Development of a Technique for Detecting Ultra Low Density of Surface Impurities by Means of Multiphoton Resonance Ionization

本项目的目标是发展一种用多光子共振电离光谱法探测超低密度表面杂质的技术。(1)多光子共振电离光谱系统的研制开发了多光子共振电离光谱系统，并结合飞行时间技术对电离后的粒子进行检测。这里所用的多光子共振电离是基于一个激发激光辐射将原子从基态激发到激发态，另一个电离激光辐射将原子从激发态电离到连续谱。用蒸气表面的金属原子束电离Ni原子时，激发激光辐射的共振波长为2290.38A^^λ、2320.46A^^λ和2346.00A^^λ，Fe原子的共振波长为2166.75A^^λ。(2)能量分布的测量 ...更多信息 用该系统测量了5 keV Ar^+离子溅射Ni靶时中性Ni原子的能量分布。结果表明，溅射Ni原子的能量分布与Thompson分布相似，峰值能量为0.7- 0.8eV。对应于低表面结合能的低峰值能量归因于镍表面处的碳化物相。在这种情况下，共振电离的效率被确认为饱和到100%。(3)用LEED-AES-RBS技术表征Si（111）ROO_<3>xROO<3>_-Ag表面用RBS技术研究发现，由于不同样品的ROO<3>_xROO_-LEED图清晰相似，<3>Ag沉积Si（111）样品退火后在Si（111）ROO_xROO_-Ag表面上的Ag覆盖率在0.62 ~ 0.82之间，部分沉积的Ag原子扩散到Si衬底中<3><3>。从Si（111）ROO xROO -Ag表面的Ag覆盖率名义上是统一的这一事实得出结论<3><3>。(4)Ag在Si（111）ROO <3>xROO<3>-Ag表面的离子碰撞脱附<3><3>用LEED AES RBS技术测量了keV Ar^+离子在Si（111）ROO xROO -Ag表面引起的Ag原子浓度衰减，测得Ag原子在5键处的脱附截面为8.0 × 10 ~（<-16>-4）cm ~ 2，由实验反冲注入截面估算出Ag原子在Si（111）ROO <3>xROO<3>-Ag表面的结合能为0.6eV。少

Goal of this project is to develop a technique for detecting ulta low density of surface impurities by means of multiphoton resonance ionization spectroscopy.In 1989, we have performed following tasks concerning with this project. (1) Development of multiphoton resonance ionization spectroscopy system A multiphoton resonance ionization spectroscopy system has been developed and combined with the time of flight technique for detecting of post-ionized particles. The multiphoton resonance ionization used here is based on that one exciting laser radiation excites an atom from the ground state to an excited state and another ionizing laser radiation ionizes from the excited state to the continuum. The resonance wavelengths of exciting laser radiation for ionization of Ni atoms are found to be 2290.38A^^ﾟ, 2320.46A^^ﾟ and 2346.00A^^ﾟ and the resonance wavelength for Fe atoms is found to be 2166.75A^^ﾟ using metal atomic beams from vapor surfaces. (2) Measurement of the energy distribution of … More Ni atoms sputtered from Ni targets The system developed here has been applied for measuring the energy distribution of neutral Ni atoms sputtered from Ni targets by 5 keV Ar^+ ions. It is found that the energy distribution of sputtered Ni atoms is similar to the Thompson distribution and the peak energy is 0.7-0.8 eV. The low peak-energy, corresponding to the low surface binding energy, is attributed to a carbide phase at the nickel surface. The efficiency for resonance ionization in this case is confirmed to be saturated to 100%. (3) Characterization of Si(111)ROO<3>xROO<3> -Ag surfaces by means of LEED-AES-RBS techniques It is found by means of the RBS technique that the Ag coverage at the Si(111)ROO<3>xROO<3> -Ag surfaces produced by annealing Ag deposited Si(111) specimens ranges from 0.62 to 0.82 and a part of deposited Ag atoms diffuse into the Si substrate, for the ROO<3>xROO<3> LEED patterns observed clearly similarly with different five specimens. It is concluded from the fact that the Ag coverage at the Si(111)ROO<3>xROO<3> -Ag surface is nominally unity. (4) Ion impact desorption of Ag from Si(111)ROO<3>xROO<3> -Ag surface The concentration decay of Ag atoms at the Si(111)ROO<3>xROO<3> -Ag surface induced by keV Ar^+ ions has been measured by means of LEED-AES-RBS techniques, It is found that the desorption cross-section of Ag atoms at 5 key is determined to be 8.0X10^<-16> cm^2 and the binding energy of Ag atom at the Si(111)ROO<3>xROO<3> -Ag surface is estimated to be 0.6 eV from the experimental recoil-implantation cross-section. Less