Plasmon scattering from holes: from single hole scattering to Young's experiment

In this article, the scattering of surface plasmon polaritons (SPPs) into photons at holes is investigated. A local, electrically excited source of SPPs using a scanning tunnelling 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 $\mu$m 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 $\approx$ 200 nm for the radius of this STM-excited source of surface plasmon polaritons is determined

Epitaxial Synthesis of Blue Phosphorene

Phosphorene is a new two-dimensional material composed of a single or few atomic layers of black phosphorus. Phosphorene has both an intrinsic tunable direct band gap and high carrier mobility values, which make it suitable for a large variety of optical and electronic devices. However, the synthesis of single-layer phosphorene is a major challenge. The standard procedure to obtain phosphorene is by exfoliation. More recently, the epitaxial growth of single-layer phosphorene on Au(111) has been investigated by molecular beam epitaxy and the obtained structure has been described as a blue-phosphorene sheet. In the present study, large areas of high-quality monolayer phosphorene, with a band gap value at least equal to 0.8 eV, have been synthesized on Au(111). Our experimental investigations, coupled with DFT calculations, give evidence of two distinct phases of blue phosphorene on Au(111), instead of one as previously reported, and their atomic structures have been determined.Comment: This paper reports on the epitaxial synthesis of blue phosphoren

Atomic-scale study of the adsorption of calcium fluoride on Si(100) at low-coverage regime

We investigate, experimentally and theoretically, the initial stage of the formation of Ca/Si and Si/F structures that occurs during the adsorption of CaF2 molecules onto a bare Si(100) surface heated to 1000 K in a low-coverage regime (0.3 monolayer). A low-temperature (5 K) scanning tunneling microscope (STM) is used to observe the topographies and the electronic properties of the exposed silicon surfaces. Our atomic-scale study reveals that several chemical reactions arise during CaF2 deposition, such as dissociation of the CaF2 molecules and etching of the surface silicon dimers. The experimental and calculated STM topographies are compared using the density functional theory, and this comparison enables us to identify two types of reacted structures on the Si(100) surface. The first type of observed complex surface structure consists of large islands formed with a semiperiodic sequence of 3 × 2 unit cells. The second one is made of isolated Ca adatoms adsorbed at specific sites on the Si(100)-2 × 1 surface.Peer reviewe

Cylindrical vector beams of light from an electrically excited plasmonic lens

International audienceThe 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°

Formation of one-dimensional self-assembled silicon nanoribbons on Au(110)-(2x1)

We report results on the self-assembly of silicon nanoribbons on the (2x1) reconstructed Au(110) surface under ultra-high vacuum conditions. Upon adsorption of 0.2 monolayer (ML) of silicon the (2x1) reconstruction of Au(110) is replaced by an ordered surface alloy. Above this coverage a new superstructure is revealed by low electron energy diffraction (LEED) which becomes sharper at 0.3 Si ML. This superstructure corresponds to Si nanoribbons all oriented along the [-110] direction as revealed by LEED and scanning tunneling microscopy (STM). STM and high-resolution photoemission spectroscopy indicate that the nanoribbons are flat and predominantly 1.6 nm wide. In addition the silicon atoms show signatures of two chemical environments corresponding to the edge and center of the ribbons.Comment: Under publication in Applied Physics Letter

Silicon Sheets By Redox Assisted Chemical Exfoliation

In this paper, we report the direct chemical synthesis of silicon sheets in gram-scale quantities by chemical exfoliation of pre-processed calcium di-silicide (CaSi2). We have used a combination of X-ray photoelectron spectroscopy, transmission electron microscopy and Energy-dispersive X-ray spectroscopy to characterize the obtained silicon sheets. We found that the clean and crystalline silicon sheets show a 2-dimensional hexagonal graphitic structure.Comment: Accepted in J. Phys.: Condens. Matte

MANIPULATION D'ATOMES ET DE MOLECULES INDIVIDUELS A L'AIDE DU MICROSCOPE A EFFET TUNNEL

PARIS-BIUSJ-Physique recherche (751052113) / SudocCentre Technique Livre Ens. Sup. (774682301) / SudocSudocFranceF

Excitation par électrons tunnel de nano-objets individuels adsorbés sur la surface de Si(100)

Les processus dynamiques induits dans des molécules par des électrons ou des photons ont été considérablement étudiés en phase gazeuse et en solution sur des assemblées de milliards de molécules. Avec le microscope à effet tunnel (STM) il devient possible d'envisager l'excitation d'une seule molécule par des électrons issus de la pointe. Nous avons d'abord étudié la désorption à l'échelle atomique d'H de la surface de Si(100)-H(2x1). La liaison Si-H est un système modèle pour l'étude des effets inélastiques des électrons tunnel en raison de la simplicité de sa structure atomique et électronique. Sa dissociation était jusqu'à présent expliquée par un modèle de chauffage vibrationnel mais les résultats des expériences plus détaillées que nous avons réalisées l'ont invalidé. Ils indiquent que la désorption d'H s'expliquerait plutôt par un modèle d'excitation cohérente. Ensuite nous avons étudié le diacétyl-paraterphényl, surnommé TRIMA. Le dépôt sous ultravide de cette molécule lourde nécessite l'utilisation d'un filament de sublimation. Son mode d'adsorption sur la surface de Si(100)-(2x1) a été analysé à la fois par STM et par spectroscopie NEXAFS avec le rayonnement synchrotron. Puis en utilisant le STM en mode manipulation nous avons induit différentes réactions de molécules individuelles de TRIMA. La probabilité de réaction est compatible avec un mécanisme d'excitation électronique du TRIMA mais les effets de champ électrique peuvent également être à l'origine de la manipulation.Dynamical processes induced in molecules by electrons or photons have been extensively studied in gas phase and in solution on assemblies of billions of molecules. With the Scanning Tunneling Microscope (STM) it becomes possible to consider the excitation of a single molecule by electrons tunneling from the tip. We first studied atomic scale desorption of H from the Si(1OO)-H(2x1) surface. The Si-H bond is a model system for the study of inelastic effects of tunnel electrons because of the simplicity of its atomic and electronic structure. Its dissociation was previously explained by a vibrational heating model but the results of more detailed experiments which we performed have invalidated it. They indicate that it must be replaced by a coherent excitation model. We then studied diacetyl-paraterphenyl, nicknamed TRIMA. The ultrahigh vacuum deposition of this heavy molecule required the use of an in situ sublimation filament. Its adsorption configuration on the Si(100)-(2x1) surface was analyzed both by STM and NEXAFS spectroscopy with synchrotron radiation. By using the STM in manipulation mode we induced different reactions of individual TRIMA molecules. The reaction probability is consistent with an electronic excitation mechanism of TRIMA but electric field effects could also be the origin of the manipulation.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF