摻銣碳六十薄膜之拉曼特性研究

Abstract

利用良好的鑑別率及較寬的波長範圍，我們能夠測量純碳六十與摻銣 碳六十薄膜之拉曼訊號；而所測得的結果與理論預測和發表的實驗數據是 吻合的。另外，由特定波長的光所造成的共振效應顯示出一些電子躍遷能 態，我們可從光電子發射能譜(photoemission spectra) 判斷這些躍遷。 例如碳六十的Ag(2) 模，它的共振發生於 2.4電子伏特，這是hu態與 t1u 態之間的躍遷所造成的。而在摻銣碳六十Rb3C60和Rb6C60薄膜上，hu態與 t1g態之間的躍遷造成具有 2.5電子伏特的共振。其他如大約在 2.2電子 伏特的共振分別為Rb3C60薄膜上電子 由hu態躍遷至 t1u態以及Rb6C60薄 膜上 t1u態躍遷至hg態。至於在Ag(1) 模和其他Hg模也顯示了上述的躍遷 以及一些具有較高和較低能量的躍遷。對於雷射在Ag(2) 模上的加熱效應 ，用三個聲子的拉曼作用( three phonon process )可以做很好的解釋。 我們發現C60 及Rb6C60薄膜上的加熱溫度分別高於1160K 和1120K 時，薄 膜會產生不可逆的相變( phase change ). 最後，我們測量了Rb3C60薄膜 的反磁性( diamagnetism )，當溫度低於28 ~ 30K的臨界溫度( critical temperature )時它顯示了超導性質。 Raman scattering has been carried out on pure C60 and doped RbxC60 films with good resolution and wide wavelength coverage. These results are consistent with the reported data and theoretical predictions. Furthermore, the resonance effect observed at the specific photon energies indicates the optical transitions which are shown in the photoemission spectra. For the Ag(2) mode of C60, the resonant enhancement is due to the hu-t1u transition at 2.4 eV. It appears at 2.5 eV from the hu-t1g transition in the Rb3C60 and Rb6C60 films. Another enhancement around 2.2 eV is resulted from the hu-t1u transition in Rb3C60 film and the t1u-hg transition in Rb6C60 film. The Ag(1)and Hg modes also display these optical transitions and some lower and higher transition energies. The thermal effect from laser heating on the Ag(2) mode is examined that can be explained well by the three phonon processes. We findthat the C60 and Rb6C60 films undergo an irreversible phase change as the temperature from laser heating is higher than 1160 and 1120 K, respectively. Finally, we detect the diamagnetism of the Rb3C60 film that shows the supercon- ductivity below the critical temperature Tc of 28 - 30 K.