2024 |
Zapata-Herrera, M., Rogez, B., Marguet, S., Dujardin, G., Boer-Duchemin, E., & Le Moal, E. (2024). Spectral shifts in tip-induced light from plasmonic nanoparticles in air. Phys. Rev. B, 109(15), 155433.
Résumé: In this article, we carry out an in-depth study of the scanning tunneling microscopy-induced luminescence spectra (STML) of individual plasmonic nanoparticles measured in air. When compared to the results of far-field light scattering measured under the same ambient conditions, the STML measurements show spectral shifts and peak broadening of hundreds of meV, even when a non-plasmonic tip is used for STML. We simulate the near-field excitation and the effect of the tip using the finite-element method and show that these effects alone cannot explain the spectral shifts and peak broadening observed for STML experiments in air. However, the experimental results are well reproduced in the numerical simulations if the screening effect of a water meniscus bridge present in the tip-nanoparticle gap is considered. Our results pave the way for finer interpretations of STML experiments in air, where ignoring this additional screening effect can lead to an incorrect mode assignment of the observed resonances.
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2023 |
Pommier, D., Hufschmitt, Z., Zhang, C., Lai, Y., Dujardin, G., Le Moal, E., Sauvan, C., Greffet, J. - J., Wang, J., & Boer-Duchemin, E. (2023). Nanoscale Electrical Excitation of Surface Plasmon Polaritons with a Nanoantenna Tunneling Junction. ACS Photon., 10(8), 2641–2649.
Résumé: Quantum tunneling-driven optical nanoantennas are key components for the development of integrated plasmonic nanodevices. In this work, we use the tunneling junction between a nanoantenna and a thin gold film to electrically excite propagating surface plasmons on the nanoscale. The nanoantenna is a chemically synthesized gold nanocube (∼50 nm side length) that is separated from a thin (50 nm) gold film by an insulating molecular layer (1,8-octanedithiols, ∼1 nm thick). A novel method for completing the electrical circuit between the nanoantenna and the gold film using an atomic force microscope (AFM) is developed. Based on the results of numerical modeling, the nanoantenna modes exciting the propagating surface plasmon polaritons are identified as hybridized gap and antenna modes. Our results demonstrate the ability to interrogate individual tunneling-driven nanoantennas, a crucial step toward the development of electrical nanosources of surface plasmon polaritons and light.
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2020 |
Cao, S., Zapata-Herrera, M., Campos, A., Le Moal, E., Marguet, S., Dujardin, G., Kociak, M., Aizpurua, J., Borisov, A. G., & Boer-Duchemin, E. (2020). Probing the Radiative Electromagnetic Local Density of States in Nanostructures with a Scanning Tunneling Microscope. ACS Photonics, 7(5), 1280–1289.
Résumé: A novel technique for the investigation of the radiative contribution to the electromagnetic local density of states is presented. The inelastic tunneling current from a scanning tunneling microscope (STM) is used to locally and electrically excite the plasmonic modes of a triangular gold platelet. The radiative decay of these modes is detected through the transparent substrate in the far field. Emission spectra, which depend on the position of the STM excitation, as well as energy-filtered emission maps for particular spectral windows are acquired using this technique. The STM-nanosource spectroscopy and microscopy results are compared to those obtained from spatially resolved electron energy loss spectroscopy (EELS) maps on similar platelets. While EELS is known to be related to the total projected electromagnetic local density of states, the light emission from the STM-nanosource is shown here to select the radiative contribution. Full electromagnetic calculations are carried out to explain the experimental STM data and provide valuable insight into the radiative nature of the different contributions of the breathing and edge plasmon modes of the nanoparticles. Our results introduce the STM-nanosource as a tool to investigate and engineer light emission at the nanoscale.
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Le Moal, E., Boer-Duchemin, E. (2020). La nano-optique sous la pointe d’un microscope à effet tunnel. Photoniques, 102, 31–34.
Résumé: Le microscope à effet tunnel (STM) n’est pas seulement un outil de sciences des surfaces qui produit de magnifiques images résolues à l’échelle atomique. Le courant tunnel sous la pointe du STM est également une source d’excitation optique extrêmement locale, ce qui en fait un extraordinaire outil de la nano-optique. Ici, nous donnons un aperçu des possibilités de cet outil en plasmonique et en électroluminescence, lorsque STM et microscopie optique sont associés dans un même instrument.
