Formation of cesium carbonate in ion-implanted graphite, examined with dual-source x-ray photoelectron spectroscopy, density functional theory calculations and thermodynamic modelling
Formation of cesium carbonate in ion-implanted graphite, examined with dual-source x-ray photoelectron spectroscopy, density functional theory calculations and thermodynamic modelling
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通过双源 X 射线光电子能谱、密度泛函理论计算和热力学模型研究离子注入石墨中碳酸铯的形成
DOI：
10.1016/j.carbon.2022.06.034
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发表时间：
2022
期刊：
影响因子：
10.9
通讯作者：
Theodosiou A
中科院分区：
文献类型：
--
作者：
Theodosiou A
采用Cs ~+离子注入高取向热解石墨（HOPG）样品，研究了Cs ~+离子注入对石墨基体的影响及Cs的化学形态。平均注入深度计算为1.22 nm，允许使用X射线光电子能谱（XPS）进行研究，其中使用传统的Al Kα X射线源和更高能量的Ag Lα源来增加更深的表面采样深度。分析发现，随着注入剂量的增加，sp2 C-C键合减少，当Cs+浓度为106 atomic %时，sp2键合完全丧失。在C 1 s光谱中较高结合能分量（285.8- 289.4eV）的显著增加不能仅仅归因于C-O物质的存在，而是指示石墨晶格的急剧重新排序以容纳和中和嵌入的Cs。XPS分析表明石墨材料内碳酸铯的形成;这通过Cs2 CO 3参比样品的分析得到加强。此外，热力学平衡模拟，支持简化的密度泛函理论（DFT）计算，进行，导致强烈的协议与XPS的研究结果，也就是说，最稳定的形式的铯石墨基质内预计是碳酸铯（Cs2 CO 3），这是在热力学平衡与脱石墨HOPG和氧化脱石墨HOPG。
A sample of highly orientated pyrolytic graphite (HOPG) was implanted with Cs+ions in order to study the effect on the graphite matrix and the chemical form of Cs once embedded. The mean implantation depth was calculated to be ∼22 nm, allowing for investigation with X-ray Photoelectron Spectroscopy, (XPS), where both a traditional Al Kα X-ray source and a higher energy Ag Lα source was used for an increased sampling depth deeper into the surface. Analysis found that there was a reduction ofsp2C–C bonding with increasing implantation dose, resulting in a total loss ofsp2character at ∼6 atomic % Cs+. A striking increase in higher binding energy components (285.8–289.4 eV) in the C 1s spectra cannot be attributed solely to the presence of C–O species, instead indicating a dramatic re-ordering of the graphitic lattice to accommodate and neutralize the embedded Cs. XPS analysis indicates the formation of cesium carbonate within the graphitic material; this is reinforced by analysis of a Cs2CO3reference sample. Additionally, thermodynamics equilibrium simulations, supported by simplified density functional theory (DFT) calculations, are performed, leading to strong agreement with the XPS findings; that is, the most stable form of Cs within the graphite matrix is expected to be cesium carbonate (Cs2CO3), which is in thermodynamic equilibrium with degraphitised HOPG and oxygenated degraphitised HOPG.