Antoine Zwick

Three dimensional design of silver nanoparticle assemblies embedded in dielectrics for Raman spectroscopy enhancement and dark-field imaging.

A strategy to design and fabricate hybrid metallic-dielectric substrates for optical spectroscopy and imaging is proposed. Different architectures consisting of three-dimensional patterns of metallic nanoparticles embedded in dielectric layers are conceived to simultaneously exploit the optical interference phenomenon in stratified media and localized surface plasmon resonances on metal nanoparticles. These structures are based on a simultaneous control of opto-electronic properties at three scales (3S) (~2/20/200 nm) and along three directions (3D). By ultralow energy ion implantation through a microfabricated stencil we precisely control the size, density, and location of silver nanoparticles embedded in silica/silicon thin films. Elastic (Rayleigh) and inelastic (Raman) scattering imaging assisted by simulations were used to analyze the optical response of these 3S-3D patterned layers. The reflectance contrast is strongly enhanced when resonance conditions between the stationary electromagnetic field in the dielectric matrix and the localized plasmon resonance in the silver nanoparticles are realized. The potential of these 3S-3D metal-dielectric structures as surface-enhanced Raman scattering substrates is demonstrated. These novel kinds of plasmonic-photonic architectures are reproducible and stable; they preserve flat and chemically uniform surfaces, offering opportunities for the development of efficient and reusable substrates for optical spectroscopy and imaging enhancement.

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.

High-spin to low-spin relaxation kinetics in the [Fe(TRIM)2]Cl2 complex

A quasi-quantitative photo-induced low-spin (LS)-->high-spin (HS) conversion of FeII ions has been observed in the [Fe(TRIM)2]Cl2 complex by irradiating the sample with blue light (488 nm) at 10 K. The time dependence of the HS-->LS relaxation has been studied between 10 K and 44 K by means of magnetic susceptibility measurements. These relaxation curves could be satisfactorily fitted by mono-exponential decays including tunnelling effect except for temperatures below 30 K. The introduction of a distribution of vibrational frequencies into this model improved significantly the fits in the low-temperature range and gave a good agreement with the experimental data in the whole temperature range suggesting a multi-rate relaxation process in this complex.

In situ Raman spectroscopy identification of the S3− ion in S-rich hydrothermal fluids from synthetic fluid inclusions

Abstract The chemical forms of sulfur in geological fluids control the behavior of this element and associated base and precious metals in magmatic, hydrothermal, and metamorphic environments. However, these forms are insufficiently known at elevated temperature (T) and pressure (P). In this study, sulfur speciation in model aqueous solutions of thiosulfate and sulfur (~3 wt% of total S) was examined by in situ Raman spectroscopy on synthetic fluid inclusions at T-P-pH-redox conditions typical of porphyry Cu-Au-Mo deposits. Fluid inclusions were entrapped at 2 kbar and 600 or 700 °C in quartz that served as a container for the high T-P fluid. Then, the inclusion-bearing quartz samples were re-heated and examined by Raman spectroscopy as a function of T and P (up to 500 °C and ~1 kbar). At T < 200 °C, all fluid inclusions show sulfate (SO4 2- ± HSO4 -) and sulfide (H2S ± HS-) in the aqueous liquid phase and elemental sulfur (S8) in the solid/molten phase; these results agree both with thermodynamic predictions of sulfur speciation and the common observation of these three S forms in natural fluid inclusions. At T > 200-300 °C, in addition to these S species, the S3- ion was found to appear and grow with increasing temperature to at least 500 °C. The formation of S3- is rapid and fully reversible; its Raman signal disappears on cooling below 200 °C, and re-appears on heating. These new data confirm the recent findings of S3 - in similar aqueous solutions at P of 5-50 kbar and T > 250 °C; they suggest that S3- may account for some part of dissolved sulfur and serve as a ligand for chalcophile metals in fluids from subduction zones and related Cu-Au-Mo deposits. This work demonstrates that in situ approaches are required for determining the true sulfur speciation in crustal fluids; it should encourage future spectroscopic investigations of natural fluid and melt inclusions at high temperatures and pressures close to their formation conditions.

