The mechanism of strontium doping to enhancing the electron emission performance of barium-tungsten cathode

The barium-tungsten cathode is widely used in vacuum electronic devices. To fulfill the application requirements for high current and stability, strontium, belonging to the same main group as barium, is extensively employed as impregnant additive in cathode research. To elucidate the enhancement mechanism of strontium on the performance of barium-tungsten cathode, we calculate the correlation between metal coverage and work function, adsorption energy, and electronic properties. The results demonstrate that the BaxSryO monolayer structures can achieve lower work functions on W(111) and W(211) surfaces with metal coverages of 0.25-0.333 ML and 0.5 ML, respectively. Hence, by adjusting the concentration of strontium, the barium-tungsten cathode can exhibit outstanding electron emission performance. In addition, Sr doping significantly enhanced the adhesion ability of Sr and Ba atoms on the surface, and then improved the evaporation resistance of the active metal atoms. The electron density analysis shows that the Sr and Ba adatoms in low work function structures exhibit electron delocalization, and the electron excitation region is expanded. The calculation of the dipole moment indicates that the weak dipole repulsion between Ba-Sr atoms amplifies the polarization effect of the adsorbent, leading to a reduction in the work function of the Sr-doped surface configuration.