Tunable Optical Absorption of Composites of Nanocrystalline Copper Prepared by in situ Chemical Reduction within a Cu 2+
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Tunable Optical Absorption of Composites of Nanocrystalline Copper Prepared by in situ Chemical Reduction within a Cu2+-Polymer Complex Cheng Huang,1 Gang Huang,2 and C. Z. Yang3 1
Materials Research Institute and Electrical Engineering Department, The Pennsylvania State University, University Park, PA 16802, [email protected] 2 Electronic Materials & Thin Film Devices Division, Physics Dept., Suzhou University, 215006, China 3 Department of Polymer Science and Engineering, Nanjing University, Nanjing 210093, China
ABSTRACT Research on nanocrystalline materials and the physics behind their properties have attracted considerable attention. A number of physical and chemical techniques have been used to synthesize different nanomaterials and nanocomposites. Optical absorption characteristics of composites containing nanosized metals or semiconductors have been investigated for potential applications in nonlinear optics and photonic crystals and also to understand the effect of particle size on the band gap of the material concerned. These materials show a large third-order nonlinear susceptibility. A polymer-matrix nanocomposite containing copper particles has been prepared by in situ chemical reduction within a polymer-metal complex solid film. The copper particle size in the order of 10 nm is controlled by the initial content of the metal ions in the complex. Their fractal pattern and the value of the fractal dimension indicate that there exists a cluster-cluster aggregation (CCA) process in the present system. Optical absorption spectra of copper-polymer nanocomposites show distinct plasma absorption bands and quantum size effect in the samples. More studies on optical properties of composites containing nanosized metals are within the Drudeframe on the basis of Mie theory, but the electrons behave in a wavelike rather than a particlelike way as the particle size decreases to below 10 nm, and the classical Drude model should be modified considering the quantum confinement effect. In this paper, the calculated blueshift of the resonance peak based on a quantum-sphere model (QSM) proposed by Huang and Lue, gives remarkable agreement with the experimental data as the size of copper particles embedded in the polymer becomes smaller. INTRODUCTION Research on nanocomposites and their properties has attracted considerable attention in recent years [1,2]. A wide variety of physical and chemical synthetic approaches have been applied to the preparation of nanocomposites [3]. The association of subunits to form large clusters in metrices is still a phenomenon central to many synthetic processes of nanocompoaites. The Witten-Sander model [4] provides a basis for obtaining a better understanding of a variety of diffusion-limited processes, e.g., an metal electrodeposition process [3], however the features of this model are unrealistic for many other real colloidal system, such as metal colloids, soot, and coagulated aerosols [5], and later Meakin further developed a model for diffusion-controlled aggregation in which gro
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