Process of magnetron sputtering

1. Rhodium coated mirrors deposited by magnetron sputtering for first mirror Process of magnetron sputtering Laurent Marota, Grégory De Temmermana b; Andrey Litnovskyb, Grégory Covarelc and Peter Oelhafena aInstitute of Physics, University of Basel, Switzerland bnow: Center for Energy Research, University of California at San Diego, USA cInstitut für Plasmaphysik, Ass. EURATOM, TEC, Forschungszentrum Jülich, Germany dMechanical Laboratory, University of Haute-Alsace, France

2. Motivation • Rhodium is a very attractive option for first mirror material: • Good reflectivity • High melting point (1966 °C) • Low sputtering yield (high Z) Calculated with (n, k) from [1] High price of the raw material calls for developing thin film technology Existing studies made with electro-deposition or magnetron (Reference: G Maddaluno 11th ITPA, N.V Klassen 10th ITPA) 1Handbook of optical constants of solids, ed. E.D. Palik, Acad. Press, 1985 and 1991

3. Process of magnetron sputtering Routine process: Total time deposition: 25 hours Total Rh thickness deposited: 35 microns • Vacuum deposition technique Typical deposition conditions: • Pressure: 0.6 Pa - argon gas • DC power, 25 W (U = -225 V / I = 0.11 A ) • Deposition rate: 0.6 nm / s • Deposition on silicon and metallic substrates • Investigated conditions: • Pressure, Power applied to the target, Deposition temperature [2] Rhodium layer on copper [2]Characterization of magnetron sputtered rhodium films for reflective coatings, L. Marot et al, submitted to Surface Coating Technology

4. Characterization of the layer / 1 • No impurities (carbon, oxygen, argon) were detected by in-situ XPS on the surface after deposition • Homogeneous rhodium film with dense columnar structure (up to 2.4 m thick) 1.2 m 1.8 m SEM cross section observation of rhodium film deposited on Si at RT SEM cross section observation of rhodium film deposited on Si at 350 °C

5. Characterization of the layer / 2 Ra = 4.2 nm / Before deposition 4 nm Crystallite size = 10 nm • No polishing after deposition • Low roughness after deposition SEM observation of a rhodium layer (1,5 m) on molybdenum Film roughness depends on the initial substrate roughness Diffuse reflectivity measured before and after deposition

6. Characterization of the layer / 3 • Film roughness depends on the deposition temperature RSpecular = RTotal - RDiffuse Specular reflectivity measured on Rh layer deposited on stainless steel at different temperatures

7. Characterization of the layer / 4 • X-ray diffraction measurements: • Polycrystalline, no specific texture, no specific orientation for the grains • Grain size around 10 nm (Calculated by Scherrer formula) Relative Intensity • Nanohardness (3 mN) measurements: • The hardness of a rhodium layer (1.7 m thick) is 9.2 GPa, in comparison to 1.2 GPa for the annealed bulk rhodium Influence of the hardness for erosion? X-ray diffraction pattern of deposited rhodium film

8. Influence of the substrate on the optical properties • Layer deposited on metallic substrate (Mo, Cu, stainless steel) for layer thickness > 1 m No influence of the substrates on the optical properties Total reflectivity measured on Rh layer deposited on metallic substrates

9. Influence of the substrates for the adhesion of the coating Scratch direction 1.7 N 4 N Lc = 9.5N 19.5 N 30 m First pad adhering First breakthrough First crack Worn out Scratch test measurements: load from 0 to 20 N at a rate of 10 N·min-1) Main part of a scratch track of rhodium film sample deposited at 170°C on stainless steel The adhesion properties increase with the substrate hardness

10. Measurement of polarization reflectivity by ellipsometry For some laser diagnostics (LIDAR, MSE) the polarisation of the linearly polarised laser radiation is relevant Reflectivity at 40, 50, 60, 70 and 80° for s and p polarizations at 660 nm of rhodium layer

11. Effect of annealing cycles on the mirror reflectivity Annealing cycles: 10 times @ 5h at 200 °C in air The optical observations did not reveal any modification or delamination of the layer Total reflectivity of Rh layer before and after annealing cycles

