Outgas of Methane from NEG Coating

WS63: SURFACE PHENOMENA LIMITING PRESSURE IN VACUUM SYSTEM Outgas of Methane from NEG Coating Chia-Mu Cheng ( 鄭家沐 ) Vacuum Group NSRRC, Taiwan 18 /09/2010 e-mail : chiamucheng@nsrrc.org.tw 1

Application of NEG coating for synchrotron light source NEG(non-evaporable getter) has been developed at CERN about thirty years ago. It can provide large pumping speed of H 2 and CO after activation for UHV systems. A NEG coated ID chamber for large synchrotron light source provide linear pumping and large area surface pumping efficiency. It can solve the problem of limited conductance. The Ti-Zr-V coating with lower activation temperature has been developed for the aluminum chambers will be feasible for the ID chambers. 2

Preparation of the Al chamber for NEG coating, Al(NEG) A6063T5 extruded pipe Chemical cleaning (CERN recipe) TIG welding (in clean room ) Leakage checking NGL cleaning (CERN) Vacuum baking (degassing) N 2 purging and Packing NEG coating (SAES Getters) 3

Surface characteristics for NEG film Concentration of NEG film Elmt Spect. Element Atomic Type % % Al K ED 0.13* 0.89* 10 μm Ti K ED 8.17 31.29 V K ED 12.84 46.28 Zr L ED 10.71 21.54 Total 31.85 100.00 1 μm 4

NEG coated Aluminum-SIMS (negative ion) 12 13 16 17 19 24 25 26 C - CH - O - OH - F - C - 2 C 2 H - C 2 H - 2 16 17 32 33 35 37 43 O - 2 HO - 2 Cl - Cl - AlO - 19 12 13 32 35 24 25 26 33 37 43 There is hydrocarbon,h 2 O and contamination (F and Cl) on the surface. 5

NEG coated Aluminum-SIMS (positive ion) 23 27 39 48 51 64 67 92 23 Na + Al + K + Ti + V + TiO + VO + Zr + 27 39 48 51 64 67 57? 92 6

AL(NEG) chamber was installed in TLS 19B(PSD) beam line for SR photon exposure Beam Line Test Chamber (2m) NEG-coated Elec. Feedthrough - I (PEY) RGA Safety shutter Absorber IG (P1) IG (P2) Bottle neck Conductance, C ~ 5 L/s E I θ SR beam energy (1.5GeV) e-beam current (300mA) photon span (0.0033rad) Pumping chambers - IG (Po) X-Y Slits - Define horiz. photon span of 2.42 mrad yield of photon stimulated desorption η =ΔQ/ΔN ΔQ =3.5x10 19 x C (ΔP 1 -ΔP 0 ) ΔN =8.05x10 17 x E x I x θ/2π 7

The typical baking and activation process for Al(NEG) chamber 180 180, 24h NEG - CH Other - CH 150 150, 8h 120 25 1h 5h 13h 17h 37h 40h 42h 8

History of photon exposure for Al(NEG) chamber at 19B beamline It motivated us to study the outgas of NEG! 9

To study the outgas of NEG film We found outgas of CH 4 and Kr from NEG chamber during activation and build up. The D 2 O has been exposed into NEG chamber for inspecting the surface phenomena. It has been found the outgas of CmDxHy compound molecules in the NEG chamber exposed to D 2 O. It shows D 2 O has been dissociated and recombined with C and H atoms on the surface. 10

Build up of AL(NEG) Chamber with D 2 O exposure, (a) before and (b) after SR exposure (a) The compound molecules of CD x, CD x H y, C m D x, and C m D x H y are observed for the AL(NEG) chamber exposed with D 2 O and after activation. (b) The compound molecules of C m D x and C m D x H y are reduced for the AL(NEG) chamber after the photon exposure. (c) The beam cleaning effect addresses the desorption of the compound molecules are from the NEG film. CD x & CD x H y C m D x & C m D x H y (a) CD x & CD x H y C m D x & C m D x H y D 2 O dissociated and outgas of C m D x, C m D x H y complex produced. SR beam cleaning (b) Ref : G. Y. Hsiung, C. M. Cheng, C. Y. Yang, C.K. Chan and J.R. Chen; AIP vol. 1099, p.17(2009) 11

SS(NEG) Chambers with D 2 O and H 2 O Exposure (a) D 2 O exposed on the activated SS(NEG) chamber The pressure build up curves for SS(NEG) chamber is similar with AL(NEG) chamber. The D 2 O has been dissociated and the outgases of high mass compound molecules of C m D x H y and C m D x are formed and desorbed. Outgas of D 2 O is not significant. (b) H 2 O exposed on the baked SS(NEG) chamber Hydrocarbon molecules, CH 4 and C m H y, are formed and desorbed. (a) SS(NEG) / D 2 O Exposure (b) SS(NEG) / H 2 O Exposure CH 4 C m H y Dissociation of D 2 O on the NEG film is confirmed Ref : G. Y. Hsiung, C. M. Cheng, C. Y. Yang, C.K. Chan and J.R. Chen; AIP vol. 1099, p.17(2009) 12

