This　paper　describes　the　surface　analyses　of　＂in　situ＂　prepared　Mo　cathodes　with　a　La　coating.　It　was　found　that　the　electron　emission　depends　strongly　on　the　atomic　La/O　ratio　at　the　surface:　the　higher　this　ratio,　the　better　the　emission.　The　emission　current　density　increases　sharply　when　the　La/O　ratio　starts　to　deviate　from　the　stoichiometric　ratio　of　La2O3.　A　model,　which　describes　the　emission　of　La　coated　Mo　cathodes　qualitatively,　is　presented.　(c)　2005　Elsevier　B.V.　All　rights　reserved.