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Raseev, G., Achlan, M. (2020). MIM thin film stack: flux enhancement due to coupling of surface plasmon polariton with wave guide modes. J. Phys. D: Appl. Phys., 53(50), 505303.
Résumé: A theoretical study is presented of the dispersion of surface plasmon polariton (SPP) and wave guide (WG) modes of a metal-insulator-metal (MIM) thin film stack. We study the dispersion of the reflectance and of the transmitted flux, originating from a local excitation source, of an asymmetric MIM air-Au-SiO2-Au-Ti-glass material system in the infrared and visible spectral region for a wide range of SiO2 and gold thicknesses, $d{\mathrm{SiO}2}$ and $d{\mathrm{Au}}$. In comparison to reference stacks of air-Au-glass or air-SiO2-glass, between 1.4 and 2.0 eV, the transmitted flux intensity is enhanced 12 or 25 times, in the emission direction of the in-plane wave vector $k\rho/k0\approx$1.05 and for a thickness of $d{\mathrm{SiO}2}\in$[300–700] nm, respectively. This enhancement is attributed to the coupling, through the avoided crossings, between the SPP${\mathrm{air}}$ and WG modes. As the fields of the SPP$_{\mathrm{air}}$ and WG modes are located in different regions of space the enhancement is nearly independent of the number of nodes in the WG mode. In summary we have identified sets of parameters giving rise to the observables enhancement. Therefore the present MIM thin film stack is a simple and a versatile system for the use in applications.
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2019 |
Cao, S., Achlan, M., Bryche, J. - F., Gogol, P., Dujardin, G., Raşeev, G., Le Moal, E., & Boer-Duchemin, E. (2019). An electrically induced probe of the modes of a plasmonic multilayer stack. Opt. Express, 27(23), 33011.
Résumé: A new single-image acquisition technique for the determination of the dispersion relation of the propagating modes of a plasmonic multilayer stack is introduced. This technique is based on an electrically-driven, spectrally broad excitation source which is nanoscale in size: the inelastic electron tunnel current between the tip of a scanning tunneling microscope (STM) and the sample. The resulting light from the excited modes of the system is collected in transmission using a microscope objective. The energy-momentum dispersion relation of the excited optical modes is then determined from the angle-resolved optical spectrum of the collected light. Experimental and theoretical results are obtained for metal-insulator-metal (MIM) stacks consisting of a silicon oxide layer (70, 190 or 310 nm thick) between two gold films (each with a thickness of 30 nm). The broadband characterization of hybrid plasmonic-photonic transverse magnetic (TM) modes involved in an avoided crossing is demonstrated and the advantages of this new technique over optical reflectivity measurements are evaluated
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2018 |
Bryche, J. - F., Barbillon, G., Bartenlian, B., Dujardin, G., Boer-Duchemin, E., & Le Moal, E. (2018). k-space optical microscopy of nanoparticle arrays: Opportunities and artifacts. J. Appl. Phys., 124(4), 043102.
Résumé: We report on the performance and inherent artifacts of k-space optical microscopy for the study of periodic arrays of nanoparticles under the various illumination configurations available on an inverted optical microscope. We focus on the origin of these artifacts and the ways to overcome or even benefit from them. In particular, a recently reported artifact, called the “condenser effect,” is demonstrated here in a new way. The consequences of this artifact (which is due to spurious reflections in the objective) on Fourier-space imaging and spectroscopic measurements are analyzed in detail. The advantages of using k-space optical microscopy to determine the optical band structure of plasmonic arrays and to perform surface plasmon resonance experiments are demonstrated. Potential applications of k-space imaging for the accurate lateral and axial positioning of the sample in optical microscopy are investigated.
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Cao, S., Le Moal, E., Jiang, Q., Drezet, A., Huant, S., Hugonin, J. - P., Dujardin, G., & Boer-Duchemin, E. (2018). Directional light beams by design from electrically driven elliptical slit antennas. Beilstein Journal of Nanotechnology, 9, 2361–2371.
Résumé: We report on the low-energy, electrical generation of light beams in specific directions from planar elliptical microstructures. The emission direction of the beam is determined by the microstructure eccentricity. A very simple, broadband, optical antenna design is used, which consists of a single elliptical slit etched into a gold film. The light beam source is driven by an electrical nanosource of surface plasmon polaritons (SPP) that is located at one focus of the ellipse. In this study, SPPs are generated through inelastic electron tunneling between a gold surface and the tip of a scanning tunneling microscope.
