Investigating Narrow Plasmons in Nanoparticle Arrays Fabricated Using Electron Beam Lithography.
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J16.1.1
Investigating Narrow Plasmons in Nanoparticle Arrays Fabricated Using Electron Beam Lithography. Erin M. Hicks*§, Linda Gunnarrsson†, Tomas Rindevicius†, Shengli Zou*, Bengt Kasemo†, Mikael Käll†, Goerge C. Schatz*, Kenneth G. Spears*, and Richard P. Van Duyne* *Department of Chemistry, Northwestern University, Evanston, IL 60208-3113 USA † Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden S-214 96 § Corresponding Author: [email protected] ABSTRACT The improvement of nanofabrication is one of the driving forces behind advancements in the fields of electronics, photonics and sensors. Precise control over nanoscale architecture is an essential aspect in relating new size-dependent material properties. Direct writing methods such as Electron Beam Lithography (EBL), enable precise “user-defined” writing of nanostructures in a wide range of materials. Using electrodynamics calculations, Schatz and coworkers have discovered one dimensional array structures built from spherical silver nanoparticles that produce remarkably narrow plasmon resonance spectra upon irradiation with light that is polarized perpendicularly to the array axis. In order to investigate these interactions, precise control of nanoparticle orientation, size, shape and spacing is necessary. If the overall structures have excessive defects then the effect may not be seen. To have the best control over array fabrication and to look at these interactions experimentally, EBL was used to construct lines of circular cylinders of varying interparticle spacings. Dark field microscopy was used to look at overall sample homogeneity and collect the single particle plasmon resonance spectrum. Additionally, a UV-visible spectrometer with a variable angle stage was used to look at the bulk line properties. With experimental verification of the theory will lead to not only a more thorough understanding of the underlying principles of nanophotonics, but also application in biosensing, that potentially improve on current technologies. INTRODUCTION Assemblies of nanoparticles often can be used to provide special functionalities that are important in sensing [1], optical waveguides [2], and filters [3]. The use of assemblies, rather than single particles, offers the ability to average a signal across several similar particles (increasing intensity and eliminating discrepancies caused by defects) and the miniaturizing equipment is much simpler. Since the design of a practical plasmonic nanodevice relies heavily on arrays of noble metal nanoparticles, the interactions between these nanoparticles is a crucial and often overlooked design parameter. These interactions can be either short or long range for a variety of structure types including both highly dense array structures [4, 5] and individual pairs of nanoparticles [6]. They can be measured and studied by observing changes in the LSPR peak shape and position. Theoretical calculations also show these unique interactions. For example, previous work by Schatz et al. has pre
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