advantage of the micelle reverse technique to control the particle growth and the efficiency of the amine silanes as sol-gel-compatible surface modifiers. The diamino silane is far from being a passive agent in the formation process of the gold particle; it strongly modifies the growth of the gold particle in the reverse micelle. The diamino silane allows the gold particles to keep their individual properties unaltered throughout the process, which ends with their incorporation into a SiO2–TiO2 sol-gel thin film.
I. INTRODUCTION
Nanostructured materials are of current scientific interest because of their attractive size-dependent properties, which have led to a series of interdisciplinary efforts. Both chemical and physical properties have been found to be useful and, in many cases, fascinating in this nanosize range. Semiconductor and metal nanoparticles are of interest due to their many important applications in the field of new materials research and development; one of them is the application in optical devices.1,2 The realization of these prospective applications will require particles to be uniformly embedded and separated from each other in a suitable medium, and a variety of techniques for preparing fine particles in dielectric matrixes has been studied: photosensitive glasses,3 ion implantation,4 radio-frequency-sputtering,5 plasma deposition,6 relaxative autodispersion,7 etc. For preparation of particle-doped glasses, the conventional melting process has disadvantages such as limited concentration and undesirable high-temperature processing. Due to the low-temperature process involving hydrolysis and condensation reactions of metal alkoxides, the sol-gel technique was successfully applied to preparation of CdS-8 and PbS-doped9 glasses. The sol-gel process allows deposition of layer on layer, which is required for fabrication of integrated optical circuits. It offers several advantages over the other competing technologies; it is cheap and simple, especially for multicomponent oxide matrixes, and since it is a chemical process in liquid medium, the dopant species can be dispersed easily, so that high homogeneity and uniformity are obtained. J. Mater. Res., Vol. 17, No. 8, Aug 2002
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The synthesis of colloidal gold (Au) particles has been widely studied by a variety of chemical methods.10–14 The sol-gel processes have also been applied to production of Au particles in situ in the film matrix by heat treatment15,16 or by using the photosensitivity of the Au complex ions17,18 after film deposition. This photogeneration is preceded by photoreduction of gold complex ions within the gels under irradiation with ultraviolet (UV) light. Radiation time and radiation intensity influence the photo
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