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2017 |
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Cao, S., Le Moal, E., Bigourdan, F., Hugonin, J. - P., Greffet, J. - J., Drezet, A., Huant, S., Dujardin, G., & Boer-Duchemin, E. (2017). Revealing the spectral response of a plasmonic lens using low-energy electrons. Phys. Rev. B, 96, 115419.
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Le Moal, E., Dujardin, G., & Boer-Duchemin, E. (2017). Electrical Generation of Light from Plasmonic Gold Nanoparticles. In Gold Nanoparticles for Physics, Chemistry and Biology. C. Louis & O. Pluchery.
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2016 |
Canneson, D., Le Moal, E., Cao, S., Quélin, X., Dallaporta, D., Dujardin, G., & Boer-Duchemin, E. (2016). Surface plasmon polariton beams from an electrically excited plasmonic crystal. Opt. Express, 24(23), 26186–26200.
Résumé: Surface plasmon polariton (SPP) beams with an in-plane angular spread of 8° are
produced by electrically exciting a 2D plasmonic crystal using a scanning tunneling microscope (STM). The plasmonic crystal consists of a gold nanoparticle (NP) array on a thin gold film on a glass substrate and it is the inelastic tunnel electrons (IET) from the STM that provide a localized and spectrally broadband SPP source. Surface waves on the gold film are shown to be essential for the coupling of the local, electrical excitation to the extended NP array, thus leading to the creation of SPP beams. A simple model of the scattering of SPPs by the array is used to explain the origin and direction of the generated SPP beams under certain conditions. In order to take into account the broadband spectrum of the source, calculations realized using finite-difference time-domain (FDTD) methods are obtained, showing that bandgaps for SPP propagation exist for certain wavelengths and indicating how changing the pitch of the NP array may enhance the SPP beaming effect.
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Cao, S., Lequeux, M., Le Moal, E., Drezet, A., Huant, S., Dujardin, G., Boer-Duchemin, E. (2016). Using a plasmonic lens to control the emission of electrically excited light. In PROCEEDINGS OF SPIE (Vol. 9884, 98841Y).
Résumé: A local, low-energy, electrical method for the excitation of localized and propagating surface plasmon polaritons (SPPs) is attractive for both fundamental and applied research. In particular, such a method produces no excitation background light and may be integrated with nanoelectronics. Here we report on the electrical excitation of SPPs through the inelastic tunneling of low-energy electrons from the tip of a scanning tunneling microscope (STM) to the surface of a two-dimensional plasmonic lens. The plasmonic structure is a series of concentric circular slits etched in a thick gold film on a glass substrate. An out-going circular SPP wave is generated from the tip-sample junction and is scattered into light by the slits. We compare the resulting emission pattern to that observed when exciting SPPs on a thin, unstructured gold film. For optimized parameters, the light emitted from the plasmonic lens is radially polarized. We describe the effects of the slit period and number, and lens diameter on the emission pattern and we diskuss how the light beam of low divergence is formed.
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Dujardin, G., Boer-Duchemin, E., Le Moal, E., Mayne, A. J., & Riedel, D. (2016). DIET (Dynamics at surfaces Induced by Electronic Transitions) at the nanoscale. Surf. Sci., 643, 13–17.
Résumé: We review the long maturing evolution of DIET (Dynamics at surfaces Induced by Electronic Transitions) that began in the 1960s when Menzel, Gomer and Redhead proposed their famous stimulated desorption model. DIET entered the « nanoscale » in the 1990s when researchers at Bell Labs and IBM realized that the Scanning Tunneling Microscope (STM) could be used as an atomic size source of electrons to electronically excite individual atoms and molecules at surfaces. Resonant and radiant Inelastic Electron Tunneling (IET) using the STM have considerably enlarged the range of applications of DIET. Nowadays, « DIET at the nanoscale » covers a broad range of phenomena at the atomic-scale. This includes molecular dynamics (dissociation, desorption, isomerization, displacement, chemical reaction), vibrational spectroscopy and dynamics, spin spectroscopy and manipulation, luminescence spectroscopy, Raman spectroscopy and plasmonics. Future trends of DIET at the nanoscale offer exciting prospects for new methods to control light and matter at the nanoscale.
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Le Moal, E., Marguet, S., Canneson, D., Rogez, B., Boer-Duchemin, E., Dujardin, G., Teperik, T. V., Marinica, D. C., & Borisov, A. G. (2016). Engineering the emission of light from a scanning tunneling microscope using the plasmonic modes of a nanoparticle. Phys. Rev. B, 93(3), 035418.
