室温におけるSi(111)-77表面へのO吸着ダイナミクス,2; SR-XPSで観た飽和吸着酸素量の並進運動エネルギー依存性

Adsorption dynamics of O on Si(111)-77 at room temperature, 2; Translational kinetic energy dependence of saturated oxygen coverage investigated by SR-XPS

吉越 章隆 ; 成廣 英介; 盛谷 浩右; 寺岡 有殿

Yoshigoe, Akitaka; Naruhiro, Eisuke; Moritani, Kosuke; Teraoka, Yuden

室温におけるSi(111)-77表面のO吸着ダイナミクスに関しては、大部分の報告が散乱分子線の検出であるため吸着過程と吸着状態の関係に未解明な部分が多い。そこで飽和吸着酸素量と並進運動エルギー(最大2.3eV)の関係を放射光XPSで調べたので報告する。実験は、SPring-8のBL23SUのSUREAC2000で行った。超音速O分子線を室温で表面に照射し、反応が飽和に至るまで放射光を用いて約15秒間隔でO1s XPSの測定を行った。0.03eV(ガス暴露条件)と2.23eVの照射エネルギー条件で得られた飽和吸着状態の高分解能O1s XPSスペクトルの比較をすると並進運動エネルギーの増加に伴い、矢印で示した+0.6eVの位置にケミカルシフトした成分(insx3-tri)の明瞭な増加が観測された。ガス暴露の報告では、この成分は600K加熱により増加することが報告されていることから、この結果は並進運動エネルギーの増加に伴い通常のガス暴露では不可能な解離吸着状態が室温において形成できる(activeated adsorption)ことを示唆している。

The questions about the relationship between the adsorption processes and adsorption states have still remained on the adsorption dynamics for O/Si(111)-77 at room temperature because the most studies has been done by molecular beam scattering experiments. Using synchrotron radiation XPS, we investigated the saturated oxygen coverages depending on the translational kinetic energy up to O. All experiments have been performed by using SUREAC2000 at BL23SU in SPring-8. The supersonic O beams were exposed on an Si(111)-77 surface at room temperature and the O1s X-ray photoelectron spectra were monitored about every 15s until saturation coverage. Comparing saturated spectra for 0.03eV (thermal gas condition) with 2.23eV condition, we clarified that the chemical shifted component at +0.6eV assigned to the insx3-tri oxygen was clearly observed with increasing the incident energy. Since the annealing at 600K only makes this component grown, the result indicated that the translational kinetic energy essentially enhanced the dissociative adsorption states which were hardly formed at room temperature, i.e. the reaction via overcoming the potential energy barriers by incident energies might be progressive (activated adsorption).