Sun light Nitrides and Oxi-Nitrides for energetic applications – SNON

first task: synthesis of Ta3N5 and TaON films
second task: caracterisation of thin films (MEB, RBS, NRA, DRX, AFM, optical gap, electrical measurements)

We have worked on synthesizing Ta-N films by HiPIMS. The morphology of the films is imaged by scanning electron microscopy (SEM) and its atomic composition is determined by Rutherford backscattering analysis (RBS) and Nuclear reaction analysis (NRA). Two different pressures, 0.5 Pa and 5 Pa, were used for the depositions. The scanning electron microscopy images show striking differences between films deposited at low and high reactor pressure. The lower pressure leads to the formation of denser films.
[N]/[N+Ta] molar fraction of thin film as a function of the N2 concentration in the injected Ar/N2 gas mixture has been measured by RBS/NRA. [N]/[N+Ta] increases with N2concentartion to saturate at 0.65 (ideal ratio 0.625). Oxygen contamination has been detected at surface and interface.
XRD analysis shows the presence of d-TaN phase.
The electrical conductivity varies from 10-10 to 1 S/cm as a function of deposition pressure. No photoelectrical properties hasve been detected.

The film stochiometry is close to the ideal one. Today, the main technical difficulty is to obtain the Ta3N5 phase. Two solutions:
- study the HiPIMS plasma in the aim to find the optimum parameters (determination of energy Ta ions for example)
- increase temperature during deposition to promote cristallisation

1. M. Rudolph, B. Bouchet-Fabre, M.-C.Hugon, J.-J Ganem, J. Letien, E. Foy, J. Alvarez, O. Antonin, T. Minea, Tantalum nitride ultra thin films for light-induced water splitting, E-MRS/MRS Spring Meeting, Lille, 2014

2.M. Rudolph, M.C. Hugon, B. Bouchet-Fabre, J. Letien, A. HAbert, E. Foy, J. Leroy, P.-O. Delzant, J.-J. Ganem, J. Alvarez, J.-P. Kleider, O. Antonin, T. Minea, Dense and porous Ta3N5 films with variable optical gap deposited by reactive HiPIMS, 2nd IAP Workshop on Plasma Diagnostics, June 10 - 11, 2014, Reims (poster)
3. M. Rudolph, M.C Hugon, B. Bouchet-Fabre, I. Vickridge, E. Briand, J.-J Ganem, E. Foy, D. Lundin, T. Minea (tbc), Mechanism of nitrogen icnorporation into Ta-N films deposited by direct current and high-power impulse magnetron sputtering, 22nd Symposium on Plasma Chemistry, Antwerp, July 5 - July 10, 2015 (poster accepted)
4. Rudolph, T. Degousée, T. Minea, V. Tiron, C. Costin, L. Sirghi, M.-C. Hugon, B. Bouchet-Fabre, Measuring the ionized flux fraction from high-power impulse magnetron discharges using a miniaturized ion energy spectrometer, ICPIG, 26 – 31 July, 2015, Ia?i, Romania (accepted poster)

The natural Sun light exploitation is one of the major goals nowadays for energy production or storage. However, the present limitation of the most of the electricity supply way is the CO2 release and their possibility to store it. SNON project is focused on this topic – aiming to improve the energy storage and the conversion yield by photo-catalytic activity. SNON project targets to design a laboratory test bed which will serve for new nitride and oxy-nitride semiconductor family materials based on Ta and Zn metals at nanometric scale. The research performed in the Romanian and French partners for this project focuses on the use of magnetron discharge glow discharge operating in high power regime 50kW during the pulse (~100 µs). This novel deposition technique could deposit interesting stable Ta(Zn)ON materials. Moreover, the colloidal lithography associate dot the conventional magnetron sputtering technique will allow developing mixed nano-textured materials: small nanoparticles on continuous films and gradient concentration films. An exploratory research on nanoparticles elaborated by laser pyrolysis will complete the material elaboration panel.

R&D research will be mainly experimental aiming to qualify the nitride and oxynitride which present attractive photo-electronic and photo electro-catalytic properties. Many characterization techniques available in all partner laboratories will be used in a synergetic way. The consortium is composed of LPGP (Orsay, France) with an expertise in HIPIMS technology for thin and ultra-thin films deposition, UAIC (Iasi, Romania) with an expertise in colloidal lithography and reactive magnetron deposition, LGEP with an expertise in conductive properties and photovoltaic development and IRAMIS (CEA, Saclay, France) with an expertise of physical-chemistry of nanostructured materials, particles, thin films and photo-electrolysis. The final goal is to find out the best material fulfilling the set of properties required for the photo-electrolysis splitting of water for hydrogen production: visible range optical gap, chemical stability under sun radiation and immerged in electrolyte, and recombination-free of photo-carriers by size reducing. SNON project goes from the material synthesis to its validation into the lab test-bed photo-electrolytic cell with relatively high electrode area for hydrogen production.
A first aim is to make dendritic ultra-thin layers and TaNOx nanoscale Islands by a parametric study of the different mixture N2/O2 plasma conditions. The second part of the work concerns the systematic characterization of these nano-materials, whether it's the thickness of a thin layer (< 20 nm), nanoscale Islands or (< 10 nm diameter) nanoparticles, nano-textured materials. And then operation of the best material test bench photo-electrolysis should enable works like the requirements for operation on large area. Cell test, although at the lab. scale will have a sufficient area of electrodes (> 10 cm ^ 2) so that the findings are significant.
As part of the energy storage, this project is located in the heart of the research for new ways of improving energy efficiency of our facilities using the chemical potential. The SNON project contributes to promote the innovative method developed in the laboratories project partners: the magnetron pulsed high-power (HIPIMS - LPGP, France), pyrolysis laser/IRAMIS CEA (France) and colloidal lithography (University, Romania).