neg films: recent r&d progress paolo chiggiato (for the est-sm-da section)
DESCRIPTION
Vacuum Issues of the LHCb Vertex Detector 28 November 2000. NEG films: recent R&D progress Paolo 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. - PowerPoint PPT PresentationTRANSCRIPT
1
NEG films: recent R&D progress
Paolo Chiggiato (for the EST-SM-DA section)
Vacuum Issues of the LHCb Vertex Detector28 November 2000
- 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 limitThe 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
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
Composite cathodes
allow the production of compounds/alloys starting from easily available pure metals
eliminate the problem of cathode pyrophoricity
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Ti-Zr-V
10-11
10-10
10-9
10-8
10-7
10-6
100 150 200 250 300 350 400 450
TiZrVTi-Zr-Vst. steel
2 Hours Heating Temperature [°C]
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
Influence of the substrate material (I)
1 µm
TiZrV/Cu
TiZrV/St.St. TiZrV/Al
Ti-Zr-V films deposited on copperand 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
10-11
10-10
10-9
10-8
10-7
10-6
100 150 200 250 300 350 400 450
2 Hours Heating Temperature [°C]
bare st. steel
Ti-Zr-V
10-13
10-12
100 150 200 250 300
24 Hours Bakeout Temperature [°C]
Stainless Steel Substrate
Aluminium Substrate
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
10-3
10-2
10-1
100 150 200 250 300 350
0.1
1
2 h Heating Temperature [°C]
H2
10-1
100
100 150 200 250 300 350
2
4
6
8
10
2 h Heating Temperature [°C]
CO
Pumping speed of a Ti-Zr-V thin film deposited on Al-6062 strips.
8
Pumping speed of Ti-Zr-V coatings: heating time
0 100
2 10-3
4 10-3
6 10-3
8 10-3
1 10-2
1.2 10-2
0 5 10 15 20 25
H2 sticking factor of a Ti-Zr-V coating (5-µm)
deposited on copper cleaned by SUBU-5
Heating Time [h]
Heating temperature 200 °C
#000_TiZrV_CuDisk_SUBU5
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S=S(Q)
10-3
10-2
10-1
100
101
10-7
10-6
10-5
10-4
10-3
10-4
10-3
10-2
10-1
1013 1014 1015 1016
Qco
[Torr l cm-2]
CO
H2
N2
Qco
[molecules cm-2]
10
Ageing (Ti-Zr-V on St. Steel)
10-4
10-3
10-2
0 10 20 30 40 50
101
102
Number of heating/venting cycles
200°C 250°C 300°C 350°C
200°C
250°C
300°C
48 h
48 h
250°C
300°C
Heating duration 24 hours
unless otherwise indicated
Updated on 27-11-2000
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Ageing (Ti-Zr-V on Aluminium)
10-4
10-3
10-2
0 2 4 6 8 10 12 14
Al-200°C
Al-180°C
St.Steel-200°C
101
102
Number of heating/venting cycles
Updated on 27-11-2000
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)
10-4
10-3
10-2
10-1
100 150 200 250 300 350 400
ESD sample 1/ St. steel tube
ESD sample 2/ St. steel tube
sample 4.1/ Cu disk
sampple 4.2/ Cu disk
2 h Heating Temperature [°C]
H2
14
Temperature of the substrate at 300°C during deposition (II)
10-3
10-2
10-1
100
101
10-7
10-6
10-5
10-4
10-3
10-4
10-3
10-2
10-1
1013 1014 1015 1016
Qco
[Torr l cm-2]
Qco
[molecules cm-2]
Tdep
=100°C
Tdep
=300°C
15
10-3
10-2
10-1
100
101
10-7
10-6
10-5
10-4
10-3
10-4
10-3
10-2
10-1
1013 1014 1015 1016
Pumping Speed [
l s
-1cm-2
]
Qco
[Torr l cm-2]
Sticking Probability
Qco
[molecules cm-2]
St-707
Ti-Zr-V/Cudep. 300°C
Temperature of the substrate at 300°C during deposition (III)
16
10-3
10-2
10-1
100
101
10-7
10-6
10-5
10-4
10-3
10-4
10-3
10-2
10-1
1013 1014 1015 1016
Pumping Speed [
l s
-1cm-2
]
Qco
[Torr l cm-2]
Sticking Probability
Qco
[molecules cm-2]
H2
N2
Temperature of the substrate at 300°C during deposition (IV)
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Microstructure of a Ti-Zr-V film deposited at 300°C
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Clean Gas Injection
RGA
RGA
BAG
BAG
BAG
BAG Pirani G.
Ar 60
Purification stage
LN2 trap
Zr spongeactivated at
400°C(at RT during
injections)
SupelcoOxysorb
8 m long TiZr coated tube
SP
SP
Penn.G.
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Clean Gas Injection
10-12
10-11
10-10
10-9
10-8
10-7
10-6
10-5
10-4
10-2
10-1
100
101
102
Ar ventingAr venting, no LN
2
Ar venting, no LN2 nor Zr sponges
Air venting (calculated)
Pressure [Torr N
2
eq. ]
Pumping Time [h]
Ion Pump ONTMP valve closed
Ultimate vacuum of the TiZr system
Venting of the 8-m long, 3.6-cm diameter TiZr coated tube
Ion Pump ONTMP valve closed
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.
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).
Ti-Zr-V films deposited on Al. Cu, Be and stainless steel have similar vacuum behaviour even if their microstructure can significantly differ.