Abstract
The activation process of Zr, ZrVHf and TiZrV non-evaporative getter (NEG) thin films, prepared by direct current magnetron sputtering, is investigated by in situ synchrotron radiation photoemission spectroscopy. The activation temperatures of Zr and ZrVHf films are found to be 300 °C and 200 °C, respectively, and the activation temperature of TiZrV film is 120 °C—the lowest activation temperature reported on TiZrV. As the heating temperature increases, the transformation of metal-C bond follows the orders of V–C, Ti–C, Zr–C, Hf–C. It is found that the order of reduction difficulty of the same element oxides, that is, Zr oxide and V oxide in different films follows Zr film > ZrVHf film > TiZrV film. The order of difficulty in the reduction of oxides in the same alloy NEG films follows HfO2 > ZrO2 > TiO2 > V2O5. We propose that the above phenomena can be explained by interstitial diffusion, grain boundary diffusion of residual gas atoms and grain boundary precipitation of V and Ti in the solid solution of the NEG films.
Highlights
Non-evaporable getters (NEG) technology was first invented at CERN in the 1990s [1] and are widely employed in particle accelerators [2] the Tokamak fusion test reactor [3], field-emission display, vacuum packaged MEMS [4] and neutron tubes [5].NEG materials have become an integral component of many ultrahigh vacuum environments mainly due to their unique surface properties, which are conducive to achieving ultrahigh vacuum (UHV) of the order of at least 10−8 Pa [6,7] by chemically adsorbing gas molecules on their surface
The activation temperature of the NEG can be characterized by the pressure distribution of the custom-made pumping speed measurement setup [11,15], the ultimate vacuum after activation [16] and the change in valence states by X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), low-energy ion scattering (LEIS) and Auger electron spectroscopy (AES) [17,18,19,20,21,22]
The Zr, ZrVHf and TiZrV NEG films were prepared by direct current (DC) magnetron sputtering
Summary
Non-evaporable getters (NEG) technology was first invented at CERN in the 1990s [1] and are widely employed in particle accelerators [2] the Tokamak fusion test reactor [3], field-emission display, vacuum packaged MEMS [4] and neutron tubes [5].NEG materials have become an integral component of many ultrahigh vacuum environments mainly due to their unique surface properties, which are conducive to achieving ultrahigh vacuum (UHV) of the order of at least 10−8 Pa [6,7] by chemically adsorbing gas molecules on their surface. Heat needs to be applied to the NEG to allow the surface gas to residually diffuse into the bulk before it can have pumping performance; this process is called “activation”. If one coats the inner wall of a vacuum chamber with NEG film, it turns the outgassing vacuum chamber into a vacuum pump without any need of additional space and energy. The activation temperature of the NEG can be characterized by the pressure distribution of the custom-made pumping speed measurement setup [11,15], the ultimate vacuum after activation [16] and the change in valence states by X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), low-energy ion scattering (LEIS) and Auger electron spectroscopy (AES) [17,18,19,20,21,22]. The challenge is to further reduce the activation temperature of NEG films and understand the activation process
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