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Study of the mechanism of thermal positive ion production on a heated metal surface and development of a themal positive ion source

加热金属表面热正离子产生机理的研究及热正离子源的开发

基本信息

批准号：
61470010
负责人：
KAWANO Hiroyuki
金额：
$ 4.16万
依托单位：
Ehime University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1986
资助国家：
日本
起止时间：
1986 至 1987
项目状态：
已结题

项目摘要

The ionization efficiency (<beta>^+) for producing Li^+ ions from LiI molecules incident upon a rhenium surface heated in a thigh vacuum (2 x 10^<-7> Torr) was measured as a function of surface temperature (T<similar or equal>1000 - 2000 K). The data thus obtained were analyzed by our original theory on dissociative positive surface ionization, thereby indicating that (1) <beta>^+ becomes unity at T<similar or equal>1200 - 1400 K because the work function (0^+) of the surface increases from about 5.5 eV up to 6.5 eV owing to adsorption by residual gas molecules (RGM), (2) <beta>^+<similar or equal> 0.1 at T<greater than or similar>1700 K where 0^+<similar or equal>5.5 eV, corresponding to an essentially clean surface, and (3) <beta>^+ begins to decrease sharply at R<similar or equal>1200 K because of co-adsorption of LiI and RGM. When Li atoms were impinged upon the surface, on the other hand, <beta>^+ and 0^+ were nearly constant at about 0.08 and 5.4 eV, respectively, at R<greater than or similar>1200 K, giving evide evidence that adsorption fo Li atoms suppresses the work function increase due to adsorption of RGM. Mass spectrometric analysis of RGM and also introduction of air up to 2 x 10^<-5> Torr into the ion source region gave the additional evidence that the work function increase found in the middle temperature region is caused mainly by adsorption of xygen, thereby promoting surface ionization of the sample molecules, just as predicted by our theory. By using a new technique developed by us, the mean adsorption lifetime of NaI, LiI, LiBr and LiCl was determined together with heat of adsorption and entropy change due to adsorption of each sample molecule. On the basis of these results, a small ion source was developed, by which alkali ions of more than 10 nA were readily produced from alkali halide molecules.

测量<beta>了在高真空（2 × 10 - 4托）中加热的锂离子表面上入射的LiI分子产生Li^+离子的电离效率（^+）<-7>与表面温度（T <similar or equal>1000 - 2000 K）的函数关系。用我们最初的表面解离正离子化理论分析了所得数据，结果表明：（1）<beta><similar or equal>由于残余气体分子（RGM）的吸附，表面功函数（0^+）从约5.5 eV增加到6.5 eV，因此^+在T 1200 ~ 1400 K时变为1;（2）<beta><similar or equal>在T 1700 K时，^+ 0.1<greater than or similar>，其中0^+<similar or equal>5.5 eV，相当于基本上清洁的表面;（3）<beta><similar or equal>由于LiI和RGM的共吸附，^+在R 1200 K时开始急剧下降。另一方面，当Li原子撞击在表面上时，<beta>在R 1200 K下，^+和0^+分别在约0.08和5.4 eV处几乎是恒定<greater than or similar>的，这证明Li原子的吸附抑制了由于RGM的吸附而引起的功函数增加。RGM的质谱分析以及向离子源区域中引入高达2 x 10^ Torr的空气<-5>给出了额外的证据，即在中温区域中发现的功函数增加主要是由氧气的吸附引起的，从而促进了样品分子的表面电离，正如我们的理论所预测的那样。利用我们开发的新技术，测定了NaI、LiI、LiBr和LiCl的平均吸附寿命以及每个样品分子的吸附热和吸附熵变。在这些结果的基础上，开发了一种小离子源，通过该小离子源，可以容易地从碱金属卤化物分子中产生大于10 nA的碱金属离子。