reports 4th IFAST annual meeting

This project has received funding from the European Union’s Horizon 2020 Research and Innovation programme under GA No 101004730. Developing ALD for superconducting thin film coatings Yasmine KALBOUSSI on behalf of CEA Saclay team 4th iFAST Annual Meeting April 10th, 2025, Polish Academy of Arts and Science, Krakow CEA Saclay Team 2 ▪Yasmine Kalboussi permanent staff –ALD / Surface characterization ▪Ivana Curci –Thesis (3nd year) –Tunneling spectroscopy / ALD - supervisor T. Proslier ▪Mathieu Lafarie –Thesis (3rd year) –Multipacting mitigation/ALD –supervisor T. Proslier/M. Belhaj (ONERA) ▪Théo Dejob –Postdoc (1st year/2) –ALD/HIPIMS ▪Fritz Moschtmann –CDD Engineer (1 st year/2) –Additive manufacturing ▪Mathieu Benko, Contrat d’apprentissage – supervisor Y. Kalboussi ▪Thomas Proslier –HDR(June 2024) - Task leader Atomic layer deposition 3 ▪ALD is a chemical gas phase deposition technique based on sequential, selfsaturating gas-surface reactions. Applications: ▪Microelectronics ▪Photovoltaics ▪Nano-patterning for biomedical applications (nano-particles, nanotubes) Advantages: ▪Precise thickness control up to subnanometer scale ▪Excellent conformality. ▪Large choice of possible materials ( oxides, nitrides and some metals … ) Limitations: ▪Low growth rates (~0.1 nm per minute) ▪New alloys require new chemistries (new precursors) ALD system for SRF cavity coating at CEA 4 ▪Interface and control: - Labview program of ALD system and Oven. - Automatic synthesis parameter control (overnight deposition) and monitoring. Front Bac k ▪High vacuum oven: - 650°C –10-6 mbar / 900°C 1bar N2 - Volume retort: Φ= 49 cm, L= 110 cm (1.3, 0.7 GHz cavities) ▪ALD system: -9 precursor lines (2 gases, 2 liquids, 4 solids, 1 Ultra high temp). - RGA synthesis monitoring. Control of Nb surface properties by ALD Al2O3Thin films 6 ▪The 10 nm Al2O3film + annealing at 650°C for few hours significantly improves the quality factors of the Nb cavity in the low field regime. ▪Optimization of the Al2O3thickness -> Ok down to 2.5 nm. Al2O3-10nm650°C10hrs Nb after EP + HPR Nb after ALD + TT 7 ZrO2thin films 800°C –3hrs / 5 nm ZrO2 •ZrO2growth cubic phase •Stable up to 900°C on Nb and sharp Nb metal/Oxide layer after air exposure and HPR. N b ZrO2 Changing NbOxstructure 8 ➢Nb EP + HPR ➢Nb EP + HPR + 650°C-10hrs + HPR 7.5 nm 4.5 nm 4.5 nm ▪World record Q values at low fields (T ≈ 15 s) after air exposure and high pressure water rinsing (!) ▪σTLS and tan(δTLS) decreased by a factor 10. ▪Change in chemical / structure of the native NbOxwith indication of NbOX(?) and Nb2O5 crystals. ▪Under investigation. Multipacting mitigation in SRF cavities 16 Al2O3/Cu –Nb deposition ▪Very similar structural and superconducting properties (tunneling spectroscopy) of Nb/Al2O3/Cu and Nb/Cu. ▪Stable at least up to 700°C. ▪Coating of a 1,3 GHz cavity EP from CERN with 15 nm of Al2O3. Send back to CERN for HPR and Nb deposition. ▪Delamination of Nb film on one beamtube, near the flange. ▪Other cavity received from CERN –ALD scheduled next week. ▪Coating Nb with higher deposition temperature increase the grain size and potentially improve RF performances. 17 ZrO2 (20 nm) /Cu ▪Crystalline ZrO2grains 5-10 nm as grown or after annealing. ▪No cracks for ZrO2films ≤ 20 nm on Cu. ▪Cubic as deposited and mixture tetragonal after annealing. ▪No copper diffusion after 700°C-2hrs. ▪ZrO2/Metallic Cu interface. ▪Verified for 10 nm ZrO2films. After annealing Before annealing XPS XRD Superconducting multilayers 19 ➢The Niobium ellipsoid was coated and annealed with the optimized NbTiN-AlN bilayer recipe. T. SAEKI, TFSRF21: Overview of thin-film studies at KEK and Kyoto University, (2021). ▪Enhancement of first penetration field demonstrated. ▪Thicker layer (~ 200 nm) to determine ξand the predicted optimal thickness Nb NbTiN AlN AlN-NbTiN multilayers NbTiN-AlN Multilayer on 1,3 GHz cavity 20 ▪Coating had a bright golden and uniform colour. ▪The cavity was annealed @ 900°C. ▪Vacuum degradation during the annealing step. ( P>10-5 mbar ) ▪Observed delamination in the beam tubes after annealing. 21 Delamination studies Height : 30 mm Diameter : 37 mm 55 by 22 mm - Leak detected and fixed. - Upscaling of the samples with tubes and curve plate Annealed at 900°C ▪Tc ~ 14.5 - 15 K (42 nm) ▪New multilayer diffusion barrier. 50 µm BSE 200 nm InLens 200 nm InLens ▪Presence of film confirmed by XRD, EDS, MEB ▪No delamination observed Tunneling spectroscopy 23 Tunneling spectroscopy ▪High Tc materials: Nb3Sn and NbTiN done with several deposition techniques (ALD, Sputtering, ECR, HIPIMS) on Nb, Cu/Nb, Cu and Sapphire substrates. 9 samples measured from INFN, STFC, CEA, Jlab, FNAL. ▪Bulk Nb surface treatments: Annealing, EP, protective layers. 6 samples measured. ▪Qubits thin films: Growth conditions of Ta, Nb, Ta/Nb. 6 samples measured from ENS, Néel Institut, CEA, FNAL. 24 Summary ▪Construction, commissioning and routine use of the ALD deposition system for 1.3 GHz cavities (Cu or Nb). Over 10 cavities coated. ▪Tunneling spectroscopy apparatus routinely use for sample measurements, cartography and temperature dependences. Over 20 samples measured. ▪Diffusion layers and thermo-current suppression implemented on Cu and trials on cavities on going for Nb.On going trials for high Tc deposition on coupons. ▪Multilayers deposition and thermal annealing implemented on coupons : increase of the first penetration fields. Trials on cavities ongoing. This project has received funding from the European Union’s Horizon 2020 Research and Innovation programme under GA No 101004730. Thank you!