X-Ray Photoelectron Spectroscopy (XPS) has been utilized to extract local electrical potential profiles by recording core-level binding energy shifts upon application of the AC [square-wave (SQW)] bias with different frequencies. An electrochemical system consisting of a coplanar capacitor with a polyethylene membrane (PEM) coated with the Ionic Liquid (IL) N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium bis(trifluoromethanesulfonyl)imide (DEME-TFSI) as the electrolyte is investigated. Analyses are carried out in operando, such that XPS measurements are recorded simultaneously with current measurements. ILs have complex charging/discharging processes, in addition to the formation of Electrical Double Layers (EDL) at the interfaces, and certain properties of these processes can be captured using AC modulation within appropriate time windows of observation. Herein, we select two frequencies, namely, 10 kHz and 0.1 Hz, to separate effects of the fast polarization and slow migratory motions, respectively. Moreover, the local potential developments after adding two equivalent series resistors at three different physical positions of the device have been carefully evaluated from the binding energy shifts in the F 1s peak representing the anion of the IL. This circuit modification allows us to quantify the AC currents passing through the device, as well as the system’s impedance, in addition to revealing the potential variations due the IR drops. The complex AC-modulated local XPS data recorded can also be faithfully reproduced using the unmodulated F 1s spectrum and by convoluting it with electrical circuit output provided by the LT-Spice software. The outcome of these efforts is a more realistic equivalent circuit model, which can be related to chemical/physical makeup of the electrochemical system. An important finding of this methodology emerges as the possibility to induce additional local electrical field developments within the device, the directions of which can be reversed controllably.

中文翻译：

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交流调制 XPS 能够从外部控制金属电极/离子液体器件上的电场分布

X 射线光电子能谱 (XPS) 已被用来通过记录施加不同频率的 AC [方波 (SQW)] 偏压时的核心级结合能变化来提取局部电势分布。电化学系统由带有聚乙烯膜 (PEM) 的共面电容器组成，该聚乙烯膜涂有离子液体 (IL) N , N-二乙基-N-甲基-N- (2-甲氧基乙基)双(三氟甲磺酰基)亚胺铵 (DEME-TFSI) ）作为电解质的研究。分析以操作方式进行，以便 XPS 测量值与当前测量值同时记录。除了在界面处形成双电层 (EDL) 之外，IL 还具有复杂的充电/放电过程，并且可以在适当的观察时间窗口内使用交流调制来捕获这些过程的某些属性。在这里，我们选择两个频率，即 10 kHz 和 0.1 Hz，分别来分离快速极化和慢速迁移运动的影响。此外，根据代表 IL 阴离子的 F 1s 峰中的结合能变化，仔细评估了在器件的三个不同物理位置添加两个等效串联电阻后的局部电势发展。除了揭示 IR 压降导致的电位变化之外，这种电路修改还使我们能够量化通过器件的交流电流以及系统的阻抗。记录的复杂交流调制本地 XPS 数据也可以使用未调制的 F 1s 频谱并将其与 LT-Spice 软件提供的电路输出进行卷积来忠实地再现。这些努力的结果是一个更现实的等效电路模型，它可以与电化学系统的化学/物理组成相关。这种方法的一个重要发现是可以在设备内诱导额外的局部电场发展，其方向可以可控地反转。