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首页> 外文期刊>Philosophical magazine: structure and properties of condensed matter >Investigating carbonization and graphitization using electron energy loss spectroscopy (EELS) in the transmission electron microscope (TEM)
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Investigating carbonization and graphitization using electron energy loss spectroscopy (EELS) in the transmission electron microscope (TEM)

机译：使用透射电子显微镜（TEM）中的电子能量损失谱（EELS）研究碳化和石墨化

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Electron energy loss spectroscopy (EELS) in the transmission electron microscope (TEM) is explored as a useful characterization technique in the study of carbonization and graphitization of organic precursors. A model series of carbon materials was prepared from highly graphitizable petroleum pitch heat treated in the range 200-2730 degrees C. Initial characterization was performed using the established techniques of X-ray diffraction (XRD), He pycnometry, TEM, electron diffraction and high-resolution lattice imaging (HREM). EELS in the TEM was then examined. Two routes are presented to quantify the change in the proportion of sp(2) type hybridization accompanying the heat treatment as the material transforms to the graphitic state. Both routes suggest an initial relative sp2 content of similar to 70%, rapidly increasing to similar to 90% during mesophase development and carbonization, and then slowly increasing to 100% during graphitization. The peak position of the bulk valence plasmon (pi + sigma) is shown to be an excellent measure of the degree of graphitic character, and its fundamental dependence upon sample density ( rho) is confirmed. The appearance and definition of features within the core loss region representing the density of unoccupied sigma* states are demonstrated to be an excellent measure of the extent of order. Finally, a method is established by which to extract the C-C bond length from core loss EELS spectra with an accuracy of +/- 0.1 pm. This method suggests an average bond length of 1.44 angstrom in samples with low heat treatment temperatures, decreasing to the theoretical length of 1.42 angstrom as both the heteroatom content and proportion of non-sp(2)-type hybridized carbon atoms decrease.
机译：透射电子显微镜（TEM）中的电子能量损失谱（EELS）被研究为有机前体碳化和石墨化研究中的有用表征技术。由在200-2730摄氏度范围内进行热处理的高度可石墨化的石油沥青制备了一系列碳材料模型。使用X射线衍射（XRD），比重瓶法，透射电子显微镜，电子衍射和高光谱技术等已建立的技术对碳材料进行了初步表征。分辨率晶格成像（HREM）。然后检查TEM中的EELS。提出了两种途径来量化随着材料转变为石墨态而伴随热处理的sp（2）型杂交比例的变化。两种途径均表明，初始相对sp2含量接近70％，在中间相发展和碳化过程中迅速增加至接近90％，然后在石墨化过程中缓慢增加至100％。体价等离激元（pi + sigma）的峰值位置显示出是石墨特性程度的极佳度量，并且证实了其对样品密度（rho）的基本依赖性。磁芯损耗区域内代表未占用的sigma *状态密度的特征的外观和定义被证明是有序程度的极好度量。最后，建立了一种从铁损EELS光谱中提取C-C键长度的方法，精度为+/- 0.1 pm。此方法建议在低热处理温度的样品中平均键长为1.44埃，随着杂原子含量和非sp（2）型杂化碳原子比例的降低，理论长度减小到1.42埃。

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