NEG films: recent R&D progress Paolo Chiggiato (for the EST-SM-DA section)

1. Vacuum Issues of the LHCb Vertex Detector 28 November 2000 NEG films: recent R&D progressPaolo Chiggiato (for the EST-SM-DA section) Summary - Higher substrate temperature during deposition - Clean gas venting - Other... - NEG films: choice and production - Pumping speed -Ageing

2. Choice of the NEG film materials High O solubility limit • The NEG film materials should allow a complete dissolution of the oxide layer at a reasonable low temperature: • High oxygen solubility limit • High oxygen diffusion coefficient • are needed. • If the activation process is limited only by diffusion the time needed to dissolve the oxide layer is: • ta ≈ D-1 (cs-co) -2 • Due to their low grain size, thin films have larger diffusivity and solubility than the respective bulk, therefore faster dissolution

3. Choice of the deposition technique • Composite cathodes • allow the production of compounds/alloys starting from easily available pure metals • eliminate the problem of cathode pyrophoricity • Sputtering is the ideal production technique because: • simple and suitable for a wide range of materials • keeps stoichiometry of alloys • suitable for distributed coating • allows co-sputtering from composite cathode • allows the production of materials far • from thermodynamic equilibrium

4. Ti-Zr-V The composition of coatings produced from a cathode made of three inter-twisted wires of the same diameter of Ti, Zr and V is 30-30-40 [at.%]. The onset of the activation process is between 150°C and 200°C (2h).

5. TiZrV/St.St. Influence of the substrate material (I) TiZrV/Cu Ti-Zr-V films deposited on copper and stainless steel have a very smooth surface, whereas those deposited on aluminium and beryllium have a granular structure. 1 µm TiZrV/Al

6. Influence of the substrate material (II) Spreading of the ESD results obtained for Ti-Zr-V films deposited on stainless steel, Al-6062 and copper Ultimate pressure achieved in Ti-Zr-V coated stainless steel and Al chambers, L = 2 m, Ø = 10 cm, applied pumping speed = 25 l s-1 for H2

7. Pumping speed of Ti-Zr-V coatings: heating temperature Pumping speed of a Ti-Zr-V thin film deposited on Al-6062 strips.

8. Pumping speed of Ti-Zr-V coatings: heating time

9. S=S(Q)

10. Ageing (Ti-Zr-V on St. Steel)

11. Ageing (Ti-Zr-V on Aluminium)

12. Influence of the temperature of the sample during deposition The standard temperature of the substrate during deposition is 100 °C, but substrate temperatures ranging from liquid N2 to 400 °C (for Al up to 200°) are applicable. Ti-Zr-V films were deposited on Cu and stainless steel at 300°C: the results are promising. Ti-Zr-V films deposited on Al, Cu and stainless steel at 200°C will be prepared soon and the results will be available before the end of the year.

13. Temperature of the substrate at 300°C during deposition (I)

14. Temperature of the substrate at 300°C during deposition (II)

15. Temperature of the substrate at 300°C during deposition (III)

16. Temperature of the substrate at 300°C during deposition (IV)

17. Microstructure of a Ti-Zr-V film deposited at 300°C

18. Clean Gas Injection

19. Clean Gas Injection

20. Conclusions • Many getter coatings were produced which undergo activation when heated at temperatures lower than 400°C. The lowest activation temperature (180°C for 24 h heating) has been recorded for Ti-Zr-V films deposited from a cathode made of three inter-twisted elemental wires. • Ti-Zr-V films deposited on Al. Cu, Be and stainless steel have similar vacuum behaviour even if their microstructure can significantly differ. • Sticking probability of about 10-2 for H2 and 5x10-1 for CO can be obtained with Ti-Zr-V films. The saturation of the surface is obtained after pumping of 5 to 7 x 1014 CO molecules cm-2. • Ti-Zr-V films deposited on Cu or stainless steel at 300°C have shown: # higher pumping speeds for the lowest heating temperatures # larger saturation value than those deposited at the standard temperature (100°C).