A Study on Change in Structure of Graphite under High Pressure by Raman Scattering

为了阐明加压引起的石墨晶体结构的变化，研究了加压下石墨的拉曼散射。采用4：1的甲醇-乙醇加压介质，将高定向热解石墨(HOPG)样品加载到金刚石压腔中。在457.9、488.0和514.5 nm激发下，在显微镜下测量了3.3 GPaHOPG基面的拉曼散射。虽然由于金刚石压头的散射和金刚石窗口与样品之间的传压介质的薄层，没有观察到几个由于高阶态密度特征而导致的拉曼频带，但观察到了-1360-cm^&lt；-1&gt；频带(D带)的E&lt；2g&gt；带和泛音(2D)。在压力作用下，E&lt；2g&gt；和2D模的频率都呈亚线性增加。2D谱带峰位的压强系数约为E&lt；2g&gt；谱带的3倍。2D带的波长依赖关系随压力变化不大，而2D带的移动幅度随波长的增大而略有增大。此外，E&lt；2g&gt；带的峰位在压力下对波长不敏感。首次观测到了2D带的压力依赖关系。实验结果表明，2D能带是解释高压引起的石墨结构变化的关键。

In order to elucidate the change in the crystalline structure of graphite caused by pressure, Raman scattering of graphite under pressure was investigated. A highly oriented pyrolytic graphite (HOPG) sample was loaded into the diamond anvil cell using 4 : 1 methanol-ethanol pressure medium. Raman scattering from the HOPG basal plane at pressures up to 3.3 GPa was measured with 457.9-, 488.0- and 514.5-nm excitation by using microscope. Although several Raman bands due to features in the density of state in the higher-order region could not be observed because of scattering from diamond anvil and the thin layr of pressure-transmitting medium between diamond window and sample, the E_<2g> band and overtone (2D) of the -1360-cm^<-1> band (D band) were observed. Both the frequencies of the E_<2g> and 2D modes increase sublinearly under pressure. The pressure coefficients of the peak position of the 2D band was about three times larger than that of the E_<2g> band. The lambda dependence of 2D band was almost unchanged by pressure, while the magnitude of the 2D band shift with increasing lambda seems to be slightly increased by pressure. In addition the peak position of the E_<2g> band was insensitive to lambda under pressure. The pressure dependence of the 2D band is the first observation. The experimental results suggest that the 2D band is the key to the clarification of the change in the structure of graphite induced by high pressure.