Ehlert Christopher, Unger Wolfgang E S, Saalfrank Peter
BAM Bundesanstalt für Materialforschung und -prüfung, D-12203 Berlin, Germany.
Phys Chem Chem Phys. 2014 Jul 21;16(27):14083-95. doi: 10.1039/c4cp01106f. Epub 2014 Jun 5.
Recently, C K-edge Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of graphite (HOPG) surfaces have been measured for the pristine material, and for HOPG treated with either bromine or krypton plasmas (Lippitz et al., Surf. Sci., 2013, 611, L1). Changes of the NEXAFS spectra characteristic for physical (krypton) and/or chemical/physical modifications of the surface (bromine) upon plasma treatment were observed. Their molecular origin, however, remained elusive. In this work we study by density functional theory, the effects of selected point and line defects as well as chemical modifications on NEXAFS carbon K-edge spectra of single graphene layers. For Br-treated surfaces, also Br 3d X-ray Photoelectron Spectra (XPS) are simulated by a cluster approach, to identify possible chemical modifications. We observe that some of the defects related to plasma treatment lead to characteristic changes of NEXAFS spectra, similar to those in experiment. Theory provides possible microscopic origins for these changes.
最近，已经测量了原始石墨（高定向热解石墨，HOPG）表面以及经溴或氪等离子体处理的HOPG的C K边近边X射线吸收精细结构（NEXAFS）光谱（Lippitz等人，《表面科学》，2013年，611卷，L1）。观察到等离子体处理后，NEXAFS光谱的变化表征了表面的物理（氪）和/或化学/物理改性（溴）。然而，它们的分子起源仍然难以捉摸。在这项工作中，我们通过密度泛函理论研究了选定的点缺陷和线缺陷以及化学改性对单层石墨烯NEXAFS碳K边光谱的影响。对于经溴处理的表面，还通过簇方法模拟了Br 3d X射线光电子能谱（XPS），以识别可能的化学改性。我们观察到，一些与等离子体处理相关的缺陷会导致NEXAFS光谱发生特征性变化，类似于实验中的变化。理论为这些变化提供了可能的微观起源。