12. Laboratory experiments for erosion / 1 Laboratory experiments for erosion by deuterium ions of rhodium mirrors [4] Deuterium RF plasma with a graphite hollow cathode Bias on sample: - 300 V to control impinging ions energy Pressure: 6 Pa Time of plasma: 13 h Fluence: 2×1020 ions/cm2 Setup for D2 plasma sputtering, for rhodium deposition and in situ XPS [4]Same process described by G. De Temmerman et al, 10th ITPA

13. Laboratory experiments for erosion / 2 Reflectivity after D2 sputtering Weight measurements allow the determination of the eroded tickness: 375 nm eroded Carbon on the surface (measured by XPS) Post Cleaning D2 RF Plasma -100 V / 30 min / 300 °C Total reflectivity measured on Rh layer (1.8 m) deposited on Mo

14. Laboratory experiments for erosion / 3 Ra = 4.2 nm Ra = 2.8 nm Ra = 5.6 nm Diffuse reflectivity measured before, after D2 sputtering and after post cleaning No significant change of roughness after erosion

15. Laboratory experiments for erosion / 4 Same experiment on 2 layers (> 1 m) deposited on Stainless Steel and Copper After erosion by deuterium ions the reflectivity is constant Total reflectivity measured on Rh layer deposited on Stainless Steel and Copper

16. Rh Uni. Basel Rh [5] SC Mo Exposure of Rh mirrors under erosion conditions in TEXTOR Mirrors exposed in the Scrape-Off layer plasma of TEXTOR • 19 shots, ~ 210 plasma seconds • Mirror temperature 300 – 500 °C • D+ energy: ~ 250 - 300 eV • Fluence = 2x1020 ions/cm2 [5] G Maddaluno 11th ITPA TEXTOR, Jülich, Germany

17. Exposure of Rh mirrors under erosion conditions in TEXTOR No significant change of the XRD measurements => No crystallographic change (temperature exposure 300 – 500 °C) => No delamination XRD measurements before and after exposure

18. Exposure of Rh mirrors under erosion conditions in TEXTOR Reflectivity of mirrors exposed in the Scrape-Off layer plasma of TEXTOR Eroded thickness for rhodium: 440 nm Rh Basel SIMS / XPS after exposure: Mo and/or MoC and MoO ( 5 - 8 %) and Amorphous Carbon Total reflectivity measured before and after exposure

19. Exposure of Rh mirrors under erosion conditions in TEXTOR Same Post Cleaning experiment with : D2 RF plasma -100 V / 45 min / 250 °C Rh Basel Before Exposure Ra = 6.3 nm Rh Basel After Exposure Ra = 8.9 nm Rh Basel Before Exposure Ra = 6.3 nm Rh Basel After Exposure Ra = 8.9 nm Post Cleaning D2 Plasma Ra = 6.5 nm Possibility of mirror cleaning

20. Conclusion • No impurities were detected by XPS on the surface after deposition • Homogeneous rhodium film with dense columnar structure ( up to 2.4 m thick) with small grain size (~10 nm) • Low roughness after Rh deposition (depending on the substrates) • No effect of annealing treatment in air on the reflectivity • (10 times @5h at 200 °C in air) • Good adhesion of coating on hard substrate (measured by scratch test) • Rh-coating has survived the exposure in erosion-dominated conditions in laboratory experiment and in TEXTOR

21. On going • Erosion test for high D+ energy :500 - 600 eV (Karkov Institute, V. Voitsenya) • Measurement of the sputtering yield of rhodium film (to compare with that of bulk Rh) • Effect of baking cycles (400 °C) in vacuum Thank you for your attention Questions ?

22. Rhodium coated mirrors deposited by magnetron sputtering for first mirror Process of magnetron sputtering Laurent Marota, Grégory De Temmermana b; Andrey Litnovskyb, Grégory Covarelc and Peter Oelhafena aInstitute of Physics, University of Basel, Switzerland bnow: Center for Energy Research, University of California at San Diego, USA cInstitut für Plasmaphysik, Ass. EURATOM, TEC, Forschungszentrum Jülich, Germany dMechanical Laboratory, University of Haute-Alsace, France

23. Exposure of Rh mirrors under erosion conditions in TEXTOR Mirrors exposed in the Scrape-Off layer plasma of TEXTOR Total reflectivity measured before and after exposure