Work function of Cs-free materials for enhanced H− surface production
摘要
Materials with low work function (WF), such as the well-known caesiated surfaces, are most efficient in producing H− ions. In view of the applicability in future negative ion sources, alternative materials to Cs evaporation are studied in a dedicated experiment. Lanthanated (WL10, WL2, MoLa, LaB6) and bariated materials (TDC) as well as molybdenum implanted with Cs are investigated regarding their achievable WF at ion source relevant conditions, in particular for temperatures below 500 ◦C. In contrast to their usual application as electron emitters at temperatures above 1000 ◦C, the work functions of the investigated materials under these conditions do not decrease below 3.6 eV (measured global minimum, achieved with LaB6). For the lanthanated materials, the obtained WF values are stable under plasma exposure times of several hours. However, for all the materials the work function is subject to degradation in absence of heating or plasma exposure. Compared to Cs evaporation, with WF values measured down to 2.1 eV, none of the materials tested so far can be regarded as an actual alternative.