Yb_(2.75)C_(60)同步辐射光电子能谱  

Synchrotron radiation photoemission study of Yb_(2.75)C_(60)

作　　者：何少龙 李宏年[1] 王晓雄[1] 李海洋[1] I.Kurash 钱海杰[2] 苏润[2] M.I.Abbas 钟俊[2] 洪才浩[2] 

机构地区：[1]浙江大学物理系,杭州310027 [2]中国科学院高能物理研究所同步辐射实验室,北京100039

出　　处：《物理学报》2005年第3期1400-1405,共6页Acta Physica Sinica

基　　金：国家自然科学基金 (批准号 :10 0 740 5 3;10 3 740 80 );北京正负电子对撞机同步辐射实验室资助的课题~~

摘　　要：在超高真空系统中制备了Yb2 75C6 0 薄膜 .对样品进行了同步辐射光电子能谱研究 .在费米能级以下约 5eV范围内的谱数据由Yb2 75C6 0 价带 (C6 0 分子轨道LUMO ,HOMO和HOMO 1导出的能带 )和芯态 (Yb 4f7 2 ,4f5 2 )能级构成 .用紫外能区不同能量的入射光子 ,用C 2p和Yb 4f光电离截面随光子能量的不同变化规律 ,通过定量拟合 ,得到了对谱线有贡献的上述各个组分的峰位、峰宽和强度 .结果表明 ,光子能量高于约 30 0eV时 ,芯态 4f的贡献使得实验结果远远偏离价带的本征态密度分布 .因此 ,研究Yb2 75C6 0 价态时 ,应使用能量低于 30 0eV的光子 .对实验和拟合结果分析 ,发现了类似纯C6 0 的光电离截面振荡现象 .振荡幅度相对于纯C6 0 较小 ,反映了化合物中C6 0 分子的化学环境对光电离截面振荡现象起着不可忽略的作用 .The Yb-2.75 C-60 thin film was prepared and studied by using the synchrotron radiation ultraviolet photoemission spectroscopy (PES) in an ultra-high-vacuum system. The spectral line obtained in the range between the Fermi level and similar to 5 eV binding energy consists of those lines from the valence band (the molecular orbital LUMO, HOMO and HOMO-1 derived energy bands of C-60) and core levels(Yb 4f(7/2) and 4f(5/2)). Taking into account the variations of the photoinization cross sections of C 2p and Yb 4f with different photon energies, we have measured the photoemission spectra under the condition of varying photon energies, and carried out simulations to deduce the component contributions. The peak positions, widths and intensities for the components are obtained quantitatively. The results reveals that the photoemission of 4f electrons has a significant intensity with the photon energies larger than similar to 30.0 eV, and that the measured spectra depart drastically from the density of states of the valence band. To observe the valence band structure, one should carry out the PES measurements by using photons with energies less than 30.0 eV. The photoionization cross-section oscillation is also observed in Yb2.75C60 with almost the same oscillation period as that for pure C-60. However, the oscillation amplitude is obviously smaller than that for pure C-60, which reveals that the chemical environment of C-60 in compounds has non-negligible effects on the photoionization cross-section oscillation phenomenon.

关 键 词：光电离 C60分子 光子能量 光电子能谱 价带 态密度分布 C60薄膜 能带 振荡现象 幅度 

分 类 号：O582[理学—物理]