Experimental study of hot spots in gold/glass nanocomposites films by photoemission electron microscopy

International audienceIn this paper, an experimental study of hot spots in gold/dielectric films using photoemission electron microscopy is reported. This technique allows a characterization of the statistical optical properties with unprecedented accuracy in the 800- to 1040-nm range. Theoretical predictions of the scaling theory on the number and intensity wavelength dependences of hot spots in the near-infrared are confirmed. Statistical properties of the intensity distribution, spectral behavior, and spatial localization of the hot spots are reported

Two-photon luminescence of single colloidal gold nanorods: revealing the origin of plasmon relaxation in small nanocrystals

The two-photon luminescence (TPL) of small 10 nm x 40 nm colloidal gold nanorods (GNR) is investigated at the single object level, combining polarization resolved TPL and simultaneously acquired topography. A very high dependence of the TPL signal with both the nanorods longitudinal axis and the incident wavelength is observed confirming the plasmonic origin of the signal and pointing the limit of the analogy between GNRs and molecules. The spectral analysis of the TPL evidences two emission bands peaks: in the visible (in direct connection with the gold band structure), and in the infrared. Both bands are observed to vary quadradically with the incident excitation beam but exhibit different polarization properties. The maximum two-photon brightness of a single GNR is measured to be a few millions higher than the two-photon brightness of fluorescein molecules. We show that the important TPL observed in these small gold nanorods results from resonance effects both at the excitation and emission level : local field enhancement at the longitudinal surface plasmon resonances (LSPR) first results in an increase of the electron-hole generation. Further relaxation of electron-hole pairs then mostly leads to the excitation of the GNR transverse plasmon mode and its subsequent radiative relaxation

Microscopie à haute résolution des champs plasmoniques par microscopie tunnel à balayage de sonde et par microscopie de photoémission multiphotonique

International audienceThe exploitation of plasmon resonances to promote the interaction between conjugated molecules and optical fields motivates intensive research. The objectives are to understand the mechanisms of plasmon-mediated interactions, and to realize molecularly-or atomically precise metal nanostructures, combining field enhancements and optical antenna effects. In this review paper, we present examples of plasmonic-field mappings based on scanning tunneling microscope (STM)-induced light emission or multiphoton photoemission (PEEM), two techniques among those which offer today's best spatial resolutions for plasmon microscopy. An unfamiliar property of the junction of an STM is its ability to behave as a highly localized source of light. It can be exploited to probe optoelectronic properties, in particular plasmonic fields, with ultimate subnanometer spatial resolution, an advantage balanced by a sometimes delicate deconvolution of local-probe influence. Alternatively, local-probe disadvantages can be overcome by imaging the photoemitted electrons, using well-established electron optics. This allows obtaining two-dimensional intensity maps reflecting the unperturbed distribution of the optical near field. This approach provides full field spectroscopic images with a routine spatial resolution of the order of 20 nm (down to 5 nm with recent aberration corrected instruments)

Photoemission electron microscopy, a tool for plasmonics

International audienceA key challenge to plasmonics is the development of experimental tools allowing access to the spatial distribution of the optical near field at the nanometre scale. A recent approach for mapping the near optical field is the use of the photoemission electron microscopy PEEM. Indeed, photoemission can be strongly enhanced upon excitation of surface plasmons. By collecting the photoemitted electrons, two-dimensional intensity maps reflecting the actual distribution of the optical near-field are obtained. In the following a brief overview of the possibilities of the photoemission electron microscopy as a tool for plasmonics is given. Main focuses will be set on experimental results regarding the mapping of the near optical field at nanometer scale, the investigation of the spatio-temporal dynamics of plasmon-polariton waves and the manipulation at will of the near field

High-resolution mapping of plasmonic modes: photoemission and scanning tunnelling luminescence microscopies

International audiencePhotonic properties of dense metal nanostructures are currently under intense investigation because of the possible local enhancements of electromagnetic fields induced by plasmonic excitations. In this review paper, we present examples of plasmonic-field mappings based on multiphoton photoemission or STM-induced light emission, two techniques among those which offer today's best spatial resolutions for plasmon microscopy. By imaging the photoemitted electrons, using well-established electron optics, two-dimensional intensity maps reflecting the actual distribution of the optical near-field are obtained. The imaging technique involves no physical probe altering the measure. This approach provides full field spectroscopic images with a routine spatial resolution of the order of 20 nm (down to 2 nm with recent aberration corrected instruments). Alternatively, an unfamiliar property of the junction of scanning tunnelling microscope is its ability to behave as a highly localized source of light. It can be exploited to probe opto-electronic properties, in particular plasmonic fields, with ultimate subnanometre spatial resolution, an advantage balanced by a sometimes delicate deconvolution of local-probe influence

Sequential growth at the sub-10 nm scale of cyanide bridged coordination networks on inorganic surfaces

International audienceThe elaboration of coordination networks’ nano-objects on surfaces can be realized by sequential growth in solution (SGS). This bottom-up strategy gives the possibility to control the size, the isolation and the organization of the objects with a precision going up to the molecular scale. Detailed descriptions of the growth of the nickel(II)–iron(II) Prussian blue analog and of the copper–molybdenum cyanide-bridged coordination network are reported to give insight about the mechanisms of the growth. Then a comparative XPS analysis has been performed to explain the different reactivity of the precursors of the growth of the nickel(II)–iron(II) and nickel(II)–chromium(III) Prussian blue analogs. This perspective article proves that SGS can be optimized for each coordination system to build molecular superstructures on surfaces, with interesting physical properties towards chemical devices