Robert Carles

The synthesis of single layers of Ag nanocrystals by ultra-low-energy ion implantation for large-scale plasmonic structures

Single layers of silver (Ag) nanoparticles embedded in silica (SiO2) have been fabricated by ultra-low-energy ion implantation. The distance between the Ag particles and the free SiO2 surface is controlled with nanometer precision. Raman scattering and reflectivity measurements strongly correlate to transmission electron microscopy analyses, allowing the use of these non-invasive techniques to monitor structural and dynamical properties. These results open up new opportunities to manipulate electromagnetic near-field interactions on wafer-scale plasmonic devices.

Stability of Ag nanocrystals synthesized by ultra-low energy ion implantation in SiO2 matrices

Ultra low energy ion implantation is a promising technique for the wafer-scale fabrication of Silver nanoparticle planar arrays embedded in thermal silica on silicon substrate. The stability versus time of these nanoparticles is studied at ambient conditions on a time scale of months. The plasmonic signature of Ag NPs vanishes several months after implantation for as-implanted samples, while samples annealed at intermediate temperature under N2 remain stable. XPS and HREM analysis evidence the presence of Silver oxide nanoparticles on aged samples and pure Silver nanoparticles on the annealed ones. This thermal treatment does not modify the size-distribution or position of the particles but is very efficient in stabilizing the metallic particles and to prevent any form of oxidation.

C ion-implanted TiO2 thin film for photocatalytic applications

Third-generation TiO2 photocatalysts were prepared by implantation of C+ ions into 110nm thick TiO2 films. An accurate structural investigation was performed by Rutherford backscattering spectrometry, secondary ion mass spectrometry, X-ray diffraction, Raman-luminescence spectroscopy, and UV/VIS optical characterization. The C doping locally modified the TiO2 pure films, lowering the band-gap energy from 3.3eV to a value of 1.8eV, making the material sensitive to visible light. The synthesized materials are photocatalytically active in the degradation of organic compounds in water under both UV and visible light irradiation, without the help of any additional thermal treatment. These results increase the understanding of the C-doped titanium dioxide, helpful for future environmental applications.

Structural characterization of Ge microcrystals in GexC1−x films

Chemical and structural characteristics of GexC1-x films grown by metalorganic chemical vapour deposition are examined. The effects of the precursor nature (tetravinyl- or tetraethylgermane), growth temperature (in the 500-580°C range) and carrier gas (He or H2) are analysed using electron microprobe, X-ray diffraction, X-ray photoelectron, infrared and Raman spectroscopies. The film structure is governed by the growth conditions. It evolves between two border-line cases: An amorphous-like Ge phase embedded in a graphitic matrix and a polycrystalline Ge phase. A comparative study of the average grain size deduced from X-ray diffraction and Raman scattering data is presented.

Fe ion-implanted TiO2 thin film for efficient visible-light photocatalysis

This work shows the application of metal ion-implantation to realize an efficient second-generation TiO2 photocatalyst. High fluence Fe+ ions were implanted into thin TiO2 films and subsequently annealed up to 550 °C. The ion-implantation process modified the TiO2 pure film, locally lowering its band-gap energy from 3.2 eV to 1.6–1.9 eV, making the material sensitive to visible light. The measured optical band-gap of 1.6–1.9 eV was associated with the presence of effective energy levels in the energy band structure of the titanium dioxide, due to implantation-induced defects. An accurate structural characterization was performed by Rutherford backscattering spectrometry, transmission electron microscopy, Raman spectroscopy, X-ray diffraction, and UV/VIS spectroscopy. The synthesized materials revealed a remarkable photocatalytic efficiency in the degradation of organic compounds in water under visible light irradiation, without the help of any thermal treatments. The photocatalytic activity has been corre...

Assessing bio-available silver released from silver nanoparticles embedded in silica layers using the green algae Chlamydomonas reinhardtii as bio-sensors

