【作者】 郝世明；

【导师】 聂祚仁；

【作者基本信息】 北京工业大学 ， 材料学， 2005， 硕士

【摘要】 真空发射管用镧钼阴极是一种新型的发射材料,有望代替传统的具有放射性的钍钨阴极。阴极发射是一种表面现象,更多依赖于表面层的成分、结构等,实验已证实阴极工作时表面形成的LaOx（x<1.5）化合体薄膜,在发射中起到重要作用,但是La/O 变化是如何影响阴极的发射性能仍不明确,由于阴极工作的真空苛刻性及La 本身易氧化等特点,在阴极发现近四十年以来一直难于得到证实。深入研究表层物质在发射中的作用,将有利于加深对阴极发射机理的认识,为推动镧钼阴极的广泛应用提供理论指导。本论文采用多功能电子能谱仪与激光脉冲沉积相连的原位阴极研究装置,利用激光脉冲沉积制备不同镧氧比的薄膜近似模拟阴极表面发射层,并在相似的阴极工作环境进行了发射性能测试及表面AES 原位分析,首次得到阴极表面La/O 变化对阴极发射性能的影响关系。在此基础上,论文理论分析了在La/O变化的不同阶段阴极所具有的发射机理,提出了不同于传统阴极发射理论的新观点,并对实际阴极的实验现象做出解释。论文通过对阴极研究装置各部分功能深入研究,结合所制备薄膜阴极的发射性能及表面分析,确定了制备薄膜阴极的最佳沉积及测试条件。工艺条件固定为沉积时间15 分钟,薄膜厚度100nm,测试温度1483K。改变沉积室真空度,制备了La/O 不同的薄膜阴极,通过发射性能测试和表面原位AES 分析,发现了表面镧氧比变化对阴极的发射性能的影响趋势。随着表面物质中La/O 增大,阴极的发射性能增强。深入研究了镧钼薄膜阴极发射性能与阴极表面La/O 变化的关系并做出相应的理论分析。在表面La/O 偏离氧化镧化学计量的不同阶段,影响趋势和发射机理都不相同。在表面La/O 稍微偏离氧化镧的化学计量时,镧以同类杂质的形式在发射体中起作用,薄膜可以看作是n 型半导体,用半导体模型来解释阴极发射机理; 在La/O 较大偏离氧化镧的化学计量时,杂质浓度加大,出现La 超微粒子。论文提出镧超微粒子埋藏于氧化镧基质的模型解释,利用能带理论,形象地描述了电子发射的过程,确定了埋藏于La₂O₃ 基质中的镧超微粒子由于其电子比La₂O₃中的价电子更容易进入导带,是电子发射的主要来源; 在La/O偏离更加增大后,超微粒子长大,不利于阴极发射,发射性能不再增长。更多还原

【Abstract】 La₂O₃-Mo cathode used for the vacuum emission tube is a new kind of emission materials which have being hoped to replace radioactive ThO₂-W cathodes. Cathode emission is a kind of superficial phenomenon. Cathode emission performance depends principally on the cathode materials’composition and configuration of the surface layer. Experiments have verified the formation of LaOx （x<1.5） which plays an important role in the La₂O₃-Mo cathode emission. How the surface La/O ratio to influence cathode property is difficult in getting proof because cathode work under the high vacuum environment as well as Lanthanum is easy to oxidize since cathode is discovered 40 years ago. Investigating thoroughly the function of surface layer in the electron emission will be benefit to the understanding of cathodes mechanism and provide the theory guiding for the extensive application. This thesis investigates firstly the task using a new device which is acquired by reforming the vacuum chamber of AES （Auger energy spectra） and connecting with PLD （pulsed laser deposition）. By means of PLD we prepare different La/O ratio thin film to simulate cathode surface active layer, test the emission properties and analyses surface composition in similar work environment. The relationship between cathode surface La/O ratio and cathode emission performance is firstly determined. The paper gave the theoretical analysis about cathode working mechanism at the different stages when cathode surface La/O is changing and put forward the new cathode emission theoretical viewpoint which is different from that of traditional theory and explained the actual experiment phenomenon. The thesis confirmed the best deposition craft by means of understanding the function of each part of the cathode device. The final craft as follow: deposition time 15 minutes, thin film thickness 100nm, test temperature 1483K. LaO_x （x<1.5） films were prepared by pulsed laser deposition （PLD） under various vacuum conditions. By controlling the ambient pressure, nonstoichiometric La-rich La–O films were gained. The electron emission properties of these cathodes were measured in the film deposition chamber without exposed to the atmosphere.更多还原