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Reporting period: 2015-04-01 to 2017-03-31

Nano-LAPS project aims at the deposition of high purity nanocomposite thin films with demonstrated optical properties (plasmonic absorption peak) using a novel equipment for the large-scale deposition of nanoparticles generated by Gas Aggregation process. This approach is based on a unique and original experimental setup combining gas flow sputtering and Plasma-Enhanced CVD processes.

While techniques such as lithography or wet chemistry have their specific advantages, they are clearly limited either by their costs, by their speed or by the size of the deposited structures. The Gas aggregation process is an economically viable approach to generate high-purity nanoparticles and nanocomposite films on a wide area and with a very high deposition rate. While this process has a great potential, it needs to be developed, both improving process stability and reproducibility. Applications of plasmonics are to be found in non-linear optics, waveguides, photonics and various new fields of nanoscience such as Nano-magneto-optics.
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 Surfa
- High purity nanocomposite thin films were deposited and plasmonic absorption peaks were characterized. Our original deposition method combining gas flow sputtering and Plasma-Enhanced CVD processes demonstrated its capacity for the deposition of plasmonic materials.
- Concrete advances were made in the understanding of nanoparticle growth models in gas aggregation chamber. In particular, our results highlight the effects of a minimal amount of impurities in the gas flows. And thus, a critical factor for the stability of NP production process has been identified.
- The discussion of those results and of their interpretation have been and continue to be carried out with the scientific community: Scientific contacts and exchanges were established in European (CZ, SE, IT, FR, SP) and international (JP, Mexico) frames. In particular, a fruitful collaboration is expected with university of Prague, with the hope for future academic and students’ exchanges. At his scale, this project made its contribution into bringing together activities of the Dresden academic/industrial cluster with neighboring Czech institutions.
- Results of this project have been regularly disseminated in the scientific community trough communications in 5 international conferences and various other events. It generated interest for our research activities, while presenting the engagement of the EC in H2020 Program.
- Specific efforts have been made to publicize the results and interact with society at large, for instance, this research has involved high-school students from the 7th and 8th class of the Martin-Andersen-Nexoe-Gymnasium (public educative institution) in Dresden. After visiting our laboratory and learning about safety, pupils experimented first-hand with the scientific equipment, gathered results, discussed their interpretation with us, and presented their work in front of their classmates.
a) slow variations of optical emission b) Collected current on a floating potential wall.
Multilayers obtained with 10 deposition cycles. Color variation is not angle-dependent.
XRD Spectrum of an Ag NP/SiOx coating sample. Scherrer size estimates given for each angle.
Gas velocity (left) and flow lines (right) for RANS laminar flow model.
Effective refractive index (L) and extinction coefficient (R) of multilayers coatings.
Highly porous Ti NP aggregate, SEM cross-section, P=4kW, fAr=1.8slpm, P=91.4Pa.
Flow streamlines (a) spread out like plane jet (b). NP trajectories affect deposition (c).
U vs I (L) and Δp (~ NP prod. rate) vs power, flow & pressure (R) calibration curves.
Optical Absorption spectra of multilayers coating sample with plasmonic absorption peak.