Al- and SS-chambers (non-coated) with D 2 O Exposure D 2 O exposure to the Al- and SSchambers without NEG-coating The pressure build up curves for the Al- and SS- chambers without NEG coating are similar. The outgas species contain the D 2 O and hydrocarbon (CH 4, C m H y ), except C m D x H y compounds, are measured. No evidence shows D 2 O is dissociated and combined with hydrocarbons. The outgas of hydrocarbon is existed. Only D 2 O and C m H y are measured. Ref : G. Y. Hsiung, C. M. Cheng, C. Y. Yang, C.K. Chan and J.R. Chen; AIP vol. 1099, p.17(2009) 13

PM-IRRAS Spectra for Al and Al- NEG samples without exposure (a), with D 2 O exposure (b), and with H 2 O exposure (c). (1) (2) (3) (4) (a) Peaks of (1) C-H stretching (2929, 2857), (2) C=O stretching (1741), (3) C=C bending (1650), (4) C-H bending (1460, 1406), (5) O-D stretching (2577), (6) O-H stretching (3456) are identified for the Al samples. Peaks (1) ~ (4) recognize the molecules adsorbed on the Al surfaces contains CH 4 and CO. (1) (5) (3) (2) (4) (b) Peaks (5) and (6) recognize the residence of D 2 O and H 2 O on the surface after exposure, respectively. There is not any peak measured for the Al-NEG surface. It is suspected (a) the strong binding energy on the adsorbed molecules from the NEG material or (b) D 2 O have been dissociated. (6) (1) (2) (3) (4) 14 (c)

NEG coating for Aluminum ID chamber at NSRRC DC sputtering coating parameters Discharge gas Kr Working pressure 2 10-2 Torr voltage -800 V current ~ 18 ma Magnetic field (center) 200 Gauss Depositing rate 0.07 nm/s 15

SEM and EDS analysis of NEG film X25000 X5000 EDS analysis Ti 30%±5% V 35%±5% Zr 35%±5% 16

Activation for AL(NEG) chamber The ultimate pressure is 8e-11 Torr. The major outgas is hydrogen and methane. 17

Exposure test with ION-NEG pump Two sets of starcell Ion pump combined with Pd/NEG chamber, 100CF and 150CF, called ION-NEG provided by Varian are for the test. Pd/NEG chamber was coating Pd film on NEG coated chamber. Pd film can prevent NEG film from oxygen contamination. 200nm Pd 850nm NEG (TiVZr) Stainless steel chamber 18

Experimental The ION-NEG pump have been baked and activated at 200 for 8h to reach ultimate pressure. The outgassing rate of ION-NEG was measured by pressure build up with TMP isolated and ion pump turned off. 19

starcell IP + 100CF Pd/NEG build up for 3 min Build Before up 3min build up The major residual gas is hydrogen, H The major outgas 2 O, CO and CO is hydrogen 2. and methane. 20

Starcell IP + 150CF Pd/NEG build up for 3 min Before Build up build 3minup The major residual gas is hydrogen, H 2 O, CO and CO 2. The major outgas is only methane. 21

Compare with pressure and outgassing rate Starcell IP + 100CF Pd/NEG system Starcell IP+ 150CF Pd/NEG system Ultimate pressure (Torr) 1.3e-10 (1.4e-10) Outgassing rate (Torr.L/sec) 3.8e-9 (7e-9) Outgassing rate of H 2 (Torr.L/sec) 3.7e-9 (6.8e-9) Outgassing rate of CH 4 (Torr.L/sec) 3e-11 (8e-11) 4e-11 3e-10 5e-12 1.4e-10 The major residual gas is hydrogen(> 90%). A pressure bellow 1e-10 Torr has been achieved for 150CF ION-NEG after baking. The 100CF Pd/NEG chamber seems to be no working. The property of ION-NEG still not stable. 22

Does Pd film protect NEG film? In order to test the function of Pd film, we expose D 2 O to 150 CF Pd/NEG chamber after it been activated. To study the outgas from Pd film surface. If there is no C m H x D y compound which is like only NEG coating chamber. It was believed that Pd film can isolate NEG from D 2 O. 23

150CF Pd/NEG chamber before exposed D 2 O H 2 H 2 O CH 4 CO C m H x There is lots of hydrocarbon before exposing D 2 O. 24

150CF Pd/NEG chamber after exposed D 2 O DHO H DH DO D 2 O 2 D2 CO CO 2 C m H x There is no C m H x D y compound. Pd film can prevent NEG film from reacting with D 2 O. 25

Conclusion D 2 O or H 2 O are dissociated and recombined with C to produce CH 4 on NEG surface. There is no C, H and O related bonding of Al(NEG) sample on the PM-IRRAS spectra. The ION-NEG (Pd/NEG chamber with IP) can reach lower ultimate pressure Pd/NEG chamber will not produce C m D x H y outgas after exposed D 2 O. 26

Thank you for attention 27