J. Phys. Chem. C 2008, 112, 10767–10772
10767
Correlating Plasmon Resonance Spectra with Three-Dimensional Morphology of Single Silver Nanoparticles Yujun Song,*,†,‡ Tao Zhang,† Wantai Yang,§ and Sacharia Albin| School of Materials Science and Engineering, Beijing UniVersity of Aeronautics & Aestronautics, Beijing, China 100083, Applied Research Center, Old Dominion UniVersity, Newport News, Virginia 23606, College of Materials Science and Engineering, Beijing UniVersity of Chemical Technology, Beijing, China 100029, and Department of Electrical and Computer Engineering, Old Dominion UniVersity, Norfolk, Virginia 23529 ReceiVed: March 13, 2008; ReVised Manuscript ReceiVed: April 4, 2008
This paper was withdrawn on October 2, 2008. pholent resonance spectra of nanoparticles fabricted osparent substrate. This involves fabricating multihierarchy arrayed microwindows on glass coverslips using UV lithography, fabricating nanoparticles of different shapes in these microwindows by a modifiedosphethographding the localized surface plasmon resonance (LSPR) spectra by a dark-field microscopy and spectroscopy, and correlating the 3D structure of individual nanoparticles obtained by atomic fFM) with their LSPR spectra. This technique allows for the correlation and orientation of the same single nanoparticles by different instruments. Here we use it to identify the optical responses of single Ag nanoparticles and study their shape-dependent and 3D local morphology dependent LSPR spectra of single nanoparticles. 1. Introduction Understanding the relationship between morphology and the physical and chemical properties of nanomaterials is critical in the design and fabrication of functional nanomaterials.1,2 Most studies investigated the properties of ensembles of nanoparticles leading to results based on many separated or aggregated nanoparticles.3–5 Since the physical and chemical properties of nanoparticles depend on the shapes of nanoparticles and can be strongly influenced by nanoparticle coupling, it is imperative to correlate the 3D morphology of a nanoparticle with its physical and chemical properties.5–7 Single nanoparticle measurements are needed to understand their chemical and physical properties and those of individual nanoparticle aggregates.8–14 The ability to correlate the physical and chemical properties of nanoscale materials with their size, shape, topography, interparticle spacing, local dielectric environment and other structure parameters, is of fundamental and practical significance.15–18 Much attention has been recently paid to the study of the surface plasmonic properties of noble metal nanoparticles because of their promising applications.1,19–25 When an electromagnetic wave penetrates into the surface of a metal nanoparticle, it interacts with free electrons in the nanoparticle causing coherent oscillations of these conduction electrons forming a localized surface plasmon resonance (LSPR).15 The LSPR frequency of nanoparticles depends on their size, shape, dielectric environments, and interparticle interaction. The study of the LSPR properties of single nanoparticles is important for designing nanoparticles with different LSPR frequency and understanding interparticle coupling. Identification of isolated * Corresponding author. Phone: 01186-10-82316192. E-mail: yjsong2007@ gmail.com. † Beijing University of Aeronautics & Aestronautics. ‡ Applied Research Center, Old Dominion University. § Beijing University of Chemical Technology. | Department of Electrical and Computer Engineering, Old Dominion University.
individual nanoparticles and correlating their morphologies with their unique LSPR responses are required for these studies. Techniques of single nanoparticle detection are mostly based on their optical or photonic responses.17,26–32 Although some of these techniques can reach subwavelength diffraction resolution, they cannot provide morphology information of the corresponding particles with the needed spatial resolution. Nanoparticle morphology can be characterized by transmission electron microscopy (TEM),3,4,33 scanning electron microscopy (SEM),34 scanning tunneling microscopy (STM),35 and atomic force microscopy (AFM),36 which will provide nanometer or even subnanometer spatial resolution. To correlate the different properties of single nanoparticles with their morphologies requires being able to identify the same nanoparticle with different instrumentations probing morphologies and the other nanoparticle properties. Correlation of optical images and TEM images of individual nanoparticles using enumerated TEM grids, position markers on a Si3N4 thin film window supported on a silicon wafer, or patterns including many nanoparticles from a wide-field optical image was reported. 5,40,41 However, TEM has to be operated in high vacuum and does not provide quantitative 3D information. Also, for TEM the nanoparticles have to be placed on a thin substrate (typically
