Plasmonic excitation and manipulation with an electron beam
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Introduction Surface plasmons have great potential for shrinking light. Since a surface plasmon polariton (SPP) has a wavelength that is shorter than the wavelength of light in vacuum, SPPs allow for the miniaturization of optics: they have the potential to bring the dimensions of optical devices down to the dimensions of modern electronic integrated circuits. This realization has led to large recent interest in this phenomenon and the promise of applications in sensing, optical circuits, spontaneous emission control, and solar cells. In recent years, many metal structures have been presented that guide, confine, and manipulate plasmons, and exploit their ability to shrink light. Plasmonic devices based on such metal structures aim to control the excitation of plasmons, their propagation, dispersion, confinement, and mode structure at a length scale that is much shorter than an optical wavelength.1 For the application of these structures, it is important to characterize their performance by accessing surface plasmon modes at the nanoscale. Optical microscopy reaches down to ∼200 nm and often allows addressing individual plasmonic
elements. However, the spatial resolution of optical microscopy is limited by diffraction, and a higher resolution technique is required to probe surface plasmon devices at nanometer length scales. Near-field techniques using very small tips offer a higher resolution (see the Weber and Willets article in this issue). Near-field scanning optical microscopy (NSOM) is able to reach down to ∼50 nm, and apertureless or scattering-type NSOM allows access to the sub-15 nm scale.2 However, these techniques suffer from challenging experimental conditions (e.g., single wavelength performance, stability, background noise) as well as interaction between the tip and the sample.3,4 In contrast to excitation of plasmons through photons in optical microscopy, surface plasmons can be directly excited by fast electrons. In fact, the first signatures of surface plasmons were obtained using electron beam experiments5,6 in the 1950s and 1960s. Since an electron incident on a metal surface functions as a point source for surface plasmons, an electron microscope, through excitation of surface plasmons, can thus open up ways to characterize plasmon devices with a resolution only limited by the size of the electron beam. Modern electron
Ernst Jan R. Vesseur, Caelux Corporation, Pasadena, CA; [email protected] Javier Aizpurua, Center for Materials Physics of the Spanish National Council for Scientific Research CSIC and DIPC, San Sebastian, Spain; [email protected] Toon Coenen, FOM Institute AMOLF, Amsterdam, The Netherlands; [email protected] Alejandro Reyes-Coronado, Institute of Physics, Autonomous University of Puebla, Mexico; [email protected] Philip E. Batson, Institute for Advanced Materials, Devices and Nanotechnology, Rutgers University; [email protected] Albert Polman, FOM Institute AMOLF, Amsterdam, The Netherlands; [email protected] DOI: 10.1557/mrs.2012.174
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MRS BULLETIN • VOLUME 37 • AUGUST
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