Résumé: The inelastic tunnel current in the junction formed between the tip of a scanning tunneling microscope (STM) and the sample can electrically generate optical signals. This phenomenon is potentially of great importance for nano-optoelectronic devices. In practice, however, the properties of the emitted light are difficult to control because of the strong influence of the STM tip. In this work, we show both theoretically and experimentally that the sought-after, well-controlled emission of light from an STM tunnel junction may be achieved using a nonplasmonic STM tip and a plasmonic nanoparticle on a transparent substrate. We demonstrate that the native plasmon modes of the nanoparticle may be used to engineer the light emitted in the substrate. Both the angular distribution and intensity of the emitted light may be varied in a predictable way by choosing the excitation position of the STM tip on the particle.
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Rogez, B., Cao, S., Dujardin, G., Comtet, G., Le Moal, E., Mayne, A. J., & Boer-Duchemin, E. (2016). The mechanism of light emission from a scanning tunnelling microscope operating in air. Nanotechnology, 27(46), 465201.
Résumé: The scanning tunnelling microscope (STM) may be used as a low-energy, electrical nanosource of surface plasmon polaritons and light. In this article, we demonstrate that the optimum mode of operation of the STM for maximum photon emission is completely different in air than in vacuum. To this end, we investigate the emission of photons, the variation in the relative tip-sample distance and the measured current as a function of time for an STM operating in air. Contrary to the case of an STM operating in vacuum, the measured current between the tip and sample for an STM in air is very unstable (rapidly fluctuating in time) when the applied voltage between the tip and sample is in the ∼1.5–3 V range (i.e., in the energy range of visible photons). The photon emission occurs in short (50 μs) bursts when the STM tip is closest to the sample. The current instabilities are shown to be a key ingredient for producing intense light emission from an STM operating in air (photon emission rate several orders of magnitude higher than for stable current). These results are explained in terms of the interplay between the tunnel current and the electrochemical current in the ubiquitous thin water layer that exists when working in air.
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2015 |
Boer-Duchemin, E., Wang, T., Le Moal, E., Dujardin, G. (2015). Electrically-driven surface plasmon nanosources. In PROCEEDINGS OF SPIE (Vol. 9361, 93610R).
Résumé: Electrical nanosources of surface plasmons will be an integral part of any future plasmonic circuits. Three different types of such nanosources (based on inelastic electron tunneling, high energy electron bombardment, and the electrical injection of a semiconductor device) are briefly described here. An example of a fundamental experiment using an electrical nanosource consisting of the tunnel junction formed between a scanning tunneling microscope (STM) and a metallic sample is given. In this experiment, the temporal coherence of the broadband STM-plasmon source is probed using a variant of Young's double slit experiment, and the coherence time of the broadband source is estimated to be about 5-10 fs.
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Rogez, B., Horeis, R., Le Moal, E., Christoffers, J., Al-Shamery, K., Dujardin, G., & Boer-Duchemin, E. (2015). Optical and electrical excitation of hybrid guided modes in an organic nanofiber-gold film system. J. Phys. Chem. C, 119, 22217.
Résumé: We report on the optical and electrical excitation of the modes of a “hybrid” waveguide consisting of a single organic nano fiber on a thin gold film. In the first set of experiments, light is used to excite the photoluminescence of an organic nano fiber on a thin gold film and the resulting emission is analyzed using Fourier-space leakage radiation microscopy. Two guided modes and the dispersion relations of this hybrid waveguide are thus determined. From numerical calculations, both a fundamental and excited mode of mixed photonic − plasmonic character are identified. In a second experiment, a local electrical nanosource of surface plasmon polaritons (SPPs) is coupled to the hybrid waveguide. The SPP nanosource consists of the inelastic electron tunnel current between the tip of a scanning tunneling microscope (STM) and the gold film. We show that the electrically excited SPPs couple to the fundamental mode and that the coupling efficiency is highest when the SPP nanosource is aligned with the nano fiber axis. Moreover, the electrically excited SPPs strongly scatter into out-of-plane light at the nano fiber end. This light from scattered SPPs measured in the substrate is phase shifted by about π with respect to the direct light emission from beneath the STM tip. These experiments lead to a better understanding of the processes that must be optimized in order to exploit such hybrid waveguide structures.
