An x-ray photoemission spectroscopy investigation of thermal activation induced changes in surface composition and chemical bonds of two gettering alloys: Zr2Fe versus Zr57V36Fe7

Abstract

We report comparative XPS (hν=1253.6 eV) core level (Zr 3d; C 1s; O 1s; Fe 2p; V 2p) results from two relevant gettering alloys: Zr2Fe and Zr57V36Fe7. The samples were studied as-received (after in-air fracturing of bulk ingots) and after different annealing treatments (up to 700 °C) performed in ultrahigh vacuum. With increasing temperature both alloys show a progressive dissolution of Zr oxides, an increase in the metallic character of the surface, the gradual loss of C based adsorbates, and a progressive increase in the surface Zr content and at the expense of the C concentration. At temperatures in the range 300–550 °C a fraction of the C atoms form metallic carbides. OH-based groups are depleted from the surface at low temperatures (200 °C), resulting in a sizable decrease of the near surface O content, while a nearly constant O concentration is found at intermediate and high temperatures. Only minor changes are observed for the near surface concentrations of Fe in Zr2Fe and Fe and V in Zr57V36Fe7 as a function of temperature. The two alloys show strong differences in the activation kinetics of these changes, with surface metallization being initiated at lower temperatures and proceeding faster in Zr57V36Fe7. Metallic carbides are found to almost completely dissolve in Zr57V36Fe7 at 600–700 °C, while they are retained even at high temperatures in Zr2Fe. The kinetic differences determined via XPS are consistent with the differences in gettering behavior of Zr2Fe and Zr57V36Fe7.

Pumping characteristics of the St707 nonevaporable getter (Zr 70 V 24.6-Fe 5.4 wt %)

“…However a relevant difference has been observed when comparing the behaviour of NEG samples of different nature, i.e NEG strip (sintered powder) or alloy ingot. In the case of the strip the maximum Zr surface concentration is already obtained after heating at 500° C [19], whereas in the case of the ingot it increases more progressively up to the maximum temperature of 700° C reached in the experiment [20,21]. This difference has been attributed to a large concentration of crystallographic defects present in the powder, which provide easier diffusion paths for surface impurities and therefore allows removal of the passive layer at lower temperature.…”

“…Measurements of this type, carried out in various laboratories [16][17][18][19][20][21], indicate that a maximum Zr surface concentration of about 70% is achieved after 700° C heating. However a relevant difference has been observed when comparing the behaviour of NEG samples of different nature, i.e NEG strip (sintered powder) or alloy ingot.…”

Development and Characterization of Non-Evaporable Getter Thin Films with Ru Seeding Layer for MEMS Applications

“…As shown in Figure 3 a–c, the evolution with temperature of the XPS spectra associated with the Ti 2p orbital of the Ti upper-layer NEGs and the one associated with the Zr 3d orbital of the Zr upper-layer NEG have two regimes. In the first regime from the as-deposited NEG sample to the activation at 275 °C, the Ti 2p (Zr 3d) spectrum evolution was mainly controlled by the decrease of the doublet peak Ti 4+ (Zr 4+ ) of bending energy (BE): = 458.8 eV, = 182.8 eV related to the TiO 2 (ZrO 2 ) oxide, accompanied simultaneously with, both, an increase in the Ti x+<4 (Zr x+<4 ) doublet peaks related to TiO x<2 (ZrO x<2 ) suboxides [ 13 , 21 , 22 , 23 , 24 , 25 , 26 , 27 ] and an emergence of a metal hydroxide Ti(OH) 2 (Zr(OH) 2 ) doublet peak located at higher bending energies ( = 459.3 eV ( = 183.4 eV)) [ 28 , 29 , 30 , 31 ]. In the second regime, over 275 °C and up to 450 °C, the Ti 2p (Zr 3d) spectrum evolution was mainly controlled by a simultaneous decrease of metal-oxide, metal-hydroxide, and metal-suboxide, accompanied with a significant increase of doublet peak related to the metallic state Ti 0 (Zr 0 ) with a BE of = 454 ± 0.2 eV (BE of = 178.9 eV) as well as some contaminant-based phases peaks such as carbides TiC, TiC–O (ZrC, ZrC–O) [ 13 , 21 , 22 , 23 , 24 , 25 , 26 , 27 ].…”

XPS analysis of the activation process in non-evaporable getter thin films

“…At room temperature the H 2 outgassing rate of stainless-steel vacuum chambers is ¾10 13 Torr l s 1 cm 2 , even after firing at 950°C and in situ baking at 300°C. Therefore, the required pumping speed should be higher than 10 3 l s 1 per square metre of chamber surface in order to obtain base pressures in the 10 12 Torr range.…”