A sharp reduction of work function occurs on a tungsten (100) surface after modifying of the surface with Er or Lu and oxygen and lasts for several hours. The fabricating process is similar to that of the standard ZrO/W(100) Schottky emitter. The calculated work functions with the aid of Fowler-Nordheirn plot are 1.8 eV for ErO/W(100) and 2.3 eV for LuO/W(100). These work functions are extremely low in comparison with both 4.6 eV for bare W(100) and 2.9 eV for ZrO/W(100). The electrical dipole moments of complex pairs ErO and LuO are evaluated to be about 6.3 and 4.5 D. respectively. (C) 2004 American Vacuum Society.