Abstract
The scattering of electrically excited surface plasmon polaritons (SPPs) into photons at the edges of gold metal stripes is investigated. The SPPs are locally generated by the inelastic tunneling current of a scanning tunneling microscope (STM). The majority of the collected light arising from the scattering of SPPs at the stripe edges is emitted in the forward direction and is collected at large angle (close to the air-glass critical angle, θ(c)). A much weaker isotropic component of the scattered light gives rise to an interference pattern in the Fourier plane images, demonstrating that plasmons may be scattered coherently. An analysis of the interference pattern as a function of excitation position on the stripe is used to determine a value of 1.42 ± 0.18 for the relative plasmon wave vector (kSPP/k0) of the corresponding SPPs. From these results, we interpret the directional, large angle (θ~θ(c)) scattering to be mainly from plasmons on the air-gold interface, and the diffuse scattering forming interference fringes to be dominantly from plasmons on the gold-substrate interface.
Highlights
Propagating surface plasmon polaritons (SPPs) may be used to transfer information and energy in metallic nanostructures with spatial resolution below the diffraction limit [1, 2]
Thanks to this local excitation and the absence of any background excitation light we have demonstrated a new method for measuring the relative wave vector of scattered SPPs
The value of kSPP/k0 = 1.42 ± 0.18 determined from the fringe pattern shift with scanning tunneling microscope (STM) tip excitation position is in agreement with the expected value of 1.57 calculated for SPPs excited on the Au/indium tin oxide (ITO)/glass interface (i.e., the “bottom” of the stripe, see Fig. 3(a))
Summary
Propagating surface plasmon polaritons (SPPs) may be used to transfer information and energy in metallic nanostructures with spatial resolution below the diffraction limit [1, 2]. STM-excitation of plasmons [23,24,25,26] has several advantages over the more common optical excitation, for example i) low energy electrical excitation (< 4 eV), which is compatible with current microelectronics, ii) very localized excitation (~10 nm) [27] and iii) the absence of background excitation light Thanks to this local excitation and the absence of any background excitation light we have demonstrated a new method for measuring the relative wave vector of scattered SPPs. In this article, we use real and Fourier plane measurements of the collected light from STM-excited plasmons to investigate their scattering properties. From these measurements it is proposed that the directional, large angle (θ~θc) scattering is mainly from plasmons on the air-gold interface, and the diffuse scattering is mostly due to plasmons on the gold-substrate interface
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