COPPER-ION FIELD-EMISSION SOURCE

The dynamics of the topographical modification of the apex of a bulk copper tip heated at a temperature varying between 0.7 T(F) and T(F) (T(F): melting temperature) have been observed "in situ" in the 3 MeV electron microscope of the L.O.E. in Toulouse. Three regimes have been pointed out: 1. the intermediate regime (T almost-equal-to 0.7 T(F)) characterized by the formation of protuberances; 2. the drops regime (T almost-equal-to 0.8 T(F)) characterized by the evolution of the apex from a spherical shape to an ellipsoidal one and then to a conical one; subsequently, if the electrostatic field is a little increased, the cone divides into drops which diffuse along the tip and explode at the apex; 3. the L.M.I.S. regime (0.9 T(F) < T < T(F)): there is enough liquid metal for a stable cone to be formed and emission occurs.