TiZrV NEG film

Outgassing

1 sourced measurement for this card, 9 declared absences. A rate means nothing without the pumping time it was read at, so each one states it or declares it missing. The whole base, filters included, is at /tools/outgassing/.

• non-evaporable getter coatings and strips. An activated getter surface is a pump, not a gas source, for the gases it chemisorbs. It does not pump methane or the noble gases.The source states that a vacuum chamber sputter-coated with a getter film may be transformed from a gas source to a pump by activating the coating during standard in situ bakeout. It also states that methane is not pumped by getters, and that the ultimate pressure of the LEP NEG pump is set by the outgassing of CH4 and Ar, gases not pumped by NEGs, divided by the pumping speed of a sputter-ion pump. A base that carries only a magnitude for these surfaces loses the sign and the species boundary, which are the two facts that matter in design.
• TiZrV coating, magnetron sputtered from intertwisted Ti, Zr and V wires. No static outgassing rate is published for the activated TiZrV coating in this source, only its activation condition and its pumping behaviour.The source states that TiZrV is practically fully activated after 24 h baking at 200 C, and that adding vanadium to TiZr shifts activation about 50 C lower for all degassing products, H2, CO, CO2 and CH4. Ultimate pressures after 24 h baking and H2 sticking coefficients are published as curves, on chambers 2 m long, 10 cm diameter, with 25 L/s applied for H2. Later literature from the same group is reported to give 180 C for 24 h, that value is not written here because the document publishing it has not been read on the page. Reading it is on the library list.
• equiatomic TiZr coating on stainless steel. Activation of the equiatomic TiZr coating starts at 150 C and is complete at 300 C for 2 h heating.Section 3 of the source, from electron stimulated desorption measurements at 20 C after 2 h heating, electron energy 500 eV, current 1 mA, without intermediate air venting. For elemental Ti, Zr and Hf coatings no degassing variation is noticeable up to 200 C. The source gives the conversion between heating times: extending from 2 h to 24 h roughly corresponds to increasing the 2 h temperature by 50 C. Desorption yields are published as curves, no static outgassing rate is tabulated.
• Sputter deposited TiZrV thin film, composition Ti 30 percent, Zr 20 percent, V 50 percent atomic, from intertwisted elemental wires. Full activation of the TiZrV coating is reached after 24 h in situ heating at 180 C. Activation begins between 120 and 150 C. This is the lowest activation temperature of some 18 different getter coatings studied by the group.The document publishes an activation temperature and not an outgassing rate, so no value field is filled. The abstract, section 2 and the caption of figure 1 all give 180 C for 24 h. Section 2 states that the same coating was found to display full activation after 24 h heating at 200 C in the earlier work of reference 3, and that the interval between 150 and 200 C was then explored to obtain a more precise value.
• TiZrV and other getter coatings after complete activation. After complete activation the measured sticking factors range between 6e-3 and 5e-2 for H2 and between 0.4 and 0.8 for CO, over the some 18 coatings produced and tested. Among the coatings tested the TiZrV films present the lowest sticking factors and also the smoothest surface.A sticking factor is a dimensionless capture probability, not an outgassing rate, so no value field is filled. The corpus carries it because it is the quantity that decides whether a getter surface is a pump or a source.
• TiZrV film 5 micrometre thick, repeatedly activated and vented to air. Film deterioration may be counteracted over more than 25 activation and air venting cycles provided the heating temperature is increased up to 350 C. The figure shows 26 cycles carried out with a 30 percent decrease of the H2 sticking factor.The document publishes an ageing behaviour and not an outgassing rate. The activation is initially carried out at 200 C and the activation temperature is progressively increased as the H2 sticking factor decreases.
• TiZrV coated chambers 2 m long, diameters 34, 58 and 100 mm. The reported experimental data cover the pressure range from 1e-12 down to 1e-13 Torr. The source concludes that the measured pressures are an instrumental artefact consequent to the degassing of the measuring instrument, and that much lower pressures would be obtained but not measured in the absence of the gauge.An ultimate system pressure is not a surface outgassing rate and never converts to one without the pumping speed and the area, so no value field is filled. The source itself declares these pressures instrument limited.
• TiZrV coating produced by sputtering from an intertwisted wire cathode. An argon content of about 3500 ppm has been measured in the coating, while for krypton the content is lower by two orders of magnitude. In both cases the source states that the room temperature degassing after activation provides a negligible contribution to the ultimate pressure.A trapped gas content in ppm is not an outgassing rate. It is carried because rare gases are not pumped by getters, so their release sets a floor the getter cannot lower.
• TiZrV coating in a 58 mm inner diameter chamber, not vented to air between baking cycles. Figure 1 of the source plots the ultimate pressure against the temperature of a 24 h heating. Read from the logarithmic axis, the pressure is about 3e-11 Torr after 24 h at 120 C, about 5e-12 Torr at 150 C, and reaches a plateau at about 6e-13 Torr at 180, 200 and 250 C. The plateau is what proves the activation complete, and the caption states it in words, activation begins between 120 and 150 C and is complete after heating for 24 h at 180 C.THESE THREE NUMBERS ARE READ FROM A GRAPH, not from a table. The source tabulates none of them. They are carried as a declaration and never as a measurement, and their uncertainty is that of a reading on a logarithmic axis, of the order of the size of a plotted point, so about 20 percent on the mantissa. A system ultimate pressure is in any case not a surface outgassing rate and does not convert to one without the pumping speed and the area.

Sources: S-CHIGGIATO-CAS-2017, S-BENVENUTI-EPAC1998, S-BENVENUTI-TIZRV-2001. Full citations and conditions at the base and in /data/outgassing.json.