Tetrathiafulvalene-based conducting deposits on silicon substrates

Tetrathiafulvalene-based molecular conductors, namely [TTF][TCNQ], (TTF)6[N(C2H5)4](HPM12O40) n(M = W, Mo), and TTF[Ni(dmit)2]2 have been processed as thin films on microrough (001)-oriented silicon substrates using three different techniques. CVD-grown [TTF][TCNQ] deposits consist of platelets (10 × 5 µm) and filaments (diameter ∼1 µm). CN stretching modes in the infrared spectrum and CC stretching modes in the Raman spectrum are in agreement with a charge transfer of ∼0.6 from the TTF donor to the TCNQ acceptor. The N(1s) photoelectron spectrum confirms the presence of a reduced tetracyanoquinodimethane moiety. The films exhibit a semiconducting behaviour with a room-temperature conductivity of ∼0.4 S cm−1. Deposits of (TTF)6[N(C2H5)4](HPW12O40) are electrodeposited on microrough Si(001) at constant current from TTF and [N(C2H5)4]3(PW12O40) in acetonitrile solution. The films are made of stacked sheets (5 < thickness < 25 µm). Vibrational spectra, conductivity measurements and magnetic susceptibility data are similar to those obtained on single crystals of (TTF)6[N(C2H5)4](HPW12O40) grown on a platinum electrode. Thin films of TTF[Ni(dmit)2]2 are grown on microrough Si(001) by an adsorption process in organic solution. The deposits are characterized by Raman micro-probe and exhibit a pseudo-metallic behaviour with a room-temperature conductivity of about 2 S cm−1.

[Cp2V(μ‐η2:η4‐butadiyne)MCp2′] (M=Ti, Zr; Cp′=C5H5, C5H4SiMe3): Heterodimetallic Complexes from a Bis(alkynyl)metallocene and Vanadocene—Unexpected Structure of [Cp2V(μ‐η2:η4‐butadiyne)Zr(C5H4SiMe3)2] Containing Two Planar‐Tetracoordinate Carbon Atoms

Titanium–vanadium and zirconium–vanadiumcomplexes are obtained from the reaction between bis(phenylethynyl)titanocene, or -zirconocene, and vanadocene. The X-ray structure analysis of [Cp2V(μ-η2-η4-butadiyne)Zr(C5H4SiMe3)2] (depicted on the right) reveals that the [Cp2V] metallocene moiety is bonded to a butadiene (or butadiyne) framework through the two internal carbon atoms and that the [(C5H4SiMe3)2Zr] moiety is bonded to this unit through the two internal carbon atoms and the two external carbon atoms. Both internal carbon atoms of the butadiene skeleton are planar-tetracoordinate.

Conducting oriented-[(n-C4H9)4N]2[Ni(dcbdt)2]5 and new (BEDT-TTF)[Ni(dcbdt)2] phases as microcrystalline films, electrodeposited on silicon substrates

Ni(dcbdt)2-based molecular materials, namely [(n-C4H9)4N]2[Ni(dcbdt)2]5, and (BEDT-TTF)[Ni(dcbdt)2] have been processed as microcrystalline films on (001)-oriented silicon substrates using the electrodeposition technique [dcbdt2−: 4,5-dicyanobenzene-1,2-dithiolato; BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene]. Electrodeposited [(n-C4H9)4N]2[Ni(dcbdt)2]5 is made of thin platelets. Elemental analysis and X-ray photoelectron spectroscopy data are in agreement with a 2 : 5 stoichiometry. X-Ray powder diffraction measurements indicate that the growth is highly anisotropic, the ab-plane being parallel to the silicon surface. The films exhibit a semiconducting behaviour with a room-temperature conductivity of about 1.2 × 10−2 S cm−1. Electrodeposition run in the presence of the BEDT-TTF donor molecule leads to faceted microcrystals (size: 5–100 μm) of (BEDT-TTF)[Ni(dcbdt)2] as evidenced by scanning electron microscopy. Single crystal data show that this new (BEDT-TTF)[Ni(dcbdt)2] phase is isostructural to the previously described (BEDT-TTF)[Au(dcbdt)2]. Again, elemental analysis and X-ray photoelectron spectroscopy data are in agreement with a 1 : 1 stoichiometry. The room-temperature conductivity of the film is about 3 × 10−6 S cm−1. This low value is comparable to that measured on (BEDT-TTF)[Au(dcbdt)2] single crystals. For both materials the charge transfer is similar, as consistently evaluated from Raman, infrared and photoemission measurements.

Acoustics at nanoscale: Raman–Brillouin scattering from thin silicon-on-insulator layers

We report on Raman–Brillouin scattering from thin single silicon layers. Starting from a 33 nm silicon-on-insulator structure, a series of layers with progressively decreasing thicknesses was prepared using a chemical treatment consisting of oxide stripping/formation cycles. In order to determine these thicknesses, experimental Raman–Brillouin spectra are compared to calculations performed in the frame of the photoelastic model. We demonstrate that subnanometer changes in the silicon layer thickness can be derived from a proper analysis of the spectral response. It is shown that a 1 nm thick oxide forms during the chemical treatment.