Sol-gel synthesis and characterization of Ag nanoparticles in ZrO 2 thin films
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ZrO2 thin films containing silver nanoparticles were prepared using the sol-gel method with Ag to Zr molar ratios [Ag]/[Zr] = 0.11, 0.25, 0.43, 0.67, 1.00, 1.50, and 2.33. After dip coating on glass substrate, coated films were annealed at 200 and 300 C in air. X-ray diffraction peaks corresponding to crystalline Ag were observed, but a specific peak corresponding to ZrO2 was not observed. At the molar ratio [Ag]/[Zr] = 0.25, the particle size of Ag distributed broadly centered at 17 nm for an annealing temperature of 200 C and at 25 nm for 300 C. The films annealed in air at 200 C showed an absorption band centered at 450 nm because of the silver surface plasmon resonance, whereas films heated at 300 C in air caused a red shift of the absorption to 500 nm. The absorption peak was analyzed using the effective dielectric function of ZrO2–Ag composite films modeled with the Maxwell-Garnett expression. I. INTRODUCTION
The synthesis of nanosized particle is a growing research field in chemical science, in accordance with the extensive development of nanotechnology.1–3 The sizeinduced properties of nanoparticles enable the development of new applications or the addition of flexibility to existing systems in many areas, such as catalysis, optics, microelectronics, and so on.4–10 In particular, nanoparticles of noble metals such as gold and silver have been attracting more attention, because they exhibit a variety of colors in the visible region based on the surface plasmon resonance, which is caused by the collective oscillations of the electrons at the surface of the nanoparticles. The resonance wave length strongly depends on the size and shape of the nanoparticles, the interparticle distance, and the dielectric property of the surrounding medium.11–13 The unique features of plasmon absorption in these noble metal nanoparticles have been exploited for a wide variety of applications including chemical sensors and biosensors. There are several techniques to synthesize silverdoped glass, e.g., sol-gel method, high temperature glass fusion, ion implantation, ion exchange, and sputtering.14–17 The sol-gel method has several advantages of high purity, ultrahomogeneity, low processing temperatures, and, most significantly, the possibility of fabricating glass films with new compositions.18–20 The gold and silver nanoparticles dispersed in dielectric constant such as SiO2, TiO2, and ZrO2 synthesized by the sol-gel technique were reported by Epifani et al.21 However, this report had insufficient information about the analya)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0314 J. Mater. Res., Vol. 24, No. 8, Aug 2009
sis of the parameter of nanoparticles and the optical absorption caused by the surface plasmon resonance. In addition, the surface plasmon resonance relating to ZrO2–Ag and TiO2–Ag were not observed clearly. In this paper, the preparation and characterization of ZrO2 thin films doped with silver nanoparticles by sol-gel processing are reported. Th
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