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

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: t a ≈ D -1 (c s -c o ) -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 Sputtering is the ideal production technique because: ß simple and suitable for a wide range of materials ß keeps stoichiometry of alloys ß suitable for distributed coating ß allows co-sputtering from composite cathode ß allows the production of materials far from thermodynamic equilibrium Composite cathodes ß allow the production of compounds/alloys starting from easily available pure metals ß eliminate the problem of cathode pyrophoricity

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 [at.%]. The onset of the activation process is between 150°C and 200°C (2h).

5 Influence of the substrate material (I) 1 µm TiZrV/Cu TiZrV/St.St. TiZrV/Al 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.

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 s -1 for H 2

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 N 2 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 ß 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. ß Sticking probability of about for H 2 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 CO molecules cm -2. ß 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). ß Ti-Zr-V films deposited on Al. Cu, Be and stainless steel have similar vacuum behaviour even if their microstructure can significantly differ.