一种简单的基于KPFM的无静电地形测量方法：SiO $_2$上PDKEEPAAAAA $_2$的情况
A simple KPFM-based approach for electrostatic-free topographic measurements: the case of MoS$_2$ on SiO$_2$
摘要：
开尔文探针力显微镜的一个简单的实施报告，使记录的地形图像的情况下，任何组件的静电力。我们的方法是基于一个闭环z-光谱数据立方体模式操作。将尖端-样品距离的曲线作为时间的函数记录到2D网格上。专用电路保持KPFM补偿偏置，并随后在光谱采集内的明确定义的时间窗口期间切断调制电压。从光谱曲线矩阵重新计算地形图像。这种方法适用于过渡金属二硫属化物（TMD）单层氧化硅衬底上的化学气相沉积生长的情况。此外，我们检查在何种程度上也可以通过记录一系列图像来执行适当的堆叠高度估计，以减小偏置调制幅度的值。这两种方法的输出被证明是完全一致的。结果表明，在超高真空下的非接触式原子力显微镜的操作条件下，堆叠高度值可以显着高估，由于在尖端表面电容梯度的变化，即使KPFM控制器无效的电势差。我们表明，原子层的TMD的数量可以安全地评估，只有当KPFM测量与调制偏置振幅减少在其严格的最小值，甚至更好，没有任何调制偏置。最后，光谱数据显示，在TMD/氧化物界面的缺陷可以有一个违反直觉的静电景观的影响，导致在一个明显的下降，通过传统的纳米原子力显微镜/KPFM相比，无缺陷的样品区域测得的堆叠高度。因此，无静电z成像被证明是一种很有前途的工具，以评估在氧化物上生长的原子级薄TMD层中是否存在缺陷
英文摘要：
A simple implementation of Kelvin probe force microscopy is reported that enables recording topographic images in the absence of any component of the electrostatic force. Our approach is based on a close loop z-spectroscopy operated in data cube mode. Curves of the tip-sample distance as a function of time are recorded onto a 2D grid. A dedicated circuit holds the KPFM compensation bias and subsequently cut off the modulation voltage during well-defined time-windows within the spectroscopic acquisition. Topographic images are recalculated from the matrix of spectroscopic curves. This approach is applied to the case of transition metal dichalcogenides (TMD) monolayers grown by chemical vapour deposition on silicon oxide substrates. In addition, we check to what extent a proper stacking height estimation can also be performed by recording series of images for decreasing values of the bias modulation amplitude. The outputs of both approaches are shown to be fully consistent. The results exemplify how in the operating conditions of non-contact AFM under ultra-high vacuum, the stacking height values can dramatically be overestimated due to variations in the tip-surface capacitive gradient, even though the KPFM controller nullifies the potential difference. We show that the number of atomic layers of a TMD can be safely assessed, only if the KPFM measurement is performed with a modulated bias amplitude reduced at its strict minimum or, even better, without any modulated bias. Last, the spectroscopic data reveal that defects at the TMD/oxide interface can have a counterintuitive impact on the electrostatic landscape, resulting in an apparent decrease of the measured stacking height by conventional nc-AFM/KPFM compared to non-defective sample areas. Hence, electrostatic free z-imaging proves to be a promising tool to assess the existence of defects in atomically thin TMD layers grown on oxides
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