新型的覆纳米粒子薄膜阴极的研究

Emission properties of impregnated cathode with nanoparticle films

采用直流磁控溅射的方法制备出Ir金属纳米粒子薄膜.利用扫描电子显微镜分析了纳米粒子的形态和分布以及不同工艺条件对粒子粒径及形貌的影响,表明纳米粒子的大小可通过调节溅射气体压强来控制.在25%孔度的W海绵基体内浸入6∶1∶2铝酸盐发射物质,然后在其表面沉积上厚度为200—500nm的纳米粒子薄膜层,最后在H2气中1200℃烧结,即制成了新型纳米粒子薄膜阴极.利用阴极发射微观均匀性测试仪对纳米粒子薄膜阴极和传统覆膜阴极的热电子发射的均匀性进行了对比研究.采用飞行时间质谱仪测试了真空本底、纳米粒子薄膜阴极、传统覆膜阴极等各种阴极蒸发物的成分,研究了阴极蒸发速率与阴极温度的关系,比较了不同阴极蒸发速率的大小.研究了Ba-W阴极覆上纳米粒子薄膜后的发射特性.

The Ir nano particle thin film was grown by dcrect current magnetron sputtering at room temperature. Microstructure of thin films grown at different sputtering pressures were measured by scanning electron microscopy. The results show that the particle size of the films depends on the deposition rate in the nucleation stage of Ir films and the deposition rate can be well controlled by sputtering pressure. A new kind of cathodes are fabricated from 25% porous tungsten impregnated with 6∶1∶2-type barium calcium aluminate and coated with the nano particulate Ir thin film. The coating processes produces a film thickness of 200-500 nm and the cathodes are fired in hydrogen atmosphere for ten minutes at 1200℃ to further improve the coating microstructure. The cathodes have been studied with thermal electron microscope by which the electron-optical picture of a thermal emission cathode could be obtained. Time of flight mass spectrometer（ToFMS） has been used in a study of evaporation from impregnated cathodes. The chemical composition of evaporation of various impregnated cathodes have been measured by ToFMS. The variation of ion current of evaporants from S-type cathode and M-type cathode（coated with iridium） and n-type cathode（coated with iridium nano-particle thin film） with temperature and time have been studied and discussed. Emission current characteristics have been measured as a function of voltage and temperature.