Non-Evaporable Getters (NEG) are solid materials working as chemical vacuum pumps. They are capable of chemisorbing gas molecules onto their surface after activation by heating in vacuum. They are widely used for a variety of applications such as in particle accelerators, solar panels, vacuum tubes, field-emission display (FED), inert gas purification systems, H2 plasma purification and in other applications in the electronic & photonic industry.
Ti-Zr-V NEG thin films have being developed at CERN for the long straight section of the Large Hadrons Collider (LHC); the whole inner surface of about 1400 vacuum chambers (6 Km of beam pipe) was coated with such material. The main advantage of TiZrV thin films is the very low activation temperature (180°C for 24h heating) and the consequent compatibility with all structural materials for vacuum systems in particle accelerators (stainless steel, beryllium, aluminium, and copper alloys). Nowadays NEG coatings are extensively used in synchrotron radiation facilities (for example ESRF and SOLEIL); they are going to be employed in the Extra Low Energy Antiproton Ring (ELENA at CERN) for anti-hydrogen production and the new MAX IV light source in Lund (Sweden).
These materials were characterised by surface analysis and vacuum measurements. The low activation temperature was recorded a wide range of composition in the Ti-Zr-V system. However, a discrepancy was measured between the surface analysis and the vacuum performance for films based on alloys of Zr and V.
The aim of this investigation was to clarify the effect of Ti in terms of pumping ability (gas sticking probability), electron stimulated desorption and surface cleanliness. The most important outcome of this study is the evaluation of the optimum Zr-V composition in order to maximize the vacuum performance of the NEG film.