COLLISION-INDUCED ELECTRON-EMISSION FROM SURFACES IN NEGATIVE-ION TIME-OF-FLIGHT MASS-SPECTROMETRY

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