Overview of the results:
- A gas flow simulation model was set up using simulation software package Comsol 5.11 and low-Re k-ε RANS equations (Figure 1). It allowed a general modeling of the reactor peculiarities and a general understanding of carrier gas flow in the NP Growth region. Gas pressure and flow curves were measured, and used as boundary conditions. The generated gas flow model was validated for Kn<0,01. Extension of model validity in the Slip flow regime (0,01 < Kn < 0.1) integrating the Brownian movement of nanoparticles in the model are works which are still carried on.
- A nanoparticle transport model was proposed: In the slit, the gas flow approaches sonic range (~0,6Ma), nanoparticles acquire a high kinetic energy inversely proportionally to their mass. The jet flow expands and while decelerates. Lower pressure results in less NP/gas interactions. Heavier nanoparticles decorrelate from gas flow pattern and impact substrate following ballistic trajectory. Lighter nanoparticles follow gas flow streamlines, and reach substrate by soft landing. This model was verified experimentally (Figure 2c).
- Characterization of NP source, calibration of DC generator power and measure of NP production rates were carried out (Figure 3). Highly porous Ti NP aggregates were synthetized (Figure 4) and characterized by means of UV-Vis spectrophotometry, FTIR, SEM and cross-section SEM. 4 standard conditions were chosen for the deposition of dielectric matrix (SiO2). Nanocomposite coatings consisting of Ti nanoparticles in SiO2 matrix displayed no plasmonic response , due to the partial oxidation of metallic Titanium into TiO2. Silver NP porous aggregate was obtained.
- Nanocomposites coatings (Ag NP in SiO2 matrix, Figure 5) display a plasmonic response (Figure 6). To confirm those results, nanocomposite coatings have been characterized in terms of effective refractive index by Dr. Sytchkova (ENEA, Rome, Figure 7) Plasmon resonance was modeled using double Lorentz oscillator, localized plasmon resonances (LPR) frequency was measured. Samples were characterized by XRD at the University of Applied Sciences Zwickau (Figure 8). The nanoparticle sizes using Scherrer formula were 25 to 55 nm. The interpretation of those results is currently discussed.
- Although rarely mentioned in the literature, issues of stability and reproducibility have been met by all groups working with aggregation process. Those issues come down to a very slow drift of the experimental conditions, with a time-constant in the order of 30min. This issue was investigated by OES (Figure 9a). The setup was modified to measure the charge carried by nanoparticles and gas (Figure 9b). All those results are currently discussed with several groups (Linköping University, Charles University Prague). They are fundamental to the understanding of the NP generation process and seem to confirm the effect of a very small amount of heteroatoms adsorbed on the surface of the metallic target. This topic is also the subject of very recent work (currently done or under review) by those groups, and will be the subject of one or several scientific publication using the results of this project.
Exploitation and Dissemination:
- Workshops: Workshop on attosecond physics and plasmonics - école de physique des Houche, Simulationen in der Photonik - laser-center Hannover.
- Conferences: META - Malaga, Escampig – Bratislava, PSE - Garmisch-Partenkirchen, MIATEC – Paris, HiPIMS – Braunschweig
- Fairs & events: Poster at the SEMICON fair and conference (5-8 oct. 2015 in Dresden). H2020 matchmaking event.
- Publications:
H. Nizard et al., proc. 23rd Europhysics Conference on Atomic and Molecular Physics of Ionized Gases, Bratislava, July 12‐16, 2016
H. Nizard et al., proc. 7th International Conference on Metamaterials, Photonic Crystals and Plasmonics, Malaga, July 25-28, 2016, pp. 2296
H. Nizard et al., Book of abstracts for the15th International Conference on Plasma Surface Engineering, Garmisch-Partenkirchen, Sept. 12-16, 2016
Several additional scientific publications in peer-reviewed journals are in discussion and in preparation.
