覆氧条件下SIMS定量分析的半理论计算

SEMI-THEORETICAL CALCULATION OF QUANTITATIVE SIMS ANALYSIS OXYGEN EXPOSURE

以金属表面覆氧时二次离子发射的实验为基础,对二次离子质谱定量分析进行了研究。注意到金属元素的正离子产额随氧压升高而增加,而电负性高的元素离子信号有上升更多的趋势,完善了“结合LTE-断键”思想。并认为断键方式形成正、负二次离子的数目不仅与表面生成了多少氧化物有关,而且与氧化物的结合强度有关。如果定量估算表面氧化物数目及氧化物键强两个因素对离子产额的影响,将它们都与元素的电负性建立一定的关系,从而推导出表面覆氧时定量考虑断键形成二次离子的离子产额理论关系式,其中包含了覆氧量及元素电负性的因素。所介绍的定量分析方法适用于较宽的实验条件,可获得较好的结果。

A method of quantitative SIMS analysis, based on the experimental results of secondary ion emission on the metallic surface exposed to oxygen, has been investigated. The development of the 'combined LTE-Bond Breaking' idea comes from the fact that the ion yields of metallic elements will be enhanced by increasing oxygen pressure, but the enhancement for the metallic element with higher electronegativity is more remarkable. The amount of positive and negative secondary ions produced in bond breaking is not only determined by how many oxides are formed on the surface, but by how strong the oxide bonds are. If the bond breaking process is considered as an ionization process in which elemental ionization potentials are supposed to be lower than their normal values, and if both the amount of oxides and the bond strength are assumed to be the functions of electronegativity, the theoretic equation of the positive secondary ion yield on the surface exposed to oxygen is obtained. In the equation, the quantity of exposure to oxygen and the elemental electronegativity are included. This quantitative method can be used under a wide range of oxygen pressure.