Surface Plasmon Excitation in Three-dimensional, Ordered, Gold Nanocrystal Arrays Using a Prism Coupler
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Surface Plasmon Excitation in Three-dimensional, Ordered, Gold Nanocrystal Arrays Using a Prism Coupler Kai Yang1, Hongyou Fan2,3, Michael J. O’Brien1, Kevin J. Malloy1, Gabriel P. Lopez2, C. Jeffrey Brinker2,4, Mansor Sheik-Bahae5 and Thomas W. Sigmon1 1 Center for High Technology Materials, 2Department of Chemical and Nuclear Engineering, University of New Mexico, Albuquerque, NM 87106 3 Ceramic Processing and Inorganic Materials Dept., 4 Self-Assembled Materials Dept., Advanced Materials Laboratory, Sandia National Laboratories, Albuquerque, NM 87106 5 Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM 87106
ABSTRACT We report plasmon excitation in 3-dimensional, ordered, gold nanocrystal(NC) arrays using a prism coupler. The gold NCs are arranged in the silica host matrix in a face-centered cubic lattice with the mono-dispersion gold core size of ~3 nm. We observed the collective optical behavior of the gold NC array and found a blue shift in the plasmon absorption peak with increasing gold volume fraction (Au loading). Plasmon resonance bands centered at 536, 530 and 520 nm are measured for gold NC arrays with gold loading factors of 0.25, 0.5 and 1.0, respectively. The corresponding angular spectra of the gold NC arrays show resonance angles at 60.3°, 63.3°, and 66.4°. INTRODUCTION Surface plasmons (SPs) have been extensively studied by physicists, chemists, materials scientists and biologists for decades. In the late sixties, optical excitation of surface plasmons by the method of attenuated total reflection (ATR) was demonstrated by Kretschmann and Otto. Recent advances in nano technology allows metals to be structured and characterized on the nanometer scale. This enables control of surface plasmon properties for revealing new aspects of the underlying science and to tailor them for specific applications. For instance, surface plasmons are being explored for their potential applications in optics, microscopy and solar cells, as well as being used to construct sensors for detecting biologically interesting molecules. The optical properties of ordered gold NC/silica arrays have been investigated in our previous work [1,2]. Collective behavior of the 3-D, ordered, gold NC systems was seen to result in a plasmon resonance absorption peak. In this work, we further evaluate plasmon excitation in these films using a prism coupler. The gold nanoparticles are arranged in the silica host matrix in a face-centered cubic lattice with the mono-dispersion gold core size of ~3 nm (variation less than 7%). Plasmon resonance bands centered at 536, 530, 520 nm were measured for gold NC arrays with gold loading factors of 0.25, 0.5 and 1.0, respectively. The blue shift in the resonance peak results from plasmon excitation (collective oscillation of free electrons) of individual gold NCs mediated by coupling interactions with neighboring NCs. Plasmon generation in the films is accomplished using a prism coupler. The corresponding angular spectra for the films exhibit resonances at an
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