Controlling Electric Field and Photoemission at the Tips of Triangular Gold Antennas
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Controlling Electric Field and Photoemission at the Tips of Triangular Gold Antennas Christopher M. Scheffler 1
&
Robert C. Word 1 & Rolf Könenkamp 1
Received: 15 July 2020 / Accepted: 15 September 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract We show that the fields of surface plasmon polaritons (SPPs)—excited by infrared ultrafast laser light—can be highly concentrated at the corners of thin, micron-scale gold triangular platelets. We present multi-photon photoemission electron microscopy (nP-PEEM) images and finite element method (FEM) simulations that show that the magnitude of the SPP electric field can be adjusted over a large range via control of the polarization, wavelength, and angle of incidence of the applied laser light. As it is well known that the strength of SPP near-fields has a strong bearing on non-linear photoelectron emission rates, localized SPP fields might effectively be used as a nano-scale adjustable electron source. Keywords Optical antenna . Photoemission . Field enhancement . Surface plasmon polaritons (SPPs) . Photoemission electron microscopy (PEEM) . Finite-element method (FEM)
Introduction Advancements in fabrication methodology and laser technology have enabled the development of sub-wavelength optical devices based on the conversion and confinement of light as surface plasmon polaritons (SPPs). So-called plasmonic devices have already been developed for applications in sensing [1], anti-counterfeiting [2], phototherapy [3], and microelectronics [4]. Such structures may also have application as critical elements of optical circuits. Reviews of the diverse areas using these devices can be found in [5, 6]. Continued development of surface plasmon-based technologies requires further progress in their characterization. Gold, due to its inert surface chemistry and favorable optical properties in the near-infrared spectrum, is commonly used as the metal layer in plasmonic structures. Single-crystalline gold nano-rods and thin triangular platelets are of particular interest because of their material qualities and ease of manufacture [7, 8]. These nano materials have interesting optical properties as-is [9–11] and as raw materials for manufactured, more complicated shapes, such as rings and gratings [12, 13]. * Christopher M. Scheffler [email protected] 1
Department of Physics, Portland State University, Portland, OR, USA
Such structures are typically milled using focused ion beams or in more recent work, electron beam lithography, which produces structures more reliably and with smaller dimensions [14]. Fine control of the fabrication process is needed for the production of bowtie antennas, for example, which are composed of two metal triangles separated by a few nanometers [15]. Even with the improvement of lithographical techniques, bowtie antennas can be challenging to manufacture with enough precision to obtain small gap dimensions and thus gain strong localized field enhancement. The thin triangular gold platelets discussed here are much simpler
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