Gap plasmon modes and plasmon-exciton coupling in a hybrid Au/MoSe2/Au tunneling junction.

The light-matter interaction between plasmonic nanocavity modes and excitons at the nanometer scale is here addressed in the scanning tunneling microscope configuration where an MoSe2 monolayer is located between the tip and the substrate. We investigate by optical excitation the electromagnetic modes of this hybrid Au/MoSe2/Au tunneling junction using numerical simulations where electron tunneling and the anisotropic character of the MoSe2 layer are taken into account. In particular, we pointed out gap plasmon modes and Fano-type plasmon-exciton coupling taking place at the MoSe2/Au substrate interface. The spectral properties and spatial localization of these modes are studied as a function of the tunneling parameters and incident polarization.

Integration of the Rhombohedral BiSb(0001) Topological Insulator on a Cubic GaAs(001) Substrate.

Bismuth-antimony alloy (Bi1 - xSbx) is the first reported 3D topological insulator (TI). Among many TIs reported to date, it remains the most promising for spintronic applications thanks to its large conductivity, its colossal spin Hall angle, and the possibility to build low-current spin-orbit-torque magnetoresistive random access memories. Nevertheless, the 2D integration of TIs on industrial standards is lacking. In this work, we report the integration of high-quality rhombohedral BiSb(0001) topological insulators on a cubic GaAs(001) substrate. We demonstrate a clear epitaxial relationship at the interface, a fully relaxed TI layer, and the growth of a rhombohedral matrix on top of the cubic substrate. The antimony composition of the Bi1 - xSbx layer is perfectly controlled and covers almost the whole TI window. For optimized growth conditions, the sample generates a semiconductor band structure at room temperature in the bulk and exhibits metallic surface states at 77 K.

Control of the deprotonation of terephthalic acid assemblies on Ag(111) studied by DFT calculations and low temperature scanning tunneling microscopy.

This paper deals with the investigations of terephthalic acid (TPA) molecules deposited on a low reactive Ag(111) surface and studied using scanning tunneling microscopy (STM) at low temperature and DFT calculations. These investigations show that two deprotonation states energetically equivalent can be produced at the single molecule level. On self assemblies, the mobility of H atoms at 77 K favours the motion of created defects in the layer. STM observations and DFT calculations show that the most stable structures are obtained when only one hydrogen atom is removed from an O-HO bond and when these deprotonated molecules are located in adjacent TPA rows.

Observation and modeling of conformational molecular structures driving the self-assembly of tri-adamantyl benzene on Ag(111).

The self-organization of tri-adamantyl (TAB) benzene molecules has been investigated using low temperature scanning tunneling microscopy (LT-STM). The molecular structures have also been studied using molecular modeling. In particular, these calculations have been performed on large areas (1000 nm(2)) from the atomic structure of the molecular building block, combining molecular dynamics (MD) and Monte-Carlo (MC) approaches. These investigations show that the structure of the molecule and its flexibility allow for the formation of different networks as a function of surface coverage. The calculations demonstrate that the stability of the largest structures is obtained through the increase of the interfacial energy induced by the rotation of the adamantyl groups, a behavior whose consequences explain the subtle contrasts observed in the experimental STM images.

Observation and manipulation of hexa-adamantyl-hexa-benzocoronene molecules by low temperature scanning tunneling microscopy.

Large molecules made of a central hexa-adamantyl-hexa-benzocoronene plateau surrounded by six adamantyl groups have been investigated by low temperature scanning tunneling microscopy and scanning tunneling spectroscopy coupled with image calculations and molecular mechanics. The structure of large self-assembled domains reveals that the intermolecular interactions between adamantyl peripheral groups dominate film growth. At very low coverage, the molecules can exhibit a certain instability for negative bias voltages which induces a partial rotation. Manipulations of single objects using the STM tip are used to create small clusters of two or three molecules. The formed structures can be obtained and manipulated provided that the flexible adamantyl moieties of neighbouring molecules are brought in close contact promoting a robust mechanical anchoring.

Adsorption of a single molecule of a diarylethene photochromic dye on Cu(111).

On the route to single (large) molecule unimolecular chemistry, the adsorption of a photochromic dithienylethene dye on Cu(111) at a submonolayer level has been studied by Ultra High Vacuum-Scanning Tunneling Microscopy at Low Temperature. This technique has shown that the observed adsorbed molecule's shape is compatible with an helical conformation but has also revealed a surrounding electronic corrugation due to the perturbed surface states. Careful examination of the standing wave pattern indicated that only a part of the molecule is indeed interacting with the metallic substrate. Geometric considerations were used to infer that the bridging ethene moiety could be responsible for the electronic scattering. Scanning Tunneling Spectroscopy has shown a substantial amount of charge transfer from the surface to the adsorbate. The hypothesis that this precise double bond is a reactive locus toward charge transfer processes is confirmed by the electrochemical results: this double bond is indeed reduced upon coulometric reduction on glassy carbon. Furthermore, the use of a copper cathode strongly facilitates the reduction since a +0.6 V shift was recorded.