1. S.M. Deambrosis*^, G. Keppel*, N. Pretto^, V. Rampazzo*, R.G. Sharma°*, F. Stivanello* and V. Palmieri*^ Padova University, Material Science Dept * INFN - Legnaro National Labs ^ Padua University, Science faculty, Material Science Dept ° Interuniversity Accelerator Center, New Delhi V 3 Si by Thermal Diffusion of SiH 4 into V

2. 1) Theory 2) Literature review 3)Technique choice reasons 4) Method 5) Work in progress 6) Conclusions Multilayer films Cosputtering Reactive sputtering Thermal diffusion Nomogram Samples caracterization Used system V Substrate preparation V 3 Si obtainment V 3 Si

3. Nomogram Theory Ideal R BCS ~ 1 nΩ At T = 4.2 K, f = 500 MHz, s = 4, R BCS depends on Δ and ρ n ~ 10 μΩcm

4. Thermally diffused V 3 Si multilayer films S. De Stefano, A Di Chiara, G. Peluso, L. Maritato*, A. Saggese* and R. Vaglio* Naples University, *Salerno University Cryogenics 1985 Vol 25 April V and Si layers sequentially deposited by Electron-beam evaporation T c vs Annealing T (600-900°C for 1h) T c measured by a 4-terminal resistive method Literature

5. Preliminary results on cosputtering of V 3 Si films by the facing-target magnetron technique Y. Zhang, V. Palmieri, R. Preciso, W. Venturini, Legnaro National Laboratory, ITALY Schematic diagram of the facing-target magnetron. Literature

6. Reactive sputtered V 3 Si films Y. Zhang, V. Palmieri, W. Venturini, R. Preciso, Legnaro National Laboratory - INFN, Italy a b Surface of two annealed samples under SEM: Grain size, (a) 0.2 m, (b) 0.5 m Before annealing After annealing T c (K) Literature

7. Thermal diffusion of V 3 Si films Y. Zhang, V. Palmieri, W. Venturini, F. Stivanello, R. Preciso, Legnaro National Laboratory, ITALY Silane pressure Heat powerTemperatureDiffuse in silane Anneal in vacuum 1.2·10 -4 mbar300W900ºC20h40h Diffusion Parameters: AC inductive measurement: T c ~ 16.0K ΔT c < 0.4K Literature

8. Technique Choice Reasons Very simple technique (RF applications!) V 3 Si by Thermal Diffusion of SiH 4 into V? There is room to improve the film quality by higher thermal diffusion temperature or by longer annealing time in vacuum. Promising old results

9. Laboratory Procedure Used system V Substrate preparation V 3 Si obtainment Samples caracterization Method

10. Vacuum System Method Vacuum system Controllers SiH 4 Gas Cabinet

11. Heating System Method Nb V substrates

12. Substrate Chemical Etching Method Sample Reactant mixtureT (°C)t (s) Erosion rate

13. V Substrate: Optical Microscope HF, HNO 3, H 3 PO 4 1:1:2 50°C, 7,8 m HF, HNO 3, H 3 PO 4 1:1:1 60°C, 36,2 m HNO 3, H 2 O, NH 4 F 25:12:1 30°C, 46,5 m HF, HNO 3 1:4 20°C, 73,8 m Method

14. HF, HNO 3, H 3 PO 4 1:1:2 50°C, 7,8 m HF, HNO 3 1:4 20°C, 73,8 m HF, HNO 3, H 3 PO 4 1:1:1 60°C, 36,2 m HNO 3, H 2 O, NH 4 F 25:12:1 30°C, 45,5 m V Substrate: Profilometer Method

15. V 3 Si obtainment Vacuum p ~ 10 -8 mbar V substrate heating To get SiH 4 decomposition and Silicon diffusion Silanization Film growth (p (SiH4) ~ 10 -3 -10 -4 mbar) Annealing in vacuum To get rid of hydrogen Method

16. SEM Process T = 850°C, p (SiH 4 ) = 5,0x 10 -4 mbar Silanization t = 10h Annealing t = 20h Method V V 3 Si

17. XRD Method Process T = 825°C, p (SiH 4 ) = 5,0x 10 -4 mbar Silanization t = 10h Annealing t = 20h

18. A Superconductive Transition Curve Method

19. T c vs Process T Method Cu Contaminations?

20. Mechanical polishing Chemical polishing 6 GHz Cavities 1. Spinning Technique Spinning Technique 2. Surface Treatments Method

21. Mechanical Polishing SiC Used media: ZrO 2 Method

22. Before the treatment After: SiC 120h + ZrO 2 96h V 6 GHz cavity: Mechanical Polishing Method

23. V 6 GHz cavity: Chemical Polishing Used recipe: Method

24. Parameters optimization: T, t and p (SiH 4 ) Work in progress Use of the best results to coat 6 GHz V cavities to test sistematically RF properties Different sperimental method to prepare V 3 Si: multilayer obtained altermatively depositing V and Si Plasma used to try to avoid the presence of hydrogen

25. Conclusions Thermal diffusion technique T, t and p(SiH 4 ) change trying to improve V 3 Si films properties Good preliminary results: T c ~ 15 K and T c ~ 0,4 K

26. Cosputtering technique: Deposition T > 500°C + sometimes annealing (800°C) Composition (RBS, EDS): composition ratio V/Si linerly dependent on the Target Voltage Ratio T c : four probe DC resistivity measurement Literature Preliminary results on cosputtering of V 3 Si films by the facing-target magnetron technique Y. Zhang, V. Palmieri, R. Preciso, W. Venturini, Legnaro National Laboratory, ITALY

27. Reactive sputtering of V-Si films by a DC facing target magnetron configuration in SiH 4 atmosphere Surface: SEM Composition: EDS Superconducting properties: DC four probe technique Important parameters: T Deposition rate SiH 4 partial pressure Literature Reactive sputtered V 3 Si films Y. Zhang, V. Palmieri, W. Venturini, R. Preciso, Legnaro National Laboratory - INFN, Italy