Dynamical study of surface photochemistry by VUV radiation

固体表面吸附分子在软x射线区域内的光化学反应对于基本化学反应的基础研究以及光化学气相沉积、蚀刻催化等方面的应用研究具有重要意义。在这些反应中，光子激发解吸反应（PSD）是一个相对简单的反应，理论上和实验上都有研究。从这个角度出发，本项目设计并构建了一个新的实验装置，包括TOF离子谱仪、俄歇电子分析仪和质谱仪，以阐明吸附在表面的分子的软x射线光化学反应的完整机制。利用该装置，我们成功地探测到了H_2O/Si（100）和PMMA/Au/Si（100）体系中俄歇电子和光子激发解吸的离子产物。结果总结如下：(1)在H_2O/Si（100）体系中，在500 ~ 700 eV范围内观察到H^+和O^+离子的光子激发离子解吸（PSID）。这些离子的PSID产率在O - k边附近表现出特征行为；H^+在530 eV时表现出急剧上升，在O k边缘以下和上方有两个宽的最大值，O^+在570 eV时表现出延迟阈值。这些结果已经与多个带电离子的形成以及与表面强相互作用的多余电荷的再中和进行了讨论。(2)在PMMA/Au/Si（100）体系的PSD中观察到单体离子参与的各种离子。碳1s电子在287.9 eV激发到π ^*和σ ^*共振态时，CH^+和CH_2^+离子显著增强。氧k边区COOCH_3^+没有升高，而HCI^+有升高。一些碎片离子已经被观察到特别地出现在原子发生核心电子激发的位置附近。基于这些观察，人们可以考虑使用可调软x射线来刺激化学反应或选择性地破坏大的有机分子。少

Photochemical reaction of the adsorbate molecules on the solid surface in a soft x-ray region is important for fundamental study of elementary chemical reactions as well as for application study of photochemical vapor deposition, etching catalysis and so on. Among these reactions, photon stimulated desorption (PSD) is a relatively simple reaction to investigate both theoretically and experimentally. From this point of view, in this project we have designed and constructed a new experimental apparatus involving an TOF ion specrtomater, Auger electron analyser and a mass spectrometer to elucidate the full mechanism of a soft x-ray photochemical reactions of the adsorbed molecules on the surfaces. Using this apparatus, we have succeeded in detecting both Auger electrons and ionic products of photon stimulated desorption in both H_2O/Si(100) and PMMA/Au/Si(100) systems. The results are summarized as follows.(1) H^+ and O^+ ions were observed in the photon stimulated ion desorption (PSID) f … More rom H_2O/Si(100) system in the range 500-700 eV. PSID yields of these ions indicate characteristic behavior near O K-edge; H^+ exhibits sharp rise at 530 eV and two broad maxima below and above O K-edge, O^+ exhibits a delayed threshold at 570 eV. These results have been discussed with the formation of multiple charged ions followed by reneutralization of the excess of charge with strong interaction with the surface.(2) Various ions involving the monomer ion were observed in PSD from PMMA/Au/Si(100) systems. Excitations of carbon 1s electron to pi^* and sigma^* resonance states at 287.9 eV show remarkable enhancement of CH^+ and CH_2^+ ions. In oxygen K-edge region, increase in COOCH_3^+ was not observed where as that in HCI^+ was observed. Some of fragment ions have been observed to occur specifically around the site of the atom where the core electron excitation takes place. Based on these observations, one might consider the use of tunable soft x-ray to stimulate chemical reactions or to selectively break large organic molecules, as one pleases. Less