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Wang, T., Rogez, B., Comtet, G., Le Moal, E., Abidi, W., Remita, H., Dujardin, G., & Boer-Duchemin, E. (2015). Scattering of electrically excited surface plasmon polaritons by gold nanoparticles studied by optical interferometry with a scanning tunneling microscope. Phys. Rev. B, 92(4), 045438.
Résumé: We study the scattering of electrically excited surface plasmon polaritons (SPP) from individual nanostructures. The tunneling electrons from a scanning tunneling microscope (STM) are used to excite an out-going, circular SPP wave on a thin (50-nm) gold film on which isolated gold nanoparticles (NPs) have been deposited. Interaction of the excited SPPs with theNPs leads to both in-plane (SPP-to-SPP) and out-of-plane (SPP-to-photon) scattering. We use SPP leakage radiation microscopy to monitor the interference between the incident and in-plane scattered SPP waves in the image plane. By changing the location of the STM tip, the distance of the pointlike SPP source to the scatterers can be varied at will, which constitutes a key advantage over other existing techniques. As well, the out-of-plane scattered radiation interferes with the direct light emission from the STM tip in the back focal plane (Fourier plane). This confirms the mutual coherence of the light and SPP emission resulting from the inelastic tunneling of an electron in the STM junction. We use this effect to demonstrate that SPP-to-photon scattering at NPs is highly directional.
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2014 |
Boer-Duchemin, E., Wang, T., Le Moal, E., Rogez, B., Comtet, G., & Dujardin, G. (2014). Local, low energy, electrical excitation of localized and propagating surface plasmons with a scanning tunneling microscope. In Proceeding of the SPIE (Vol. 9126, 91260K). Nanophysics V.
Résumé: The highly confined nature of the fields from surface plasmons makes them excellent candidates for future nano-optical devices. Most often, optical excitation is used to excite surface plasmons. However, a local, low energy, electrical method for surface plasmon excitation would be preferable for device applications.
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Cao, S., Le Moal, E., Boer-Duchemin, E., Dujardin, G., Drezet, A., & Huant, S. (2014). Cylindrical vector beams of light from an electrically excited plasmonic lens. Appl. Phys. Lett., 105(11), 111103.
Résumé: The production of cylindrical vector beams from a low-energy, electric, microscale light source is demonstrated both experimentally and theoretically. This is achieved by combining a “plasmonic lens” with the ability to locally and electrically excite propagating surface plasmons on gold films. The plasmonic lens consists of concentric circular subwavelength slits that are etched in a thick gold film. The local excitation arises from the inelastic tunneling of electrons from the tip of a scanning tunneling microscope. We report on the emission of radially polarized beams with an angular divergence of less than 4°.
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Rogez, B., Yang, H., Le Moal, E., Lévêque-Fort, S., Boer-Duchemin, E., Yao, F., Lee, Y. - H., Zhang, Y., Wegner, D., Hildebrandt, N., Mayne, A. J., & Dujardin G. (2014). Fluorescence lifetime and blinking of individual semiconductor nanocrystals on graphene. J. Phys. Chem. C, 118, 18445–18452.
Résumé: A new class of optoelectronic nanodevices consisting of 0D semiconductor nanocrystals and 2D single graphene layers is attracting much attention. In particular, such a system may be used to investigate and control the transfer of energy and charge in low-dimensional systems. To this end, the fluorescence dynamics of individual colloidal quantum dots(QDs) on graphene are investigated on both the 10−9 to 10−8 s time scale (fluorescence lifetime) and the 1−100 s time scale(blinking statistics) in this paper. We find that (i) a nonradiative energy transfer rate of ≈5 × 10+8 s−1 is obtained from the reduced lifetimes of QDs on graphene as opposed to those on insulating substrates such as glass; (ii) QDs still exhibit fluorescence intermittency (“blinking”) on graphene; (iii) the cumulative distribution functions of the “off” times may be described by power-law statistics; (iv) QD coupling to graphene increases the time spent in the “on” state while the time spent in the “off” state remains relatively unchanged; and (v) the fluorescence emission spectrum of the QDs is practically unaltered by the QD−graphene coupling.
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Schull, G., Boer-Duchemin, E., Comtet, G., & Dujardin, G. (2014). Émission de lumière sous la pointe d’un microscope à effet tunnel. Reflets de la Physique, 38, 4–9.
