Real-space imaging of nanotip plasmons using electron energy loss spectroscopy

Schröder, Benjamin; Weber, Thorsten; Yalunin, Sergey V.; Kiel, T.; Matyssek, Christian; Sivis, Murat; Schäfter, Sascha; Cube, Felix von; Irsen, Stephan; Busch, Kurt; Roper, Claus; Lindén, Stefan

doi:10.1103/physrevb.92.085411

Cited by 45 publications

(58 citation statements)

References 45 publications

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“…The EFTEM images of the taper region are readily understood by assuming that the electron beam indeed couples mostly to the m = 0 monopole mode of the taper. Recent EELS measurements and simulations [86,89,91] confirm the broadband, non-resonant character of the field enhancement at the taper apex. The observation of oscillations in the spectra recorded at larger distances from the apex was interpreted as a characteristic signature of the excitation of higher order angular momentum modes [86].…”

Section: Plasmonic Eigenmodes Of Circular Wires and Tapersmentioning

confidence: 89%

“…The observation of oscillations in the spectra recorded at larger distances from the apex was interpreted as a characteristic signature of the excitation of higher order angular momentum modes [86]. The formation of standing waves due to the back reflection of SPP modes near the apex may also give rise to spectral oscillations for certain taper geometries, as evidenced in [89,91].…”

Section: Plasmonic Eigenmodes Of Circular Wires and Tapersmentioning

confidence: 95%

“…When coupling ultrafast laser pulses to propagating SPPs at the shaft of those tapers, nanometre-localized light spots with pulse durations as short as 10 fs are created at the taper apex with high efficiency [42,76]. Consequently, the optical properties of such antennas have been studied in considerable detail, both experimentally and theoretically, during the past several years [42,63,64,70,[75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91].…”

Section: Introductionmentioning

confidence: 99%

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Plasmonic nanofocusing – grey holes for light

Groß

Esmann

Becker

et al. 2016

Advances in Physics: X

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Improving the resolution and sensitivity in all-optical microscopy and spectroscopy is inevitably one of the most important challenges in contemporary optical and nanoscience. Here, we discuss a novel approach, plasmonic nanofocusing, towards broadband, coherent all-optical microscopy with ultrahigh temporal and spatial resolution. The conceptual idea is to launch radially symmetric surface plasmon polariton modes onto the shaft of a sharp, conical metal taper. While propagating towards the apex of the pointed taper, the spatial extent of the plasmonic mode gradually shrinks, from several microns in diameter to a spot size of less than 10 nm at the pointed apex of the conical taper. Concomitantly, the local field amplitude of the plasmon mode gradually increases, resulting in a pronounced field enhancement at the apex and -thus -a bright and spatially isolated coherent light source with dimensions far below the diffraction limit. In this review, we characterize the optical properties of such three-dimensional conical metal tapers and demonstrate nanofocusing of radially symmetric plasmon modes. We use this nanolight source for coherent light scattering spectroscopy and demonstrate the sensitivity enhancement resulting from the pronounced spatial field confinement. It is shown that such off-resonant plasmonic nanoantennas facilitate the creation of nanofocused light spots with few-cycle time resolution. As a first application of this ability to nanolocalize ultrashort plasmon wavepackets, we demonstrate remotely-triggered multiphoton-induced photoemission from the very apex of the taper and implement this novel ultrafast electron gun in a point-projection electron microscope. Our results not only indicate the favourable optical properties of this plasmonic nanolens but also suggest that it may find interesting applications in ultrafast scanning optical spectroscopy and might enable new types of ultrafast electron holography and scanning tunnelling microscopy.

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Section: Plasmonic Eigenmodes Of Circular Wires and Tapersmentioning

confidence: 89%

Section: Plasmonic Eigenmodes Of Circular Wires and Tapersmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

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Plasmonic nanofocusing – grey holes for light

Groß

Esmann

Becker

et al. 2016

Advances in Physics: X

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“…For comparison with theory, we performed numerical calculations of the CL signal based on the DGTD method [26]. To this end, we used the framework that has been developed in the past for the simulation of EELS experiments [27,31]. The system composed of the gold disk, the TEM substrate and the surrounding air was discretized in a tetrahedral mesh with element size between 80 nm in air away from the ND, 10 nm close to the ND and 5 nm inside the ND itself using a third-order Lagrange polynomial basis and evolved in time using a fourth-order low-storage Runge-Kutta integrator.…”

Section: Numerical Calculationsmentioning

confidence: 99%

Importance of substrates for the visibility of "dark" plasmonic modes

Fiedler¹,

Raza²,

Ai³

et al. 2020

Opt. Express

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Dark plasmonic modes have interesting properties, such as a longer lifetime and a narrower linewidth than their radiative counterpart, as well as little to no radiative losses. However, they have not been extensively studied yet due to their optical inaccessibility. Using electron-energy loss (EEL) and cathodoluminescence (CL) spectroscopy, the dark radial breathing modes (RBMs) in thin, monochrystalline gold nanodisks are systematically investigated in this work. It is found that the RBMs can be detected in a CL set-up despite only collecting the far-field. Their visibility in CL is attributed to the breaking of the mirror symmetry by the high-index substrate, creating an effective dipole moment. The outcoupling into the far-field is demonstrated to be enhanced by a factor of 4 by increasing the thickness of the supporting SiN membrane from 5 nm to 50 nm due to the increased net electric dipole moment in the substrate. Furthermore, it is shown that the resonance energy of RBMs can be easily tuned by varying the diameter of the nanodisk, making them promising candidates for nanophotonic applications.

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“…Recent technological developments, including the application of THz transients [16,33], shaken pulse-pair excitation (SPPX) [50,51], two-color SPPX [52,53], two-pulse picking [22,23] and cross-polarized double beat methods [54,55] have led to a reliable laser coupling to STM. Further near-field schemes, such as plasmonic nanofocusing, have the potential to further enhance the coupling to the tunneling gap [56][57][58][59][60].…”

Section: Introductionmentioning

confidence: 99%

Controlling photocurrent channels in scanning tunneling microscopy

et al. 2020

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We investigate photocurrents driven by femtosecond laser excitation of a (sub)-nanometer tunnel junction in an ultrahigh vacuum low-temperature scanning tunneling microscope (STM). The optically driven charge transfer is revealed by tip retraction curves showing a current contribution for exceptionally large tip-sample distances, evidencing a strongly reduced effective barrier height for photoexcited electrons at higher energies. Our measurements demonstrate that the magnitude of the photo-induced electron transport can be controlled by the laser power as well as the applied bias voltage. In contrast, the decay constant of the photocurrent is only weakly affected by these parameters. Stable STM operation with photoelectrons is demonstrated by acquiring constant current topographies. An effective non-equilibrium electron distribution as a consequence of multiphoton absorption is deduced by the analysis of the photocurrent using a one-dimensional potential barrier model.

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Real-space imaging of nanotip plasmons using electron energy loss spectroscopy

Cited by 45 publications

References 45 publications

Plasmonic nanofocusing – grey holes for light

Plasmonic nanofocusing – grey holes for light

Importance of substrates for the visibility of "dark" plasmonic modes

Controlling photocurrent channels in scanning tunneling microscopy

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