Microstructure and Optical Properties of Au-Y 2 O 3 -stabilized ZrO 2 Nanocomposite Films
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nocomposite films consisting of gold nanoparticles embedded in an yttria stabilized zirconia (YSZ) matrix were synthesized at room temperature by radio-frequency co-sputtering from YSZ and Au targets at a 5 mTorr working pressure. The films were subsequently annealed for 2 h in 1 atm argon, with the annealing temperature varied from 600 to 1000 °C in steps of 100 °C. The composition, microstructure, and optical properties of the films were characterized as a function of annealing temperature by Rutherford backscattering spectrometry, scanning electron microscopy, Auger electron spectroscopy, x-ray diffraction, and absorption spectroscopy. An optical absorption band due to the surface plasmon resonance (SPR) of the Au nanoparticles was observed around a wavelength of 600 nm. Furthermore, the SPR band full width at half-maximum exhibited an inverse linear dependence on the radius of the Au nanoparticle, with a slope parameter A ⳱ 0.18, indicating a weak interaction between the YSZ matrix and the Au nanoparticles. The experimentally observed SPR dependence on nanoparticle size is discussed within the context of the Mie theory and its size-dependent optical constants.
I. INTRODUCTION
Nanosized metal particles embedded in various oxide matrices are currently of significant interest because they exhibit customizable optical, electronic, and magnetic properties that could be utilized in a myriad of novel technologies, including optoelectronic devices, portable sensors, and high-density information storage applications.1,2 In particular, silver (Ag) and gold (Au) nanoparticles exhibit a strong surface plasmon resonance (SPR) band, whose spectral position and shape are not only highly dependent on the size, shape, and density of the nanoparticles, but also on the structural and chemical characteristics of the host medium.2 Although it has been demonstrated that noble metal nanoparticles exhibit significant potential in optical sensing devices,3 embedding the nanoparticles in an appropriate matrix is believed to broaden their operational range, thus permitting a new and expanded array of technological applications.4 In this context, a vast majority of
a)
Present address: Centre for Renewable Energy Systems Technology, Department of Electronic and Electrical Engineering, Loughborough University, Loughborough, LE11 3TU, UK. b) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0300
the investigations to date of the optical properties of embedded Au nanoparticles has concentrated on studying the optical properties of Au in amorphous binary oxide matrices, including silicon oxide (SiO2) and aluminum oxide (Al2O3). Although these matrices are generally considered inert, evidence indicates that the material and microstructural properties of the matrix may cause unexpected changes in the SPR peak position dependence on the nanoparticle diameter. More specifically, while it is widely accepted that the SPR band of free spherical Ag or Au nanoparticles will red shift with an increa
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