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利用多光子共振电离光谱检测超低密度表面杂质的技术。1989年，我们完成了与该项目有关的以下工作。(1)多光子共振电离光谱分析系统研制了一种多光子共振电离光谱分析系统，并与飞行时间技术相结合，用于检测电离后粒子。这里使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从激发态电离到连续谱。利用蒸气表面金属原子束，测得Ni原子激发激光电离的共振波长为2290.38A^ﾟ，2320.46A^ﾟ和2346.00A^ﾟ，Fe原子的共振波长为2166.75A^ﾟ。(2)…的能量分布测量用该系统测量了5keV Ar~(++)离子从Ni靶溅射的中性Ni原子的能量分布。结果表明，溅射的Ni原子的能量分布类似于Thompson分布，峰值能量为0.7-0.8 eV。与低表面结合能相对应的低峰能归因于镍表面的碳化物相。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技术对Si(111)Roo&lt；3&gt；xROO&lt；3&gt；-Ag表面进行了表征。用RBS技术研究发现，在Si(111)Roo&lt；3&gt；xROO&lt；3&gt；3&gt；对于不同的五个样本，LEED模式观察得很清楚。结果表明，Si(111)Roo&lt；3&gt；xRoo&lt；3&gt；-Ag表面的Ag覆盖率在名义上是统一的。(4)Si(111)Roo&lt；3&gt；xROO&lt；3&gt；-Ag表面的离子碰撞脱附用LEED-AES-RBS技术测量了离子诱导的Ag原子在Si(111)Roo&lt；3&gt；xROO&lt；3&gt；-Ag表面的浓度衰变，得到Ag原子在Si(111)Roo&lt；3&gt；-16&gt；cm^2处的脱附截面为8.0x10^-lt；-16&gt；cm^2。从实验的反冲注入截面估算出3&gt；xROO；3&gt；-Ag表面为0.6 eV。较少

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