Collision-induced electron emission from surfaces in negative-ion time-of-fliht mass spectrometry

Measurements of collision induced secondary electron emission from surfaces under standard vacuum conditions normally used in time-of-flight mass spectrometers (i.e. 10^-6 to 10^-8 mbar) are performed. The relative electron emission yield of copper, nickel and gold meshes under bombardment with negative ions with kinetic energies in the range between 200 and 1000 eV and the temperature dependence of the electron emission were studied. The results show that the secondary electron emission is considerable, even at low kinetic energies of the projectiles, and that the electrons are mainly emitted from the adsorbated residual gases. Nevertheless, there is a significant dependence on the substrate material. Practical consequences for time-of-flight analyzers for negative ions or electrons are discussed.