Optical and Structural Characteristics of Gold Nanocrystallites Embedded in a Dielectric Matrix
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Optical and Structural Characteristics of Gold Nanocrystallites Embedded in a Dielectric Matrix A.K. Sharma, J.F. Muth', A. Kvit, J. Narayan and R.M. Kolbas' Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695-7916. 1Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695.
ABSTRACT We have fabricated Gold (Au) crystallites in amorphous alumina matrix by pulsed laser deposition. The characterization of these multilayer sequences was performed by high resolution transmission electron microscopy (HRTEM) and optical transmission measurements. TEM studies revealed the morphology and the microstructure of these composites. The optical transmission spectra showed characteristic surface plasma resonance of Au particles confined by the host dielectric matrix. These resonances fall in the visible spectral range. The importance of pulsed laser deposition in fabricating these composite films is discussed. INTRODUCTION The study of colloidal metal particles has a long and distinguished history due to the strong optical resonances in the visible portion of the spectrum permitting the design of colored glasses for stained glass in cathedrals and artware [1]. The Mie theory of absorption, which explains much of the fundamental characteristics of colloidal particles, was published in 1908 [2]. Since then there has been substantial work in many fields concerning the optical characteristics of small particles and aerosols [3]. Many methods [4] have been developed to produce these particles including: precipitation in solution, sol-gel, ion implantation, precipitation of metal clusters via annealing, chemical synthesis, co-sputtering, electron-beam lithography and low energy cluster-beam [5]. Advances in computer technology have also made available various computer codes, which may be used to calculate the resonances of non-spherical particles [3]. The optical response of metallic nanoparticles has a direct correspondence to the particles electronic structure and is strongly dependent on the particle size and shape, which create what are termed Morphological Dependent Resonances (MDRs). The optical absorption bands of noble metals such as gold, and silver fall in the ultravioletvisible spectral range. The strong absorption is the manifestation of the excitation of their characteristic surface plasmon resonance or interband transitions. The spectral position of surface plasma resonance of the metallic particles can be varied by embedding them in appropriate dielectric matrices. Controlling the size, shape and the composition of the surrounding matrix provides us a way to tailor the optical properties of the metal-dielectric composite as a function of the size of the metal particles and their volume fractions. Thus to better understand the behavior of metallic nanoparticles
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methods of creation which permit the size and shape and therefinements encapsulating environment to be controlled are strongly preferred. In conjunction with of th
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