Thin Films coating CERN TE 9604 Progress presentation

Thin Films coating CERN- TE 9604 Progress presentation Joao Mira Coroa Msc. Micro and Nanotechnology FCT – UNL Supervisor – Pedro Costa Pinto April 2019 TE/VSC/SCC

Contents I. Introduction II. Objectives and Strategy III. Involvement IV. Future Work V. Final Thoughts Joao Mira Coroa 2

I. Introduction Inside the accelerator – e-cloud problem Beam pipe walls - - - + ++ + SE - - [2] PE – Primary electrons/ Photoelectrons SE – Secondary electrons Joao Mira Coroa - + ++ + - - - + + + - - - - + ++ + PE - - - - + + -+ ++ + -- - - - - + ++ + -- Electron cloud formation • Beam stability • Heat load (SPS) • Efficiency of particle accelerator Radiation 3

I. Introduction CERN’s solution How to decrease the Secondary electrons? • By having surfaces with low secondary electron yield (SEY ≡ δ): - Ti. Zr. V for LHC - a-C for SPS How low should be the SEY? • The electron multipacting depends on the SEY of the surface, geometry of the chamber, bunch spacing, etc. How can these surfaces be obtained? • One of the ways is through thin film coatings. . CERN’S : 1. 1 – 1. 5 Joao Mira Coroa 4

I. Introduction Thin Films coating What is it? Why we do it? How we do it? Joao Mira Coroa Layer of any material ranging from a nanometer (10 -9 m) to several micrometers (10 -6 m) It can change dramatically the surface properties independently of the bulk material beneath it Through vacuum deposition systems that help us deposit the material atom by atom (or molecule by molecule) 5

I. Introduction Thin Films coating Substrate/Samples Sputtering Pumping Process gas Why? ? What happens during deposition? - Cathode (e. g. Carbon) SEY = 2 SEY ≈ 1 1, 5 1, 4 SEYmax Chemical Vapor deposition (CVD) • %H 2 SEY increase Ar+ Thin Films Coating Physical Vapor Deposition (PVD) BUT… 1, 3 1, 2 1, 1 1 0, 9 Stainless Steel Joao Mira Coroa Amorphous Carbon (a. C): > 50 nm 0, 00 0, 10 0, 20 % H 2 in Ar mix 0, 30 0, 40 6

II. Objectives & Strategy My role at CERN v Understand how H 2 affects the amorphous carbon thin film; v Find a mitigation method to counter the increase of SEY. 1 Organize what is happening during deposition: is H 2 reacting with carbon atoms at the plasma? At the cathode surface? Or on the surface of the growing film? [3] Hint: Diamond sp 3 bonds ; Graphite sp 2 bonds 2 a-C Bandgap: 0 e. V Low SEY N 2 bandgap H 2 vs N 2 ? N 2 Joao Mira Coroa Bandgap: 4 e. V High SEY H 2 bandgap H 2 SEY vs. Bandgap ? 7

III. Involvement The last five months • Samples with 1%N 2 and different %H 2 were produced; Ø More H 2 in the mixture, the more SEY Ø More N 2 in the mixture, the lower SEY • Launched collaboration with FCT-UNL (Prof. Isabel Ferreira) for bandgap measurements; Ø More H 2 in the mixture, the more SEY and bigger the bandgap Ø More N 2 in the mixture, the lower SEY and smaller the bandgap Joao Mira Coroa 8

IV. Future Work Cx. Hy ? OES Access if the chemical reaction between carbon atoms and hydrogen/nitrogen atoms is happening in the plasma, at the cathode surface or at the growing film. RGA In assembling… Cw N z ? How much %N in the mixture? Joao Mira Coroa 9

V. Final Thoughts A big thank you to: - FCT and CERN for providing this opportunity My supervisor Pedro Costa Pinto All the vacuum group Paulo Gomes and Jennifer Dembski Any questions? Joao Mira Coroa 10

References [1] - https: //www. scientificamerican. com/article/particle-physicists-turn-to-ai-to-cope-with-cerns-collision-deluge/ [2] - https: //www. ioshmagazine. com/article/cern-collision-course [3] - Robertson, J. (2002). Diamond-like amorphous carbon. Materials Science And Engineering: R: Reports, 37(4 -6) [4] - https: //commons. wikimedia. org/wiki/File: Band. Gap-Comparison-E. PNG Joao Mira Coroa 11