Résumé: Une source de lumière de dimension atomique est réalisée à l’aide d’un microscope à effet tunnel (STM). Cette source de photons est localisée à la jonction entre une pointe, que l’on peut déplacer avec une précision atomique, et un échantillon métallique. Elle se distingue par une excitation de nature électronique (le courant tunnel), et fait également intervenir des plasmons de surface présents dans la jonction tunnel. La jonction tunnel est ainsi une « source électrique » de plasmons de surface. Cependant, on est encore loin de comprendre le fonctionnement de cette source optique et plasmonique et d’en avoir exploité toutes les possibilités.
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Wang, T., Boer-Duchemin, E., Comtet, G., Le Moal, E., Dujardin, G., Drezet, A., & Huant, S. (2014). Plasmon scattering from holes: from single hole scattering to Young's experiment. Nanotechnology, 25(12), 125202.
Résumé: In this paper, the scattering of surface plasmon polaritons (SPPs) into photons at holes is investigated. A local, electrically excited source of SPPs using a scanning tunneling microscope (STM) produces an outgoing circular plasmon wave on a thick (200 nm) gold film on glass containing holes of 250, 500 and 1000 nm diameter. Fourier plane images of the photons from hole-scattered plasmons show that the larger the hole diameter, the more directional the scattered radiation. These results are confirmed by a model where the hole is considered as a distribution of horizontal dipoles whose relative amplitudes, directions, and phases depend linearly on the local SPP electric field. An SPP-Young's experiment is also performed, where the STM-excited SPP wave is incident on a pair of 1 μm diameter holes in the thick gold film. The visibility of the resulting fringes in the Fourier plane is analyzed to show that the polarization of the electric field is maintained when SPPs scatter into photons. From this SPP-Young's experiment, an upper bound of approximate to 200 nm for the radius of this STM-excited source of surface plasmon polaritons is determined.
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Wang, T., Comtet, G., Le Moal, E., Dujardin, G., Drezet, A., Huant, S. & Boer-Duchemin, E. (2014). Temporal coherence of propagating surface plasmons. Opt. Lett., 39(23), 6679–6682.
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2013 |
Le Moal, E., Marguet, S., Rogez, B., Mukherjee, S., Dos Santos, P., Boer-Duchemin, E., Comtet, G., & Dujardin, G. (2013). An electrically excited nanoscale light source with active angular control of the emitted light. Nano Lett., 13(9), 4198–4205.
Résumé: The angular distribution, polarization, and spectrum of the light emitted from an electrically controlled nanoscale light source arises from the local, low-energy, electrical excitation of localized surface plasmons (LSP) on individual gold nanoparticles induced by a scanning tunneling microscope (STM). The gold nanoparticles (NP) are chemically synthesized truncated bitetrahedrons. The emitted light is collected through the transparent substrate The angular distribution, polarization, and spectrum are found to strongly depend on the lateral position of the STM tip with respect to the upper triangular face of the gold NP. The resulting light emission changes orientation when the electrical excitation via the STM tip is moved from the base to the vertex of the triangular face. Comparison with an analytical dipole model and finite-difference time-domain (FDTD) calculations shows that this behavior is linked to the selective excitation of the out-of-plane and in-plane dipolar LSP modes of the NP.
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Zhang, Y., Boer-Duchemin, E., Wang, T., Rogez, B., Comtet, G., Le Moal, E., Dujardin, G., Hohenau, A., Gruber, C., & Krenn, J. R. (2013). Edge scattering of surface plasmons excited by scanning tunneling microscopy. Opt. Express, 21(12), 13938–13948.
Résumé: 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, θc). 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. From these results, we interpret the directional, large angle 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.
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2011 |
Wang, T., Boer-Duchemin, E., Zhang, Y., Comtet, G., & Dujardin, G. (2011). Excitation of propagating surface plasmons with a scanning tunnelling microscope. NANOTECHNOLOGY, 22(17), 175201.
Résumé: Inelastic electron tunnelling excitation of propagating surface plasmon polaritons (SPPs) on a thin gold film is demonstrated. This is done by combining a scanning tunnelling microscope (STM) with an inverted optical microscope. Analysis of the leakage radiation in both the image and Fourier planes unambiguously shows that the majority (up to 99.5%) of the detected photons originate from propagating SPPs with propagation lengths of the order of 10 μm. The remaining photon emission is localized under the STM tip and is attributed to a tip-gold film coupled plasmon resonance as evidenced by the bimodal spectral distribution and enhanced emission intensity observed using a silver STM tip for excitation.
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