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Localized or delocalized unoccupied electronic states in polymers

有機ポリマーにおける局在及び非局在した非占有電子状態

池浦 広美*; 関口 哲弘  

Ikeura, Hiromi*; Sekiguchi, Tetsuhiro

内殻電子励起吸収端領域におけるX線吸収(XAS)測定法は一般に空軌道バンドの状態密度やエネルギー幅に関する情報を提供するため、放射光を利用して数多くの化合物について測定されてきた。本研究において種々の固体状態多原子分子についてXASスペクトル、及び共鳴オージェ電子スペクトルを測定し空状態のエネルギー的な広がりを調べた。分子軌道計算等により行われ報告されている基底状態における伝導帯との比較を行った。結果、X線励起の場合、内殻正孔の存在による空状態の局在化が起こるため、基底状態よりもかなり狭いバンド幅を与えることが明らかになった。

X-ray absorption spectroscopy (XAS) is commonly used as probing unoccupied electronic states. However, XAS can not distinguish localized and delocalized electronic states. In metal system, plotting the normal Auger yields (in Resonant Auger spectroscopy (RAS)) around the XAS region exhibit unoccupied conduction band state near the Fermi level (EF). In polymer system, RAS spectra can be interpreted based on two competing decay channels: that is, core-hole decay and core-excited resonant electron delocalization. If the resonantly excited electron remains long enough to be localized in the vicinity of a core-hole site during the core-hole decay, the decay process results in final states of two holes with one electron (2h1e), known as "spectator Auger". In contrast, if it delocalizes to the conduction band prior to the core-hole decay, the decay process results in final states of two holes (2h), known as "normal Auger". Thus, If polymer has a delocalized conduction band, an excited electron can delocalize along the polymer chain before core-hole decay. Consequently, the normal Auger yields exhibit the conduction band structure, as similar to the metal system. We show that the localized or delocalized band structure can be probed by the normal Auger yields.

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