Silver nanoparticles (AgNPs) because of their strong antibacterial activity are widely used in health-care sector and industrial applications. Their huge surface-volume ratio enhances the silver release compared to the bulk material, leading to an increased toxicity for microorganisms sensitive to this element. This work presents an assessment of the toxic effect on algal photosynthesis due to small (size <20nm) AgNPs embedded in silica layers. Two physical approaches were originally used to elaborate the nanocomposite structures: (i) low energy ion beam synthesis and (ii) combined silver sputtering and plasma polymerization. These techniques allow elaboration of a single layer of AgNPs embedded in silica films at defined nanometer distances (from 0 to 7nm) beneath the free surface. The structural and optical properties of the nanostructures were studied by transmission electron microscopy and optical reflectance. The silver release from the nanostructures after 20h of immersion in buffered water was measured by inductively coupled plasma mass spectrometry and ranges between 0.02 and 0.49μM. The short-term toxicity of Ag to photosynthesis of Chlamydomonas reinhardtii was assessed by fluorometry. The obtained results show that embedding AgNPs reduces the interactions with the buffered water free media, protecting the AgNPs from fast oxidation. The release of bio-available silver (impacting on the algal photosynthesis) is controlled by the depth at which AgNPs are located for a given host matrix. This provides a procedure to tailor the toxicity of nanocomposites containing AgNPs.

Controlled synthesis of buried delta-layers of Ag nanocrystals for near-field plasmonic effects on free surfaces

We report on the shallow synthesis by low energy ion implantation of delta-layers of Ag nanocrystals in SiO2 at few nanometers under its free surface. Transmission electron microscopy observations, ballistic simulations, and reflectance measurements are coupled to define the conditions for which the synthesis is fully controlled and when, on the contrary, this control is lost. We show that low dose implantation leads to the formation of a well-defined single plane of nanocrystals, while for larger doses, sputtering and diffusion effects limit the control of the size, position, and volume amount of these nanocrystals. This paper provides the experimental evidence of the incorporated dose saturation predicted in the literature when implanting metal ions at high doses in glass matrices. Its consequences on the particle population and the plasmonic optical response of the composite layers are carefully analyzed. We show here that this saturation phenomenon is underestimated in standard simulation predictions ...

Ag doped silicon nitride nanocomposites for embedded plasmonics

The localized surface plasmon-polariton resonance (LSPR) of noble metal nanoparticles (NPs) is widely exploited for enhanced optical spectroscopies of molecules, nonlinear optics, photothermal therapy, photovoltaics, or more recently in plasmoelectronics and photocatalysis. The LSPR frequency depends not only of the noble metal NP material, shape, and size but also of its environment, i.e., of the embedding matrix. In this paper, Ag-NPs have been fabricated by low energy ion beam synthesis in silicon nitride (SiNx) matrices. By coupling the high refractive index of SiNx to the relevant choice of dielectric thickness in a SiNx/Si bilayer for an optimum antireflective effect, a very sharp plasmonic optical interference is obtained in mid-range of the visible spectrum (2.6 eV). The diffusion barrier property of the host SiNx matrix allows for the introduction of a high amount of Ag and the formation of a high density of Ag-NPs that nucleate during the implantation process. Under specific implantation conditions, in-plane self-organization effects are obtained in this matrix that could be the result of a metastable coarsening regime.

Controlled elaboration of large-area plasmonic substrates by plasma process

Elaboration in a controlled way of large-area and efficient plasmonic substrates is achieved by combining sputtering of silver nanoparticles (AgNPs) and plasma polymerization of the embedding dielectric matrix in an axially asymmetric, capacitively coupled RF discharge maintained at low gas pressure. The plasma parameters and deposition conditions were optimized according to the optical response of these substrates. Structural and optical characterizations of the samples confirm the process efficiency. The obtained results indicate that to deposit a single layer of large and closely situated AgNPs, a high injected power and short sputtering times must be privileged. The plasma-elaborated plasmonic substrates appear to be very sensitive to any stimuli that affect their plasmonic response.

Combining elastic and resonant inelastic optical spectroscopies for multiscale probing of embedded nanoparticle architectures

Composite materials consisting of metal nanoparticles (NPs) embedded in a dielectric matrix have a great potential for photonic and plasmonic applications. A set of expensive, time-consuming, and destructive methods (like electron microscopy, electron energy loss, or secondary ion mass spectroscopy) are extensively being used for the structural characterization of such buried NP assemblies. Here, we show the power of combining complementary, noninvasive optical techniques to characterize planar arrays of Ag NPs embedded in a silica film. We use UV-Vis optical reflectivity and resonant Brillouin–Raman scattering, sustained by simulations, to show the sensitivity of these methods to the presence, density, size distribution, and spatial localization of NPs. The accuracy of the results is validated by transmission electron microscopy investigations. Finally the method is applied to obtain images of embedded plasmonic structures from reflectivity and Raman scanning microscopy.