为了研究镧钼阴极表面发射机制，采用专为研究阴极设计的与俄歇能谱仪相连的脉冲激光沉积装置制备薄膜阴极。通过测量阴极发射性能和原位分析表面成分(原子数分数)，研究了阴极表面元素镧La和氧O变化对阴极发射性能的影响。实验发现随着阴极表面镧膜变薄，阴极发射性能逐渐减弱；阴极发射性能与表面元素La，O的含量有关，表面层中La／O越高，阴极的发射性能越好。结果表明，传统的单原子层理论无法解释镧钼阴极的发射机制；超额镧在镧钼阴极的发射中起到了关键作用。

In order to study the surface emission mechanism of La₂O₃-Mo cathode,film cathodes were studied by using a set of equipment,specially designed for cathode research,with which film cathode can be prepared by pulse laser deposition. In order to gain insight into the relation between cathode emission properties and the cathode surface La/O ratio,electron emission properties and surface compositions(lanthanum and oxygen)of the cathodes were investigated experimentally. Experiment results indicate that the emission current densities descent gradually along with surface lanthanum film thickness attenuation;the cathode emission properties are determined intensively by the surface atomic La/O ratios. The higher the La/O ratio gets,the better the emission property reaches. Then the theory of La₂O₃-Mo cathode emission mechanism was discussed. It indicates that the theory of monoatomic layer can't explain perfectly emission mechanism of La₂O₃-Mo cathode;the excess active lanthanum is crucial element to the improvement of thermionic emission.